Abstract There has been no research conducted thus far on the semiconducting behaviour of biomaterials. In this study, we present an n-type semiconducting biomaterial composed of amorphous kenaf cellulose fibre (AKCF) paper with a voltage-controlled N-type negative resistance. The AKCF generates an alternating-current wave with a frequency of 40.6 MHz from a direct-current voltage source at its threshold voltage (electric field of 5.26 kV/m), which is accompanied by a switching effect with a four-order resistance change at 293 K. This effect is attributed to the voltage-induced occurrence of strong field domains (electric double layers) at the cathode and depletion at the anode of the AKCF device. The proposed AKCF material presents considerable potential for applications in flexible/paper electronic devices such as high frequency power sources and switching effect devices.

Abstract The electric charge storage properties of amorphous cellulose nanofiber (ACF) supercapacitors with different metal carboxylate radicals (COOM; M: Na(I), Ca(II), Al(III)) was investigated in terms of charging/discharging behaviours, alternating current impedance analysis, and plane-wave-based first-principles density functional calculations. Na-ACF exhibited a higher storage effect than Ca- and Al-ACFs. The charge storage mechanism for an Na-ACF supercapacitor was proposed using an electric double layer model in a C₁₂H₁₇O₁₁Na electrolyte with an electrical resistivity of 6.8 × 10³ Ω cm, based on the migration of protonic soliton. The supercapacitor, which demonstrated fast charging upon voltage application, could illuminate a white LED for 7 s after charging with 10 mA at 18.5 V.

Numerical modeling for geothermal reservoir engineering is a crucial process to evaluate the performance of the reservoir and to develop strategies for the future development. The governing equations in the geothermal reservoir models consist of several constitutive parameters, and each parameter is given to a large number of simulation grids. Thus, the combinations of parameters we need to estimate are almost limitless. Although several inverse analysis algorithms have been developed, determining the constitutive parameters in the reservoir model is still a matter of trial-and-error estimation in actual practice, and is largely based on the experience of the analyst. There are several parameters which control the hydrothermal processes in the geothermal reservoir modeling. In this study, as an initial challenge, we focus on permeability, which is one of the most important parameters for the modeling. We propose a machine-learning-based method to estimate permeability distributions using measurable data. A large number of learning data were prepared by a geothermal reservoir simulator capable of calculating pressure and temperature distributions in the natural state with different permeability distributions. Several machine learning algorithms (i.e., linear regression, ridge regression, Lasso regression, support vector regression (SVR), multilayer perceptron (MLP), random forest, gradient boosting, and the k-nearest neighbor algorithm) were applied to learn the relationship between the permeability and the pressure and temperature distributions. By comparing the feature importance and the scores of estimations, random forest using pressure differences as feature variables provided the best estimation (the training score of 0.979 and the test score of 0.789). Since it was learned independently of the grids and locations, this model is expected to be generalized. It was also found that estimation is possible to some extent, even for different heat source conditions. This study is a successful demonstration of the first step in achieving the goal of new data-driven geothermal reservoir engineering, which will be developed and enhanced with the knowledge of information science.

© 2021 Elsevier Ltd The mechanical and electrical properties of multiwalled carbon nanotube (MWCNT) yarns with a wide variety of MWCNT diameters were studied to understand the relationship between the microscopic structures of MWCNTs and the load/charge transport properties of macroscopic MWCNT assemblies. The MWCNT diameters were varied from 14.6 nm to 41.6 nm by varying the amount of catalyst loaded in the synthesis by the chloride-mediated chemical vapor deposition method. We found a drastic change in the tensile behavior of twisted yarns from nonlinear deformation to elastic manner associated with the increases in the tensile strength, Young's modulus, and electrical conductivity of the twisted MWCNT yarns for smaller-diameter MWCNTs. These improvements are due to the increase in the surface area of MWCNTs in the yarn structure. We also carried out microscopic direct tensile tests on the MWCNTs in a scanning electron microscope to investigate the tensile properties of the individual MWCNTs. The in situ experiments revealed that the obtained high value of the Young's modulus of the yarn originated from that of the individual MWCNTs.

To apply carbon nanotubes (CNTs) as reinforcing agents in next-generation composites, it is essential to improve their nominal strength. However, since it is difficult to completely remove the defects, the synthesis guideline for improving nominal strength is still unclear, i.e., the effective strength and the number of nanotube layers required to improve the nominal strength has been undermined. In this study, molecular dynamics simulations were used to elucidate the effects of vacancies on the mechanical properties of CNTs. Additionally, the relationships between the number of layers and effective and nominal strengths of CNTs were discussed theoretically. The presence of extensive vacancies provides a possible explanation for the low nominal strengths obtained in previous experimental measurements of CNTs. This study indicates that the nominal strength can be increased from the experimentally obtained values of 10 GPa to approximately 20 GPa by using six to nine nanotube layers, even if the increase in effective strength of each layer is small. This has advantages over double-walled CNTs, because the effective strength of such CNTs must be approximately 60 GPa to achieve a nominal strength of 20 GPa.

<title>Abstract</title>Despite the intense interest in cellulose nanofibers (CNFs) for biomedical and engineering applications, no research findings about the electrical energy storage of CNF have been reported yet. Here, we present the first electroadsorption effects of an amorphous cellulose nanofiber (ACF) supercapacitor, which can store a large amount of electricity (221 mJm⁻², 13.1 Wkg⁻¹). The electric storage can be attributed to the entirely enhanced electroadsorption owing to a quantum-size effect by convexity of 17.9 nm, an offset effect caused by positive polar C₆=O₆ radicles, and an electrostatic effect by appearance of the localised electrons near the Na ions. The supercapacitor also captures both positive and negative electricity from the atmosphere and in vacuum. The supercapacitor could illuminate a red LED for 1 s after charging it with 2 mA at 10 V. Further gains might be attained by integrating CNF specimens with a nano-electromechanical system (NEMS).

<title>Abstract</title>In this study, the electric storage effect of AlO₆ clusters in amorphous alumina (AAO) supercapacitors was investigated in terms of cluster morphologies under electron-beam irradiation. Based on first-principles density functional calculation, the optimised structure of AlO₆ clusters around an O-vacancy is characterised by a large vacant space created by the absence of an O atom and its neighbouring Al atom. The localised electrons present near the two-atomic vacancies induce positive charges on the inside of the insulating oxide surface, ensuring the adsorption of many electrons on the surface. Electron-beam irradiation (adsorption) from 100 to 180 keV causes the lengths of the Al–O bonds of the cluster to shrink, but then return to the original length with decreasing voltage energy, indicating a rocking-chair-type charge-breathing effect accompanied by a volume expansion of approximately 4%. The <italic>I–V</italic> and <italic>I–R</italic> characteristics depicted Coulomb blockade for the switching effect of both the negative and positive potentials. The Ragone plot of the AAO supercapacitor is located at capability area of the second cell.

PURPOSE: The state of adhesion between root dentin and a resin composite core material was inspected using acoustic emission (AE). METHODS: A total of 14 human incisors and premolars were used to prepare "no-adhesive group" and "adhesive group" specimens. For "adhesive group" specimens, a bonding agent was applied to root canal dentin. The entire post space was subsequently filled with a resin composite for both specimen groups. The prepared specimens were fixed onto a jig on which an AE sensor was installed. A zirconia ball was used for the impact test, and a vibration wave generated by the collision was measured by the system using an AE sensor. The obtained data were subjected to time-frequency analysis using analysis software (LabVIEW), and the relationship between the amplitude indicating the loudness and the frequency indicating the sound component was analyzed. RESULTS: Zirconia-ball collision tests using AE revealed differences between the groups with respect to the waveform of vibration waves transmitted to the root dentin through the root dentin-resin interface. The time-frequency analysis of the obtained data confirmed that multiple peaks were observed for each specimen in the no-adhesive group, whereas a single characteristic vibration peak was observed for all specimens in the adhesive group. CONCLUSIONS: The state of the adhesive interface was successfully evaluated by AE. This demonstration is expected to lead to the development of a device that can detect problems at the bonding interface between the prostheses and tooth substances.

PURPOSE: The state of adhesion between root dentin and a resin composite core material was inspected using acoustic emission (AE). METHODS: A total of 14 human incisors and premolars were used to prepare "no-adhesive group" and "adhesive group" specimens. For "adhesive group" specimens, a bonding agent was applied to root canal dentin. The entire post space was subsequently filled with a resin composite for both specimen groups. The prepared specimens were fixed onto a jig on which an AE sensor was installed. A zirconia ball was used for the impact test, and a vibration wave generated by the collision was measured by the system using an AE sensor. The obtained data were subjected to time-frequency analysis using analysis software (LabVIEW), and the relationship between the amplitude indicating the loudness and the frequency indicating the sound component was analyzed. RESULTS: Zirconia-ball collision tests using AE revealed differences between the groups with respect to the waveform of vibration waves transmitted to the root dentin through the root dentin-resin interface. The time-frequency analysis of the obtained data confirmed that multiple peaks were observed for each specimen in the no-adhesive group, whereas a single characteristic vibration peak was observed for all specimens in the adhesive group. CONCLUSIONS: The state of the adhesive interface was successfully evaluated by AE. This demonstration is expected to lead to the development of a device that can detect problems at the bonding interface between the prostheses and tooth substances.

© 2020 The Authors. Published by Wiley-VCH GmbH Despite the ultrahigh intrinsic strength of multiwalled carbon nanotube (MWCNT), the strengthening effect on ceramic matrix composite remains far from expectation mainly due to the weak load transfer between the reinforcement and ceramic matrix. With the assistance of the in situ pullout test, it is revealed that the liquid-phase sintering (LPS) can serve as a novel strategy to achieve effective load transfer in MWCNT reinforced ceramic matrix composites. The YAlO3 formed liquid phase during spark plasma sintering of SiC composite greatly facilitates radical elastic deformation of MWCNT, leading to highly increased interfacial shear strength (IFSS) as well as interlayer shear resistance (ISR) of nested walls. The liquid phase with superior wettability can even penetrate into the defects of MWCNT, which further increases the ISR of MWCNT. Moreover, the first-principles calculation indicates that the oxygen terminated YAlO3 phase displays much stronger bonding compared with SiC matrix, which is also responsible for the large IFSS in the composite. As a result, as high as 30% improvement of bending strength is achieved in the composite with only 3 wt% MWCNT in comparison to the monolithic ceramic, manifesting the unprecedented strengthening effect of MWCNT assisted by LPS.

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Mechanical properties of nickel and yttria-stabilized zirconia (Ni–YSZ) anodes of solid oxide fuel cells undergo changes not only because of extrinsic conditions but also because of Ni, YSZ and pore proportions. In this study, elastic modulus and fracture behavior of Ni(NiO)–YSZ composites are investigated with changing Ni and pore volume fractions as the main parameters. NiO–YSZ composite stiffness at 800 °C monotonically increases with increasing NiO. However, the reduced form of Ni–YSZ shows drastic changes in elastic modulus and strength around 30 vol% Ni where the deformation behavior and fracture made transition from brittle-like to ductile. Both stiffness and strength show linear decreases with porosity, of which the degree of deterioration at 800 °C was duller than at room temperature. The influences of Ni content and porosity on elasticity are quantified using multiple-linear regression analysis. Pore volume fraction shows large negative effects on elasticity at room temperature in air. However, at 800 °C, Ni volume shows larger negative effects than pore volume under reducing atmospheres.

© 2019 Elsevier B.V. Alumina composites reinforced with acid-treated multiwalled carbon nanotubes (MWCNTs) are prepared, and the tribological properties of the composite are investigated under water-lubricated conditions using a ball-on-disk technique against an alumina ball. The coefficient of friction (COF) in the steady-state region of the composite with acid-treated MWCNTs is found to be 0.06, which is 32–37% lower than that of the monolithic alumina and the composite with pristine MWCNTs. Microstructural observations and in-depth Raman spectroscopy analyses of the disk samples and counterparts before and after the friction tests reveal that the MWCNTs located in pits on the disk surface pull-out and that the resultant MWCNT fragments adhere to the friction surface of the counterparts. The enhanced tribological performance shown in the composite with acid-treated MWCNTs is mainly because the negatively charged functional groups adsorbed on the MWCNTs participate in the hydrogen-bond network of the hydrodynamic lubrication film and lead to acceleration of the transformation from a boundary lubrication regime to a mixed lubrication regime.

<p>Carbon nanotube yarn, which is an aggregation of Carbon nanotubes (CNTs), enables CNTs to be used on macro scale. However, tensile strength of the CNT yarn is much lower than CNT itself, and improvement of the mechanical properties is a challenge for practical application of the yarns. CNTs composing the yarns include some defect structures and impure materials, and their presence can cause a decrease in tensile strength of the yarn. In this study, untwisted CNT yarns were fabricated by dry spun method and graphitized at a temperature of 2800°C for the purpose of improving mechanical properties. Additionally, strength of a CNT composing the yarn and interactive force between the CNTs were evaluated to clarify strength development mechanism of the graphitized CNT yarn. Crystallinity of the CNT yarn was improved more than ten times, and defect structures and impure materials was removed by the graphitization treatment. As a result of single fiber tensile tests, strength of the yarn was increased by 20~35% after the graphitization. On the other hand, strength of the CNT composing the yarn was decreased. The breaking form of the CNT yarn was changed from pulling out of CNT bundles to rapture of the bundles by the graphitization, indicating an increase of interactive force between the bundles. In addition, as a result of pulling out simulations by molecular dynamics method, it was indicated that the pulling out of the CNT bundles were suppressed by increase in van der Waals force. Consequently, the improvement of mechanical properties of the untwisted CNT yarns was not due to the change in the strength of the CNT in the yarns but the main cause was the increase in the interactive force between the CNTs.</p>

Deep geological repositories for nuclear wastes consist of both engineered and natural geologic barriers to isolate the radioactive material from the human environment. Inappropriate repositories of nuclear waste would cause severe contamination to nearby aquifers. In this complex environment, mass transport of radioactive contaminants displays anomalous behaviors and often produces power-law tails in breakthrough curves due to spatial heterogeneities in fractured rocks, velocity dispersion, adsorption, and decay of contaminants, which requires more sophisticated models beyond the typical advection-dispersion equation. In this paper, accounting for the mass exchange between a fracture and a porous matrix of complex geometry, the universal equation of mass transport within a fracture is derived. This equation represents the generalization of the previously used models and accounts for anomalous mass exchange between a fracture and porous blocks through the introduction of the integral term of convolution type and fractional derivatives. This equation can be applied for the variety of processes taking place in the complex fractured porous medium, including the transport of radioactive elements. The Laplace transform method was used to obtain the solution of the fractional diffusion equation with a time-dependent source of radioactive contaminant.

By using aligned multi-walled carbon nanotube (MWCNT) reinforced epoxy composites possessing a negative coefficient of thermal expansion (CTE) as well as high Young's modulus and aluminum foils, novel electrothermal bimorph actuators are fabricated. U-shaped bimorph actuators are formed by cutting out the middle part of the composite/aluminum laminates, where the MWCNT-aligned direction is parallel to the length direction of the U-shaped bimorph actuators. We demonstrate that the bimorph actuators with a free length of 16 mm show a large bending displacement and force output, and their values are 7.6-10.0 mm and 0.8-7.8 mN under a DC voltage of 5.2-6.0 V. Based on these results, the bending displacement and force output of the bimorph actuator are modeled by combining strength-of-materials theories and rule of mixtures (Voigt model and Turner's model). By using these models, we indicate contributions from two sources toward the increased bending displacement and force output in the bimorph actuator: (i) designing the Young's modulus and negative CTE of the composite layer by controlling the MWCNT volume fraction and the dimensional parameters (especially thickness) of the bimorph actuator; (ii) selecting materials having a high Young's modulus as well as a large CTE as the second layer. (C) 2017 Elsevier B.V. All rights reserved.

Ni sintering in the Ni/YSZ porous anode of a solid oxide fuel cell changes the porous structure, leading to degradation. Preventing sintering and degradation during operation is a great challenge. Usually, a sintering molecular dynamics (MD) simulation model consisting of two particles on a substrate is used; however, the model cannot reflect the porous structure effect on sintering. In our previous study, a multi-nanoparticle sintering modeling method with tens of thousands of atoms revealed the effect of the particle framework and porosity on sintering. However, the method cannot reveal the effect of the particle size on sintering and the effect of sintering on the change in the porous structure. In the present study, we report a strategy to reveal them in the porous structure by using our multi-nanoparticle modeling method and a parallel large-scale multimillion-atom MD simulator. We used this method to investigate the effect of YSZ particle size and tortuosity on sintering and degradation in the Ni/YSZ anodes. Our parallel large-scale MD simulation showed that the sintering degree decreased as the YSZ particle size decreased. The gas fuel diffusion path, which reflects the overpotential, was blocked by pore coalescence during sintering. The degradation of gas diffusion performance increased as the YSZ particle size increased. Furthermore, the gas diffusion performance was quantified by a tortuosity parameter and an optimal YSZ particle size, which is equal to that of Ni, was found for good diffusion after sintering. These findings cannot be obtained by previous MD sintering studies with tens of thousands of atoms. The present parallel large-scale multimillion-atom MD simulation makes it possible to clarify the effects of the particle size and tortuosity on sintering and degradation.

21st International Conference on Composite Materials, Xi’an, China, August 21-25, 2017

ONLINE ISSN: 2187-9745

Proceedings of 15th International Symposium on Solid Oxide Fuel Cells (SOFC-XV), July 23-28, 2017, Hollywood, Florida, USA, Diplomat Resort &amp; Spa, pp. 2355-2363, 180 (Poster presentation)

Long-term reliability and durability are of great importance for the commercialization of SOFCs. Mechanical behaviors of ceramic components, including cell fracture, are necessary to be understood in order to ensure stability of SOFCs. For the multiscale simulation of the thermo-chemo-mechanical behavior, various related materials properties are indispensable. This paper reports the evaluation procedure of material properties for comprehensive analysis of chemically- and thermally induced mechanical behavior of SOFCs.

Feasibility of using multi-walled carbon nanotubes (MWCNTs) for the control of coefficients of thermal expansion (CTEs) of composite materials was evaluated, based on experimental data of CTEs and Young's modulus newly obtained using a combined testing procedure. The axial CTE of the MWCNTs were evaluated over the temperature range -5 degrees C to 85 degrees C by using the MWCNT's Young's modulus and CTE of the aligned MWCNT reinforced epoxy composites in Turner's model. The Young's moduli of the MWCNTs were calculated by using Voigt model and the composite Young's modulus measured by tensile tests. The MWCNTs were shown to possess negative CTEs, and the nanotube CTEs tended to become less negative with increasing temperature. Owing to their large Young's modulus, aspect ratio and negative CTEs, the use of MWCNTs aligned axially was shown to be effective at controlling the CTE of polymer composites at lower volume fractions compared to conventional negative CTE materials. (C) 2016 Elsevier Ltd. All rights reserved.

The interface bonding strength between carbon nanotubes (CNTs) and the metal matrix in CNT/metal composites can be increased by depositing metal particles onto the CNT surface. However, theoretical calculations have revealed that metals having an affinity with CNTs formed bonds between the metal and carbon atoms, such that the tensile strength of the CNTs was decreased. Here, we investigated the influence of supported PtPd nanoparticles on the tensile strength of individual multi-walled CNTs (MWCNTs) in situ by scanning electron microscopy. The obtained results revealed that the average tensile strength of individual MWCNTs with deposited PtPd nanoparticles was slightly lower than that of the as-grown MWCNTs. Since X-ray photoelectron and Raman scattering spectroscopic data showed bonds between the PtPd nanoparticles and the MWCNTs, the slight decrease in the tensile strength observed for the PtPd nanoparticle-supported individual MWCNTs can be attributed to the induction of local distortions in the nanotube structure caused by the covalent bonds between the nanoparticles and the CNT basal plane.

Fracture matrix interactions strongly affect anomalous heat transfer in geological sites. This study investigates effects of the interactions between fractures and rock matrix by using the method of multiple interacting continua (MINC). The MINC generates different temperature histories for varied fracture spacings. Two analytical solutions of each porous model and fracture model are used to fit the numerical results for temperature histories due to cold-water injection. The porous model is good agreement with the result for small fracture spacing, while a solution of the fracture model fits the result for large fracture spacing. The MINC yields intermediate behaviors in between a porous medium and a single fracture. A fractional heat transfer equation (fHTE) has been developed to describe anomalous thermal diffusion in a fractured reservoir. The fHTE accounts for heat flux from fracture into matrix by using a temporal fractional derivative. The fHTE can capture numerical results for temperature histories with different fracture spacings. The fracture spacing has correlations to the fHTE best-fit parameters (i.e., the orders of fractional derivatives and the retardation parameters). The fHTE with varying time fractional derivatives can cover descriptions of subdiffusion, Fickian diffusion, and superdiffusion. (C) 2016 Elsevier Ltd. All rights reserved.

Fault zones affect the flow paths of fluids in groundwater aquifers and geological reservoirs. Fault-related fracture damage decreases to background levels with increasing distance from the fault core according to a power law. This study investigated mass transport in such a fault-related structure using nonlocal models. A column flow experiment is conducted to create a permeability distribution that varies with distance from a main conduit. The experimental tracer response curve is preasymptotic and implies subdiffusive transport, which is slower than the normal Fickian diffusion. If the surrounding area is a finite domain, an upper truncated behavior in tracer response (i.e., exponential decline at late times) is observed. The tempered anomalous diffusion (TAD) model captures the transition from subdiffusive to Fickian transport, which is characterized by a smooth transition from power-law to an exponential decline in the late-time breakthrough curves.

Quantitative characterization of interfacial shear strength (IFSS), in multi-walled carbon nanotube (MWCNT)-reinforced Al matrix composites, has been carried out using an in-situ pull-out technique. The end of an MWCNT protruding out of the tensile fracture surface of the composite was bonded to the tip of an atomic force microscopy (AFM) cantilever using an electron-beam-induced deposition method. The MWCNT was pulled out from the Al matrix using a nanomanipulator system installed inside a scanning electron microscope (SEM). The effective embedded length of the MWCNT incorporated in the Al matrix was evaluated by observing the pulled out MWCNT under high-resolution transmission electron microscopy (HRTEM). Valid results were obtained for six MWCNTs with straight, visibly damage-free embedded parts nearly perpendicular to the fracture surface. The IFSS between the MWCNT and the Al matrix was 24.8 +/- 3.2 MPa. The ultimate tensile strength (UTS) of the MWCNT/Al composites is in good agreement with that estimated by the shear lag model using these IFSS values, resulting in the realization of 60% load transfer efficiency at the directly contacted MWCNT-Al interface in the MWCNT/Al composites. No MWCNT failure was observed during the pullout in this study. (C) 2016 Elsevier Ltd. All rights reserved.

ONLINE ISSN: 2187-9745

Silicon is a promising anode material for lithium-ion battery application due to its high specific capacity. Unfortunately, silicon undergoes a volume expansion of 300 similar to 400% full lithiation and suffers from severe capacity fade, which limit its successful application in commercial cells. In this study, we used in situ acoustic emission and laser microscope observation method for detecting the volume change in silicon negative electrodes. It was shown that the long-term performance of the silicon negative electrode was dictated by its spallation during the discharge steps, while only the first lithiation caused its delamination and spoliation in the charge step. This strongly indicates that the energy of emission, and hence the amount of damage, is related to capacity loss. This study demonstrate that AE is a powerful tool to survey the real-time mechanical damage and electrochemical degradation in the electrode.

This paper presents the experimental results of the investigation of mechanical damage in Solid Oxide Fuel Cell (SOFC) under fuel starvation conditions using in-situ Acoustic Emission (AE) and electrochemical technique. The cell was oxidized electrochemically and AE signal has begun to be detected when the oxidation spread from anode/electrolyte interface to anode substrate after Ni/NiO equilibrium. The hydrogen was supplied again and AE signal detection was stopped. Before and after Redox cycling, OCV showed the same value, but the maximum power density decreased by 50 %. After experiment, there was delamination in anode/electrolyte interface, but there was not electrolyte cracking in active cell area. In this experiment, the decrease of maximum power density is thought to be due to causing delamination in anode/electrolyte caused by electrochemical oxidation.

Silicon is a promising anode material for lithium ion batteries application due to its high electrochemical capacity. Unfortunately, silicon undergoes a volume expansion of 300∼400% under the full lithiation condition and suffers from severe capacity fade, which limits its successful application in commercial cells. In this study, we used in situ acoustic emission method for detecting mechanical damage in the silicon electrode. The present study revealed the mechanism of degradation in a silicon electrode of the lithium ion batteries. It was shown that the long-term performance of silicon electrode was dictated by its spallation during the discharge processes. This study demonstrated that the AE method developed was a powerful tool to examine the mechanical damage and electrochemical degradation in lithium ion battery electrodes.

Compared with liquid organic electrolytes, lithium ion conductive solid electrolytes offer improved safety, reliability and leakage-free properties, as well as the advantageous wider electrochemical voltage ranges and the possibility for structural batteries. For this reason, all-solid-state Lithium-Ion Batteries (LIBs) have attracted great interest in recent years. In this regard, electrode deposition technology is expected to play an important role in the development of all-solid-state LIBs. We propose a new method for preparing a cathode film using a cold spray technique. In this study, LiCoO2 films were deposited using a cold spray technique. From SEM observations, the average thickness of the LiCoO2 films was estimated to be approximately 20 micrometers. Cyclic voltammetry showed the LiCoO2 film prepared with cold spraying to be electrochemically active. While the electric capacity of the LiCoO2 cathode film decreased monotonically until 70th cycle, it tended to give a relatively constant value after the 70th cycle. The cold spraying method may provide a useful route for the development of all-solid-state LIBs.

Due to their superior material properties, carbon nanotubes (CNTs) have many potential applications such as actuators, composites and electronic components. These CNT-based devices may experience high temperature during manufacture and operation. This leads to thermal expansion and residual stress in devices, and affects the device reliability. Therefore, the coefficient of thermal expansion (CTE) of CNTs is an important property for CNT-based devices. Although the CTE in radial direction of CNTs have been investigated using X-ray diffraction, there is no experimental determination for the axial CTE of CNTs and only numerical and theoretical predictions exit. Here, we investigated the CTE of aligned multi-walled CNT (MWCNT) reinforced epoxy composites in the MWCNT alignment direction in the temperature range of 30-60 degrees C. We demonstrated that the CTE of the composites in the MWCNT alignment direction became negative by addition of more than 10.4 vol.% MWCNTs, and the axial CTE of MWCNTs was deduced to be -1.2 x 10(-5) K-1 using the rule of mixtures. In addition, the thermal contraction phenomenon was observed in thin sheets of MWCNTs alone. The negative CTE may be explained by out-ofplane atomic vibrations predicted by theoretical and numerical studies. (C) 2015 Elsevier Ltd. All rights reserved.

MWCNT/alumina composites were prepared by a flocculation method combined with acid treatment of the MWCNTs and spark plasma sintering. The effects of varying the processing conditions, namely the acid treatment temperature (50-80 degrees C), MWCNT content (0-10 vol.%) and sintering temperature (1200-1600 degrees C) on the composites' microstructure, electrical conductivity and mechanical properties were investigated. This found that flocculation processing brings about a good dispersibility of the MWCNTs, especially with higher acid treatment temperature, which enhances their reinforcing and grain refining effect. When combined with a low sintering temperature, this significantly improves the mechanical properties of the composites.As a result, a composite prepared using a sintering temperature of 1200 degrees C and an acid treatment temperature of 80 degrees C exhibited a fracture toughness greater than that of a monolithic alumina, even with a MWCNT content as high as 10 vol.%. (C) 2015 Elsevier Ltd. All rights reserved.

Alumina composites reinforced with multiwalled carbon nanotubes (MWCNTs) at up to 3.7 vol% are prepared by a precursor method followed by a spark plasma sintering. We systematically and quantitatively investigate the effects of acid-treatment time of the MWCNTs on not only bending strength and fracture toughness of the composites but also on the mechanical strength and dispersibility of the MWCNTs, the grain size of the alumina matrix, and the interfacial strength between MWCNT and alumina. The main objective of this study is to evaluate how these parameters influence the mechanical properties with the aid of multiple regression analysis. We demonstrate that the matrix grain size, the mechanical strength of the MWCNTs, and the interfacial strength have little impact on the mechanical properties for the composites prepared in this study. On the other hand, the dispersibility of MWCNTs has the significant influence on the mechanical properties. Both the dispersibility of the MWCNTs and the mechanical properties of the composites increase as the acid-treatment time increases up to 2 h at low MWCNT content (0.9 vol%). Conversely, at a higher amount of MWCNTs, the degradation in the mechanical properties is shown to be associated with the deterioration of MWCNTs' dispersibility. As MWCNT agglomerates are anticipated to act as imperfections, they may override the effects of the strength of MWCNTs, matrix grain size, and interfacial strength. By means of the multiple regression analysis, we quantitatively show that improving MWCNTs' dispersibility is one of the most important factors in enhancing the mechanical properties of MWCNT/alumina composites.

We investigated the influence of the microstructure on the true stress-strain curve of silicon nitride based ceramics. The materials were processed by spark plasma sintering technique. Si3N4 with fine, average and coarse microstructures were obtained. Load versus displacement curves (P-h) were obtained by means of instrumented indentation technique using diamond coni-spherical tip. The experimental data were coupled with a minimization method based on the Levenberg-Marquardt algorithm and the non-linear part of the mechanical response was identified. Based on the obtained stress-strain curves, rolling contact simulations were performed. In addition, the nature of Hertzian contact damage was examined in the material with coarse microstructure using diamond indenters of radii 0.2 and 1 mm. The surface damage was observed under optical microscopy while Focused Ion Beam Sectioning technique permitted to image the subsurface damage. An evident size effect was noticed: fracture consisting of classical ring cracks dominated at large scale while distributed microcracks beneath the indent dominated at small scale. (C) 2015 Elsevier B.V. All rights reserved.

This study provides a method to evaluate the effects of cold-water injection into an advection-dominated geothermal reservoir. A fractional advection-dispersion equation (fADE) and a fractional heat transfer equation (fHTE) are applied to fault-related structures in geothermal areas where the fracture density is described by a power-law model. Synthetic production data generated by a numerical reservoir simulator reveal that the fADE and the fHTE are in reasonable agreement with the tracer responses and temperature change in a fault zone. Tracer analysis based on the fADE has potential to elucidate fault-related structures and to predict premature thermal breakthroughs quickly and efficiently. (C) 2015 Elsevier Ltd. All rights reserved.

This work investigates the Hertzian contact damage in Si3N4 ceramics with 3 and 18% porosity processed by spark plasma sintering technique. Low densification was achieved by sintering at pressures lower than needed for a full density. The indentation tests were performed using diamond spheres of various sizes to evaluate the Hertzian contact damage at different scales. Surface damage was observed under electron microscopy while subsurface damage was examined using focused ion beam sectioning technique. Different failure modes were noticed, depending on the size of the volume solicited and the porosity content. At small scale, short cracks initiate from the existing pores then coalesce leading to a quasi-plastic failure mode. At larger scale and for high porosity content, surface ring and radial cracks usually observed for dense brittle materials vanish; the damage mode is mostly related to the fragile rupture of bridges between collapsed pores. (C) 2015 Elsevier Ltd. All rights reserved.

© 2015 IOP Publishing Ltd. In this paper, we develop a novel electroplating method for the synthesis of carbon nanotubes (CNTs)-nickel (Ni) nanocomposite, and present the fabrication of a silicon micromirror with the CNTs-Ni nanocomposite beams to evaluate the mechanical stability of the micromirror in terms of resonant frequency. CNTs are pretreated to have positive charges on their surface and added into a Ni electroplating solution to form a CNTs-Ni nanocomposite electroplating suspension. The weight fraction of the CNTs in the electroplated nanocomposite is 2.4 wt%, and the ultramicroindentation hardness is 18.6 GPa. The mechanical strengthening phenomenon is found in the nanocomposite in comparison with a Ni film. Moreover, the addition of CNTs in the nanocomposite beams effectively increases the shear modulus compared with the pure Ni. The maximum variation of the resonant frequency of the micromirror during a long-term stability test is approximately 0.25%, and its scanning angle is approximately 20. It shows the potential suitability of the CNTs-Ni nanocomposite with proper design for micromechanical element applications.

© 2015 IEEE. We present the fabrication and characterization of a silicon micromirror with carbon nanotubes (CNTs)-nickel (Ni) composite beams, and evaluate the mechanical stability of the micromirror in terms of resonant frequency. A novel electroplating method is developed for the synthesis of the CNTs-Ni composite. The weight fraction of the CNTs in the electroplated composite is 2.6 wt%, and the ultramicroindentation hardness of the composite is 18.6 GPa. The maximum variation of the resonant frequency of the fabricated micromirror during a long term stability test is approximately 0.25%, and its scanning angle is approximately 20°. It shows the potential ability of the CNTs-Ni composite for micromechanical elements application.

This research proposes a numerical scheme for evaluating the effect of cold-water injection into a geothermal reservoir. A fractional heat transfer equation (fHTE) is derived based on the fractional advection-dispersion equation (fADE) that describes non-Fickian dispersion in a fractured reservoir. Numerical simulations are conducted to examine the applicability of the fADE and the fHTE in interpreting tracer and thermal responses in a fault-related subsidiary structure associated with fractal geometry. A double-peak is exhibited when the surrounding rocks have a constant permeability. On the other hand, the peak in the tracer response gradually decreases when the permeability varies with distance from the fault zone according to a power law, which can be described by the fADE. The temperature decline is more gradual when the permeability of surrounding rocks varies spatially than when they have a constant permeability. The fHTE demonstrates good agreement with the temperature profiles for the different permeabilities of surrounding rocks. The retardation parameters in the fADE and the fHTE increase with the permeability of the surrounding rocks. The orders of the temporal fractional derivatives in the fADE and the fHTE vary with the permeability patterns.

The fractional advection-dispersion equation (fADE) has been proposed to describe mass transport in a fractured reservoir. This study develops a finite discrete method to solve the fADE and tests its accuracy against analytical solutions. Tracer simulation uses a three-dimensional simulation of flow analysis (FRACSIM-3D). The solution to the fADE incorporating a spatial fractional derivative shows reasonable agreement with the tracer response from FRACSIM-3D, which shows highly anomalous behaviors such as a long tail. The prediction by the fADE model is reasonably similar to those of FRACSIM-3D irrespective of differing well intervals. (C) 2014 Elsevier Ltd. All rights reserved.

Understanding the sintering mechanism in porous anodes is necessary for developing durable anodes suitable for use in solid oxide fuel cells. A multi-nanoparticle sintering simulation method based on molecular dynamics (MD) calculation was developed for this purpose [J. Xu et al., J. Phys. Chem. C, 2013, 117, 9663-96721. The method can be used to calculate the effect of the porous structure properties, such as the porosity and framework structure, on the sintering, unlike previous sintering simulations with conventional nanoparticle models. We revealed that, in a Ni/YSZ porous anode, the YSZ nanoparticle framework suppresses sintering of Ni nanoparticles by disrupting the growth of the neck between two Ni nanoparticles. In this paper, we used our method to reveal the effect of ceramic type on the sintering processes. We investigated the difference between the sintering and degradation processes in Ni/YSZ and Ni/ScSZ anodes. In the simulation, the degree of sintering of the Ni nanoparticles in Ni! ScSZ was smaller than that in Ni/YSZ. The stronger adhesion of Ni to ScSZ nanoparticles than to YSZ nanoparticles prevented the Ni nanoparticles from approaching each other in the Ni/ScSZ anode, inhibiting sintering. Our multi-nanoparticle sintering MD simulations revealed the different sintering processes for Ni nanoparticles in Ni/YSZ and Ni/ScSZ anodes. We also investigated the effect of sintering on degradation. The hydrogen adsorption sites and electrochemical reaction sites of the hydrogen oxidation decreased as the degree of sintering increased. A low degradation of the Ni/ScSZ anode relative to that of the Ni/YSZ anode was observed. Furthermore, we showed the effect of porosity on degradation induced by sintering in Ni/YSZ and Ni/ScSZ, and found an optimal porosity. These findings cannot be obtained by conventional two- or three-nanoparticle sintering MD simulations. Our multi-nanoparticle sintering simulation method is useful for revealing the types of ceramics suitable for inhibiting sintering and degradation in anodes, and can be used to design durable anodes.

Fracture strength and Young's modulus of ceria doped with 10 mol.% Gd and 10, 20 and 30 mol.% Y were investigated by means of small punch testing method under controlled temperature (1073 K) and oxygen partial pressure (log((p(O&lt inf&gt 2&lt /inf&gt )/atm)= -1.1, 17.5, -21.4, -22.0). Under the reducing conditions, the color of fractured doped ceria specimen changed from pale yellow to gray it is therefore indicated that oxygen nonstoichiometry affects mechanical properties of the doped ceria. Under low oxygen partial pressure, Young's modulus of all specimens decreased monotonically. The fracture strength, by contrast, increased at log(p(O&lt inf&gt 2&lt /inf&gt )/atm) = -17.5, and lower oxygen partial pressures each yttria doped ceria with different Y content showed different variation trends. The oxygen partial pressure dependence of the fracture strength of doped ceria could be arranged as a function of the reduction expansion of the lattice constant a/a&lt inf&gt 0&lt /inf&gt .

This paper describes a testing method which enables us to determine experimentally the interfacial strength between multi-walled carbon nanotube (MWCNT) and ceramic matrix in MWCNT/ceramic composites. The testing method developed in this research, named "Inclined slit-based pullout method", includes a single nanotube pullout technique and a focused ion beam (FIB) technique, which enables MWCNTs to be pulled out from the ceramic matrix during the pullout tests. Single MWCNTs embedded in a fracture surface of an alumina matrix composite are pulled out using a nanomanipulator system in a scanning electron microscope. Embedded lengths of the MWCNTs are controlled by using the FIB technique, i.e., by making an inclined through-slit near the fracture surface of the composite. The average interfacial strength between the MWCNTs and alumina matrix is evaluated to be 19.2 +/- 6.6 MPa for 3 MWCNTs tested in this research. This value is found to be approximately close to that estimated from pullout lengths of the MWCNTs on the fracture surface of the composite, supporting the validity of the testing methods developed in this research. (C) 2014 Elsevier Ltd. All rights reserved.

In order to achieve a sufficiently high volume fraction and the preferred alignment of long carbon nanotubes (CNTs), CNT spun yarns were used as preforms for fabricating epoxy-based composite materials with excellent mechanical properties using the pultrusion technique. Epoxy resin was well impregnated into the preforms, resulting in better load transfer from the resin to the CNTs. By using CNT spun yarn as the preform, the Young's modulus and tensile strength were improved by up to 15 times and 7 times over those of the epoxy resin, respectively. SEM observation suggested that the dominant fracture mode of the composite was fiber breakage of the CNTs. (C) 2014 Elsevier Ltd. All rights reserved.

We prepared ethylenediaminated single-walled carbon nanotubes (SWCNTs) from fluorinated SWCNTs by substituting fluorine groups with ethylenediamine groups. The ethylenediaminated SWCNTs were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman scattering spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area measurement by nitrogen adsorption, contact angle measurement, zeta potential analysis, and thermogravimetry. In addition, the properties of 30 wt % sulfuric acid aqueous electrolyte-based electric double-layer supercapacitors (EDLSCs) with free-standing ethylenediaminated SWCNT electrodes were investigated. The degree of ethylenediamine functionalization was 0.603 mmol/g and 1.46 mu mol/m(2), and the specific surface area was similar to 413.3 m(2)/g. From HRTEM observation, isolated nanotubes disentangled from the bundled SWCNTs were present in many observed areas, and the structures retained a nanotube skeleton. The properties of the EDLSCs with the ethylenediaminated SWCNT electrodes included an average specific capacitance of 94 F/g at a low scan rate of 10 mV/s and an energy density of 2.6 Wh/kg at a power density of 0.24 kW/kg. The EDLSCs exhibited an average specific capacitance of 67 F/g at a high scan rate of 1000 mV/s and an energy density of 1.3 Wh/kg at a power density of 24 kW/kg, values that were superior to those of carboxylated SWCNT electrodes.

In this Communication, we use density functional theory (DFT) to examine the fracture properties of ceria (CeO2), which is a promising electrolyte material for lowering the working temperature of solid oxide fuel cells. We estimate the stress-strain curve by fitting the energy density calculated by DFT. The calculated Young's modulus of 221.8 GPa is of the same order as the experimental value, whereas the fracture strength of 22.7 GPa is two orders of magnitude larger than the experimental value. Next, we combine DFT and Griffith theory to estimate the fracture strength as a function of a crack length. This method produces an estimated fracture strength of 0.467 GPa, which is of the same order as the experimental value. Therefore, the fracture strength is very sensitive to the crack length, whereas the Young's modulus is not. (C) 2014 AIP Publishing LLC.

A fabrication method of carbon nanotube (CNT)-carbon composite microstructures has been developed. CNT-carbon composite microstructures with dimensions from 10 micrometers to several hundred micrometers have been fabricated by pyrolysis process from the patterned SU-8 photoresist mixed with 1 wt% of CNTs at temperature of ~600 C under inert atmosphere. The resulting composite microstructures with a high aspect ratio of ~34 can be successfully fabricated by this novel fabrication method. This research provides a simple approach that is compatible with microfabrication technology and is capable of fabricating composite microstructures with reproducible shape and dimensions, at desired locations. This approach has potential for the further exploring of applications of composite micro/nano structures as functional units in various microdevices. Also the ultramicroindentation hardness of the CNT-carbon composite films was investigated by nanoindentation measurement. © 2013 Springer-Verlag Berlin Heidelberg.

The mechanical properties of individual multi-walled carbon nanotubes (MWCNTs) synthesized by a catalytic chemical vapor deposition (CVD) method followed by a series of high temperature annealing steps at 1200, 1800, 2200 and 2600 degrees C are investigated by a manipulator tool operated inside a scanning electron microscope. To investigate the relationship between the MWCNT structure and mechanical properties, such MWCNTs with a significantly different nanostructure are separately tested in tension, and subsequently observed their nanostructure and fracture morphology by a transmission electron microscope. The results show that the thermal annealing is effective for improving both the strength and modulus of the catalytic CVD-grown MWCNTs. The MWCNTs annealed at 1800, 2200 and 2600 degrees C display enhancements to their strengths by factors of similar to 5.4, similar to 5.1 and similar to 15.6, and moduli by factors of similar to 5.9, similar to 13.2 and similar to 18.9, respectively, compared to the MWCNTs annealed at 1200 degrees C. This effect is associated with the degree of waviness of the graphitic planes, along the nanotube axis as well as the degree of crystallinity of the MWCNTs: the strength and modulus of the MWCNTs increases with a higher degree of orientation of the 002 graphitic planes and with a lower degree of defect concentration in the MWCNT structure. (C) 2013 Elsevier Ltd. All rights reserved.

In order to assess the thermoelastic influence on the long-term performance of hot dry rock (HDR) reservoirs, a simple three-dimensional (3-D) thermoelastic model has been developed based on an assumption of a spherically symmetric volume of cooled rock within reservoir. This model has been incorporated into a 3-D stochastic network model, FRACSIM-3D, which incorporates a fracture network designed to mimic natural fracture distributions as well as stimulation and circulation. The model has been used to evaluate the possible long-term performance of the deep HDR reservoir at Hijiori, Japan. Simulation results showed that thermoelasticity could exert a significant influence on production temperature, injection pressure and water loss. For a multi-well geothermal system, thermoelasticity seemed to have a potential to cause the development of high flow rate/rapidly cooling flow paths (thermal short circuits). (C) 2013 Elsevier B.V. All rights reserved.

Multi-walled carbon nanotube (MWCNT)/alumina composites with different amounts of MWCNTs were prepared by a simple mechanical mixing method followed by a pressureless sintering. The effects of microstructures including grain size, MWCNT location, fracture patterns of the matrix and dispersibility of MWCNTs on the mechanical properties of the resultant composites were investigated. It was demonstrated from microstructural observations and fracture tests of the composites that grain size, MWCNT location and fracture patterns had no significant impact on the mechanical properties of the composites prepared under the processing conditions used in this research. In contrast, the state of MWCNT dispersion within the composites was shown to be one of the important factors affecting the strength and toughness enhancement in our composites. The dispersibility of MWCNTs decreased monotonically as a function of MWCNT volume fraction. The degradation in the mechanical properties observed for the composites with a higher amount of MWCNTs was shown to be associated with the dispersibility of MWCNTs, and a MWCNT agglomerate was anticipated to act as imperfections and led to a reduction of mechanical properties.

Systematic atomic simulations based on molecular mechanics were conducted to investigate the pull-out behavior of a capped carbon nanotube (CNT) in CNT-reinforced nanocomposites. Two common cases were studied: the pull-out of a complete CNT from a polymer matrix in a CNT/polymer nanocomposite and the pull-out of the broken outer walls of a CNT from the intact inner walls (i.e., the sword-in-sheath mode) in a CNT/alumina nanocomposite. By analyzing the obtained relationship between the energy increment (i.e., the difference in the potential energy between two consecutive pull-out steps) and the pull-out displacement, a set of simple empirical formulas based on the nanotube diameter was developed to predict the corresponding pull-out force. The predictions from these formulas are quite consistent with the experimental results. Moreover, the much higher pull-out force for a capped CNT than that of the corresponding open-ended CNT implies a significant contribution from the CNT cap to the interfacial properties of the CNT-reinforced nanocomposites. This finding provides a valuable insight for designing nanocomposites with desirable mechanical properties. © 2013 AIP Publishing LLC.

The purpose of this study is to examine the CO2 sorption amount for Kimachi sandstone and Berea sandstone in water-saturated and air-dry states using the pressure decay method (manometric method) at 50 degrees C and pressures of up to 20 MPa and to provide useful information for assessing the effect of water saturation state on sorption behavior of CO2 in host reservoir rocks. (c) 2013 The Authors. Published by Elsevier Ltd.

Understanding of interfacial interactions among supercritical CO₂ (scCO₂), water, and mineral phase is necessary for a precisely prediction of CO₂ migration into aquifers. The purpose of this study is to assess the impact of scCO₂ on flow property of Kimachi sandstone and Iidate granite in a CO₂ rich dense phase i.e., the condition of which scCO₂ is expected to displace formation water in the course of CO₂ injection. In this experiment, the permeability test for CO₂ gas was conducted before and after a CO₂ saturation procedure that is filled with scCO₂ in pores of rocks. To investigate a mechanical property of rock specimen in the presence of scCO₂, the axial strain was also measured using a laser displacement sensor during scCO₂ saturation processes. Our results showed that both Kimachi sandstone and Iidate granite samples tested have a more or less decreasing trend of gas permeability with increasing exposure time to scCO₂. It was further shown that the axial strain of Kimachi sandstone and Iidate granite increased as scCO₂-exposure time increased. Additionally, increases in masses and dimensions of test samples before and after scCO₂ saturation processes were clearly observed under atmospheric pressure conditions. It can, therefore be said that Kimachi sandstone and Iidate granite could be capable of swelling and permeability change accompanied by CO₂ sorption into their internal structures in the presence of scCO₂. Furthermore, the observed significant reduction in permeability cannot fully be explained by two model predictions based on Kozeney-Carman equation and Hagen-Poiseuille law, considering CO₂ sorption onto mineral phases. The present results pointed out that CO₂ sorption on rocks under geological CO₂ storage conditions could have a significantly impact on flow property of rocks during CO₂ injection and storage processes.

The durability and reliability of segmented-in-series (SIS) type cells-stack was investigated by multimodal assessment in which Tokyo Gas collaborated with research institutes under NEDO project, "Development of system and elemental technology on SOFCs". The SIS cells-stack, developed by Tokyo Gas in cooperation with Kyocera, has many advantages such as reduced temperature operation, high-voltage/low-current power generation, and lower in material cost of electrical insulating substrate compared to Ni based substrates for anode-supported cells. Another key advantage is that there is no need for alloy interconnects. This would make the cell-stack more durable than other types of cell-stacks having metallic interconnects. Durability of the stacks was investigated by the operations in electric furnaces at Tokyo Gas, Central Research Institute of Electric Power Industry (CRIEPI), and Kyushu University. After the operations post analyses were conducted by the research institutes, such as National Institute of Advanced Industrial Science and Technology (AIST), Tohoku University, Kyoto University, The University Tokyo, and Kyushu University. Through the multimodal assessment durability and reliability of the SIS stacks for long-term operation and thermal cycles have been shown to be high enough for 40,000 h life and more.

We previously developed a technique by which to measure the mechanical damage of SOFC using the acoustic emission (AE) method. In the present paper, we applied an adapted Self-Organizing Map (SOM), which is an artificial neural network model, to produce a cluster map reflecting the similarity of AE events. The obtained map visualized the change in occurrence patterns of similar AE events, revealing six phases of damage progress. Moreover, we inferred mechanical interactions among components of SOFC from a series of AE events by our proposed data mining method called co-occurring cluster mining. Our methods provide a common foundation for a comprehensive damage evaluation system and a damage monitoring system.

The effects of pore volume in Ni-YSZ cermets on their mechanical properties under redox cycling were examined using a small punch (SP) testing method. The volume fractions of pores Vp in as-sintered NiO-YSZ specimens were in the range of 0-30%, and with the Ni/YSZ mixture ratio of 50:50%. All the measurements were conducted at 800 C. For Vp&gt;20%, the measured Young's modulus and strength of re-oxidized NiO-YSZ cermets were almost close to those of the as-sintered cermets. The experimental result indicates that the appropriate selection of Vp is necessary for ensuring the mechanical properties during redox cycling.

Our group has attempted to construct an SOFC multiscale model which can simulate inelastic deformation under operating conditions. In this study, we have focused on mechanical properties of Ni-YSZ anode and aimed to identify creep parameter which is a key factor of inelastic deformation. Measurements were performed at elevated temperatures under controlled oxygen partial pressures using in-situ mechanical testing equipment. Creep parameters of Ni-YSZ anode were optimized to have least difference between the result of numerical material test and experiment, using Particle Swarm Optimization (PSO) algorithm of the approximate optimization techniques based on behavior of self-organized system. As a result, we could confirm transit creep on Ni-YSZ cermet, and identify parameters of it. Simulated creep curves showed good fitting to experimental curves at applied stress up to 5MPa, but deviated at higher applied stresses.

Understanding of the sintering mechanism of nickel nanoparticles in the Ni/YSZ anode is requested for long-term durability of solid oxide fuel cell. To elucidate the effects of a porous structure of the Ni/YSZ anode on the sintering, we investigated the sintering process in the Ni/YSZ anodes with different porosities by using our developed multi-nanoparticle molecular dynamics simulation method. We found that the nickel nanoparticle size significantly increased although the YSZ nanoparticles showed little change during the sintering in all the Ni/YSZ models. Since the decrease in the porosity leads to the decrease in the pore size of the YSZ framework, the sintering of the nickel nanoparticles in the Ni/YSZ model with the less porosity is more prevented by suppressing the neck growth in the small pore. On the other hand, the excessively large porosity increases the distance between the nickel nanoparticles and prevents the nickel nanoparticles from contacting.

Use of fractional Advection-Dispersion Equation (fADE) has been proposed to describe mass transport in a fractured reservoir. In this study, a finite discrete method to solve the fADE is developed and its accuracy is tested against analytical solutions.<br>Tracer simulation is carried out using a 3D simulation code for flow analysis (FRACSIM-3D). The fADE mathematical model is applied to fit the numerical tracer results, which show highly anomalous behaviors such as a long tail. The solution to the fADE including a spatial fractional derivative is shown to be in reasonable agreement with the tracer response produced by FRACSIM-3D. The fitting parameters of the fADE equation obtained for well interval of 50 m are used to make predictions of tracer responses for well intervals of 100 m - 500 m. It has been shown that the tracer responses predicted by the fADE model are reasonable close to those obtained by FRACSIM-3D irrespective of the different well intervals. This study demonstrates that the fADE offers a method for predicting tracer responses in a fractured reservoir.

The pull-out force of some outer walls against other inner walls in multi-walled carbon nanotubes (MWCNTs) was systematically studied by molecular mechanics simulations. The obtained results reveal that the pull-out force is proportional to the square of the diameter of the immediate outer wall on the sliding interface, which highlights the primary contribution of the capped section of MWCNT to the pull-out force. A simple empirical formula was proposed based on the numerical results to predict the pull-out force for an arbitrary pull-out in a given MWCNT directly from the diameter of the immediate outer wall on the sliding interface. Moreover, tensile tests for MWCNTs with and without acid-treatment were performed with a nanomanipulator inside a vacuum chamber of a scanning electron microscope (SEM) to validate the present empirical formula. It was found that the theoretical pull-out forces agree with the present and some previous experimental results very well. (C) 2012 Elsevier B.V. All rights reserved.

Small-punch tests and determination of fracture toughness J(IC) were conducted at 4 and 77 K on new cryogenic JN1, JJ1 and JK2 austenitic stainless steels, after isothermal aging. Equivalent fracture strain epsilon(qf) was determined by measuring the reduction of thickness in the small-punch test specimen. A linear dependence of J(IC) on epsilon(qf) was found in these new materials. Regression analysis of experimental data produced the following linear relation J(IC) = 1304.1 epsilon(qf) + 8.09 [kJm(-2)]. An analysis of present work relation was pursued on the basis of material properties and evaluation method of J(IC). Results showed that the slope value has a strong dependence on material yield strength and J(IC) evaluation method. This linear relation is useful for the evaluation of fracture toughness J(IC), measuring the equivalent fracture strain epsilon(qf) by means of small-punch test. Thus it can be useful for assessing the degradation of fracture toughness in small areas such as, the heat-affected zone in welded components.

We prepared and characterized multi-walled carbon nanotube (MWCNT) solids by de-fluorination of fluorinated MWCNTs using spark plasma sintering. In order to investigate the influence of the structure of MWCNT on the mechanical strength of the resulting solids, MWCNTs used in this experiment were as-defected MWCNTs modified by nitric acid and as-purified ones as non-defected nanotubes by comparison. The bend strength and modulus of the resulting solids were lower than those of de-fluorinated MWCNT solids derived from as-purified MWCNTs. The mechanical properties of the resulting MWCNT solids were found to be strongly dependent on the structure of the MWCNT. (C) 2011 Elsevier Ltd. All rights reserved.

In this study, a redox evaluation system for anode supported SOFCs using in-situ acoustic emission (AE) and electrochemical technique has been developed. The system consists of a gas blending unit, moisture controlling unit, AE cell evaluation probe, gas cooling exhaust, electrochemical cell test system and AE signal measurement system. The anode supported coin cells, which have the same thickness dimension as practical SOFCs have, can be evaluated under temperature and atmosphere controlled conditions. The oxygen partial pressure in the anodic atmospheres can be gradually controlled from air to reducing atmosphere using the gas blending unit which is connected to 6 gas cylinders. Humidity in the anodic atmospheres can be controlled by moisture controlling unit which consists of 2 bubblers form 0.86% (5 degrees C saturation) up to 80% (94 degrees C saturation). Redox process of the anode can be simulated in this system by controlled three oxidation modes, i.e. O-2 gas oxidation, steam oxidation and electrochemical oxidation, which correspond to actual troubles, i.e. gas leakage, degradation of downstream and fuel depletion, respectively. An AE transducer can monitor the cell condition via an inner tube for a guide of exhaust from the cathode. Redox cell test for the anode supported coin cell has been examined at 770 degrees C using this system. After the reduction of the anode substrate in moist H-2, current 0.5Acm(-2) loaded to the cell. And then H-2 gas concentration had been reduced by stages. The cell voltage was down to below -6V after H-2 gas concentration was reduced to p(H2)=2%. This drastic cell voltage drop and AE signal generation occurred at the same time. It is considered that Ni re-oxidation with fracture started at this time. Local delamination between anode and electrolyte, and also cracks at the electrolyte and cathode were observed after redox test. It was confirmed that AE sensing is effective for redox evaluation.

Multi-walled carbon nanotubes (MWCNTs) underwent failure during crack opening in a MWCNT/alumina composite. Transmission electron microscope observations and single nanotube pullout tests revealed that the MWCNTs, rather than pulling out from the alumina matrix, broke in the outer shells and then the inner core was pulled away, leaving fragments of the outer shells in the matrix (i.e., they underwent failure in a "sword-in-sheath" fracture mode, as observed for MWCNTs under tensile loading). Some MWCNTs failed leaving either a very short sword-in-sheath failure or a clean break. Theoretical predictions based on the MWCNT failure and pullout models suggested that the use of MWCNTs having a much higher load carrying capacity may lead to composites with a higher fracture toughness. These results may provide new insight into the fracture mechanisms and suggest a new design methodology for MWCNT-based ceramic composites, leading to improved fracture toughness. (C) 2011 Elsevier Ltd. All rights reserved.

La0.8Sr0.2Co0.8Fe0.2O3 (LSCF) nanopowders, which are being investigated as a promising cathode material for low-temperature solid oxide fuel cells (SOFCs), were synthesized by citric acid gel combustion method. The LSCF nanopowders synthesized at 700 degrees C are single perovskite phases and have an average particle size of less than 30 nm. In order to evaluate the use of the synthesized LSCF nanopowders as cathode material of low-temperature SOFCs, anode-supported SOFCs were fabricated from the synthesized LSCF nanopowders and tested in the conditions of humidified hydrogen for anode and oxygen for cathode. The anode-supported single cell with the LSCF cathode sintered at 700 degrees C showed high electrical performance with the maximum power density of 771 mW cm(-2) at 600 degrees C. The results show that the synthesized LSCF nanopowders are suitable to be applied as cathode material for low-temperature SOFCs. [DOI: 10.1115/1.4004176]

La0.8Sr0.2Co0.8Fe0.2O3 (LSCF) nanopowders, which are being investigated as a promising cathode material for low-temperature solid oxide fuel cells (SOFCs), were synthesized by citric acid gel combustion method. The LSCF nanopowders synthesized at 700 degrees C are single perovskite phases and have an average particle size of less than 30 nm. In order to evaluate the use of the synthesized LSCF nanopowders as cathode material of low-temperature SOFCs, anode-supported SOFCs were fabricated from the synthesized LSCF nanopowders and tested in the conditions of humidified hydrogen for anode and oxygen for cathode. The anode-supported single cell with the LSCF cathode sintered at 700 degrees C showed high electrical performance with the maximum power density of 771 mW cm(-2) at 600 degrees C. The results show that the synthesized LSCF nanopowders are suitable to be applied as cathode material for low-temperature SOFCs. [DOI: 10.1115/1.4004176]

The pull-out of a carbon nanotube (CNT) from an alumina (alpha-Al(2)O(3)) matrix was investigated using molecular mechanics simulations to study the interfacial properties due to van der Waals and electrostatic Coulombic interactions. The pull-out force of the CNT was found to be proportional to its diameter, but independent of its length and alumina grain boundary type. A theory was proposed to predict the force for an arbitrary pull-out of a CNT from the alumina matrix using the outermost wall diameter of CNT. (C) 2011 Elsevier Ltd. All rights reserved.

This paper presents an original method to measure the phase transition and macroscopic density fluctuation of supercritical carbon dioxide using a resonant microcantilever beam. There is a significant reduction of the resonant frequency near the phase transition point where the density and viscosity of carbon dioxide exhibit large variations, while the vibration amplitude of the micromechanical resonator displayed a large shift up due to generation of microscopic density fluctuation. The average length of the density fluctuation of supercritical fluid could be calculated from this large shift of the vibration amplitude and the value is in the range of millimeter. © 2011 American Institute of Physics.

We produced boron-mixed multi-walled carbon nanotube solids (B-mixed MWCNT solids) by heating and pressing the powder of purified MWCNTs mixed with 1, 5, and 10 wt % boron in the temperature range 1400-1800 degrees C every 200 degrees C under a constant pressure of 20 MPa in vacuo, and investigated the influence of boron addition on nanotube structure and the mechanical and electrical properties of the resulting B-mixed MWCNT solids. The structure of the prepared material was characterized by scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy-electron energy loss spectroscopy, Raman scattering spectroscopy, and X-ray diffraction, and their mechanical properties and conductivity were measured using a mechanical and Vickers indentation tester and an electric resistor, respectively. It is notable that part of the nanotubes in the B-mixed MWCNT solids solidified at 1800 C had dramatically changed into rod-like graphitic carbons (RLGCs). The occupancy distribution of RLGCs increased with increasing boron contents. However, boron was not detected in the energy-loss near-edge structure spectrum of RLGCs. Furthermore, RLGCs were not observed in the boron-unmixed sample treated with the same solidified condition, indicating that adding boron causes a remarkable ability to transform the phase of MWCNT. Transformation from MWCNTs to RLGCs resulted in increased specific bending strength and modulus, Vickers hardness, and electrical conductivity of B-mixed MWCNT solids with increasing boron content and solidified temperature.

In this study, NiO-Ce0.8Sm0.2O1.9 (SDC) nanocomposite powders with NiO content of 40-60 mass% were successfully synthesized by hydroxide co-precipitation method. The effect of NiO content on crystal phase, crystallite size, average particle size and particle size distribution of the NiO SDC nanocomposite powders was investigated. The average particle size of the NiO SDC nanocomposite powders increased and the particle size distribution became wider with an increase in the NiO content. Anode-supported solid oxide fuel cells (SOFCs) were fabricated from the NiO SDC nanocomposite powders with different NiO content and electrochemical performance was tested at 500-650 degrees C using humidified hydrogen as fuel. Results showed that the NiO SDC nanocomposite powders were suitable to be applied as anode materials for low-temperature SOFCs. The anode-supported SOFC fabricated from the NiO SDC nanocomposite powders with 50 mass% NiO demonstrated the highest electrical performance among the anode-supported SOFCs fabricated from the NiO SDC nanocomposite powders with the NiO content of 40-60 mass%. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The influence of uniaxial compressive strain/stress on the O2- ion conductivity of an yttria-stabilized zirconia (YSZ) sample was investigated by using electrochemical measurement. The conductivity was investigated by the AC four-probe method and molecular dynamics simulation. The applied compressive strain/stress ranged from 0 to 0.0003 (stress: 1.5-55 MPa) for the specimen in air at 873, 973, and 1073 K. To clarify the reason for the phenomenon of the decline in conductivity, the relaxation time for the conductivity after the application of strain/stresses was measured. The experimental result revealed that as the applied compressive strain/stress increases, the carrier concentration remains steady, whereas the mobility decreases. The conductivity was decreased with increasing compressive strain, and this trend agreed with that of the simulation results. Therefore, the decrease in mobility was considered to be the reason for the decline in conductivity under compressive strain/stress conditions. (C) 2011 The Japan Society of Applied Physics

NiO-Ce0.8Sm0.2O1.9 (NiO-SDC) nanocomposite powders applied as promising anode material for low-temperature solid oxide fuel cells (SOFCs) were synthesized by hydroxide co-precipitation method using NH3 center dot H2O, NaOH and NH3 center dot H2O+NaOH as precipitation agents. The crystal phases, morphologies and sintering behavior of the synthesized NiO-SDC nanocomposite powders were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and sintering experiments. The effect of precipitation agents on the synthesis of the NiO-SDC nanocomposite powders was discussed. Results show that different precipitation agents influence greatly the synthesis and characteristics of the NiO-SDC nanocomposite powders. The NiO-SDC nanocomposite powders synthesized with NH3 center dot H2O deviate from the original composition due to the loss of Ni. The loss of Ni is avoided and nano-sized NiO-SDC composite powders are synthesized, when NaOH and NH3 center dot H2O+NaOH are used as precipitation agents. The NiO-SDC nanocomposite powders can be synthesized at relatively low temperature using NH3 center dot H2O+NaOH as precipitation agent, and the synthesized NiO-SDC nanocomposite powders show good sintering characteristics.

The paper provides an introduction to fundamental concepts of mathematical modeling of mass transport in fractured porous heterogeneous rocks. Keeping aside many important factors that can affect mass transport in subsurface, our main concern is the multi-scale character of the rock formation, which is constituted by porous domains dissected by the network of fractures. Taking into account the well-documented fact that porous rocks can be considered as a fractal medium and assuming that sizes of pores vary significantly (i.e. have different characteristic scales), the fractional-order differential equations that model the anomalous diffusive mass transport in such type of domains are derived and justified analytically. Analytical solutions of some particular problems of anomalous diffusion in the fractal media of various geometries are obtained. Extending this approach to more complex situation when diffusion is accompanied by advection, solute transport in a fractured porous medium is modeled by the advection-dispersion equation with fractional time derivative. In the case of confined fractured porous aquifer, accounting for anomalous non-Fickian diffusion in the surrounding rock mass, the adopted approach leads to introduction of an additional fractional time derivative in the equation for solute transport. The closed-form solutions for concentrations in the aquifer and surrounding rocks are obtained for the arbitrary time-dependent source of contamination located in the inlet of the aquifer. Based on these solutions, different regimes of contamination of the aquifers with different physical properties can be readily modeled and analyzed. (C) 2010 Elsevier Ltd. All rights reserved.

In this study, we synthesized La0.8Sr0.2Co 0.8Fe0.2O3 (LSCF) nanopowders by citric acid gel combustion method. The single perovskite phases LSCF nanopowders with an average particle size of less than 30 nm could be synthesized at 700 °C. In order to evaluate the use of the synthesized LSCF nanopowders as cathode material of solid oxide fuel cells (SOFCs), anode-supported SOFCs were fabricated from the synthesized LSCF nanopowders and tested in the conditions of 3%H2O-H2 for anode and oxygen for cathode. The anode-supported single cell with the LSCF cathode sintered at 700 °C showed the maximum power density of 771 mW/cm2 at 600 °C. This means that the synthesized LSCF nanopowders are suitable to be applied as cathode material for low-temperature SOFCs. © 2011 Ceramic Society of Japan.

Small-punch tests were conducted at 4, 77 and 293 K on three types of austenitic stainless steels JN1, JJ1 and JK2, which were solution treated, water-quenched and then aged at 923, 973, 1023 and 1073 K for 5 h. Small-punch test energy was employed for the evaluation of the aging-induced embrittlement behavior in these materials. Fracture surface of small punch test specimen for the solution treated steels exhibited a ductile fracture, showing the highest SP test energy values. The presence of intergranular brittle fracture was observed in aged specimens. Small-punch test energy decreased significantly as the aging process progressed. The highest and lowest decrease in small-punch test energy with aging temperature occurred in JN1 and JK2 steels, respectively. The decrease in small-punch test energy showed to examine appropriately the aging-induced embrittlement in these materials. The difference in aging-induced embrittlement behavior for these steels was explained based on the volume fraction of intergranular precipitates in aged samples.

The crack bridging behavior of multi-walled carbon nanotube-reinforced alumina matrix composites has been investigated using a single fiber pullout testing method. Contradictory to the conventional understanding (which have reported that pullout phenomena evidently occurred in the bulk nanotube-reinforced alumina composites), the pullout experiments using an in situ SEM method with a nanomanipulator system demonstrated that strong load transfer was revealed, and no pullout behavior was observed for all 15 MWCNTs. The MWCNTs, rather than pulling out from the alumina matrix, broke in the outer-shells and the inner section was pulled away, leaving the outer-shells of the fragment in the matrix. This implies that tougher ceramics with MWCNT can be obtained by creating the appropriate interaction between the matrix and MWCNT: not too week but also not too strong to permit an adequate load transfer between the two parts and thus a consequent pulling out without breakage of MWCNT. Our finding suggests important implications for the design of tougher ceramic composites with MWCNTs. The important factor for such tougher ceramic composites will thus be the use of 'strong' MWCNTs having higher mechanical performance (as well as a good dispersion in the matrix).

We report the mechanical properties and microstructures of multi-walled carbon nanotube (MWCNT)/alumina composites made with MWCNTs that absorb negatively charged functional groups at the MWCNT ends and along their length from an acid treatment. We conducted the fracture surface observations of the composites, in order to evaluate the effects of the acid treatment conditions of MWCNTs on the mechanical properties of the composites and the microstructures such as dispersibility and protrusion length of MWCNTs. According to the SEM observations, it was found that the dispersibility of MWCNTs affected the mechanical properties of the composites, and the protrusion length of MWCNTs decreased with increasing of the acid treatment time of MWCNTs. These observations revealed that the high structural homogeneity rather than pullout behavior of MWCNTs leads to an increase in the mechanical properties of the MWCNT/alumina composite. There is an optimal acid treatment time for improving the mechanical properties of the composites. The dispersibility of the MWCNTs and mechanical properties of the composites was increased by the acid treatment with treated for 2 hours compared to the pristine MWCNTs and acid treatment MWCNTs with treated for 0, 0.5, 1, 3 and 4 hours.

Anode-supported solid oxide fuel cells (SOFCs) have attracted much attention in recent years because of their lower operating temperature. For the preparation of anode-supported SOFCs, one of the key steps is the production of dense electrolyte films on the porous anode substrate. In this study, Ce0.9Gd0.1O1.95 (GDC) electrolyte films with the thickness range of 1-75 mu m are successfully prepared on porous NiO-GDC substrates by simple, rapid and cost-effective methods: dry co-pressing method and spray dry co-pressing method. The open porosity of the NiO-GDC substrates is approximately 23%, and the porosity including closed pores of the GDC electrolyte films is less than 2.6%. The prepared GDC electrolyte films are homogenous, dense and well adhered to the porous NiO-GDC substrates, without cracks and connecting pores observed. The results of helium gas permeability tests show that the prepared GDC electrolyte films are gas-tight. Therefore, it is expected that the developed method for thin electrolyte films provides a simple and useful technique for producing electrolytes for anode-supported SOFCs. (C) 2010 Elsevier B.V. All rights reserved.

Numerical simulations are performed to characterize the micro- and macro-scale aspects of the electro-chemo-mechanical coupling behavior of a positive-electrolyte-negative (PEN) structure under SOFC operation. The mathematical homogenization method is applied to evaluate the macroscopic material properties of porous electrodes by performing the corresponding microscopic analyses. In particular, the potential transfer conditions at pore surfaces and triple-phase boundaries are homogenized to be source terms in the macroscopic electron-ion coupled transport problem. A case study is conducted to identify the major source of generation and evolution of cracks running through a disc-shaped cell. In this context, we are concerned especially with the effects of the radius of the cell, the thickness of the electrolyte and the profile of temperature's in-plane distribution on the macroscopic tensile circumferential stress distributions.

Effects of redox cycling on the mechanical properties of Ni-YSZ cermets were investigated by using an in-situ small punch (SP) testing method. The Ni contents in the Ni-YSZ cermets tested in this study were 0, 15, 30 and 50 vol.%. Electrical conductivity measurements suggested that Ni particles formed a network-like structure at Ni contents greater than 20 vol.%. Experimental results obtained from the in-situ SP tests at 800 degrees C demonstrated that ductile-like deformation was induced under reducing environment (at an oxygen partial pressure of 10(-18) atm) for the Ni contents of 30 and 50 vol.%. The ductile-like behavior was attributable to the formation of Ni network. The first complete re-oxidation of Ni-YSZ cermets then caused critical damage and resulted in drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ cermets under reducing environments.

Deformation and mechanical damage measurement techniques were developed in order to investigate the degradation process of SOFC cell/stack and module under SOFC operation. In this study, the deformation and mechanical damage test was applied to simulated cell and stack. The deformation, microcrack and delamination in the cell and stack were detected by displacement gauge and acoustic emission (AE) method. The observation method determined location of signal and mechanism of the deformation and microcrack in the SOFC cell/stack. By using this method, it was possible to show the possibility that the detailed deterioration process can be evaluated, visually, and in real-time, even when applied to cell and stack at the actual equipment level.

Segment-in-series cell fabricated by Mitsubishi Heavy Industries have been investigated from various experimental approaches. Examined samples are type 1 cells which were operated for up to 10,000 h by CRIEPI. Analyses were made by AIST on materials transport with dynamic SIMS, by CRIEPI on microstructure observation with EPMA, by Kyoto University on microstructure change with FIB-SEM, by Kyushu University on chemical states with S-TEM, and by Tohoku University on mechanical properties in the microscopic zone with micro indentation technique. On the bases of accumulated knowledge on these samples, the materials deterioration model has been established with a focus on the movement of the Ca component in the cathode layers. The degradation rate observed in the analyses by CRIEPI can be interpreted in terms of the Cr deposited on the three phase boundaries and also of the change in microstructure.

In the present paper, we investigated the electrical performance of anode-supported solid oxide fuel cells (SOFCs) composed of Gd0.1Ce0.9O1.95 (GDC) electrolyte films of 1-75 mu m in thickness prepared by simple and cost-effective methods (dry co-pressing process and spray dry co-pressing process), and discussed the effect of thickness of the GDC electrolyte films on the electrical performance of the anode-supported SOFCs. It was shown that reducing the thickness of the GDC electrolyte films could increase the maximum power densities of the anode-supported SOFCs. The increase of the maximum power densities was attributed to the decrease of the electrolyte resistance with reducing the electrolyte thickness. However, when the thickness of the GDC electrolyte films was less than a certain value (approximately 5 mu m in this study), the maximum power densities decreased with the decrease in the thickness of the GDC electrolyte films. The calculated electron fluxes through the GDC electrolyte films increased obviously with reducing the thickness of the GDC electrolyte films, which was the reason why the maximum power densities decreased. Therefore, for anode-supported SOFCs based on electrolytes with mixed electronic-ionic conductivity, there was an optimum electrolyte thickness for obtaining higher electrical performance. (C) 2010 Elsevier B.V. All rights reserved.

The influence of chemically induced expansion on the fracture damage of a nonstoichiometric oxide (ceria) based solid oxide fuel cell (SOFC) single cell laminate was investigated by using numerical stress analyses under oxidizing/reducing gradient condition. The single cell examined in this study was composed of electrolyte (Ce(0.8)Sm(0.2)O(2-delta)), anode (Cermets of Ni-Ce(0.8)Sm(0.2)O(2-delta)). and cathode (La(0.6)Sr(0.4)Co(0.2)Fe(0.8)O(3-delta)), respectively. The finite element method (FEM) was employed to calculate the residual stress, thermal stresses, and chemically induced expansion stresses for the single cell. The residual and thermal stresses were calculated touch smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically induced expansion stresses were shown to remarkably increase for the temperature range greater than 973 K and accounted their magnitude for primary part of the induced stress. It was shown from the FEM that the maximum circumferential stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission (AE) method. (C) 2010 Elsevier B.V. All rights reserved.

In this study, NiO-Ce0.9Gd0.1O1.95 (NiO-GDC) nanocomposite powders were synthesized by hydroxide co-precipitation method, and applied to improve the microstructure of solid oxide fuel cell (SOFC) anodes. The NiO-GDC anodes prepared from the NiO-GDC nanocomposite powders showed uniform microstructure with uniform distribution of NiO and GDC phases. Due to the uniform phase distribution, the Ni-GDC anodes prepared from the NiO-GDC nanocomposite powders had longer triple phase boundary (TPB), which resulted in enhanced electrochemical reactions. The anode-supported SOFC fabricated from the co-precipitated NiO-GDC nanocomposite powders exhibited higher electrochemical performance than the anode-supported SOFC fabricated from the mechanically mixed NiO-GDC nanopowders. The experimental results show that the use of the Ni-GDC anodes with uniform microstructure can effectively improve the electrochemical performance of anode-supported SOFC. (C) 2010 Elsevier B.V. All rights reserved.

The clarification of the sliding behavior between nested walls in a multi-walled carbon nanotube (MWCNT) is crucial for its applications in nano-electro-mechanical systems. The pull-out processes of some outer walls against other inner walls in MWCNTs are studied by molecular mechanics simulations to investigate this sliding behavior between nested walls. The pull-out force for both double-walled carbon nanotube (DWCNT) and MWCNTwith more than two walls is found to be proportional to the diameter of the critical wall (i.e., the immediate outer wall at the sliding surface), and independent of nanotube length and chirality. The underlined mechanism for this phenomenon is systematically explored by investigating the interfacial shear stress during the pull-out and the corresponding surface energy density. The importance and necessity of considering MWCNTs with more than two walls are indicated from their higher surface energy densities than that of DWCNT. Furthermore, the obtained result demonstrates that the conventional definition of the interfacial shear strength is inappropriate for the sliding behavior between nested walls in MWCNTs. Finally, a simple universal theory is proposed for the first time to predict the pull-out force for an arbitrary sliding in a given MWCNT, directly from the diameter of the critical wall. (C) 2010 Elsevier Ltd. All rights reserved.

We report the mechanical behavior of a unique type of multi-walled carbon nanotube (MWCNT) and an acid-treated version of this MWCNT type that have nanoscale defects on their surfaces from the acid treatment. These defects, from scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging have a &apos;channel-like&apos; appearance, as if a ring of material was cut away from the MWCNT around the circumference. The mechanical properties of individual MwCNTs have been experimentally shown to strongly depend on their structure and structural disorder can drastically reduce the mechanical properties. Tensile-loading experiments using a nanomanipulator tool operated inside a SEM revealed that the tensile strengths of 10 pristine MWCNTs ranged from similar to 2 to similar to 48 GPa (mean 20 GPa). For 10 acid-treated MWCNTs with channel-like defects, tensile strengths ranged from similar to 1 to similar to 18 GPa (mean 6 GPa, thus roughly 70% lower than those of the pristine MWCNTs). Microstructural observations revealed that the fracture of the acid-treated MWCNTs occurred at a channel-like defect region in 8 of the 10 samples. This indicates that the channel-like defects associated with the acid etching are typically going to be the weakest points in the acid-treated MWCNT structure and that stress concentration is present at the defect region. (C) 2010 Published by Elsevier B.V.

We report the mechanical behavior of a unique type of multi-walled carbon nanotube (MWCNT) and an acid-treated version of this MWCNT type that have nanoscale defects on their surfaces from the acid treatment. These defects, from scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging have a &apos;channel-like&apos; appearance, as if a ring of material was cut away from the MWCNT around the circumference. The mechanical properties of individual MwCNTs have been experimentally shown to strongly depend on their structure and structural disorder can drastically reduce the mechanical properties. Tensile-loading experiments using a nanomanipulator tool operated inside a SEM revealed that the tensile strengths of 10 pristine MWCNTs ranged from similar to 2 to similar to 48 GPa (mean 20 GPa). For 10 acid-treated MWCNTs with channel-like defects, tensile strengths ranged from similar to 1 to similar to 18 GPa (mean 6 GPa, thus roughly 70% lower than those of the pristine MWCNTs). Microstructural observations revealed that the fracture of the acid-treated MWCNTs occurred at a channel-like defect region in 8 of the 10 samples. This indicates that the channel-like defects associated with the acid etching are typically going to be the weakest points in the acid-treated MWCNT structure and that stress concentration is present at the defect region. (C) 2010 Published by Elsevier B.V.

This report described the effects of Ti surface modification with NaOH hydrothermal solution on adhesion strength of HA coating produced by newly developed hydrothermal (DC-HHP) method. 2 kinds of surface layer (containing anatase-type TiO2 or not) were formed on Ti surface by immersing to 5 mol/L NaOH solution before HA coating process. Pull out tests were conducted to obtain an estimate for the adhesion properties of the HA coating. Shear strength of specimens with 5 mol/L NaOH treated at 423 K for 2 hours was estimated in the range of 4.1-5.7 MPa. The enhancement of the HA adhesive properties as well as more than three times values was achieved, in comparison to the specimens without the surface layer (approximate 1.5 MPa). It was demonstrated that 423 K hydrothermal treatment with 5 mol/l NaOH solution on Ti surfaces is significantly effective to enhancing adhesion strength of the HA coating produced by the DC-HHP method. (C) 2010 The Ceramic Society of Japan. All rights reserved.

A simple, rapid and cost-effective technique, spray dry co-pressing process, was developed to prepare dense electrolyte thin films on porous anode substrates. Gadolinium doped ceria (GDC) electrolyte thin film with the thickness of 4 mu m was prepared successfully on porous NiO-GDC anode substrate by the spray dry co-pressing process. The GDC electrolyte thin film was dense and uniform, and was well bonded to the porous NiO-GDC anode substrate. An anode-supported solid oxide fuel cell (SOFC) with 4 mu m GDC electrolyte thin film was fabricated and its performance was evaluated at 400-600 degrees C with humidified hydrogen (3 vol.% H(2)O) as the fuel. The single cell showed an open circuit voltage (OCV) of 0.91 V and maximum power density of 771 mW cm(-2) at 600 degrees C. The results demonstrate that the dense GDC thin films prepared by the spray dry co-pressing process are suitable for low-temperature anode-supported SOFC applications. (c) 2009 Elsevier B.V. All rights reserved.

The objective of this work is to study relationship between oxygen potential and mechanical properties of an oxygen nonstoichiometric compound with Ce_<0.9>Gd_<0.1>O_<2-δ> Under high temperatures and reducing conditions, oxygen content in Ce_<0.9>Gd_<0.1>O_<2-δ> changes and oxygen defects are generated. Therefore Mechanical properties of Ce_<0.9>Gd_<0.1>0_<2-δ> can change under such conditions. In this study, we developed a new testing apparatus for small punch test, which is able to measure mechanical properties under high temperatures and controlled atmospheric conditions. The fracture stress Ce_<0.9>Gd_<0.1>O_<2-δ> was almost constant regardless of oxygen partial pressure, while elastic modulus decreased with decreasing oxygen partial pressure in reducing atmospheres. Elastic modulus relates oxygen vacancy concentration.

This paper examined mechanical properties, Young's modulus, shear modulus, Poisson's ratio and internal friction, of La_<0.6>Sr_<0.4>Co_<0.2>Fe_<0.8>O_<3-δ> in the temperature range between 298 and 1173 K, and the oxygen partial pressure (P(O_2)) range between 0.1 and 10^<-4> bar by using resonance method. The Young's modulus of La_<0.6>Sr_<0.4>Co_<0.2>Fe_<0.8>O_<3-δ> gradually decreased in the temperature range between 298 and 823 K and then drastically increased above 873 K. P(0_2) dependencies of Young's modulus showed different trends depending on temperature. At 1173K, Young's modulus decreased with decreasing P(O_2), while increased down to 5.0×10^<-3> bar and then decreased with decreasing P(O_2) at 1073K. At 973K, it monotonically increased with decreasing P(O_2), and at 873K, slightly increased with decreasing P(O_2).

Effects of redox cycling on the mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol. %, 15:85 vol. %, 30:70vol. %, and 50:50 vol. %. Electrical conductivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol. %. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment (at oxygen partial pressure 1 × 10^<-18>atm) for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of Ni-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment.

Dense gadolinium doped ceria (GDC) electrolyte thin films were prepared on porous NiO-GDC substrates by spray coating process. Microstructure of the GDC thin films and effect of preparation process on the microstructure were examined. SEM results show that uniform and dense GDC thin films with a thickness of approximately 1 mu m were successfully prepared on porous NiO-GDC anodes. Anode-supported single cell with the thin GDC electrolyte film was tested using humidified hydrogen as a fuel, and exhibited relatively high electrical performance at low operating temperature (the maximum power density of 135 mW/cm(2) at 600 degrees C). This means that the thin GDC film may be applicable to an electrolyte for anode-supported SOFCs. The experimental results suggest that the spray coating method developed in this study may offer a useful route for preparing thin and dense electrolytes of SOFCs.

Multi-walled carbon nanotube (MWCNT) reinforced alumina composites were prepared by spark plasma sintering using pristine MWCNTs and acid-treated MWCNTs. The effect of acid treatment on the structure and surface potential of the MWCNTs was examined by transmission electron microscopy (TEM) and zeta potential analyzer. It is demonstrated that with the acid treatment of the MWCNTs, we have deliberately introduced nanoscale defects and negatively charged functional groups on the surface of the MWCNTs. The average depths of the defects are typically 4.8-10.8 nm. Mechanical measurements revealed that surface modification of the MWCNTs is effective in improvement of bending strength and fracture toughness of the MWCNT/alumina composites. Only 0.9 vol.% acid-treated MWCNT addition results in 27% and 25% simultaneous increases in bending strength (689.6 MPa) and fracture toughness (5.90 MPa m(1/2)), respectively.

Multi-walled carbon nanotube (MWCNT) reinforced alumina composites were prepared by spark plasma sintering using pristine MWCNTs and acid-treated MWCNTs. The effect of acid treatment on the structure and surface potential of the MWCNTs was examined by transmission electron microscopy (TEM) and zeta potential analyzer. It is demonstrated that with the acid treatment of the MWCNTs, we have deliberately introduced nanoscale defects and negatively charged functional groups on the surface of the MWCNTs. The average depths of the defects are typically 4.8-10.8 nm. Mechanical measurements revealed that surface modification of the MWCNTs is effective in improvement of bending strength and fracture toughness of the MWCNT/alumina composites. Only 0.9 vol.% acid-treated MWCNT addition results in 27% and 25% simultaneous increases in bending strength (689.6 MPa) and fracture toughness (5.90 MPa m(1/2)), respectively.

Solute diffusion from a fracture into a porous rock with an altered zone bordering the fracture is modeled by a system of two diffusion equations (one for the altered zone and another for the intact porous matrix) with different coefficients of effective diffusivity. Since experimental studies of diffusion into rock samples with altered zones indicate that mathematical models of diffusion based on Fick's law do not adequately describe the concentration field in a sample, fractional order diffusion equations are chosen in this study for modeling the anomalous mass transport in the rocks. In the case of significantly higher porosity of the altered zone (e.g., this is typical for carbonates) the effective diffusivity here can be much higher than the effective diffusivity of non-altered rocks. By introducing a small parameter that is the ratio of effective diffusivities in the non-altered and altered regions and applying the technique of perturbations, approximate analytical solutions for concentrations in the altered zone bordering the fracture and in the intact surrounding rocks are obtained. Based on these solutions, different regimes of diffusion into the rocks with different physical properties are modeled and analyzed. It is shown that, using experimentally obtained data, the orders of the fractional derivatives in the differential equations can be readily calibrated for the every specific rock.

We report the mechanical properties of multi-walled carbon nanotube (MWCNT)/alumina composites made with a pristine MWCNT and an acid-treated version that have nanoscale defects on their surfaces from an acid treatment. In order to evaluate the effects of sintering additives on the mechanical properties of the composites, we employed three sets of the composites having different sintering additives. Mechanical properties of the MWCNT-based alumina composites were dependent mostly on the type of sintering additives. The composites with magnesia sintering additive, having 0.9 vol.% acid-treated MWCNT, showed a higher bending strength (689.6MPa) and fracture toughness (5.90 MPa·m1/2), than those of the composites with silica sintering additive.

The utilization of anode-supported electrolytes is a very promising strategy to improve the electrical performance in solid oxide fuel cells (SOFCs) application, because it is possible to decrease considerably the electrolytes thickness. In this paper, ultra-thin ceria-based electrolyte films were successfully prepared on porous NiO/GDC anode support. The electrolyte films with thickness of 0.5-1 µm were deposited by a novel citrate sol-gel route combined with a suspension spray coating technique. The characterization and microstructure of the ultra-thin films were investigated by DTA/TGA, XRD and FE-SEM. The results showed that ceria-based films prepared were pure fluorite type nanocrystalline, homogenous and almost fully dense. Electrochemical performance of single cells based on the ultra-thin electrolyte films was also tested. The single cell with electrolyte thickness of 1 µm provided an OCV of 0.832 V at 500 °C which was close to that of the reported single cell with thicker ceria-based electrolyte film of 10 µm, and maximum power densities of 59.6, 121.9 and 133.8 mW/cm<SUP>2</SUP> at 500, 600, and 700 °C, respectively. These ultra-thin electrolyte films showed good combination with the porous NiO/GDC anode supports, and good insulating ability for inactive electron migration at temperatures less than 600 °C.

Anode-supported solid oxide fuel cells (SOFCs) have attracted extensive attention due to low operating temperatures and high electrical performance. In the anodesupported SOFCs, the key is to prepare dense electrolyte films on porous anode substrates. In this study, a simple and cost-effective technique, spray coating process, is introduced to prepare dense electrolyte films. In the spray coating process, the preparation of powder suspension is very important, which affects the quality of resulting electrolyte films. A well-dispersed Ce<SUB>0.9</SUB>Gd<SUB>0.1</SUB>O<SUB>1.95</SUB> (GDC) suspension were prepared in isopropyl alcohol by adding 2 mass% surfactant. Using the well-dispersed GDC suspension, dense and crack-free GDC electrolyte films with thickness of 2-10 µm were successfully prepared on porous NiO-GDC anode substrates by the spray coating process. In order to evaluate the GDC electrolyte film as electrolyte for SOFC, anode-supported SOFC was fabricated and its electrical performance was measured. Results show that the GDC electrolyte film prepared by the spray coating process can be used as electrolyte of SOFC. The GDC electrolyte film is well adhered to the anode substrate, and there is no crack and delamination observed after electrical performance test.

Carbon nanotube is nature's smallest fiber and predicted to have a range of unusual mechanical and electrical properties. One possible route to harnessing these properties for applications would be to incorporate nanotubes in a composite material. Here, we report the mechanical properties of multi-walled carbon nanotube (MWCNT) reinforced alumina composites made with a pristine MWCNT and an acid-treated version that have nanoscale defects on their surfaces from an acid treatment. It was demonstrated that surface modification of the MWCNT is effective in improvement of bending strength and fracture toughness of the MWCNT-reinforced alumina composites. On the basis of the results, we also prepared three sets of the acid-treated MWCNT-reinforced alumina composites having different sintering additives, in order to investigate the effects of sintering additives on their microstructures and mechanical properties. Mechanical properties of the composites were dependent mostly on the type of sintering additives and amount of MWCNT. The 0.9 vol.% acid-treated MWCNT-reinforced alumina composites with MgO sintering additive gave the highest bending strength (689.6 ± 29.1 MPa) and fracture toughness (5.90 ± 0.27 MPa·m<SUP>1/2</SUP>), respectively.

Sorption isotherms, which describe CO<SUB>2</SUB> storage capacity of rocks, are important for estimating CO<SUB>2</SUB> sequestration potential of geological reservoirs. This study examined CO<SUB>2</SUB> sorption capacity of Kimachi sandstone and Iidate granite in the CO<SUB>2</SUB> rich dense phase, the condition of which is expected to occur mostly in the course of CO<SUB>2</SUB> injection into geological reservoirs because of the displacement of formation water by CO<SUB>2</SUB> pressurization in geological reservoirs as storing CO<SUB>2</SUB> into aquifers, at geological temperature and pressure. CO<SUB>2</SUB> sorption measurements were conducted using both volumetric and gravimetric methods at temperatures of 33∼200°C and pressures up to 20MPa. It was found that Kimachi sandstone and Iidate granite were capable of sorbing CO<SUB>2</SUB> into their internal structures. At 50°C, the amount of CO<SUB>2</SUB> sorption reached the maximum value of 1.4 mmol/g (= 31.4 scc/g) for Kimachi sandstone and 0.7 mmol/g (=15.7 scc/g) for Iidate granite, respectively. Comparison among model predictions (monolayer adsorption, solubility and pore-filling) suggests that the sorption of CO<SUB>2</SUB> onto rock minerals may contribute to a significant portion of the CO<SUB>2</SUB> storage capacity in the course of CO<SUB>2</SUB> injection. <BR>This investigation points out the significance of CO<SUB>2</SUB> sorption onto rock minerals for the possible mechanism in CO<SUB>2</SUB> geological storage.

Evaluation of CO<SUB>2</SUB> storage capacity in water saturated reservoir rocks is very complex because various trapping mechanisms that act at different rates are involved and, at times, all mechanisms may be operating simultaneously. Thus, in terms of the water saturated reservoir rocks, a reliable estimate of CO<SUB>2</SUB> storage capacity requires a thorough understanding of the mechanisms of CO<SUB>2</SUB> trapping in this system.<BR>The objective of this study is to provide a fundamental knowledge about interactions among CO<SUB>2</SUB>, water and rock, and contributes to development of standards for CO<SUB>2</SUB> storage capacity estimation in the water saturated reservoir rocks. In this experiment, CO<SUB>2</SUB> sorption was measured for rock samples (quartzose arenite, greywacke, shale, granite and serpentine) , and mineral samples (quartz and albite) in a CO<SUB>2</SUB> rich dense phase at 50ºC and 100ºC, and pressures up to 20MPa, the condition of which is expected to occur mostly during CO<SUB>2</SUB> injection into pores of the water saturated reservoir rocks. The result obtained from the experiment exhibited a significant sorption capacity of CO<SUB>2</SUB> on all of the samples. At 50ºC and 100ºC, quartzose arenite indicated largest sorption capacity among the other samples in higher pressures (>10 MPa) . Furthermore, comparison with model prediction based on the pore filling model, which assumed that pores of the rocks and minerals will be filled with CO<SUB>2</SUB>, suggested the importance of the sorption mechanism in the CO<SUB>2</SUB> geological storage in addition to the pore-filling mechanism.<BR>The present results indicate that the sorption process may have significant and meaningful effect on the assessment of CO<SUB>2</SUB> storage capacity in geological media.

An anode-supported solid oxide fuel cell (SOFC) with a thin Gd(0.1)Ce(0.9)O(1.95) (GDC) electrolyte film of 3 mu m in thickness and nanostructured La(0.8)Sr(0.2)Co(0.8)Fe(0.2)O(3) (LSCF) cathode showed high electrochemical performance at low operating temperatures, with a maximum power density of 0.99 W cm(-2) at 600 degrees C using hydrogen as fuel.

Dense gadolinium doped ceria (GDC) electrolyte thin films were prepared on porous NiO-GDC substrates by spray coating process. Microstructure of the GDC thin films and effect of preparation process on the microstructure were examined. SEM results show that uniform and dense GDC thin films with a thickness of approximately 1 mu m were successfully prepared on porous NiO-GDC anodes. Anode-supported single cell with the thin GDC electrolyte film was tested using humidified hydrogen as a fuel, and exhibited relatively high electrical performance at low operating temperature (the maximum power density of 135 mW/cm(2) at 600 degrees C). This means that the thin GDC film may be applicable to an electrolyte for anode-supported SOFCs. The experimental results suggest that the spray coating method developed in this study may offer a useful route for preparing thin and dense electrolytes of SOFCs.

For the commercialization of solid oxide fuel cell (SOFC), in addition to the electrical reliability, it is also important to ensure the mechanical reliability of SOFC. Thus, the establishment of a suitable mechanical testing method under various temperatures and oxygen partial pressure conditions is a prerequisite for the development of reliable SOFCs. This paper presents the experimental results of the investigation of elastic modulus and fracture strength on the SOFC components under reducing conditions. An in-situ mechanical testing method was developed in order to investigate the elastic modulus and fracture strength of solid oxide fuel cells components under high oxidizing/reducing environments. The elastic modulus was shown to change under reducing condition, and the behavior was most likely due to non-stoichiometry. It was demonstrated that the in-situ mechanical testing method enabled us to estimate the internal stress in the SOFC cell and stack.

The conductivity and elastic modulus Of (CeO2)(1 - x)(YO1.5)(x) for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y2O3: this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity. the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content Of Y2O3 dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y2O3 dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y2O3, which also agreed with the experimental results. It was shown that the Y-O-Y bonding energy increased with the increasing content of Y2O3 dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y-O-Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y2O3 dopant content of approximately 20 mol%. (C) 2009 Elsevier B.V. All rights reserved.

LaC(2)@CNC/LaB(6) nanocomposites were prepared using a spark plasma sintering system. and their mechanical properties and the intensity of characteristic La X-rays from the composites were characterized for application as X-ray target material. Using LaB(6) as a binder, we succeeded in producing LaC(2)@CNC/LaB(6) nanocomposites with a bulk density (2.91 g/cm(3)) and specific electric resistance (3.12 x 10(-4) Omega cm) through solidification at 2123 K. The fracture bending strength of LaC2@CNC/LaB6 nanocomposites (224 MPa) was 1.5 times larger than that observed for graphite/LaB(6) composites. The most emitted characteristic La La X-ray from LaC(2)@CNC/LaB(6) nanocomposites was 7743 counts/mm(2)/s in comparison with 6372 counts/mm(2)/s for graphite/LaB(6) composites. (C) 2009 Elsevier B.V. All rights reserved.

Dense zeolite membrane without defects such as pinholes and cracks was synthesized on a porous alumina support by a newly modified hydrothermal technique, i.e., double-layered capsule hydrothermal method.

LaC(2)@CNC/LaB(6) nanocomposites were prepared using a spark plasma sintering system. and their mechanical properties and the intensity of characteristic La X-rays from the composites were characterized for application as X-ray target material. Using LaB(6) as a binder, we succeeded in producing LaC(2)@CNC/LaB(6) nanocomposites with a bulk density (2.91 g/cm(3)) and specific electric resistance (3.12 x 10(-4) Omega cm) through solidification at 2123 K. The fracture bending strength of LaC2@CNC/LaB6 nanocomposites (224 MPa) was 1.5 times larger than that observed for graphite/LaB(6) composites. The most emitted characteristic La La X-ray from LaC(2)@CNC/LaB(6) nanocomposites was 7743 counts/mm(2)/s in comparison with 6372 counts/mm(2)/s for graphite/LaB(6) composites. (C) 2009 Elsevier B.V. All rights reserved.

Homogenous NiO-Ce0.9Gd0.1O1.95 (GDC) nanocomposite powders were successfully synthesized by a hydroxide co-precipitation method. The synthesized powders consist of NiO and GDC double phases, and the average particle size is in the range of 10-40 nm. A solid oxide fuel cell (SOFC) with anode prepared from the synthesized NiO-GDC nanocomposite powders shows high electrical performance at low operating temperatures. Results indicate that the synthesized NiO-GDC nanocomposite powders are suitable anode materials for low-temperature SOFCs. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

SOFCs are a next-generation power generating technology employing hydrogen, and improving their reliability is the most important issue for achieving practical use. In this research, we are conducting studies to ensure overall long-term reliability by examining the interaction of mechanical, electrochemical factors in SOFC in a simulated operating environment. Especially the establishment of a suitable in-situ mechanical damage testing method is a pre-requisite for the development of reliable SOFCs. This paper presents the experimental results of the investigation of mechanical damage under redox cycle conditions.

The objective of this work is to study relationship between oxygen potential and mechanical properties of oxygen nonstoichiometric compound with Ce_<0.9>Gd_<0.1>O_<2-x>. Under high temperature and reducing conditions, oxygen content in Ce_<0.9>Gd_<0.1>O_<2-x> changes and oxygen defect is generated. Therefore Mechanical properties of Ce_<0.9>Gd_<0.1>O_<2-x> can change under such conditions. In our study, we developed new test apparatus for small punch test, which is able to measure mechanical properties under high temperature and reducing conditions. And several tests ran already with this new test apparatus. Advanced investigation would explain how mechanical properties behave in these conditions.

In this study, Crystal structure and mechanical properties of K_2NiF_4 type oxides were measured by high temperature X-ray diffractometry and in-situ small punch test as a function of oxygen partial pressure, P(O_2) and temperature. Chemically induced volume change was evaluated by nonstoichiometric data and the variation of the lattice constants with P(O_2). The elastic modulus and the fracture strength become larger at higher P(O_2) condition. This may be caused by the structural change due to the variation of oxygen content.

The paper provides an introduction to fundamental concepts of mathematical modeling of mass transport in fractured porous heterogeneous rocks. Keeping aside many important factors that can affect mass transport in subsurface, our main concern is the multi-scale character of the rock formation, which is constituted by porous domains dissected by the network of fractures. Taking into account the well documented fact that porous rocks can be considered as a fractal medium and assuming that sizes of pores vary significantly (i.e. have different characteristic scales), the fractional order differential equations that model the anomalous diffusive mass transport in such type of domains are derived and justified analytically. Analytical solutions of some particular problems of sub-diffusion and super-diffusion in the fractal media of various geometries are obtained by the method of Laplace transformations. Extending this approach to more complex situation when diffusion is accompanied by advection, solute transport in a fractured porous medium is modeled by the advection-dispersion equation with fractional time derivative. In the case of confined fractured porous aquifer, accounting for anomalous non-Fickian diffusion in the surrounding rock mass, the adopted approach leads to introduction of an additional fractional time derivative in the equation for solute transport. The closed-form solutions for concentrations in the aquifer and surrounding rocks are obtained for the arbitrary time-dependent source of contamination located in the inlet of the aquifer. Based on these solutions, different regimes of contamination of the aquifers with different physical properties can be readily modeled and analyzed. © 2009 SPIE.

Utilizing the double-porosity approach it is assumed that porous medium Is constituted by two groups of pores in such way that major mass transport takes place mostly along the network of larger pores (group 1) and these larger (stern) pores are Surrounded by the medium formed by the dead-end porous of fractal geometry (group 2). Solving analytically equation for the stern pore from the group I and accounting for the mass exchange with pores from the group 2, it is proved that diffusion in a stern pore should be described by the fractional differential equation. Based on this result. equation of mass flux that models non-Fickian diffusion in complex fractal medium is proposed. Applying this generalized form of mass transfer equation for modeling the contaminant transport in fractured porous aquifer leads to a fractional order differential equation, where mass exchange between blocks and fractures is modeled by the temporal fractional derivatives. This equation is solved analytically.

Utilizing the double-porosity approach it is assumed that porous medium is constituted by two groups of pores in such way that major mass transport takes place mostly along the network of larger pores (group 1) and these larger (stem) pores are surrounded by the medium formed by the dead-end porous of fractal geometry (group 2). Solving analytically equation for the stem pore from the group 1 and accounting for the mass exchange with pores from the group 2, it is proved that diffusion in a stem pore should be described by the fractional differential equation. Based on this result, equation of mass flux that models non-Fickian diffusion in complex fractal medium is proposed. Applying this generalized form of mass transfer equation for modeling the contaminant transport in fractured porous aquifer leads to a fractional order differential equation, where mass exchange between blocks and fractures is modeled by the temporal fractional derivatives. This equation is solved analytically. Copyright © 2008 by ASME.

Spray coating method is a cost-effective technique suitable for the preparation of uniform and large-area thin films. This article presents findings on the preparation of dense electrolyte thin films by spray coating method. Dense, crack-free Gd-doped CeO2 (GDC) thin films with a thickness of approximately 2m were successfully prepared on porous NiO-GDC substrates. The influence of the dispersion of GDC nanopowders in susupension on the microstructure of the thin films was investigated. Results show that agglomeration of GDC nanopowders in suspension resulted in a porous microstructure and a densely packed microstructure was obtained for the film prepared from a well-dispersed suspension.

Engineering ceramics have high stiffness, excellent thermostability and relatively low density, but their brittleness impedes their use as structural materials. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to produce CNT/ceramic composites with both high toughness and high temperature stability. Until now, however, materials fabrication difficulties have limited research on CNT/ceramic composites. The mechanical failure of CNT/ceramic composites reported previously is primarily attributed to poor CNTs-matrix connectivity and severe phase segregation. The connectivity with, and uniform distribution within the matrix are essential structural requirements for the stronger and tougher CNT/ceramic composites. Here we show that a novel processing approach based on the precursor method for synthesis of Al₂O₃ and acid-treated multi-walled carbon nanotubes (MWCNTs) can diminish the phase segregation, and render MWCNT/Al₂O₃ composites highly homogeneous. Combined with mechanical interlock induced by the chemically modified MWCNTs, this approach leads to improved mechanical properties. Direct toughness measurements, using the single edge notched beam method, reveal that only 0.9 vol.% acid-treated MWCNT addition results in 25% increases in fracture toughness (5.90±0.27 MPa·m^1/2).

In this paper, we discuss the effects of different oxygen partial pressures on the elastic modulus and fracture strength of 8 mol% yttria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC). The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 degrees C under different oxygen partial pressures in the range of 0.2 to 10(-22) atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10(-15) atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ.

Crystal structure and mechanical properties of La2NiO 4+δ were measured by high temperature X-ray diffractometry and in-situ small punch test as a function of temperature and oxygen partial pressure. As P(O2) increases, the lattice parameter perpendicular to the perovskite layer increases and that parallel to the layer slightly decreases, and the lattice volume slightly increases. Apparent and true thermal expansion coefficients were calculated from the variation of the lattice constants. The elastic modulus and the fracture strength become larger at higher P(O2) condition. This may be caused by the structural change due to excess oxygen. ©The Electrochemical Society.

Mechanical damages and their formation mechanisms in SOFC were investigated. Generalized schemes of the occurrence of mechanical failures were summarized, and among them, common features in various cell designs were extracted. They were discussed in three categories of (a) deformation of a cell due to its asymmetry, (b) propagation of mechanical defects, and (c) effects of irregular operations. Prototype-cell experiments were designed to reproduce the key features, and to develop a quantitative evaluation scheme of operational margins for prediction of the short and long term reliability of a specific cell design. Numerical calculation tools based on finite element method and homogenization method are designed. Experimental methods were developed to acquire high-temperature mechanical behaviors of the materials and cell stacks.

Engineering ceramics have high stiffness, excellent thermostability and relatively low density, but their brittleness impedes their use as structural materials. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to produce CNT/ceramic composites with both high toughness and high temperature stability. Until now, however, materials fabrication difficulties have limited research on CNT/ceramic composites. The mechanical failure of CNT/ceramic composites reported previously is primarily attributed to poor CNTs-matrix connectivity and severe phase segregation. The connectivity with, and uniform distribution within the matrix are essential structural requirements for the stronger and tougher CNT/ceramic composites. Here we show that a novel processing approach based on the precursor method for synthesis of Al₂O₃ and acid-treated multi-walled carbon nanotubes (MWCNTs) can diminish the phase segregation, and render MWCNT/Al₂O₃ composites highly homogeneous. Combined with mechanical interlock induced by the chemically modified MWCNTs, this approach leads to improved mechanical properties. Direct toughness measurements, using the single edge notched beam method, reveal that only 0.9 vol.% acid-treated MWCNT addition results in 25% increases in fracture toughness (5.90±0.27 MPa·m^1/2).

Sorption isotherms, which describe CO2 storage capacity of the host rock, are important for estimating the CO2 sequestration potential of geological formations. In this study, the sorption capacity of a sandstone and granite were evaluated experimentally by using a gravimetric method, and the experimental data corrected for the volume of sorbed CO2 phase were compared with storage models (adsorption monolayer, solubility and pore-filling models). The sorption measurement results indicated that CO2 sorption behavior could take place onto silica minerals in CO2-water-rock system, and it further indicated that CO2 sorption onto rocks may play an important role in storing CO2 in subsurface rock masses. (C) 2008 Elsevier Ltd. All rights reserved

In order to predict CO2 storage potential of candidate geological reservoirs, this study investigated the CO2 sorption capacity of sandstone and granite under air-dry and water-saturated conditions using a volumetric technique, at temperatures of 33, 40, and 50 degrees C and pressures up to 20MPa. The sandstone and granite have the potential to sorb CO2 under the both conditions. A comparison with model predictions (monolayer adsorption, solubility and pore-filling models) indicated that the sorption of CO2 onto rock minerals offers an important mechanism for the CO2-rock interactions which may take place in the course of CO2 injection. (C) 2008 Elsevier Ltd. All rights reserved

In this paper, we discuss the effects of different oxygen partial pressures on the deformation property and fracture characteristics of representative constituent materials for solid oxide fuel cells (SOFCs). The elastic modulus and fracture strength of 8 mol% yittria stabilized zirconia (8YSZ) and 10 mol% gadolinia doped ceria (10GDC) treated under different oxygen partial pressures were evaluated using the small-punch testing method in this study. The specimens of 8YSZ and 10GDC prepared by a sintering process were treated at 800 C under an oxygen partial pressure in the range of 0.21 to 10(-22) atm for 1 hour. The treated specimens were then fast cooled down to a room temperature, and their mechanical properties were measured under an atmospheric pressure condition by using the small-punch testing method. The experimental results revealed that both the elastic modulus and fracture strength of the 10GDC decreased drastically when the oxygen partial pressure of the treatment was less than 10-15 atm, whereas no significant variation in both the mechanical properties was observed for the 8YSZ. The elastic modulus and fracture strength of 10GDC for the treatment under 10(-22) atm was reduced down to 10-20 % of those treated under the atmospheric pressure. SEM observations revealed that the fracture surface of the 10GDC specimens was changed from transgranular mode to intergranular mode when the oxygen partial pressure was reduced, whereas the fracture surface of the 8YSZ specimens was transgranular regardless of the different oxygen partial pressures.

Engineering ceramics have high stiffness, excellent thermostability, and relatively low density, but their brittleness impedes their use as structural materials. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to provide CNT/ceramic composites with both high toughness and high temperature stability. Until now, however, materials fabrication difficulties have limited research on CNT/ceramic composites. The mechanical failure of CNT/ceramic composites reported previously is primarily attributed to poor CNT -matrix connectivity and severe phase segregation. Here we show that a novel processing approach based on the precursor method can diminish the phase segregation of multi-walled carbon nanotubes (MWCNTs), and render MWCNT/alumina composites highly homogeneous. The MWCNTs used in this study are modified with an acid treatment. Combined with a mechanical interlock induced by the chemically modified MWCNTs, this approach leads to improved mechanical properties. Mechanical measurements reveal that only 0.9 vol% acid-treated MWCNT addition results in 27% and 25% simultaneous increases in bending strength (689.6 +/- 29.1 MPa) and fracture toughness (5.90 +/- 0.27 MPa m(1/2)), respectively.

Blast furnace water-cooled slag (BFWS) has been solidified hydrothermally with tobermorite formation. The experimental results showed that the addition of fly ash and quartz was favorable to the formation of tobermorite, and the strength development of solidified body depended on both of the tobermorite formation and filling degree of formed tobermorite in the spaces between BFWS particles. The fly ash added appeared to have a higher reactivity than the quartz used during the initial hydrothermal processing due to the higher solubility of glassy phase in fly ash. The tobermorite formation seemed to be very sensitive to the fly ash content, e.g., the addition of fly ash 10-20 mass% was favorable to tobermorite formation, while the excessive addition of fly ash (&gt; 20 mass%) appeared to impede the tobermorite formation. The excessive addition of quartz was also shown to exert a negative effect on the tobermorite formation, which causes strength deduction. (c) 2008 Elsevier Ltd. All rights reserved.

Multi-walled carbon nanotubes/alumina composites were prepared by precursor method. Here, the distilled water with a small amount of surfactant (2,2,2-nitrilotriethanol) was used as a dispersing agent for MWCNTs. In order to evaluate the effects of MWCNT addition on mechanical properties and micro/narrostructure of the resultant composites, we employed two sets of the composites having different sintering additives (silica and magnesia). XRD analysis revealed that MWCNT/alumina composites were successfully synthesized by the dehydration of aluminum hydroxide-MWCNTs mixture at 1500 degrees C during spark plasma sintering. However, fracture property tests have shown that no improvement of the bending strength and fracture toughness of both the composites was achieved by addition of MWCNTs. According to the fracture property tests and SEM data, in conjunction with the relationship between porosity and bending strength, the MWCNT aggregate in the matrix may possess no load-carry ability. (C) 2008 Elsevier B.V. All rights reserved.

Binder-free single-walled carbon nanotube (SWCNT) solids were evaluated for solid lubrication applications. The steady-state friction coefficients (mu) for the SWCNT solids were found to reach values as low as 0.22-0.24, according to unidirectional sliding friction tests using Si3N4 counterparts in air. The values were slightly higher than that of bulk graphite material (mu = 0.20). SEM and Raman analyses showed that most SWCNTs that existed in the friction surface transformed into SWCNT-derived transferred film made up of amorphous carbon during sliding. The resultant friction behavior may be related to the smearing of transferred film over the contact area, which was expected to permit easy shear and then help to achieve a lubricating effect during sliding.

The electrical properties of polymer nanocomposites containing a small amount of carbon nanotube (CNT) are remarkably superior to those of conventional electronic composites. Based on three-dimensional (3D) statistical percolation and 3D resistor network modeling, the electrical properties of CNT nanocomposites, at and after percolation, were successfully predicted in this work. The numerical analysis was also extended to investigate the effects of the aspect ratio, the electrical conductivity, the aggregation and the shape of CNTs on the electrical properties of the nanocomposites. A simple empirical model was also established based on present numerical simulations to predict the electrical conductivity in several electronic composites with various fillers. This investigation further highlighted the importance of theoretical and numerical analyses in the exploration of basic physical phenomena, such as percolation and conductivity in novel nanocomposites.

The hydrothermal autoclave experiments were conducted to simulate the interactions in the scCO(2)/water/rock minerals (quartz, biotite and granite) reaction systems using a Hastelloy C reaction cell at 100 degrees C. The dissolution characteristics of rock minerals and their surface texture alternation after hydrothermal treatment were examined by ICP-AES and SEM/EDX investigation, respectively. The results suggested that the hydrolysis of plagioclase phase should be mainly responsible for the elements dissolved from the Iidate granite samples. The dissolution was encouraged by the introduction of CO(2) in the water/granite system, and generated an unknown aluminosilicate. No distinct chemical alternations occurred in the water-free scCO(2)/granite system, which indicated that rock minerals should be chemically stable in the water-free scCO(2) fluids under the current mild experimental conditions. Both the highest concentration of Ca existing in the scCO(2)/vapor/granite system and the SEM observation results of calcite deposit, suggested that a meaningful CO(2) minerals trapping process should be potential in the CO(2)-rich field during a short physicochemical interaction period.

A hydrothermal processing method has been used to solidify blast furnace water-cooled slag (BFWS), in which the BFWS could be solidified in an autoclave under saturated steam pressure (1.56 MPa) at 200 degrees C for 12 h by the additions of quartz or coal fly ash. The experimental results showed that the addition of the quartz or fly ash was favorable to the formation of tobermorite, and the tobermorite formation in turn exerted a signifiant influence on tensile strength. The strength development depended on both tobermorite formation and the density of the tobermorite formed. The excessive addition of quartz appeared to cause strength deterioration due to the fact that the residual quartz affected the formation of tobermorite in the solidified specimens. Fly ash could be used as an additive for the hydrothermal solidification of BFWS, which may offer both energy saving and cost reduction.

In order to improve the interface strength in the bonded body of hydroxyapatite (HA) ceramics and Ti disks prepared by a hydrothermal hot-pressing (HHP) method, the effects of Ti surface modification on the bonding behavior were investigated. The reaction layer composed of titanium dioxide and sodium titanate was formed on the Ti surface using a 5 M NaOH solution with the objective of increasing the interface strength between the Ti substrate and HA ceramics to be formed by the HHP method. Three conditions with different temperature and treatment times were tested to modify the Ti surface. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HA. Solidification of HA and its bonding with Ti were achieved simultaneously by using the HHP method at the low temperature as low as 323 K. 3-point bending tests were conducted to obtain an estimate of the interface fracture toughness of HA/Ti. The Ti surface modification conducted at 323 K for 2 h using the hydrothermal NaOH solution was shown to be most effective among the three conditions tested. The hydrothermal Ti surface modification enabled us to increase significantly the interface fracture toughness. The enhancement of the interface fracture toughness was possibly due to the presence of anatase formed on the Ti surface and the good adhesion in the bioactive layer. (c) 2006 Elsevier B.V. All rights reserved.

In order to improve the interface strength in the bonded body of hydroxyapatite (HA) ceramics and Ti disks prepared by a hydrothermal hot-pressing (HHP) method, the effects of Ti surface modification on the bonding behavior were investigated. The reaction layer composed of titanium dioxide and sodium titanate was formed on the Ti surface using a 5 M NaOH solution with the objective of increasing the interface strength between the Ti substrate and HA ceramics to be formed by the HHP method. Three conditions with different temperature and treatment times were tested to modify the Ti surface. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HA. Solidification of HA and its bonding with Ti were achieved simultaneously by using the HHP method at the low temperature as low as 323 K. 3-point bending tests were conducted to obtain an estimate of the interface fracture toughness of HA/Ti. The Ti surface modification conducted at 323 K for 2 h using the hydrothermal NaOH solution was shown to be most effective among the three conditions tested. The hydrothermal Ti surface modification enabled us to increase significantly the interface fracture toughness. The enhancement of the interface fracture toughness was possibly due to the presence of anatase formed on the Ti surface and the good adhesion in the bioactive layer. (c) 2006 Elsevier B.V. All rights reserved.

There are a tremendous number of asbestos-containing buildings without any surveys on the presence of asbestos because of the difficulty to detect asbestos in building materials simply and quickly, although a great deal of worldwide effort was put into removing asbestos of which inhalation causes serious diseases. In this study, we newly developed a simple dyeing method to detect chrysotile asbestos, the most commonly used type of asbestos, in asbestos-cement composite materials using magnesium-chelating organic dyes. As an essential process for selective dyeing of chrysotile asbestos, special pretreatment with a calcium-chelating agent was developed to prevent the dyes from reacting with calcium, which is the major component of concrete materials. Our developed selective dyeing method was shown to possess sufficient sensitivity for detecting chrysotile asbestos in an amount greater than 0.1 mass% in concrete specimens, and there was an approximately linear relationship between the area fraction of dyed spots and the mass fraction of chrysotile asbestos. Our results may provide a basis for further development of a simple on-site detection method for chrysotile asbestos in building materials and may facilitate the progress of control and removal of asbestos in the environment.

We produced large binder-free multi-walled carbon nanotube (MWNT) blocks from fluorinated MWNTs using thermal heating and a compressing method in vacuo. This technique resulted in the formation of covalent MWNT networks generated by the introduction of Sp(3)-hybridized carbon atoms that cross-link between nanotubes upon de-fluorination. The resulting carbon nanotube blocks are lighter than graphite, can be machined and polished, and possess average bending strengths of 102.2 MPa, a bending modulus of 15.4 GPa, and an electrical conductivity of 2.1 X 10(2) S/cm. Although each nanotube exhibits a random structure in these blocks, the mechanical properties are 3 times higher than those obtained for commercial graphite. On the basis of theoretical molecular dynamics simulations, a model is presented for the nanotube interconnecting mechanism upon de-fluorination.

Multi-walled carbon nanotube (MWCNT)/Al2O3 Composites with MWCNTs content up to 10 mass% were prepared by precursor method. XRD analysis revealed that MWCNT/Al2O3 composites were successfully synthesized by the dehydration of aluminum hydroxide-MWCNTs mixture at 1500 degrees C in vacuum. The steady-state friction coefficient (mu) of the composites decreased with increasing up to 4 mass% MWCNT and stayed constant (mu = 0.33) with further addition of MWCNT, which value was substantially lower than that of MWCNT-free monolithic Al2O3 (mu = 0.57). Microstructural observations showed that resultant friction behavior may be related to the smearing of transferred film over the contact area, which was expected to permit easy shear and then help to achieve a lubricating effect during sliding. However, fracture property tests have shown that no improvement of the fracture strength and fracture toughness of the composites was achieved by addition of MWCNTs. It may be mainly due to the agglomeration of MWCNTs and the weak interface between MWCNTs and the Al2O3 matrix. (C) 2007 Elsevier B.V. All rights reserved.

It is an important step to understand the capacity of host reservoir rocks for CO_2 storage in order to assess the potential of CO_2 geological sequestration. In this study, CO_2 sorption capacity of rocks (granite and sandstone) under air dry and water saturated conditions was evaluated experimentally at temperatures of 33, 40 and 50℃, and pressures up to 20 MPa using a volumetric method. As a result, sorption isotherms for CO_2 showed that the CO_2 sorption capacity of both the rocks increased with the increasing CO_2 pressure, and decreased with the increasing temperature under both the air dry and water saturated conditions. The amount of CO_2 sorption are significantly larger than theoretical value based on a solubility model, which assumes that CO_2 injected within water-filled reservoir will dissolve into pore water. These CO_2 sorption capacities could not fully be explained by CO_2 dissolution in water alone. Furthermore, it has been shown very interestingly that the amount of CO_2 sorption measured for the air dry condition was close to that obtained for water saturated condition. The amount of CO_2 sorption for the sandstone is approximately two times larger than that of the granite. This investigation may point out the significance of CO_2 sorption onto rock minerals for the possible mechanism in CO_2 geological sequestration.

Powder Jet Deposition (PJD) method is one of the film forming technique& Ceramics films can be fabricated by this method Ytariastabilized zirconia (YSZ) thin films were deposited on various substrates by PJD method YSZ thin film was fabricated in systemically changed substrates, particle sizes and carrier gas pressures. The microstructures of YSZ films were observed by scanning electron microscope (SEM). From this study results, the amount of deposition rate by PJD method varies according to substrate hardness and powder size. Similarly, the film structures are affected by substrate and powder size. Additionally, the electrical conductivity of YSZ film on Al_2O_3 substrate was measured as a function of temperature using impedance and two-probe A.C. method From this measurement, the amount of this film's electrical conductivity is good agreement from other studies of YSZ bulks. This result shows probability of application to high temperature ceramics devices such as Solid Oxide Fuel Cells (SOFCs), gas sensors.

With multi-walled carbon nanotubes (MWCNTs) as reinforcement, MWCNT/alumina composites were prepared at the MWCNTs mass% of 0.5. A flexural strength of 572.1 +/- 28.3 MPa and fracture toughness of 4.80 +/- 0.42 MPa.m(1/2), 1.2 times that of MWCNT-free monolithic alumina prepared under the same processing condition, was achieved. Experimental results showed that the dispersibility of the MWCNTs in the composite was crucially important in order to improve the mechanical properties of the MWCNT/alumina composite material.

The influence of chemically-induced expansion on the fracture damage of a ceria based solid oxide fuel cell (SOFC) was investigated by using numerical stress analyses. The single cell examined in this study was composed of electrolyte [(CeO<SUB>2</SUB>) <SUB>0.8</SUB> (SmO<SUB>1.5</SUB>) <SUB>0.2</SUB>], anode (Cermets of NiO-20 SDC), and cathode (La<SUB>0.6</SUB>Sr<SUB>0.4</SUB>Co<SUB>0.2</SUB>Fe<SUB>0.8</SUB>O<SUB>3</SUB>), respectively. The finite element method was employed to calculate the residual stress, thermal stresses, and chemically-induced expansion stresses for the single cell. The residual and thermal stresses were calculated much smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically-induced expansion stresses were shown to remarkably increase for the temperature range greater than 973 K and accounted their magnitude for the primary part of the induced stress. It was shown from the stress analysis that the maximum stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission method. The above-mentioned calculation results suggest that the chemically-induced expansion should be taken into account for the use of ceria based ceramics materials in SOFCs.

Carbon dioxide (CO2) is considered to be one of the greenhouse gases that may contribute most to global warming on the earth. Disposal of CO2 from stationary sources into subsurface structures has been suggested as a possible means for reducing CO2 emissions into the atmosphere. However, much remains to be done in the issues regarding the safety and reliability of CO2 geological sequestration. In this study, we have developed a simulation code by using the mathematical model of two phase flow in porous media to analyze the flow dynamics in the subsurface. The equation of state for CO2 covering the fluid region from the triple point to the supercritical region is employed to model the states of CO2 gas, liquid and supercritical state. The correct understanding of the CO2 state under the geological formation condition is an important factor to predict the injection pressure and CO2 fluid permeation because the fluid density has a great effect on the injection behavior. The numerical simulation was implemented under several geological conditions including gas, liquid and supercritical states to examine the optimal injection condition. Comparing the numerical results obtained using the equation of state for CO2 with those obtained using the ideal gas equation, it has been shown that the difference in the injection pressure appears to be significant near the condition of the critical point of CO2 and the phase equilibrium curves between the gas and liquid states. The numerical simulation has been implemented to examine the effect of the reservoir condition on the injection behavior. The injection pressure is decreased at the lower reservoir temperature and higher hydrostatic pressure condition. The CO2 permeation is also strongly affected by the reservoir condition, and the spatial CO2 saturation becomes higher with increasing reservoir temperature. It has been demonstrated that the simulation code developed in this study may be useful to provide knowledge required to select the reservoir condition for CO2 geological sequestration. (c) 2007 Elsevier Ltd. All rights reserved.

NiO-Ce0.8Sm0.2O1.9 (SDC) composite nanopowders, which are being investigated as a promising anode material for intermediate-low temperature solid oxide fuel cells (SOFCs), were successfully synthesized by hydroxide co-precipitation method. The effects of calcination temperature and time on crystal phase, crystallite size, average particle size and particle size distribution of the synthesized powders were investigated by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis showed that the synthesized powders consisted of two phases, NiO and SDC, without any other noticeable phase. The NiO and SDC phases were formed after calcining at 500 degrees C. The calcination temperature is the most important factor which affects the crystal phase, particle size and particle size distribution. With an increase in the calcination temperature, the average particle size of the synthesized powders increased and the particle size distribution became wider. The average particle size of the powders calcined at 600-900 degrees C was in the range of 9.8-39 nm according to the TEM analysis.

Nanoparticles of La0.8Sr0.2Co0.8Fe0.2O3, which are being investigated as cathode materials for intermediate-low temperature solid oxide fuel cells, were successfully synthesized by a novel sol-gel process. The thermal decomposition behavior of gel precursor was examined using TG/DTA analysis. Development of crystalline phases in the powders calcined at various temperatures was monitored by x-ray diffraction. Single phase La0.8Sr0.2Co0.8Fe0.2O3 could be obtained after calcining at 800 degrees C. A small amount of impurity phase existed in the powders calcined at the temperature below 700 degrees C. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy. The synthesized powders had an average particle size of 30 similar to 90 nm at 600 similar to 1100 degrees C. The average particle size of the powders increased with increase in calcination temperature. Noticeable changes occurred at temperature above 800 degrees C, and the coarse particles existed in the powders calcined at high temperatures.

In this paper, 10-20% samaria-doped ceria (10SDC and 20 SDC) electrolyte films were successfully prepared by a citrate sot-gel route combined with a sot suspension spray coating technique. The characterization and microstructure of the thin film were investigated by XRD and FE-SEM. The results show that the SDC film prepared was pure fluorite type nanocrystalline, homogenous and almost fully dense, as well as indicate the flexibility of adjustable SDC chemical compositions. Electrochemical performance of a single cell based on the thin 20SDC film with thickness of 500 nm and La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) as cathode material was examined. The cell provided an OCV of 0.83 V at 600 degrees C which was close to that of the thicker ceria cell (10 mu m) and maximum power densities of 41, 90, 78, 32 mW.cm(2) at 600, 700, 800 and 900 degrees C, respectively. It was demonstrated that the thin SDC film less than several mu m showed a good combination with the porous Ni-GDC anode substrate and good insulating ability for electrons migration at temperatures less than 700 degrees C. The thin ceria electrolyte prepared was potential to use for the IT-SOFCs.

Extensive usage of chrysotile asbestos has resulted in the remains of large numbers of chrysotile asbestos-containing buildings to be surveyed. We have recently developed a simple dyeing method for detecting chrysotile asbestos in building materials, which involves pretreatment with calcium-chelating agent and dyeing treatment with magnesium-chelating organic dyes. In this study, we further developed a method which eliminates dyed asbestos substitutes containing magnesium, potentially present in building materials. In the new method, post-treatment with formic acid was conducted to dissolve the non-chrysotile asbestos materials in order to delineate dyed chrysotile asbestos. The calcium-masking process was also shown to be an essential process even when the post-treatment was conducted. It was shown that the new method developed in this study may enable us to dye chrysotile asbestos only without detecting asbestos substitutes in building materials.

Transition from opening-mode wing crack growth to shear type fracture has been investigated by conducting triaxial compression tests under confining pressures, using epoxy resin cylindrical specimens. The epoxy resin used exhibited viscoplastic deformation characteristics under confining pressures, which is expected to simulate the nonlinear deformation observed commonly for rocks at great depths and to provide useful insight in understanding of the fracture transition in rocks. Under the range of confining pressures, 10 MPa-30 MPa, an array of opening-mode wing cracks were initiated from a preexisting inclined penny-shaped crack, as the axial stress was increased. Only the extension of a wing crack was observed to take place under no confining pressure condition. It was shown that the growth of the wing cracks were suppressed when higher confining pressures were applied and shear type fracture consisting of several wing cracks was induced as the deformation progressed. The experimental observation suggests the possibility of occurrence of shear type fracture in such a homogeneous material under higher confining pressures, and the mechanical interaction between cracks plays a crucial role in the generation of shear type fracture rather than the inhomogeneity of rocks.

With multi-walled carbon nanotubes (MWCNTs) as reinforcement, MWCNT/alumina composites were prepared at the MWCNTs mass% of 0.5. A flexural strength of 572.1±28.3MPa and fracture toughness of 4.80±0.42MPam 1/2, 1.2 times that of MWCNT-free monolithic alumina prepared under the same processing condition, was achieved. Experimental results showed that the dispersibility of the MWCNTs in the composite was crucially important in order to improve the mechanical properties of the MWCNT/alumina composite material. © 2008 American Institute of Physics.

In this study, Ni-Gd0.1Ce0.9O1.95 (GDC) anode-supported ceria electrolyte film was prepared by a citrate so]gel route. A simulated environment testing method which was combined with acoustic emission (AE) monitoring was developed to investigate the electrochemical performance and fracture process of a fuel cell Ni-GDC/Sm0.2Ce0.8O1.9 (20SDC)/La0.6Sr0.4CO0.2Fe0.8O3-delta (LSCF) based on this thin film with thickness of 500 nm. The damage testing method was applied o anode-supported thin creia electrolyte single cells. The results showed that the AE monitoring detected the fracture process at cell performance temperatures of 700-900 degrees C, which showed the delamination of LSCF cathode from the SDC electrolyte film, which presented a drastic decrease of electrical performance. It was demonstrated that the AE monitoring conducted in this study was useful to detect and analyze the fracture process of the single cell with the electrochemical measurement.

Polymer/carbon nanotubes nanocomposites were fabricated by an in situ polymerization process using multi-wall carbon nanotubes (MWNT) as filler in an epoxy polymer. Effects of curing process, mixing speed, mixing time, addition of ethanol, timing of hardener addition, etc., in the fabrication process on the electrical properties of nanocomposites have been investigated. In the fabrication process, the effective formation of macroscopic conducting network in matrix is most important to enhance the electrical properties of nanocomposites. It was found that the curing temperature and the mixing conditions are key factors in the fabrication process, which influence the formation of conducting network significantly. Therefore, careful design of these factors in the fabrication process is required to achieve high electrical performances of nanocomposites. The experimental percolation threshold of the resultant nanocomposites was around 0.1 wt%. Moreover, a statistical percolation model was built up to numerically investigate the percolation threshold. The experimental electrical conductivity increases from the percolation threshold following a percolation-like power law with the identified critical exponent t as 1.75. (C) 2008 Published by Elsevier Ltd.

The fracture strength and creep rate of rear earth (Y and Gd) doped ceria are systematically studied from the viewpoints of dopant concentration, oxygen partial pressure and temperature dependences. Fracture strength and creep rate are measured by modified small punch test and four point bending method, respectively. From results of fracture test, the highest fracture strength is obtained on the samples sintered at 1600 degrees C for Y and Gd-doped CeO(2). The unique temperature dependence of fracture strength on doped CeO(2) is observed. It shows the local minimal value at around 600 degrees C and the fracture strength increases with increasing temperature. The fracture surface structure drastically changes with changing temperature observed by SEM. Since we observed the close coincidence between the fracture strength and the ratio of transcrystalline fracture surface for all samples, it is concluded that the increase of fracture strength at high temperature in doped CeO(2) can be attributed to the temperature dependence of transcrystalline fracture strength. Typical creep curves of 2, 5, 10 and 20 YDC were measured under constant load in air. The creep rate decreases with increasing the dopant concentration. From the analysis of creep properties, the creep is controlled by cerium vacancy diffusion and change of ceria vacancy concentration decreases creep rate.

Electrical conductivity of 10 mol% yttria-stabilized zirconia (10YSZ) and YBa2Qi307-s (YBCO) under stress were measured in the temperature range from 600°C to 800°C for 10YSZ and at 600°C for YBCO. It was observed that conductivity under stress slightly decreased for 10YSZ and increased for YBCO. In the case of 10YSZ, the conductivity change was caused by the change in mobility. In the case of YBCO, the conductivity change was caused by the change in mobility and change in carrier concentration. ©The Electrochemical Society.

Blast furnace water-cooled slag (BFWS) has been solidified using a hydrothermal processing method, in which the BFWS could be solidified in an autoclave under saturated steam pressure (1.56 MPa) at 200 degrees C for 12 h by the additions of quartz or coal flyash. The tensile strength development was shown to depend on the formation of tobermorite and the packing state of the formed tobermorite in the solidified bodies. The additions of quartz or fly ash were proved to be favorable not only to the formation of tobermorite but also to the transformation of hibschite, the former improving the strength, and the latter deteriorating the strength. The excessive addition of quartz appeared to cause strength deterioration due to the fact that the residual quartz affected the formation of tobermorite in the solidified bodies.

Solute transport in the fractured porous confined aquifer is modeled by the advection-dispersion equation with fractional time derivative of order gamma, which may vary from 0 to 1. Accounting for diffusion in the surrounding rock mass leads to the introduction of an additional fractional time derivative of order 1/2 in the equation for solute transport. The closed-form solutions for concentrations in the aquifer and surrounding rocks are obtained for the arbitrary time-dependent source of contamination located in the inlet of the aquifer. Based on these solutions, different regimes of contamination of the aquifers with different physical properties are modeled and analyzed.

Hydroxyapatite (HA) ceramics were prepared by a hydrothermal hot-pressing (HHP) method at a low temperature (300 degrees C). DCPD (CaHPO4 center dot 2H(2)O) + Ca(OH)(2), OCP (Ca8H2(PO4)(6)center dot 5H(2)O) + Ca (OH)(2), DCPD + NH3 center dot H2O, OCP + NH3 center dot H2O or alpha-TCP (Ca-3(PO4)(2)) + NH3 center dot H2O were used as the precursors. The mixture was treated by HHP under a condition of 300 degrees C/40 MPa. In sample DCPD + Ca (OH)(2) and OCP + Ca(OH)(2), the HA ceramics obtained showed a porous and homogenous microstructure, and the bending strength were 9.9 MPa and 10.9 MPa, respectively. In sample alpha-TCP+NH3 center dot H2O, rod-like HA crystals produced. When the starting materials were DCPD + NH3 center dot H2O, OCP + NH3 center dot H2O, the HA particles produced exhibited plate-like features. It appeared that the plate-like HA particles stacked into a lamellar structure. Tie formation of the lamellar structure leads to a noticeable improvement in fracture property of the HA ceramic. The bending strength and the fracture toughness of the sample prepared from OCP and ammonia water reach 90 MPa and 2.3 MPam(1/2), respectively.

One of the key issues for the development of high toughness carbon nanotube ( CNT) reinforced composites is the control of the interfacial bond between the CNT and the matrix. Here, we introduce a novel technique to facilitate the homogeneous coating of single-walled carbon nanotube ( SWCNT) bundles with polycarbosilane ( PCS)-derived SiC nanoparticles. The PCS dissolved in n-hexane was used as a precursor for SiC nanoparticles. The results obtained from XRD, TEM and EDXS analyses confirmed the formation of beta-SiC nanoparticles of about 20 nm in diameter, which possessed a relatively homogeneous distribution on the SWCNT bundles. It was shown that the number of SiC nanoparticles per unit of SWCNT surface area could be adjusted by changing the weight ratio of PCS and SWCNTs. This approach may provide a useful route for the preparation of SiC/SWCNT nanocomposites that have a tunable interface property with the matrix and potentially with an enhanced anchor effect, which may have potential applications as a reinforcing element in CNT/ceramic composites.

Anthropogenic effects on the climate can be mitigated through various artificial measures. Amongst others CO_2 sequestration on geological reservoirs including deep saline aquifers, depleted oil/gas reservoirs, and coal seams is expected to provide a powerful means for drastically reducing emissions of CO_2 to the atmospheric. It may be an important step to understand the capacity of the host reservoir rock for CO_2 storage in order to assess the potential of CO_2 geological sequestration. In this study, CO_2 sorption capacity of rocks (granite, sandstone and natural quartz) under air dry condition was evaluated experimentally at temperatures of 50 and 100℃, and pressures up to 20MPa using a magnetic suspension balance (MSB), which allows us to measure the rock weight under the presence of supercritical CO_2. The CO_2 sorption isotherms of the rocks obtained showed that the CO_2 sorption capacity increased with the increasing pressure and decreased with the increasing temperature. Especially, the CO_2 sorption isotherms of the natural quartz were nearly the same as that of the granite. The present experimental results obtained from the weight measurements suggest that the sorption of CO_2 onto silica minerals may be the important mechanism for the CO_2 storage in reservoir rocks.

To understand the initial reactions of granite in a CO2-saturated hydrothermal system, experiments were conducted using a batch-type autoclave over a temperature range of 100-350 degrees C at up to 250 bar and numerical computations of phase equilibria based on the experimental results were carried out. The experiments showed that the dissolution of granite and the deposition of secondary minerals were encouraged by the addition of CO2. Solution chemistry and examination of the granite's surface texture suggested that its initial dissolution is characterized by the release of Na and Ca (from the dissolution of plagioclase) and that initial precipitation occurs by deposition of some secondary minerals on to plagioclase and/or biotite in the CO2-saturated system. However, the effect of CO2 was small at 350 degrees C owing to the low activity of H2CO3. According to EDX analysis and numerical phase equilibrium calculations, the secondary minerals formed might be kaolinite, muscovite, smectite and calcite. That is, the granite as a whole might have the potential to take-up dissolved CO2. The results suggest that the alteration of granite under CO2-saturated hydrothermal conditions has the potential to capture CO2 when it is injected at moderate temperatures (150-250 degrees C) into granite-hosted rock masses. (c) 2006 Elsevier Ltd. All rights reserved.

Three types of austenitic stainless steels JK2, JJ1 and JN1 were isothermally aged at temperatures from 600 to 900 degrees C for 10 to 1000 minutes in order to study the microstructural evolution and its effect on the fracture toughness at cryogenic temperatures. The Charpy V-Notch fracture energy at 77 K showed a significant decrease with aging time in JJ1 and JN1 steels because of their higher contents of C and N. In contrast, the fracture energy corresponding to the aged JK2 steel decreased gradually with aging time. The abundant intergranular precipitation of carbides and nitrides seems to be the responsible for the fracture toughness deterioration in the aged JJ1 and JN1 steels. On the other hand, the intergranular precipitation of carbides was less abundant in the aged JK2 steel. The scanning electron microscope fractographs of the CVN test specimens corresponding to the aged JJ1 and JN1 steels showed mainly an intergranular brittle fracture and its fraction increased with aging time and temperature. In general, the presence of a more abundant intergranular precipitation resulted in a more rapid decrease in toughness with aging time.

In this paper, a spark plasma sintering (SPS) method was employed to solidify single-walled carbon nanotubes (SWCNTs) only, and the effect of processing conditions on the mechanical properties of the SWCNT solids were examined using a small punch (SP) testing method. The sintering temperatures used was in the range of 600∼1400°C, and the sintering pressures used was 40 MPa and 120 MPa. It was demonstrated that the SPS method allowed SWCNTs to be solidified, without any additives. The experimental results showed that the purification of raw soot was critically importance. The SWCNT solids prepared from purified raw soot showed significant non-linear deformation response, producing quasi-ductile fracture behavior. In contrast, raw soot produced brittle solids. The Young's modulus, fracture strength and work of fracture increased with the increasing sintering temperature and pressure. The Raman and SEM analyses showed that the amount of the graphite-like materials were observed to increase with the increasing temperature and pressure, which indicate that the structure of the SWCNTs was changed partially into the graphite-like materials. The formation of graphite-like materials increased tendency of brittle fracture in the SWCNT solids. TEM observations revealed that the fracture surfaces of the SWCNT solids were characterized by pull out of SWCNT bundles. This observation suggests that it may be possible to improve the mechanical properties of SWCNT solids by increasing the cohesion between SWCNTs.

Binder-free single-walled carbon nanotube (SWCNT) solids were evaluated for solid lubrication applications. The steady-state friction coefficient (p) for the SWCNT solids were found to reach values as low as 0.22-0.24, according to unidirectional sliding friction tests using Si3N4 counterpart in air, which values were slightly higher than that of bulk graphite material ( mu=0.20). SEM and Raman analyses showed that most of SWCNTs that existed in the friction surface transformed into SWCNT-derived transferred film made up of amorphous carbon during sliding. The resultant friction behavior may be related to the smearing of transferred film over the contact area, which was expected to permit easy shear and then help to achieve a lubricating effect during sliding.

The Al2O3/MWCNT composites with MWCNT content up to 10 mass% have been prepared by spark plasma sintering. The effect of MWCNT addition on the tribological and strength properties was investigated, The experimental results revealed that the steady-state friction coefficient (mu) of the composites decreased with increasing up to 4 mass% MWCNT and stayed constant (mu=0.33) with further addition of MWCNT, which value was substantially lower than that of MWCNT-free monolithic Al2O3 (g=0.57). These properties seem to be related to the formation of MWCNT-derived transferred film made up of carbonaceous material during sliding. However, it has not been demonstrated that the presence of MWCNTs improves the fracture strength and fracture toughness of the composites. It is mainly due to the agglomeration of M`WCNTs and the weak interface between MWCNTs and the Al2O3 matrix.

Preparation procedure of multi-walled carbon nanotube (MW CNT) films shows as follows. First, as-grown MWCNTs heated in the air and treated with hydrochloric acid to remove amorphous carbon and catalytic metal particles respectively. Then, the o1btained MWCNT samples were treated with nitric acid at 373K to add carboxylic acid and hydroxyl groups on their surface. Finally, MWCNT films were prepared by employing a condensation reaction utilizing 1,3-dicyclohexylearbodiimide (DCC) to cross-link each MWCNT with chemical bonds. Morphological changes in the resultant MWCNT films were monitored using scanning electron microscopy, and showed that the MWCNTs were randomly intertwined in the films. The prepared MWCNT films were 17mm in diameter and 20 mu m in thickness, and the apparent density was 0.59 g/cm(3). Fourier transform-infrared spectroscopy confirmed that each MWCNT modified with carboxylic acid and hydroxyl groups was cross-linked through the ester bond. It was found that the ratio of the number of ester cross-links and carbon atoms of the nanotubes per unit apparent volume (cm) of condensed-MWCNT films was 5.23x10(-3) using TGA. The tensile strength and Vickers hardness of condensed-MWCNT films achieved an average of 15MPa and 9.2MPa, respectively, and was greater than those of free-standing MWCNT films without ester bond.

In this study, laboratory supercritical fluid CO2-rock interactions experiments were conducted in a Hastelloy C-276 hydrothennal autoclave apparatus at 100 degrees C and a CO2 pressure of 10 MPa. The dissolution characteristics of rock minerals and their surface texture alternation after CO2 treatment were carefully examined by ICP-AES, CrC/MASS and SEM/EDX investigation, respectively. The results showed that Si element was present in the treated scCO(2) fluid, and its concentration increased with the increasing reaction time. In addition, a high C content film deposit-like carbon was found to be present on the treated quartz surface. These suggested that a minute quantity of water in the form of porewater or vapor and reactive Hastelloy C in the autoclave should be mainly responsible for the dissolution of quartz into scCO(2) fluid and the formation of carbon deposit on the quartz surface. High catalysis of Hastelloy C also contributed to a significant reduction among CO2, H2O and rock minerals to produce some organics, such as some organic silicon compounds that could dissolve in the sCO(2) fluids. Consequently, a long-term investigation on the interactions between CO2 and rock minerals should be requisite for evaluation of safety and feasibility of geologic CO2 sequestration.

Carbon dioxide (CO2) is considered to be one of the greenhouse gases that may most contributes to global warming on the earth. Disposal CO2 from stationary sources into subsurface has been suggested as a possible means for reducing CO2 emissions into the atmosphere. However, much remains to be done in the issues regarding the safety and reliability Of CO2 sequestration. In this study, we have developed a simulation code by using the mathematical model of multi-phase multi-component flow in porous media to analyze the flow dynamics in the subsurface. The equation of state for CO2 covering the fluid region from the triple point to supercritical region is employed to model the state of CO2 gas, liquid and supercritical state. The effect of CO2 dissolution in water on the injection behavior is taken into account by using Henry's law extended to CO2/water system. The simulation was implemented under several geological conditions inelliding gas, liquid and supercritical state to analyze optimal injection condition. The injection pressure is lowered at the lower temperature condition and the higher hydrostatic pressure condition. The lower injection pressure inav prevent the fracturing of the injection well and excessive permeation of CO2 in the reservoir. The CO2 dissolution is slightly lowefing the injection pressure and the effect on the injection pressure is negligible under the realistic hydrostatic pressure and temperature condition. It has been demonstrated that the simulation code developed in this study may be useful to provide fundamental knowledge required for the design of CO2 injection.

An international consensus has emerged that deep geological disposal on land is one of the most appropriate means for high level radioactive wastes (HLW). The fluid transport is slow and radioactive elements are dangerous, so it's impossible to experiment over thousands of years. Instead, numerical model in such natural barrier as fractured underground needs to be considered. Field observations reveal that the equation with fractional derivative is more appropriate for describing physical phenomena than the equation which is based on the Fick's law. Thus, non-Fickian diffusion into inhomogeneous underground appears to be important in the assessment of HLW disposal. A solute transport equation with fractional derivative has been suggested and discussed in literature. However, no attempts' were made to apply this equation for modeling of HLW disposal with account for the radioactive decay. In this study, we suggest the use of a novel fractional advection-diffusion equation which accounts for the effect of radioactive disintegration and for interactions between major, macro pores and fractal micro pores. This model is fundamentally different from previous proposed model of HLW, particularly in utilizing fractional derivative. Breakthrough curves numerically obtained by the present model are presented for a variety of rock types with respect to some important nuclides. Results of the calculation showed that for longer distance our model tends to be more conservative than the conventional Fickian model, therefore our model can be said to be safer.

A computer program, which enables us the calculation of the non-Fickian diffusion in a fractured porous media, has been developed. The conventional mathematical model of solute transport in a rock is based on the Fick's law. In general, rock masses contain a number of preexisting fractures. In the fractured porous media, the conventional model tends to predict smaller solute travel distance than that in the actual transport process. In contrast, the non-Fickian diffusion model, which is described as a fractional advection-dispersion equation, can provide realistic representation of actual fluid flow in the heterogeneous media. We provide a numerical solution of the fractional advection-dispersion equation by using implicit-finite difference method. The numerical results obtained for one dimensional fractional advection-dispersion equation using the computer program was shown to be in a good agreement with the analytical solution.

Anthropogenic effects on climate can be mitigated through various measures. Among them being CO2 sequestration into geological reservoirs including deep saline aquifers, depleted oil/gas reservoirs and coal seams are interested in a powerful means for drastically reducing emissions of CO2- When CO2 would be injected into geological reservoir, it should be necessary to know the potential of CO2 storing into the reservoir. In this study, amount of CO2 sorption of granite was to evaluate experimentally at temperatures 50, 70, 100 and 200 degrees C and pressure up to 20 MPa using a magnetic suspension balance (MSB), which allows to measure under supercritical condition. As a result,we confirmed that the granite have the potential of CO2 sorption. Sorption isotherms obtained from the MSB experiment showed that amount of CO2 sorption increased with the increasing pressure and decreased with the increasing temperature for all experimental conditions. Especially, amount of CO2 sorption at 50 degrees C compared with that at other temperatures (70, 100 and 200 degrees C) increased rapidly in the vicinity of the critical state. In addition, the granite showed a maximum of CO2 sorption into granite could reach up to about 1.0% by weight at 50 degrees C and 14.4NMa. The present results may provide a fundamental knowledge for the development of CO2 geological sequestration technology.

Self-Organizing Map (SOM) method was developed in order to investigate the fracture process of SOFC module under operating environments. The damage testing method was applied to ceria electrolyte-supported single cells. The vertical crack in the electrolyte and crack in the glass seal were detected by AE method. The SOM method identified two types of damage. By using this method, it was possible to show the possibility that the detailed deterioration process can be evaluated visually and in real-time, even when applied to modules at the actual equipment level.

Solidification of municipal incineration bottom ash (MIBA) has been carried out using a hydrothermal processing method, in which the MIBA was first compacted in a mold at 5-20 MPa, and then hydrothermally cured in an autoclave under saturated steam pressure at 150-250 degrees C for 10-72 h. Experimental results showed that the tensile strength of the solidified body was greatly influenced by the addition of NaOH solution and fresh cement in the MIBA. The hydrothermal curing temperature and time exerted a significant influence on the development of tensile strength of solidified body. The strength development is speculated to be due primarily to the formation of 1.1 nm tobermorite. Laboratory leaching tests were conducted to determine the amount of heavy metals dissolved from the solidified bodies and the results showed that under the hydrothermal conditions of this study the leaching of heavy metals was very low. As such, the hydrothermal processing method may have a high potential for recycling MIBA. (c) 2006 Elsevier Ltd. All rights reserved.

Solidificatioin of hydroxyapatite (HA:Ca-10(PO4)(6)(OH)(2)), and its bonding with titanium (Ti) was achieved simultaneously by using a hydrothermal hot-pressing (HHP) method with no special surface treatment of the Ti. In this study, the relationship between the HA/Ti bonding properties and the the HHP processing temperature is examined. Mixed powders of calcium hydrogen phosphate dehydrate and calcium hydroxide were used as the starting material for the HA ceramics. The powder mixture and the Ti disk were put into an autoclave for the HHP process. The applied pressure was maintained at 40 MPa. The autoclave was heated up to 373 - 573K at a heating rate of 10K/min., and then the temperature was held constant for 2 hours. The optimal operating temperature was 423K. The bonding of HA to Ti was not achieved at temperatures over 423K.

To investigate the possibility of fixing CO2 as carbonates in high temperature formations, hydrothermal reaction experiments were conducted in CO2-saturated fluid at 200 and 300 degrees C. Numerical computations of phase equilibria based on the experimental results were carried out. The experiments with granite and calc-silicate rock showed that the dissolution of Ca-bearing minerals and the deposition of secondary minerals were encouraged in CO2-saturated system. According to EDX analysis and numerical phase equilibrium calculations, the secondary minerals formed might be diaspore, kaolinite, clay minerals (such as smectite, muscovite), Ca-alminosilicates (such as clinozoisite, laumontite, prehnite, wairakite) and calcite. However, there was no direct evidence for the formation of calcite. It is implied that the precipitation rate of calcite is relatively slow and the formation of Ca-alminosilicates occur much easily than calcite even if solution is supersaturated with respect to calcite.

Multi-walled carbon nanotube (MWCNT) films were prepared by employing a condensation reaction utilizing 1,3-dicyclohexylcarbodiimide (DCC) to cross-link each MWCNT with carboxylic acid and hydroxyl groups. Morphological changes in the resultant MWCNT films were monitored using scanning electron microscopy and showed that the MWCNTs were randomly intertwined in the films. The prepared MWCNT films were 17 mm in diameter and 20 Am in thickness, and the apparent density was 0.59 g/cm(3). Fourier transform-infrared spectroscopy confirmed that each MWCNT modified with carboxylic acid and hydroxyl groups was cross-linked through the ester bond. It was found that the ratio of the number of ester cross-links and carbon atoms of the nanotubes per unit apparent volume (cm(3)) of condensed-MWCNT films was 5.27 x 10(-3) using thermogravimetric analysis (TGA). The tensile strength and Vickers hardness of condensed-MWCNT films achieved an average of 15 and 9.2 MPa, respectively, and were greater than those of free-standing MWCNT films without ester bond.

Hydroxyapatite (HAp) ceramics have been prepared from alpha-tricalcium phosphate (alpha-TCP) with addition of water or ammonia water by hydrothermal hot-pressing (HHP) method under a condition of 300 degrees C/40 MPa/2 h. When the additive is water, it appears that the HAp grains produced show whisker-like and plate-like features. The bending strength of the HAp ceramic obtained is measured to be 24.5 MPa. When the additive is ammonia water, the obtained HAp ceramic consists of HAp-whiskers only. The bending strength and fracture toughness reach 56 MPa and 1.52 MPa.m(1/2), respectively. Treating alpha-TCP with addition of ammonia water by the HHP method is thus a useful method for in situ fabrication of HAp-whisker ceramics.

Solidification of blast furnace water-cooled slag ( BFWS) has been carried out using a hydrothermal processing method, in which the BFWS could be solidified in an autoclave under saturated steam pressure ( 1.56 MPa) at 473 K for 12 h by the addition of quartz. Experimental results showed that the strength development of the solidified specimen was significantly affected by the curing time and quartz particle size. With increasing curing time, the amount of tobermorite increased, and the formed tobermorite, in turn, enhanced the tensile strength. The particle size of the quartz added exerted a significant influence on the strength development, and the optimal quartz content for the strength development appeared to depend on the quartz particle size. The results also suggested utilization of finer quartz had the advantage of reducing the addition of quartz.

A new hydrothermal method is proposed, which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 gm could be coated to a Ti cylindrical rod at the low temperature as low as 135 degrees C under the confining pressure of 40 MPa. The HA coating layer had a porous microstructure with the relative density of approximately 60%. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0-5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HAM interface in the pull-out tests. This observation suggests that the fracture property of the HAM interface was close to or higher than that of the HA ceramics only. It is expected that the low temperature double capsule method may provide a useful method for producing bioactive HA ceramic coatings on curved prostheses surfaces. (c) 2005 Elsevier B.V. All rights reserved.

Binder-free macroscopic single-walled carbon nanotube (SWCNT) solids were prepared by spark plasma sintering (SPS) of purified SWCNTs. The effects of processing temperatures and pressures on the mechanical properties of the SWCNT solids and structural change of SWCNTs in the SWCNT solids were investigated. Transmission electron microscope observation of the SWCNT solids revealed that the high-temperature treatment has transformed some part of the SWCNTs into amorphous-like structure and the rest of the SWCNTs remained buried into the above structure. The mechanical properties of the SWCNT solids increased with the increasing processing temperature, probably reflecting the improvement of interfacial strength between SWCNTs and disordered structure of carbon due to the spark plasma generated in the SPS process.

Apparent fracture toughness in Mode I of microcracking materials such as rocks under confining pressure is analyzed based on a cohesive crack model. In rocks, the apparent fracture toughness for crack propagation varies with the confining pressure. This study provides analytical solutions for the apparent fracture toughness using a cohesive crack model, which is a model for the fracture process zone. The problem analyzed in this study is a fluid-driven fracture of a two-dimensional crack with a cohesive zone under confining pressure. The size of the cohesive zone is assumed to be negligibly small in comparison to the crack length. The analyses are performed for two types of cohesive stress distribution, namely the constant cohesive stress (Dugdale model) and the linearly decreasing cohesive stress. Furthermore, the problem for a more general cohesive stress distribution is analyzed based on the fracture energy concept. The analytical solutions are confirmed by comparing them with the results of numerical computations performed using the body force method. The analytical solution suggests a substantial increase in the apparent fracture toughness due to increased confining pressures, even if the size of the fracture process zone is small.

This paper discusses the applicability of the tension-softening model in the determination of the fracture toughness of rocks, where the fracture toughness evaluated based on the tension-softening model is compared with the crack growth resistance deduced from laboratory-scale hydraulic fracturing tests. It is generally accepted that the fracture process is dominated by the growth of a fracture process zone for most types of rocks. In this study, the J-integral based technique is employed to determine the fracture toughness of Iidate granite on the basis of the tension-softening model, where compact tension specimens of different dimensions were tested in order to examine the specimen size effect on the measured fracture toughness. It was shown that the tension-softening relation deduced from the J-integral based technique allowed us to determine the specimen size independent fracture toughness K-c of Iidate granite. Laboratory-scale hydraulic fracturing tests were performed on cubic specimens (up to a 10 m sized specimen), where cyclic pressurization was conducted using a rubber-made straddle packer to observe the extent of the hydraulically induced crack. The experimental results of pressure and crack length were then used to construct the crack growth resistance curve based on the stress intensity factor K. The crack growth resistance obtained from the hydraulic fracturing tests was observed to initially increase and then level off, giving a constant K value for a long crack extension stage. The plateau K value in the crack growth resistance curve was found to be in reasonable agreement with the fracture toughness K-c deduced from the tension-softening relation. It was demonstrated that the tension-softening model provides a useful tool to determine the appropriate fracture toughness of rocks, which may be applicable for the analysis of the process of large-scale crack extension in rock masses.

A simple mechanical damage testing method, combined with Acoustic Emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells under simulated environments. The damage testing method was applied to ceria electrolyte-supported single cells. The damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damage was most likely due to chemical expansion-induced stresses. It was demonstrated that the AE method enabled us to detect the above-mentioned damage process and to determine the condition for the onset of the damage in the single cell.

Geothermal energy is one of the most enviroment-conscious resources among the natural resources. In developing an enhanced geothermal energy extraction system, a hydraulic fracturing is the key technology to emerge an efficient geothermal reservoir. The formation of the geothermal reservoir induced by the hydraulic fracturing has to be predicted to design the geothermal energy extraction system. In this study, crack propagation induced by the hydraulic fracturing of an inclined crack is numerically analyzed. In the numerical model, shear slip deformation is taken into account. When the fluid pressure acts on the inclined crak, shear slip deformation is takes place prior to crack opening due to the pressure that overcomes the normal stress acting on the crack plane. Furthermore, the numerical results suggest that the crack can be propagated by a critical fluid pressure less than the minimum tectonic stress under typical tectonic stress condition, since the stress state at the crack tip is intensified by shear slip deformation. Therefore, the critical fluid pressure for the inclined crack is characterized by the effective shear stress that indicates shear slip condition of the crack.

Hydraulic stimulation is performed by high-pressure fluid injection, which permanently increases the permeability of a volume of rock, typically transforming it from the microdarcy into the millidarcy range. After a period of stimulation, fluid injection and recovery boreholes are introduced into the stimulated rock volume, and heat is extracted by water circulation. In the present study a simplified mathematical model of non steady-state hydraulic stimulation is proposed and analyzed. Fluid flow is assumed to be radial, injected flow rate constant; and fluid density, rock porosity, and permeability depend on fluid pressure. The conventional boundary of the growing stimulated rock volume is introduced as a surface where the porosity and permeability of the stimulated rock exhibit a sharp decline and remain constant within the undisturbed area. The problem is solved analytically by a modified method of integral correlations. As a result, approximate close-form solutions for pressure distributions in the stimulated and nonstimulated (undisturbed) areas are obtained, and an equation for the moving boundary of the stimulated volume is derived. The correctness of the approximate solution is validated by comparison to an exact self-similar solution of the problem obtained for the particular case when the well's radius is assumed to be equal to zero.

Solidification of Coal Fly-ash (CFA) has been carried out using a hydrothermal processing method. In the hydrothermal processing, the CFA was first compacted in a mold at 20 - 50 MPa, and then hydrothermally cured in an autoclave. The hydrothermal curing was performed at 150 - 250 degrees C for 15 - 60 h. The experimental results showed that NaOH solution, Ca(OH)(2) content, compaction pressure, autoclave curing temperature and time significantly affected the strength of solidified bodies. The most important strength-producing constituent in the solidified bodies produced with CFA was tobermorite, or tobermorite-like calcium silicate hydrate. When the CaO/SiO2 ratio of the starting material was close to 0.83, tobermorite readily formed and the formed tobermorite enhanced the strength of solidified bodies. The tensile strength determined by the Brazilian test reached more than 10 MPa under the hydrothermal processing. As such, the hydrothermal processing method may provide a high potential for recycling CFA on a large scale. (c) 2006 Springer Science + Business Media, Inc.

Solidification of Coal Fly-ash (CFA) has been carried out using a hydrothermal processing method. In the hydrothermal processing, the CFA was first compacted in a mold at 20 - 50 MPa, and then hydrothermally cured in an autoclave. The hydrothermal curing was performed at 150 - 250 degrees C for 15 - 60 h. The experimental results showed that NaOH solution, Ca(OH)(2) content, compaction pressure, autoclave curing temperature and time significantly affected the strength of solidified bodies. The most important strength-producing constituent in the solidified bodies produced with CFA was tobermorite, or tobermorite-like calcium silicate hydrate. When the CaO/SiO2 ratio of the starting material was close to 0.83, tobermorite readily formed and the formed tobermorite enhanced the strength of solidified bodies. The tensile strength determined by the Brazilian test reached more than 10 MPa under the hydrothermal processing. As such, the hydrothermal processing method may provide a high potential for recycling CFA on a large scale. (c) 2006 Springer Science + Business Media, Inc.

In order to establish a sustainable society, with practical material recycling, it is appropriate to focus on a range of guiding "Earth Principles", including the character and application of hydrothermal processes. In this paper, it is demonstrated that information obtained from the study of fundamental Earth Principles can be used to inspire the development of new methods for material recycling, such as the following: (1) Hydrothermal hot-pressing processes, simulating the formation of sedimentary rock sequences, can be used for the solidification of toxic and hazardous materials. (2) Organic materials could be formed from CO2 under hydrothermal conditions (using Fe and Ni metals, and low valence Fe oxides), at temperature and pressure conditions consistent with a subduction (tectonic) setting, such as (under Japan) where the Pacific Plate sinks beneath the (Eurasian) continental plate. (3) Diamond-structured carbon may be formed from toxic chlorinated hydrocarbon, in very high pressure regions of the Earth, and at high alkaline hydrothermal conditions, where magma formation may occur. (4) High temperature dry steam in rock fractures (at near critical conditions - i.e. below saturated vapor pressure, but relatively high pressure) is not only a source/carrier of noble metals, including gold, silver and copper, but also ceramic materials, silica and alumina. Its laboratory simulation may also be a guide for the formation of thin layer silicate ceramics on metal plates (e.g. SUS-304 nickel alloy). (5) To design an underground boiler in hot dry rock, non-equilibrium dissolution and deposition hydrothermal processes may be studied using a tube reactor, which simulates fluid flow and temperature gradients in fractured hot rock. (c) 2006 Springer Science + Business Media, Inc.

Solute transport in the fractured porous confined aquifer is modeled by the advection-dispersion equation with fractional time derivative of order γ, which may vary from 0 to 1. Accounting for diffusion in the surrounding rock mass leads to the introduction of an additional fractional time derivative of order 1/2 in the equation for solute transport. The closed-form solutions for concentrations in the aquifer and surrounding rocks are obtained for the arbitrary time-dependent source of contamination located in the inlet of the aquifer. Based on these solutions, different regimes of contamination of the aquifers with different physical properties are modeled and analyzed. Copyright © 2006 by ASME.

Single-walled carbon nanotubes (SWCNTs) were successfully solidified without any additives using a spark plasma method. Purification of raw soot was crucially important in order to improve the mechanical properties of the SWCNT solid, which exhibited a significant nonlinear deformation response in contrast with brittle fracture of an unpurified SWCNT solid. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A mixture of 6 mol of CaHPO4 center dot 2H(2)O and 4 mol of Ca(OH)(2) was reacted to produce hydroxyapatite (HA) by spark plasma system (SPS). The reaction was carried out at 300-1200 degrees C under pressure of 20-670 MPa for 10 min in a vacuum. HA formation started at 300 degrees C at 600 MPa and was completed at 500 degrees C at 670 MPa, the same product being obtained at 1200 degrees C in air using a furnace. The temperature of the HA formation increased with decreasing pressure and was 1150 degrees C under 20 MPa. There was a linear relationship between the reaction temperature and pressure. The crystal size of the HA prepared at 500 degrees C at 670 MPa and that at 600 degrees C at 600 MPa by SPS were less than 1 and 2 mu m, respectively. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Binder-free macroscopic single-walled carbon nanotube (SWCNT) solids were prepared by the hot-pressing and the spark plasma sintering (SPS) of purified SWCNTs at temperatures of 1000, 1400 and 1800 degrees C under a pressure of 120 MPa. The effects of processing conditions of the SWCNT solids on mechanical properties and microstructures were investigated. The SPS method was useful to increase the Young's modulus and fracture strength of the SWCNT solid with respect to the hot-pressing method. The mechanical properties of the SWCNT solids prepared by SPS were always higher than those of the SWCNT solids prepared by hot-pressing under the identical processing temperature. The maximum value for the average Young's modulus and fracture strength were 25.1 GPa and 106.8 MPa, respectively. TEM observation revealed that the high temperature treatment has converted some part of the SWCNTs into graphite-like materials and the rest of the SWCNTs remained buried into the above structure. The mechanical properties of the SWCNT solids were increased with the increasing processing temperature, reflecting probably the improvement of interfacial strength between SWCNTs and graphite-like materials.

In this study, Multi-Walled Carbon Nanotubes (MWCNTs)/Hydroxylapatite (HAp) composites were made to improve mechanical properties by using Spark Plasma Sintering (SPS) method. Slurry 6 mol of CaBPO(4)(.)2H(2)O (DCPD), 4 mol calcium hydroxide and MWCNTs were mixed and sintered by using SPS at 5-120 Wa pressure, 1200-1250 degrees C and in vacuum or N-2 atmosphere. The fracture toughness of sintered MWCNTs/HAp composites was increased.

Carbon dioxide (CO2) is considered to be one of the greenhouse gases that may most contributes to global warming on earth. Disposal Of CO2 from stationary sources into subsurface has been suggested as a possible means for reducing emissions of greenhouse gases into the atmosphere. However, much remains to be done in the issues regarding the safety and reliability Of CO2 sequestration. In this study, we have developed a simulation code by using the mathematical model of two-phase flow in porous media to analyze the flow dynamics in the subsurface. The effect Of CO2 dissolution in water on the injection behavior is taken into account by using Henry's law. The CO2 solubility in water has been shown to be an important factor which affects the pressure distribution and the migration of the CO2 front. It has been demonstrated that the simulation code developed in this study may be useful to provide fundamental knowledge required for design Of CO2 injection.

The reductions of CO2 under hydrothermal conditions were investigated by using the micro autoclave (45cm(3)) lined with Hastelloy-C alloy. Sodium hydrogen carbonate (NaHCO3) was used as a starting material. H-2 gas was used as reducing agents. NaHCO3 powder, H2 gas and water put into the autoclave simultaneously. The autoclave was heated upto, 300 degrees C by induction heater. In this study, effects of pH value of the NaOH solution in the autoclave are investigated. Reaction products were analyzed with gas chromatographs (GC), liquid chromatographs (LC), X-ray diffractometor (XRD) and Scanning electron microscopy (SEM). The following things were showed in this research: CO2 was reducted to HCOO- and CH4 at high conversion ratio under hydrothermal conditions. HCOO- was formed at high selectivity using Hastelloy-C reactor in the alkaline solution with Raney Ni catalyst. Raney Ni was exellent methanation catalyst, and CH4 formation progressed via HCO3-, not via CO. It is cleared that the NaOH solution in the autoclave should be kept pH value 11.0 for the highest conversion ratio from CO2 to useful carbonic compounds (CH4, HCOO-).

Solidification of hydroxyapatite (HA) and its bonding with titanium (Ti) was achieved simultaneously by using a hydrothermal hot-pressing (HHP) method at the low temperature as low as 150 degrees C. A mixture of calcium hydrogen phosphate dihydrate(DCPD) and calcium hydroxide was used as a starting powder material for solidifying HA. 3-point bending tests were conducted to obtain an estimate of the fracture toughness for the HA/Ti interface. Application of pressures greater than 20MPa was necessary for bonding, and the interface strength increased with the increasing applied pressure. However, the degree of HA formation was lower when the pressure was increased. Excessively long term HHP treatment was shown to be ineffective for the bonding and there was an optimal treatment time. The optimal pressure and treatment time for bonding were estimated to be 40MPa and 12hrs, respectively.

Single-walled carbon nanotube (SWCNT)/SiC composites were successfully prepared by direct thermal decomposition of polycarbosilane (PCS) precursor. The SWCNT/SiC composites were prepared by the hot-pressing the SWCNTs-PCS (7:3 mass%) mixture at temperatures of 1000, 1400 and 1800 degrees C under a pressure of 120 MPa. The effects of SiC synthesis and processing temperatures on the mechanical properties of the resultant composites were investigated by comparing the experimental data obtained from the SWCNT/SiC composites and the binder-free SWCNT solids. The XRD and TEM-EDS analyses revealed that the P-SiC was successfully prepared through direct thermal decomposition of PCS precursor. The specific modulus and strength of the SWCNT/SiC composites were always about 8 GPa/Mg/m(3) and 20 MPa/Mg/m(3) higher than those of the binder-free SWCNT solid under identical processing temperatures. Such remarkable stiffening and strengthening by SiC synthesis may be due to the load-transfer efficiency of SWCNTs in the SWCNT/SiC composites.

Solidification of hydroxyapatite (HA:Ca-10(PO4)(6)(OH)(2)) and its bonding with titanium (Ti) was achieved simultaneously by using the hydrothermal hot-pressing method at temperatures as low as 150 degrees C with no special surface treatment of Ti. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as the starting powder material for solidifying HA. Three point bending tests were conducted to obtain an estimate of the fracture toughness for the HA/Ti interface as well as for the HA ceramics only. The fracture toughness tests showed that the induced crack from the pre-crack tip deviated from the HA/Ti interface and propagated into the HA. It is cleared that water in starting materials must be crystallized in starting materials in order to achieve the bonding HA ceramics and Ti by the HHP method. The fracture toughness determined on the bonded HA/Ti specimen was close to that of the HA ceramics only (approximate 0.3 Mpam(1/2)).

A computer program has been developed which enables us to calculate the non-Fickian diffusion equations based on the Caputo fractional derivative. In recent years, the geological disposal method is, among to others, one of the most promising ways to dispose high-level radioactive wastes. It is therefore necessary to develop models for predicting solute transport in subsurface rock masses in order to assess and ensure the reliability for the geological disposal method. The conventional mathematical model of solute transport in rock masses is based on the Fick's law. However, because of existing complex fractures in the rock matrix, the conventional model tends to predict smaller solute travel distance than that in the actual transport process. The deficiency in the conventional model calls for the necessity of a more quantitative model which is applicable to the fractured porous media. In contrast, the non-Fickian diffusion model can provide realistic representation of actual fluid flow in the heterogeneous media. In the non-Fickian diffusion, the diffusion equation is described by fractional-in-space derivative of order a, which may vary from 0 to 1. In this study, we take advantage of the Caputo fractional derivative equation in order to develop a numerical method for analyzing the non-Fickian diffusion. We provide a numerical solution of the fractional derivative equation using implicit-finite difference method. The numerical result obtained for one dimensional diffusion equation using the computer program was shown to be in a good agreement with the analytical solution. The numerical method developed in this study was also verified with the result of laboratory experiment, in which a thermoluminescence technique was employed to trace the solute transport front in a granite sample. It has been shown that the numerical method based on the non-Fickian diffusion equation provides a better characterization of the experimental result, compared with the conventional diffusion equation.

A new hydrothermal method is proposed which enables us to prepare thin hydroxyapatite (HA) ceramic coatings on Ti substrates with a curved surface at low temperatures. The method uses double layered capsules in order to produce a suitable hydrothermal condition; the inner capsule encapsulates the coating materials and a Ti substrate, and the outer capsule is subjected to isostatic pressing under the hydrothermal condition. In this study, it is demonstrated that a pure HA ceramic layer with the thickness of 50 mu m could be coated to a Ti cylindrical rod at the low temperature as low as 135 degrees C under the confining pressure of 40 MPa. Pull-out tests were conducted to obtain an estimate for the adhesion properties of the HA coating prepared by the double layered capsule method. The shear strength obtained from the pull-out tests was in the range of 4.0-5.5 MPa. It was also shown that the crack propagation occurred within the HA coating layer, not along the HA/Ti interface in the pull-out tests.

The purpose of present research is to estimate the degradation mechanism of solid oxide fuel cell (SOFC) by using combining non-destructive test and electrochemical measurement during loading test Mechanical degradation and chemically degradation were investigated by acoustic emission (AE) measurement system and electrochemical measurement,respectively. In the investigation of fracture process with AE amplitude distributions, high amplitude signal, middle amplitude signal and low amplitude signal correspond to vertical craking, delamination in the cathode, and vertical cracking in the elctrolyte respectively. It was demonstrated that the AE method enabled us to detect the above-mentioned mechanical damage and to determine the condition for the onset of the damage in the single cell.

Single-walled carbon nanotubes (SWCNTs) are often produced in a form of bundles during their synthesis process. However, the bundles could slide easily on each other as they are held together by a weak van der Waals interaction. This weak cohesion is one of the major obstacles in the preparation of strong macroscopic solid structures composed of SWCNTs. Here, we have attempted to improve the stability of the links between SWCNTs within and between the bundles by introducing polycarbosilane (PCS) (10 mass%) to purified SWCNTs. Then, the SWCNT-PCS composite was prepared by the hot-pressing the SWCNT-PCS mixture at temperatures between 1000 and 1800 degrees C under a pressure of 120 MPa. The effect of processing temperatures on the mechanical properties of the composites was examined by conducting three-point bending tests. For comparison, SWCNT solids were also prepared without addition of PCS. In the case of the SWCNT-PCS composite prepared at 1000 degrees C, the specific strength and specific modulus were about two and four times higher than that of the binder-free SWCNT solid, respectively. The reason for the increment is believed due to the stable PCS links formed between SWCNTs within and between the bundles.

Single-walled carbon nanotubes (SWCNTs) are often produced in a form of bundles during their synthesis process. However, the bundles could slide easily on each other as they are held together by a weak van der Waals interaction. This weak cohesion is one of the major obstacles in the preparation of strong macroscopic solid structures composed of SWCNTs. Here, we have attempted to improve the stability of the links between SWCNTs within and between the bundles by introducing polycarbosilane (PCS) (10 mass%) to purified SWCNTs. Then, the SWCNT-PCS composite was prepared by the hot-pressing the SWCNT-PCS mixture at temperatures between 1000 and 1800 degrees C under a pressure of 120 MPa. The effect of processing temperatures on the mechanical properties of the composites was examined by conducting three-point bending tests. For comparison, SWCNT solids were also prepared without addition of PCS. In the case of the SWCNT-PCS composite prepared at 1000 degrees C, the specific strength and specific modulus were about two and four times higher than that of the binder-free SWCNT solid, respectively. The reason for the increment is believed due to the stable PCS links formed between SWCNTs within and between the bundles.

Single-walled carbon nanotubes (SWCNTs) were successfully solidified without any additives by hot-pressing and spark plasma sintering (SPS). The elastic modulus and fracture strength of the SWCNT solid prepared by the SPS method were about three and two times higher than that of the hot-pressed SWCNT solid prepared under the same processing condition. The enhancement of the mechanical properties of the SPS specimen may be due to the formation of comparatively stronger bond between SWCNTs, which is possibly brought about by the spark plasma generated in the SPS process.

Solute transport in a fractured porous confined aquifer is modelled by using an equation with a fractional-in-time derivative of order gamma, which may vary from 0 to 1. Accounting for non-Fickian diffusion into the surrounding rock mass, which is modelled by a fractional spatial derivative of order alpha, leads to the introduction of an additional fractional-in-time derivative of order alpha/(1+alpha) in the equation for solute transport. Closed-form solutions for solute concentrations in the aquifer and surrounding rocks are obtained for an arbitrary time-dependent source of contamination located at the inlet of the aquifer. Based on these solutions, different regimes of contaminant transport in aquifers with various physical properties are modelled and analysed.

A simple fracture testing method, combined with acoustic-emission (AE) monitoring was developed in order to investigate the mechanical performance of solid oxide fuel cells (SOFCs) under simulated environment. The fracture testing method was applied to ceria electrolyte-supported single cells. The fracture damage process was shown to involve vertical cracking and delamination in the cathode, and vertical cracking in the electrolyte, and the fracture damages were most likely due to chemical expansion induced stresses. It was demonstrated that the AE method may enable one to detect the above-mentioned fracture process and to determine the onset condition for fracture damage in the single cell.

For a high-sensitivity ultrasonic transducer in air, it was considered that nanofoam be applied to its acoustic matching layer. Nanofoam is a porous material that is made by the sol-gel process. Since nanofoam has an extremely low acoustic impedance, it is effective for the acoustic matching layer of an ultrasonic transducer in air. In this study, we have fabricated an ultrasonic transducer that had two acoustic matching layers and estimated its acoustic properties. The two matching layers were made of silica nanofoam and porous ceramic. The sensitivity of the developed ultrasonic transducer was about twenty times higher than that of a conventional ultrasonic transducer in air.

In the present study, a hydrothermal hot pressing (HHP) method was used to fabricate porous hydroxyapatites with high strength. In particular, an interconnected matrix of hydroxyapatite was achieved by solution precipitation and the application of compressive stress during HHP. Hydroxyapatite samples post-sintered after this HHP treatment had a lower relative density and higher open porosity than those prepared by normal sintering. An examination of the pore characteristics suggested that the samples after HHP treatment and post-sintering had a high amount of open pores with a large and round morphology, whereas the samples prepared by normal sintering showed a denser microstructure, with a sharp-edged-pore morphology.

Solidification of hydroxyapatite (HA:Ca-10(PO4)(6)(OH)(2)) and its bonding with titanium (Ti) was achieved simultaneously by using the hydrothermal hot-pressing method at temperatures as low as 150degreesC with no special surface treatment of Ti. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as the starting powder material for solidifying HA. Three-point bending tests were conducted to obtain an estimate of the fracture toughness for the HAM interface as well as for the HA ceramics only. The fracture toughness tests showed that the induced crack from the pre-crack tip deviated from the HAM interface and propagated into the HA. The fracture toughness determined on the bonded HAM specimen was close to that of the HA ceramics only (similar to0.30 MPa m(1/2)). (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hydraulic stimulation is performed by a high-pressure fluid injection, which leads to a permanent increase in permeability of a volume of rock, typically transforming it from the microdarcy into the millidarcy range. The present paper provides an overview of the recent results in mathematical modeling of this process obtained at Tohoku University, Japan. Several mathematical models are proposed and realized. Within the steady-state approach, the geothermal reservoirs are characterized by parameters measured from field data and the model incorporates the approximations of the fracture mechanical behavior and fluid dynamics in fractured media. Along with the fractal-type distribution of the fracture lengths, the fracture surfaces are also assumed to follow fractal geometry. The latter allows numerical simulation of the natural rock fracture dilation caused by fracture shear offset. Recently, a new simplified non-steady mathematical model of the stimulation process was proposed. This model can be used for assessing the rate of the stimulated volume growth subject to injection pressure and flow rate and for approximate calculation of time required for creating the specified size of the stimulated region.

Drilling in brittle crystalline rocks is often accompanied by a fluid loss through the finite number of the major fractures intercepting the borehole. These fractures affect the flow regime and temperature distributions in the borehole and rock formation. In this study, the problem of borehole temperature variation during drilling of the fractured rock is analyzed analytically by applying the approximate generalized integral-balance method. The model accounts for different flow regimes in the borehole, for different drilling velocities, for different locations of the major fractures intersecting the borehole, and for the thermal history of the borehole exploitation, which may include a finite number of circulation and shut-in periods. Normally the temperature fields in the well and surrounding rocks are calculated numerically by the finite difference and finite element methods or analytically, utilizing the Laplace-transform method. The formulae obtained by the Laplace-transform method are usually complex and require tedious numerical evaluations. Moreover, in the previous research the heat interactions of circulating fluid with the rock formation were treated assuming constant bore-face temperatures. In the present study the temperature field in the formation disturbed by the heat flow from the borehole is modeled by the heat conduction equation. The thermal interaction of the circulating fluid with the formation is approximated by utilizing the Newton law of cooling at the bore-face. The discrete sinks of fluid on the bore-face model the fluid loss in the borehole through the fractures. The heat conduction problem in the rock is solved analytically by the heat balance integral method. It can be proved theoretically that the approximate solution found by this method is accurate enough to model thermal interactions between the borehole fluid and the surrounding rocks. Due to its simplicity and accuracy, the derived solution is convenient for the geophysical practitioners and can be readily used, for instance, for predicting the equilibrium formation temperatures. (C) 2004 Elsevier Ltd. All rights reserved.

In this paper, a spark plasma sintering (SPS) method was employed to solidify single-walled carbon nanotubes (SWCNTs) only, and the effect of sintering conditions on the mechenical properties of the SWCNT solids were examined using a small punch (SP) testing method. The sintering temperature used in the range of 600-1 400°C, and the sintering pressure used 40 MPa and 120 MPa. It was demonstrated that the SPS method allowed SWCNTs to be solidified, without any additives. The experimental results showed that the purification of raw soot was critically importance. The SWCNT solid prepared from purified raw soot showed significant non-linear deformation response, producing quasi-ductile fracture behavior. In contrast, unpurified raw soot produced brittle SWCNT solids. The Young's modulus, fracture strength and work of fracture increased with increasing sintering temperature and pressure. The Raman scattering and SEM observations showed that the amount of the graphite-like materials were observed to increase with the increasing temperature and pressure, which indicate that the structure of the SWCNTs was changed partially into the graphite-like materials. The formation of graphite-like materials increased tendency of brittle fracture in the SWCNT solids. TEM observations revealed that the fracture surfaces of SWCNT solids were characterized by pull out of SWCNT bundles. This observation suggests that it may be possible to improve the mechanical properties of SWCNT solids by increasing the cohesion between SWCNTs.

The multi-walled carbon nanotube (MWNT) was not consolidated without additives by the spark plasma system (SPS). The phenol resin of 33 wt% was added to promote the consolidation. The MWNTs were aligned perpendicular to pressing direction of SPS in the consolidated compact. Bulk density and Young's modulus were more than 1.7 g/cm3 and 10 GPa for the MWNT consolidated at 120MPa at 1200°C and 1400°C. The fracture behavior on bending test was a kind of quasiplastic deformation and was based on pull out of the MWNTs.

The Small Punch Creep Tests (SP-C tests) are simulated by a Finite Element Method (FEM). The objective of the present study is to establish a foundation for the SP-C test method by investigating the deformation and stress state of the SP-C test specimen. The emphasis is placed on the dependence relation of the creep strain and the stress on the measurable quantities, such as applied loads and the central deflections. Simulation works are conducted for two different materials, one is the tungsten-alloyed 9% Cr ferritic steel and the other is 12Cr1MoV steel. The numerical results for the central deflection versus time curves are quantitatively similar to the experimental results obtained on tungsten-alloyed 9% Cr ferritic steels. From the numerical results, the relationship between the central deflection and the equivalent creep strain is approximately independent of load, temperature, and material properties. The magnitude of the equivalent stress in the central region of the SP-C specimen shows no significant change with respect to time at the secondary creep stage, an approximate equation is proposed for the assessment of the equivalent stress in the SP-C specimen. As a farther result, the high temperature creep properties of the 12Cr1 MoV steel and tungsten-alloyed 9% Cr ferritic steel are appraised by numerical simulation. The results are in good agreement with the results from the standard test method. The results indicate that the small punch test technique is an effective method for the evaluation of the high-temperature creep properties of materials.

The influences of the sintering additive content of rare-earth oxide (Y2O3, Gd2O3, Sm2O3) on microstructure and mechanical properties of ceria ceramics were investigated by scanning electron microscopy and small specimen technique. A small punch testing method was employed to determine the elastic modulus and biaxial fracture stress of the ceria-based ceramics, and the fracture toughness was estimated by Vickers indentation method. Grain growth in the rare-earth oxides doped ceria ceramics was significantly suppressed, compared to the pure ceria ceramics. However, the elastic modulus, fracture stress and fracture toughness were decreased significantly with increasing additive content of the rare-earth oxides, possibly due to the oxygen vacancies induced by the rare earth oxides doping. The experimental results suggest that the change in the mechanical properties should be taken into account in the use of ceria-based ceramics for solid oxide fuel cells, in addition to the improvement of oxygen ion conductivity. (C) 2004 Kluwer Academic Publishers.

A numerical study is presented that simulates small punch creep (SP-C) tests using a finite-element method (FEM). The objective of the present study is to develop a miniaturized testing methodology for high-temperature creep properties. The numerical simulations have been shown to produce deflection versus time curves that are quantitatively similar to the experimental results obtained on tungsten-alloyed 9 % Cr ferritic steels. It is also demonstrated that the numerically predicted curves show the steady state (secondary) creep stage. Furthermore, the numerical simulations reveal that the magnitude of the equivalent stress in the central region of the SP-C specimen shows no significant change with respect to time at the secondary creep stage, supporting the use of the present SP-C testing method to characterize the secondary creep deformation rate. Finally, an approximate equation is proposed for the assessment of the equivalent stress in the SP-C specimen in terms of the load and testing parameters.

The present study is related to the rimming flow of non-Newtonian fluid on the inner surface of a horizontal rotating cylinder. Using a scale analysis, the main characteristic scales and non-dimensional parameters, which describe the principal features of the process, are found. Exploiting the fact that one of the parameters is very small, an approximate asymptotic mathematical model of the process is developed and justified. For a wide range of fluids, a general constitutive law can be presented by a single function relating shear stress and shear rate that corresponds to a generalized Newtonian model. For this case, the run-off condition for rimming flow is derived. Provided the run-off condition is satisfied, the existence of a steady-state solution is proved. Within the bounds stipulated by this condition, film thickness admits a continuous solution, which corresponds to subcritical and critical flow regimes. It is proved that for the critical regime solution has a corner on the rising wall of the cylinder. In the supercritical flow regime, a discontinuous solution is possible and a hydraulic jump may occur. It is shown that straightforward leading order steady-state theory can work well to study the shock location and height. For the particular case of a power-law model, the analytical solution of steady-state equation for the fluid film thickness is found in explicit form. More complex rheological models, which show linear Newtonian behavior at low shear rates with transition to power-law at moderate shear rates, are also considered. In particular, numerical computations were carried out for Ellis model. For this model, some analytical asymptotic solutions have been also obtained in explicit form and compared with the results of numerical computations. Based on these solutions, the optimal values of parameters, which should be used in the Ellis equation for correct simulation of coating flows, are determined the criteria that guarantee the steady-state continuous solutions are defined the size and location of the stationary hydraulic jumps, which form when the flow is in the supercritical state, are obtained for the different flow parameters. Copyright © 2004 by ASME.

A multi-walled carbon nanotube (MWNT) was mixed with phenol resin and consolidated by the spark plasma system (SPS). Properties of the MWNT consolidated at 1200degreesC at 120 MPa were as follows: bulk density was 1.74 g/cm(3); apparent porosity was 16.3%; Young's modulus was 11.1 GPa. Hydroxyapatite was coated on the consolidated MANT at 1000degreesC and 120 MPa by SPS, using the suspension prepared from 6 moles of CaHPO(4)(.)2H(2)O and 4 moles of Ca(OH)(2).

The influences of the sintering additive content of rare-earth oxide (Y<SUB>2</SUB>O<SUB>3</SUB>, Gd<SUB>2</SUB>O<SUB>3</SUB>, Sm<SUB>2</SUB>O<SUB>3</SUB>) on microstructure and mechanical properties of ceria ceramics were investigated by scanning electron microscopy and small specimen technique. A small punch testing method was employed to detemine the elastic modulus and biaxial fracture stress of the ceria-based ceramics, and the fracture toughness was estimated by vickers indentation method. Rare-earth oxides doped ceria powders with a composition of (CeO<SUB>2</SUB>) <SUB>1-x</SUB> (RO<SUB>1.5</SUB>) <SUB>x</SUB> (R=Y, Gd, Sm and x=0, 0.10, 0.15, 0.20, 0.30, 0.40, 1.00) were prepared by a coprecipitation method. The powders were compacted by die pressing (50 MPa) followed by cold isostatic pressing (120 MPa), and sintered at 1 500°C in air for 5h. Grain growth in the rare-earth oxides doped ceria ceramics were significantly suppressed, compared to the pure ceria ceramics. However, the elastic modulus, fracture stress and fracture toughness were decreased significantly with increasing additive content of the rare-earth oxides, possibly due to the oxygen vacancies induced by the rare-earth oxides doping. The experimental results suggest that the change in the mechanical properties should be taken into account in the use of ceria-based ceramics for solid oxide fuel cells, in addition to the improvement of oxygen ion conductivity.

In this paper, cracking behavior of distributed microcracks is discussed using a numerical simulation. The microcracks are initially distributed in a rectangle region. The directions and locations of the cracks are chosen at random. Three kinds of length distributions are used, such as a uniform length, a random length distribution and a fractal length distribution. The crack propagations from the initially distributed cracks are analyzed under a uniaxial tensile load using liner elastic fracture mechanics. The global behaviors of various crack distribution are studied. Results obtained from the numerical calculations indicate that the effect of the crack length distribution is minor in term of the macroscopic behavior of the cracked body.

Elastic-plastic fracture toughness tests were conducted at 77K and 4K to examine an influence of thermal aging on fracture properties of an austenitic stainless steel JN 1 at cryogenic temperature, which is a candidate material for superconducting magnet structures of fusion reactors. The tests were applied to solution-treated material and materials aged at 923-1073 K for 5 h. The experimental results showed that the fracture toughness <I>J<SUB>IC</SUB></I> measured on the thermally aged materials were smaller than that on the solution-treated material and decreased with increasing aging temperature. This decrease in fracture toughness due to thermal aging was caused by precipitation and coarsening of grain boundary M<SUB>23</SUB>C<SUB>6</SUB> carbides. Additionally, small punch (SP) tests were conducted at cryogenic temperatures to investigate the relationship between the obtained <I>J<SUB>IC</SUB></I> and SP properties. It was found that the equivalent fracture strain ε<SUB>qf</SUB> in SP specimens was linearly correlated with <I>J<SUB>IC</SUB></I> irrespective of testing temperature. This correlation suggests that the SP testing technique provides a useful tool for evaluating <I>J<SUB>IC</SUB></I> at cryogenic temperature.

Rimming flow on the inner surface of a horizontal rotating cylinder is investigated. Simple lubrication theory is applied since the Reynolds number is small and liquid film thin. Since the Deborah number is very small the flow is viscometric. A general constitutive law for this kind of flow requires only a single function relating shear stress and shear rate that corresponds to a generalized Newtonian liquid. For this case the run-off condition for rimming flow is derived. Provided the run-off condition is satisfied, the existence of a steady-state solution is proved. In the bounds implied by this condition film thickness admits a continuous solution, which corresponds to subcritical and critical flow regimes. In the supercritical case when the mass of liquid polymer exceeds a certain value or the speed of rotation is less than an indicated limit, a discontinuous solution is possible and a hydraulic jump may occur. As an example, the location and height of the hydraulic jump is determined numerically for Ellis model.

Hydraulic fracturing or hydraulic stimulation is one of the most effective methods of enhancing hot dry rock (HDR) geothermal system productivity. In the present study, network models of "fractal geometry" approximate a 31) structure of fractured rocks. The fracture network models are generated by distributing fractures randomly in space and assuming the fractal equation correlating the number of fractures and fracture lengths. Based on this approach, a mathematical model of hydraulic rock fracturing is proposed. The model incorporates approximations of the fracture mechanical behavior drawn from the rock mechanics literature, a very simplified analysis of the operative physical processes, and mapping of the connectivity of fracture network to a cubic regular grid. It is assumed that the flow properties of a stochastic fracture network depend on the fluid pressure. Along with the fractal-type distribution of the fracture lengths, the fracture surfaces are also assumed to follow fractal geometry. The latter allows numerical simulation of the natural rock fracture dilation caused by fracture shear offset. On of the problems that can be resolved by fracture surface modeling is the apparent limitation on the number of fractures that can be analyzed experimentally. In this respect, the suggested mathematical model can be used to simulate fractal surfaces identical to fractures found in the natural rocks. Taken together, these approaches permit the approximate engineering resolution of the multiparametric, highly complex mechanical problem.

The numerical model FRACSIM developed by the research group in Tohoku University for the hot-dry-rock (HDR) geothermal reservoir is proved to be an appropriate approximate model capable to address simultaneously the problems associated with hydraulic stimulation, fluid circulation and heat extraction. The structure of the fractured rock is approximated with the network models of "fractal geometry". The adopted procedure makes it possible to characterize geothermal reservoirs by parameters measured from the field data. As is proved both theoretically and experimentally for the fluid flows in the fractured and porous media with relatively high fluid velocities, the values of the effective thermal conductivities in the longitudinal and transverse to the flow directions are directly proportional to the values of the fluid velocity. The water/rock chemical interaction (WRCI) is the other factor that inevitably exerts an influence on the permeability of the high temperature deep HDR circulating system. In the present study the mathematical model, which accounts for the effects of thermal dispersion and WRCI (in terms rock chemical dissolution and precipitation), is proposed. The numerical analysis based on the 3D model of the reacting fluid flow within the fractured media proves the importance of the thermal dispersion and WRCI factors for the assessment of the overall reservoir thermal and hydraulic performance. © 2004 Elsevier Ltd. All rights reserved.

Laboratory results from simulated hydraulic stimulation tests on granite are presented where fracture and fluid flow behavior were examined under temperatures up to 600 °C and confining pressures up to 100 MPa at various injection rates. The results show that under high temperatures, fluid flow dominant behavior occurs for relatively lower injection rates, whereas macroscopic fracture tends to takes place at higher injection rates. Continuous injection tests under supercritical water conditions reveal that the fluid flow dominant behavior is due to the generation of a grain-scale extensive microcracks induced by the interaction between supercritical water and rock-forming minerals. It is proposed to utilize the discovered supercritical water-induced microcracking phenomenon in order to create an artificial reservoir in deep-seated rock masses whose temperature and pressure conditions exceed the critical point of water. © 2004 Elsevier Ltd. All rights reserved.

In this study, the triaxial compression experiments were conducted to investigate the temperature and pore pressure effects on fracture strength of a granite. The experiments were conducted at temperatures and pressures up to 600°C and 150MPa both under water (supercritical) and air-dry environment. Experimental results show that the strength of the granite under air-dry conditions is temperature insensitive within the temperature range of this study. The strength of the granite was also nearly constant up to 350°C under water-saturated conditions. In contrast, under temperatures above the critical point of water (374°C and 22MPa or more temperature and pressure), the strength decreases rapidly with increasing temperature. We observed the micro-structural change around fracture surface using l00gm thick thin section of granite samples. Optical observation results around the fracture surface revealed that the crack density gave a higher value in supercritical water condition than in sub-critical water conditions. It was shown that the strength decrease under supercritical water conditions was due to the formation of micro-fractures induced by the effect of supercritical water as well as the stress effect, which may be referred to as supercritical water enhanced stress corrosion cracking. These experimental results suggest that it may be possible to generate a volume-like (microcrack predominant) reservoir in supercritical rock masses utilizing the stress corrosion cracking phenomena under supercritical water conditions, which is more advantageous to extract the heat energy compared with a crack-like reservoir. © 2004 Elsevier Ltd. All rights reserved.

The process of borehole grouting in the regions of permafrost is more complicated than in normal climatic conditions due to the possible thawing of the frozen rock, which can be induced by the heat produced during cement hydration. In order to prevent thawing of the surrounding formation, the main conditions that should be imposed on the grouting off technology and properties of the cementing slurries are rapid cement hydration and low heat generation during chemical reaction. Mathematical model of the grouting off process in permafrost, presented in this study, accounts for heat transferred from the borehole circulating mud and heat generated due to cement hydration. The problem is solved analytically by the approximate integral-heat-balance method. As a result, the close-form solutions for the temperature field in the cemented region and surrounding formation are obtained. On the basis of these analytical solutions, analytical criteria for the borehole grouting off regimes that take place without thawing of the frozen rock are proposed. These criteria can be readily used for assessing physical and chemical properties of the cement slurries and their suitability for grouting off the borehole in permafrost. © 2004 Elsevier Ltd. All rights reserved.

Mechanical properties of creep rate and fracture strength were investigated on rare earth doped ceria. The samples were prepared by coprecipitation method. and relative density was over 90% for each composition. Creep test of yttria doped ceria (Ce(1-x)Y(x)O(2-x/2)x=0 similar to 0.2) was performed using 4-point bending method under a cons ant load at temperature range of 1050-1125 degrees C. applied stress of 20 similar to 50 MPa and oxygen partial pressure of P(O-2)=0.21-10(-) (15.2) atm. The testing conditions were decided taking into the operating conditions of SOFC. Steady state strain rate calculated from creep curve showed clear oxygen partial pressure dependence. The creep rate increased as decreasing P(O-2) and showed a peak at P(O-2)= 10(-) (13.6) atm. The activation energy of creep was increased from 264kJmol(-1) to 333kJmol(-1) in accordance with P(O-2) decreasing. The activation energy was much higher than reported activation energy of anion diffusion in ceria. So it is concluded that creep control species is cation in air and reduction atmosphere. Since the electrical conductivity and nonstichiometry of this material show similar P(O-2) dependence. the results obtained this work suggest the coincidence between cation and anion diffusion processes in this material. 11 is also found that the creep mechanism of Ce0.8Y0.2O1.9 changed from Nabarro-Heriing creep to grain boundary sliding in reduction atmosphere which P(O-2) was lower than 10(-14.5) atm. Fracture strength of rare earth doped ceria (Ce1-xRxO2-x/2,R=Y,Sm,Gd,x=0 similar to 0.2) was measured by small punch testing method. Test was performed in air at room temperature. Fracture strength showed significant dependence on dopant density, and had a minimum value at x=0.05 and a maximum value at x=0.1. The paper will discuss between the relationship between the mechanical properties and electrical properties on doped ceria.

A multi-walled carbon nanotube (MWNT) was mixed with phenol resin and consolidated by the spark plasma system (SPS). Properties of the MWNT consolidated at 1200degreesC at 120 MPa were as follows: bulk density was 1.74 g/cm(3); apparent porosity was 16.3%; Young's modulus was 11.1 GPa. Hydroxyapatite was coated on the consolidated MANT at 1000degreesC and 120 MPa by SPS, using the suspension prepared from 6 moles of CaHPO(4)(.)2H(2)O and 4 moles of Ca(OH)(2).

A number of rock types exhibit a nonlinear deformation induced by distributed microcracking, followed by a post-peak softening behavior due to grain bridging action, when subjected to a uniform tension. Numerical analyses of hydraulically induced geothermal reservoirs at great depths conducted to date neglect the effect of the distributed microcracking. In this paper, the formation of the distributed microcracking is studied using a numerical technique in order to characterize the growth of artificial subsurface cracks by hydraulic fracturing. A numerical fracture model based on a finite element method is developed. The progressive nonlinear deformation is analyzed on the basis of the Rankine criterion. A cohesive crack model is adopted to analyze the crack growth. In the numerical simulation, the crack is represented using an embedded crack element. The results obtained by numerical analyses show that the distributed microcrack zone induced by hydraulic fracturing at great depth conditions is significantly suppressed by tectonic stress. An energy consumption of the distributed microcrack zone is much smaller than that of the bridging zone.

We report the preparation, properties and biocompatibility of multi-walled carbon nanotube (MWCNT) disk. Sintered Multi-walled carbon nanotube disk was fabricated by spark plasma sintering the MWCNT and phenol resin mixture by using the Spark Plasma System (SPS) under 1273 K and 80 MPa in vacuum. As the concentration of phenol resin in the sintered MWCNT disk increases, the bending strength and Young's modulus increased. However, the inflammatory response was observed in the tissue exposed to the surface of the sintered MWCNT disk. This was believed due to the residual phenol resin in the disk. The result indicates that the disk has to be annealed at higher temperatures under inert gas atmosphere to perfectly convert phenol resin to graphitic materials.

Hydraulic stimulation is performed by high-pressure fluid injection, which permanently increases the permeability of a volume of rock, typically transforming it from the microdarcy into the millidarcy range. After a period of stimulation, fluid injection and recovery boreholes are introduced into the stimulated rock volume, and heat is extracted by water circulation. In the present study a simplified mathematical model of non-steady-state hydraulic stimulation is proposed and analyzed. Fluid flow is assumed to be radial, injected flow rate constant and fluid density, rock porosity, and permeability depend on fluid pressure. The conventional boundary of the growing stimulated rock volume is introduced as a surface where the porosity and permeability of the stimulated rock exhibit a sharp decline and remain constant within the undisturbed area. The problem is solved analytically by a modified method of integral correlations. As a result, approximate close-form solutions for pressure distributions in the stimulated and non-stimulated (undisturbed) areas are obtained, and an equation for the moving boundary of the stimulated volume is derived. The correctness of the approximate solution is validated by comparison to an exact self-similar solution of the problem obtained for the particular case when the well's radius is assumed to be equal to zero. Copyright © 2004 by ASME.

Assessment of the heat either delivered from high temperature rocks to the borehole or transmitted to the rock formation from circulating fluid is of crucial importance for a number of technological processes related to borehole drilling and exploitation. Normally the temperature fields in the well and surrounding rocks are calculated numerically by finite difference method or analytically by applying the Laplace-transform method. The former approach requires tedious and, in certain cases, non-trivial numerical computations. The latter method leads to rather bulky formulae that are inconvenient for further numerical evaluation. Moreover, in previous studies where the solution is obtained analytically, the heat interaction of the circulating fluid with the formation was treated on the condition of constant boreface temperature. In the present study the temperature field in the rock formation disturbed by the heat flow from the borehole is modeled by a heat conduction equation, assuming the Newton model for the convective heat transfer on the bore-face, with boundary conditions that account for the thermal history of the borehole exploitation. The problem is solved analytically by the generalized heat balance integral method. Within this method the approximate solution of the heat conduction problem is sought in the form of a finite sum of functions that belong to a complete set of linearly independent functions defined at the finite interval bounded by the radius of thermal influence and that satisfy the homogeneous boundary conditions on the bore-face. In the present study first and second order approximations are obtained for the composite multi-layer domain. The numerical results illustrate that the second approximation is in a good agreement with the exact solution. The only disadvantage of this solution is that it depends on the radius of thermal influence, which is an implicit function of time and can only be found numerically by iterative algorithms. In order to eliminate this complication, in this study an approximate explicit formula for the radius of thermal influence and new close-form approximate solution are proposed on the basis of the approximate solution obtained by the integral-balance method. Employing the non-liner regression method the coefficients for this simplified solution are obtained. The accuracy of the approximate solution is validated by comparison with the exact analytical solution found by Carslaw and Jaeger for the homogeneous domain. (C) 2003 Elsevier Ltd. All rights reserved.

The problem of formation temperature stabilization during the shut-in period is solved analytically by the approximate generalized integral-balance method. The model accounts for the thermal history of the borehole exploitation, which may include a finite number of circulation and shut-in periods, and different flow regimes during circulation periods. The latter is determined by the temperatures of the circulating fluid and different Biot numbers that depend on intensity of the heat transfer on the bore-face. Normally the temperature fields in the well and surrounding rocks are calculated numerically by the finite-difference and finite-element methods or analytically, by applying the Laplace-transform method. Formulae, analytically obtained by Laplace transform, are rather bulky and require tedious non-trivial numerical evaluations. Moreover, in previous research the heat interactions of the circulating fluid with formation were treated under the condition of constant bore-face temperatures. In the present study the temperature field in the formation disturbed by the heat flow from the borehole is modelled by the heat conduction equation and thermal interaction of the circulating fluid with formation is approximated by the Newton relationship on the bore-face. The problem for circulation and shut-in periods is solved analytically using the heat balance integral method, where the radius of thermal influence, which defines the thermally disturbed domain, is a function of time, which satisfies the algebraic equation. Within this method, the approximate solution of the heat conduction problem is sought in the form of a finite sum of functions which belong to a complete set of the linearly independent functions defined on the finite interval bounded by the radius of thermal influence and satisfy the homogeneous boundary condition on the bore-face. It can be proved theoretically that the approximate solution found by this method converges to the exact one. Numerical results illustrate quite good agreement between the approximate and exact solutions. As a result of its simplicity and accuracy, the derived solution is convenient for geophysical practitioners and can be readily used, for instance, for predicting equilibrium formation temperatures.

Hydraulic fracturing or hydraulic stimulation is one of the most effective methods of enhancing hot dry rock (HDR) geothermal system productivity. The 3D structure of the fractured rock is approximated by the network models of 'fractal geometry'. The models of fracture networks are generated by distributing fractures randomly in space and assuming the fractal correlation N-r = Cr-D that incorporates the number of fractures N-r, fractal length r, fractal dimension D and fracture density within the rock mass C. This procedure makes it possible to characterize the geothermal reservoirs using parameters measured from field data. Based on this approach, a mathematical model of the hydraulic rock fracturing is proposed. The model incorporates approximations of the fracture mechanical behaviour drawn from the rock mechanics literature, a very simplified analysis of the operative physical processes and mapping of the connectivity of fracture network to a cubic regular grid. Along with the fractal-type distribution of the fracture lengths, the fracture surfaces are also assumed to follow fractal geometry. The latter allows numerical simulation of the natural rock fracture dilation caused by fracture shear offset. The other problem that can be resolved by fracture surface modelling is the apparent limitation on the number of fractures that can be analysed experimentally. In this respect, the suggested mathematical model can be used to simulate fractal surfaces identical to fractures found in the natural rocks. Taken together, these tools permit the approximate engineering resolution of the multi-parametric, highly complex mechanical problem. The reliability of the developed model was validated by comparisons with the experimentally determined data for the Hijiori deep reservoir. This implicitly justifies the numerical results and conclusions drawn in the present research. In particular, a series of computations indicate that the connectivity of the fracture network is greatly affected by the fractal dimension of the fracture network. The strong effect of the fractal dimension on the reservoir's size is also observed. The numerical results illustrate the controlling effect of the pressure and flow rate in the stimulating well for reservoir growth. Copyright (C) 2003 John Wiley Sons, Ltd.

Experiments were conducted using a batch type micro-autoclave over a temperature range of 100-350 degreesC to understand granite and sandstone reactions in hot water in the absence or presence of excess CO2. Our experiments, for one-week duration, show that the dissolution of granite and sandstone, and the deposition of secondary minerals, is enhanced by the presence Of excess CO2. Major element concentrations of the residual solution from the batch autoclave experiments were higher for the rock (granite or sandstone)/H2O/CO2 system, than in the rock (granite or sandstone)/H2O system, but the sample weight loss was lower in the rock/H2O/CO2 system than in the rock/H2O system. Changes in sample weight and CO2-gas volume content concur with the deposition of aluminium silicate and calcium-aluminosilicate secondary minerals, which indicate fixation Of CO2 in the rock. Our results suggest that it may be possible for granite and/or sandstone to 'capture' CO2, at hydrothermal conditions, and that underground disposal may be a feasible solution to reducing atmospheric emission Of CO2. (C) 2002 Elsevier Science Ltd. All rights reserved.

Polypropylene discontinuous fiber reinforced cementitious composites were prepared by extrusion molding and tested in uniaxial tension to determine the mechanical properties such as ultimate composite strength and strain, and the critical volume fraction for multiple cracking. It was shown that the experimentally determined critical fiber volume fraction reasonably agreed with the theoretical value predicted by a micromechanics model. The extruded fiber composites yielded the ultimate composite strength of 9.0 MPa and composite strain of 0.55% at the fiber volume fraction of 7.4%. Our experimental results suggest that there is an optimal fiber aspect ratio and fiber volume fraction for enhancing the fracture properties. (C) 2002 Elsevier Science Ltd. All rights reserved.

Composite materials heve been prepared using a CO2 solidification process from milling dust of autoclaved lightweight concrete (ALC; as matrix material), reinforced by addition of crushed glass (bottle) waste. The effect of varying glass collet size (0.08-5 mm) and glass volume (10-30%) on the fracture properties in the glass/ALC composite was examined by four point bending tests. For the glass/ALC composite cured under atmospheric conditions, we show, by conducting CO2 solidification experiments at different CO2 gas pressures (atmospheric, and 4-10 MPa), that the rate of reaction at the sample surface is faster under pressure, than under atmospheric conditions. At 4-10 MPa experimental conditions, a solidified 'reaction rim' is formed away from the sample surface characterized by the deposition of calcite, and a long internal fracture is created inside the sample, which reduces bending strength, although these characteristic features are not evident in samples cured at atmospheric conditions. Creation of the 'reaction rim' impedes further diffusion of CO2 into the sample. Our results indicated that the CO2 solidification of glass/ALC composite materials is best advanced under atmospheric conditions. The result also indicated that for &lt;0.5 nun cullet size, the bending strength is enhanced, without being detrimental to fracture characteristics. However, increasing size of the crushed glass cullet (0.5 mm-5 mm) reduced the strength of the solidified composite. The interface between the ALC powder matrix and glass cullet was weak, and a fraction glass cullets 0.08-0.5 mm size may be incorporated in the waste concrete matrix by as much as 30 vol%.

The theoretical model for the blister test method was used to analyze the interface fracture toughness of zirconia coating deposited on an SUS304 stainless steel substrate by a plasma-spraying method The elastic parameters of the debonded coating were determined by testing the oil pressure q and maximum deflection w(0). SEM observation, compliance method and ultrasonic detection were used to determine the radius of the debonded coating. The three methods gave the same results for the debonded coating radius. Micro-observations showed that the interfacial crack propagates by the growth of voids or microcracks ahead of the main crack and coalescence with the main crack. The energy release rate Go with phase angle psi = 0 for type A coating and type B coating was, respectively, 14.54similar to25.88 J/m(2) and 11.88-16.21 J/m(2). The corresponding interface fracture toughness for type A TBC coating and for type B TBC coating is, respectively, 0.77 similar to 1.02 MPa . m(1/2) and 0.52similar to0.61 MPa.m(1/2). The stable phase angle was approximately -31.5degrees and -30.2degrees for coating A and coating B, respectively.

Rimming flow on the inner surface of a horizontal rotating cylinder is investigated. Using a scale analysis, a theoretical description is obtained for steady-state non-Newtonian flow. Simple lubrication theory is applied since the Reynolds number is small and the liquid film is thin. Since the Deborah number is very small the flow is viscometric. The shear-thinning number, which characterizes the shear-thinning effect, may be small or large. A general constitutive law for this kind of flow requires only a single function relating shear stress and shear rate that corresponds to a generalized Newtonian liquid. For this case the run-off condition for rimming flow is derived. Provided the run-off condition is satisfied, the existence of a continuous steady-state solution is proved. The rheological models, which show Newtonian behavior at low shear rates with transition to power-law shear thinning at moderate shear rates, are considered. Numerical results are carried out for the Carreau and Ellis models, which exhibit Newtonian behavior near the free surface and power-law behavior near the wall of the rotating cylinder. (C) 2003 Elsevier Science B.V. All rights reserved.

An improved three-dimensional simulating model (FRACSIM-3D) for heat and fluid flow within a geothermal reservoir is presented. The model effectively simulates two main stages of the geothermal reservoir exploitation, namely, the hydraulic stimulation of the existing natural fracture of the Hot Dry Rock (HDR) reservoir and the forced convection through the fracture media when the filtrating fluid extracts the heat from the hot rock and delivers it to the production wells. Modeling of the first stage incorporates the mechanical rock-fluid interaction during hydraulic stimulation and quantitatively predicts the 3D reservoir growth behavior. In this model the pre-existing fractures are generated stochastically. The fractal size distribution of the penny-shaped fractures with random orientation is assumed. The fractal fracture radius γ distribution is modeled by equation γ_α=((1-α)γ^<-D>_<min>+αγ^<-D>_<max>)^<-1/D>; where α is a random parameter in the interval [0,1]; γ_<min> and γ_<max> are the lower and upper fracture radius limits, respectively; D is fractal dimension of the fracture length (radius) distribution. Thus, for the purpose of simulation, it is necessary to specify the length of the smallest and largest fractures, as well as fractal dimension D. The fluid flow is approximated by the Darcy law equation. Pressure distribution within the fracture rock is used for calculating the growth of the cracks apertures and shear displacements. This requires several iterations; solving the complete flow model simulating the fracture system anew each time and recalculating the shear displacement using the inner fracture pressure from the previous iteration. The heat extraction stage of the reservoir exploitation is simulated by the unsteady energy conservation equation. Since the flow rate within the reservoir is relatively high, the mathematical model accounts for the effect of thermal dispersion. Since the heat accumulated by the fluid within the system of injection boreholes can constitute the substantial fraction of the total thermal output of the geothermal power plant, the model of heat and mass transfer in the fractured media at the heat extraction stage should be coupled with the equations which describe the heat transport in the system of injection and production wells. Mathematical model of heat flow within the multi-borehole circulating system is proposed in this study. The schematic sketch of the multi-borehole system under consideration, which has a number of injection wells and one production well, is presented in figure below. [figure] On the basis of this model the major parameters that affects the thermal productivity of the geothermal power plant are analyzed. The effective regimes of the fluid circulation and optimal geometry of the multi-borehole system are proposed.

Assessment of the heat either delivered from the high temperature rocks to the borehole or transmitted to the formation from the circulating fluid is of crucial importance for a number of technological processes related to borehole drilling or exploitation. Normally the temperature fields in the well and surrounding rocks are calculated numerically by the finite difference method or analytically, applying the Laplace-transform method. The obtained formulae are rather bulky and require tedious non-trivial numerical evaluations. Moreover, in the publications where the solution is obtained analytically heat interactions of circulating fluid and with formation was treated under condition of constant bore-face temperature. In the present study the temperature field in the formation disturbed by the heat flow from the borehole is modeled by the heat conduction equation and thermal interaction of the circulating fluid with formation is approximated by the Newton relationship on the bore-face. The problem is solved analytically by the heat balance integral method, where the radius of thermal influence, which defines the thermally disturbed domain, is function of time that can be found from the algebraic equation. Within this method the approximate solution of the heat conduction problem is sought in the form of a finite sum of functions which belong to a complete set of the linearly independent functions defined on the finite interval bounded by the radius of thermal influence and satisfy the homogeneous boundary condition on the bore-face. It can be proved theoretically that the approximate solution found by this method converges to the exact one. In the present study the first and the second order approximations are obtained. Numerical results illustrates that second approximation is in a quite good agreement with the exact solution. The only one shortcoming of this solution is that it depends on the radius of thermal influence, which is the implicit function or time determined by the algebraic equation. In order to eliminate this complication, in this study on the basis of the approximate solution the new approximate formulae for the radius of thermal influence, which asymptotically coincides with the implicit one, is proposed as l(Fo)&ap;1+A(Bi)√<Fo>, where Bi=h_wr_w/k_S, Fo=τD_S/(r_w)^2,τ is time D_S is heat diffusivity of the formation, r_w is radius of the borehole, k_S is heat conductivity of the formation, h_w is heat transfer coefficient on the bore-face. The behavior of parameter A versus Bi is found comparing the approximate solution with the exact one and employing the non-linear regression method. The latter leads to A(Bi)=(2.084+0.704Bi)/(1.554+0.407Bi). For the constant temperature on the bore-face the heat flux on the bore-face can be computed with an approximate formula q^^&acd;(Fo)&ap;1/{1+Biln[1+A(Bi)√<Fo>]}. The correctness of this approximate solution is validated by comparison with an exact analytical solution found by Carslaw and Jaeger. Due to the Duhamel theorem for the arbitrary temperature on the bore-face the heat flux and bore-face temperature can be presented respectively as q_w=T_L(z, Fo)+∫^^<Fo>__0T_L(z, p)∂/(∂Fo)q^^&acd;(Fo-p)dp and T|_<r=1>=-∫^^<Fo>__0T_L(z, p)∂/(∂Fo)q^^&acd;(r, Fo-p)dp , where T_L(z, Fo) accounts for the thermal history of the formation temperature and possible axial (along the vertical axis z) variation of generally unsteady temperature in the borehole.

Composite materials heve been prepared using a CO2 solidification process from milling dust of autoclaved lightweight concrete (ALC as matrix material), reinforced by addition of crushed glass (bottle) waste. The effect of varying glass collet size (0.08-5 mm) and glass volume (10-30%) on the fracture properties in the glass/ALC composite was examined by four point bending tests. For the glass/ALC composite cured under atmospheric conditions, we show, by conducting CO2 solidification experiments at different CO2 gas pressures (atmospheric, and 4-10 MPa), that the rate of reaction at the sample surface is faster under pressure, than under atmospheric conditions. At 4-10 MPa experimental conditions, a solidified 'reaction rim' is formed away from the sample surface characterized by the deposition of calcite, and a long internal fracture is created inside the sample, which reduces bending strength, although these characteristic features are not evident in samples cured at atmospheric conditions. Creation of the 'reaction rim' impedes further diffusion of CO2 into the sample. Our results indicated that the CO2 solidification of glass/ALC composite materials is best advanced under atmospheric conditions. The result also indicated that for &lt 0.5 mm cullet size, the bending strength is enhanced, without being detrimental to fracture characteristics. However, increasing size of the crushed glass cullet (0.5 mm-5 mm) reduced the strength of the solidified composite. The interface between the ALC powder matrix and glass cullet was weak, and a fraction glass cullets 0.08-0.5 mm size may be incorporated in the waste concrete matrix by as much as 30 vol%.

The numerical model FRACSIM developed by the research group in Tohoku University is proved to be an appropriate approximate model of the hot-dry-rock geothermal reservoir capable to address simultaneously the problems associated with hydraulic stimulation, fluid circulation and heat extraction. The structure of the fractured rock is approximated with the network model of fractal geometry. The adopted procedure makes possible to characterize the geothermal reservoirs by parameters measured from the field data. In the present study an improved mathematical model, which accounts for the effect of thermal dispersion on forced convection during the geothermal energy extraction, is proposed. Since the typical flow rate in the fractured reservoir is relatively high, the values of the effective thermal conductivities in the longitudinal and transverse directions are taken to be directly proportional to the values of the fluid velocity. The importance of the thermal dispersion factor for assessment of the total thermal output of the geothermal reservoir is proved.

The changes of the stress regime in the natural rocks often cause the fracture shear displacements, which lead (due to fracture surface roughness) to fracture dilation. The simple approach for simulating this natural process is proposed. The method incorporates the experimental measuring of the real fracture surface topography, mathematical modeling of the synthetic fracture surfaces that share the same physical properties as real fracture, and numerical simulation of the fracture dilation due to fracture lateral slipping (shear dilation). Mathematical model is based on the spectral synthesis method and accounts for the fractal nature of the fracture surfaces. It is shown that the topography of the lengthy fracture surfaces in the natural rocks can be properly characterized with the data obtained from the small fragments of these surfaces. The algorithm for computing and predicting the fracture dilation and shear dilation angles in the natural rocks as functions of shear offset is proposed.

Solidificatioin of hydroxyapatite (HA) and its bonding with titanium (Ti) alloys was achieved simultaneously by using a hydrothermal hot-pressing (HHP) method. The reaction temperature used for the HHP treatment was as low as 150 degreesC. Two types of Ti alloys; Ti-15Mo-5Zr-3Al and Ti-6Al-2Nb-1Ta were tested to examine the effect of NaOH hydrothermal treatment. The NaOH treatment was shown to be useful to enhance the interface fracture property in the bonded HAM body for both Ti alloys. The use of Ti-15Mo-5Zr-3Al was more effective in the NaOH treatment and the bonded HAM body provided approximately three times higher interface toughness compared with that for the non-treated Ti alloy.

This paper discusses the generation of micro-fractures in a granite under super critical water environment. In order to create an artificial pathway of water in geothermal reservoir with limited permeability, hydraulic stimulation technology is commonly employed. In this study, simulated hydraulic stimulation tests were performed using thick-walled cylindrical specimens of 45 mm outer diameter, under temperatures up to 600degreesC and confining pressures up to 100 MPa. The experimental results of simulated hydraulic stimulations showed that no macroscopic fracturing took place and predominant fluid flow occurred at high temperature regime. The permeability of the granite was also measured using the same cylindrical specimen configuration as used in the simulated hydraulic stimulation tests. The permeability test results showed that the permeability of the granite was enhanced drastically when the temperature exceeded the critical point of water, whilst no significant increase in the permeability was observed under the subcritical water condition. Optical microscopy of the microstructural change revealed that the enhanced permeability was due to the formation of micro-fractures under the supercritical water environment. This laboratory-scale test result suggests that it may be possible to generate a micro-fracture network by injecting water into a high temperature rock mass whose conditions exceed the critical point of water and to extract the heat energy through the generated fracture network from the supercritical rock mass.

Elastic analysis has been used to estimate the driving force for interface edge-crack growth in TBC system with layered FGM coat under an uniform change in temperature. According to some simplified assumptions, closed-form solutions of thermal stresses are obtained and the energy release rates are estimated. For the case of layered FGM, the energy release rate is a function of the geometry parameters of the layers and thermo-mechanical properties of each layer. In addition, the FGM coating system is designed for the purpose of minimizing the energy release rate.

パーライトを混合して軽量化したセメント系ポリビニルアルコール(PVA)繊維複合材料を押出成形により作製し,その破壊特性を直接引張試験により評価した。パーライトを10%添加したPVA繊維複合材料(密度1.259/cm^3)においては,顕著な擬似ひずみ硬化挙動を誘起でき,ピーク応力時の破断ひずみは2.4%に達することを示し,パーライト無添加の場合と比べて顕著に破断ひずみを増大させることに成功した。これは,上述のパーライト添加条件の下では,マトリックスの破壊靭性の低下に伴うマルチプルクラック形成の促進と同時に,界面せん断強度の低減を抑制できているためであると推察される。

The mechanism of initiation and propagation of wing crack emanating from the tips of closed flaw under compressive stresses is discussed. The approximate expression of stress intensity factor for relatively long wing crack was derived and was found to agree well with the detailed numerical result. A wing crack extends stably where mode-I stress intensity factor decreases with the extension of crack. Wing crack propagation in an infinite domain as well as wing crack propagation in a semi-finite and finite regions were treated. Deflection of the surrounding boundaries was found to accelerate the growth of wing crack.

Solidificatioin of hydroxyapatite (HA) and its bonding with titanium (Ti) alloys was achieved simultaneously by using a hydrothermal hot-pressing (HHP) method. The reaction temperature used for the HHP treatment was as low as 150 degreesC. Two types of Ti alloys; Ti-15Mo-5Zr-3Al and Ti-6Al-2Nb-1Ta were tested to examine the effect of NaOH hydrothermal treatment. The NaOH treatment was shown to be useful to enhance the interface fracture property in the bonded HAM body for both Ti alloys. The use of Ti-15Mo-5Zr-3Al was more effective in the NaOH treatment and the bonded HAM body provided approximately three times higher interface toughness compared with that for the non-treated Ti alloy.

The mechanical background why the compressed brittle material fails in a shear mode is studied. Compression-induced shear fracture was experienced in a standard compression test of cylindrical mortar sample whereas a mode I crack branching almost parallel to compression was dominant in a cracked specimen. In a uniaxial compression test of artificially-flawed PMMA plate, formation of a number of minute-surface cracks (en echelon cracks) as well as growth of wing cracks emanated from the artificial flaw tips were observed. The damage zone composed by en echelon-mode-I cracks can be considered as a possible source of the macroscopic shear faulting. The relevance between the genesis of en echelon cracks and the compression-induced shear failure is discussed based on experimental observations and numerical analyses.

Delamination cracking in thermal barrier coating (TBC) system is studied with the newly developed theoretical model. A semi-infinite long interface crack is pre-existing. The thermal stress and temperature gradient in TBC system are designated by a membrane stress P and a bending moment M. In this case, the effects of plastic deformation, creep of ceramic coating, as well as thermal growth oxidation and temperature gradient in TBC system are considered in the model due to the fact that these effects are considered in the calculation of thermal stress. The energy release rate, mode I and mode H stress intensity factors, as well as mode mixed measure psi, are derived. The emphatic discussion about PSZ/Ni-alloy reveals that the TBC system may not fail in the form of coating delamination during the period of heat hold. However the failure may be in the form of coating delamination during cooling or in the heating period during the second cycle or later cycles. The conclusion is consistent with the experimental observations. The delamination of ceramic coating is induced by the compressive load in the coating.

An approximate mathematical model of contact melting of an unfixed material in elastic cylindrical and spherical capsules is developed. Since the density of the solid is higher than that of the melt, the melting solid resides at the bottom supported by a thin layer of the generated, convecting, melt, and the capsule swells. The main characteristic scales and non-dimensional parameters, which describe the principal features of the melting process and the liquid flow, are found. Linearisation with regard to the Stefan number as well as the small difference between the densities of the solid and liquid enables us to derive a closed-form evolution equation for the motion of the solid, which also determines the melting rate, Numerical solution of the evolution equation shows that the swelling of the capsule during melting, which is caused by the decrease of the density during phase transition, leads to slowing down of the melting process. This effect is due to flattening of the lower surface of the capsule, which entails fall of the pressure along with thickening of the molten layer. The latter determines the decrease of the melting rate. (C) 2002 Published by Elsevier Science Ltd.

The creep properties for SUS 316 HTB austenitic stainless steel were evaluated by using the small-punch creep test at 650 degreesC for loads of 234, 286, 338, 408, and 478 N and at 700 degreesC for loads of 199 and 234 N. The creep curves, determined by means of the small-punch creep test, were similar to those obtained from a conventional uniaxial creep test. That is, they exhibited clearly the three creep stages. The width of secondary creep stage and rupture time t(r) decreased with the increase in testing load level. The creep rupture strength for the service-exposed material was lower than that of the as-received material at high testing loads. However, the creep resistance behavior was opposite at relatively low load levels. This difference in creep resistance was explained on the basis of the difference in the creep deformation and microstructural evolution during tests. It was also found that the ratio between the load of small-punch creep test and the stress of uniaxial creep test was about I for having the same value of creep rupture life.

Uniaxial tension and four-point bending tests were conducted on two-layer (non-function ally graded material) plasma-sprayed rectangular specimens, boasting a new, functionally graded material (FGM) layer. The top coat layer was composed of stabilized yttria-zirconia (YSZ), and the bond coat layer was NiCrAlY. The FGM was composed of five layers: 100% YSZ; 80% YSZ+ 20% NiCrAlY; 60% YSZ + 40% NiCrAlY, 40% YSZ + 60% NiCrAlY; and 20% YSZ + 80% NiCrAlY. Fracture in the thermal barrier coating (TBC) system was examined by scanning electron microscopy (SEM), which showed that vertical multiple cracking first occurred in the top coat, followed by propagation of interface cracking between the top and bond coats. Spallation of non-FGM coating occurred in tensile/bending experiments, but not for the FGM-coated specimens, with only localized delamination observed along the interface between FGM layers and the substrate. For specimens prepared with a gun-substrate distance of approximately 120 turn and gun operating power of approximately 32.5 kW, the interface fracture toughness, evaluated by a shear lag model for the uniaxial tensile test, was 0.94 and 0.67 MPa m(1/2) for type-A and -13 coatings, respectively. Here, types A and B correspond to an average roughness of the bond coat surface of 12.8 mum and 6.8 mum, respectively. The interface fracture toughness evaluated by the Suo-Hutchinson model was 1.05-1.27 and 1.0-1.17 MPa m(1/2) for type-A and -B coatings, respectively. The results are very close to data obtained by the blister test method. For specimens prepared with a gun-substrate distance of 125-130 mm and gun operating power of approximately 38.5 kW, the interface fracture toughness, evaluated by the Suo-Hutchinson model for four-point bending, was 4.26-7.21 MPa m(1/2). (C) 2002 Elsevier Science B.V. All rights reserved.

Zn- and Li-birnessites were synthesized from Na-birnessite by ion-exchange reactions. The ion-exchange reaction, chemical lithiation reaction in non-aqueous solution, and stability for these birnessites were investigated by XRD, TG-DTA, and chemical analyses. The Zn-birnessite showed greater thermal stability than Li-birnessite. The Zn- and Li-birnessites can be lithiated up to Li/Mn molar ratios of 0.45 and 1.08, respectively, by reaction in a LiI-acetonitrile solution. The lithiation of Zn-birnessite progressed by a redox topotactic reaction, but the Li-birnessite was unstable during the lithiation reaction. The lithiated Zn-birnessite showed greater thermal stability than lithiated Li-birnessite. The Zn species in the interlayer space of lithiated Zn-birnessite acts as a pillar for the stabilization of the layered structure. (C) 2002 Kluwer Academic Publishers.

Small-punch tests were conducted at 4, 77, and 293 K on three newly developed cryogenic austenitic stainless steels, JN1, JJ1, and JK2, which were solution treated, water-quenched, and then aged at 923, 973, 1023, and 1073 K for 5 h. Small-punch test energy was employed for the evaluation of the aging-induced embrittlement behavior in these materials. An SEM analysis of the fracture surface for the solution-treated steel specimens indicated a ductile fracture, having the highest SP test energy values. On the contrary, intergranular brittle fracture was observed in aged specimens. The small-punch test energy of materials decreased significantly as the aging process progressed. The highest and lowest decrease in small-punch test energy with aging temperature occurred in JN1 and JK2 steels, respectively. The decrease in small-punch test energy was shown to follow appropriately the aging-induced embrittlement in these materials. The difference in aging-induced embrittlement behavior for these steels was explained on the basis of the volume fraction of intergranular precipitates in aged samples.

A three-dimensional (3-D) water/rock chemical interaction model has been developed to examine the effect of water/rock chemical interaction (WRCI) on the long-term performance of hot dry rock and hot wet rock (HDR/HWR) reservoirs. The model, which integrates many field observations and thus generates a fracture network, very similar to the natural fracture distribution in the reservoir, can predict the influence of WRCI on the overall fractured reservoir. Factors affecting WRCI and the effect of WRCI on long-term performance of Hijiori deep reservoir (Japan) have been modelled, Simulated results show that fluid chemistry, initial rock temperature, magnitude of flow rate and well spacing have a major effect on WRCI, and for such a multi-well Hijiori geothermal system, WRCI seems to make the flow distribution tend towards uniformity. The model described deals solely with chemical interactions as a function of flow rate and temperature, and takes no account of aperture variation as a result of thermoelastic effects. It is only a partial model, though it could form an important module of a coupled model. (C) 2002 CNR. Published by Elsevier Science Ltd. All rights reserved.

The paper presents the experimental and theoretical investigation on the thermal fatigue failure induced by delamination in thermal barrier coating system. Laser heating method was used to simulate the operating state of TBC (thermal barrier coating) system. The non-destructive evaluation such as acoustic emission (AE) detect was used to study the evolution of TBC system damage. Micro-observation and AE detect both revealed that fatigue crack was in two forms: surface crack and interface delamination. It was found that interface delamination took place in the period of cooling or heating. Heating or cooling rate and temperature gradient had an important effect on interface delamination cracking propagation. A theoretical model on interface delamination cracking in TBC system at operating state is proposed. In the model, a membrane stress P and a bending moment M are designated the thermal loads of the thermal stress and temperature gradient in TBC system. In this case, the coupled effect of plastic deformation, creep of ceramic coating as well as thermal growth oxidation (TGO) and temperature gradient in TBC system was considered in the model. The thermal stress intensity factors (TSIFs) in non-FGM (functional gradient material) thermal barrier coating system is analytical obtained. The numerical results of TSIFs reveal some same results as obtained in experimental test. The model is based on fracture mechanics theory about heterogeneous materials and it gives a rigorous explanation of delaminations in TBC system loaded by thermal fatigue, Both theoretical analysis and experimental observation reveal an important fact: delaminations are fatigue cracks which grow during thermal shocks due to compressive stresses in the loading, this loads the delaminations cracks in mixed I and II mode. (C) 2002 Elsevier Science Ltd. All rights reserved.

A three-dimensional model (FRACSIM-3D) developed in Tohoku University for numerical simulation of heat and fluid flow within the fractured media is used in the analysis of geothermal reservoir performance. The model effectively simulates two main stages of the geothermal reservoir exploitation, namely, (i) hydraulic stimulation of the existing natural fractures within the Hot Dry Rock (HDR) reservoir and (ii) forced convection through the fractured media when the filtrating fluid extracts the heat from the hot rock and delivers it to the production well. Since the heat accumulated by the fluid within the system of injection boreholes can constitute a substantial fraction of the total thermal output of the geothermal power plant, the model of heat and mass transfer in the fractured media at the heat extraction stage should be coupled with the equations which describe the heat transport in the system of injection and production wells. Mathematical modeling of heat flow within the multi-borehole circulating system is proposed in this study. On the basis of this model the major parameters that affect the thermal productivity of the geothermal power plant are analyzed. The effective regimes of the fluid circulation and optimal geometry of the multi-borehole system are proposed.

This paper presents an experimental investigation on the thermal fatigue failure in thermal barrier coating (TBC) system at high temperature. The thermal fatigue failure was induced by temperature gradient along TBC system thickness direction and oxidation between TBC and bond coat. Laser heating method was employed to simulate the operating state of TBC system. The non-destructive evaluation methods such as acoustic emission (AE) and impedance spectroscopy (IS) were used to examine the evolution of TBC system damage. Both micro-observation and acoustic emission (AE) detection revealed that the fatigue damage consisted of vertical crack in the top coat layer and interface delamination between the top and bond coat. The life of thermal fatigue was shown to be reduced by the formation of alumina at interface. It was also found that the temperature gradient between the inner and outer surface of specimen accelerated the growth of alumina layer.

Small-punch (SP) and fracture toughness tests were conducted at 4 and 77 K on newly developed cryogenic austenitic stainless steels after isothermal aging. Equivalent fracture strain epsilon(qf) was determined by measuring the reduction in thickness of SP specimens. A linear dependence of J(IC) on epsilon(qf) was found for these new materials. Regression analysis of experimental data produced the linear relation: J(IC) = 1304.1epsilon(qf) + 8.09 (kJ m(-2)). An analysis of the correlation was pursued on the basis of material properties and evaluation method of J(IC). The results Showed that the slope value was influenced by the J(IC) evaluation method. This linear relation enables the prediction of J(IC) to be made from the equivalent fracture strain epsilon(qf) by conducting small punch tests. Thus, it is expected that the SP testing method provides a useful basis for assessing the degradation of fracture toughness in small areas, such as heataffected zones in welded components. (C) 2002 Elsevier Science Ltd. All rights reserved.

Hydroxyapatite (HAp) ceramics were prepared by hydrothermal hot pressing (HHP) processes through the reaction between octacalcium phosphate (OCP) and ammonia water, at 300℃. When the amount of ammonia was over the chemical stechiometric ratio, pure HAp ceramics was obtained. The high concentration of ammonia water was advantageous for the solidification of the HAp ceramics. The appropriate amount of water improved the toughness, but greatly reduced the tensile strength. With addition of 10% high concentration ammonia water, HAp ceramic was achieved at 300℃ by HHP method. The density, fracture toughness, and tensile strength of the ceramics reached 2.82g/cm^3, 1.07MPam^<1/2>, and 18.2MPa, respectively. The present study demonstrated that the HHP method was a useful method for preparing HAp ceramics at low temperature.

A small punch creep testing technique using miniaturized specimen with a dimension of 10 × 10 × 0.3^t mm has been demonstrated for evaluating change in creep property of high temperature components due to long-term service operation. This technique was applied to SUS 316 HTB secondary superheater boiler tube actually used for 100,600 h in a fossil power plant. The overall shapes of the creep curves determined by the small punch creep test were similar to those obtained from a conventional uniaxial creep test. That is, they exhibited clearly three creep stages. The extent of secondary creep stage and rupture time t_r decreased with a increase of testing load level. The creep rupture life of the service-exposed tube was shorter than that of the unexposed tube at a temperature of 650℃ and at high load levels, i.e. 338 N and 408 N. However, to the contrary, the former became longer than the latter at relatively low load levels, i.e. 234 N and 286 N. The difference in rupture life between them had a tendency to increase with a decrease of testing load level. These small punch creep behaviors of SUS 316 HTB superheater boiler tubes have been examined from a metallographic point of view.

As a part of a research programme investigating the geothermal reservoir potential of deep-seated high-temperature rock masses, experiments have been undertaken to determine the crack behaviour induced by hot-rock/water interaction. Cylindrical specimens of Iidate Granite were heated, whilst subject to static water conditions, under some confining pressure. The effect of temperatures of up to 600℃ was investigated, whilst the pore fluid and confining pressures were maintained at 50 and 100 MPa respectively. The time-dependence of the water/rock interaction, under these conditions, was also determined, with experiments ranging in duration from 0.5 to 96 hours. Experiments to date, have investigated the quartz constituent of the Iidate Granite samples and results show that crack healing in quartz grains is significant at temperatures of 330℃ and above. This temperature effect is also enhanced with increasing time. No crack healing in quartz is observed at temperatures of 250℃. Additional experiments, using the indentation fracture method, show that these healed cracks recover strength to that of the matrix quartz grains. Although these results might appear to indicate that significant permeability enhancement should not be expected in a supercritical geothermal reservoir, micro-structural data show that significant intragranular micro-cracking also occurs at the temperatures greater than 400℃ due to the water/rock interaction. This micro-cracking phenomenon results in an overall increase in the permeability of the granite. This research presents important results which require due consideration in the potential development of a supercritical deep-seated geothermal reservoir.

Geothermal energy is one of the most environment-conscious resources among the natural resources. Recently, the development of a supercritical geothermal system at great depth has been proposed to enhance the geothermal heat extraction. In order to design the supercritical geothermal reservoir whose temperature and pressure conditions exceed the critical point of water, the formation behavior of the geothermal reservoir under the great depth conditions has to be examined. In this study, we develop a new numerical analysis code for analyzing the hydraulic fracturing behavior in deep-seated rock mass. This code consists of two parts: "flow analysis" which computes the pressure distribution in the induced crack, and "crack propagation analysis". The former is based on a finite difference method. The later is based on a finite element method with embedded crack element. In the "crack propagation analysis", the mixed-mode fracture behavior with process zone formation is modeled. A shear dilation is accounted for in the fracture model. The numerical results show that the crack growth behavior, i.e. the mode of crack propagation depends on the depth. Under a typical tectonic stress condition, the crack growth mode is dominated by the opening fracture mode above the depth of 4 - 5 km, whereas the influence of the shear fracture mode increases with increasing the depth. This result may suggest that the current target of supercritical geothermal reservoirs may be formed mainly under the opening fracture mode.

Solidificatioin of hydroxyapatite (HAp) and its bonding with titanium (Ti) was achieved simultaneously by using a hydrothermal hot-pressing method at the low temparaure as low as 150℃. A mixture of calcium hydrogen phosphate dihydrate and calcium hydroxide was used as a starting powder material for solidifying HAp. The joining behavior of HAp and Ti depended on the surface finishing condition of the titanium. From Raman spectroscopy of the Ti surfaces, it was found that TiO_2 formed at the Ti surface affected the bonding characteristics of the HAp/Ti interface. 3-point bending tests were conducted to obtain an estimate of the fracture toughness for the HAp/Ti interface as well as for the HAp ceramics only. Core-based specimens were used for the fracture toughness tests and a pre-crack was introduced along the HAp/Ti interface of the bonded specimens. The fracture toughness tests showed that the induced crack from the pre-crack tip deviated from the HAp/Ti interface and propagated into the HAp. The fracture toughness determined on the HAp/Ti specimen was closed to that of the HAp ceramics only (〜0.30MPa).

A prediction of host rock permeability in the deep seated geothermal reservoir is essential for the assessment of a potential geothermal energy extraction system. In order to test the permeability of granite under high temperature and high pressure conditions, experiments were undertaken using thick-walled cylindrical specimen of 45 mm outer diameter and 5 mm inner diameter. The permeability of the sample specimen was estimated from flow rate, and the pressure difference between borehole pressure (internal pressure) and confining pressure, based on Darcy's law. Permeability tests were conducted at temperatures of up to 600 ℃ and confining pressures of up to 100 MPa. Experimental results show that the permeability of granite increased with increasing temperature, particularly above 350 ℃. Examination of microcracks, by optical microscopy, showed that crack density in granite, after experiments at 600 ℃, and confining pressures of both 25 MPa and 100 MPa, was larger than at a confining pressure of 20 MPa. This indicates that water-rock interaction processes at supercritical conditions directly affect micro-cracking of granite. In addition, it was noted that hydrothermal cracking occurs at a temperature above 400 ℃ and a pore pressure above 25 MPa, This result indicates that it may be possible to increase granite permeability and to create a porous type reservoir in a supercritical rock mass, by hydrothermal cracking.

In this paper an improved three-dimensional simulation model (FRACSIM-3D) is presented. It incorporates the mechanical rock-fluid interaction during hydraulic stimulation in more rigorous way than the existing two-dimensional model FRACSIM-2D and quantitatively predicts the 3D reservoir growth behavior. In this model the pre-existing fractures are generated stochastically. The fractal size distribution of the penny-shaped fractures with random orientation is assumed. The fluid flow through the discrete fracture network is simulated by mapping the connectivity of the fractured rock to a regular cubic grid under condition of constant injection pressure. The fluid flow is approximated by the Darcy law equation. Pressure distribution within the fractured rock is used for calculating the growth of the cracks apertures and shear displacements. This requires several iterations; solving the complete flow model simulating the fracture system anew each time and recalculating the shear displacement using the inner fracture pressure from the previous iteration. The results of this numerical solution for hydraulic stimulation are in good agreement with the existing field data collected at the Hijiori hot-dry-rock (HDR) reservoir.

In the present paper, a method for determining the fracture characteristic of the ceramic coat layer/bond coat interface was developed. The uniaxial tension and four point bending tests were conducted on plasma-sprayed rectangular specimens of two-layer system and functionally gradient material (FGM) layer. The top coat layer was yttria-partially-stabilized zirconia (YSZ) and the bond coat layer was MCrAlY, both of which were deposited by plasma-spraying technique. FGM consisted of 5 layers: 100% YSZ, 80%YSZ+20%NiCrAlY, 60%YSZ+40%NiCrAlY, 40%YSZ+60%NiCrAlY, 20%YSZ+80%NiCrAlY. The detailed fracture process in the thermal barrier coating system was examined by using scanning electron microscopy (SEM). It was shown that vertical multiple cracking preceded in the top coat followed by the propagation of interface crack between top coat and bond coat. A shear lag model was used to evaluate the interface strength. The experimental results show that FGM specimens have higher interface strength than non-FGM specimens.

It is well known that the tension-softening model can describe the macroscopic fracture behavior of quasi-brittle materials containing pre-existing microcracks such as rocks, ceramics and concretes. The problem studied in this paper is a tension-softening behavior in brittle materials based on the growth of a non-coplanar parallel crack array. Crack growth analyses are performed numerically using the body force method. The problem calculated is a non-coplanar crack array subjected to uniform tensile stress at infinity. The plane strain condition is assumed. The maximum principal stress criterion is employed to determine the each crack growth direction and the global stress required for crack propagation. The tension-softening behavior is studied from the remote tensile stress and deformation of the numerical result. The deduced tension-softening curve is consistent with experimental data obtained for granites. This evidence revealed that the overlapping of non-coplanar cracks, i.e. the ligamentary bridging, is the main source of the tension-softening behavior of granites.

The paper presents the experimental investigation on the fracture of thermal barrier ceramic coating (TBC) at high temperature. The fracture was induced by temperature gradient along TBC system thickness direction and oxidation between TBC and bond coat. Laser heating method was used to simulate the operating state of TBC system. Both micro-observation and acoustic emission (AE) detection revealed that fatigue crack was in two forms: surface crack and interface delamination. One can understand the failure mechanism from the plane of TBC surface temperature and substrate surface temperature. It was found that the life of thermal fatigue was reduced by the formation of alumina at interface. On the other hand, it was found that the temperature gradient between inner and outer surface of specimen accelerated the growth of alumina layer.

In the investigation, the piezoelectric thin film Pb(Zr_xTi_<1-x>)O_3(PZT) was prepared by a pulse laser deposition method. The properties of PZT films were strongly dependent on substrate temperature and oxygen pressures. The residual stress in piezoelectric thin film was tested by indentation fracture method. The relation of properties such as microstructures, piezoelectric response with residual stress was investigated. A theoretical model for the formation of residual stress is proposed. The model is based on the combined effects of the difference of thermal mismatch between substrate and thin film, the phase transformation and the different of lattice constant between thin film and substrate.

A small punch creep(SP-Creep) test using miniaturized specimen(10×10×0.5mm) has been described for the development of the new creep test method for structural components operated at high-temperature and pressure. The SP-Creep test technique has been applied to 9CrlMoVNb steel used as valve material in boiler components. The creep test temperatures were varied at 575℃〜625℃, and the applied loads at 40kg〜100kg. The overall deformations of SP-Creep curve were definitely depended on creep test conditions and showed the creep behaviors of three regions like those of conventional uniaxial tensile creep curve. The steady state creep rate (ε^・_<qf-ss>) in SP-Creep test increased with increase of applied load and creep temperature. Furthermore, the power law's exponent decreased with increase of creep temperature, and the activation energy(Q_<SPC>) obtained from SP-Creep test decreased as applied load increases. These behaviors were similar to those of conventional uniaxial creep test. Also, a predicting equation of SP-Creep rate was suggested and a good agreement between experimental and calculated values was shown. And several creep results of 9CrlMoVNb steel were compared with those of 2.25Cr-1Mo and 1Cr-0.5Mo steels that has been widely used as boiler tube and header materials, respectively.

Thermal damage of SiC particulate-reinforced aluminum composites (MMCs) caused by laser thermal shock was investigated. The damage was induced by a combination of laser beam thermal shock and mechanical loads. The MMCs have two kinds of particle distributions, one is uniform and another is heterogeneous. The damage initiation, crack propagation, as well as the failure evolution, were observed. A damage parameter was defined and it was tested. One found that the damage mechanism was very different for crack initiation and crack propagation and for MMCs with different spatial particle distributions. The mechanism of MMCs failure is discussed by the ideas of shear stress transfer between matrix and reinforcement. The discussion can explain the distinct mechanism of damage and failure in SiC particulate-reinforced aluminum composites.

The thermal stress fields in thermal barrier coating (TBC) system are studied in the present paper. The thermal stress fields are induced by the non-linear coupled effect of temperature gradient, oxidation, thermal fatigue, creep, morphology of TBC system as well as cooling rate. TBC system is assumed to be partially stabilized ZrO(2) by 8 wt.% Y(2)O(3) (PSZ) or mullite over a NiCrAlY bond coat sprayed on nickel superalloy or steel substrate. The TBC system is a composite medium with four layers in cylindrical coordinate system. The temperature fields for the non-homogeneous problem with energy generation in medium are analytical solved by using Taylor transformation and Green&apos;s function approach. The analytical solutions for thermal stress fields in composite medium are obtained when eigenstrain rate is taken into consideration. The constitutive equations, such as the creep of ceramic coating (PSZ and mullite) and substrate (Ni-superalloy), plasticity of bond coat are given by a general formula. Thermal growth oxidation (TGO) and the temperature dependence of thermal-mechanical parameters are taken into consideration. The calculated results of temperature fields and thermal stresses fields are given and the related results are discussed. TGO does not affect the temperature fields in PSZ coating systems. But it has influence on temperature fields in mullite coating systems. The residual stress with TGO considered is larger than that with TGO non-considered, It is very interesting to have the conclusion that TGO may make the residual tangent stress from tensile to compressive. The characterization of thermal stresses in PSZ coating system is very different from that in mullite coating system. It may be due to the difference of mechanical behavior such as creep, thermal mismatch as well as mechanical mismatch which is reflected by Dundurs&apos; parameters a and B. The geometrical radius not only affects the quantum of thermal stress but also affects the characterization of thermal stress. The effect of cooling rate on residual stress is due to the high creep rate of ceramic coating operating at high temperature. The effect of cooling rate on residual stress is not large for system operating at relative low temperature. (C) 2001 Elsevier Science Ltd. All rights reserved.

The tetragonal-to-monoclinic phase transformation in ZrO2-3mol.%Y2O3 containing 0-5% Al2O3 during aging in hot water (370 K) under 100 MPa stress is investigated. It is found that while a small tensile stress accelerates the degradation, a compressive stress has little affect on the degradation. The degradation of PSZ under tensile stress is considered to be caused by the reaction between Y2O3 and H2O. Small amount of Al2O3 addition does not change the degradation mechanism of PSZ, but it prevents further continuation of degradation when the transformed volume reaches a certain value. (C) 2001 Elsevier Science B.V. All rights reserved.

Polypropylene discontinuous fiber reinforced cementitious composites were prepared by extrusion molding and tested in uniaxial tension to determine the mechanical properties such as ultimate composite strength and strain, and the critical volume fi-action for multiple cracking. It was shown that the experimentally determined critical fiber volume fraction reasonablely agreed with theoretical value predicted by a micromechanics model conducted in this study. The extruded fiber composites are yielded the ultimate composite strength of 8.9MPa and the composite strain of 0.55% at the Fiber volume fraction of 7.4%. Our experimental results suggest that there is the apparent bound for suitable fiber volume fraction.

Geothermal energy is one of the most environment-conscious resources among the natural resources. Recently, the development of a supercritical geothermal system has been proposed to enhance the geothermal heat extraction. In order to design the supercritical geothermal reservoir whose temperature and pressure conditions exceed the critical point of water, the formation behavior of the geothermal reservoir under the great depth condition has to be examined. In this study, we develop a new numerical analysis code for analyzing the hydraulic fracturing behavior in deep-seated rock mass. This code consists of two parts : "flow analysis" which computes the pressure distribution in the induced crack, and "crack propagation analysis". The former is based on FDM. The later is based on FEM with embedded crack element. In the "crack propagation analysis", the mixed-mode fracture behavior with process zone formation is modeled. A shear dilation is accounted for in the fracture model. The numerical result shows that the crack growth behavior, i.e. the mode of crack propagation changes from mode I to mode II as the depth increases. Under a typical tectonic stress condition, the crack growth mode is dominated by the mode I component above 4-5 km depth, whereas the influence of mode II component increases with increasing the depth. This result may suggest that the current target of supercritical geothermal reservoirs may be formed mainly under the mode I fracture.

A mechanochemical method for treatment of powdered (recycled) waste glass and calcium hydroxide is combined with a CO2 solidification process for strength development of solidified products. Our work has potential for reducing CO2 emission, which has been identified as a major cause of global warming. Poorly crystalline pre-pulverized waste glass cullet and calcium hydroxide powder was mixed with similar to70 wt % water and cured at room temperature, prior to CO2 carbonation, to produce a solidified sample. Solidified samples were heated to examine phase transformations. Sample density, Vickers hardness and flexural strength were determined. Effect of grinding time, Ca/Si ratio and water content on the mechanical properties was investigated. The mechanochemical reaction has a strong influence on the hardening process, due to formation of calcium carbonate. TG-DTA results show that the decomposition temperature of the glass/calcium hydroxide mixture is decreased after mechanochemical treatment, indicating enhanced reactivity of the mixture. Vickers hardness is increased after CO2 solidification. Our method is effective for the production of various building materials.

Recent research directed toward the development of a computer simulation model for fractured type geothermal reservoirs and a research project aimed at aiding the development of "supercritical" geothermal reservoir system at Tohoku University is briefly described. Outline of a numerical model (Fracsim-3D) developed for designing hydraulically induced fracture type geothermal reservoirs is presented. Then, the potential of creating microcrack network in supercritical rock masses is demonstrated for the energy extraction from deep-seated rock masses.

This study is to utilize a hydrothermal hot-pressing technique and prepare hydroxyapatite ceramics. The starting powder OCP (Ca8H2(PO4)(6).5H(2)O) and ammonia water were heated to 300degreesC at a rate of 10degreesC/min, and sintered under 40MPa for 2h. The effects of the amount and concentration of ammonia water were investigated. The results show that OCP reacted with NH4OH and produced HAp; the high concentration of ammonia water is advantageous for the solidification of the ceramics. The density, fracture toughness, and tensile strength of the ceramics that prepared with 10% high concentration ammonia water reach 2.82g/cm(3), 1.07MPam(1/2), and 18.2MPa, respectively.

Thermal failure of thermal barrier coating (TBC) was investigated. The fracture was induced by temperature gradient along TBC system thickness direction and oxidation between TBC and bond coat. Laser heating method was used to simulate the operating state of TBC system. Micro-observation and acoustic emission (AE) detect both revealed that fatigue crack was in two forms: surface crack and interface delamination. One can understand the failure mechanism from the plane of TBC surface temperature and substrate surface temperature. It was found that the life of thermal fatigue was reduced by the formation of alumina at interface. On the other hand, it was found that the temperature gradient between inner and outer surface of specimen accelerates the growth of alumina layer.

A three-dimensional (3-D) stochastic network model for simulating a hot dry rack (HDR) or hot wet rock (HWR) engineered geothermal system formed in fractured crystalline rock is presented. The model addresses the problems of fracture network characterization from in situ field data, such as fracture orientation, size, spacing, and other mechanical properties. The model can simulate the changes that occur within the rock mass during stimulation (i.e., large volume fluid injection at pressures sufficient to allow shear slip on natural fractures). It can also be used to simulate steady state circulation of the heat exchange system thus created and includes provision for predicting tracer response curves and heat extraction history. The model has been applied to data gathered during the stimulation and circulation of a 2.2-km-deep HDR reservoir at Hijiori, Japan. The predicted shape of the stimulated and shear-propped fractures closely matched the distribution of seismic source distribution of acoustic emission (AE), regardless of realization of the fracture network, suggesting that the geometry of the stimulated volume can be robustly predicted from knowledge of the fracture population and in situ stresses. However, hydraulic behavior and tracer tests during the circulation could only be satisfactorily simultaneously reproduced by a small subset of realizations. These selected realizations, obtained by matching initial circulation and tracer data, are considered to give the best prospect of satisfactory long-term thermal modeling. The success in simultaneously modeling diverse data (hydraulic, microseismic, and tracer) lends confidence to the thermal predictions. The results indicate that a large improvement in the long-term thermal performance of the Hijiori reservoir could result from increasing well spacing from 100 to 150 m without major degradation of the hydraulic performance.

The transition temperatures of Cr-0.5Mo, Cr-Mo, and Cr-Mo-V steels were determined using the Charpy V-notch (CVN) and the small punch (SP) tests. It was confirmed that there was a linear correlation between the transition temperature of ductile-brittle behavior determined by the Charpy V-notch test and that obtained from the small punch test. However, the estimation of CVN transition temperature by means of this linear equation is not completely reliable because of the large experimental scatter of data. In order to improve the reliability of the transition temperature estimation, a multiple linear regression (MLR) analysis was conducted to evaluate the effect of different variables of the manufacturing process and service conditions. This analysis permitted the determination of the following regression equation: CVNDBTT = 1.35 SPDBTT - 0.84 x 10(3) d(-1/2) + 326. This equation enables one to assess more accurately the transition temperature corresponding to the Charpy V-notch test using that of the small punch test and the austenitic grain size, expressed by d(-1/2).

A small punch creep (SP-C) testing technique using miniaturized specimens has been demonstrated for evaluating creep properties and material deterioration due to thermal aging. This technique has been applied to tungsten-alloyed 9%Cr ferritic steels. Experimental results revealed that the overall shapes of the creep curves obtained from the SP-C tests were qualitatively similar to those obtained from conventional uniaxial creep tests and reflected closely the degradation of creep rupture strength of the materials. A correlation with uniaxial creep was also determined in terms of stress (load) exponent and apparent activation energy for creep deformation. The correlation suggests that the SP-C testing technique may provide a useful tool for evaluating degradation of creep properties for structural components in-service.