Two types of low-density carbon/carbon preforms which had different fiber volume fractions and fiber orientations, i.e., a carbon woven fabric (≈55vol%)/carbon and a chopped carbon fiber (≈40vol%)/carbon composites, were reaction-bonded with a silicon melt at 1750°C in vacuum to fabricate dense carbon fiber/Si/SiC composites. The reaction-bonding process increased the density to -2.1g/cm³ from 1.6 and 1.15g/cm³ for carbon woven and chopped carbon preforms, respectively. All of the composites fractured with extensive fiber pullout. The higher the density, the higher the stiffness and proportional limit stress. The carbon woven fabric/Si/SiC composites with a density of 2.06g/cm³ exhibited a -120MPa ultimate strength and a -80MPa proportional limit in bending test.

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The β-spodumene (Li₂O⋅Al₂O₃⋅4SiO₂, LAS) powders were prepared by the sol-gel process using a mixture of silica sol, alumina sol and lithium nitrate solution. Si(OC₂H₅)₄, Al(OC₄H₉^sec)₃ and LiNO₃ were used as the starting compounds. Thermogravimetric and differential thermal analyses (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), wavelength-dispersive spectroscopy (WDS), transmission electron microscopy (TEM) and electron diffraction (ED) analysis were utilized to characterize the β-spodumene powders prepared by the sol-gel process. The crystallization temperature of the LAS gel powder estimated by TG/DTA was about 630°C. When the LAS dried gel was heated from 600 to 850°C, the crystallized powders of the single phase β-spodumene were obtained.

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Ti(CN) ceramics with 0-2mol% WC were prepared by sintering in a flowing nitrogen environment at 1973 and 2073K for 3.6ks. Part of the WC particles were dissolved in the liquid, and triggered a faster sintering. As the WC content increased, the grain size initially increased, and then decreased due to increasing number of WC particles surviving dissolution. The flexural strength was inversely related to the grain size. The hard ness of Ti(CN)-2mol% WC sample was increased by a post-sintering heat treatment in an argon environment.

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The aim of this study is to prepare dense MgF₂ sintered body by normal sintering combined with capsule-free hot-isostatic pressing (HIPing) treatment. LiF was effective sintering aid for MgF₂. MgF₂ body of 95% relative density was obtained by adding 0.4mass% of LiF in the sintering at temparature above 798K. The relative density decreased in the temperature range above 923K. MgF₂ above 97% relative density after normal sintering was almost densified to the theoretical density by capsule-free HIPing treatment at 823K under the pressure of 180MPa in Ar atmosphere. The decrease of relative density at higher temperatures was explained by the growth of pores at grain boundary with grain growth and the evaporation of LiF during sintering. Bending strength, Vickers hardness, Young's modulus and thermal expansion coefficient of MgF₂ were also measured.

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The temperature dependence of Vickers hardness (H) of TeO₂-Based glasses such as 15Na₂O⋅15ZnO⋅70TeO₂ as host glasses for rare-earth doped optical amplifier was measured from room temperature to the glass transition region. The following features were found; (1) crack formation under the indenter easily occurs, the Vickers hardness at room temperature being around 3GPa; (2) the temperature coefficient of the hardness, dH/dT, is around -4.5×10^-3GPa·K^-1; (3) the relative change of hardness with temperature is closely related to thermal expansion coefficient, and hardness sharply decreases in the glass transition region. It was demonstrated that TeO₂-Based glasses are fragile even from the point of view of mechanical properties. The reason for poor mechanical performance in TeO₂-Based glasses is their weak bond strength and open atomic packing structures. The hardness (H=4.8GPa) of a transparent glass-ceramic (with nanocrystalline particles) of 15K₂O⋅15Nb₂O₅⋅70TeO₂ showing second harmonic generation is much larger than that of the precursor glass (H=3.3GPa), meaning that the improvement in the fragile character of TeO₂-Based glasses is due to crystallization. A soda-lime silicate glass of 14Na₂O⋅13CaO⋅73SiO₂ has a value dH/dT=-6.5×10^-3GPa·K^-1, and in contrast to TeO₂-Based glasses, its hardness decrease in the glass transition region is gradual, and a value H≈2GPa is obtained even at the glass transition temperature.

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Effect of polycarbosilane (PC), with high ceramic yield of 85%, added to Al₂O₃ was investigated. Green density of the Al₂O₃ powder compact increases by the PC coating. Al₂O₃ ceramics containing 5 to 10vol% SiC derived from PC were fabricated by the hot-press sintering at temperatures between 1600°C and 1800°C. After hot-pressing at 1600°C, almost all PC-derived SiC-phase exists at grain boundaries as fine crystalline grains, which results in a significant decrease in Al₂O₃ grain-growth rate and in a low fraction of porosity as well. Some of the PC-derived SiC-phase may be drawn inside the Al₂O₃ grains during grain growth at 1800°C to form intragranular SiC nanoparticles. Four-point bending strength of Al₂O₃ was increased, and the scatter in bending strength values significantly decreased by the PC coating. Intragranular fracture mode was observed in the PC-coated Al₂O₃ composite, while Al₂O₃+SiC powder composite exhibited intergranular fracture.

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The kinetics of phase separation in 15Na₂O⋅85B₂O₃ binary glass was investigated using ¹¹B nuclear-magnetic-resonance (NMR) spectra together with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results showed that the product of sodium-rich phase after heat-treated at 500°C was not Na₂O⋅4B₂O₃ as suggested by previous phase diagram. It was found that the high growth rate of boron-rich phase can force residual glass to much higher concentrations of sodium oxide. After reaching equilibrium, a 15Na₂O⋅85B₂O₃ glass was separated into Na₂O⋅9B₂O₃ and 3Na₂O⋅B₂O₃ according to NMR measurement.

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A parametric computational study, using the Monte Carlo method, was performed to examine the effect of γ_s1/γ_ss value and Monte Carlo step (MCS) on the key microstructural characteristics of aluminum nitride (AlN)/yttrium aluminate system. The γ_sl/γ_ss values studied in the simulation ranged from 0.1 to 1.0 and covered the non-wetting and wetting situations for this liquid phase sintered material. Grain morphology and contiguity of the resultant microstructures were determined. Validation experiments were performed on sintered and heat-treated AlN ceramics to study the effect of time, temperature, and grain boundary phase level on the microstructural development. In addition to contiguity, dihedral angle and grain boundary phase chemistry were also measured. The mimicking of experimental and computational results suggested that the remarkable microstructural changes observed during heat treatment at 1800°C might be the result of variations in the γ_s1/γ_ss value with temperature. There was also good agreement between the simulated microstructures and the AlN ceramics with different liquid phase fractions. Dihedral angle measurements of the ceramic materials confirmed the appropriateness of the γ_s1/γ_ss values used in the simulation.

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Molecular-level and particle-dispersed inorganic-organic hybrids, containing TiO₂ as the inorganic component, have been prepared in order to study the effect of the introduced inorganic phase dimension on the structure and properties of the hybrids. The hybrids prepared from silanol-terminated polydimethylsiloxane (PDMS) and titanium ethoxide (Ti(OEt)₄) in the molar ratios of Ti(OEt)₄/PDMS=1, 2 and 4 were transparent with no visible particles, thus considered as molecular-level hybrids. Inorganic particles of about 50nm in diameter prepared from titanium isopropoxide were dispersed into the molecular level hybrids in the molar ratio of Ti(OEt)₄/PDMS=1 to synthesize particle-dispersed hybrids. As a result of differential scanning calorimetry (DSC), increasing the Ti(OEt)₄/PDMS ratio in the molecular-level hybrids were found to fix the free PDMS chains more effectively into a three-dimensional network than dispersing particles. The molecular-level hybrids showed a higher Young's modulus and a smaller elongation at break due to the better developed network structure. In the particle-dispersed hybrids, the tensile strength was twice the one without particles. The mechanical properties of the hybrids were found to be affected by the incorporated inorganic phase dimension reflecting the structure of the hybrids.

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Natural calcite single crystal from Chihuahua Mexico was treated at 873K for 1.5h in a furnace and cooled in air. Thirty minutes later it began to cleave spontaneously by residual thermal stress along (1014) plane in a desiccator. An atomic force microscope (AFM) was used to observe the cleaved (1014) surface structure in air. Atomic scale AFM images were obtained for the first time in air, which show the periodicity of regular atomic arrangement of (1014) surface. The lateral linear dimensions of surface parameters from AFM images show a general agreement with those obtained from X-ray diffraction measurement for bulk material. It was found that there was 0.06nm difference in height of alternating oxygen atom rows in the AFM images. The difference was considered due to reconstruction of calcite surface structure under the balance of atomic interaction on the surface in which half of [CO₃]^2- rotated by 35.4±5.2° around the C-O bond axis lying in the (1014) surface to reach a small slope with respect to the (1014) surface.

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The generation of buffer domain in a dough strongly influences plasticity. In this investigation, the effect on plasticity of water-absorbability of the additive, which forms the gel and acts as buffer domain, was studied using alumina dough. Three agars having different water-absorbability were used as the gel materials. Agar having higher water-absorbability resulted in decrease of pores among the alumina particles, the particle packing was improved. Such a densification seems to improve the rigidity and the plasticity.

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Dependence of the glass and transparent glass-ceramics forming region on the kind of rare earth fluoride in the SiO₂-Al₂O₃-PbF₂-CdF₂-LnF₃ (LnF₃: rare earth fluoride) system are clarified and optical properties of the Er³⁺-doped transparent SiO₂-Al₂O₃-PbF₂-CdF₂ glass-ceramics are investigated. Composition with heavier rare earth fluorides tends to give wider glass and transparent glass-ceramics forming region. Optical transition characteristics of Er³⁺-doped transparent glass-ceramics revealed that the inter-ionic distance of Er³⁺ in the glass-ceramics is much smaller than that in homogeneous glasses.

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Silicon nitride containing Y₂O₃-Nd₂O₃ additives and one-dimensionally aligned β-Si₃N₄ whiskers was sintered at 2473K with different sintering times, under 30MPa in N₂, and its microstructure was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the grain-growth behavior of one-directionally aligned Si₃N₄ grains obeyed the empirical grain growth law. SEM and TEM analyses suggested that the second phase, which consisted of Y, Nd, Si, O and N elements, existed as precipitated within elongated silicon nitride grains. The second phase precipitated in β-Si₃N₄ grains did not generate large elastic strain fields, resulting in negligible phonon-impurity scattering. The apparent thermal conductivity-grain size relationship in the obtained materials followed the Goldsmid and Penn equation, which predicts thermal conductivity to be proportional to the 1/2 power of grain size.

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The stress relaxation behavior of granules has been evaluated by dividing it into three parts: plasticity, viscosity and elasticity. It is shown that addition of binder or increasing dispersant concentration reduces the granule plasticity and increases the granule viscosity. It is also shown that the transient behavior of plasticity and viscosity is well correlated to the breaking and/or deforming behavior of granules, as observed by optical microscopy. It is expected that a homogeneous green body may be obtained using viscous granules.

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The stress in a through hole area after the firing process was numerically calculated by Finite Element method (FEM) analysis using a 3-dimensional elastic deformation model for Al₂O₃ multilayer ceramic substrate. The relationship between the property of W conductor material and the stress in the through hole interface was investigated. The stress value is closely related to the mismatch of thermal expansion coefficient between Al₂O₃ ceramic and W conductor material and the Young's modulus of W conductor material as well, the larger the thermal expansion coefficient difference and Young's modulus, the larger the stress. Similarly, the relationship between the diameter/pitch of the through hole and the stress was investigated, the larger the ratio of the through hole diameter to the through hole pitch, the larger the stress. The maximum stress in the through hole interface was generated near the surface of the Al₂O₃ ceramic substrate. The numerically computed results were almost coincident with the experimental results.

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An Au/Si₃N₄ interface was obtained by vapor deposition of Au on a Si₃N₄ substrate in vacuum, both at room temperature and 600°C. The interface structure and chemical composition were investigated by high resolution and analytical electron microscopy. A damaged phase was observed between Au and Si₃N₄ crystals. The thickness of this phase increased when the substrate surface was polished or the substrate was heated. This phase was found to be amorphous and merely composed of Si and N.

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Fracture behavior of an O-ring specimen compressed by diametrically opposite external concentrated loads has been analyzed in terms of crack growth effect using a finite element method. The resulting advantages of the O-ring compression test may enable to evaluate and distinguish between the fracture stress of internal and external surfaces of tubular cross sections. However, it is clarified by comparison with the C-ring compression test results that the fracture stress evaluation at the internal and external surfaces is difficult in a SiC ceramic filter. The difficulty arises from the occurrence of stable crack growth as confirmed by applying a compliance analysis.

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To investigate the relaxation processes of 4f excited levels of Er³⁺, the fluorescence spectra and lifetimes were measured for various single crystals and glasses containing a large amount of Er³⁺, which showed negative nonlinear absorption (NNA) effect. The lifetimes of the ⁴I_11/2 level decreased exponentially with an increase of phonon energy of the host. In Y₃Al₅O₁₂ single crystals with various Er³⁺ concentrations, the lifetime of the ⁴I_11/2 level was unchanged, whereas that of the ⁴I_13/2 level was varied drastically with Er³⁺ concentration. Temperature dependence of the lifetime of the ⁴I_13/2 level was quite different between samples with high concentration of Er³⁺ and those with low concentration. In a YLiF₄: Er³⁺ single crystal, the decay curve of the ⁴I_13/2→⁴I_15/2 was varied drastically when excited wavelength was changed from 970nm (⁴I_11/2←⁴I_15/2) to 800nm (⁴I_9/2←⁴I_15/2). It was found that a cross relaxation process occurs in the ⁴I_9/2 level, resulting in anomalous decay and temperature dependence of the lifetime of the ⁴I_15/2 level.

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An air side current collector (ASCC) for a solid oxide fuel cells (SOFC) was fabricated and evaluated. Thirty mass% YSZ-LSM, was selected as a candidate material for ASCC. Its electrical conductivity at 1000°C and its average thermal expansion coefficient between room temperature and 1000°C were 65S·cm^-1 and 10.9×10^-6K^-1, respectively. The gas channel width of ASCC is very important factor, because the current collecting resistance depends on it strongly. A 1cm² cell was operated with different current collecting length, which corresponded to the width of the gas channel. We made it clear that the current collecting resistance was very small when the channel width was ≤3mm. The SOFC short-stack was built with a 140cm² cell and two ceramic gas separators. The separator was composed of MgO-MgAl₂O₄ separate plates, La(Sr)CrO₃ current passages and current collectors. The electric power generation test was carried out at 1000°C for 700h. The cell attained the output power 36W at the current 48A. The voltage loss at the gas separator with a current 45A was 68mV, accordingly the electric resistance of the separator was 1.5mΩ. The electric resistance did not change after a thermal cycle conducted between 1000°C and room temperature.

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The effect of frit added in Ag-paste on warpage of co-firing multilayered glass-ceramics substrate was investigated. BaO-Al₂O₃-SiO₂ system glass was used as the added frit. The difference of shrinkage between Ag paste and the glass-ceramics increased with increasing the frit added in the Ag-paste. But, the warpage of co-firing multilayered substrate reduced with increasing the frit added. From these results, it was found that the warpage in our system was not due to the shrinkage mismatch between the substrate and the inner conductor materials, but it was caused by the change of glass-ceramics sintering behavior according to diffusion of silver, as previously reported by other investigators. Electron probe micro-analysis (EPMA) revealed that the glass layer suffered modifications from the added frit formed around the Ag-inner conductor, and that this layer prevented Ag from diffusing into the glass-ceramics. Therefore, the sintering behavior of the glass-ceramics in the neighborhood of the Ag-inner conductor did not change locally, and the warpage of cofiring substrate reduced with increasing the frit added in Ag-paste.

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Silicon nitride with unidirectionally oriented elongated grains was fabricated by the combination of seeding and extrusion process. Development of such highly anisotropic microstructure is due to the high shear stress exerted during the extrusion process, which allowed the unidirectional alignment of rod-like seed particles. Small matrix grains were almost consumed by selective grain growth into larger grains grown from seed particles, consequently, large elongated grains with high aspect ratio were dominant in the microstructure of this material. Such microstructure development is related to the fact that the unidirectional alignment of seeds along a precise direction inhibits mutual impingement of elongated grains during growth along their length direction. Both high strength of about 1.4GPa and high fracture toughness of about 14MPa·m^1/2 could be achieved by testing in the direction parallel to grain alignment.

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Nb₂O₅ thin films were formed on aluminum foils by a sol-gel process in order to increase the capacitance of the aluminum foils which are used as aluminum electrolytic capacitors. Investigations focussed on the preparation and characterization of the coating solution, the formation of Nb₂O₅ thin films on aluminum foils, and the heat treatment and anodization of the films. The phase transition and electrical properties, such as capacitance, leakage current, and withstand voltage of the Nb₂O₅ thin films were also measured. The Nb₂O₅ thin films annealed at temperatures below 550°C were found to be amorphous, but they were crystallized to the orthorhombic phase by annealing at temperatures higher than 580°C. The capacitance of the coated samples increased with an increase in the thickness of the formed Nb₂O₅ thin films, but an increase in leakage current and a decrease in withstand voltage were also observed in those samples. The product of capacitance and withstand voltage of the aluminum foils coated with Nb₂O₅ thin film increased by 30 to 70% compared with those of the non-coated foils.

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Molecular dynamic simulations with quantum correction were performed on an alumina-magnesia system. First, interatomic potential parameters were determined empirically for alumina, magnesia and spinel so as to reproduce the lattice constants at 300K and higher temperatures. Then, the thermal expansivity, specific heat capacity and bulk modulus were simulated and compared with the experimental values to inspect the utilization of the estimated parameters.

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KrF excimer laser was irradiated on insulating SrTiO₃ polycrystals sintered in air and diffused with metal oxides through grain boundary. Surface varistor layer with nonlinear coefficient of 2.8-5.2 was formed by the laser irradiation. The exhibition of nonlinear I-V characteristics is attributed to surface grains made semiconductive by laser irradiation and the potential barrier at grain boundaries preserved after laser irradiation. The varistor layer was found to be formed by excimer laser irradiation on SrTiO₃-based ceramics without the heat treatment in reducing atmosphere.

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