The preparation of MoSi₂-WSi₂ alloy powder by a carbothermal reduction process was investigated using ammonium paramolybdate, ammonium paratungstate, quartz and active carbon in Ar+H₂ atmosphere. The optimum starting composition for preparing MoSi₂-50mol% WSi₂ powder was Mo:W:Si:C=1:1:7:17. Mo₂C and WC appeared at a low temperature in the course of heating. At 1400°C an alloy of the lower silicides (Mo₅Si₃, W₅Si₃) was formed, subsequently changing into a MoSi₂-WSi₂ alloy. The alloy particles were fine with a size of 0.5-2μm. The sintered body exhibited a homogeneous distribution of Mo and W compared with a sintered body obtained from a mixture of coarse MoSi₂ and WSi₂ particles.

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The dependence of the residual stress in cylindrical solid oxide fuel cells (SOFCs) on the structures and the process temperatures was estimated using the analytical modeling of an axisymmetric structure. From the results of the analysis the following points were discovered. In the case of a 4-layered structure, which is supported by a porous insulation tube of calcia-stabilized zirconia (CSZ), the circumferential and axial stresses induced in the electrodes are so high that they can break the structure under the assumed realistic conditions. A method for reducing these stresses is discussed. On the other hand, in the case of a 3-layered structure which is supported by an inner electrode tube, tensile stresses in the electrodes can be reduced to several MPa if the total thickness of two electrodes is more than 60 times the thickness of the electrolyte. New material for the substrate tube is proposed on the basis of the obtained results.

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This study investigated the degradation in mechanical properties of an alumina subjected to thermal shock loading by systematic experiments on bend-bar specimens of two sizes, 3×4×45mm and 9×12×45mm. Thermal loading was applied by water-quench method with several well defined temperature differences. Critical temperature difference (ΔT_c) was defined as the lowest applied temperature difference above which a loss in flexure strength occurred. ΔT_c values for the large and small specimens were found to be 175 and 200°C, respectively. The reduction in thermal shock resistance with increasing sample size can be well described by the thermal elastic and fracture energy theories. However, if the size effect on the initial, unshocked fracture strength is considered, the size effect on the transport of heat during quench test might play a less important role in reducing the thermal shock resistance of large specimen.

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β-alumina type ionic conductors were synthesized in the SrO-MgO-Al₂O₃ system by a direct sintering method and their electrical conductivity was measured at 873 to 1373K by an a.c. impedance method in order to apply the β-alumina to solid electrolyte of a gas sensor at high temperatures. Sr β-aluminas in a single phase were obtained in the composition range of SrO:MgO:Al₂O₃=1:1:4.8-5.2. The bulk and grain boundary conductivities were separated from the total conductivity at SrO:MgO:Al₂O₃=1:1:4.8 and 1:1:5.0. The bulk conductivity of the Sr β-alumina was around 6.7×10^-3S·m^-1 at 1373K.

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Silicon nitride whiskers were obtained by the heat treatment of porous bodies at 1373 to 1773K in nitrogen stream, which were produced by polymerization and drying of polymerizable W/O-type emulsions containing polycarbosilane and milled carbon fibers. The whiskers were deposited on the surface and inside of the porous bodies. At 1473K the whiskers were apparently observed as rod-like ones. The tape-like whiskers were observed beside the rod-like ones at 1573K and the tape-like ones were mainly observed at 1673K. Scanning electron microscopic analysis revealed that the rod-like whiskers were formed via the vapor-liquid-solid (VLS) process, and grow in a preferential direction via the vapor-solid (VS) process, resulting in the formation of the tape-like ones. It was found that the whiskers were mainly α-type Si₃N₄ and that the α-phase content of the whiskers obtained at 1673K was 96.7% by X-ray diffraction analysis. It was proved by infrared spectroscopy and chemical analysis that Si₃N₄ whiskers grew remarkably with decreasing Si-O bondings. It can therefore be presumed that the formation mechanism of Si₃N₄ whiskers was analogous to that of the silica-carbothermal reduction-nitridation and that the optimum temperature for the formation of Si₃N₄ whiskers was around 1673K.

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The dependence of the third-order nonlinear optical properties of the La₂S₃-Ga₂S₃ and MS-La₂S₃-Ga₂S₃ (MS=PbS, Ag₂S and Na₂S) glasses on the composition, linear refractive index and optical band gap was examined. The χ⁽³⁾ of the glasses was -10^-12esu, which was about 100 times as large as that of silica glass, and was increased with the increase of La₂S₃ content in the La₂S₃-Ga₂S₃ binary glasses, while it was increased with the substitution of PbS or Ag₂S for La₂S₃ and decreased when La₂S₃ was replaced by Na₂S. The χ⁽³⁾ of the glasses was found to increase with the increase of linear refractive index and the decrease of band gap, being in accordance with the empirical Miller's rule and optical band gap model.

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This work seeks to explain the mechanism of the dramatic strength increase obtained by dispersing nanometer sized particles within a monolithic ceramic matrix relative to the pure matrix material. The crack tip toughness, along with long crack toughness of the material, is experimentally investigated, along with slow crack growth rates. A simple consideration of Griffith criteria shows that strength increases cannot be explained simply in terms of increased toughness. Additionally, critical crack sizes for fracture are considerably smaller than the grain size. It is proposed therefore that the inclusion of the nanoparticles changes the residual stress conditions within the material, hindering microcrack initiation in the stress field around a pore and reducing the facet length of such microcracks.

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The plasma facing component (PFC) in nuclear fusion reactors such as divertor and first wall armors (tiles) will be always exposed to high temperature plasma of hydrogens. Therefore, heating tests should be imposed on all new materials (PFM) developed for PFC as well as usual erosion and recycling tests with hydrogens. Heating tests by electron beam irradiation and thereafter by in situ plasma discharge in JT-60 were done on new composite ceramics made of boron carbide-carbon fibers which were fabricated by hot-pressing in a vacuum at 2100°C. It is shown that the composite ceramics containing carbon fibers in curled plain fabrics (CFCPF) were not broken by the two kinds of heating test, though a composite ceramics containing one dimensional or uni-directional carbon fibers cracked in a heating test by electron beam irradiation. The composite ceramics containing CFCPF could withstand 572 shots of in situ plasma discharge in JT-60 without cracking, where NBI (neutral beam injection) heating was used with a maximum power of 30MW for 1-2s. Very small melted parts were locally formed near the edge of the tiles of the composite ceramics.

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Uneven packing structure of consolidated powder bed due to particle shape was experimentally investigated. Angular stainless steel particles were processed in several steps toward sphericity by means of Hybridizer and consolidated under a piston press. The vertical pressure distribution was measured and correlated with the voidage for different shaped particles. As a result, it was found that the ratio of horizontal to vertical pressure, k, decreases with increasing overall voidage and sphericity. Thus, for preparation of powder compacts with low voidage and uniformly distributed voids, it is effective to make particles spherical or adjust the particle shape as required.

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The factors for the flocculation control of ceramic powder (alumina and alumino-silicate) slurries by various water soluble polymers with different ionicities were investigated through floc size, porosimetry, and polymer adsorption. The results are summarized as follows; (1) Floc size depends on the sign and the strength of charged sites on ceramic particles, ionicities of polymers, solid loading, and slurry pH. (2) Cationic polymers make mainly particles containing SiO sites flocculate, and the floc size increases with increasing pH and solid loading. Anionic and nonionic polymers make particles containing Al (O, OH) sites flocculate, and the floc size increases with decreasing pH and increasing solid loading. (3) The peak pore diameter in a dried floc obtained at high pH is smaller than that at low pH which shows a wide pore distribution. The high pH floc is denser than the low pH floc. (4) It was found that there are two systems showing different floc size behavior. In one system the floc size increases with increasing polymer adsorption, while in the other system it increases with decreasing adsorption. The former is anionic and nonionic polymer systems, the latter is cationic polymer system. This behavior suggests the difference in the mechanisms of polymer adsorption and/or flocculation.

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Phase transformations during the isothermal heat treatments of alkaline-earth aluminosilicate glasses with compositions of RO⋅Al₂O₃⋅2SiO₂ (R=Mg, Ca, Sr, Ba) were studied based on the time-temperature-transformation (TTT) diagram. The crystallization conditions of metastable and stable phases such as cordierite (MgO⋅Al₂O₃⋅2.5SiO₂), anorthite (CaO⋅Al₂O₃⋅2SiO₂) and celsian (SrO⋅Al₂O₃⋅2SiO₂, BaO⋅Al₂O₃⋅2SiO₂), are determined. The onset time of crystallization is related to the viscosity of supercooled liquid measured in the previous works. The transformation processes of metastable-to-stable phases are discussed in terms of anion structure and cation radius.

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Third-harmonic generation (THG), optical Kerr shutter (OKS) and degenerate four-wave mixing (DFWM) measurements clarified third-order nonlinear optical properties of chalcogenide glasses. We studied the dependence of third-order nonlinear optical susceptibility measured by THG method on refractive index and absorption edge wavelength of glasses. It was shown that the larger susceptibility increased with increasing refractive index absorption edge wavelength, thereby producing the maximum susceptibility of 1.4×10^-11esu. We also found that the susceptibilities determined by TUG and OKS methods almost coincided within the range of experimental errors. The chalcogenide glass provided the twice OKS transmittance of the conventional carbon disulfide. The DFWM experiment indicated that high-speed switching operation was attainable with the chalcogenide glasses. This value was compared with the bismuth containing oxide glasses.

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Piezoelectric ceramics such as lead zirconate titanate (PZT) have found wide applications because of their excellent piezoelectric properties. We have developed a dynamic displacement measurement system for PZT pellet with the resolution of 1/100μm, under the conditions which is same one for stack actuator, i.e., several voltage, from 6 to 100Hz of frequency, from 0 to 27.7MPa of pre-load. The relationships between electrical and displacement properties were studied and discussed using the domain switching properties which is influenced by voltage and pre-load.

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The influence of curing condition for slag alkaline cement on it's microstructure and the Cr⁶⁺ diffusivity through the pastes was investigated. Sodium silicate and sodium hydroxide have been used as alkaline activators. The slag alkaline cement pastes activated by sodium silicate and sodium hydroxide were cured at 25°C for 28d and at 105, 150 and 200°C for 12h by autoclave treatment. The ordinary portland cement has been used for comparing sample. The total pore volume decreased with increasing curing time and at higher curing temperature in all samples. The ordinary portland cement pastes cured at 25°C for 28d, the volume of pore with radii less than 5nm had the largest. The slag alkaline cement pastes autoclaved at 105°C for 12h, the volume of pore with radii less than 5nm had the largest. That volume of pore with radii less than 5nm for alkaline cement pastes autoclaved at 105°C was larger than that of ordinary portland cement pastes cured at 25°C. The apparent diffusion coefficient of Cr⁶⁺ decreaesd linearly with increasing volume of pores with radii less than 5nm and was determined by the volume of pores with radii less than 5nm. The smallest apparent diffusion coefficient of Cr⁶⁺ of 7.0×10^-13cm²/s was obtained for slag alkaline cement pastes autoclaved at 105°C for 12h with addition of sodium silicate as activator.

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The deformation behavior of kaolinitic clay green bodies, Kuyama kibushi clay, Georgia kaolin and Kentucky Tennessee clay, was investigated by the uniaxial compression test to determine the formability for the wet-forming process. In accordance with a plastic deformation theory, linear relationships and yield points were observed on stress-diameter/height curves. Below the yield points, the slopes of the stress-strain curves at the initiation of compression were obtained by differentiating the approximation formulas of the curves. Because the slopes were not influenced by the yield points, the deformation behavior of the green bodies below the yield points was considered to be viscoelastic. Since the yield point is related to load during forming and the slope of the stress-strain curve at the initiation of compression is related to form retentivity, the formability of kaolinitic clay green bodies for wet-forming can be determined from the relationship between the yield point and the slope of the stress-strain curve at the initial stage.

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The effect of phase separation on ferroelastic domain switching in 3mol% Y₂O₃-ZrO₂ pseudo-single crystals annealed at 1700°C was examined. Domain switching occurred in two steps. From TEM analysis, the first step seemed to be the switching of t′-phase, and the second to be that of t-phase. The effect of phase separation is as follows. First by, the switching amount of t′-phase decreased with decrease of the volume fraction, whereas that of t-phase increased with increase of the one. Secondly, the critical stress of t′- and t-phase increased with growth of t-phase colony. This is because that the clamping force among these phases for domain switching increase. Especially the critical stress of t-phase was strongly effected by the colony size of t-phase.

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Thermodynamic stability (i.e., bound strength from solid surfaces) of liquid layer on the surface of several crystalline oxide powders in water or in cyclohexane was evaluated by cooling DSC changing of liquid layer thickness, t. Water was firmly bound by the solid surface and the stability of water layers showed an exponential decrease with a distance from the surface. Two or one exothermal peaks depending on the oxides were detected on the DSC thermogram in water/powder samP_Les. In the case of two peaks (P_L and P_H) occurrence, the P_L comes from the water layer of the most stable and the nearest to the surface due to the structural changes during cooling. Onset temperature Tr and peak area Ht of the P_L were kept constant in regardless of t. But the P_H peak which decreases in Tr and Ht with decrease of t comes from the water layers existing outer area of the P_L layers in between the most stable and the bulk free states. The close relation was found between thermodynamic stability of surface water and ionicity in the chemical bonding between cation and anion in respective oxides. On the DSC thermograms in case of cyclohexane, single exothermic peak was detected and the Ht did not show a great change with t of cyclohexane. Therefore the stabilization of cyclohexane layer on the surface of oxides was not observed as in the case of water.

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Three-dimensional Tyranno^® fiber-reinforced silicon carbide composites were fabricated by using polycarbosilane as the precursor for matrix and some types of fiber with different surface structures. Composites made of a fiber with an excess carbon layer at the surface had the highest values of bending strength and fracture toughness at room temperature. Composites of a fiber with a double layer of oxide and carbon had the largest value of work of fracture and a superior oxidation resistance property.

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Alumina/aluminum/silicon composites were fabricated by reaction between aluminum and Amakusa pottery clay (“Amakusa”). On heating the “Amakusa” powder compact contacting with aluminum, reaction occurred above 1473K. Sintering the “Amakusa” compact at 1623K before the reaction lowered the reaction temperature to 1173K and increased the reaction rate. Three kinds of composites obtained from the “Amakusa” compact, the sintered body and the sintered body containing alumina powder (20mass%), named C (A), C (B) and C (C), respectively, were characterized. They contained -10vol% of metal phase and showed microstructure with three-dimensionally interconnected metal phase. Their relative densities were 94-99%. The bending strength of the composites, C (A), C (B), and C (C), were 143, 210 and 240MPa, respectively. Their fracture toughnesses were 2.3, 3.9, and 4.3MPa·m^1/2, respectively.

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The extrusion forming of silicon nitride produced by imide decomposition was studied to fabricate Si₃N₄ ceramic parts. Green bodies were prepared from a slurry containing 60% solids (92% Si₃N₄, 4% Al₂O₃ and 4% Y₂O₃), 40% distilled water and 0.12% deflocculant (polyacrylic ammonium) with binder (curdlan). The green bodies were dried after formed by vacuum extrusion, and sintered in the range of 1650 to 1800°C under N₂ gas at 0.9MPa. The most dense body (3.22×10³kg·m^-3) was obtained by sintering at 1800°C for 4h. These results indicate that dense silicon nitride parts can be produced by an extrusion method.

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Potassium hexatitanate short fiber/A-W glass-ceramic composite was prepared, and the chemical and morphological change of the fibers during firing and the mechanical properties of the composite were investigated. Potassium in the fibers started to disappear at 800°C. As potassium hexatitanate has a unidirectional tunnel structure, in which potassium ion occupy the tunnel space, potassium ions diffuse from the fiber to the matrix along the tunnel once flaws are formed in the fiber. As a result, the fibers developed a specific morphology in which the rutile grains were arranged fibrously. The bending strength of the composite was lower than that of the monolithic glass-ceramic, however, the fracture toughness improved with increasing firing temperature.

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The fused quartz is one of the most typical materials of low thermal expansion. However, it was found that compacts prepared by isostatic compression of ground powder of fused quartz showed an anomalously high thermal expansion of 7×10^-6/°C, i.e., about 10 times of that of the normal fused quartz. The density of the glass powder increased with grinding time and with increasing pressure of compaction. Release of the compaction strain by heating can be the reason of this high thermal expansion of the compacts of fused quartz powder.

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