Boron Nitride (BN) coating on sintered SiC fibers (Tyranno SA) by a continuous chemical vapor deposition (CVD) process was developed with the ultimate goal of controlling the interface in SiC/SiC composites. BN coating by a continuous CVD process was conducted at 1580°C under a pressure of approximately 1.3×10²Pa. Reactant gases were NH₃ and BCl₃, both diluted by Ar; the yarn speed was 4.5mm/s. Conventional experiments revealed that the BN coating thickness across the tow varied significantly. Hence, the CVD process was modified not only by adjusting the amounts of reactant gases, but also by reducing the yarn tension and setting a new furnace for removing the sizing agent of the fiber tow. The BN coating thickness obtained by the modified process was significantly more uniform than that achieved by a conventional process. The BN coating had a layered structure; it was nearly stoichiometric and pure, with little O or C. The BN-coated SA fiber retained 90% of the strength of the as-received SA fiber. Moreover, a minicomposite reinforced with a BN-coated SA fiber of 1600 filaments (fiber volume fraction: 10.8%) was fabricated by a polymer infiltration and pyrolysis (PIP) method. This minicomposite exhibited a higher fracture strength (199MPa) at room temperature and a higher retention ratio (82%) of the fracture strength at 1400°C in air as compared to a minicomposite obtained by a conventional process (173MPa and 73%).

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The purpose of this study is to elucidate the effect of cristobalite on the strength and thermal properties of alumina-strengthened porcelain. The effects of milling time and sintering condition of mixtures on strength, density and thermal expansion properties were investigated by controlling the proportions of raw materials in compositions that generate cristobalite crystals upon heat treatment. At a composition of 15mass% corundum, 8mass% feldspar and 37mass% fine-grained quartz powder, the highest bending strength of 230MPa was attained with a bulk density of 2.6×10³kg·m^-3 under appropriate milling conditions and with sintering above 1300°C. Although thermal expansion below 150°C was somewhat greater than that of general porcelain or alumina-strengthened porcelain, test bars of the porcelain resisted quenching with a temperature difference of 140°C, which assured its usability as porcelain for tableware.

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α(6H)-SiC powders mixed with 11 types of metal boride, B and C were sintered at high temperatures (1800-2200°C for 30min). MoB, NbB₂, TaB₂, TiB₂, VB₂, WB, and ZrB₂ promoted the densification of SiC powder and sintered SiC had a high fracture toughness (4.07-4.75MPa·m^1/2). The addition of metal boride enabled us to control the grain growth and densify SiC powder containing a fairly large amount of B. Metal borides dispersed in SiC grains, precipitated in triple points, and appeared to obstruct grain growth and crack propagation. CaB₆, CrB, LaB₆, and YB₆ did not promote sintering of SiC powder. These latter metal borides resulted in highly exaggerated grain growth and the SiC powder became porous after sintering. The starting 6H-SiC powder tended to be partially transformed into a 4H polytype which was accompanied by grain growth.

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Microstructures and texture of yttria-stabilized zirconia (YSZ) layers prepared by electron beam physical vapor deposition (EB-PVD) were investigated, addressing the effect of processing parameters. All the YSZ layers investigated in this study showed a columnar structure. However, significant differences were found in their microstructures. Morphology, porosity, and texture of the layers changed drastically by substrate manipulation during deposition. Without rotation, the layer showed a dense columnar structure with less intercolumnar gaps and obscure feather-like structures, and no preferred growth orientation. Rotation was very effective in developing feather-like structures within each column and hence increasing porosity. In addition, substrate rotation caused strong (100) texture. These results are attributed to the flux shadowing effect induced by oblique vapor incidence caused by substrate manipulation. The influence of electron beam power and substrate temperature was also investigated.

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Centrifugal slip casting was applied to the fabrication of an Al₂O₃-5vol%ZrO₂ (3Y-TZP) composite and the effect of solid contents in the slurry was investigated on various kinds of inhomogeneities and segregations. When a relatively thick slurry (40 or 45vol%) was used, mutually hindered settling occurred quite effectively and thus essentially no segregations were observed in the distribution of grain sizes and the dispersion of the two phases. Even the zirconia aggregates contained in the starting powders were found distributed over the entire body of a sample. On the other hand, when a slurry of moderate thickness (30vol%) was used, the Al₂O₃ and ZrO₂ particles were still uniformly distributed but the zirconia aggregates were found accumulated in the thin layer of the bottom section. The results were discussed with a model calculation and shown to be in general agreement with the theoretical prediction.

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The recovery of lead from PLZT ((Pb_0.9La_0.1)(Zr_0.52Ti_0.48)O₃) ceramics was investigated by the wet ball-mill method using 1.4-11.3MH₂SO₄ aqueous solutions. The wet ball-mill treatment was performed in a pot mill apparatus at room temperature for 0-72h with a rotational speed fixed at 300rpm. It was found by X-ray diffraction (XRD) analysis that the treatment time required for completely converting from crystalline PLZT to PbSO₄ nano-particles could be shortened with increasing H₂SO₄ concentration. According to inductively-coupled-plasma atomic-emission (ICP-AES) analysis of the components dissolved into the solution, the amount of dissolved zirconium and titanium ions increased with increasing treatment time. The dissolution of both components was closely related to the disintegration behavior of crystal structure of PLZT ceramics. The amount of dissolved lead ion was about 0.1% of the lead included in the non-treated PLZT under the whole experimental conditions, while that of lanthanum ion was below 60%. The amount of lanthanum ion dissolved into the solution was dependent on the concentration of H₂SO₄ aqueous solution used for treatments. These results indicated that the wet ball-mill method gave a yield of PbSO₄ as high as 99%, and the purity of the collected PbSO₄ from PLZT ceramics was about 91-95%.

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The relationship between electrical conductivity and crystal structure in Ln₂Ce₂O₇ (Ln=La, Nd, Sm, Eu, Gd, Y and Yb) systems was investigated. The crystal phases were assigned to a fluorite (F)-type phase accompanying the rare earth C-type superstructure, when the ionic radius ratio, r(Ln³⁺)/r(Ce⁴⁺) were larger than 1.17. On the other hand, La₂Ce₂O₇ was the only F-type phase without the superstructure. The lattice constant increased linearly with increasing the ionic radius of Ln³⁺ independent of whether or not the superstructure was present. Oxygen partial pressure dependence of the electrical conductivity suggested that the charge carrier was oxide-ion, except for the Nd system. The electrical conductivity at 800°C in air for the Ln₂Ce₂O₇ systems also increased with increasing the ionic radius ratio. The activation energy for the conduction decreased remarkably in the fluorite-type phase region. The compositional change of the oxide-ion conductivity was understood by the introduction of an unit cell free volume. This result was also supported by Raman spectra.

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Both p- and n-type Si_0.8Ge_0.2 powders were prepared by gas atomization of a mixture of Si and Ge with the addition of B or P. A part of the gas-atomized powders was further pulverized by ball-milling for 10h in Ar. Then, dense bodies were formed from both the as-atomized and pulverized powders by pulse-current sintering. The thermoelectric properties such as the thermal conductivity, electric resistivity and Seebeck coefficient of the dense bodies were determined from room temperature to 1073K, followed by the evaluation of the figure of merit (ZT). The thermal conductivities of p- and n-type fine-grained Si-Ge from pulverized powders were 8 and 10% lower on average in the temperature range of 300-1073K, respectively, than those of the as-atomized powders. However, this phenomenon was accompanied with an increase in electric resistivity due to the reduced grain size and increased oxygen content, resulting in the decrease in ZT by 13 and 8% for p- and n-type Si-Ge, respectively. The ZT of n-type Si-Ge exceeded that of p-type because of the high Seebeck coefficient of n-type samples. Finally, the largest ZT value of 0.66 was obtained for the Si-Ge dense body from n-type gas-atomized powder. It was found that the application of the gas-atomized powder for fabricating Si-Ge sintered body has the advantage of the reduction in oxygen content and resistivity compared to the case of the pulverized powders.

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Oxidation resistance of SiC satin fabric (25-29vol%) or aluminosilicate plain fabric (25-33vol%)/mullite matrix porous composites was investigated at 1000-1200°C in air for 24h using thermogravimetric analysis. The composites were produced by a polymer impregnation and pyrolysis (PIP) method using a mullite precursor solution of the mixtures of Si(OC₂H₅)₄ and Al(NO₃)₃. The oxidation rate of the sintered SiC fibers with a stoichiometric SiC composition and well-crystallized microstructure was controlled by the diffusion process of gases through dense SiO₂ layer formed on the SiC surface. The activation energy for the oxidation of the SiC fibers was 299kJ/mol. This value was close to the activation energy for the diffusion of oxygen atom in silica glass. The SiC satin fabric/mullite matrix composite heated in an Ar atmosphere showed pseudoductility due to the delamination along the fabric layers. The four point-flexural strength decreased slightly with increasing heat treatment temperature. However, the composite heated in air at 1100-1200°C showed brittle fracture behavior without delamination because of the increased strength of interfacial bond between the oxidized SiC fibers and mullite matrix. On the other hand, the amorphous aluminosilicate fibers/mullite matrix composite showed little weight change during the heat treatment at 1000-1200°C. Crystallization of mullite occurred in the mullite precursor-derived amorphous solid and aluminosilicate fibers at 1100 and 1200°C in air, respectively. However, no microstructural change was observed in the heat-treated composite. The significant pseudoductility and strength of the aluminosilicate plain fabric/mullite matrix composite were maintained after the heat treatment. The fracture energy increased with increasing heat treatment temperature.

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Silicon nitride (Si₃N₄) matrix composites reinforced with 1.5-8.1mass% Mo₅Si₃ particles were fabricated by sintering molybdenum solution-infiltrated porous Si₃N₄ at 1850°C in nitrogen atmosphere, and the sliding wear and solid particle erosion behaviors of the Mo₅Si₃-Si₃N₄ composites were evaluated. During sliding wear, the formation of an adherent layer on wear scar of Mo₅Si₃-Si₃N₄ composite was inhibited, and the frictional resistance reduced compared with Si₃N₄ due to the self-lubricant effect of the Mo₅Si₃ particle. The friction coefficients of Mo₅Si₃-Si₃N₄ composites were in the range of 0.52-0.58, -6-16% lower than that of Si₃N₄. The specific wear rate of the Mo₅Si₃-Si₃N₄ composite decreased with decreasing content of Mo₅Si₃ particle, and was 0.61×0^-8mm²/N for the 8.1mass% Mo₅Si₃-Si₃N₄ composite, lower than that of Si₃N₄ by -50%. As for solid particle erosion, when Mo₅Si₃ particles of 2mass% or less were incorporated into Si₃N₄, remarkably better wear resistance than Si₃N₄ was shown. However, when a large fraction of Mo₅Si₃ particle was incorporated, the erosion rate was higher than that of the Si₃N₄, and increased with increasing content of Mo₅Si₃. This was due to the lower values of both fracture toughness and hardness of the composites.

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The mechanism for formation of a weld line in slip casting of large potteries was clarified to prevent the occurrence of cracks in the dried green body. It was found from the observation of flow of the slurry during the slip casting that the weld line was formed by contact between surfaces of slurry in which the moisture content was decreased by the contact with the inner surface of the gypsum mold. The formation of weld line was prevented by vibrating the gypsum mold during slip casting.

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In conjunction with the study of glass strength upon shock wave loading, stress generation of 300mm×300mm laminated glass plates against shock wave and blast wave loading was investigated using a vertical shock tube. Stress waves generated in the laminated glass plates showed similar wave pattern to monolithic glass, and were calculated by applying a numerical method valid in monolithic glass analysis.

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A micro-Raman spectroscopic investigation has been performed to observe structural disorder in each grain of aluminum nitride ceramics as semiconductor equipment parts. A selective thermal oxidation treatment normalizes a different rate of a corrosion reaction depending on the crystal face and consequently improves the corrosion resistance. Upon thermal oxidation treatment, line widths of Raman bands increased more in grains including mainly crystals with (100) preferred orientation than in those of (002), indicating that (100) faces oxidize preferentially rather than (002) faces. According to Raman shift from the oxidized sample, oxidation induces residual compressive stress for grains including a large number of (100) prefer-oriented crystals. On fluorination of the oxidized sample, no increase of line widths was observed in both kinds of grains, suggesting that prior anisotropic thermal oxidation treatment of (100) faces, which are more sensitive to corrosion than (002) faces, inhibits the progress of corrosion.

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