The sinterability and electrical conductivity of La_1-XSr_XMnO₃ were studied as a function of calcination temperature (500° to 1200°C), firing temperature (1200° to 1500°C), atmosphere (air or vacuum) Sr content (0≤X≤0.5), and cation deficiency. Both density and electrical conductivity increased with either decreasing calcination temperature or increasing firing temperature. Sintering in vacuum increased the density and decreased the electrical conductivity. The content of Sr, X, influenced these characteristics remarkably, The density decreased drastically with increasing X, giving the lowest value at X=0.4. On the other hand, the electrical conductivity increased with increasing X, giving the maximum value at X=0.15. The temperature dependence of the electrical conductivity of La_0.85Sr_0.15MnO₃ was confirmed to be consistent with the small polaron hopping transport mechanism. The cation deficiency improved the sinterability of La_1-XSr_XMnO₃ ceramics. These results indicated that the density and electrical conductivity of La_1-XSr_XMnO₃ are largely influenced by the concentration of incorporated oxygen.

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In the phase diagram study on the system Ga₂O₃-Sm₂O₃, the liquidus and eutectic temperatures were measured from the cooling curves of specimens by the specular reflection method with a heliostat type solar furnace. Quenched specimens from the melt were examined by X-ray diffractometry and chemical analysis. In the system, four compounds were found; garnet-type 3Sm₂O₃⋅5Ga₂O₃, perovskite-type SmGaO₃, monoclinic 2Sm₂O₃⋅Ga₂O₃ and orthorhombic 3Sm₂O₃⋅Ga₂O₃. These compounds, showed no phase transition during repeated heating and cooling cycles. The compound 3Sm₂O₃⋅Ga₂O₃ was found to melt incongruently at 1755±20°C. The lattice parameter were determined to be a₀=12.431Å for 3Sm₂O₃⋅5Ga₂O₃, a₀=7.658Å, b₀=10.856Å, c₀=11.560Å, β=109.240 for 2Sm₂O₃⋅Ga₂O₃ and a₀=11.400Å, b₀=5.515Å, c₀=9.070Å for 3Sm₂O₃⋅Ga₂O₃. The solidification points of 3Sm₂O₃⋅5Ga₂O₃ and 2Sm₂O₃⋅Ga₂O₃ were determined as 1680±20°C, and 1708±20°C, respectively. The phase diagram shows three eutectic points at 1555°C, 1640°C, and 1690°C with 22.5, 55, and 70mol% Sm₂O₃ composition, respectively. A high temperature phase diagram for Ga₂O₃-Sm₂O₃ system was proposed.

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The reactions between TiC or TiN powder and H₂O have been studied at 200°-650°C under 100MPa. The reaction of TiC with H₂O above 400°C for 3h yielded anatase, CH₄, CO₂ and H₂, and above 500°C rutile was formed additionally. TiN powder with an average grain size of 1.4μm reacted with H₂O above 290°C to yield anatase, NH₃ and H₂, while TiN powder of 9μm reacted H₂O above 480°C and yielded rutile, NH₃ and H₂. The oxidation rate calculated from the weight gain was compared with that from various model kinetic equations. In TiC the rate was best described by the Avrami-Erofeev equation (n=1.3), while the core-shrinking model fitted as well. This suggests that the reaction was controlled by the phase boundary reactions. In TiN the Jander-type model was the best, which suggests that the reaction was controlled by the diffusion through the oxide scale. An Arrhenius plot of the rate constants gave an apparent activation energy of 98kJ/mol. The difference of reaction mechanism between TiC and TiN is attributed to the difference in the gaseous species of reaction products.

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The purpose of this paper is to modify the surface of ceramics by nitridation using NH₃ gas at low temperature. Two kinds of SiC specimens, sintered and reaction bonded, were used. In evaluation, surface layers were analyzed by ESCA and thin film X-ray diffraction, and mechanical properties were studied by micro Vickers hardness and scratch test. More nitrogen penetrated in the reaction bonded specimen treated at higher temperature. The maximum penetration depth of nitrogen was about 100Å in reaction bonded SiC treated with NH₃ gas at 900°C. The formation of Si₃N₄ and the change from 12H-SiC to 8H-SiC were detected by ESCA spectra and thin film X-ray diffraction. On the other hand, Vickers hardness and critical load by scratch test increased with increasing nitrogen on the surface of specimens. The maximum increase in Vickers hardness was 42% for reaction bonded SiC. The strain on the nitridated surface of SiC ceramics is possibly responsible for these phenomena.

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Surface analysis of the joining interface between silicon nitride (Si₃N₄) and metal with an active metal foil was carried out by XPS, SEM-EDX to make clear joining mechanism and action of brazing metals. The reaction product layer of the specimen which contained brazing metal was constituted two layers, and was about 5μm thick. Layer I facing Si₃N₄ was composed of titanium nitride (TiN), and layer II facing brazing metals was composed of TiN and titanium silicide (Ti₅Si₃). The reaction product layer of a specimen without brazing metal was about 0.4μm thick and composed of TiN, Ti₅Si₃ and elemental silicon (Si). On the basis of the data obtained by this analysis, it was considered that;
(a) During the initial stage of joining, Si₃N₄ reacts with titanium at the interface to produce TiN and Si according to reaction (1).
Si₃N₄+4Ti→4TiN+3Si (1)
(b) At a system contained brazing metals, diffusion of Si into the inside was accelerated to react with non-reacted Ti and from Ti₅Si₃ according to reaction (2).
3Si+5Ti→Ti₅Si₃ (2)
(c) Action of brazing metals accelerates the diffusions of Si, TiN, Ti₅Si₃ and Ti, and products wide reaction layer.

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The thermal properties of plasma sprayed coating of zirconia stabilized with 8wt% of yttria was studied by the laser flash method. The experimental results were used for the thermal conduction analysis of stabilized zirconia coated materials with a penny-shape crack at interface using the finite element method. The analysis was conducted to find nondestructively the interfacial crack from the surface temperature distribution of coating. It was verified that the interfacial cracks become less detectable with increasing coating thickness and with decreasing crack size. It was also confirmed by the experiment using infrared thermography that fairly good agreement between the measured and real crack size was obtained for the crack diameter not less than 3mm. The results indicated that the thermography method as a new technique was useful for nondestructive testing to detect the interfacial cracks of coated materials.

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A Zr-Al metallo-organic compound was spray-dried and calcined in air to form ZrO₂-Al₂O₃ hollow particles. The particles were sintered to prepare ZrO₂-Al₂O₃ porous composites. The concentration of the starting solution of spray-drying affected the particle size of the calcined powder and the bulk density of sintered porous ceramics. The porous ceramics have a high fraction of tetragonal ZrO₂ and high bending strength, 100MPa.

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The AlN ceramics containing 5 and 10wt% Y₂O₃ were densif ied at 1800°C for 1h in N₂ gas, and annealed at 1900°C for 1, 3, 6 and 24h in N₂ gas and reducing carbon gas atmospheres. The grain boundary phases, containing both Y₄Al₂O₉ and Y₂O₃ or Y₂O₃ only, decreased with increasing annealing time. Y₄Al₂O₉ decomposed into Y₂O₃ and Al₂O₃, which migrated towards the surface of the sintered body, and were nitrided on the surface to form a surface layer of YN and AlN. Shrinkage of the sintered body occurred during annealing with the elimination of the grain boundary phases from sintered body, and pore-free bodies were formed.

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The electron irradiation-induced crystalline to amorphous (C-A) transition in the Co-B binary system was examined by ultra-high voltage electron microscopy. The five equilibrium phases (i.e., Co, Co₃B, Co₂B, CoB, and B) in the system were irradiated with 2 MeV electrons at a fixed temperature of approximately 110K, and the tendency towards the amorphization was compared. Of the five, only Co₃B and Co₂B underwent a C-A transition by the irradiation while the other three remained crystalline. The tendency towards the amorphization under electron irradiation is best correlated with the position of the materials in the corresponding temperature-composition phase diagram; those compounds located near the bottom of the deep valleys of the liquidus in the diagram are rendered amorphous, while those which are located away from such valleys do not exhibit the C-A transition.

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The penetration of various liquids into the channels composed of two parallel plates has been studied by measuring the height and rate of penetration. The effects of wetting characteristics of plates and their combination were also studied. The penetration behavior of liquids was better evaluated by the rate of penetration rather than by the penetration height, implying that kinetics plays a more important role in immersional wetting. The immersional-wettability of the channels depends on the equivalent channel diameter. The difference in wetting characteristics between two plates affects the penetration especially at low equivalent channel diameters, the extent of which depends on the liquid species. In some cases, decrease in equivalent diameter suppressed the penetration, probably due to the asymmetry of the meniscus. When a stripe plate composed of two phases, hydrophilic and hydrophobic, was coupled with a hydrophilic plate, direction of penetration and stripe pitch, rather than the fractional area of the two phases, determined the penetration behavior.

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The dynamic fracture toughness of ceramics was evaluated by the strain gage method over a wide range of loading rates with using testing machines conventional Instron-type and newly developed drop-weight type. The validity of the method was demonstrated by the 2-dimensional dynamic finite element method. Six kinds of ceramics were tested: fine and coarse grained alumina, tetragonal zirconia polycrystal (TZP), silicon nitride, silicon carbide and sialon. All the specimens were precracked before testing by the bridge indentation method. The fracture toughness of alumina and TZP increased with increasing loading rate, while that of others remained almost constant. For alumina, the increased toughness has been explained by microcracking and branching near the precrack tip. In TZP, on the other hand, both slow crack growth and transformation to monoclinic phase contributed to the increased toughness.

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The evaluation method of defect rate was examined to determine the defect rate in ceramics film (Cr₂O₃+SiO₂+Al₂O₃) coated on zirconium alloy by the chemical densification coating method. Chronoamperometry and chemical impedance methods were selected for quantitative determination of defect rate. It is concluded that the chronoamperometry method determines the defect by the rate of change in the minute eletrolysis current in potential step eletrolysis, and that the chemical impedance method established good correlation between defect rate and reciprocal maximum electrical resistance over a wide range of frequency (100mHz-10kHz).

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Plasma sintered SiC-C composites were observed by transmission electron microscopy in order to investigate the existing state of carbon, interface structure between SiC and C, and grain boundary structure in SiC. The present observation was helpful in discussing the sintering mechanism and in explaining the high hardness and high toughness of plasma sintered SiC-C composites. The results obtained are summarized as follows.
(1) Graphite in plasma sintered SiC-C composites existed as (1) fine polycrystals, (2) fibrous crystals and (3) single crystals. The fine polycrystals and fibrous crystals had no orientation around a pore, but some orientation between SiC grains because of the compressive stress generated by the difference in the thermal expansion coefficient between SiC and graphite. Single crystals of graphite were observed at grain boundaries between SiC crystals. In the graphite, cracks were formed parallel to the basal plane because of the thermal stress.
(2) High hardness and high toughness of plasma sintered SiC-C composites are presumably due to the residual compressive stress caused by the difference in the thermal expansion coefficient. It is also considered that the toughness was improved by the cracks in graphite grains which inhibited the crack propagation.
(3) At the interface between SiC and graphite, there existed the structures that the basal plane of graphite was parallel to the interface, that SiC was transformed near the interface and that SiC had step structures in an amorphous layer formed by reaction on graphite. These structures might be formed to reduce high energy at the interface.
A second phase was not observed at grain boundaries in SiC, however, structure relaxation might occur within a thickness of 1nm.

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The effects of heat treatment in air on the bending strength and fracture toughness of sintered silicon nitride containing CeO₂, MgO and SrO additives were studied. The bending strength at elevated temperatures was improved 15 to 20% by the heat treatment (1000°C/2h), but the bending strength at room temperature was not affected. The apparent values of fracture toughness for notched specimens increased by the oxidation at the notch root.

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The powders of α-Si₃N₄, α-Al₂O₃ and AlN were mixed to fabricate β-sialon (formula Si_6-ZAl_ZO_ZN_8-Z with 4 excess oxygen eq.% over Z=1, 2, 3 and 4). A SiC powder was added to the β-sialon powder mixture and hot pressed to get β-sialon-SiC composites. A powder mixture of α-Si₃N₄, 5 wt% Y₂O₃, 2wt% α-Al₂O₃ and 50 wt% SiC was hot-pressed under the same conditions to get a Si₃N₄-50 wt% SiC composite material. Thermal expansion data of the sintered material was measured from 25 to 1000°C by dilatometric method.
The results are obtained as follows:
(1) The thermal expansion coefficient of the β-sialon-SiC composites gradually increased with an increase in SiC addition up to 30wt%.
(2) The thermal expansion coefficient of β-sialon-50 wt% SiC composites gradually increased with an increase of Z value.
(3) The thermal expansion coefficient of Si₃N₄-50% SiC composite was 3.18×10^-6/°C, This value was a little higher than Si₃N₄ sintered material but lower than that of SiC sintered material.

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The structures of boron oxide and sodium borate glasses, simulated by a molecular dynamics (MD) method, were analyzed in detail in comparison with X-ray diffraction data. There is good agreement between the MD-calculated and observed s·i(s) and g(r) (PCF) curves for 0.25Na₂O⋅0.75B₂O₃ and 0.33Na₂O⋅0.67B₂O₃ glasses. It suggests that the structures of glasses satisfy the random network model. On the other hand, the MD-calculated g(r) curve for B₂O₃ glass agrees with that of B₂O₃ melt rather than that of glass.

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The formation of Hidasuki, a characteristic red-colored pattern on the surface of Bizen-yaki, was investigated from the viewpoints of its mineral composition and coloration. Hematite, corundum and quartz were found in Hidasuki. Corundum was formed regardless of the cooling rate after heat treatment of a mixture of Bizen-clay and 8 to 10wt% potassium chloride at 1300°C for 3h. Hematite was not formed when the mixture was quenched. However, the amount of hexagonal plate like hematite in the heated mixture increased with the lowering of the cooling rate, and the color of the heated mixture became more reddish with the increase of the amount of hematite. The same phase composition, coloration and morphology as those of Hidasuki were obtained when a mixture of Bizen-clay and 8 to 10wt% potassium chloride was heated at 1300°C for 3h followed by cooling at the rate of 0.2 to 0.5°C/min in air.

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α-Al₂O₃-β-Si₃N₄ whisker composite ceramics with a whisker content of 20wt% were prepared by hot-pressing at prescribed temperature between 1300°-1800°C for 30min under the pressure of 30MPa. Fairly dense composites were obtained at sintering temperature above 1500°C. The composites obtained below 1700°C are consisted of α-Al₂O₃ and β-Si₃N₄, while β'-sialon was produced in the composite sintered at 1800°C. The composite fired at 1600°C had a bending strength of about 620MPa, whose value was 50% larger than that of hot-pressed Al₂O₃ at the same sintering temperature, but could not exceed the maximum bending strength of monolithic Al₂O₃ (about 830MPa). The fracture toughness (4.3-4.8MPa·m^1/2) was one and half times as large as that of Al₂O₃ sintered at 1400°-1600°C.

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Superconducting properties of YBCO ceramic superconductors were investigated. Specimens were prepared by uniaxial hot-pressing at pressures of 1-4t/cm² and at temperatures lower than 500°C, followed by annealing at 950°C for 5 hours in air or pure oxygen. Bulk densities of 91% of the theoretical value (6.36g/cm³) were attained by hot-pressing above 4t/cm² at 300°C. The critical current density (J_c) was measured by the standard four-probe method at 77K. Specimens annealed in oxygen showed higher J_c, 180-220A/cm², while annealing in air resulted in low J_c of 5-30A/cm². The relationship between the decrease in J_c and the microstructure was discussed.

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A precursor for borosilicate fibers was prepared by a new method via polyborosiloxane (PBS) prepared by condensation polymerization of silicon tetraacetate (STA) with boron trialkoxide (BTA). A spinnable polymer was obtained from PBS by partial alkoxylation, subsequent hydrolysis, and aging for various time periods.

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