Dispersion, rheology and consolidation of the colloidal suspension in the alumina powder-silicon nitride whisker system were studied to control the microstructure and density of the green compact. Al₂O₃ particles with an average diameter of 0.15μm and Si₃N₄ whiskers with an average size of 0.4μm×3.7μm were electrostatically dispersed in water in the pH range 3 to 10 and consolidated by filtration. Well-dispersed stable suspensions were obtained at low pH. Decreasing the viscosity and at the same time increasing the solid content of the suspension is the key step in making the green compact with high density and a narrow pore size distribution. Application of isostatic pressing to compacts consolidated by filtration increased green density and shifted the pore size distribution to smaller size. These green compacts by colloidal processing were densified to relative densities of 98.4-99.4% by hot-pressing at 1500°C at a pressure of 39MPa in N₂ atmosphere.

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A new inorganic titanium compound with high selective adsorbability for Li⁺ was prepared by acid-treatment of precursory Li₂TiO₃-rich products synthesized by heating an equimolar mixture of powdered Li₂CO₃ and TiO₂ (anatase) in air at 450°-950°C. These products were examined by X-ray diffraction, chemical analysis, specific surface area (BET method), shape (TEM) and thermal (TG & DTA) analysis. For the examination of adsorbability for Li⁺ on the products, adsorption of Li⁺, Na⁺, K⁺ and Ca²⁺ for the acid-treated products was determined by a batch method in weakly basic media. The results are summarized as follows:
(1) Crystalline Li₂TiO₃ transformed to a new crystalline phase (TOH), which was characterized by the XRD peaks at d=4.74, 4.53 and 2.45Å, on acid-treatment. But the conversion decreased with increasing preparation temperature of the precursory products.
(2) Li⁺ was adsorbed selectively only on acid-treated products containing the TOH phase, suggesting that the TOH material contributed significantly to the selective adsorption of Li⁺.
(3) As the TOH phase contains TiO₂ and H₂O in the 1:1 molar ratio, it is considered that lithium-free titanium oxide hydride, H₂TiO₃, was formed from Li₂TiO₃ by the acid-treatment.
(4) When the TOH adsorbs Li⁺, a topotactic phase transformation to Li₂TiO₃ was observed. In the same manner as γ-MnO₂, the following mechanism of cation exchange is supposed for the selective Li⁺-adsorption on the TOH phase: TOH(H₂TiO₃)+2Li⁺→←Li₂TiO₃+2H⁺.
(5) The amount of adsorption of Li⁺ on TOH was influenced by the texture. The specific surface area (SSA) of the acid-treated products depended remarkably on the preparation conditions of the precursory products. The ratios of the amount of adsorbed Li⁺ to the exchange capacity increased with increasing SSA.

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Mechanical properties of hot-pressed mullite-SiC whisker composites were studied in relation to the whisker content and chemical composition of matrix. Grain growth of mullite was suppressed by the existence of SiC whisker in the matrix, but the densification was not inhibited by the loading of whisker up to 30 vol%. The room temperature flexural strength of specimens was improved by the addition of SiC whisker in every chemical compositions of the matrix examined, more pronouced with increasing SiO₂ content in the matrix. The high temperature strength was almost the same as that at room temperature up to 1300°C. In specimens containing a glassy grain-boundary phase, addition of SiC whisker to mullite did not significantly affect K_IC value. Combination of single phase mullite (74 wt% Al₂O₃) and SiC whisker gave the best effect on the K_IC value both at room temperature and elevated temperature. These phenomena can be explained by the presence of a glassy grain-boundary phase, which causes the matrix to the whisker bonding.

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The leaching behavior of hot-pressed and pyrolytic boron nitride (BN) was studied under hydrothermal conditions at 150°C and 0.48MPa for 1-10 days. A large degree of weight loss was observed in the hot-pressed BN specimens at the initial stage, due to dissolution of a grain boundary phase. The weight of the pyrolytic BN specimen decreased slowly with increasing time. SEM observation and EPMA of leached specimens and chemical analyses of leached solutions revealed that BN reacted with H₂O to produce H₃BO₃ and NH₃, and the grain boundary phase was rapidly dissolved, and the hydrated layer was not left. These results suggested that the chemical stability of h-BN ceramics under hydrothermal conditions depends on the difference in the grain boundary structure, though BN is fairly stable.

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Post-indentation slow crack growth in soda-lime-silica glass in various aqueous solutions was investigated. Measurements of crack length and streaming potential at the glass/solution interface were carried out in order to understand the mechanism of slow crack growth of glass. The crack growth depended on the pH of electrolyte, and was enhanced by the change of pH from 1 to 10. This behavior was in good agreement with the prediction obtained from the charged state at the interface. These results were discussed in terms of the charged state at glass/solution interface and its effect on the stress corrosion reaction in electrolytes.

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Thins film of magnetoplumbite type ferrite (MFe₁₂O₁₉, M=Ba, Sr) have been prepared by the dip-coating method from solgel process. Ferric nitrates, other metal nitrate and titaniumoxiacetylacetonate were used as law materials, and glycerol was used as solvent. A film was prepared by dipping a silica glass plate. The magnetoplumbite type ferrite was obtained by heattreatment at 750°C for 5h in air. The film thickness was about 0.08μm. The coercive forces (H_c) of the film and powder with the composition of 15BaO⋅85Fe₂O₃ was 3300 and 3050 Oe by heat-treatment at 850°C for 48h respectively. These films were shown to have much larger H_c than the powder. The effect of substitution of titanium and cobalt ion in barium hexaferrite films and powders were investigated. The saturation magnetization of the powder in the system 15BaO⋅85 [(100-2x) Fe₂O₃⋅xTiO₂⋅xCoO] was almost constant in the range of 0≤x≤8.33. But the H_c changed drastically with increasing titanium and cobalt ion content. The H_c of the powder was controllable in the range of 50 Oe and 3050 Oe by changing the substitution contents for the same system. The H_c of the films was controllable in the range of 300 Oe and 3300 Oe for the same system.

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Reactions among Si₃N₄, SiC, ZrC, ZrN and C were investigated under 1 atm N₂ at 1650°C. Compatibility relations among the compounds coexisting with 1 atm N₂ in the system Si-Zr-C-N were determined. Equilibrium states were confirmed by the fact that reaction products obtained from nitridation reactions were identical with those from decomposition of nitrides and by thermochemical calculation. The reaction products obtained from the starting sample of ZrC-Si₃N₄ were zirconium carbonitride and SiC, and those from ZrN-SiC were zirconium carbonitride and Si₃N₄. The lattice parameter of the zirconium carbonitride varied with the composition of the starting sample. The isobaric and isothermal section of the system Si-Zr-C-N includes 2 three-phase triangles: the area [I] ZrC_xN_1-x (x=0.43)+C+SiC, the area [III] ZrC_yN_1-y (y=0.32)+SiC+Si₃N₄ and 2 two-phase regions: the area [II] ZrC_1-bN_b (0.32<1-b<0.43)+SiC, the area [IV] ZrC_cN_1-c (0≤c<0.32)+Si₃N₄. On the assumption that zirconium carbonitride might be a regular solution between ZrC and ZrN, the interaction parameter of zirconium carbonitride was estimated to be -6--10kcal/mol from thermochemical calculation.

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In order to make clear the grindability of ceramics, a series of alumina-zirconia composite ceramics was ground using diamond grinding wheel, because the physical properties of this kind of ceramics vary greatly. Grinding force was adopted as a criterion of grindability, and bending strength, elastic modulus, Knoop hardness and fracture toughness were also measured as properties related to material removal mechanism. The results are summarized as follows:
(1) The grindability was dominated by hardness and fracture toughness in plastic deformation and in brittle fracture, respectively.
(2) A normal force increased with grinding time. The increasing rate was closely connected with the wear of abrasive grain and influenced by the nature of work material.

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Polysilazanes, high potential precursors for Si₃N₄ materials, were synthesized from trichlorosilane and methyldichlorosilane. The molecular weight of these polysilazanes increased as the mixing ratio of trichlorosilane to methyldichlorosilane increased. Their pyrolysis behavior were studied by TG, DTGA (Differential Thermal Gas Analysis) and Mass spectrometer. The major chemical species of gas evolved from samples in He atmosphere was ammonia at 350°C, and methane at 570°C. Moreover, on heating the samples in N₂, the DTGA curve showed that the reaction occurred from 400° to 950°C, and especially two DTGA peaks appeared at 570° and 750°C. When these polysilazanes were heated at 1300°C in N₂, α-Si₃N₄ formed, but a mixture of α-Si₃N₄ and β-SiC was obtained by heating them at 1400°C in Ar.

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Fine powders of partially stabilized zirconia containing 2mol% Y₂O₃ were synthesized from water-alcohol solutions of ZrO(NO₃)₂⋅2H₂O and YCl₃⋅6H₂O with various concentrations, [Zr⁴⁺+Y³⁺]=0.25-0.9mol/l, by the spray pyrolysis technique using a 2-fluids nozzle. The powders obtained were calcined between 1100° and 1300°C and milled for 12h. The powders so obtained were characterized by crystallite size and specific surface area measurements, TEM and SEM observations. On the basis of these results, the influence of powder properties such as primary particle size, degree of agglomeration, and green density on the density of the ceramic bodies (Y-TZP) fabricated by pressureless sintering at 1300° to 1500°C was investigated. The green density increased with an increase in calcining temperature, but was slightly affected by the concentration of solutions. With decreasing calcining temperature and/or decreasing concentration of solution, the size and degree of aggregation of primary particles decreased. Sintered bodies with 98% T. D. was obtained from the powders prepared in the present method by firing at 1300°C. The sinterability of the powders at 1400°C was almost independent of the concentration of solution, and 98% T. D. was obtained from the powder prepared from a concentrated solution of 0.9mol/l.

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SiC whisker-reinforced NbC composites were fabricated by the hot-pressing method. NbC, SiC whisker (V_f=10-30%) and 1wt% Cr₇C₃ were mixed with a ball mill, then hot-pressed at 1600°C, 330kg/cm² for 1h in Ar atmosphere. Flexural strength (σ_f), fracture toughness (K_IC) and Vickers hardness (H_v) were measured at room temperature. All of these mechanical properties were improved by whisker reinforcement. For the composite having V_f=30%, σ_f, K_IC and H_v were 880MPa, 5.74MPa√m and 24.7GPa, respectively. Crack deflection and grain growth inhibition of the matrix were observed as a result of whisker incorporation.

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Electrical properties of PbTiO₃-MgTiO₃ (MgO=2000-6000ppm) single crystals grown by the flux cooling method were studied. Arrhenius plots of σ_dc for PbTiO₃-MgTiO₃ (MgO=4000-6000ppm) exhibited high linearity. The apparent activation energy U_a and conductivity σ obtained were 0.9eV and (3.0-3.4)×10³ exp (-0.9/kT)Ω^-1·cm^-1, respectively. I-V characteristic curve was separated into two ranges at the temperature above 300°C independent of the quantity of doped MgO. Thermal breakdown of specimens caused by joule heat was frequently observed in the high field range. The relationship between the quantity of doped MgO and temperature dependence of E_H showed that the effects of doped Mg²⁺ ions remarkably decrease with increasing temperature. It is possible to apply the poling dc-electric field approximately 30-50V/cm by the electric field cooling method in the range from high temperature above T_c to room temperature.

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For comparing crack growth characteristics, subcritical crack growth data for soda-lime glass subjected to sustained load in water were obtained using conventional CT specimens with long crack and bend specimens with small Knoop indented crack. The relation between crack velocity V and stress intensity factor K_I obtained from as-indented specimens containing indentation crack shows that there is residual stress effect which increases crack growth in the region of lower K_I values. In addition, the slopes of the V-K_I curves for the as-indented specimens are much less than those for the CT specimens. However, the V-K_I curve for the indented and subsequently annealed specimen shows almost the same trend as that for the CT specimens. Thus, the effective stress intensity factor K_Ieff including the residual stress effect can be used to explain the anomalous growth of the indentation crack in its as-indented state.

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Tricalcium phosphate (TCP) was HIP'ed in a glass capsule at 800°-1100°C and 100MPa for 30min. Soda-lime glass was more suitable than Pyrex glass as a capsule material because of less thermal expansion mismatch from HIP-sintered TCP. Alumina powder was suitable as a barrier layer between glass capsule and sample, but boron nitride powder seemed to be reacted with the sample. The dense and transparent TCP ceramics were obtained by HIPing above 1000°C. In the comparison with pressureless sintering, the HIP treatment lowered the densification temperature as much as 200°C and also improved mechanical properties, 120MPa for bending strength and 0.8MPa·m^1/2 for fracture toughness.

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The superconducting properties of the Bi-Sr-Ca-Cu-O ceramics has been studied in terms of the microstructure. The powders were uniaxially hot pressed at 5t/cm², 500°C for 5min. Then the compacts were heated and sintered again at 870°C in air for 10 and 100h, followed by furnace cooling. Resistivity of the specimens was measured by standered four-probe method. Zero resistivity was observed at 80.0K when the compact was heated at 870°C for 10h, while after heated for 100h the off-set was at high as 105.5K. The critical current density at 77K was very low as 168.4mA/cm². The specimens simply heated and sintered at 870°C for 10 and 100h after cold pressing at 5t/cm² (without hot pressing) showed very low off-set temperatures. It was found, however, that the prolonged heating at 870°C with or without hot pressing increased the formation of the high T_c phase in the Bi-Sr-Ca-Cu-O ceramics. The hot pressing prior to the heating at 870°C increased the bulk density and the grain sizes of the specimens. The improvement of the sintering behavior may assist the formation of superconducting contacts among the grains of the high T_c phase in the Bi-Sr-Ca-Cu-O ceramics.

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Preparation of SiC ultrafine particles from SiH₂Cl₂-C₂H₄ mixtures by using CO₂ laser was investigated. Powders with specific surface areas of 8 to 150m²/g, were obtained by irradiating CO₂ laser beam to SiH₂Cl₂-C₂H₄ gas mixture at atmospheric pressure. The power density of laser beam was 3.66kW/cm² and wave length was 10.6μm. XRD of the products showed that Si, β-SiC and free carbon were produced and that the composition of powders depended on the C₂H₄/SiH₂Cl₂ ratio. Reaction temperature changed with the power density of laser beam and C₂H₄/SiH₂Cl₂ ratio. Hysteresis was observed between reaction temperature and power density of laser beam.

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Oxidation behavior of mullite composites containing 10 to 30vol% of SiC-whisker (SiC-w) has been studied at 1300°C in dry air. As the volume fraction of SiC-w increased, the weight gain increased. The weight gain curve obeyed the parabolic law for the SiC-w content of 10vol% and at the oxidation time shorter than 200h. However, the weight gain of the specimen containing more than 20vol% SiC-w was accelerated when the oxidation time exceeded 200h. It was found that impurities such as Na₂O, K₂O and CaO, originally contained in the SiC-w, were concentrated near the surface of the specimen. The acceleration of the weight gain for longer oxidation duration is explained in terms of corrosion of mullite and SiC-w by the liquid phase formed through the reaction between oxidized SiC-w and the impurities.

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