SiC whisker reinforced TiB₂ matrix composites containing 10 to 30vol% whisker were prepared by hotpressing at 1600 to 1900°C. The flexural strength of 867±77MPa and K_IC of 5.8±0.12MPa√m were obtained for the 1800°C hot-pressed samples containing 10vol% whisker. No significant increase in K_IC was observed by the whisker reinforcement because of the chemical reaction between matrix and whisker, which enhanced strong interfacial bonding and whisker agglomeration.

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Variation of the chemical composition of an Na₃AlF₆-Al₂O₃ growth solution in the growth process of single corundum crystals was studied by the chemical analysis. The concentrations of aluminum and fluorine decreased with time, whereas the concentration of sodium increased. The optical quality and the advancing rate (g/h) of the growing crystal were improved by adding a small amount of AlF₃ compound as sources of aluminum and fluorine, and large crystals with good quality were obtained.

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A novel hydrogen sensing device consisting of palladium thin film was prepared on a glass substrate by radio-frequency magnetron sputtering. When the sample was exposed to hydrogen, the optical transmittance increased and saturated at a constant value. The transmittance returned to its initial value by exposing the sample to dry air. Its optical transmittance was found to depend on the hydrogen concentration in the ambient atmosphere. This phenomenon is proposed to be utilized as a new type of hydrogen sensor.

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The load-point displacement of SiC whisker/Si₃N₄ composites sintered at various temperatures was measured precisely during fracture in bending, and the effective fracture energy (Γ_eff) was evaluated. It was noted that Γ_eff was affected by the sintering temperature, and that composites had a higher Γ_eff than monolithic Si₃N₄, particularly when sintered at high temperatures. The effect of whisker reinforcement was discussed, and it was revealed that the whiskers acted to restrain catastrophic failure and to increase the Γ_eff rather than improving the fracture toughness, K_IC.

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Effects of the Al/P ratio on the crystallization of apatite and anorthite were investigated by differential thermal analyses on a series of glasses with the nominal composition of 3.0wt% MgO, 35.0wt% CaO, 41.4 wt% SiO₂, and 20.6wt% (Al₂O₃+P₂O₅). It is shown that the activation energy for crystallization of apatite decreases with decreasing Al/P ratio, but that for crystallization of anorthite, on the contrary, increases. The Avrami parameter, n, was also estimated to be 2 and 1 for apatite and for anorthite, respectively.

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YBa₂Cu₃O_7-x (123 or YBCO phase) films were prepared on YSZ substrates by the sol-gel method. The reaction between the YECO film and the YSZ substrate, the c-axis orientation of the 123 crystals in the film, and their influence on the critical current density (J_c) and the critical temperature (T_c) have been investiated. When the coating films were fired at temperatures higher than 950°C, the films reacted heavily with the substrate, the c-axis orientaion of the 123 crystals in the films perpendicular to the substrate increased, and the 123 phase in the films changed to the 211 phase and further to the 202 phase as the reaction of the films with the substrate progressed. It has been found that J_c and T_c were improved as the c-axis orientation of the films increased and the film-substrate reaction decreased, indicating that the orientation of films increased as the film-substrate reaction was reduced when the volume fraction of the BaZrO₃ formed by the film-substrate reaction was between about 5 and about 13%.

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The electrical joining of Si₃N₄ ceramics using a local heating system was studied to clarify the relevant heating mechanism. In this study, a CaF₂/kaolinite mixture with suitable electroheating characteristics and good reactivity with Si₃N₄ ceramics was used as a joining agent. The temperature characteristics of conductivity of the joining agent, the electrical characteristics during electroheating and the composition of the joint layer were examined. The heating process in this joining method consisted of preheating by a gas flame and principal heating by electroheating. The electrical conduction of the joining agent was due to ionic conduction of CaF₂ and the conductivity was enhanced by preheating. Starting electrical charging to the joining agent, joule heat was generated and the entire joining plane was heated to high temperature by the self-controlling mechanism arising from changes in the composition of the joining agent. In addition, the maximum temperature in the joining plane was estimated about 1800°C by thermal conduction analysis.

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Dispersibility and fluidity of aqueous alumina slurry containing 3.75wt% polyacrylic acid (binder), 3.75wt% polyetylene glycol (plasticizer), and 1wt% polyacylic ammonium (dispersant) were studied for controlling density and microstructure of green sheet and sintered body by tape casting. At pH 1, the slurry behaved as Newtonian liquid with low viscosity and formed green sheet with 57.8% of theoretical density. The green sheet was densified to 99.2% of theoretical density by sintering at 1600°C for 1h. In the slurry at pH 1.8 to 4.8, the apparent viscosity decreased with increasing shear rate (shear thinning behavior). The slurry at the isoelectric point (pH 2.4) showed the highest viscosity and yield stress because of the formation of particle agglomerates. The green sheet with 52.5% of theoretical density resulted in non-uniform structure of 98.6% of theoretical density by sintering at 1600°C for 1h. On the other hand, the low-viscosity slurry showing Newtonian flow at pH>5.8 led to green sheet of 55.7% theoretical density and sintered body of 99.8% of theoretical density with uniform structure at 1604°C for 1h.

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Effect of SiO₂ and TiO₂ additions on the phase formation, sinterability, and microstructure of alumina ceramics was studied by differential thermal analysis, X-ray powder diffractometry, SEM, TEM, and dilatometry. Alumina-based mixture powders were prepared from starting materials of α-Al₂O₃ powder, Si(OC₂H₅)₄ and Ti(OC₃H₇)₄. The silica gel obtained from the hydrolysis of Si(OC₂H₅)₄ was coated on Al₂O₃ particles to form a thin surface layer. During the firing process, the silica gel didn't crystallize to cristobalite but reacted with Al₂O₃ to form mullite above 1500°C. The silica gel, mullite and/or Al₂O₃-SiO₂ liquid phase retarded the densification and the grain growth of alumina. As TiO₂ was added to the alumina-silica gel mixture, the sinterability was enhanced and the formation temperature of mullite was lowered.

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Nb₂O₅-added R (ramsdellite) phase was syntbesized by the melt-quenching method. Addition of 3 to 5mol% Nb₂O₅ accelerated the R→H (hexagonal phase) transformation, retarded the H→S+r (spinel and rutile) successive decomosition reaction, and stabilized the H phase at high temperatures. These effects were possibly caused by the preferential incorporation of Nb₂O₅ in the H phase. The phase changes in the Nb₂O₅-added R phase occurred similarly to the non-added R phase following the route quenched-R→H→S+r→R during heating and R→H→S+r during cooling, respectively. The R phase containing 3mol% Nb₂O₅ was heated to 850°C at 2°C/min in air, then quenched, and the H phase was obtained although very small amounts of rutile and spinal were contained. Lattice constants of the obtained H phase were a=0.8777(8)nm and c=6.988(2)nm, and the effect of Nb₂O₅ addition was hardly recognized. The linear thermal expansion coefficient of the H phase was determined to be α=1.34×10^-5K^-1 between room temperature and 900°C. Investigation on the phase changes in the H phase during heating clarified those in the R phase.

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Ca(OH)₂ and H₃PO₄ were used as starting materials for synthesizing hydroxyapatite (HAp). When the stoichiometric amount of 1mol/l solution of H₃PO₄ was added dropwise to a Ca(OH)₂ slurry in a N₂ at-mosphere, pH of the slurry was shifted from 11.7 to 3.7, and resultant HAp became Ca-deficient. The Ca/P molar ratio of HAp was strongly affected by pH of the reaction slurry. Stoichiometric HAp(Ca/P=1.67) was prepared by keeping the slurry at pH=7.0 with a tris (hydroxymethyl) aminomethane solution (Tris buffer) and by aging for 48h at 60°Cin a N₂ atmosphere. The Ca/P molar ratio of HAp was regulated by using Tris buffer to 1.66 under pH=6.0 and to 1.68 under pH=8.0, respectively. The stoichiometric HAp was stable up to 1300°C, and the lattice constants of the HAp calcined at 1100°C were a₀=0.94185(2)nm and c₀=0.68807(2)nm.

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The influence of grain size and secondary phase on the fracture toughness K_IC for sintered MgO bodies was in-vestigated. Sintered MgO bodies doped with 1-10wt% CoO were made by hot-pressing. The grain size was changed by annealing. The fracture toughness K_IC was measured by a chevron-notched beam method. The fracture toughness of sintered MgO bodies doped with CoO was nearly independent of the grain size and the amount of CoO, and indicated almost the same value as that of pure MgO. The fractography revealed that CoO-doped MgO bodies had the mixed mode of transgranular and intergranular fracture on the fracture surfaces, which is the same result as pure MgO. This result corresponded to little change in the fracture toughness by doping CoO to sintered MgO bodies. It was considered that fracture mode did not change in CoO-doped MgO because residual thermal stresses did not generate in MgO⋅CoO solid solutions. Furthermore, the relationship between the fracture toughness and the fraction of transgranular fracture was quantitatively estimated for MgO-based composites including the previous results. Toughening ceramics was discussed in connection with changing fracture mode.

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Y₃NbO₇ powders with excess oxygen vacancies were prepared by calcining coprecipitated powders of (YO_1.5)_1-x(NbO_2.5)_x(x=0.20-0.30) at 1200°C in an Ar gas flow, which was synthesized from YCl₃ and NbCl₅ using the liquid phase coprecipitation method. Also number of oxygen vacancies in the synthesized powders was estimated from the density, and conductivity of the resulting sintered bodies was measured. The number of oxygen vacancies in the Y₃NbO₇ powder in the x=0.25 composition synthesized in Ar was around 1.48 in unit cell even after heat treatment in air. The number of oxygen vacancies in the x=0.20 and 0.30 compositions synthesized in air increased by the change of valence number in Nb. On the other hand, after synthesizing the powder comprised of the x=0.20 composition in Ar, the number of oxygen vacancy of the powder reheated in air was 2.06. The conductivity of sintered bodies fabricated from the Y₃NbO₇ powders synthesized in Ar was raised by a half digit higher than that of the sintered body fabricated from the powders synthesized in air. The conductivity of the sintered bodies obtained from the synthesized powders increased almost linearly with an increase in the number of oxygen vacancies. Therefore, it was found that the introduction of oxygen vacancies by controlling composition and the powder preparation was an important factor for increasing in conductivity of Y₃NbO₇ sintered body.

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The kinetics and the mechanism of reaction of Si₃N₄ with Cr have been investigated in an atmosphere of N₂. Using powder mixtures of Si₃N₄ and Cr, the reaction rates were measured by means of a thermobalance at temperatures from 773K to 1573K, and reaction products were examined by X-ray diffraction. Below 1423K, N₂ gas reacted with Cr particles to produce Cr₂N and CrN. Above 1473K, Cr nitrides were produced at the initial stage of the reaction, and a CrSi solid solution and Cr₃Si were formed on the nitride layer at the late stage. The initial reaction followed the linear rate law. Below 923K, the activation energy was 35kJ/mol and the rate-determining step was the diffusion of N₂ to the surface of the Cr partides. Above 973K, the activation energy was 202kJ/mol and the rate was probably mixed-controlled by the gaseous diffusion and the interfacial reaction. When the Cr particles were covered with the reaction products, the kinetics was described by the parabolic rate law. The activation energies were 148kJ/mol below 1273K and 305kJ/mol above 1323K. The solid State diffusion through the reaction layer may be considered as the rate-determining step.

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The Critical Powder Volume Concentration (CPVC) of compound for plastic forming was investigated. Prior to compounding ceramic powders with resins, the effect of the experimental conditions on the CPVC was examined using a torque rheometer and model liquids. It was found that there are optimum conditions for mixing speed and powder loading ratio. The CPVC obtained at the proper conditions is also dependent on the vehicle used for measurement; i.e. CPVC_o (oleic acid)>CPVC_w (ion-exchanged water)>CPVC_k (kerosene). The critical powder volume concentration for the powder/thermoplastic resin system (CPVCM), which was determined by a flowability test, was from 0.85 to 0.90 of the CPVC_o. Characteristic mixing torque-time curves appeared near the CPVCM. The microscopic observation of texture of compound suggested that the time-dependent odd behavior reflected the dynamic process wherein the particles were being dispersed into the melt with high viscosity.

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In this study, c-axis oriented Y₁Ba₂Cu₄O₈(124) films and high critical current dendity (J_c) Y₁Ba₂Cu₃O_7-x films were obtained by the Metalorganic Deposition (MOD) method and the MOD metbod with application of the decomposition process (124→123+CuO) respectively. C-axis oriented 124 phase films could not be fabricated from direct heat-treatment in the stable temperature region of 124. In order to obtain c-axis oriented 124 phase films, c-axis oriented 123 phase films were synthesized prior to reaction with CuO. In this process, however, single-phase films of 124 were hardly synthesized even changing the heat-treatment conditions or the ratio of CuO. First the 124 phases were syntesized, and then the high-J_c 123 phase films were synthesized by transforming the 124 phases into the 123 phases. The reason why the high-J_c 123 phase films were obtained is probably due to the existence of impurity phase in the 123 phase as pinning centers and/or refinement of the 123 grain boundaries.

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The preparation of sodium borosilicate glass-alumina composites has been studied and the effects of the addition of NaF and AlF₃ on the thermal and dielectric properties of the sintered composites has been examined. The sintering temperature of specimens was lowered by about 100-150°C by the addition of fluorine compared with the specimens without fluorine. The specimens containing fluorine showed slightly lower dielectric constants than those of the specimens without fluorine addition.

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We proposed an expression for the strength of ground ceramics. The expression is the function of the maximum grain depth of cut g and the fracture toughness of the workpiece material, assuming that the nucleation of median crack during grinding is explained in the same way as that in Vickers indentation test. In this paper, the strength at elevated temperature has been estimated by using the expression. Under the condition that increasing temperature does not affect the crack size, the estimation was applicable to the strength of hot-pressed silicon nitride and sintered silicon carbide ceramics by considering the temperature dependence of the fracture toughness. At an elevated temperature, both materials showed an increase in critical value of g for the strength degradation after grinding. It is suggested that the setting g based on the strength of ground material at elevated service temperature leads to the reduction in the machining time to obtain the inherent strength of the workpiece material.

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Carbon-based composites with dispersed β-SiC and B₄C particles were prepared by normal pressure sintering. The spherical β-SiC particles with a diameter of 1μm in the dense matrix of carbon grew into rods with a diameter of 3 to 5μm and a length of up to 50μm by heat-treatment above 2300°C. The anisotropic growth of SiC did not occur when the matrix contained less than one percent B₄C, but the anisotropic growth rate increased with increasing amount of B₄C. Dimensional change of the composites caused by the growth of SiC rods was less than 5vol%. The composites were toughened hy a crack deflection mechanism caused by SiC rods dispersion.

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Dispersion of fumed silica powders having specific surface areas (S_BET) of 50-500m²⋅g^-1 was investigated based on the optical absorption (τ) in the wavelength (λ) range of 460-700nm. Light scattering index (n) was evaluated by using the equation τ=αλ^-n. In the fumed silica-water disperse system, n and τ at λ=700nm changed rapidly to reach n* and τ*_700nm, respectively, in the steady state under strong ultrasonic agitation conditions. n* and τ*_700nm were found to be more useful than S_BET as a dispersibility index of fumed silica. In general n* tended to increase as S_BET increased, indicating that aggregated silica particles became finer in water as the size of primary silica particles dccreased. Dispersion behavior of fumed silica was also well correlated with τ*_700nm. The fumed silica having a larger τ*_700nm easily reached an ultimate dispersion state in water under mild ultrasonic agitation, while that having small τ*_700nm started dispersion as rather grossy particles, which were subsequently divided into finer pieces to reach a very fine dispersion state eventually. Fumed silica was dispersed similarly in other polar media such as methanol and acetone but not in nonpolar or poorly polar media such as n-hexane and toluene.

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Oxygen in four kinds of oxide ceramics (Y₂O₃, ZrO₂, TiO₂ and Al₂O₃) was determined by the inert gas fusion method. To examine the gas extraction, Fe, Ni, Cu, Sn and Ti were used as a bath metals. From the analytical values and the gas extraction curves, it was considered that the promoting ability of these metals was higher in the order, Ti<Sn<Cu-Ni<Fe. The analytical results of ZrO₂, TiO₂ and Al₂O₃ obtained with Fe (or Ni), Cu and Fe, respectively, did not agree with the theoretical values, though the gas extraction curves showed rapid and complete decomposition. In the crucible after measurement, the metal bath formed a dome. Above results suggest that both bath metal and the sample were pushed up to the top of crucible by the generated CO gas, and that the decomposition was stopped or CO gas was adsorpted on the bath metal, by cooling down of the bath temperature. Use of Sn-Ni or Sn-Fe bath suppressed the dome formation and the analytical results were agreed well with the theoretical values.

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Continuous Pb(Zr_1-xTi_x)O₃ ceramic fibers have been prepared by the alginate method, which is based on a gelation of sodium alginate aqueous solution by sodium ion-exchange with protons or multivalent metal ions. In this work, a new process by use of a 5% sodium alginate aqueous solution mixed with ZrO₂-sol and TiO₂-sol has been studied. The Pb-Zr-Ti-alginate precursor fibers were converted to Pb(Zr_1-xTi_x)O₃ ceramic fibers by firing at 1200°C for 3h. The Pb(Zr_1-xTi_x)O₃ ceramic fibers were examined by the powder X-ray diffraction tedhnique and scanning electron microscopy.

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Composite alumina ceramics with a mullite whisker content of up to 30vol% were fabricated by hot-pressing at 1400 to 1600°C under 30MPa for 30min. The bending strength, hardness, elastic modulus and fracture toughness of the hot-pressed bodies were investigated. Considerably dense alumina-mullite whisker composite ceramics were obtained by sintering at 1600°C with a whisker content of up to 30vol%. The composite with a whisker content of 10vol% and sintered at 1600°C exhibited the highest room temperature bending strength of around 750MPa. This value is still lower than the maximum strength of alumina ceramic which is about 850MPa. However, the composites exhibited greater high temperature strength and hardness than alumina. The elastic modulus decreased with an increase in whisker content. No improvement was ohserved in the fracture toughaness of the alumina by the addition of mullite whiskers, as very little crack deflection by the whiskers and pull-out of the whiskers occurred in these composites.

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Intermediates produced in the carbonation process of a Ca(OH)₂ slurry were analysed by X-ray photoelectron spectroscopy (XPS). The molar ratios of CO₃^2- to Ca²⁺ of the intermediates, determined from the peak areas of Ca2p and Cls of XPS spectra, indicated that the rate of carbonation in the vicinity of the surface was comparable to that in the bulk. The binding energy of Ca2p_3/2 was found to have shifted linearly toward higher binding energies with increasing formation of CaCO₃. These facts support the view that decrease in the Ca²⁺ concentration in the early stages of the process was caused by the formation of an amorphous phase with the formula Ca_1+xCO₃(OH)_2x⋅yH₂O(x>0.05, y=0.6-0.8).

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