The influence of thermal stresses on the mechanical properties of thermal-shocked Nicalon SiC fibre/Pyrex composites has been analysed by considering the effect of thermal-mismatch stress on the mechanical properties of composite constituents. The thermal-mismatch stresses developed between devitrified cristobalite, and fibre and glass matrix were calculated using the values of material parameters obtained from experiment. This shows that the high thermal mismatch stresses originating from larger coefficient of thermal expansion of devitrified cristobalite extended the preexisting matrix crack, and caused fibre debonding. Thus, the reductions in the modulus and the interfacial stress of thermal-shocked composites in comparison with those of as-fabricated composites resulted from the matrix devitrification. The lower proportional limit of thermal-shocked composite was attributed to the lower interfacial stress and larger pre-existing cracks compared with those of as-fabricated composite. The reduction in ultimate strength of thermalshocked composite was correlated with the decreases of fiber hardness and interfacial stress.

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Attempts have been made to prepare the 110K phase of Bi-Sr-Ca-Cu-O (BSCCO) superconductor oxide, however, synthesis of a pure phase in a short time remains difficult. In this work, unleaded BSCCO was synthesized by three previously reported methods (solid-state reaction, firing of coprecipitated powders and annealing of melt-quenched powders). Wavy temperature firing between two temperatures t₁ and t₂ for 10 min was performed. The 110K phase was obtained in the temperature ranges of 845 to 875°C in the solidstate reaction, 840 to 860°C from the coprecipitated powders and 840 to 878°C from the melt-quenched powders. Wavy temperature firing resulted in a better effect than normal firing at a constant temperature. Synthesis using fine powders obtained by coprecipitation showed the best results at low temperatures.

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Six composites in the CaO-P₂O₅-SiO₂ system with and without B₂O₃, consisting of Ca/P ratios: 1.50, 1.67 and 2.00, were prepared by a sol-gel process. When the gel powders were heated at 900°C or higher, Ca₃(PO₄)₂ and CaSiO₃ were formed from the samples without B₂O₃, while boron-containing apatite and hydroxyapatite were formed from those with B₂O₃. When the compressed powders were fired at 1100°C for 1h, the relative density (bulk density/true density) was as low as about 65% in the samples without B₂O₃, but attained 98% in the samples with B₂O₃. The bending strength of the latter sample with B₂O₃ was 82 MPa.

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New forming process of nano-sized particles without a binder was proposed. Compacts of spherical amorphous agglomerated monodispersed titanium dioxide particles (-0.7μm) synthesized by the alkoxide method were hydrothermally treated in an autoclave to crystallize the primary particles (-13nm) to anatase single crystal. The hydrothermally treated compacts were compressed by cold isostatic press (CIP) and the hydrothermally treated particles were crushed to many nano-sized anatase particles to form again dense green bodies (61%) without a binder by CIP. The high formability of nano-sized anatase particles is considered to result in the agglomerated structure of hydrothermally treated particles. Green compacts obtained by this process showed high sinterability. Dense rutile bodies (99% of the theoretical density) were obtained by sintering at 900°C for 24h.

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The Si-Ti-C-O fiber (STC (6)) with a low oxygen content of 6mass% was oxidized at temperatures in the range of 1273 to 1773K in order to measure its oxidation rate and thereby to elucidate its oxidation behavior. These results were compared to those of the commercial fibers having 18 and 13mass% O (STC (18) and STC (13)). The kinetic data of STC (6) were expressed by the contracting-cylinder formula. The activation energies were calculated to be 72 and 430kJ/mol at the low-temperature (T<1473K) and the high-temperature (T>1473K) regions, respectively. On the other hand, STC (18) and STC (13) had activation energies of oxidation of E=72kJ/mol and E=70kJ/mol within the whole temperature range, respectively. Oxidation of STC (6) with a low oxygen content is considered to be similar in kinetic behavior to that of pure SiC.
The oxide film consisted of SiO₂ and TiO₂; and the former was amorphous during the low-temperature oxidation process tending to be crystallized into cristobalite at higher temperatures. The average size of crystallized β-SiC particles of the interface between the oxide film and unoxidized core fiber was larger than that of core of the fiber. This is because the progress of the crystallization in O₂ stream is considered to have been suppressed when the fiber was completely covered with the oxide film. When the fiber was oxidized at 1773K, the interface between the oxide film and the unoxidized core fiber contained many microcracks; moreover, the core fiber lost 75% of its original strength at room temperature. It is quite possible that these defects were produced by a contraction due to transformation of cristobalite (α-β) during cooling from the oxidation temperatures.

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Thermal shock resistance of silicon nitride was evaluated by a quenching test using precracked specimens and molten solder as a cooling medium. A thermal shock parameter, R_c (=ΔT_c*⋅√C), which corresponds to fracture toughness and is obtained easily from a general quenching test has been defined. Here, C is the half length of a precrack and ΔT_c* is the applied temperature difference when the first small propagation of the precrack is observed. As a result, it was confirmed that R_c is almost constant regardless of the crack length and temperature dependence of material properties. In addition, a critical temperature difference for an uncracked specimen was predicted from ΔT_c* and C using an equivalent crack length of natural fracture origin. This numerical prediction was also applied to the estimation of the thermal shock resistance of other ceramics.

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The following conclusions were reached from the results of this study.
(1) By using partially hydrolyzed complex alkoxide solutions, nearly monodisperse spherical particles were formed. In general, the mean size and size distribution of particles were smaller and the yield was lower in method 1 than in method 2.
(2) The mean size and size distribution of particles decreased with increasing ratio of [H₂O]/[M(OR)₄].
(3) The size distribution was not greatly affected by the amount of surfactant. However, the mean size was inversely related to it in method 2.
(4) The oxide composition of particles formed by method 2 was closer to the theoretical value, but more organic materials tended to be contained in particles. TiO₂ content was always higher than the theoretical value in particles formed by method 1.
(5) In method 2, the mean size, size distribution, oxide composition and yield of particles were affected significantly by the time taken to prepare the gelling solution up to putting it into the reaction cup.

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Electrical and mechanical properties of ceramic composites were investigated in order to establish a fracture prediction technique. Ceramic composites consist of calcium fluoride as an insulating matrix and silicon carbide as electrically conductive additives. An electrical conduction path was formed by adding more than 4vol% of SiC additives in the composites and the fracture strength increased by the increase of SiC additives. By applying mechanical load, electrical resistance of the composites increased up to fracture under tension while did not change or slightly decreased under compression. The changes in electrical resistance were suggested to occur by the change of connectivity of conduction path in the composites. These results suggest the possibility of predicting fracture in ceramic composites.

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Microstrucutre of Al₂O₃ xerogels and aerogels prepared from aluminum-tri-sec-butoxide (Al (O-sec-Bu)₃) modified with ethylacetoacetate (EAcAc) was investigated for controlling the microstructure of Al₂O₃. The specific surface area and the pore volume of heat-treated xerogels decreased with an increase in the EAcAc/Al (O-sec-Bu)₃ molar ratio, whereas the size of pores was not affected by the ratio. The specific surface area of aerogels decreased monotonously with an increase in the heat-treatment temperature up to 1000°C and was larger than that of xerogels in the whole temperature range of heat treatment, while that of xerogels decreased with increasing temperature due to sintering and drastically decreased at 1000°C.

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Many kinds of analyzers based on various principles have been developed for measuring particle size distribution of fine ceramics powders. But the reproducibility of the results, interchangeability of the models, reliability of the ends of the measured distribution have not been investigated for each principle. In this paper, these important points for particle size analysis were clarified by measuring raw material powders of fine ceramics. (1) in the case of laser diffraction and scattering method, the reproducibility in the same model is good, however, interchangeability of the different models is not so good, especially at the ends of the distribution. Submicron powders having high refractive index show such a tendency remarkably. (2) the photo sedimentation method has some problems to be conquered, especially in measuring submicron powders having high refractive index or flaky shape particles. The reproducibility of X-ray sedimentation method is much better than that of photo sedimentation. (3) the light obscuration and electrical sensing zone methods, show good reproducibility, however, sometime bad interchangeability is affected by calibration and so on.

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Yttrium-containing monoclinic hydrous-zirconia fine particles were heated from 300 to 700°C to investigate the phase change to 2.8mol% Y₂O₃-doped tetragonal ZrO₂. Both ZrOCl₂⋅8H₂O and YCl₃⋅6H₂O were dissolved into aqueous solutions and then boiled to make the hydrous-zirconia particles. The hydrous-zirconia particles containing Y(OH)₃ were prepared by dropping aqueous ammonia into the boiled solutions, while hydrous-zirconia particles containing YCl_x(OH)_y⋅nH₂O were obtained by spray-drying of the boiled solutions. The monoclinic-to-tetragonal phase change of hydrous-zirconias containing Y(OH)₃ was observed at 400°C by X-ray diffraction. The hydrous-zirconias containing YCl_x(OH)_y⋅nH₂O transformed to tetragonal phase at 500°C. The results of chemical analysis indicated that the atomic ratio of Cl/Y decreased with increasing heat-treatment temperature. At 500°C, this atomic ratio became less than 1. These experimental results suggested that the hydrous-zirconias containing YCl_x(OH)_y⋅nH₂O transformed to tetragonal phase through the decomposition reaction of YCl_x(OH)_y⋅nH₂O. Therefore, it is concluded that as the decomposition of YCl_x(OH)_y⋅nH₂O affects phase change, the temperature of phase change of hydrous-zirconias containing YCl_x(OH)_y⋅nH₂O becomes higher than those containing Y(OH)₃. X-ray diffraction and BET specific surface area measurements revealed that for hydrous-zirconia containing Y(OH)₃, the primary particle of small size with monoclinic phase was transformable to tetragonal phase at lower temperature comparing with that of large size. The hydrous-zirconias containing YCl_x(OH)_y⋅nH₂O with smaller particle size also showed the similar tendency. This tendency can be explained by the increase of the points contacted with yttrium and the shortening of diffusion length in the hydrous-zirconia particle with small size.

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A test technique for measuring elastic modulus at elevated temperatures was developed by using impact sound. The elastic moduli of SiC, Si₃N₄ and SiAlON decreased slightly with increasing temperature. The elastic modulus of Al₂O₃ decreased by about 12% with an increase in temperature by -1000°C. The Poisson's ratio did not depend upon the temperature. Prismatic beam specimens were more effective than rod beam specimens for measuring the natural frequency of torsional vibration by using this method, because the natural frequency of torsional vibration was measured and then the Young's modulus, the shear modulus and the Poisson's ratio could be calculated therefrom.

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In the thermal shock test by means of a heated ceramic disk specimen with constant heat flux, temperature distributions in the specimen and time to fracture can be easily measured. Therefore, thermal stress in the ceramics can be estimated without measuring the heat transfer coefficient whose measurement is needed in case of water quenching test. On the other hand, the temperature dependence of thermal properties of material substantially affects the temperature distribution and thermal stress history. In this paper, numerical calculations of non-steady-state temperature distribution in thin disk, which was heated from outside with constant heat flux, were conducted to estimate the generated thermal stress. Temperature dependence of thermal conductivity and thermal diffusivity was assumed to be exponential functions. Time-dependent thermal stress was expressed with the correlative equations containing coefficients of temperature dependence of thermal properties, the supplied heat flux and Fourier's number. The last factor was a nondimensional parameter with specimen size and time. Based on the proposed equations, the effect of temperature dependence of thermal properties on thermal stress and the suitable experimental conditions in above-mentioned thermal shock test were discussed.

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A solution of dilute zirconium oxide sulfate was hydrothermally treated at 240°C for different times. Metastable pseudo-zirconium oxide sulfate (PZOS) was formed at first with a decrease in SO₄^2- ion concentration and then monoclinic ZrO₂ was formed with an increase in SO₄^2- ion concentration as a result of dissolution of PZOS. Monoclinic ZrO₂ particles had crystals with elongated c-axis: flaky single crystals and bundles of (100) twin crystals. It seemed that the formation of two crystal types depends on the difference of crystal nuclei formed by dissolution of PZOS. Monoclinic ZrO₂ particles formed from solutions of low Zr and high H₂SO₄ at ZS(0.01/0.3), which indicates the mixed solution of 0.01mol/l zirconyl carbonate and 0.3mol/l H₂SO₄, and ZS(0.01/0.4) were like chestnut buries. It was thought that the morphology change of monoclinic ZrO₂ formed hydrothermally was caused by formation and dissolution of metastable PZOS and ZOS, the type of Zr-O solute species, and nucleation and growth of monoclinic ZrO₂, which were affected by the concentration of sulfuric acid in the solution.

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The effect of fabrication process operations on the sintered density was empirically discussed in order to optimize operation conditions. High purity alumina powders were used as raw powders: One η/θ-phase and three a-phase alumina powders. Their crystal phase, specific surface area, particle size, degree of aggregation and shape of primary particle are characterized. Alumina with the η/θ-phase had a large specific surface area. Three a-phase alumina powders were different each other in the primary particle shape or the degree of aggregation. The alumina powders were formed by uni-axial pressing and sintered. The following process operations were changed: milling, additive, binder, spray drying, CIPing. Each green compact was sintered under the same condition. An empirical equation is established for correlating the sintered density with the compact green density under any process conditions. A diagram is proposed from the empirical equation, and the effect of process operations on the green and sintered densities was discussed on the diagram. The effects of the process operations on the green and sintered bodies depended on the primary particle properties, especially particle shape. The CIPing and addition of additives always increased the green and/or sintered densities. However, spray drying and milling were efficient in powders consisting of dendritic primary particles, but no or negative effect of spray drying and milling on the green and sintered densities was observed in powders consisting of round primary particles and weak aggregates.

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HfO₂-Xmol% YO_1.5 solid solutions (X=0-22) were prepared by arc melting to investigate the compositional dependence of the unit-cell parameters of diffusionlessly formed metastable phases through X-ray powder diffraction measurements at room temperature. Unitcell parameters of monoclinic and tetragonal phases of HfO₂-Xmol% YO_1.5 (X=0, 2, 4, 5, 6, 7, 8 and 9) were refined by the Rietveld analysis. The lattice parameter and oxygen displacement were estimated for samples of X=10 to 22 by the profile-fitting technique. In the monoclinic phase (0≤X≤7), the lattice parameter a increased, while the b and the β angle decreased with an increase of YO_1.5 content. In the tetragonal phase, the lattice parameter a increased (6≤X≤13), while the c and the axial ratio c/a_f decreased (7≤X≤13) with increasing of YO_1.5 content, and then a_f and c axes values coincided each other at X=13, where the suffix f denotes the distorted pseudo-fluorite cell. In the tetragonal hafnia (10≤X≤16), the oxygen displacement from the ideal fluorite site decreased with increasing of YO_1.5 content. The HfO₂-13mol% YO_1.5 sample exhibited an axial ratio of unity within the experimental resolution, but showed 112_f reflection peak, strongly suggesting the existence of the t″-form, which is defined as a tetragonal phase with a c/a_f of unity. The t″-form is interpreted to appear in the compositional region of 13 to 16mol% YO_1.5.

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Influence of dissolved oxygen in molten iron in the reaction between aluminum nitride, AlN, and molten iron has been studied to find the optimum conditions for applying AlN materials to the refractories in the steelmaking process. AlN specimens dipped into molten irons containing 41 to 347 ppm oxygen at 1630°C at 300rpm for 30 min were not attacked, whereas silicon nitride, Si₃N₄, specimens were attacked severely at these oxygen content levels. Optical microscope and scanning electron microscope observations showed the formation of 10 to 20μm thick Al₂O₃-based films on the AlN surface which did not corrode. In contrast, there were none of these films on the Si₃N₄ specimens dipped in below -300-ppm oxygen irons. The reaction mechanism was discussed thermodynamically. In conclusion, iron with any dissolved oxygen level forms Al₂O₃ on the AlN surface at the beginning of the reaction, which acts as a protection layer for the AlN. On the other hand, the Si of Si₃N₄ dissolves into the molten iron without SiO₂ formation at the low dissolved oxygen level.

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Utilizing self-combustion synthesis and high pressure generated by underwater-shock wave, titanium carbide (TiC) with high density was fabricated in this study. Also the process which denser TiC compacts can be obtained was established. Titanium and charcoal activated powders were used as raw materials, which were mixed at range from 0.6 to 1.0 of C/Ti atomic ratio. The combustion velocity was accelerated with increasing quantity of the charcoal activated powder. Density and micro Vickers hardness of the TiC compacts became higher as C/Ti ratio increased. TiC_1.0 compact indicated maximum values of 4.72×10³Kg/m³ and 32GPa, respectively. It is expected that TiC compacts with excellent mechanical properties which compare to commercial TiC product may be obtained because the present compacts indicated similar fracture morphology to the commercial product.

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A low purity β-silicon nitride powder for refractory materials was classified or acid treated to remove metallic impurities. The purified powder was gas-pressure sintered at 1900°C for 4h in nitrogen gas of 10 MPa using 4mol% Y₂O₃-Nd₂O₃ as sintering aids. Acid treatment decreased the Fe and Ca contents to increase the strength of sintered materials. Powder classification eliminated coarse particles including Fe as well as large silicon nitride particles. As the result, the strength of sintered materials increased up to 843 MPa. Thus, this material can be used as structural components.

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Slurries of various mixture ratios of aluminum hydroxide sol, ZrO₂ powder and methyl cellulose as a binder were prepared, and green sheets were formed by the doctor blade method. The green sheets were heat treated in the temperature range from 1200 to 1600°C in air. Thus, the Al₂O₃/ZrO₂ composite sheets with a thickness of about 0.1mm were obtained. A homogeneous composite texture was found at the mixture ratio of Al₂O₃/ZrO₂=80/20, and a tetragonal phase (t-phase) of ZrO₂ component was stabilized in such a thin sheet. Also the t-phase was transformed to a monoclinic phase partially by powdering. If α-alumina fine powder was added to aluminum hydroxide sol as a seed previously, a sinterability was promoted. But as a result of composing, a sinterability became unremarkable. In order to apply a composite sheet for a practical use, it is necessary to improve the technique of composing sheet having a higher density.

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The crack-growth law in HAp materials were studied by using the DT method. The K_I-V diagrams of HAp were found to be markedly affected by the environment.
(1) The K_I-V diagram in air exhibited three distinct regions. The region 2 was observed at crack velocities from 10^-3 to 10^-4m/s. In water, only the region 1 of K_I-V diagram was observed.
(2) As the temperature increased the crack-propagation curves in water shifted to lower applied stress intensity factors. The observed activation energy for crack motion was 166kJ/mol.
(3) Intergranular fracture was dominant for the fracture in water (region 1).
(4) A low Ca/P ratio phase was observed at the grain boundary.

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Transparent, conductive cadmium stannate (Cd₂SnO₄) thin films were successfully prepared by the dip-coating method. Smooth Cd₂SnO₄ thin films up to 200 nm thick were obtained by a single dip-coating procedure. The resistivity of the crystalline Cd₂SnO₄ thin films fired above 550°C for 1h, was 2-4×10^-3 Ω·cm. Conductive amorphous films were also obtained at 500°C. The transmittance of the Cd₂SnO₄ thin films was 70 to 80% in the wavelength range from 550 to 1100 nm

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