The variations of ultimate flexural strength, proportional limit and modulus of Nicalon SiC fibre (-50vol%)/Pyrex composites have been analysed in terms of fibre hardness and interfacial shear stress and matrix modulus. The ultimate flexural strength increased with an increase in fibre hardness. A relatively high measured interfacial stress contributed to the high ultimate strength and proportional limit. From these experimental findings, the important parameters controlling the mechanical properties of Nicalon/Pyrex composite were identified, i.e., the degree of fibre damage influencing the ultimate strength, the interfacial stress influencing the proportional limit, and the matrix devitrification influencing composite modulus.

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In an attempt to prepare zeolites of a new type or those having new surface properties, their synthesis in a nonaqueous solvent system using methanol, 2-propanol, ethylene glycol or monoethanolamine was studied. Sodalite of high crystallinity was obtained using monoethanolamine as solvent, and tetraethoxysilane, aluminum triisopropoxide, and sodium hydroxide as raw materials. The synthesis conditions were SiO₂/Al₂O₃=2, Na₂O/SiO₂=5, solvent/Na₂O=90 molar ratio at 150°C, and 22-490h of aging time. The properties of these crystals were compared with those obtained from 2-propanol containing water (1.2 vol% of solvent) and from pure water. Our crystals had a slightly larger lattice constant and adsorbed a large amount of N₂ gas; in particular, the shape of the adsorption isotherm was unique compared with those of others. This greater adsorption may be attributed to adsorption at the inner surface, that is, the windows of sodalite allow the penetration of N₂ into the pore structure. This was also suggested by the larger lattice constant.

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Copolymer of polysilastyrene and perhydropolysilazane was obtained by the reaction of polysilastyrene with zirconium n-butoxide and perhydropolysilazane. Zirconium n-butoxide and perhydropolysilazane were essential to render the thermosetting property. The thermosetting copolymers were converted into silicon carbide-based ceramics by pyrolysis at 1000°C in a stream of N₂ with about 80 mass% ceramic yield. The main phase of the pyrolysis product at 1500°C in N₂ was small crystallite β-SiC. Free carbon, based on rule-of-mixtures composition in the final ceramics could be reduced by varying the ratio of polysilastyrene/perhydropolysilazane. The copolymer was dry spun and pyrolyzed to produce a ceramic fiber. Pyrolysis in N₂ at 1500°C yielded a silicon carbide-based fiber. Tensile strength of 1.0 GPa and elastic modulus of 190 GPa were obtained for the fiber from 10 to 12μ in diameter. Crystallization to α-Si₃N₄, β-Si₃N₄, β-SiC, and ZrN proceeded on annealing in N₂ at 1700°C for 1 h.

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The mechanical properties of alumina fabricated by injection molding and sintered at 1650°C in air are described. The Weibull statistics of 4-point flexural strength is used as an index of processing stability and mechanical behaviors of different solid contents in the mixture. The results indicate that the optimum mixture which gives the Weibull modulus of 11.02 and average flexural strength of 322 MPa is 55 vol% alumina with 45 vol% binders. The flow behaviors affecting injection molding are also discussed.

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Colloidal dispersion and pressure-casting to prepare SiC green pieces of two types and pressureless sintering of SiC were sequentially conducted to obtain homogeneous, dense SiC bodies. Polyethyleneimine (PEI) was selected as a dispersant, and Al₂O₃/Y₂O₃ additives served as a sintering aid for the ceramic systems. The dispersion behavior of the SiC in solutions with PEI dispersant was characterized by their surface potential and isoelectric point (IEP), and interpreted according to the chemistry and adsorption of the PEI dispersant. The resulting crystalline phases and grain morphologies of sintered SiC were investigated by quantitative X-ray diffractometry (QXRD), scanning and transmission electron microscopies (SEM & TEM) and high resolution transmission electron microscopy (HRTEM). α-SiC was sintered at ambient pressure to a higher density than β-SiC with Al₂O₃ and Y₂O₃. The densification and resulting microstructure depended greatly on the polytypes of the starting SiC powders, types of packing powder to buy samples, and types and amount of sintering additives. The effects of seeding with 6H-SiC powder on phase evolution, the transformation temperature and densification of the β-SiC matrix are discussed.

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The cell dimensions for a series of β-Ca₂SiO₄ solid solutions were determined as a function of concentration of foreign oxides (Na₂O, Al₂O₃ and Fe₂O₃). The angle β varied most sensitively with the Na/(Na+Ca) ratio (=x) according to β(°)=94.55-8.86x(0≤x≤0.03). The decrease in x that accompanies the remelting reaction was therefore detectable by the increase in β. When the crystals were cooled at a constant rate γ(°C/s) over the temperature range in which the remelting reaction occurred, the fraction remelted was expressed by 1-exp(-1.33r^-0.25).

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In the interior of glass-ceramic A-W, both the apatite and β-wollastonite were homogeneously dispersed in a glassy matrix, taking a form of rice grain 50 nm in width and 100 nm in length. The apatite layer formed on the glass-ceramic in the simulated body fluid consisted of fine needle-like apatite crystals about 10 nm in thickness and 100 nm in length, which are elongated along c-axis and randomly oriented. The apatite crystals in the surface layer were in direct contact with those within the glassceramic without intervention of such silica gel layer as observed for Bioglass®-type glasses. No crystallographic relation was observed between them. The apatite crystals in the surface layer were calciumdeficient, and contained small amounts of Mg and Si.

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Sintered ceramics and RF-sputter deposited thin films of AgSbO₃ with defect pyrochlore structure were prepared and their electrical conductivities and optical properties were measured. Sintered ceramics of AgSbO₃ showed n-type electric conduction with a conductivity of -2×10^-1Ω^-1·cm^-1 and the cut off wavelength of -400 nm for optical transmittance at room temperature. Polycrystalline thin films obtained by post-annealing at 675°C in O₂ gas flow also showed n-type conduction with a conductivity of -10⁰Ω^-1·cm^-1 at room temperature. The optical transmission spectrum of the film with the thickness of -200 nm showed the optical transmittance of -80% at a wavelength of 400 nm. The carrier concentration and the Hall mobility of the polycrystalline film were -3×10¹⁸cm^-3 and -8cm²·V^-1·s^-1, respectively.

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Nickel was infiltrated into porous alumina compacts of 37-62% of theoretical density by electrochemical reaction of Ni²⁺ ions with direct and conical current in an aqueous solution of nickel nitrate/urea/ethylene glycol/ammonium sulfate. The weight of Ni deposited was in proportion to t^0.22-0.64 (t: deposition time). The deposition rate of Ni was higher for direct current than for conical current, and for a higher-porosity alumina compact. Use of conical current seemed to suppress the dendritic growth of Ni which was observed in a porous alumina with direct current.

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Several silicon nitride pre-sintered bodies with different α-phase contents were prepared by hot-pressing. The grain growth behavior was investigated by annealing pre-sintered bodies for 1 to 4h at 1800°C or 2h at 1900°C. The microstructure of annealed body became finer with the increase of α content in pre-sintered body. The α/β phase transformation was completed at the early stage of annealing. The materials developed “in-situ composite” microstructures consisting of large grains and fine matrix grains. The β nuclei were formed or grown to the large grains with phase transformation. On the other hand, the matrix grains were elongated with phase transformation. In the following stage of the annealing, grain growth behavior was dominated by the grain size distribution which formed at the early stage of annealing. In the case of material from α powder, the microstructure becomes fine and a few β nuclei form during phase transformation. So, the material developed an “in-situ composite” microstructure because the driving force of grain growth is high. On the other hand, the microstructure of material from β powder becomes homogeneous because the driving force of grain growth decreased by presence of large number of nuclei.

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The oxidation mechanism of C-SiC composite fiber, which was prepared from carbon fiber (Kynol) and ethyl silicate, has been investigated. The oxidation rate was determined by means of a thermobalance in an atmosphere of O₂ at temperatures from 673 to 1473K. The oxidation curves were characterized by S-shape. In the second stage, the oxidation obeyed a linear rate law. The oxidation rate of the composite fiber was lower than that of the carbon fiber. Below 973K, the activation energy for the oxidation was estimated to be 115kJ·mol^-1, and the gas diffusion through the porous SiC layer was a rate-determining step. Above 973K, the activation energy was estimated to be 24kJ·mol^-1. The oxidation was considered to be controlled jointly by the gas diffusion to the surface of the fiber and the gas diffusion through the porous SiC layer.

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Hydration characteristics of Al₄C₃ and the hydration prevention by adding Si were investigated. The results showed that the addition of Si could inhibit the hydration of the formed Al₄C₃, which was attributed to the dissolving of Si in Al₄C₃ and to the formation of Al₄SiC₄ which had an excellent hydration resistance. Influences of the addition amount and the grain size of Si and the heating temperature on the hydration resistance under the above conditions were also discussed.

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Carbon/carbon composites are promising material for use at ultra high temperature in gas turbines, space plane airframes and engines because of their low density and high thermal resistance. However, one of the problems with carbon/carbon composites is their low oxidation resistance. In this study, multi-layer coated carbon/carbon composites by the CVD technique were developed to improve the oxidation resistance. Four kinds of multi-layer coating with TiC and SiC were applied to carbon/carbon composites by the CVD technique and the oxidation resistance were evaluated in air at high temperatures. In multi-layer-coated carbon/carbon composites with thin TiC layer, cracks in the coating layer were far narrower than those in the single-layer-coated carbon/carbon composites. As results of oxidation tests at 1773K and 1273K, the multi-layer-coated carbon/carbon composites showed much better oxidation resistance than the single-layer coated carbon/carbon composites. This improvement is thought to be caused by two reasons; (1) in multi-layer coated carbon/carbon composites, the cracks of the coating-layer close at much lower temperature than in single-layer coated carbon/carbon composites. (2) TiO₂ produced by oxidation of TiC in multi-layer coating seals the cracks of the coating-layer.

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The critical current density (J_c) in small-grained YBa₂Cu₃O_x ceramics with varied sintered densities has been found to show characteristic behavior with a peak around a relative sintered density (R. D.) of 90%. This characteristic behavior of J_c in the materials has been investigated from the view points of the changes of both their grain morphologies and grain boundary dislocation structures (GBD) associated with sintered density. GBD networks occurred to relax the localized strain at the grain boundaries regardless the degree of lattice matching thereof, which was estimated using a coincidence-site-lattice (CSL) model. The GBD networks existing at the boundaries were found to reduce the J_c of the materials. The width (δ) of GBD in the materials, determined by transmission electron microscopy, was found to increase rapidly above 90% R. D. The increase in δ is explained in terms of accumulated internal stresses at the grain boundaries, which are assumed to originate from an increase in the aspect ratio of the ceramic grains.

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Excellent transparent YAG ceramics, which contain Nd additives from 1.2 to 7.2 at%, were fabricated by the solid-state reaction method using high purity powders (>99.99 mass%) of Al₂O₃, Y₂O₃ and Nd₂O₃. The precipitated phase (Y_1-δNd_δAlO₃) in accordance with increase in Nd content was clearly observed in Nd: YAG ceramics undoped with ethyl silicate. In the case of Nd: YAG ceramics doped with ethyl silicate, the precipitated phases in Nd: YAG ceramics disappeared with adequate addition of ethyl silicate. The Nd: YAG ceramics doped with ethyl silicate were confirmed optical perfect isotropy in dark field image under cross nicols and fully transparent. Beam scattering was hardly observed when the He-Ne laser beam was irradiated into the polished 4.8 at% Nd: YAG ceramics.

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Thermal shock damage in ceramic disks heated from outside under constant heat flux conditions was evaluated from fragmentation of fractured specimens. Temperature disturibution in disk specimens in radial direction were measured to evaluate the thermal fracture stress and thermal fracture energy. Work-of-fracture of the specimen was estimated from the total area of the fractured surface, and the elastic strain energy was calculated from the nth-power functional fitting of measured temperature distributions at fracture. Two types of ceramics were used for the experiments; alumina ceramic having higher strength, elasticity and thermal couductivity, and mica ceramics having lower strength, elasticity and thermal conductivity. Work-of-fracture in thermal fractured specimens had a mutual relation with elastic strain energy, and corresponded to approximately one third of the total elastic strain energy. Furthermore, according to the thermal shock damage resistance of ceramics, the fracture energy varied with temperature distribition. Therefore, thermal shock test by heating disk specimens is effective to evaluate the thermal shock damage resistance of ceramics.

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The measuring results of particle size distributions obtained by various equipments do not always agree, even if the same sample is measured. To clarify the agreement for each measuring principle, the results obtained by optimized and standardized sample preparation condition should be compared systematically. In this study, silicon carbide and silicon nitride as submicron non-oxide powder and boron nitride having flaky shape were used as common samples, and the agreement of measuring principles was investigated for each sample. The following results were obtained. (1) in the measurement of submicron powders, the position of the scatter of the distributions measured by different principle changes depending on the size distribution of the primary particle and the strength of the agglomerate. The scatter of the equipments is more remarkable than micron powders. (2) in the measurement of flaky shape samples, the effect of the shape on measured results can be explained by considering the orientation of the particles in the suspension.

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Composite ceramics of alumina mixed with up to 30 vol% titanium carbide whiskers were fabricated by hot-pressing at 1400 to 1700°C under 30MPa for 30 min. The mechanical properties of the hot-pressed bodies were studied. Dense composites with relative densities above 98% were obtained at 1600°C when the whisker content was up to 30vol%. The composite containing 10vol% whiskers and fired at 1500°C showed the highest bending strength of around 510MPa, which is lower than the maximum strength of alumina, around 650MPa. These composites are superior to monolithic alumina in high temperature bending strength and Vickers hardness. Increasing whisker content decreased the elastic modulus monotonously, but increased the fracture toughness from around 3.5MPa·m^1/2 for alumina to around 5.7MPa·m^1/2 for composite ceramics containing 30vol% whiskers.

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In order to recycle concrete wastes, a new processing method for solidifying pulverized concrete wastes has been developed using a hydrothermal hot-pressing method. The effect of addition of fresh cement was examined to further increase the strength of solidified concrete wastes. Hydrothermal hot-pressing tests were carried out at 200-250°C with the water content of 10-30 mass% under the pressure of 20MPa for 20 min. Fresh cement of 0-50 mass% was added to the mixture. It is shown that the formation of tobermorite improved the tensile strength. The tensile strength determined by a Brazilian test reached approximately 13MPa under the conditions; the temperature: 230°C, fresh cement content: 50 mass%, and water content: 30 mass%.

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The pyroelectric properties of highly c-axis-oriented lanthanum- and magnesium-modified PbTiO₃ (PLMT) thin films were investigated in detail by the method of measuring of static pyroelectric properties. The figures of merit F. M. for voltage responsivity of pyroelectric IR sensors showed higher values in the region of x=0.005-0.010 than those in other regions; in particular, the sample with x=0.010 exhibited the highest F. M. of around 1.05×10^-10C·cm/J, around 1.5 times as large as that of the PL10 (PLMT; x=0) sample. In conclusion, thin films with the composition of (1-x)Pb_0.9La_0.1Ti_0.975O₃+xMgO, where x=0.010, show a great promise as element materials for pyroelectric IR sensors.

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The thermal decomposition behavior of Ln-Co (1:1) cyano complexes and the composition of decomposition products have been examined. Decomposition of their CN-bridged structures proceeded on heating at about 300°C in air, generating amorphous phases containing carbonate complexes. For the complexes comprising La-Nd, submicron sized particles of perovskite-type oxide were formed (without single phase oxides Co₃O₄ and Ln₂O₃) from an amorphous phase by heating at about 620°C. For the complexes comprising Eu, Gd and Dy, a mixture of single oxides (Co₃O₄ and Ln₂O₃) and perovskite-type oxide was formed. The content of the perovskite-type oxide increased with the increase in decomposition temperature. For the complexes containing Ho and Yb the corresponding perovskite-type oxide could not be obtained even when the complex was decomposed at 1100°C.

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High-thermal-expansion ceramics consisting of nepheline (NaAlSiO₄) and leucite (KAlSi₂O₆) were prepared by sintering mixture of their powders. The ceramics obtained had the relative density of 70 to 90%, bending strength of 60 to 100MPa and linear thermal expansion coefficient of 15×10^-6/°C to 28×10^-6/°C from room temperature to 600°C. The thermal expansion coefficient of the ceramics increased with increasing leucite content.

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Thermal shock fracture resistance on several kinds of ceramics was evaluated by the rapid heating thermal shock test using disk specimens. The thermal shock resistance parameter R_c=σ_F/Eα (σ_F: Thermal fracture strength, E: Young's modulus, α: Thermal expansion coefficient) was obtained by measuring the temperature distributions in the disk at the fracture. The measured thermal shock resistance parameter R_c was compared with other thermal shock test data including water quenching test. Compatible data were obtained regardless of the difference between heating test or quenching test.

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The stability of an infinite-layer compound ACuO₂ (A=Sr, Ca) at high temperature was studied by molecular dynamics simulation. For SrCuO₂ the infinite-layer structure was well reproduced at 300K. However inspection of the simulated structure revealed that oxygen ions displaced from initially planar CuO₂ layer to the c-direction by ±19 pm alternatively. This structure was stable up to 1200K and transformed to an amorphous phase above 1300K. For CaCuO₂ the infinite-layer structure was unstable even at 300K. Simulations in which cation in A site was substituted revealed that large cation in A site is responsible for the stabilization of the structure, consistent with the experimental results.

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