Monolithic SiC and SiC-AlN composites were prepared by liquid-phase sintering. Polytypes of SiC, transformation of its polytypes and microstructure of the sintered materials were investigated. The SiC-AlN composites were composed of the 2H phase with dispersed SiC grains. The microstructure of sintered monolithic SiC varied depending on the polytypes of the starting SiC powders, α and β, as well as on the sintering conditions. The SiC-AlN composites showed the same microstructure irrespective of the initial phase of SiC. The 2H phase was a SiC-AlN solid solution and had a spherical grain shape, and the 4H-SiC had a platelike shape.

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Influence of residual porosity on the flexural strength and fracture toughness of pressureless-sintered α-SiC ceramic with controlled microstructure, characterized by equiaxed-grain and a mixture of equiaxed/plate grains were investigated together with the trend of σ-K_IC behavior. Both the flexural strength and the fracture toughness of the SiC ceramics showed an exponential decrease with porosity, but the extent of the porosity dependence was dependent on the microstructure; a higher porosity-dependent strength was seen for the equiaxed-grain microstructure, while the dependence became weak for the mixed one. The trend of flexural strength-toughness dependence appeared to be positive and became more pronounced for the SiC ceramics with mixed-grain morphology, suggesting a strengthening effect due to the presence of reinforced platelike phase. Crack deflection appeared to be the principal mechanism for toughness improvement in the SiC-Al₂O₃-Y₂O₃ ceramics.

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SiC whiskers were coated with Ti, Al, Y or C by RF-sputtering or plasma CVD in order to modify the interfacial strength between whisker and matrix. These whiskers with various coatings were used to fabricate Si₃N₄ matrix composites. The mechanical properties of the composites were correlated to the interfacial strength (τ) between whisker and matrix, which was measured for the composites reinforced with SiC continuous fibers with the same coatings as the whiskers. The samples with low τ (5-10MPa) showed higher fracture energy than those with high τ (90-100MPa), while the high τ samples exhibited better fracture toughness and strength. These results suggest that whiskers with low τ affect the crack wake by pull-out or crack bridging, while those with high τ affect the crack tip before crack propagation starts.

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Accurate refractive indexes of Na₂O-GeO₂ glasses containing 5-30mol% Na₂O were measured in the wavelength range of 0.334 to 1.710μm using the minimum deviation method. The influence of glass structure on the refractive index and its dispersion has been discussed in terms of the number of the oxygen ion in a unit volume and the apparent refractivity of the oxygen ion. With the addition of Na₂O, the refractive index n_d increased at 5<Na₂O<15mol%, showed a maximum around 15mol% Na₂O, and decreased with further addition. The Abbe number v_d decreased monotonically. The variations of n_d and v_d with Na₂O content were related to the oxygen coordination number of Ge ions.

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The sinterability and thermal conductivity of Y₂O₃ doped AlN powders with diverse specific surface areas (42-2.9m²g^-1) and oxygen contents (0.2-2mass%) were evaluated. It was found that sintering of fine powders induces the densification at lower processing temperatures, and for raw AlN powders with specific surface area larger than 20m²g^-1 and oxygen content higher than 1.1mass%, densified specimens were obtained by sintering at 1650°C for 4h. However, the resultant thermal conductivity of AlN specimens fabricated from fine powders was extremely lower than the theoretical thermal conductivity of AlN, at a level of 80Wm^-1K^-1. The deterioration of the thermal conductivity has been attributed to the agglomeration of primary particles, and to subsequent formation of oxygenrelated defect in grown AlN grains occurring at an early stage of sintering.

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Toughening and strengthening effects, addressed as intrinsic material properties, are discussed in the case of ceramic-ceramic and ceramic-metal nanocomposites according to fracture mechanics argument. The theoretical approach followed is conceptually the same as that usually adopted for explaining the mechanical behavior of brittle metals, polymers or other monolithic ceramics. The theory cannot substantiate any tangible synergistic effect by nanosized ceramic dispersoids, it is worked out either in terms of toughness or in terms of strength. It is suggested that the improved mechanical properties, as reported in some ceramic-ceramic nanocomposites, may be related to residual microstresses stored into the material after the sintering process or even be affected by extrinsic factors related to the specimen preparation and/or to the testing procedure. Addition of metallic nanodispersoids seems to be a potentially suitable way to obtain a 30-40% increase in the inherent material strength, although a much larger dispersoid size may be required for gaining better toughness. The present theoretical treatment, although simplified in order to obtain solutions in close form, may provide some general and physically sound directives for the development of ceramicmatrix composites. This study intends to provide a theoretical counterpart to recent empirical practices in the field which are lacking in scientific logic.

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The effect of heat treatment on electrical properties of a quartz glass prepared by flame fusion was investigated and the following results were obtained. (1) When the glass was heated at 1000°C, the electrical conductivity increased irreversibly with time at first and then decreased. (2) The increase in conductivity went on uniformly in the interior of the glass. On the other hand, the decrease in the conductivity started at the surface layer of the glass and spread to the interior. (3) The glass approached finally a state in which the electrical conductivity changed reversibly between high and low conductive states depending on the secondary heat treatment conditions. Such irreversible and reversible changes can be explained by considering the chemical equilibrium between OH group and molecular water in silica glass, outward diffusion of molecular water and protonic conduction.

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The n-type (Bi₂Te₃)_0.95(Bi₂Se₃)_0.05 was synthesized by modified pulverized and intermixed sintering elements (PIES) method and its figure of merit was evaluated to be 1.8×10^-3/K (25°C). The milling mechanism obeyed to the Kick's law and Tanaka's equation. No anisotropy of electrical transport phenomena in thermoelectric properties was observed, because the microstructure consisted of non-oriented grains due to use the milling powders of Bi, Te, and Se as starting materials. Thermal conductivity was smaller than that of single crystal by the large phonon scattering due to small grain, and Seebeck coefficient and resistivity were smaller than that of single crystal due to imcompletely formate solid solution and oxides of sintered body.

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For evaluation of thermal shock resistance of ceramics by the quenching method, it is important to estimate the thermal stress distribution and history in the specimen. Thermal stress under quenching can not be measured directly in the experiment. Therefore, the temperature distribution generated by quenching was numerically calculated and the transient thermal stress distribution was estimated for the ceramic disk. The calculated maximum thermal stress and the time required were proposed as the correlative equations, respectively. The former equation of maximum thermal stress is useful to evaluate the thermal shock resistance of ceramics. The fracture time can be estimated by the latter equation of the time at the maximum thermal stress. If the experimental fracture time agrees with the calculated one, it is considered that the fracture occurs only by the thermal stress. Furthermore, these equations were compared with those of slab specimens to discuss the differences in thermal stress history and distribution. The effects of temperature dependence of thermal constants on thermal shock resistance have been evaluated. The strain energy accumulated in the disk during the fracture process was also calculated by the tensile thermal stress at the surface.

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Graphite powder was coated with a chelate compound of aluminum and heated at 500°C in air to prepare Al₂O₃-coated graphite powder. The sedimentation volume and the heat of immersion in water indicated that the wettability of the graphite powder by water was improved by the Al₂O₃ coating. The oxidation resistance of Al₂O₃-coated powder was higher than that of the uncoated one. The first and second adsorption isotherms of water vapor indicated that H₂O vapor was adsorbed not only physically but also chemically on the Al₂O₃-coated layer. The specific surface area by N₂ and the second adsorption isotherms of water vapor suggest that the layer has micro pores<0.4nm in diameter.

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One of the alkoxyl groups of zirconium tetrabutoxide was allowed to react with carboxylic acids of various chain lengths such as acetic acid, hexanoic acid or decanoic acid and converted to a carboxylato complex. The butoxy groups of this compound were hydrolyzed with alcohol containing water to form a zirconium carboxylato complex. This zirconium carboxylato complex was then subjected to pyrolysis at temperatures up to 1100°C to form ZrO₂. It was found that the amounts of tetragonal ZrO₂ crystals formed increased as the carbon chain length of the carboxylato group of the zirconium carboxylato complex increased. In terms of morphology, no carboxylato complexes consisting of 2 or 6 carbon chain lengths were observed, however, monodispersed spheres of 1-2 micronmeter in diameter were formed when the carbon chain length was 10.

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Vacuum-pressure-assisted slip casting was studied to develop a forming method for the fabrication of silicon nitride engineering ceramics with complicated shapes. A well-dispersed and high solid-content slurry was prepared, the consolidation kinetics of the slurry was studied by using a vacuum-pressure-assisted slip casting system with a porous resin mold, and the mechanical properties of sintered bodies were investigated. From a slurry containing 67mass% solid (92mass% α-Si₃N₄, 3mass% Al₂O₃, 5mass% Y₂O₃), 0.01mass% deflocculant, 0.1mass% defarmer, 4mass% binder, green bodies with densities of 1.55-1.62g/cm³ were prepared in the pressure range of 0.1-0.7MPa. The green body density gradually decreased with increasing slip casting pressure, while the density of sintered bodies was independent of the pressure. Based on the Adcock and McDowall's equation, calculated values of the rate of cake buildup (k) were well coincident with observed values by taking into account the green body density. The silicon nitride sintered at 1775°C for 10h at 0.9MPa N₂ pressure showed a density of 3.25g/cm³, a flexural strength of 1.1GPa, and a Weibull modulus of 14. It was found that the vacuum-pressure-assisted slip casting was useful for the forming of silicon nitride.

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CrSi₂ powders were prepared by the solid-state reaction between chromium and silicon powders with 0.1-10.0 mass% chlorides at 650-900°C for 2h in an argon atmosphere, and the effect of addition of chlorides on the reaction temperature and particle size of the system was studied. When the atomic ratio Si/Cr in the starting materials was 2.0 in the presence of 5.0 mass% of KCl or 1.0 mass% of NaCl, the single phase of CrSi₂ was obtained at 900°C, 400°C lower than without the additives. When the chloride was not added, the product formed at 1300°C exhibited particles with a grain size of about 30μm in diameter. When KCl or NaCl was added, the product formed at 900°C exhibited particles with a grain size of about 1μm in diameter. The lattice constants of the CrSi₂ formed in the presence of chlorides were as follows: for 5 mass% KCl: a=0.4424 (2) nm, c=0.6360 (2) nm; for 1 mass% NaCl: a=0.4423 (2) nm, c=0.6359 (2) nm.

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Oxidation resistance of sintered TiB₂-xB₄C composites (x=0.3, 0.5, 0.7, 1.0) prepared by high pressure sintering was examined in air for 1-50h from room temperature to 1400°C. The sintered composites exhibited comparatively high oxidation resistance in air up to 600°C with formation of traces of TiO₂ and B₂O₃. A protective film composed of solid TiO₂ and liquid B₂O₃ was formed in the temperature range of 700 to 800°C and prevented further oxidation of the bulk composites. In the temperature range of 800 to 1000°C, the oxide layer thickness increased with increasing oxidation time and TiB₂ content in the composites. Rapid oxidation of the sintered composites occurred at temperatures above 1000°C.

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Pitch- and PAN-based semiconductive carbon fibers were prepared by final heat treatments at 400 to 900°C in pure N₂ (O₂ concentration<10^-10%) and in O₂-mixed N₂ (O₂ concentration=0.2%). Electrical resistivity at 20°C, thermistor constant and resistivity changes by applying high-voltage pulses were measured and compared with two kinds of carbon fibers. Below the heat treatment temperature of 700°C, the pitch-based fibers showed higher resistivities than the PAN-based fibers. The difference in resistivity of these fibers increased by heat treatments at lower temperatures and in pure N₂. The pitch-based fibers showed smaller thermistor constants than the PAN-based fibers with the same resistivity, but those values became closer wthen heattreated in pure N₂. Results of XPS showed that oxygen concentration on fiber surfaces was higher in fibers heat-treated in O₂- containing N₂ and that the effect of heat treatment atmosphere was evident in deeper region from the surface in the pitch-based fibers. It was assumed that the O₂ concentration in atmosphere influences the electrical properties mainly at the surface for PAN-based fibers and in the core for pitchbased fibers.

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An infrared radiation heating method was proposed previously as a new technique for estimating thermal shock resistance of ceramics, and a concept of thermal shock fracture toughness and stress intensity factors for a disk-shaped specimen with an edge crack was expressed. The method uses a thin circular disk which is heated by infrared ray at the central area with a constant heat flux. The technique makes it possible to evaluate the thermal shock strength, R_1c, and thermal shock fracture toughness, R_2c, directly from the electric power charged and the time to fracture, despite the fact that R_1c and R_2c consist of the thermal properties of the material tested. In this report, the thermal shock strength and the thermal shock fracture toughness for float glass at room and high temperature are evaluated by the infrared radiation heating technique, and shown as a function of temperature when the specimen failures. The thermal shock parameters obtained experimentally are also compared with the estimated values which are calculated by combining the temperature-dependent mechanical properties of float glass.

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Utilizing blast furnace slag, porous light weight materials have been prepared at room temperature in order to apply them as heat insulators of general purpose for buildings and residences. For 28-d age specimens prepared from slurries of blast furnace slag mixed with hemihydrate and portlandite, physical properties such as thermal conductivities, bulk densities, porosities and compressive strengths were measured, each showing 0.22-0.30W/m·K, 780-1100kg/m³, 45.2-66.6% and 16-81MPa depending on W/S (water/solid) ratio. These results indicate that present materials have a potential to contribute to saving air conditioning energies as well as reducing green house effect on earth, especially for high W/S materials.

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Multilayer capacitors with silver internal electrodes and low-temperature firable glass composite materials were fabricated. By short firing of 10-min-hold-time and glass addition to the internal electrodes, devices free from dispersion of silver and structural defects were obtained. Studies on the effect of composition of internal electrodes and firing conditions revealed that the Q factor at high frequency depends on the density of the silver electrode and the smoothness of the interface between the internal electrode and the dielectrics. The obtained capacitor was in the level of practical use in reliabilities, and the Q factor at 1GHz was more than two times as much as that of conventional capacitors with palladium internal electrodes.

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Highly oriented AlN thin films were prepared on polycrystalline MoSi₂ substrates by rf magnetron sputtering. The films responded to mechanical impact and produced voltage. The maximum produced voltage increased almost linearly with the impact intensity. Furthermore, the capacitance of the films increased almost linearly with applied pressure, indicating that the films can measure the pressure. The films responded to thermal shock. These results suggested that the films possessed various functions like human skin.

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Beta-Si₃N₄ powder made by the imide-decomposition method was gas-pressure sintered at 1800°C for 4h in 1MPa N₂ gas. This material had a microstructure of “in-situ composite” and excellent mechanical properties (strength: 780MPa, fracture toughness: 7.5MPa·m^1/2), whereas β-Si₃N₄ powder made by the silicon nitridation method required sintering temperatures higher than 1900°C to attain similar microstructure and mechanical properties. β-Si₃N₄ powder by the imide-decomposition method had excellent properties for grain growth at low temperatures.

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The viscosities of 70mass% alumina suspensions retaining poly (acrylic ammonium) (PAN) or poly (30% methyl acrylate-70%acrylic ammonium) (PAM) were studied. The viscosities of suspensions retaining PAN showed two minima, the first at 0.60% PAN and the second at about 0.90%, and a maximum between the minima. This maximum viscosity moved to high content side of PAN and gradually decreased with an increase in milling time. While, the viscosities of suspensions retaining PAM showed only the first minimum. This difference between the viscosities of suspensions was explained, based on the different states of PAN and PAM adsorbed on the alumina particles.

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A new punching method of thin glass plates (t=0.15-0.20mm) was developed by using a hot die in a punchless punching technique. The present simple punching technique realizes the formation of holes (1-15mm in diameter) as well as the formation of many holes by a single operation.

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