Thermal conductivities of sintered aluminum borates were determined in the temperature range from room temperature to 873K by a laser flash method. The thermal conductivities decreased linearly with increasing porosity. By extrapolating these conductivities to zero porosity, the thermal conductivity of a pore-free sintered body was determined. The obtained thermal conductivity had a linear relationship with the reciprocal of absolute temperature. Although the thermal conductivity obtained here is for polycrystalline materials, the value is applicable to single crystals in the same temperature range. The porosity dependence of thermal conductivity is also discussed with several theoretical equations and observed pore structures.

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The composite silica gel which supported nanometer-size TiO₂ fine particles with platinum was prepared by the sol-gel method in order to obtain a high photocatalytic activity and to discuss the mechanism of photocatalytic hydrogen generation by TiO₂ fine particles in aqueous solution.
The heat-treated composite gel showed a hydrogen generation rate almost 4 times larger than that of the TiO₂ sol in aqueous ethanol solution. However, little hydrogen was generated from pure deionized water.
The photocatalytic activity of the composite gel is considered to be affected by both the surface condition and the crystalline phase of TiO₂ fine particles when the correlation among the changes with heat treatment in hydrogen generation rate, the amount of photo-generated Ti³⁺ ions and the structure of composite gel was examined. The superiority of the hydrogen photogeneration rate of the composite gel compared with a TiO₂ suspension system is attributed to its controllability of the crystallite size and the crystalline phase of semiconductor fine particles since they remain in a highly dispersive condition during heat treatment.

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The influence of temperature on elastic modulus and strength of 9mol% MgO-containing partially stabilized zirconia (Mg-PSZ) aged around 1100°C was studied. Elastic moduli on heating increased with increasing temperature after showing minimum values around 600°C. Elastic moduli on cooling monotonously increased with decreasing temperature. The strength of as-recieved specimen A have a maximum value around 200°C. The strengths of aged specimens on heating increased with increasing temperature after showing a minimum value around 600°C. On cooling, the strength of specimen B aged for 2h increased remarkably with decreasing temperature to a maximum value at 450°C, and then decreased remarkably. On the other hand, the strength of specimen C aged for 8h showed a constant value between 1000 and 400°C and decreased slightly below 400°C.

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Sialon composites composed of Y-α′-sialon and β′-sialon obtained by hot-pressing powder mixtures of Si₃N₄, Y₂O₃ and AlN, were annealed at 1850°C to investigate the thermal stability of Y-α′-sialon. The amount of Y-α′-sialon was reduced and it was transformed into β′-sialon. When the transformation proceeded, Y and N were excluded to grain boundaries and their concentration at grain boundaries increases with time. It is considered that these elements then diffuse to the remaining Y-α′-sialon and dissolve again, resulting in an increase in lattice constants (solubility) of the remaining Y-α′-sialon with time.

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Thermal shock fracture behavior of KZr₂(PO₄)₃ ceramic, which has a near-zero thermal expansion coefficient, was evaluated by the water-quenching test. The specimens having almost the same density, strength, Young's modulus, and thermal expansion coefficient, but different grain sizes, were prepared by adjusting the sintering conditions. The maximum temperature difference (ΔT_max), to which the specimens were subjected without failure in the thermal quench test, increased with decreasing grain size. KZr₂(PO₄)₃ ceramic composed of fine grains<3μm withstood the test without lowering of strength even when quenching from 1300°C into water was repeated 20 times. The grain size dependence of ΔT_max has been attributed to residual stress caused by the thermal expansion anisotropy. As a result, grain size and thermal expansion anisotropy were incorporated into the equation for the thermal shock resistance.

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Electrical anisotropy of dielectric and DC/AC conducting properties of single crystals of barium bismuth titanate (BaBi₄Ti₄O₁₅), which is a member of bismuth layer-structured ferroelectrics, has been studied and compared with those of polycrystalline samples. It was found that BaBi₄Ti₄O₁₅, when measured at 1MHz, showed about 6 times and 58 times higher dielectric permittivity in the direction parallel to bismuth layer (crystallographic a (b)-axis) than those in the perpendicular direction (c-axis) at room temperature and the Curie temperature, respectively. DC/AC conductivity showed a higher value in the direction parallel to the bismuth layer than those in the perpendicular direction. On the other hand, the activation energy for electric conduction in the direction parallel to the bismuth layer showed a lower value. Polycrystalline samples had intermediate properties of those of the two directions in single crystals. Complex impedance measurements also showed anisotropy in the dielectric and the DC conducting properties even for paraelectric phase. Thus, the bismuth layer was thought to act as an insulating and paraelectric layer in BaBi₄Ti₄O₁₅.

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Pressureless sintering of the SiC-AlN system with Y₂O₃ as a sintering aid was carried out. Composites with<50vol% SiC were densified to above 98% of the theoretical density in N₂ atmosphere of 0.1MPa at temperatures below 1900°C using commercial SiC and AlN powders. The densification behavior was investigated and analyzed on the basis of microstructural observation. The strength and deformation of the densely pressureless-sintered AlN and SiC-AlN composites were measured from room temperature to 1500°C by small punch testing. The sintered AlN and SiC-AlN composites showed no strength decrease at temperatures below 1200°C, whereas the SiC-AlN composites showed higher strength at room temperature and retained them to higher temperature. At 1500°C, plastic-like deformation was observed in the SiC-50 and 70vol% AlN composites. The microstructural observation suggested that the fine microstructure with a uniform and fine grain size in the SiC-AlN composites was a dominant factor responsible for the plastic-like deformation at high temperature.

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Porous calcium phosphate films could be formed on α-Al₂O₃ substrates by spray-pyrolysis technique. The use of calcium metaphosphate as a binder was effective to enhance the binding strength of calcium phosphate films to substrates. The films obtained by spray-pyrolyzing the starting solutions were heated at a temperature between 1000 and 1400°C for 5h. The crystalline phase of the heated films was mainly β-calcium orthophosphate. The thickness of this film was dependent on the spraying time and the pore sizes were about 15μm.

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An ion-exchangeable layered perovskite compound, Na₂La₂Ti₃O₁₀, was directly synthesized by a solid-state reaction. The crystal structure of Na₂La₂Ti₃O₁₀ was determined by electron diffraction analysis and Rietveld analysis for the powder X-ray diffraction pattern. The unit cell is tetragonal with a=0.383528 (7) nm, c=2.85737 (7) nm and Z=2 with the space group I4/mmm (No. 139). The structure of this compound is analogous to that of the Ruddlesden-Popper phases. The ionic conductivity of Na₂La₂Ti₃O₁₀ was not very high compared with those of niobate compounds, NaLaNb₂O₇ and NaCa₂NaNb₄O₁₃. Such a low ionic conductivity is due to the rigid rock-salt-type coordination around sodium ions located at the interlayer.

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Spherical amorphous monodispersed titanium dioxide particles were synthesized by hydrolysis of titanium-tetra-ethoxide (Ti(OC₂H₅)₄) in dilute ethanol solution and were hydrothermally treated using an autoclave. The amorphous monodispersed titanium dioxide particle were crystallized and many nano-sized particles of anatase single crystal produced in the particle by the hydrothermal treatment. The internal microstructure of the hydrothermally treated monodispersed titanium dioxide particle was homogeneous. The growth mechanism of the nano-sized anatase single crystal particles was discussed and a dissolution-reprecipitation mechanism was proposed.

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The water content in cement mortar and flowing water in concrete were measured with CFGFRP (carbon fiber-glass fiber-reinforced plastics) composites used as electrodes. The electrical resistance and conductivity of cement mortar and concrete were influenced by frequency, applied voltage and temperature. The frequency of 1kHz and applied voltage of 5V were used for measuring in the present study. The conductivity of cement mortar decreased with decreasing water content. The conductivity of cement mortar and concrete increased in short time with adsorbing or flowing water. CFGFRP composites are promising as electrode of intelligent concrete structures measuring both water content and flowing water.

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Thermal expansion behavior of a composite consisting of titanium diboride and zirconium carbide has been described. The specimen was a high density sintered body prepared from powders of zirconium diboride and titanium carbide by substitutional reaction sintering. As the density of the sintered body was very high, thermal expansion of this composite was measured. The average value of linear thermal expansion coefficient was 7.8×10^-6/K between 298 and 1173K, which agreed with the result from XRD analysis of a powder mixture of titanium diboride and zirconium carbide.

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Na₂O⋅2SiO₂ glass plates were leached in a buffer solution (pH 7) at temperatures between 16 and 44°C. Cracks in the form of a network appeared a few minutes after the start of leaching. The crack depth coincided with the thickness of the hydrated layer and was proportional to the amount of sodium leached out. The concentration of sodium remaining in the hydrated surface layer was about 20% regardless of leaching time. A formula was derived for the leaching rate of sodium by considering the effect of the increase in surface area due to crack propagation on the amount of sodium leached out. The experimental data on the leaching rates of sodium were consistent with the formula.

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Preparation and their properties of the precursors capable of forming variously shaped YBCO superconducting oxides were investigated. The precursors were prepared as viscous liquid or powder by the reaction of ethyl acetoacetate complexes of metals (M(etac)_n:M=Y, Ba, Cu; n=2, 3) with triethanolamine (TEA) under reflux of ethanol, followed by concentration of the solvent and heating in vacuo. The precursors were soluble in alcohols, chloroform and THF. Since good spinnability was observed for the liquids or molten solutions, continuous fibers, therefore, were prepared by melt-spinning of the powders. YBa₂Cu₃O_6.8 superconducting oxide of zero resistance temperature of 88.2K was obtained by heat treatment of the powders. A possible structure of precursor was estimated by the spectroscopic, elemental and GC analysis of the reaction products.

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Effects of wet air on the formation and thermal stability of 12CaO⋅7Al₂O₃(C₁₂A₇) were studied in atmospheres with controlled water vapor content. The formation process of C₁₂A₇ in fired products was examined by X-ray powder diffraction and the water included in 11CaO⋅7Al₂O₃⋅Ca(OH)₂(C₁₁A₇⋅Ca(OH)₂) was identified by means of Fourier transform infrared spectrophotometer (FT-IR). Anhydrous C₁₂A₇ was prepared in dry atmosphere at temperatures above 1150°C. On the other hand, C₁₁A₇⋅Ca(OH)₂ including hydroxide ions was formed at above 1000°C in flowing wet air and the humidity accelerated the formation of the hydrate. It was difficult to make the distinction of X-ray diffraction patterns between C1₂A₇ and C₁₁A₇⋅Ca(OH)₂, but the stretching vibration band of O-H at about 3560cm^-1 measured by means of FT-IR enabled to identify the hydrate. In a flow of dried helium gas, the hydrate C₁₁A₇⋅Ca(OH)₂ decomposed into 5CaO⋅3Al₂O₃(C₅A₃) with dehydration when it was heated in the temperature range of 1100 to 1250°C. At temperatures above 1250°C, C₅A₃ changed into C₁₂A₇. On the contrary, C₅A₃ changed into C₁₁A₇⋅Ca(OH)₂ by heating at about 1100°C in a flow of wet air.

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Monodispersed, spherical fine mullite powders were prepared by hydrolysis of Al-Si alkoxide in alcohol/dipolar aprotic solvent. The addition of dipolar aprotic solvent to Al-Si alkoxide/alcohol solutions caused precipitation of Al-Si double alkoxide emulsion. Acetonitrile was most efficient of all dipolar aprotic solvent for the formation of monodispersed fine mullite powders. Monodispersed fine mullite powders were obtained when the volume ratio of octanol/acetonitrile was 3:2. Synthesis factors such as reagent concentration, volume ratio of solvent and reaction temperature influenced the formation of monodispersed fine mullite powders. The Al₂O₃/SiO₂ ratio of as-prepared powders determined by ICP analysis was about 3:2. Powder X-ray diffraction showed that as-prepared powders were amorphous and crystallized to mullite at 1000°C. The spherical morphology was retained after the crystallization.

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The fracture behavior was investigated on autoclaved lightweight concrete (ALC) block samples, which were prepared from lime, cement and quartz sand at 180°C under the saturated steam pressure for 1 to 16h. After 1h autoclaving, the samples gave C-S-H as an initial product, which further reacted with quartz sand to form 1.1-nm tobermorite. The compressive strength increased from 2.0 to 5.7MPa with the formation of tobermorite, while the fracture energy G_F increased from 5.1 to 6.4N/m. The fracture behavior interpreted from the tension softening curves was strongly affected by the formation of tobermorite. Extended autoclaving increased the energy for the initial microcrack formation but resulted in brittle crack growth behavior.

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Y₂O₃-Al₂O₃-doped β-Si₃N₄ was sintered at 1700 to 1900°C for 4h in 1 and 10MPa N₂ to investigate the effect of amount of the additives on sinterability, strength, fracture toughness and microstructure. Dense materials were obtained by firing the compositions for 6-10mol% additives at 1700°C, 4-6mol% at 1800°C, and 1-4mol% at 1900°C. Rod-like β-Si₃N₄ grains developed during firing at 1900°C to increase the fracture toughness, strength, and Weibull modulus.

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Epitaxially grown Pb(Zr, Ti)O₃ [PZT] films were deposited on (100) MgO substrates by CVD and the effects of deposition parameters on the epitaxial growth of the films were investigated. The films consisting of PZT single phases were deposited from about 0.4 to 0.5 of Pb/(Pb+Zr+Ti) and the epitaxially grown film was obtained near 0.5 of Pb/(Pb+Zr+Ti). Epitaxially grown PZT films were deposited over wide deposition conditions; 600-700°C of the deposition temperature, 1.1-6.7kPa of the total gas pressure and 64Pa-1.1kPa of the oxygen partial pressure.

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Oxidation behavior of a spinel (Mg₂Al₄O₈) composite containing 30vol% SiC whisker has been studied at 1300°C in air. The weight gain curve obeyed the parabolic law up to the oxidation time of 120h, indicating that the oxidation rate was controlled by diffusion of oxygen in the matrix. Bending strength of the oxidized composite increased appreciably with the oxidation time up to 5h but degraded to 70% of the initial strength after the oxidation for 120h. Grain sizes of crystals and cracks formed in the oxidized layer became larger with the oxidation time. Periclase (MgO) and a small amount of α-cordierite (Mg₂Al₄Si₅O₁₈) as well as the spinel and β-SiC were observed in the layer.

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Morphology of the in-situ growth of SiC in the carbon based composite bodies consisting of β-SiC and B₄C particles were investigated. To observe correctly the morphologies of grown SiC, the matrix carbon in the polished surface of the composites was burned off with oxygen plasma at low temperatures. A great part of SiC grains were found to be disks showing irregular outlines and rugged surface. The rod shape grains of SiC were also observed in the fracture surface of the composites, of which cross sections revealed various morphologies such as triangle, rectangular and irregulars.

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