Properties of (20-30)mol% CeO₂-(16-23)mol% Al₂O₃-(47-62)mol% SiO₂ glasses prepared in an atmosphere of N₂ have been investigated. Experimental results showed that the glass transformation temperature, dilatometric softening temperature and transmittance in the visible region decrease with increasing ceria content; and that the thermal expansion coefficient and microhardness increase with increasing ceria content. The cerous ions in cerium aluminosilicate glasses exhibited a broad fluorescence spectrum with a large Stoke shift at 450nm from the excitation spectrum peak of 366nm. The fluorescence peaks shifted to the shorter wavelength but cutoff wavelength of ultraviolet spectra shifted to the longer wavelength as cerium aluminosilicate glasses were prepared in air instead of in N₂ for the specimen of the same composition.

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The effect of urea addition on the formation of hydroxyapatite (HAp) through the spray-pyrolysis technique was examined. The crystalline phases of the powders prepared from the spraying solution without urea were HAp and a small amount of β-tricalcium phosphate; however, only carbonate-containing HAp was formed from the solutions with urea concentrations of 1.00mol·dm^-3 or higher. The SEM observations showed that the particle size of the as-prepared powder decreased with increasing urea concentration in the spraying solution. This reduction of the particle size may be due to the foaming action of CO₂ generated by the decomposition of urea. The relative density of the sintered body which originated from the solution with an urea concentration of 5.00mol·dm^-3 was comparable to that from the calcined and crushed powder which was obtained by spray-pyrolysing the solution without urea. The calcining and crushing operations before the fabrication of the sintered body may be omitted when the powders are prepared from starting solutions containing some urea.

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Barium titanate fine particles with average particle sizes from 20 to 90 nm were prepared by a hydrothermal method using titanium tetrahydroxide gel and barium hydroxide. The particle size was inversely proportional to the Ba/Ti atomic ratio in the starting material, while it was independent of temperature in the narrow range from 70 to 150°C. For the explanation of these findings, we proposed the following mechanism for the formation of barium titanate fine particles, i.e., the nuclei of barium titanate form via the reaction of titanium tetrahydroxide gel with barium hydroxide and then grow. In these particles, there were many lattice defects in the form of hydroxyl groups and barium vacancies, and their concentration increased with decreasing particle size. We explained this result using the model that a particle can be divided into two parts: a defective surface layer with many defects and the bulk with fewer defects. The crystal structure of barium titanate particles was cubic with an expanded lattice (a-0.402nm) independent of particle size. This result indicated the possibility that the lattice defects influenced the crystal structure.

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Si₃N₄/SiC-chopped-fiber composites with various amounts of SiO₂ at the grain boundary were fabricated by hot isostatic pressing (HIP). The SiC fibers (average diameter 130μm) were chopped with high aspect ratio and randomly dispersed in the matrix. Emphasis was placed on characterizing the fracture properties of the composites in comparison with the Si₃N₄ matrix material. A carbon layer of about 3μm, deposited on the surface of the fibers, was found to be very suitable for enhancing the pull-out process during fracture extension. As a result, catastrophic fracture from notches or pre-existing cracks could be avoided and the work of fracture (WOF) of the composite materials displayed values about 7-8 times higher than that of the matrix (i.e., ≈80J/m²). However, some physical limitations mainly related to the stereological arrangement of the fibers in the matrix, made the critical stress intensity for crack propagation (K_IC) of the composites almost the same as that of the matrix, independently of the presence of the SiC fibers and the added amount of SiO₂.

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Electric field dependence of the strain characteristics on the (Pb, Ba, Sr) (Zr, Ti, Sn, Nb)O₃ compositions were investigated. It was found that the measured strain (δ) increases with increasing applied DC electric field. The δ was larger than the strain of calculated value (δ_cal) from multiplying the piezoelectric constant (d₃₁) by the applied DC electric field (E). The difference strain (δ_p) between δ and δ_cal increased with increasing applied DC field. On high DC electric field, the δ_p was saturated with compositions near the morphotropic phase boundary and the rhombohedral structure. We deduced that δ and δ_p were involved with the electric field dependence on rotation of domain which was measured by XRD analysis. These results indicated that the δ_p was caused by rotation of domain. The electric field dependence on the change of δ in the durability test, under repetitious DC electric field, was investigated. Higher applied DC electric field produced larger change of δ_cal and decreasing the δ_p. We found that the increase of δ_cal and the decrease of δ_p were caused by accelerating the polarization.

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Si₃N₄ ceramic specimens were ground under different conditions with high-speed (wheel speed: 55m/s) and speed-stroke (table speed: 45-90m/min). The grindability was evaluated by grinding force, specific grinding energy and grinding ratio in comparison with conventional surface grinding. The strength degradation and surface roughness of ground workpieces were examined. The main results are summarized as follows. (1) This grinding conditions showed lower normal grinding force and specific grinding energy in a higher stock removal rate. And, the strength degradation and the surface roughness were not changed significantly even by increasing stock removal rate. (2) The lower normal grinding force and specific grinding energy were caused by a lower mean value of the maximum grain depth of cut. (3) This grinding conditions showed lower specific grinding energy in increasing stock removal and higher grinding ratio.

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Remarkable improvement in the magnetic shielding property of Bi(Pb)-Sr-Ca-Cu-O superconducting tubes, which were prepared by sintering rolled Bi(Pb)-Sr-Ca-Cu-O green sheets, has been achieved by applying intermediate cold isostatic pressing between the sintering treatments. The magnetic shielding property was increased from 4.0 to 7.0 mT by this modified process. Furthermore, the time dependence of the trapped magnetic flux density was changed and the relaxation rate decreased also.

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Sr_0.3Ba_0.7Nb₂O₆(SBN30) compacts with 1mol% V₂O₅ addition were fabricated at relatively lower temperatures by liquid phase sintering. A considerable elongation and coarsening of grains were observed after prolonged sintering at 1200°C. The ferroelectric properties were improved by the addition of V₂O₅: sharpening of the dielectric peak and shift in Curie temperature from 175 to 225°C. The modified ferroelectric properties might be attributed to decrease in the internal stress and compositional fluctuation with coarsening of grains. The pyroelectric coefficient of V₂O₅-added compacts (1200°C, 14h) at room temperature was 8.0×10^-5C/m²·K.

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A numerical simulation of crack bowing and deflection was performed on glass matrix-alumina particulate composite to evaluate the effects on these toughening mechanisms of composite and was compared with the experimental data of previous works by the authors. The numerical simulation revealed that a crack deflection was predominant in the fracture process of glass matrix-alumina particulate composite and that the crack bowing hardly emerged. If it is assumed that the crack extended into an alumina particle, the crack bowing emerges. With an increase in the difference of the fracture toughness between the particles and the matrix, the toughening by crack bowing becomes more effective and is more effective than that by crack deflection. Under the assumption that the interfacial precipitation promotes the crack bowing, the results of the numerical simulation were in agreement with experimental data of the present authors.

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The long-term variations in the resistivity of SnO₂ films in air containing water vapor or reducing gas (denoted as wet air or test gas, respectively) were investigated quantitatively. Analyses of electronic properties, weight increase, film structure and chemical bonding condition of thin films showed that the resistivity increase in wet air and the decrease in the test gas were caused by a decrease and an increase in amount of oxygen vacancy in the lattice, respectively, accompanied with a change of carrier concentration.

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Release of water from hydroxyapatite (HAp), partially stabilized zirconia (PSZ) and mixture of HAp and PSZ powders at elevated temperature has been measured by gas chromatography. These powders were heated at a constant heating rate of 2°C/min up to 1400°C in helium and the released gas sampled every 15min. At temperatures ranging from 160 to 190°C PSZ released weakly absorbed water and the released water diminished with increasing temperature. Both HAp powder and the mixed HAp/PSZ powder showed four water release peaks during heating in the whole temperature range. The first peak in the temperature range from 160 to 190°C was from the weakly absorbed water as in the PSZ powder. The second peak, which appeared between 200 and 1000°C for HAp and 200 and 600°C for the mixed powder, was attributed to the strongly bound water. The third one, which was found only in mixed HAp/PSZ powders, was of dehydroxylation of HAp which caused transformation into oxyhydroxyapatite (OHA). In the case of HAp powder, no peak was observed for dehydroxylation of HAp by gas chromatography, but infrared spectra showed the dehydroxylation by the existence of OH^- absorption and it has been confirmed that it occurred above 1000°C. The last peak indicates the decomposition of HAp into α-TCP which occurred above 1150 and 1000°C for the HAp and for the mixed powder, respectively. After this decomposition, cubic zirconia and CaZrO₃ were also detected in the mixed powder by XRD. The PSZ mixed in HAp enhanced the decomposition of HAp, as well as evolution of water, and had an effect of lowering the temperatures of HAp decomposition and releasing the strongly bound water on HAp.

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We have investigated thermoelectric properties and I-V characteristics of the sintered n-type iron disilicide, Fe_0.95Co_0.05Si_2.00. Partial oxidation of the surface to form an oxidized-layer/semiconductor junction was found to increase both Seebeck coefficient and resistivity at room temperature to 700°C. I-V characteristics of this junction obeyed an equation of the Poole-Frenkel type emission, indicating formation of an electronic potential barrier by the oxidized layer, Fe-O/SiO₂. It is considered that increase in Seebeck coefficient and resistivity are due to the potential barrier.

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Load-displacement curves and fracture behavior of individual ceramic granules were investigated by compression test. Three types of load-displacement curves were recognized for the granules: Granules of Al₂O₃ (A) showed elastic deformation and were ultimately broken, while no breaking of granules was observed for SiC and Si₃N₄ which showed elasto-plastic and plastic deformation, respectively. Surface and inner structures of green bodies prepared by cold isostatic pressing (CIP) were observed to relate data from mechanical characterization of individual granules and the macroscopic compaction behavior. No deformation of granules was observed in compacting some Al₂O₃ with a CIP pressure of 340MPa, while SiC and Si₃N₄ granules were deformed easily under a CIP pressure of 100MPa and 25MPa, respectively. It is discussed that load-displacement curves of individual granules in compression test can be closely related to the macroscopic compaction behavior of ceramics.

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The morphological control of calcium carbonate hexahydrate and its dehydrate was investigated. Synthetic calcium carbonates were characterized by means of X-ray diffraction pattern, thermal analysis (TG-DTA), infrared spectrum and scanning electron microscopic observation. The hexahydrate was synthesized by aging amorphous calcium carbonate which formed by adding aqueous ammonia into calcium hydrogen carbonate solution at 0-9°C. The crystal shape and particle size of the hexahydrate were remarkably affected by synthetic conditions such as temperature (0-9°C), calcium ion concentration (2.94-11.34×10^-3mol·dm^-3) and stirring speed (150-250rpm). For example, the particle size of hexahydrate having hexagonal platelike crystals was controlled to approximately 5-25μm below 3°C. The hexahydrate unstable above room temperature was easily changed to spherical vaterite at 30-60°C and to needlelike aragonite above 90°C by dipping the hexahydrate in water at 30-100°C. Moreover, an amorphous calcium carbonate hydrate containing 5% methoxyl group in skeleton structure of original hexagonal platelike particles was formed by dipping the hexahydrate in methanol for 1min. This compound was converted to hexagonal platelike calcite by heating at 300°C.

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Thermal conductivity of mullite-zirconia composites was measured. Since the thermal conductivity of zirconia is smaller than that of mullite, the conductivity of composites gradually decreased with the addition of zirconia up to 30vol% into mullite, which is consistent with the results estimated from the Eucken's equation. However, it was remarkably lowered with the further additions and the minimum value, 3.26W·m^-1·K^-1, was attained at about 50vol% of zirconia fraction. In the ZrO₂-rich composites, on the other hand, a small decrease in conductivity compared to that of ZrO₂ was found in spite of the addition of higher conductive mullite. It has been supposed that the reaction occurred between yttria stabilizer and silica and/or alumina from mullite during sintering and it resulted in the formation of a glassy phase at the grain boundaries, which was responsible for the decrease in thermal conductivity.

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The effects of UV-irradiation on the properties of Al₂O₃ gel films obtained from Al(O-sec-Bu)₃ chemically modified with benzoylacetone have been studied. These gel films showed an optical absorption band at around 325nm characteristic of the π-π* transition in the chelate ring. The irradiation of UV-light of 365nm on the gel films dissociated the chelate ring and simultaneously decreased the solubility of the gel films in acetone solutions containing HNO₃. This finding was successfully applied to the fine patterning of Al₂O₃ films. The gel films were irradiated with UV-light and then leached in HNO₃-acetone solutions, followed by the heat treatment at 400°C to form finely patterned Al₂O₃ films on a variety of substrates.

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Polycrystalline bodies of La_2-xSr_xMnO_4+δ (1.0≤x≤2.0) with a K₂NiF₄-structure were prepared by a standard ceramic method. Lattice parameters, electrical conductivity and Seebeck voltage were measured. Furthermore, optical absorption spectra were recorded to obtain information on changes in the electronic structure in the vicinity of the energy band gap. Changes in lattice parameters were attributed to the disappearance of Jahn-Teller distortion of MnO₆-octahedra upon Sr-doping. The results suggested that holes doped in the present system were mainly localized on manganese ions. The temperature dependence of electrical conductivities of all the samples was almost Arrhenius-type. Seebeck voltages and optical absorption spectra changed drastically in the composition ranges of 1.0<x<1.2 and 1.6<x<2.0. It was suggested that the electronic structure near the energy band gap changed drastically in those composition ranges.

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The transition liquid-phase sintering is assumed to be a dominant densification mechanism of β′-o′ sialon. The liquid is formed by the reaction between silicon nitride, alumina and oxidized layer on the surface of silicon nitride particles. To study the effect of heating rate on densification of β′-o′ sialon, green compacts of a silicon nitride powder and boehmite sol were prepared. The density of sintered β′-o′ sialons increased with increasing the heating rate. From the above result, it was considered that the transition liquid phase formed by the sintering with a high heating rate survives at a higher formaion temperature than the case with a low heating rate.

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Pseudoboehmite coating films containing dispersed gold nanoparticles were prepared by sol-gel method. A pseudoboehmite sol was prepared by refluxing a mixture of aluminum tri-sec-butoxide and hydrochloric acid, and then tetrachloroauric acid tetrahydrate was dissolved in the resultant sol. Gel films were deposited on slide glass substrates by spin-coating, dried at 120°C, and exposed to hydrazine vapor at room temperature in order to precipitate gold particles in the films. Transmission electron microscopic observation of the coating films revealed precipitation of aligned, elongated gold nanoparticles of aspect ratios of 2-4. The optical absorption due to surface plasma resonance of gold particles, however, did not show any dependence on the direction of polarization, implying that the elongated gold particles are aligned only in a microscopic region.

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