As an important oxygen storage material, ceria-zirconia solid solution is widely used in automotive three-way catalysts. For the Ce-Zr solid solution being usually used with a noble metal, the evaluation of oxygen storage capacity (OSC) should be conducted with the Ce-Zr solid solution loaded with a noble metal. The measured OSC of noble-metal-loaded Ce-Zr solid solution consists of two parts: the stored oxygen within the solid solution itself and the adsorbed oxygen on the loaded noble metal particles. Therefore, it is very necessary to clarify the influence of metal loading on the measured OSC in order to ascertain the exact OSC of the solid solution itself. In this research, the authors attempted to clarify the above issues by characterizing the OSC performance of Ce-Zr solid solutions with platinum (Pt) loading from 0.0001-10 mass%. We found that increasing the amount of Pt loading increases the oxygen storage and release rates and that increasing the temperature also increases the oxygen storage rate, although the oxygen release rate is not affected by increasing the temperature. The apparent OSC reached saturation over a certain amount of Pt loading and temperature. The saturated OSC increased with increasing temperature.

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High-temperature strength, fracture behavior and microstructure were observed for monazite-coated alumina fiber-reinforced alumina matrix composites hot-pressed at 1200-1300°C. The composites with 27-41 vol% alumina fiber showed no significant change in strength at 25-1100°C. However, the strength of the composites decreased markedly at a test temperature higher than 1100°C. The composites hot-pressed at a temperature lower than 1250°C fractured in a pseudoductile manner in the test temperature range from 25°C to 1100°C. Young's modulus of the elastic region decreased with increasing test temperature. These composites showed larger deformation at a test temperature above 1100°C. On the other hand, the composites hot-pressed at more than 1250°C fractured in a brittle manner at 25°C-1200°C of test temperature. The fracture energy of the composite increased with increasing test temperature and decreased with sintering temperature.

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A novel approach to fabricating highly-oriented, nm-scale potassium titanate K₂Ti₆O₁₃ rod arrays on titanium substrates was demonstrated. The fabrication process was template-free, and simply involved coating the titanium substrates with pulverized potassium metaborate and its derivatives, and subsequent heating at 700°C for 5 h. When the samples were soaked in hot water, the coating layers were readily removed, leaving an array of titanate crystallites on the titanium substrates. Even the slightest change in the composition of the potassium borates resulted in various microstructures, while K₂O•1.03B₂O₃ yielded highly-oriented nanorod arrays of K₂Ti₆O₁₃. Bioactivity of the as-achieved nanorod arrays was proved by the deposition of apatite in simulated body fluid (SBF: Kokubo solution). When soaked in SBF, the K₂Ti₆O₁₃ nanorod arrays deposited apatite within one day accompanying the release of potassium ions from the crystallites into SBF and the arrays were covered with apatite layers in three days. Ion exchange between the potassium ions in the crystal and calcium ions in SBF is proposed as the mechanism operative to favor the deposition of apatite.

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Orientation structure of particles was evaluated quantitatively by an optical method based on polarized light microscopy in an alumina green body prepared by slip casting method using porous alumina and plaster mold. The dehydration rate in the alumina mold was higher than that of the plaster mold. The alumina particles in the green body were always orientated parallel to the surface of the mold. The degree of orientated particles was affected by the dehydration rate during development of the cake. The degree of orientation in the alumina mold system was higher than in plaster mold system for rapid dehydration. The highest degree of particle orientation was obtained at regions near the mold, which was developed at the beginning stage of slip casting. The degree of orientation was explained by the dehydration rate in the mold system.

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New yellow-green pigments based on cerium orthophosphate were synthesized by the solid-state reaction in order to develop ecological and environmentally-friendly specific pigments. The pigments were obtained by doping alkaline earth metal ions into a cerium orthophosphate lattice to form their solid solutions. The products were characterized by using X-ray powder diffraction, UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and colorimetric assessment. From these results, it has been evidenced that the formation of solid solution is necessary to have color coordinates in the synthesized pigment samples. Since the color of the pigments was almost the same yellow-green in all solid solution samples, the origin of the coloration was attributed to the appearance of the principal broad absorption band corresponding to the 4f-5d electron transition of Ce³⁺ and the additional O_2p-Ce_4f charge transfer transition of Ce⁴⁺ by the doping of alkaline earth ion into CePO₄ lattice.

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Calcium phosphate nanoparticles were prepared by hydrothermal treatment of several types of calcium salt and phosphate aqueous solution. Crystalline phase and particle morphology of as-prepared particles were influenced by types of starting solution. Homogeneous hydroxy Apataite (HAp) nanoparticles were obtained by a hydrothermal treatment of CaCl₂-Na₂HPO₄- NaOH aqueous solution. X-ray fluoreseence analysis showed the Ca/P ratio of HAp nanoparticles was 1.67. The use of alternative combination of calcium salts and phosphate led to the formation of HAp with calcium phosphate, dibasic, anhydrous (DCPA) or calcium phosphate, dibasic, 2-hydrate (DCPD). The pH of starting solution influenced the ones unit of crystalline phase in the nanoparticles. The aspect ratio of HAp particles decreased with increasing concentration of starting solution.

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Inorganic waste (municipal incinerator residue, sewage sludge ash, coal ash and mineral waste etc.) is one of the most serious social problems from the points of environmental loading, and its reuses or recycles as a starting material have been urgently required. Glass-ceramics are one of the targets of the products. In this study, the glass-ceramics in the CaO-Al₂O₃-SiO₂ system based on inorganic waste were prepared and crystallizations were investigated using scanning electron microscope (SEM) and powder X-ray diffraction (XRD). Glass-ceramics of this CaO-Al₂O₃-SiO₂ system were expected for the construction materials. Model batches were prepared by mixing a molar ratio of 87-141 SiO₂, 0-35 Al₂O₃, 40-110 CaCO₃, 19 Na₂CO₃, 2 Fe, 3 Na₂SO₄ and 8 C, or 87-121 SiO₂, 15-35 Al₂O₃, 40-60 CaCO₃, 9-19 Na₂CO₃, 2-9 Fe, 3 Na₂SO₄, 8 C and 0-0.6 [Ca₃(PO₄)₂]₃•Ca(OH)₂, respectively. The glass samples were produced by melting the batches at 1450°C. The glass samples were reheated at 700-950°C for 1 h, to induce nucleation in the glasses. In addition, the glasses were reheated at 950-1200°C for 1-4 h, to form glass-ceramics. The results of the SEM photographs and powder X-ray diffraction patterns of the glass-ceramics showed that the main crystalline phases, prismatic crystals of Wollastonite (CaO•SiO₂) and Anorthite (CaO•Al₂O₃•2SiO₂), were precipitated homogeneously by bulk crystallization. It was found that Nepheline (Na₂O•Al₂O₃•2SiO₂) and/or Gehelenite (2CaO•Al₂O₃•SiO₂) were also precipitated.

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The distribution and the morphology of glass phase in polycrystals are affected by the dihedral angle and the volume fraction of the glass phase. The effects of temperature and chemical composition of intergranular glass on dihedral angle of glass-doped 3-mol%-yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) were studied by transmission electron microscopy (TEM). The intergranular glass was either SiO₂ (melting point of 1700°C) or Y₂O₃-Al₂O₃-SiO₂ eutectic glass (YAS glass: melting point of 1350°C). The average dihedral angles of SiO₂-doped and YAS-doped 3Y-TZP, which were sintered at 1300°C, were found to be 70° and 50°, respectively. The dihedral angle in YAS-doped 3Y-TZP decreased to 25° after annealing at 1500°C, whereas that in SiO₂-doped 3Y-TZP remained constant. From the relationship between the dihedral angle and the ratio of grain boundary energy to solid/glass interface energy (γ_SS/γ_SL), it was suggested that γ_SS/γ_SL increased at elevated temperatures higher than the melting point of glass.

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The state of small amount of elements containing impurity in silicon nitride produced by the post sintering method from low-grade silicon powder was investigated. Iron reacted with other components in the raw materials in the sintering process to form iron silicide particles which were subsequently distributed. Most particles were as large as 2 μm in diameter. Linear voids that were considered to originate in the difference of thermal expansion coefficients were observed in their perimeter. Ta₂O₅ also reacted with other elements and it was observed in the form of tantalum silicide particles. The size was few hundreds nanometer. Calcium was detected from multigrain pockets. However, not a particular particle segregation could be observed. For this reason, it is presumed that Calcium was solved into the grain-boundary phase.

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We investigated the effect of ferroelectric property on heat treatment at high oxygen partial pressure or vacuum for Bi_4-x+yLa_xTi₃O_12-δ (x=0.75, y=0; x=0.50, y=0; x=0.75, y=0.15). The remnant polarization (P_r) increases with increasing oxygen partial pressure during heat treatment. The coercive electric field (E_c) showed the same tendency as P_r at x=0.75 and y=0. In x=0.5 and y=0, E_c decreased with increasing oxygen partial pressure during heat treatment. T_c decreased by heat treatment under high oxygen partial pressure.

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