Some recent developments of phosphate glass-ceramic biomaterials are briefly reviewed. Bioactive calcium pyrophosphate glass-ceramics can be prepared by including small amounts of TiO₂ and Na₂O (totally ≤10 mol%): they are easy to be machined using conventional tools and they are strongly coated on a β-type titanium alloy using a conventional glazing technique. These materials are expected to be applicable to some surgical treatments such as custom-made implants, Kirschner-wires and so on. New types of dental materials using phosphate glass-ceramics are also discussed. Phosphate glass-ceramics containing a large amount of TiO₂ (∼20 mol%) includes a functional Nasicon-type crystal, which has silver-ion exchangeability with excellent chemical durability: they are applied to a castable dental crown with bacteriostatic activity. Phosphate glass-ceramic fillers, which are rapidly sintered by CO₂ laser irradiation, have been also newly developed for sealing fissures at the surface of a tooth crown.

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Physical properties of Kutani-ware glaze were investigated considering the glaze slurry's particle size distribution. Even for identical glaze compositions, physical properties, such as the thermal expansion coefficient, changed with the amount of coarse particles in the glaze. The amount of quartz remaining in the glaze after firing was strongly influenced by the amount of coarse particles in the glaze slurry. The thermal expansion coefficient of the glaze was calculated using the Appen factor; the value was approximately equal to the experimental one. Too much quartz in the glaze after firing rendered the glass parts in the product inhomogeneous and its composition became rich in alkaline elements. In contrast, less quartz in the glaze after firing yielded homogeneity of glass parts in the product and created a silica-rich composition. The amount of residual quartz in the glaze must affect the crazing and over-glaze color exfoliation.

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Alumina ceramics have been used as components of artificial hip joints because of their high hydrophilicity and hardness. However, improvement of fracture toughness and fatigue resistance of the alumina ceramics is required to enhance their reliability in clinical use. In this study, we synthesized a novel alumina-zirconia composite and evaluated its mechanical performance. It has superior mechanical properties, such as a 4-point bending strength of 1250 MPa and fracture toughness of 4.7 MPa•m^0.5. Namely, the bending strength and fracture toughness of the composites were similar to those of commercial Y₂O₃-stabilized zirconia ceramics. We then evaluated the cyclic fatigue properties of the composites. The alumina-zirconia composite did not break even after 10⁷ cycles under 625 MPa, but all of the pure alumina samples broke after the same number of cycles under 484 MPa. It appears that the alumina-zirconia composite has higher survival reliability under cyclic loadings than the alumina, although anti-fatigue properties could not be quantitatively interpreted. These phenomena can be attributed to the dispersion of rod-shaped particles in the matrix and the fine grain size of the composites.

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Dielectric relaxations were investigated for 10 mol% Ca-doped CeO₂ (Ce_0.9Ca_0.1O_2-δ) having a cubic fluorite-type structure, which is a typical oxide-ion conductor. The dielectric constants (ε_r′) showed anomalously large values at low frequencies and high temperatures. Numerical analysis of the frequency dependence of ε_r′ clarified that the large ε_r′ originated from superimposition of both the electrolyte-electrode interfacial and Debye-type polarizations. The ac conduction dispersion was also successfully explained by the interfacial and Debye-type polarizations. Two kinds of Debye-type relaxations observed were ascribed to defect associates, (Ca_Ce″-V_O^••) which have different distances between the dopant and the oxygen vacancy.

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Magnetite (Fe₃O₄) nanoparticles were fabricated by hydrolyzing Fe²⁺ and Fe³⁺ ions with NaOH diffusing through a half-permeable membrane. The Fe₃O₄ nanoparticles, about 15 nm in diameter, showed ferrimagnetism with very small coercivity and remanent magnetization. The nanoparticles were combined with Sphaerotilus natans, a Gram negative bacterium used in biosorption of heavy metal ions in water, to prepare a composite biosorbent. The composite biosorbent showed excellent sorption properties to Pb²⁺ ion in a pH range between 6 and 8, and to Cr₂O₇ ^2- ion in a pH range below 4. The combination of Fe₃O₄ nanoparticles made it easy to separate the composite biosorbent from water by the use of a magnetic field and improved the sorption properties. It was also shown that the composite biosorbent was reusable after being rinsed with a dilute hydrochloric acid solution.

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Residual silicon in the reaction-bonded silicon carbide (RBSiC) can be replaced by refractory MoSi₂ by using Si-Mo alloy as infiltrants instead of pure Si. Transmission electron microscopy of these materials clarified the following results. The MoSi₂ existed in the SiC grain boundaries and many fine grains of SiC were found in the MoSi₂ phase. The carbon particles were thought to be dissolved into the Si melt including Mo and reprecipitated as SiC particles in the solution-reprecipitation mechanism. The Mo concentration in the Si-Mo melt increased with the reprecipitation of SiC particles, and the MoSi₂ was precipitated in the grain boundaries. The presence of the fine SiC particles in the MoSi₂ phase suggests that the carbon have a fairly strong interaction with silicon in the melt and diffuse not as isolated atoms, but as C-Si pairs.

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Micron-sized PbO-B₂O₃-SiO₂ glass powders were directly prepared by high temperature flame spray pyrolysis. The flow rates of fuel and carrier gas in the flame spray pyrolysis were critical to the control of morphologies of PbO-B₂O₃-SiO₂ glass powders. The optimum flow rate of fuel gas to prepare the PbO-B₂O₃-SiO₂ glass powders with spherical shape and micron-size was 20 L/min. The powders prepared at low flow rates of carrier gas had bimodal size distributions with nanometer and micron sizes. The number of the nanometer size powders increased with decreasing the flow rate of carrier gas. When the flow rate of carrier gas was 30 L/min, the prepared powders had spherical shape and micron size. The transmittances of the dielectric layers were higher than 90% regardless of the flow rates of carrier gas when the dielectric layers were sintered at temperatures between 520 and 580°C.

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The surface of the electrode of the oxygen sensor for an automobile shows a complicated phenomenon due to reactions to the exhaust gas that is composed of various elements. Moreover, variations in the air/fuel ratios make it difficult to treat the reactions on the surface of the electrode on account of the coverage of oxygen. Therefore, its surface reactions of the oxygen sensor cannot be completely clarified, and this has been a bottleneck problem for the development of a sophisticated precision oxygen sensor. In this study, we applied the density functional theory and the ab-initio molecular dynamics theory to the reactions of the gas molecules on the surface of the electrode in different air/fuel ratios. As a result, we had a better understanding about the surface reactions on the molecule level and made it clear that the oxygen sensor outputs are influenced by exhaust gases such as NO, CO, CH₄, and H₂.

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The CO₂ absorption property of Li₄SiO₄ was investigated by thermogravimetry. Two kinds of sintered Li₄SiO₄ samples were prepared at 700°C and 1000°C. The CO₂ absorption rate of the powdered Li₄SiO₄ samples was measured in 100 vol% CO₂ atmosphere at nine selected temperatures in the 620~700°C region, and the measured data were discussed by the rate theory. The CO₂ absorption reaction of the Li₄SiO₄ would be a pseudo first order reaction. For these samples, apparent reaction rate constants k were measured at different measurement temperatures, and activation energies were estimated by the Arrhenius plot. For both the samples, the estimated activation energies were about 115 kJ/mol in the 620-660°C region and about 56 kJ/mol in the 680-700°C region. The large difference between these activation energies seems to depend on the surface state of the Li₄SiO₄ particle reacting with CO₂.

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A Nb₂O₅ thin film is a DRAM capacitor material with over 4 Gbit because the specific inductive capacity is 60. In CVD process, pentaethoxyniobium (PENb) is usually used as precursor. There are several problems attributed to this such as the thermal decomposition of the superheating, and it is necessary to keep the highest temperature in the evaporator and transport process because the PENb vapor pressure is very low, such as 406 K at 13.3 Pa. To improve the problems, a flashing spray CVD (FS-CVD) method is proposed. In FS-CVD, the precursor is supplied through the injector, which is set at the top of the CVD chamber as a pulsed spray into lower ambient than the precursor vapor pressure in the chamber. The spray is evaporated rapidly and forms a homogene vapor by flash boiling. Also the precursor and low boiling point organic solvent mixed solution is used as a raw material. The high boiling point precursor is converted to lower boiling point material by mixing low boiling point organic solvent with vapor liquid equilibrium. In the experiment, PENb was used as the precursor. The low boiling point material for PENb was selected from vapor-liquid equilibrium considering the mutual solubility and vapor pressure. As a result, ethanol was selected for PENb. Nb₂O₅ film and was deposited on an 8 inch Si wafer by the FS-CVD method. The influence of the film thickness distribution by the distinction of the mixing fraction of ethanol was observed. The mixing molar fraction of ethanol, X was 0.4 and 0.9. Then, the relationship between the injection cycle and film thickness was observed. As a result, the film thickness distribution on an 8 inch wafer is evaluated as +/-14% or less at X=0.4 and +/-2% or less at X=0.9. The distribution of X=0.9 was better than 0.4 due to the rapid and homogeneous PENb and the ethanol vapor formation. The film thickness with molecular scale size might be accomplished by a FS-CVD process.

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Silicon nitrides are widely used as structural components. Those with an as-sintered surface are often provided for practical use, since a surface finish by machining is a costly procedure. To ensure reliability of such components, it should be important to examine the strength taken from an as-sintered surface. However, there hasn't been a research focus within this area. In this research, a specimen with an as-sintered surface, having traces by green machining, was provided for investigation. Strength from the as-sintered surface was lower than that from the machined surface. Directions of traces by green machining did not affect the strength of the as-sintered surface. Fracture origins were considered to be surface flaws introduced by green machining.

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Spherical shape cobalt oxide powders with fine size were directly prepared by spray pyrolysis using a filter expansion aerosol generator (FEAG). These cobalt oxide powders were then compared with the powders prepared by ultrasonic spray pyrolysis. The cobalt oxide powders prepared using a FEAG are finer and have more narrow size distribution and filled morphologies than those prepared by ultrasonic spray pyrolysis. The mean sizes of the cobalt oxide powders prepared using a FEAG increased from 230 to 860 nm when the concentration of the spray solution was increased from 0.01 to 2 M.

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Photocatalytic HCa₂Nb₃O₁₀ samples were prepared by a polymerizable complex method and tested for H₂ evolution from aqueous methanol solution under UV-light irradiation. These samples demonstrate significant enhancement in the hydrogen production rate compared to the reference samples synthesized by conventional solid-state reaction.

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