The synthesis of Cr(VI)-ettringite was attempted in portlandite suspensions for the immobilization of hazardous hexavalent Cr. The reagents NaAlO₂ and CrO₃ were used by dissolving them in deionized water to obtain 0.1 mol/L solutions, which were mixed with portlandite suspensions and stirred for 3 h at room temperature in CO₂-free synthetic air. Ca/Al atomic ratios were varied from 1.0 to 5.0 against the Cr/Al atomic ratios 1.0, 1.5 and 2.0. Run products were evaluated by XRD, XRF and FE-SEM. The results showed that Cr(VI)-ettringite formed under the conditions of pH 10.9 and more always associates with calcite. The calcite was also formed due to the carbonation of the remaining portlandite Ca(OH)₂ during drying in ambient air. The calculated yields of Cr(VI)-ettringite generally exceeded 80 mass%, and 85.6 mass% was reached for the stoichiometric mixture. In the run products obtained at pH lower than 10.9, no Cr(VI)-ettringite was identified, and the XRF analysis showed free-CaO and free-Al₂O₃ other than free-CrO₃ potentials each corresponding to calcite, ill-crystallized gibbsite (gibbsite gels) and the soluble chromatite CaCrO₄ adsorbed and trapped in the jelly gibbsite gels.

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Silica mesoporous structures incorporated with phosphorus were prepared and their proton conductivity was evaluated at temperatures of up to 150°C under saturated or controlled water vapor pressure. The fixing of phosphoric acid through heat treatment after forming the mesostructure had a limited effect on the improvement in proton conductivity only in a relatively low-temperature region. The incorporation of phosphorus during mesoporous silica formation decreased the surface area but was effective in improving proton conductivity. A sample with a low P/Si atomic ratio of 0.07 showed the highest proton conductivity above 10^-2 Scm^-1 at 100 to 120°C under saturated water vapor pressure. A sample with a high P/Si atomic ratio of 0.25 showed relatively high conductivities being maintained even at low relative humidity at 150°C. An adequate phosphorus concentration and a large surface area were found necessary for high and humidity-independent proton conductivity in mesoporous silica.

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Densification of a ceramic coating based on SiO₂-Al₂O₃-TiO₂ using wet processing was investigated by controlling microscopic grains of materials used. The grains of the materials used in coating slurry were reduced from their initial size of about 10 μm to less than 5 μm in diameter using ball-milling. The ceramic composite films thus prepared were deposited about 100 μm in thickness on a steel plate by slurry coating with a doctor blade, followed by drying and calcination in air. It was found that the coating prepared was stable to heating up to 800°C in air, although the use of overly small grains easily caused cracks on the surface. By optimizing the amount of alkali silicate, however, such cracks could be eliminated from the coating, and the number of through-holes in the coating could be drastically decreased. The ceramic coating obtained by both the control of grain size in powders and the optimal addition of the alkali silicate showed excellent densification, thermal stability and adhesion strength.

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The BaTiSi_3-xGe_xO₉ crystalline phases were synthesized, and their phase-stability and photoluminescent (PL) properties were investigated. The benitoite and tetragermanate-type phases were crystallized in the range of x=0.75-1.5 and x=2.0-3.0, respectively. It was suggested that Ge⁴⁺ occupies the octahedral Ti site due to the closeness of each ionic radii. The diffuse-reflection spectra revealed an increase in the oxygen-defect center by substitution of Ge in the crystalline phase. Although the BaTiSi_2.25Ge_0.75O₉ phase showed an efficient blue PL at room temperature, the PL intensity decreased drastically with the increasing x, and eventually the BaTiGe₃O₉ phase indicated a very weak PL in spite of almost the same structure as benitoite, that is, the absolutely-isolated TiO₆ octahedral unit and the Ge₃O₉ ring. It was suggested that the reduction of the PL intensity in the BaTi(Si, Ge)₃O₉ phase was caused by the increase in the oxygen-defect center.

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The particle-packing structure of alumina slurry was evaluated by constant pressure filtration. The cake forming behavior were classified into four patterns by plotting the resistance of the formed cake as a function of the particle volume in the cake; the plots were (a) a straight line, (b) a convex curve, (c) a concave curve, and (d) the combination of a concave curve and a flat line. A method of a estimation of the distribution of packing fraction in the formed cake was proposed. The distribution of packing fraction in the formed cake could be calculated unless the average packing fraction of the cake increased as the filtration proceeded ((c) concave curve). It was found that the distribution of packing fraction estimated by the proposed method was in good accordance with the experimental value obtained by γ-ray transmission measurement.

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Carbon short fibers with high graphite content were added into a submicron SiC powder and consolidated by hot-pressing to prepare SiC/C composite materials. With the amount of added carbon fibers varying between 0 and 20 vol%, all samples could be densified to relative densities over 98%. The incorporation of carbon short fibers resulted in improved fracture toughness but degraded bending strength of the composites, and such effects were more obvious with increasing amount of carbon fibers. The tribological properties of the materials were studied using block-on-ring sliding tests at normal loads of 5 and 50 N. While the SiC/C composites always showed good wear resistance, their friction behaviors were different when tested under low and high load conditions. Under low load conditions, the added carbon fibers did not bring about any lubricating effect. Under high load conditions, the friction coefficients of the SiC/C composites were obviously lower than that of the monolithic SiC.

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The improvement in the flexural strength of porcelain by applying surface compressive stress was investigated. Sandwich-structured slab samples were fabricated using traditional porcelain clay and composition-modified clay at a firing temperature of 1533 K. The flexural strength of the samples was measured. Preliminary results showed that the flexural strength was improved when surface compressive stress was introduced, and reduced when tensile stress was induced in the surface layer. The similarity between the thickness dependence of the flexural strength and that of surface elastic energy indicated that surface compression stress is important in reinforcing the porcelain body.

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Composites synthesized from β-tricalcium phosphate (β-TCP) and polylactic acid (PLA) are attracting attention as novel bone substitutes owing to their bioresorbability and high workability. The preparation of this type of composite through stirring of the starting materials and subsequent pressing has been previously reported. In this study, we attempted ball-milling after the stirring of the starting materials in the preparation of the β-TCP/PLA composites. Effect of ball-milling time on mechanical properties of the composites was examined. A slurry was prepared from β-TCP and PLA with a molecular weight of 120000 to 200000 in a mass ratio of 75 : 25. This was ball-milled at ambient temperature for periods up to 48 h, and then hot-pressed to form dense composites. The mechanical properties of the composites were evaluated using a three-point bending test. The bending strength of the composites increased with increasing ball-milling time and decreased with increasing molecular weight of the PLA. In particular, composites prepared from PLA with a molecular weight of 120000 that were ball-milled for 48 h showed a mechanical strength of 80 MPa, which is nearly equal to that of human cortical bone. The increase in bending strength is attributed to a decrease in the size of the β-TCP aggregates due to ball milling.

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Highly efficient dicing blades with 28 vol% porosity were fabricated by using a doctor blade casting method and pulsed electric current sintering (PECS). WC and W₂C were formed between diamond grains and tungsten matrix materials during a sintering and enhanced the bonding strength between diamond grains and the matrix materials. Fabricated dicing blades and commercial dicing blades which were 0.09 mm in thickness, were evaluated by a constant feeding force dicing machine under 3.0 N constant feeding force. Al₂O₃-TiC composites which had 1.2 mm in thickness were used as a cutting sample. Speeds of fabricated dicing blade and commercial dicing blade were 6.2 mm/s and 2.9 mm/s at 750 mm of cutting length, respectively. Number of diamonds on surfaces of the fabricated dicing blades was kept constant before and after dicing tests, however, that on the commercial dicing blades decreased to half. Specific grinding energy for the fabricated dicing blades and the commercial ones were 133 GJ/m³ and 213 GJ/m³, respectively. Therefore, efficient dicing blade was produced by introducing pores and increasing bonding strength between diamond grains and matrix.

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We studied new preparation conditions for scallop shell phosphors to suppress weathering and the disappearance of fluorescence, and measured the fluorescence properties of these phosphors. When a shell was fired to 900°C in a carbon dioxide atmosphere, weathering and the disappearance of fluorescence could be suppressed. It was found that the higher brightness of the shell phosphor fired at 860°C was about 6cd/m², when the power of irradiated UV light was about 1.6 W/m². The emission spectrum shows three bands, with peaks at about 420 nm, 485 nm and 585 nm. The bands at 420 nm and 485 nm are presumed to be due to Cu, and the band at 585 nm is presumed to be due to Mn.

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An effective additive for enhancing the hydrophilic properties of alumina was identified. The mechanical and frictional properties of the resultant material were characterized. The contact angle varied greatly depending on the kind of additive. ZnO was found to be the additive that most reduced the water contact angle of conventional alumina. ZnO-added alumina, with such enhanced hydrophilic properties, naturally exhibited excellent frictional properties in the boundary-lubrication region. Its strength (388 MPa) was equivalent to that of conventional alumina.

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Because aluminum nitride (AlN) has a high thermal conductivity and a high electrical resistivity, it is used for substrates and packaging for high power or high density circuits. Silicon chips need to be protected from faults caused by exposure to ultra-violet rays. AlN packaging and substrates have to be shaded for UV protection. The characteristics of AlN are influenced by a number of factors. Specifically, metallic impurities affect the shading and thermal conductivity, and are particularly easily mixed with AlN as minerals or solutions during processing. It is very important to understand how metallic impurities influence the characteristics of AlN, and either refine processing to eliminate such effects, or add metal to achieve the desired industrial characteristics. Iron (Fe), silicon (Si), magnesium (Mg), and titanium (Ti) are metals that are easily mixed, so it is important to understand their influence. The metallic impurities Fe, Si, Mg, and Ti were added to raw powder AlN and uniformly distributed at a molecular level. The powder was sintered and tested for any effects on shading or reduction in thermal conductivity. Some Ti compounds were found at the grain boundaries, but these did not reduce the AlN thermal conductivity and provided efficient shading. In contrast, Si and Mg compounds were not found at the grain boundaries but formed solid solutions in the AlN grains, so they significantly reduced the AlN thermal conductivity and provided no shading. The effect of Fe was intermediate between that of Ti and Si and was characterized by its tendency to form solid metal ion solutions in the AlN grains.

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The low temperature decomposition of crysotile in sprayed asbestos was investigated under the coexistence with salts such as NaF, NaCl, CaCl₂, and CaCO₃. When a high cement-containing sprayed asbestos containing CaCl₂ was heated at 800°C for 2 h, the needle-like shapes of crysotile disappeared. In the case of a low cement-containing sprayed asbestos containing both CaCl₂ and CaCO₃, crysotile was also decomposed at the same temperature and over the same time period.

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We prepared T-La_2-xY_xCuO_y thin film using the spin coating-pyrolysis method. We then investigated the relationship between the phase, lattice constants, and conductivity with the changing oxygen content using heat treatment. The lattice constant, c, decreased and conductivity increased with the decreasing P_O2. Although the resistivity of most thin films decreased remarkably at less than 60 K, they did not exhibit zero resistivity.

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