Fracture toughness of fine ceramics depends on notch root radius, crack length and grain size. The effects of notch root radius on fracture toughness were investigated using gypsum and polymer gypsum composite. The notch root radius were varied in size ranging from 0.1 mm to 1.0 mm. Experiments were conducted at room temperature. The results were discussed based on the process zone size fracture criterion. The relationship between notch root radius and fracture toughness was in good agreement with the theoretical one deduced from the criterion. Polymer gypsum composite was confirmed to be excellent materials showing high fracture toughness and bending strength in compared with gypsum.

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It was investigated improvement in efficiency of manufacturing concrete product and reduction of environmental burden with ultra high early strength additive. The strength necessary for stripping was obtained even in shortening precuring and steam curing time and strength after stripping was increased because hardening with condensation was accelerated with ultra high early strength additive. It was found that even in the case of using ultra high early strength additive and blast furnace slag cement, the strength was more than strength with normal portland cement, which leads to great reduction of environmental burden. Also, high efficiency of manufacturing concrete product and the reduction of possessing mold become possible because it is possible to attain a high use degree efficiency of mold.

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The effect of primary particle-size distribution on the sintering of magnesium-oxide (MgO) powder was examined. Two kinds of MgO powders with average primary particle sizes of 107 nm and 261 nm, which were designated as F (107) and G (261), respectively, were used in the experiment. The primary particle sizes for the F (107) powder were distributed within the range of 350 nm (“narrow” distribution), whereas those for the G (261) powder were distributed within the range of 550 nm (“broad” distribution). The particle/ grain growth for the F (107) compact occurred with thermal shrinkage. In the case of G (261) compact, the coalescence of smaller particles into larger particles had occurred below 1100°C before the marked shrinkage started. At a fixed temperature of 1300°C, the relative density of F (107) compact increased with firing time and attained 98.0% after 150 h firing. Although the relative density of G (261) compact increased with firing time, the relative densities were always lower than those of F (107) compact. The average grain size for the F (107) compact increased with firing time, whereas that for the G (261) compact increased gradually till 20 h firing but more rapidly with a further increase in firing time. Overall, it was found that the sintering of MgO powder with broad primary particle-size distribution caused rapid inhomogeneous grain growth and restriction of densification, both due to the entrapment of pores within the grains.

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Phosphate glass can contain many kinds and amounts of modifier oxides. Chemical durability of the glass is inferior to other oxide glasses, because phosphate glass has nonbridging oxygen, and this causes the limitation of application field of the glass. To improve the defect of the glass, the preparation of phosphate glass containing nitrogen was carried out under usual atmosphere by using cyclo-tri-μ-imido-triphosphate as raw material. According to IR study, it was found that the phosphate glass containing nitrogen as an imino group. The phosphate glass containing sodium was dark brown, and the phosphate glass containing magnesium or calcium was not colored. The solubility of phosphate glass containing nitrogen decreased very much in comparison with phosphate glass without nitrogen.

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In order to achieve mercury-free flat fluorescent lamp, prevention of the sputtering of the electrode and determination of an appropriate sealed gas composition are necessary. In this study, a flat transparent electrode covered with glass layer was applied to a flat fluorescent lamp. The effects of the sealed gas composition, the sealed gas total pressure and the distance between a pair of electrodes were investigated to determine a condition under which the lamp exhibits a similar luminance to that of the corresponding commercial mercury lamp. As a result, an appropriate condition was determined.

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Formation of SnO was examined by the homogeneous precipitation method in which SnCl₂, (NH₂) ₂CPO and halogenide were used. The minimum concentration of the additive on SnO formation depended on the kind of halogenide and the concentration of halogenide became lower in the order chloride, bromide, iodide. The process of SnO formation is via 5SnO.2H₂O or unknown compound as an intermediate in the solution with pH 2-8.

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[in Japanese]

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