The characteristics of hexavalent chromium compound i.e. Ca4Al6CrO16 and CaCrO4 formed in the use Chrome refractory was investigated in this study. The amount of Cr（Ⅵ） ion in water was low in the early stage of leachate test of Ca4Al6CrO16 and it increased gradually with time. On the other hand, the amount of the ion was high in the early stage of the test of CaCrO4 and it decreased rapidly. Ca4Al6CrO16 was quite stable against the heat treatment, whereas CaCrO4 changed its chemical form easily during the heat treatment. For the practical use of Chrome refractory, Cr2O3 content should be increased to form CaCrO4 which is easy to treat as waste in workability and safety.

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[in Japanese]

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Composite materials consisting of aluminum boron carbide（Al8B4C7）and alumina platelets were fabricated at 1650℃ by PECS（Puls Electric Current Sintering）, and the relative density of the compacts exceeded 98%. These materials exhibited non-linear mechanical properties. Fracture surfaces of the composite samples exhibited layer-by-layer destruction behavior, which was easily observed in the MAX phases and seemed to absorb fracture energy, resulting in improved mechanical properties. The Young’s modulus, three-point bending strength, and single-edge notched beam fracture toughness were examined at elevated temperatures. These measurements indicated that the Young’s modulus and fracture toughness of the composite increased at 800 ℃ due to the compressive strength generated by the thermal expansion mismatch between Al8B4C7 and alumina and grain growth caused by the formation of liquid phase in air. On the other hand, the bending strength decreased at 800℃ due to the grain growth.

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