Papers by Author: Yutaka Sawada

Abstract: Several boride sintered bodies such as TiB2, ZrB2, and SiB6 were previously reported. In the present study, the sinterability and physical properties of chromium boride (CrB2) containing chromium carbide (Cr3C2) sintered bodies were investigated in order to determine its new advanced material. The samples were sintered at desired temperature for 1 hour in vacuum under a pressure by hot pressing. The relative density of sintered bodies was measured by Archimedes’ method. The relative densities of CrB2 addition of 0, 5, 10, 15 and 20 mass % Cr3C2 composites were 92 to 95 %. The Vickers hardness of the CrB2 with 10 and 15 mass % Cr3C2 composites were about 14 and 15 GPa at room temperature, respectively. The Vickers hardness at high temperature of the CrB2 addition of 10 mass % Cr3C2 composite decreased with increasing measurement temperature. The Vickers hardness at 1273 K of the sample was 6 GPa. The Vickers hardness of CrB2 addition of Cr3C2 composites was higher than monolithic CrB2 sintered body. The powder X-ray diffraction analysis detected CrB and B4C phases in CrB2 containing Cr3C2 composites.

Abstract: Mechanochemical synthesis of zinc ferrite, ZnFe2O4, was attempted from a powder mixture of iron (III) oxide, alpha-Fe2O3 and zinc (II) oxide, ZnO. Nanocrystalline zinc ferrite, ZnFe2O4 powders were successfully synthesized only by milling for 30 hours. The X-ray diffraction spectrum of the as-milled powders (without heating) showed twelve ZnFe2O4 peaks and four weak peaks of coexisting unreacted Fe2O3. The crystallite size of the mechanochemicallysynthesized ZnFe2O4 was 26.3 nm. Evidence of the ZnFe2O4 formation was absent for the powders milled for 10 and 20 hours; milling lowered the crystallinity of the starting materials. Heating after milling enhanced the formation of ZnFe2O4, the crystal growth of ZnFe2O4 and the unreacted starting materials. The unreacted starting materials decreased their amounts by heating at higher temperatures.