Mg還元テルミット法によるZrC微粉末の合成と生成過程

抄録

In the ZrO₂-Mg-CH₄ system, ZrC fine powders have been prepared by two different methods; (1) direct preparation from ZrO₂ and Mg in a CH₄ gas flow and (2) reduction of ZrO₂ with Mg in an Ar flow and subsequent carbonization of the reduced materials in a CH₄ flow. The formation process of the ZrC powders of single phase has also been studied. In the method (1), the appropriate synthesis conditions were Mg/ZrO₂ molar ratio≥4, heating temperature≥700°C and heating time=1h. In the method (2), on the other hand, the optimum conditions were as follows; Mg/ZrO₂ molar ratio=4, and reduction time=1h in an Ar flow and carbonization time=1h in a CH₄ flow at 800°C. The formation process of ZrC powders in the ZrO₂-Mg-CH₄ system was as follows: in the case of Mg/ZrO₂≥4 molar ratio, (1) 600°-; ZrO₂+2Mg→α-Zr+2MgO, (2) 650°-800°C; 3CH₄+2Mg→Mg₂C₃+6H₂, (3) 650°-750°C; α-Zr+H₂→δ-ZrH₂, (4) 700°C-; Mg₂C₃→2Mg+3C, (5) 750°C-; δ-ZrH₂→α-Zr+H₂ and (6) 700°C-; α-Zr+C→ZrC. Comparison of the two methods (1) and (2) indicated that the former was highly efficient because of an exothermic reaction by the thermite reaction.