2015 年 64 巻 6 号 p. 438-441
Porous MgAl2O4-Al2O3 ceramic composites were fabricated by impregnating porous Al2O3 bodies calcined at various temperatures with Mg(NO3)2 aqueous solution under reduced pressure, followed by firing at 1500℃. Porous Al2O3 bodies were with continuously long-ranged pore structure was prepared by a unidirectional freeze casting using aqueous slurries and then calcined at 1300℃ 1400℃. The effects of the calcination temperature of Al2O3 bodies and the number of Mg(NO3)2 impregnation on spinel formation at 1500℃ were investigated. The amount of spinel in the bodies sintered at 1500℃ increased with increasing the number of the impregnation with Mg(NO3)2 solution and decreasing calcination temperature of Al2O3 bodies. When the Al2O3 bodies calcined at 1400℃, Mg(NO3)2 solution was difficult to penetrate into Al2O3 ceramic walls because of the densification of Al2O3 ceramic walls. Thus, spinel tended to form near the Al2O3 bodies calcined at 1300℃, Mg(NO3)2 solution penetrated deeper into Al2O3 ceramic walls. And therefore, Mg widely distributed in the Al2O3 ceramic walls and a large amount of spinel formed ever at less number of the impregnation of Mg(NO3)2 solution.