遊星ボールミル処理したアルミナ粉末のコンタミネーションと焼結性

Abstract

The contamination of planetary milled alumina powder has been studied and correlated to sinterability. The powder contained Si-and N-contaminations caused by the wear from the grinding media and mill wall made of Si3N4. A part of worn-out Si3N4 was oxidized into Si(OH)4 by H2O contained in CH3OH used as the grinding liquid. The strong shear stress between the media generated during planetary milling promoted mechanochemical reactions among worn-out Si3N4, Si(OH)4 and Al2O3 forming an amorphous reaction layer on the alumina particles. This provided possibilities of planetary milling by applying the surface modification of ceramic powders despite the problem of contamination. The surface layer containing the contaminations resulted in the formation of the mullite phase at the grain boundary during sintering. The low diffusion coefficient of the mullite phase degraded sinterability even at a contamination as low as 400ppm-Si. When the contamination increased to 0.5wt%-Si, irregular grain growth and the formation of closed pores took place, suggesting the degradation of the mechanical properties.