Ball Milling and Sintering of Bayer Aluminas

Abstract

Dry ball milling of four reactive and semi-reactive aluminas was investigated in terms of milled powder characteristics, compaction and sintering behaviour. The crystal and agglomerate morphologies of the unground powders determined the milling characteristics and, therefore, the subsequent compaction and sintering behaviour of each alumina. Powders with smaller ultimate crystal sizes milled to smaller median particle sizes, were more reactive and could be sintered at a lower temperature. These aluminas produced the finest, most even-grained sintered microstructures. Ball milling beyond a certain length of time produced no improvement in surface area. The time at which this plateau in surface area occurred increased for the powders with smaller ultimate crystal sizes. Ball milling was also found to be more effective in fracturing the smaller crystals of the higher surface area powders than the larger crystals of the semi-reactive aluminas.