Influence of AlF3 and ZnF2 on the phase transformation of gamma to alpha alumina

This paper focused on the effect of AlF3 and ZnF2 additives on the phase transformation of gamma to alpha alumina. AlF3 and ZnF2 were found to be effective accelerating agents on the gamma to alpha phase transformation. A single phase of alpha alumina, with an average particle size of 22 nni, can be obtained at 920 degreesC with AlF3 additive. ZnF2 can reduce the gamma to alpha transformation temperature to 900 degreesC, the average size of the particles is about 40 nni and the morphology of some particles is platelike with an aspect ratio of 2-4. The reduction of the transformation temperature was mainly attributed to the formation of intermediate compound of AlOF, which was considered to accelerate the mass transportation from transition alumina to alpha alumina. Moreover, mechanical milling and introducing alumina seeds uniformly worn from the milling mediums are also beneficial for reducing the transformation temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.