KINETICS AND MECHANISM OF CORUNDUM FORMATION IN THE THERMAL-DECOMPOSITION OF BASIC ALUMINUM-CHLORIDE GELS

Compositions and corundum contents in products, formed by thermal decomposition of a basic aluminium chloride gel at temperatures up to 600-degrees-C, were determined at variable temperatures and times of decomposition. For the kinetics of alpha-alumina crystallization a model is proposed, valid for diffusion-controlled two-dimensional growth. A mechanistic interpretation of these results and of those from previous examinations is based on the essential influence of the gel structure and of the atmosphere in thermal decomposition. As the rate-controlling step of corundum formation the transportation of HCl and H2O molecules is discussed.