Influence of addition of AlF3 on thermal decomposition of gibbsite and phase transition of the intermediate alumina to α-Al 2O3

Abstract

The addition of aluminum fluoride to gibbsite retarded the phase change to boehmite by chemisorption of hydrogen fluoride on gibbsite particles. In the specimen with addition of aluminum fluoride, the spinel type phase transformed directly to α-Al2O3, without passing through κ- and θ-Al2O3 phases. The formed α-Al2O3 consisted of clear, hexagonal plate-like particles about 1 μm, Without taking over a relic of the gibbsite particle. The formation of automorphic crystals suggests that a surface diffusion also contributes to the mechanism of this material transport in addition to the vapor phase transport.