Synthesis of aluminum oxide platelets

Aqueous solutions of boehmite and hydrofluoric acid (HF) were used to prepa re homogeneous mixtures of alumina and aluminum fluoride. Calcination at te mperatures as low as 1000 degreesC resulted in the formation of well-define d hexagonal-shaped alpha -alumina platelets. Containment of the aluminum fl uoride by covering the calcination crucible promoted crystal growth presuma bly by a reaction of continuous evaporation-condensation of aluminum fluori de. Hexagonal-shaped platelet alpha -alumina was observed with average diam eters ranging from 7 to 33 mum. Large platelets with a narrow size distribu tion and average diameter of over 25 mum were prepared by controlling the i nitial concentration of HF and the calcination time, temperature, and atmos phere.