Preparation of Fine-Grained Corundum Powders with Given Properties: Crystal Size and Habit Control

Abstract

The processes of obtaining fine-grained corundum with a given crystal size and habit are considered. It is shown that thermocouple treatment in aqueous supercritical fluid allows one to obtain corundum from various precursors in a wide range of crystal sizes (0.01–500 μm). Powders with a crystal size in the range 20–500 μm can be obtained directly from hydrargillite prepared in the course of the Bayer Process. The size and habit of the crystals are determined by the parameters of the thermocouple treatment and properties of the process activators used. Powders with a crystal size falling in the range 30–1000 nm can be obtained by using synthesized or commercially available boehmite as a precursor for the thermocouple treatment. The crystal habit is determined by the habit of the boehmite crystals used. New methods of boehmite synthesis have been developed that allow one to obtain nonaggregated crystals with a size of 10 nm with a narrow distribution curve.