Methods for High-Purity Aluminum Oxide Production for Growth of Leucosapphire Crystals (Review)

Methods for the preparation of raw materials to produce leucosapphire are considered. It is shown that the main directions in the production of high-purity aluminum oxide raw materials are: electrochemical oxidation of aluminum, decomposition of alkoxides, high-temperature treatment of aluminum oxide in a halogen-containing atmosphere, and preliminary purification of aluminum-containing compounds followed by their decomposition. It is shown that methods of the purification of aluminum hydroxide and oxide obtained by the Bayer process are the most promising for industrial use. These methods include the complex purification and simultaneous preparation of ceramic preforms starting from aluminum hydroxides or oxides by their treatment in subcritical or supercritical steam and the following heat treatment in a halogen-containing medium.