1. Powder Preparation
At present, the methods for producing high-purity alumina mainly include multiple crystallization methods (including pyrolysis of aluminum ammonium sulfate and ammonium aluminum carbonate), alkoxide hydrolysis, direct hydrolysis (choline method) and modified Bayer method. Only a few domestic enterprises have the production technology of the improved Bayer method, the hydrolysis method of aluminum alkoxide and the hydrothermal synthesis method. Japanese companies have the most advanced production technology for high-purity alumina. Representative companies, Sumitomo Chemical and Daming Chemical, respectively, use aluminum alkoxide hydrolysis and ammonium aluminum carbonate pyrolysis to produce high-purity alumina with a purity of more than 99.995%. Aluminum and high-purity ultra-fine alumina.
2. Sintering process
High-purity alumina ceramics usually need to be sintered at a temperature higher than 1600 ℃. The sintering temperature of high-purity alumina ceramics can usually be reduced by adding appropriate additives and other measures. At present, the sintering temperature of 99.99% alumina powder in Japanese companies is only 1300 ℃. , and the domestic need to above 1600 ℃. Most of the preparation of alumina ceramic balls for bearings adopts hot isobaric sintering technology.
3. Finishing
Alumina ceramic materials have high hardness, so they are usually ground and polished with harder materials such as SiC, C or diamond. Generally, Al2O₃ powder or diamond smaller than 1μm can be used for grinding and polishing, as well as grinding and polishing methods such as laser processing and ultrasonic processing.
