Alumina ceramics can be divided into high-purity type and common type.
      High purity alumina ceramics with Al2O3 content of more than 99.9% are generally made into molten glass to replace platinum crucible due to their sintering temperature of 1650-1990 ℃ and transmission wavelength of 1-6 μ m; they are used as sodium lamp tubes by their light transmittance and alkali corrosion resistance; they can be used as integrated circuit substrates and high-frequency insulation materials in the electronic industry.
      According to the content of Al2O3, ordinary alumina ceramics can be divided into 99, 95, 90 and 85 ceramics. Sometimes, alumina ceramics with Al2O3 content of 80% or 75% can also be classified as ordinary alumina ceramics. Among them, 99 alumina ceramic materials are used to make high temperature crucible, fire-resistant furnace tube and special wear-resistant materials, such as ceramic bearing, ceramic seal and water valve plate, etc.; 95 alumina ceramic is mainly used as corrosion-resistant and wear-resistant parts; 85 ceramics can be sealed with molybdenum, niobium, tantalum and other metals, and some of them can be used as electric vacuum devices.