At present, it is divided into high-purity type and common type. The high-purity alumina ceramic is a ceramic material with Al2O3 content of more than 99.9%. Because its sintering temperature is as high as 1650-1990 ℃, the transmission wavelength is 1~6 μ m. Generally, molten glass is made to replace platinum crucible: its light transmittance and alkali metal corrosion resistance are used as sodium lamp tubes; It can be used as integrated circuit substrate and high-frequency insulating material in the electronic industry. Ordinary alumina ceramics are classified into 99 porcelain, 95 porcelain, 90 porcelain and 85 porcelain according to different Al2O3 content. Sometimes those with Al2O3 content of 80% or 75% are also classified as ordinary alumina ceramics. Among them, 99 alumina ceramic materials are used to make high-temperature crucibles, refractory furnace tubes and special wear-resistant materials, such as ceramic bearings, ceramic seals and water valve pieces; 95 Alumina porcelain is mainly used as corrosion-resistant and wear-resistant parts; Because some talc is often mixed in 85 ceramics, the electrical properties and mechanical strength are improved. It can be sealed with molybdenum, niobium, tantalum and other metals, and some are used as electric vacuum devices.