Alumina is widely used in ceramics, abrasives, refractories, petrochemical and other fields due to its excellent physical and chemical properties.In order to meet the needs of different industries, Al(OH)3 or γ -al2o3 for special treatment, such as roasting, grinding, hydraulic separation and other treatments, will be obtained in particle size, specific surface area and shape of alumina completely different.For ultra-fine activated alumina (γ -al2o3 or η -al2o3), generally used as adsorbent or catalyst carrier.Columnar or spherical alumina is usually filtered by carrier or ceramic membrane.High temperature series of alumina is mainly prepared by industrial alumina with cosolvent calcination, generally used in ceramics and refractories and other aspects.Polished alumina is mainly used in glass, metal and non - oxide ceramics, etc.

Alumina belongs to tripartite system, melting point is 2054℃, boiling point is 2980℃.Due to the difference of vapor partial pressure, temperature and pressure, there are many homogeneous Al2O3 crystals before Al(OH)3 is completely dehydrated into α -al2o3 at high temperature. It has been reported that there are 12 crystal structures such as α, β and γ. The most common crystal types are α, β and γ. Their density, specific surface area, porosity and acidity vary with the dehydration conditions and the initial aluminum hydroxide.