Alumina (Al ₂ O ₃) is a kind of compound high hardness, melting point is 2054 ℃, boiling point is 2980 ℃, is at high temperatures is ionization ion crystal, often used in the manufacture of refractory products. Industrial Al2O3 is by bauxite (Al2O3 forced the 3 h2o) and preparation of diaspore, for the high purity requirements of Al2O3, usually prepared by chemical methods.
Al2O3, there are many similar crystal, at present there are more than 10 kinds of known, there are mainly three kinds of crystal type, namely the gamma Al2O3, beta Al2O3, alpha Al2O3 (corundum). Which structure is different, with different properties in high temperature above 1300 ℃ is almost entirely into alpha Al2O3.
Alumina containing aluminum and oxygen. If the bauxite raw materials through chemical processing, removal of silicon, iron, titanium oxide and the product is of high purity alumina raw materials, Al ₂ O ₃ content is in commonly 99% above. Mineral phase by 40% ~ 76% of gamma - Al ₂ O ₃ and 24% ~ 60% of alpha Al ₂ O ₃ composition. Gamma - Al ₂ O ₃ in 950 ~ 1200 ℃ can be transformed into alpha Al ₂ O ₃ (corundum), at the same time the volume shrinkage of significantly.
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