Aluminum oxide (Al?O?) is a high-hardness compound with a melting point of 2054°C and a boiling point of 2980°C. It is an ionic crystal that can be ionized at high temperatures and is often used to make refractory materials. Industrial Al2O3 is prepared from bauxite (Al2O3?3H2O) and diaspore. For Al2O3 with high purity requirements, it is generally prepared by chemical methods.
There are many isomorphic crystals of Al2O3, and there are more than 10 known ones at present. There are mainly three crystal forms, namely γ-Al2O3, β-Al2O3, and α-Al2O3 (corundum). Different structures have different properties, and they are almost completely converted into α-Al2O3 at high temperatures above 1300°C.