Among the oxides with melting points over 2000°C, alumina is the most flexible and inexpensive material. Alumina ceramics are the most widely used, widely used and most productive ceramic materials among oxide ceramics. Al2O3 has 12 kinds of homogeneous polymorphisms, but there are mainly 3 kinds of applications, namely α-Al2O3, β-Al2O3 and γ-Al2O3, these 3 kinds of crystals have different structures, so their properties have great difference.
α-Al2O3 is a trigonal crystal system with the most compact structure, low chemical activity, good high temperature stability, excellent electrical properties and the best mechanical properties.
β-Al2O3 is a polyaluminate mineral with a high content of Al2O3. Its chemical composition contains a certain amount of alkaline earth metal oxides and alkali metal oxides, and it can also exhibit ionic conductivity.
γ-Al2O3 is a spinel-type cubic structure. It is unstable at high temperature and has poor mechanical and electrical properties. But it has high specific surface area and strong chemical activity, and can be used as an adsorbent material after technical improvement.