Alumina, Structure and Properties

Alumina materials are a family of ceramics whose principal constituent is α-Al2O3. On a weight basis, these materials have the largest share of the ceramics world market. First, the crystalline structure and the main properties of single-crystal α-Al2O3 are described. Then, production of α-Al2O3 and fabrication of alumina materials are briefly addressed. The mechanical, thermal and functional properties of alumina materials are discussed in relation to those of sapphire and the microstructure of the materials. The effect of temperature on the properties is addressed. Alumina materials have a unique combination of properties retained at high temperature – hardness and stiffness, wear resistance, chemical inertness and associated corrosion resistance and sufficient strength. They can also present excellent electrical insulating properties and, when fully dense, they can be translucent and even transparent depending on grain size. Chemical inertness of alumina allows also its use in biological environments, biocompatibility being one of the most valuable properties of alumina. In addition to such a unique set of properties, alumina raw materials are available at relatively low cost and alumina components with wide ranges of shapes and sizes and controlled microstructure can be fabricated by pressureless sintering. The main applications of alumina materials are described on the basis of the required properties.