Diffusion in Alumina Single Crystals

Abstract

Alumina one of the oxide ceramics is the most cost effective and widely used material. With an excellent combination of properties and attractive price alumina has a wide range of application. It is available in purity ranges of 94–99.8 % and usable for critical high temperature application. Alumina exhibits strong ionic interatomic bonding giving rise for its excellent properties such as high hardness, high melting point and its wear resistance. The chemical inertness is of particular interest at high temperature. The measuring and understanding of self-diffusion and other diffusion phenomena, which control many properties, such as sintering, grain growth, creep and most solid-state reactions, have been matters of interest for the successful operation of alumina. The composition of the ceramic body can be changed to enhance particular desirable material characteristics thus for example improving hardness (strength properties) and change color, which is achieved by adding various solutes. Therefore a knowledge of solute diffusion is also essential to understand and maintain the desired property on exposure to high temperature. Since diffusion controlled reactions in grain boundaries and dislocations are faster than in bulk, measuring and understanding the diffusion properties in these locations is of great interest. Its excellent dielectric properties, makes alumina an exceptionally good high temperature electrical insulator. Diffusion data (self, solute, grain boundary and dislocation) are compiled at the end of the chapter.