Alumina

Alumina (Al 2 O 3 ) is synthetically produced aluminum oxide. It is not soluble in water or ethanol. It is a white, colorless, crystalline substance made from bauxite, a naturally occuring ore containing variable amounts of hydrous, or water containing, aluminum oxides. Alumina has a low electic conductivity, high strength, extreme hardness (it is a 9 on the Mohs hardness scale) and a high melting point of 2,050° C or 3,700° F. Alumina is used in aluminum metallurgy, industrial ceramics, and chemical processing.

white or nearly colourless crystalline substance that is used as a starting material for the smelting of aluminum metal. It also serves as the raw material for a broad range of advanced ceramic products and as an active agent in chemical processing.

Alumina is the most cost effective and is widely used material in the family of engineering ceramics.


 * Properties**
 * hard, wear-resistant
 * resists strong acid and alkali attack at elevated temperatures
 * good termal conductivity
 * excellent size and shape capability
 * high strength and stiffness

The Bayer Process
Most aluminca is made through the Bayer process. In the Bayer process, bauxite is crushed and then mixed in a solution of sodium hydroxide. It is then seeded with crystals to precititate aluminum hydroxide. It is then heated in a kiln so that the water is driven off to produce a dry, or powdery substance. Some alumina, however, is still produced by melting bauxite in an electirc furnace.

Uses and Types
There are different types and uses of alumina. Smelter-grade alumina makes up 90% of all alumina produced. Smelter-grade alumina is electrolyzed into aluminum metal. Calcined alumina is used to make ceramic products such as spark plug indicators, bone and dental implants, labratory ware, sandpaper grits and grinding wheels. Alumina is also used to make synthetic sapphires and rubys. With the addition of zirconia particles, alumina is used in industrial cutting tools. When a small amount of magnesia is added, alumina is used as the clear, gas container in a high pressure sodium-vapor street lamp.
 * Occurs in nature as a the mineral corundum and gemstone form. i.e Sapphire or Ruby.