allumina

Allumina is a common name for aluminium oxide, a chemical compound with the formula Al2O3. It occurs naturally as the mineral corundum, which, in its varieties, forms the gemstones sapphire and ruby. Industrially, alumina is produced from bauxite ore and is a key intermediate in the production of aluminum metal as well as used directly in various applications.

Alumina exists in multiple crystalline forms. The most stable form at ambient conditions is alpha-alumina (corundum), a hard, dense material with a melting point around 2072°C. Other polymorphs, such as gamma-alumina, have higher surface areas and are used as catalysts and catalyst supports. Alumina is known for its high hardness, high melting point, chemical inertness, and electrical insulation.

Production and use. In industry, bauxite is refined by the Bayer process to produce alumina. This alumina is then subjected to Hall–Héroult electrolysis to yield aluminum metal, though alumina itself has many direct applications without smelting. Alumina’s properties make it valuable as an abrasive (sandpapers and grinding wheels), a refractory material for furnace linings, and as ceramic components in wear-resistant parts and biomedical implants. It is also employed as a catalyst support, in filtration and membrane technologies, and as a substrate material for sapphire in optics and electronics.

Safety and handling. Fine alumina powders can be abrasive and may pose inhalation risks; handling protocols in industrial settings emphasize dust control and personal protective equipment. Overall, aluminium oxide is regarded as chemically stable and relatively inert in many environments.