Aluminina

Aluminina, commonly called alumina, is the oxide of aluminum with the chemical formula Al2O3. It occurs naturally as the mineral corundum, which in its pure form is colorless; trace impurities produce the gem varieties sapphire and ruby, while other colors are caused by different dopants. Synthetic and technical grades of alumina are widely manufactured for industrial use.

Alumina has a hexagonal, close-packed crystal structure in its most stable form, known as alpha-alumina or corundum. It is a hard, high-m refractoriness ceramic with a high melting point (about 2072 °C), a density of around 3.95 g/cm3, and Mohs hardness of 9. It is an electrical insulator with a wide band gap, and it exhibits chemical inertness under many conditions. It is amphoteric, dissolving in both acids and bases under appropriate conditions.

Production and sources: commercially, alumina is produced from bauxite ore via the Bayer process, which converts bauxite to purified Al2O3. The alumina is then refined into primary aluminum metal by electrolysis in the Hall–Héroult process. Alumina is also manufactured as a high-purity ceramic material for specialized applications.

Applications: alumina is used as an abrasive (grinding wheels, polishing powders), as a refractory and ceramic material in crucibles and reactors, and as protective coatings and substrates in electronics. It serves as catalyst support, a filter and membrane material in industrial processes, and, in gem form, as a durable gemstone and synthetic sapphire for optical and technical uses.

Safety and environmental notes: handling fine alumina powders requires precautions to avoid inhalation, as prolonged exposure can pose health risks; general industrial use emphasizes appropriate containment and ventilation.