Aluminiumoxiden

Aluminium oxide, with formula Al2O3, is a family of inorganic compounds. The most common natural form is corundum, a hard crystalline oxide. Impurities in corundum produce gemstones such as ruby (red) and sapphire (various colors). The material is valued for hardness, chemical stability, and wide industrial use.

Alpha-alumina (alpha-Al2O3) is the most stable crystalline form. It has Mohs hardness 9, a melting point around 2072°C, and a high refractive index, making it important in jewelry and optics. It is an excellent electrical insulator and chemically resistant to most acids and bases, though it dissolves in strong caustics.

Industrial production starts with bauxite and the Bayer process to produce alumina (Al2O3·xH2O). Alumina is then reduced to aluminum metal by the Hall–Héroult process, using cryolite as a flux. As a material, alumina is used as an abrasive, in refractories and ceramics, and as a catalyst support. Activated alumina serves as a desiccant and filtration medium.

Safety: Aluminium oxide is relatively non-toxic, but fine dust can irritate the lungs and eyes. Handling and dust control are important in workplaces; it is inert in many environments but can dissolve in strong alkali or some acids to form aluminates.