Aluminium oxide (Al2O3), also known as alumina, is a chemical compound made up of aluminium and oxygen. It is a chemical compound composed of aluminum and oxygen. It is the most common of several aluminum oxides and has been specifically identified as aluminum oxide. It is a white or nearly colorless crystalline powder with a melting point of 2,072°C and a boiling point of 2,977°C. In various forms and applications, it is known as alumina and may also be known as aloxide, aloxite, or alundum.
Aluminium oxide is a common material used in various industrial applications due to its hardness, high melting point, and electrical insulation properties. It is commonly used as an abrasive in sandpaper, grinding wheels, and polishing compounds.
Al2O3 is an electrical insulator but has a relatively high thermal conductivity (30 Wm−1K−1) for a ceramic material. Aluminium oxide is insoluble in water. In its most commonly occurring crystalline form, called corundum or α-aluminium oxide, its hardness makes it suitable for use as an abrasive and as a component in cutting tools.
- Chemical formula: Al2O3
- Molar mass: 101.960 g·mol−1
- Appearance: white solid
- Odor: odorless
- Density: 3.987 g/cm3
- Melting point: 2,072 °C (3,762 °F; 2,345 K)
- Boiling point: 2,977 °C (5,391 °F; 3,250 K)
- Solubility in water: insoluble
- Solubility: insoluble in all solvents
It occurs naturally as the mineral corundum in its crystalline polymorphic phase α-Al2O3, varieties of which form the precious gemstones ruby and sapphire. Al2O3 is important in the production of aluminum metal, as an abrasive due to its hardness, and as a refractory material due to its high melting point.
Corundum is the most common crystalline form of aluminium oxide found in nature. Rubies and sapphires are gem-quality forms of corundum that get their colors from trace impurities. Traces of chromium give rubies their distinctive deep red color and laser qualities. Sapphires come in a variety of colors due to impurities such as iron and titanium. The mineral deltalumite contains an extremely rare form.
Aluminium oxide also has many other applications such as in the production of ceramics, electrical insulators, catalysts, and as a filler material in the manufacturing of plastics and rubber.
It is also used in the production of aluminium metal, as it is the main raw material for the electrolysis process used to extract aluminium from its ore, bauxite.