Alumina, which is also known as aluminium oxide or alumina (British English) is a chemical compound of aluminum and oxygen with the formula Al2O3. It is the most common of all the aluminium oxides.
It occurs naturally in its crystalline alpha phase as mineral corundum, varieties of which form the precious gemstones ruby and sapphire. It is an odorless, colorless, solid, non-oxidizing material.
In its crystalline alpha phase it is the most stable form of aluminium oxide. It is a very hard mineral with a hardness of 9 on the Mohs scale, making it an excellent abrasive.
Some of the most popular abrasive materials use this mineral as their main ingredient. It is used to make many types of sandpaper, including billiard cue tip “chalk.”
Alumina is also useful as a catalyst in a number of industrial processes, such as hydrodesulfurization, which converts hydrogen sulfide waste gases into elemental sulfur. It is also a catalyst support for a wide range of industrial catalysers, such as those used in the Claus process.
It is also a refractory material, and is used for lining high-temperature appliances like kilns, furnaces, incinerators, and reactors of all sorts.
Alumina is an amphoteric substance, meaning that it reacts with both acids and bases, forming sodium aluminate or alpha-Al2O3 depending on the acidity and the base used. This is because the alumina ions in a molecule of this material are bonded to two oxygen atoms, which allows them to interact with both types of compounds. This is what makes alumina a good choice for refractory coatings.