Aluminum Oxide

Aluminum Oxide is most significant use is in the production of aluminum metal, although it is also used as an abrasive due to its hardness and as a refractory material due to its high melting point. The Production of Aluminum Oxide is by first digesting Bauxite ore, containing a maximum of 55% alumina, in a hot sodium hydroxide solution. At temperatures of around 175°C, the aluminum dissolves and forms sodium aluminate. High-purity alumina is filtered from the compound, and the resulting solution is transitioned to a precipitator tank for cooling. As it cools, the solution becomes seeded with extremely fine-grained aluminum hydroxide (Al(OH)₃) crystals. These crystals are moved to a kiln for calcination at temperatures approaching 1,260°C, yielding aluminum oxide powder.

High aluminum oxide refractories are a mainstay in petrochemical applications, particularly syngas reactors which have demanding thermochemical and thermomechanical process conditions. Another critical application of Al₂O₃ ceramics is in autothermal reforming (ATR). By using Aluminum oxide the refractories are an extremely robust, with high hardness, strong resistance to abrasion and high compression strength. It is highly resistant to thermal shock and chemical attack even at raised temperatures. These properties are why aluminum oxide stands out as the material of choice for low-cost production and manufacturing. Large tonnages of aluminium hydroxide, from which alumina is derived, are used in the manufacture of zeolites, coating titania pigments, and as a fire retardant/smoke suppressant. Aluminum oxide is an electrical insulator but has a relatively high thermal conductivity (30Wm−1K−130Wm−1K−1) for a ceramic material. It is thus used as insulating material in power electronics.