Alumina (Aluminium Oxide) - The Different Types of Commercially Available Grades Very large tonnages are also used in the manufacture of monolithic and brick refractories. It is also mixed with other materials such as flake graphite for other, more difficult applications are envisaged, such as pouring spouts and sliding gate valves. Key Properties Aluminium Oxides key properties are shown below. High compression strength High hardness Resistant to abrasion Resistant to chemical attack by a wide range of chemicals even at elevated temperatures High thermal conductivity Resistant to thermal shock Annual Production Annual production of aluminum oxide is 45 million tonnes. 90% of this is used in the manufacture of aluminium metal by electrolysis. Where Does Alumina Come From? Most of the aluminium oxide produced commercially is obtained by the calcination of aluminium hydroxide (frequently termed alumina trihydrate or ATH). The aluminium hydroxide is virtually all made by the Bayer Process. This involves the digestion of bauxite in caustic soda and the subsequent precipitation of aluminium hydroxide by the addition of fine seed crystals of aluminium hydroxide. Phases Aluminium oxide exists in many forms, α, χ, η, δ, κ, θ, γ, ρ; these arise during the heat treatment of aluminium hydroxide or aluminium oxy hydroxide. The most thermodynamically stable form is α-aluminium oxide. Commercial Grades Low Soda Many applications, particularly in the electrical/electronic areas, require a low level of soda to be present in the aluminum oxide. A low soda alumina is generally defined as with a soda content of