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    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.