Page 26 - Curriculum Visions Dynamic Book

Anodising aluminium
The word anodising refers to a shiny protective coating that is often applied to aluminium
to improve its looks. It is the opposite to the process of electroplating.
An anode is the electrode of a cell on which
a substance oxidises (corrodes). Anodising is
a process that uses electricity to produce this layer of oxide in a controlled way, in order to protect a surface from further corrosion.
The anodising process
Aluminium is placed in a chemical bath that will carry electricity, usually sulphuric or chromic acid. The aluminium acts as an anode. A cathode, often a carbon rod, is also placed in the bath. This makes an electrolytic cell. An electric current is passed through the cell and the surface of the aluminium immediately begins to change. The acid liberates oxygen at the anode and this combines with
the aluminium to make aluminium oxide.
In air aluminium would develop a very thin surface
coating of oxide, but in anodised aluminium, the oxide is a far thicker protective coating. It is also possible to add colour during this process. And because anodising is a change to the surface of the metal, it does not chip or wear off as a paint or plastic coating might.
Anodised aluminium is used as a decorative form of aluminium on hi-fi and other electrical equipment. It is used for vehicle parts, and can be used for both lighting and electrical fittings.
 These cowboy spurs are anodised so that they will not corrode even when used for long periods out in the rangelands.
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