A protective layer is formed naturally on the surface of aluminium metal by reaction with oxygen in air.
In the anodizing process, this layer is made of the desired thickness. Anodizing is done by electrolysis.
Dilute Sulphuric acid is taken in the electrolytic cell and the aluminium article is dipped in it as the anode.
When an electric current is passed, hydrogen gas is released at the cathode and oxygen gas at the anode.
A reaction with oxygen occurs and a layer of hydrated aluminium oxide is formed on the anode. Therefore, aluminium article is used as an anode in the anodizing process.
