Question

Aluminium protects itself against corrosion. Discuss why it is necessary to anodize aluminium to make it corrosion resistant.

Answer 1

Aluminium reacts with air and forms a thin layer of aluminium oxide on it. This layer of oxide prevents further reactions and protects the metal from corrosion. This is how aluminium protects itself against corrosion.
$4\mathrm{Al}+3{\mathrm{O}}_2\to 2{\mathrm{Al}}_2{\mathrm{O}}_3$
But this oxide layer is not uniform and may lead to corrosion over a period of time. If it is more uniform, the metal below the layer would be well-protected. This can be made with the help of a process called anodising. In this process, electric current is passed through sulphuric acid, utilising aluminium as anode. Oxygen, which is liberated at anode, reacts with aluminium and forms a uniform oxide layer of aluminium, which protects the metal from corrosion. This is why anodising of aluminium is essential.