Question

(a) Why does aluminium not corrode right through?
(b) What is meant by 'anodising'? Why is it done?

Answer 1

(a) Aluminium is a highly reactive metal. It reacts easily with oxygen in the air and forms a layer of aluminium oxide on its surface. This layer is very tough and does not allow air to enter the metal for further reaction. This prevents aluminium from further corrosion. Thus, aluminium articles become unreactive toward air and water and do not corrode easily due to the presence of strong aluminium oxide layer on it. Hence, aluminium is highly resistive to corrosion.

(b) Anodising is a method that involves the formation of tough layer of aluminium oxide on aluminium substances by making it anode in the electrolysis of sulphuric acid. Generally, the formation of aluminium oxide layer on aluminium protects it from corroding further. However, if this oxide layer on aluminium is made thicker (by anodising), it will become a strong coating and will prevent corrosion to the maximum.