what are examples where corrosion is useful 2 us?
Corrosion as such is an undesirable phenomenon. It is the process in which metals objects are deteriorated by action of air, moisture, chemicals etc. Corrosion causes damage to car bodies, bridges, iron railings, ships and all objects made of metals (especially Iron). Rusting of iron causes great economic loses every year.
However, corrosion of aluminium is useful. Corrosion of Aluminium occurs when the metal is exposed to oxygen, according to the following reaction :
4 Al(s) + 3 O2 (g) → 2 Al2O3 (s)
Thus a protective layer of aluminium oxide is formed on the surface of the metal, which renders the metal passive and prevents its further corrosion.