Prevention of corrosion :
The corrosion can be prev ented by the following methods.
1) Barrier protection :
In this method the metal surface is not allowed to come in contact with moisture, oxygen and carbon dioxide. This can be achieved by the following.
a) By coating iron with oils, paints, coal tar, grease, pitch, etc.
b) By blowing steam over red hot iron to form protective coating of Fe3O4 .
c) By alloying iron with Ni, Cr, Si, etc.
2) Sacrificial protection:
Sacrificial protection means covering the iron surface with a layer of metal which is more electropositive than iron thus prevents iron from losing electrons. It is done by following methods.
a) By galvanisation (by dipping iron in a bath of molten zinc).
b) By tinning (by dipping iron in molten tin).
c) By the coating of copper.
d) Decorative coating : By using Zn, Mg and A/ powders mixed with paints.
3) Electrical protection:
In this method, the iron object to be protected from corrosion is connected to more active metal eg. magnesium, zinc or aluminium directly or through a wire. The iron object acts as cathode and the protective metal acts as anode. The anode is gradually used up to the oxidation of metal to its ions due to loss of electrons. Hydrogen ions collect at cathode and prevent rust formation.
4) Using anti-rust solution:
On applying alkyl phosphates and alkyl chromates to the iron objects corrosion can be prevented.
