Corrosion is the attack of atmospheric gases on metal surface to change it into salts like oxides, carbonates, sulphides etc. It is a redox reaction and reverse of extraction of metals.
Rusting of Iron: It can be explained according to electro-chemical theory as follows:
Rust is hydrated ferric oxide, i.e.,
Factors increasing corrosion:
(i) Presence of impurities in the metal
(ii) Presence of electrolyte e. g. saline Water
(iii) Presence of moisture or rainy season
Prevention of Corrosion:
It is possible by following methods:
(i) Barrier protection: Metal surface is coated with oil, paints, grease or by electroplating
(ii) Sacrificial protection: Here metal is coated by a more electro-positive metal i.e. it is sacrificed, e.g., Zn is coated over iron, it is called Galvanization.
(iii) Electrical protection: Here metal is connected to a more electro-positive metal by a wire.
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