The term corrosion generally refers to the deterioration of a metal by an electrochemical process. There are many examples of corrosion, including rust on iron, tarnish on silver, and the green layer that forms on copper and brass.
Iron undergoes a redox reaction in the presence of air or water to form hydrated iron (III) oxide (Fe2O3.nH2O) called rusting of iron.
Rusting requires oxygen and water. The iron is oxidised, in this reaction:
4Fe(s) + 3O2(g)+ 4H2O(l) → 2Fe2O3.2H2O(s)
The corrosion of iron and steel has a special name: rusting. The red-brown substance formed is rust.
