The spontaneous destructive oxidation of metals is called corrosion .
Corrosion takes place through an electrochemical cell.
The two half-reactions use the corroding metal itself as both the electrodes and the electronic conductor of the external circuit. The ionic conductor is usually a film of aqueous solution on the surface of the metal. All of us know that iron rusts, and that iron pipes corrode in wet soil. This reaction of corrosion is an electrochemical process. In many corrosion reactions the metal is oxidized to a soluble form.