Corrosion is a phenomenon of oxidation of metal in the presence of oxygen when it is exposed to external environmental factors which include moisture, acid rain, etc., and chemicals like acids, bases, etc.
For example - Rusting of Iron, tarnishing of Silver wares, green coating on Copper vessels.
It can be prevented by a number of methods like paints and varnishes, alloy formation, galvanization, etc.
The main causes of corrosion are given below.
Weather conditions - Metals on exposure to environmental elements like water, wind, and moisture oxidize the metal surface and corrode it. For example formation of an Oxide layer on any metal surface like Fe, Al, etc forming Iron (III) oxide ( ), Aluminium oxide ( ) etc.
Harmful gases and chemicals - Corrosive substances like Sulfur oxide, Hydrogen oxides, acids, bases, etc also promote corrosion of certain electrical equipment. For example - Oxidation of Copper wires.
Biological Substances - Dirt and bacteria also cause corrosion in metals. For example - inland water pipes, waste pipes etc.