**6. Classification**

Corrosion has been classified into different methods. They are


Wet corrosion occurs when the metal is in contact with an electrolytic conducting liquid or when two dissimilar metals or alloys are either immersed or dipped partially in the electrolytic conducting solutions. This is always associated with low temperature conditions. The corrosion process involves two reactions.

At anode:

M (metal) → Mn+ + ne<sup>−</sup> (oxidation) Mn + (metal ion) → Dissolves in solution Mn + (metal ion) → Forms compound such as oxide At Cathode:

2H+ + 2e<sup>−</sup> → H2↑ (in acid solution) 2H2O + 2e<sup>−</sup> → H2↑ + 2OH<sup>−</sup> (in alkaline solution) O2 + 2H2O + 4e<sup>−</sup> → 4OH<sup>−</sup> (in neutral solution)

Dry corrosion takes place mainly through the direct chemical action of atmospheric gases and vapors present in the environment 30. This is most often associated with high temperature.
