ABSTRACT
In general terms, corrosion is defined as the degradation of a structural material
by chemical reactions with the environment. From a chemical point of view,
any type of corrosion is basically an oxidation reaction where a metal atom M
loses a number x of negatively charged electrons e to become a positively charged
ion, i.e.,
M ! Mþxe þ xe Metals in particular are the most susceptible to the above type of reaction because
of their characteristic electronic structure. It is recalled from Chap. 2 that metals
have a few valency electrons in the outermost electron shells, which are loosely
bound to the nucleus. As a result, these electrons can be easily separated from the
respective atoms, leaving behind positive ions as indicated by the above reaction.
Naturally, metals exist in the form of oxides or salts corresponding to the most
stable or lowest energy state. Therefore, a metal recovered from its naturally
existing ore always exhibits a tendency to transform to its most stable state result-
ing in corrosion; i.e., corrosion is basically the result of metals seeking their
lowest energy state. It is then evident that corrosion products consist of oxides
or salts.
