Pourbaix diagram for iron in aqueous solutions There is, it seems, a feeling, perhaps unconscious, that the method is basically unsound, and the purpose of the present paper is to explain, in as simple a way as possible, why anodic protection is possible, and when it may be expected to be useful.
It is probably because of this that this method, which is extremely powerful and is often applicable just when cathodic protection is not possible, has not been easily accepted as a practical proposition and is still regarded as only a laboratory curiosity. It is not so well known that corrosion can also be prevented in suitable cases by anodic polarisation, and it is certainly very much more difficult to understand why this should be so from the somewhat oversimplified theory of corrosion which the non-specialist is bound to have. In fact, the position is somewhat more complicated and, in many cases, other factors override this apparently simple one. Corrosion involves the oxidation of the metal and it is reasonable to expect that cathodic polarisation, which discourages oxidation and favours reductions at the metal surface, should tend to cause protection. It is well known that corrosion can sometimes be controlled by cathodic currents and, even with an elementary knowledge of electrochemistry, it is easy to appreciate why this should be so.
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