What do we mean by electrochemical corrosion?

Smart Alec, Bedford

Corrosion of metals can be split into 2 main types; high temperature corrosion and aqueous corrosion. High temperature corrosion occurs due to oxidisation of a metal or alloy and high temperatures usually above 350°C. Aqueous corrosion is an electrochemical process, which requires (as the name suggests) liquid water to be present.

What we mean by electrochemical is that it involves both an oxidation process or anodic process, i.e. metal dissolution and a reduction or cathodic process, such as oxygen reduction or hydrogen evolution. In neutral waters, the main cathodic reaction is oxygen reduction, whilst in acids the dominant cathodic reaction is hydrogen evolution. Since in freely corroding situations, the anodic reaction rate must equal the cathodic reaction rate, a simple way of reducing the corrosion rate in neutral waters is to remove the dissolved oxygen.


                                M → Mz+              +             ze-                           Anodic

                e.g.        Fe → Fe2+            +             2e-


                2H2O + O2            +  4e-       →         4OH-                      Cathodic

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