ANTI‐CORROSION METHODS AND MATERIALS: 2: Forms of corrosion Part 1: Galvanic and concentration cells

Galvanic corrosion It is commonly held that it is the electrochemical potential between two surfaces that is the controlling factor for the rate of corrosion. Table 1.2 in chapter one of this series lists the standard oxidation potentials. However, the difference between the potentials of the two metals plus the difference in the e.m.f. due to the concentration of ions is the reversible electrochemical potential, which only applies when there is no current flowing. The degree of corrosion that occurs is based on the potential difference existing when there is a known current flowing. Thus the baser of two connected metals can be extremely corrosion‐resistant, even if the potential difference is quite large, provided at least one of them has good polarisation characteristics. Metals that are particularly damaging to ferrous metals not only have a very low potential, but are also to all practical purposes insoluble in the corrosive environment around the steel. Thus it is that one of the worst is copper.