Cathodic protection can be achieved by either one of two main methods; that is, by using current supplied from some external source, as a motor-driven generator, or by means of galvanic action resulting from contact of an anodic metal with the structure to be protected. In this paper, attention will be directed mainly to the second method of cathodic protection.
When a dissimilar metal or alloy is used to supply current to a steel structure, the first requirement is that the dissimilar metal or alloy must be definitely anodic to steel. The solution potentials of metals or alloys depend, to a considerable extent, on the medium in which they are exposed. However, a reasonable means of comparing the inherent reactivity of different metals is based on measuring the solution potential of each metal in a solution which is unit activity in the ions of that particular metal. Generally, these potentials...
