The Polarization Curve and Anodic Protection

Polarization curves provide the basic information for derivation and study of anodic protection. Methods are surveyed for the measurement of polarization curves, one of them based on slow continuous or stepwise change of the applied potential under constant electrochemical conditions. The other method, applicable also to variable conditions, derives polarization curves from multipoint current-density-time curves. The analysis of polarization curves and of their components is discussed with respect to pure metals and alloys. In the survey of anodic protection of alkaline pulping digesters the effect of polysulfides as depolarizers and of reducing reagents is explained. In many other applications of anodic protection the absence of reducing reagents demands the application of a potentiostat to prevent a shift to the transpassive range. An equation is given of the extension of anodic protection reached in a pipe with current supply from one point. Stability considerations provide a basis for the choice between anodic and cathodic protection. 2.3.5, 5.2.5.