Electrochemical Techniques for Measurement And Interpretation of Corrosion

Corrosion of metals proceeds by electrochemical processes in most aqueous environments. Hence, electrochemical techniques can be used to study and interpret corrosion phenomena and, in certain instances, to measure the rate of corrosion. Corrosion-potential measurements furnish information on whether the anodic or cathodic process, or both, are controlling corrosion. They may also furnish useful information on film breakdown or film repair. Measurement of the potential distribution in solution by the probe method is laborious but does afford a means of determining corrosion rate and distribution of corrosion. Some of the difficulties of the probe method can be overcome by using a rotating-electrode technique that permits direct observation of the distribution of anodic and cathodic areas. Divided-cell experiments, in which pitted areas are separated from unpitted areas, permit determination of local-cell polarization diagrams as well as rate of corrosion. The polarization behavior of corroding metal electrodes can be used in several different ways to measure the rate of corrosion. A promising recent development in this area is the polarization-resistance method, in which the initial slope of a polarization curve can be used to obtain a reliable estimate of the rate of corrosion.