A revised model for predicting corrosion of materials induced by alternating voltages

A model that is an improvement upon the previous models for the corrosion of materials under superimposed voltages is proposed. In this model both impedance due to faradaic processes as well as charging current due to the double layer capacitance are considered. Closed form solutions for DC corrosion current and the root-mean-square current are obtained. It is shown that for the model under consideration, the root-mean-square current is a better indicator of the corrosion processes involved than the DC current. The root-mean-square current increases with the peak potential of the voltage and is found to be a minimum at a certain DC potential. The minimum root-mean-square current and the attendant DC potential are found to be a function of the absolute ratio of the anodic Tafel slope to the cathodic slope ( r). For example, for r less than and greater than unity, the DC potential at which the root-mean-square current is a minimum is, respectively, more active and more noble than the DC corrosion potential. For r equal to unity, the DC potential at which the root-mean-square current is a minimum is equal to the DC corrosion potential. The total r.m.s. current is found to increase with the frequency of the superimposed alternating voltage and the Tafel slope ratio, r.