The Dynamic Micropolarization Method: I . Application to Aluminum

Abstract

A new approach is proposed for the study of the rate of corrosion and its decay with time after a protective surface layer is removed by abrasion in situ. The method, termed the dynamic micropolarization (DMP) method, was tested for aluminum electrodes in neutral and mildly acid solutions. The corrosion rate of the in situ‐abraded surface is determined as a function of time (from milliseconds to days). A short current pulse is applied at a given time from the end of each abrasion, and the overpotential is measured in the linear region. The total charge passed during measurement is not enough to form more than a few percent of a monolayer and has a negligible effect on the rate of growth of the oxide. Tafel slopes are determined from macropolarization measurements. They are found to be independent of time after abrasion. The corrosion currents are derived from the measured faradaic resistance using these values of the Tafel slopes. The rate of corrosion varies by an order of magnitude over a period of 18h, the first measurement taken 0.5s after termination of abrasion. Depending on the kinetic parameters of the system, a double pulse method may have to be used, to allow rapid charging of the double layer, before any secondary effects could influence the overpotential. The on‐line computerized system used, with averaging of repeated experiments, yields highly reproducible data, not commonly obtained in electrochemical measurements on solid electrodes. Thus, the experimental system developed here may also have future applications for the accurate determination of kinetic parameters of electrode reactions on solid electrodes.