Determination of Pit Growth Rates on Aluminum Using a Metal Foil Technique

Abstract

Abstract A new method to study the pit growth kinetics is proposed. On metal foils, the perforation time of growing pits is easily measured by an appropriate detecting system on the unexposed side of the specimen. Using metal foils of different thicknesses, the pit growth kinetics can be determined. The results obtained on aluminum show that the pit growth rate is not only time dependent but also markedly influenced by the applied potential and the chloride concentration of the electrolyte. Additions of foreign ions either accelerate or inhibit pit growth depending on the type and concentration of the ions added. The accelerating effect depends directly on the conductivity of the electrolyte. Furthermore, pit growth limiting potentials have been determined, below which pit growth is not possible. From the results obtained on aluminum, it can be concluded that the potentiostatically determined pitting potentials depend primarily on pit growth rather than on pit initiation.