The Rate-Determining Stage in the Anodic Dissolution of Metals

Abstract

An experimental study has been made, using the potentiostat technique, of the limiting current densities of metal dissolution in electrolytic polishing solutions. The limiting current densities show the features expected for diffusion currents, and the effect of the addition of the metal dissolution product to the electrolyte indicates that it is the diffusion of this substance away from the anode which determines the overall rate of the electrode reaction. Electrolytic polishing does not occur until the limiting current density has been reached, and experiments with composite anodes show that the diffusion current densities at peaks in the surface are much higher than at cavities. These observations are interpreted by a simple diffusion layer treatment of the kinetics of the anode reaction, and their bearing upon the mechanism of electrolytic polishing is reviewed. Some practical recommendations for electrolytic polishing are made.