Diffusion and migration in the electropolishing and anodic dissolution of metals

The solution of the Nernst-Planck equation for the electropolishing of metals is presented. The migration and diffusion equations are solved for the cases where the metal ion is transported independently of the anion of the electrolyte and when ion pairing occurs. It is concluded that under polishing conditions, the surface concentration of acid is decreased by the salt solubility. It is shown that this has important practical consequences for defining the conditions required for electropolishing and in the selection of the acid used.