Diffusion and Solid‐Film Formation during Electropolishing of Metals

Abstract

Various metals and electrolytes were used for potentiostatic electropolishing. When measuring the current‐time behavior over several orders of magnitude and for the different temperatures, three stages were observed: (i) a short stage I , during which the current density was approximately constant; (ii) during the following stage II saturation of the dissolved metal ions (reaction products) was obtained in the vicinity of the anode surface, and the current density decreased with the reciprocal square root of time; and (iii) after sufficiently long times, during stage III a steady‐state current density was approached by an exponential time law. The known theoretical models, based on the work of Elmore, are able to explain the relations between current density, time, and temperature for stage I and II . For stage III a new model is presented which takes convection within the electrolyte into account. The possible formation of a solid film at the transition from stage I to stage II is thought to be responsible for characteristic deviations from the expected current‐time behavior. A mathematical treatment of this formation yields film thicknesses of 3–30 nm.