Reaction Mechanisms of High-Rate Copper Electrochemical Machining in Chloride and Sulfate Electrolytes

The electrochemical dissolution behavior of copper in sodium chloride and sodium sulfate electrolytes is analyzed mainly by measuring polarization curves. The nature and the influence of the surface film formed at the limiting current density plateau, on the reaction mechanism and etching behavior were examined. For high current densities, novel complexation mechanisms for the dissolution were assumed. These "Solvo-Chlorination" and "Solvo-Sulfatization" mechanisms were similar to the "Solvo-Nitration" mechanism that has recently been postulated for nitrate electrolytes. Differences in the limiting current density and the re-rise voltage (15-35 V in NaCl, 35 V in Na2SO4) were strongly connected to the properties of the surface film and the valence of dissolution.