Analysis of Convective Mass Transfer by Potential Relaxation: III . Active and Passive Copper Dissolution at a Rotating Disk

Abstract

A linear potential relaxation technique was used successfully to determine effective liquid‐phase mass transfer boundary‐layer thicknesses during active dissolution and cupric sulfate salt film thicknesses during passive etching for a copper rotating disk electrode immersed in a electrolyte. Experimentally measured concentration over‐potentials immediately after current interruption were found to decay linearly with the square‐root of time. A theoretical model was derived to calculate liquid‐phase effective mass transfer boundary‐layer thicknesses or salt film thicknesses from the slope and intercept of the linear potential decay regime. For active copper dissolution, effective mass transfer boundary layer thicknesses were ≈56% smaller than those for cathodic deposition. The following Sherwood‐Schmidt‐Reynolds number correlation was developed from these relaxation experimentsThe effective mass transfer boundary‐layer thicknesses were used to accurately predict the critical current density for prepassive salt film formation. Experimentally determined salt films ranged in thickness from , depending on the anode potential, the passivation time, and the disk rotation speed. Steady‐state film thicknesses were dependent on the 1/3 power of the applied potential and were inversely proportional to the disk rotation speed raised to the 1/3 power.