Conditions leading to surface brightening during ECM in passivating electrolytes were investigated by studying high rate transpassive nickel dissolution in acidified nitrate electrolytes under controlled hydrodynamic conditions. The experimental apparatus consisted of a flow channel cell in which constant electrolyte linear velocities between 100 and 1760 cm/sec could be reached. Dissolution experiments were performed galvanostatically at current densities ranging from 0.5 to 30 A/cm2. Over‐all current voltage behavior, current efficiency for metal dissolution and surface appearance were evaluated as a function of applied current density, flow rate, and electrolyte composition. Results indicate that the onset of surface brightening is mass transfer controlled and coincides with the formation of a salt precipitation layer at the anode.
Dr. Madhav Datta and Landolt, D., “Surface brightening during high rate nickel dissolution in nitrate electrolytes”, Journal of the Electrochemical Society, vol. 122, pp. 1466–1472, 1975.