KINETICS OF OXIDE FILM PASSIVATION IN ALUMINUM ETCH TUNNELS

摘要

The kinetics of oxide film passivation in aluminum etch tunnels were investigated using decreasing current ramps after constant current anodic etching in 1 N HCl at 70℃. The ramps caused the dissolving area at the tunnel tip to be continuously reduced by passivation around its perimeter. Analysis of potential transients and tunnel width profiles shows that the two additive processes contribute to the passivation rate: a potential-dependent Tafel-type kinetic expression, and a term proportional to the time derivative of the potential. The potential driving force is the difference between the potential at the dissolving surface and the repassivation potential there. The kinetic model for passivation is consistent with both potential transients and tunnel width profiles, over a range of current ramp rates. The rate-controlling step of passivation is thought to be potential-dependent desorption of chloride ions from the dissolving surface.