Breakdown of the Passive Film on Polycrystal and Single Crystal (100) Nickel by Chloride

Chloride ion‐induced breakdown of the passive films on polycrystal and single‐crystal (100) nickel surfaces was studied in terms of the film breakdown potential and induction time as a function of chloride concentration. The film was grown in a deaerated chloride‐free borate buffer solution at to a constant thickness of 4.5 mC/cm2, and and were determined potentiodynamically and potentiostatically, respectively, after injecting chloride ion into the solution. The film breakdown potential was found to increase linearly with the potential scan rate, and the critical pitting potential (the breakdown potential at zero scan rate) decreased linearly with . The presence of grain boundaries on the polycrystal surface decreases the intercept of the relationship slightly, but did not significantly change the slope. The intercepts are higher than most of the values reported in the literature, although the slope is similar to previously found values. The induction time for pit nucleation on the two crystal forms for was found to decrease with increasing potential. The experimental data are analyzed in terms of the halide nuclei and point defect models for passivity breakdown.