Film conversion and breakdown processes on carbon steel in the presence of halides

The kinetics of oxide film formation/conversion on carbon steel in the presence of halide anions at pH 10.6 were studied by electrochemical and surface analytical techniques. While variations in breakdown potential are observed in the presence of the different halides, the breakdown potential does not show any systematic dependence on halide type and concentration, and never occurs below 0.0 V vs. SCE. It is proposed that the conversion of Fe₃O₄/γ-Fe₂O₃ to γ-FeOOH leads to a volume change, causing the film to fracture. The halide anion then takes advantage of the opportunity to accelerate breakdown and inhibit repassivation.