Kinetics of Iron Corrosion in Concentrated Acidic Chloride Solutions

The kinetics of active iron dissolution at 25°C has been studied in deaerated 1 N and 6 N chloride solutions for hydrogen ion concentrations of 0.1–6.0 N . For 1 N chloride solutions with , the dissolution reaction is described by anodic Tafel slope and electrochemical reaction order with respect to hydrogen ion activity . These parameters are characteristic of a dissolution mechanism in which chemisorbed halide ions interact with adsorbed hydroxyl ions in a two‐electron rate‐determining step. For 6 N chloride solutions, this mechanism holds only over a narrower (H + ) region up to 0.24 N , in which . With increased ; and for , indicating that the hydrogen ion (and no longer the hydroxyl ion) catalyzed the dissolution reaction. A positive value of ensues for synergistic adsorption of hydrogen ions on the halide ion covered surface. A formal detailed dissolution mechanism is proposed, giving and , in agreement with experiment. Alternate dissolution mechanisms including one‐electron transfer schemes are discussed.