Film Breakdown Processes on Carbon Steel in the Presence of Large Anions

Abstract

The objective of this research is to determine the features, which cause film breakdown leading to pitting in solutions containing halide anions, (e.g., Cl-, Br- and I-). It is commonly accepted that the influence of Cl- on passive film properties is the key feature in breakdown, and the possibility that transformations in the oxide are responsible has not been considered. While variations in breakdown potential are observed in the presence of the different halide anions, the key feature leading to breakdown appears to be subtle changes in oxide structure/composition. A potential interpretation may be the field-assisted conversion of the FeII/III oxide (Fe3O4 to Gama-Fe2O3) to Gama-FeOOH, resulting in a considerable volume change with the consequential exposure of the underlying metal.