Passive film growth on carbon steel and its nanoscale features at various passivating potentials

In this work, the passivation and topographic sub-structure of passive films on a carbon steel in a carbonate/ bicarbonate solution was characterized by electrochemical measurements, atomic force microscopy and X-ray photoelectron spectroscopy. When passivating at a potential near the active-passive transition, the film contains the mixture of Fe3O4, Fe2O3 and FeOOH, with numerous nanoscale features. As the film-forming potential shifts positively, the passive film becomes more compact and the nanoscale features disappear. When the film is formed at a passive potential where the oxygen evolution is enabled, the content of FeOOH in the film increases, resulting in an amorphous topography and reduced corrosion resistance. (C) 2016 Elsevier B.V. All rights reserved.