In-situ spectroelectrochemistry (UV-visible and infrared) of anodic films on iron in neutral phosphate solutions

Abstract

The composition of anodic films on iron formed at different potentials in neutral solutions has been investigated by in-situ UV–vis and IR spectroscopies in the presence of PO4 3−, a non-contaminant inhibitor used in anticorrosive paints. Optical and electrochemical determinations were used to detect and characterize two well-defined current waves in the active region of Fe and a following passive zone at more positive potentials. The response has been associated with the presence on the surface, in the dissolution zone, of Fe3 II[PO4]2 as the main species and probably some [FeIIIPO4]. [FeIIIPO4] has been detected in the passive region by in-situ IR spectroscopy. Only minor amounts of Fe2+ and Fe3+ species in solution have been detected optically. These phosphated overlayers are believed to provide extra protective properties to the passivating film.