Kinetics of H2O2 reaction with oxide films on carbon steel

The nature of carbon steel surfaces in 0.01 M borate solutions (pH 10.6) have been characterized using a range of electrochemical techniques and ex situ analyses such as Raman and Auger spectroscopy. Their subsequent behaviour on exposure to 10(-3) M H2O2-containing solutions has also been studied. The anodically oxidized carbon steel surfaces have been characterized according to three regions: (I) the potential range <-0.5 V (vs SCE), when the surface is active and covered by Fe-II/ Fe-III oxide/hydroxide; (II) the potential range -0.5 V to similar to 0.0 V when the surface is passivated by an outer layer of Fe-III oxide/hydroxide over the inner layer of Fe-II/Fe-III oxide/hydroxide; and (III) potentials >0 V when further growth of the underlying layer appears to lead to minor film breakdown/restructuring. The addition of H2O2 to films grown in the passive region or above (II and III) leads initially to a degradation of the outer layer allowing increased growth of the inner layer. Subsequently, the outer passivating layer is repaired and passivity re-established. These changes appear to be confirmed by Raman spectroscopy. (c) 2007 Elsevier Ltd. All rights reserved.