Corrosion processes occurring on stainless steel 304 surfaces under anodic polarization have been characterized using scanning electrochemical microscopy (SECM) and the scanning vibrating electrode technique (SVET), complemented with conventional potentiodynamic polarization curves. Stable pit formation has been detected by SVET on the samples as result of surface modification under electrochemical control, which may include the previous electrochemical reduction of passive oxide layer if the media is not aggressive enough to induce pitting at small overpotentials. Additionally, the sample generation -tip collection operation mode of the SECM has enabled the detection of local release of iron (II) ions, as well as their conversion to iron (III), both processes being greatly affected by the potential applied to the substrate.

Keywords: corrosion protection steel metasilicate ions surface modification anodic treatment scanning vibrating electrode technique a b s t r a c t Anodic processing in metasilicate solution was investigated for the improvement of the corrosion resistance of various steels, namely F111 low alloy carbon and 304 stainless steels, as well as on galvanized steel cut edges. The efficiency of the prior electrochemical treatment for each material was tested during their exposure to naturally-aerated aqueous chloride solutions of different aggressiveness. Analysis was performed using the scanning vibrating electrode technique (SVET) in order to detect local ionic current distributions over the samples under study associated to the corrosion reactions. The onset of corrosion processes was greatly inhibited after anodic processing with metasilicate on both the low alloy carbon steel and the galvanized steel cut edge. Conversely, SVET analysis of unbiased 304 steel samples tested in 0.1 M chloride-containing solution did not show differences between pristine and metasilicate-treated surfaces. Differences in the electrochemical reactivity between treated and non-treated 304 steel surfaces were only observed after partial removal of the corresponding passive layers under operator-controlled polarization.

No abstract