Evaluation of the corrosion protection of steel by anodic processing in metasilicate solution using the scanning vibrating electrode technique

•Microelectrochemical characterization of the protection imparted to steels by prior anodization in metasilicate solution•Susceptibility to localized corrosion influenced by surface modification of the surface•Onset of anodic local dissolution monitored by SVET as function of steel composition and substrate polarization•Distinct effect of polarization on the onset of pit nucleation for pristine and metasilicate treated stainless steel

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.

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