Journal
ELECTROCHIMICA ACTA
Volume 329, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2019.135159
Keywords
Stainless steel; Oxide film; Passivity breakdown; Corrosion; Surface analysis
Categories
Funding
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (ERC Advanced Grant) [741123]
- Region Ile-de-France
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Electrochemical polarization measurements were combined with surface analysis by Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) to study the alterations of the passive film on 316 L austenitic stainless steel induced by the presence of chlorides in sulfuric acid electrolyte. The work was performed at a stage of initiation of localized corrosion preceding metastable pitting at the micrometer scale as verified by current transient analysis and AFM. The results show that Cl- ions enter the bilayer structure of the surface oxide already formed in the native oxide-covered initial surface state at concentrations below the detection limit of XPS (<0.5 at%), mostly in the hydroxide outer layer where Fe(III) and Mo(IV,VI) species are concentrated but barely in the oxide inner layer enriched in Cr(III). Their main effect is to produce a less resistive passive state by poisoning dehydroxylation and further Cr(III) and Mo(IV,VI) enrichments obtained in the absence of chlorides. This detrimental effect can be suppressed by pre-passivation in a Cl- -free electrolyte, which blocks the entry of chlorides in the passive film, including in the outer exchange layer, and enables the beneficial aging-induced variations of the composition to take place despite the presence of chlorides in the environment. (C) 2019 Elsevier Ltd. All rights reserved.
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