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Microbiologically influenced corrosion inhibition (MICI), can be considered as a new environmentally friendly strategy for corrosion inhibition. Nevertheless, at present, most of the findings in MICI research are obtained under optimized laboratory conditions, generally involving a single microorganism. To upgrade the knowledge in this research field and increase the potential applications, more studies under real conditions are needed, since environmental complexity and biological diversity coexist in field environments impacting the corrosion process of metal surfaces. In this context, one of the main objectives of the MICOATEC project (“New concept of Microbially Inspired anticorrosion coating technology”) is to understand the microbially induced formation of a protective layer on the Al-Mg surface during exposure in marine field. The present work is part of this study. N/A

A key factor for effective inhibition by organic molecules of the initiation of localized corrosion by pitting is their ability to form a protective organic film in locally de-passivated zones exposing the bare metal next to the oxide-covered surface. Herein, based on quantum chemical DFT calculations, we study the chemistry of the interface between 2-mercaptobenzimidazole (MBI) and a copper surface partially covered by a Cu2O passive oxide film. The results show the adaptability of the molecule to adsorb strongly on the different zones, oxide or metal, of a locally de-passivated surface. However, differences in the local adsorption configurations, involving covalent bonding with H-bonding depending on oxide or metal and on conformer, thione or thiolate, lead to the formation of an inhomogeneous organic film. Increasing order of local adsorption strength is oxide walls < metal surface < oxide surface < oxide edges for the thione species, whereas there is no significant difference of local adsorption strength for the thiolate species. Our results suggest that both species of MBI can heal the oxygen and copper low coordinated sites as well as can protect the exposed metal surface, thus enhancing the barrier properties of the passivated surface even when locally defective.

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A combined X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and electrochemical approach was used to investigate the mechanisms of molybdenum and chromium enrichment of a passive lm formed on a model austenitic stainless steel single crystal in aqueous acid media and the effect that thermal pre-oxidation at 250 C plays in the composition, thickness, and stratification of the film. A clean FeCrNiMo (100)-oriented surface, prepared under ultra-high vacuum (UHV), was exposed to ultra-low pressures of oxygen at 250°C, forming a thin oxide film, rich in iron and chromium, as well as containing molybdenum. An argon- lled glovebox, directly attached to the UHV system, allowed for electrochemical alterations to be carried out without exposure to ambient air. After being held at open circuit potential for 30 minutes, hydroxylation of chromium and molybdenum was promoted, with a marked enrichment of both elements in the oxide film. A distinct bilayer film was observed. Anodic polarisation resulted in a significant growth of the inner layer and further enrichment of chromium. Pre-oxidation at 250°C, using an ultra-low pressure of oxygen, was found to promote protection against transient active dissolution during anodic passivation, and to cause enrichment of molybdenum in the outer layer of the passive film.