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International audience; The adsorption of 2-MBT organic inhibitor on copper and its effects on anodic oxide growth in NaOH were investigated using cyclic voltammetry, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry techniques. It is shown that 2-MBT significantly impedes the growth of the Cu(I) oxide by forming a multilayered organic film on the surface. A major factor influencing the formation and properties of the organic barrier layer is the presence and structure of the interfacial native oxide on which it forms. The 2-MBT multilayer bonds to the metallic copper substrate mostly via its sulphur atoms along with a small fraction of the nitrogen atoms also bonding to the metallic substrate. Additionally, there is an interaction between the inhibitor molecules and copper released from the surface to form metal-organic complexes in the outer layers of the thicker films.

International audience; Electrochemistry along with advanced surface analyses (X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry) were implemented to investigate copper corrosion inhibition by 2-mercaptobenzothiazole (2-MBT) in hydrochloric aqueous solution and the effects of electrochemical control on the formation of the inhibiting interface. It is shown that reducing the native surface oxide by cathodic reduction prior to exposure to the inhibitor drastically decreases the rate of anodic dissolution. Additionally, increasing the exposure time of the metal surface to the inhibitor results in even better protection against dissolution. 2-MBT adsorbs as multilayers and bonds to both metallic copper and residual copper oxide islands via its sulphur atoms. Partial dissociation of the molecule, releasing the exocyclic sulphur, which then bonds to metallic Cu, is observed. Further dissociation of the molecule, releasing the endocyclic sulphur, is induced by anodic polarization, forming defects in the organic layer and thus compromising the barrier properties of the organic layer.

The effects of water on 2-mercaptobenzothiazole (2-MBT) film pre-formed on copper at low pressure and room temperature was investigated in situ by X-ray photoelectron spectroscopy. Upon exposure to water vapour at 5 × 10-6 mbar, the 2-MBT molecules not directly bonded to copper desorb, until only one monolayer remains adsorbed. Further exposure leads to cleavage of the bond between exocyclic sulphur and copper, whereas nitrogen remains bonded to copper. Dissociative adsorption of water is observed, without copper oxidation for exposure up to 3 × 106 L. This work brings new molecular scale insight into corrosion inhibition mechanisms in water-containing environments.

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.

A model experimental approach, providing molecular scale insight into the build up mechanisms of a corrosion inhibiting interface, is reported. 2-mercaptobenzimidazole (2-MBI), a widely used organic inhibitor, was deposited from the vapor phase at ultra-low pressure on copper surfaces in chemically-controlled state, and X-ray photoelectron spectroscopy was used in situ to characterize the adsorption mechanisms upon formation of the inhibiting film. On copper surfaces prepared clean in the metallic state, the intact molecules lie flat at low exposure, with sulfur and both nitrogen atoms bonded to copper. A fraction of the molecules decomposes upon adsorption, leaving atomic sulfur on copper. At higher exposure, the molecules adsorb in a tilted position with sulfur and only one nitrogen bonded to copper, leading to a densification of 2-MBI in the monolayer. A bilayer is formed at saturation with the outer layer not bonded directly to copper. In the presence of a pre-adsorbed 2D oxide, oxygen is substituted and the molecules adsorb intactly without decomposition. A 3D oxide prevents the bonding of sulfur to copper. The molecular film formed on metallic and 2D oxide pre-covered surfaces partially desorbs and decomposes at temperature above 400 °C, leading to the adsorption of atomic sulfur on copper.