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X-ray photoelectron spectroscopy analysis was applied to investigate the thermal stability under ultra-high vacuum environment of the surface oxide film formed by electrochemical passivation of a newly-designed Cr15Fe10Co5Ni60Mo10 (at. %) multi-principal element alloy and providing the alloy superior localized corrosion resistance compared to conventional stainless steels and alloys. A spectral decomposition methodology involving the subtraction of Auger peaks overlapping the Fe2p and Co2p core level regions was applied for quantification of the oxide film composition and thickness. The results show that, at 100 °C, the passive oxide film is mainly dehydrated and dehydroxylated. Obvious loss of Ni hydroxide and conversion of Mo(VI) to Mo(IV) species are observed at 200 °C, with further reduction of Mo species to Mo(III) observed at 300 °C. In this temperature range, the total cation quantity in the oxide film remains stable despite the compositional alteration. At 400 °C, Cr(III) oxide forms at the expense of Fe and Mo oxides, resulting in an oxide film essentially consisting of chromium oxide. At 500 °C, Cr(III) oxide is eliminated, making the passive film unstable at this temperature. Possible Cr oxide removal mechanisms are discussed.

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.

Surface analysis by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry was applied to investigate the origin of the enhanced surface passivity and resistance to a chloride-induced breakdown provided by the protective ultrathin oxide films formed on Cr–Fe–Co–Ni–Mo single-phase fcc multi-principal element alloys. A bilayer structure of the oxide films is observed with the inner barrier layer mostly constituted of Cr(III) oxide and the outer layer enriched in Cr(III) hydroxides and Mo(IV,VI) oxides. The Mo(VI) and Mo(IV) species are mainly located in the outer and inner parts of the outer layer, respectively. Anodic passivation promotes mainly the growth of the inner layer on the alloy of higher Cr bulk content and the outer layer on the alloy of higher Mo bulk content. Passivation also promotes the enrichment of Cr(III) hydroxide and Mo(IV) and Mo(VI) oxides in the outer layer. Depth distribution analysis suggests that the ultra-thin protective inner barrier contains Cr(III)-depleted heterogeneities acting as weak sites for chloride attack, which are reinforced by the Mo(IV) oxide species concentrated close to the inner barrier layer. This elemental distribution provides an explanation for the reinforcement of the resistance to localized corrosion observed on these Cr–Fe–Co–Ni–Mo alloys.

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.

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

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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.

Inspired by an industrial process to protect manufactured glass windows against atmospheric alteration during their storage and transport, the current research is focused on the potentiality that a surface deposit of a small amount of zinc salts may efficiently reduce the alteration kinetics of chemically unstable ancient glass (alkali (Na,K)–rich silicate). To this purpose, the protective action of zinc salts was investigated by the mean of ageing experiments (temperature and humidity control) on a relevant ancient glass composition replica. When the treatment was performed on pristine glass (about 1 μg/cm2 of deposited Zn2+ ions), treated glass plates developed a significantly thinner hydrated layer than the untreated one at 80°C or 40°C (85 RH%). Furthermore, the zinc salts treatment modifies the nature of salts on glass surface. Different Zn(II) species were identified on the glass surface prior to or after the ageing. The study of the Zn(II) speciation on glass surface by grazing incidence GI-XAS (Grazing Incidence-X-ray Absorption Spectroscopy) showed the insertion of Zn(II) into the silicate network with the ageing. Several hypotheses about the protective action of Zn(II) against glass atmospheric alteration are formulated. They highlight the predominant role of the chemisorbed zinc species in the protective action. Because these chemisorbed species are formed by thermal activation, a moderate heating step in the treatment protocol is necessary. From preliminary results, the glass surface state prior to the zinc treatment appears critical regarding its efficiency and should be investigated deeper in view of the application., En s’inspirant d’un procédé industriel employé pour protéger les verres de vitrage durant leur stockage et leur transport, cette étude vise à évaluer la potentialité de faibles quantités de sels de zinc pour réduire efficacement la cinétique d’altération de certains verres du patrimoine peu durables (silicates riches en alcalins). Pour cela, l’action protectrice de sels de zinc a été évaluée par la conduite d’expériences de vieillissement (contrôle de la température et de l’hygrométrie) sur une composition de verre réplique, représentative de compositions chimiquement instables du patrimoine. Nos résultats montrent l’effet bénéfique des sels de zinc déposés en faible teneur (de l’ordre du μg/cm2 de zinc) sur la diminution des cinétiques d'hydratation à 80 °C ou à 40 °C (85 % HR), lorsque le traitement est réalisé sur une surface non préalablement altérée. De plus, le traitement modifie la nature des sels formés à la surface du verre altéré. Différentes espèces de zinc (II) sont identifiées à la surface du verre avant ou après les essais de vieillissement. Notamment, l’étude de la spéciation des ions Zn2+ par GI-XAS (spectroscopie d'absorption X en incidence rasante) montre leur insertion progressive au sein du réseau silicaté au cours du vieillissement. Plusieurs hypothèses sur l’origine de l’action protectrice des sels de zinc sont avancées. Elles mettent en avant le rôle prédominant des espèces de zinc chimisorbées dont la formation est thermiquement activée dans les mécanismes de protection. Aussi, ce type de traitement ne pourrait être envisagé qu’avec une étape de chauffage modéré du verre. De plus, sur la base de résultats préliminaires, les performances du traitement apparaissent fortement dépendantes du degré d’altération de la surface avant le dépôt. Ce point est déterminant pour l’application visée et doit être approfondi.

International audience

International audience; The development of new efficient protective methods for ancient glass objects that decay under atmosphere could only be achieved through a better understanding of the alteration mechanisms on a very small scale. To this end, ageing experiments (temperature and humidity control) are conducted on relevant chemically unstable ancient glass composition replicas (alkali (Na,K)–rich silicate). Ageing temperature and glass composition effects on the chemical, morphological and structural evolution of the glass surface replica are evaluated by a combination of multi-tool analysis. Our results put in evidence the non-correlation between the weathering process (formation of a hydrated surface layer) and the departure of alkalis. The slow diffusion of alkalis may be related to the all-solid-state character of the altered layer: all molecular water is H-bound to the network or as Si-OH. These water molecules do not have the same solvation properties than liquid water. Moreover, we highlight a strong influence of the ageing conditions and of the glass composition on the atmospheric alteration mechanisms. In particular, these parameters affect the proportion of alkali elements that are retained into the hydrated layer, which would severely impact the glass chemical durability. Based on preliminary results, a rinse operation promoting the removal of a fraction of alkalis from the altered layer appears very interesting from a glass conservation perspective.

International audience

NSFC[21003102, 20833005, 21021002]; Special Funds for Major State Basic Research Project of China[2009CB220102]