Assemblages bois-fer et biocorrosion : étude des sulfures de fer formés en conditions anoxiques dans des bois d’épaves

Les conséquences de la corrosion des renforts de fer dans les assemblages de bois peuvent compromettre la durabilité d’une structure. Si le bois est gorgé d’eau, les conditions à la surface du métal deviennent anoxiques. La présence de fer et l’activité microbiologique favorisée par la présence de matière organique font des systèmes composites bois-fer des milieux propices à l’apparition de sulfures de fer. Or ces derniers se transforment soit en milieux anaérobies sulfurés, soit lorsque l’oxygène diffuse dans le bois, soit lors d’une remise à l’air de la structure, avec pour conséquence de contribuer à la dégradation du bois. Afin de mieux comprendre les mécanismes impliqués, nous étudions des bois d’épaves archéologiques. Cet article sera illustré par des exemples d’époques récentes (18ème s. 19ème s.) et antiques et par une approche analytique multi-techniques originale. La mackinawite, la greigite et la pyrite ont été identifiées et il semble que la nature des sulfures de fer présents soit liée à l’âge du vestige conformément aux schémas proposés dans la littérature d’évolution de ces composés. La greigite est intéressante à considérer. Seule phase détectée quel que soit l’âge, elle peut s’avérer un bon marqueur de la biocorrosion du fer dans les assemblages bois-fer

Oxidation of chukanovite (Fe 2 (OH) 2 CO 3 ): Influence of the concentration ratios of reactants

International audienc

Corrosion of Carbon Steel in Marine Environments: Role of the Corrosion Product Layer

This article presents a synthesis of recent studies focused on the corrosion product layers forming on carbon steel in natural seawater and the link between the composition of these layers and the corrosion mechanisms. Additional new experimental results are also presented to enlighten some important points. First, the composition and stratification of the layers produced by uniform corrosion are described. A focus is made on the mechanism of formation of the sulfate green rust because this compound is the first solid phase to precipitate from the dissolved species produced by the corrosion of the steel surface. Secondly, localized corrosion processes are discussed. In any case, they involve galvanic couplings between anodic and cathodic zones of the metal surface and are often associated with heterogeneous corrosion product layers. The variations of the composition of these layers with the anodic/cathodic character of the underlying metal surface, and in particular the changes in magnetite content, are thoroughly described and analyzed to enlighten the self-sustaining ability of the process. Finally, corrosion product layers formed on permanently immersed steel surfaces were exposed to air. Their drying and oxidation induced the formation of akaganeite, a common product of marine atmospheric corrosion that was, however, not detected on the steel surface after the permanent immersion period

Influence of soil moisture on the corrosion processes of carbon steel in artificial soil: Active area and differential aeration cells

International audienc

Role of previously formed corrosion product layers on sulfide-assisted corrosion of iron archaeological artefacts in soil

International audienceIron archaeological nails (16th century) were used as representative of the mild steel structures envisaged for the storage of nuclear waste. The influence of sulfide species on the corrosion behavior of the nails was investigated via the thorough description of the modifications undergone by the corrosion products surrounding the metal after re-immersion in deaerated sulfide solution. The only observed modification was the formation of FeS at the corrosion product layer/soil interface. The corrosion product layer, mainly composed of FeCO3, acts as protective barrier, the reactivity of FeCO3 preventing sulfide species to reach the metal and influence the corrosion process

Electrochemical Monitoring of Steel/Soil Interfaces during Wet/Dry Cycles

International audienc

On the formation and transformation of Fe(III)-containing chukanovite, FeII2-xFeIIIx(OH)2-xOxCO3

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End-Cretaceous akaganéite as a mineral marker of Deccan volcanism in the sedimentary record

An enigmatic chloride-rich iron (oxyhydr)oxide has been recently identified together with mercury anomalies in End-Cretaceous marine sediments coeval with the Deccan Traps eruptions. The mineral was observed in Bidart (France) and Gubbio (Italy), suggesting a widespread phenomenon. However, the exact nature and origin of this Cl-bearing mineral remained speculative. Here, we characterized the accurate composition and nanostructure of this chloride-rich phase by using micro-Raman spectroscopy, Transmission (TEM) and Scanning (SEM) Electron Microscopy on Focused Ion Beam foils. We also provide new evidence of its occurrence in Zumaia, a reference KPg section from Spain. Results confirm akaganéite (β-FeOOH) as the main phase, with chloride content of 3-5 atomic weight %. Akaganéite particles are constituted by the aggregation of nanorods of akaganéite. Internal structures contain empty spaces, suggesting formation in a low-density (atmospheric) environment. This new mineralogical evidence supports the hypothesis that the observed akaganéite was formed in the Deccan volcanic plume and was transported to the Atlantic and Tethysian realms through the stratosphere. Therefore, akaganéite provides a potential new sedimentary marker to identify the imprint of the Deccan eruptions in the stratigraphic record and is evidence of volcanic halogen degassing and its potential role for the Cretaceous-Tertiary mass extinction

Characterization of model samples simulating degradation processes induced by iron and sulfur species on waterlogged wood

Reduced iron and sulfur species accumulated within waterlogged archaeological wood artefacts during their burial time. Oxygen exposure of the artefacts during recovery leads to acidification and salts precipitation, which causes irreversible physical and chemical damages. Prior to accurately evaluating novel extraction methods, the procedures for creating analogous samples were evaluated for efficacy. Waterlogged wood analogues provide access to a whole set of homogeneous and sacrificial samples that replicate characteristics of waterlogged archaeological wood in terms of content degradation and the presence of reduced iron and sulfur species. In this study, we evaluated the preparation of model samples from fresh balsa wood artificially contaminated with reduced iron and sulfur species. Wood degradation and the formation of reduced iron and sulfur species were assessed by Fourier Transformed Infrared (FTIR) and Raman spectroscopies and validated through statistic methods, such as Principal Component Analysis (PCA). Among the three impregnation protocols investigated, one method appeared to be the most effective in term of iron sulfide formation, especially partially oxidized mackinawite Fe1-xS. The selected protocol proved reproducible and efficient on both fresh balsa and Neolithic oak samples. From these observations confirmed by the PCA analyses on spectroscopic dataset, a suitable method to model waterlogged archaeological wood was established