Investigation of corrosion behaviour of carbon steel in simulated soil solution from anodic component of polarisation curve

Abstract: Marine structures and buried pipelines are constantly exposed to extreme conditions with elements such as temperature variation, soil ion content, dissolved metals, etc posing a continuous threat on the integrity and lifespan of the structures. Quantification of these elements has been limited to studying only a few of the parameters, with the resulting corrosion behaviour not fully understood. The purpose of this study was to investigate the corrosion behaviour of carbon steel in simulated soil solution using the anodic component attained from modelled polarisation curves. The behaviour of the metal/electrolyte interface was studied using non-invasive in-situ electrochemical techniques at OCP. A combination of voltammetry, electrochemical impedance spectroscopy with X-ray diffraction analysis of the mineral layer were utilised. The expression for the anodic component of the current as a function of potential was attained from log|ja| vs. potential plots. Mathematical modelling of the experimental polarisation curves was done using OriginPro Data Analysis & Graphing Software. Results showed that at OCP, lepidocrocite, carbonated green rust, calcite and aragonite were found as the corrosion process involved anodic and cathodic zones. Voltammetry around OCP (VAOCP) and linear polarisation resistance (LPR) showed the necessity for corrosion protection as the adopted electrochemical system resulted in a progressively corrosive environment. Kinetics and mechanism of the anodic and cathodic process indicated corrosion processes similar to aerated soil conditions

Characterisation of iron (II) sulfides in wet archaeological woods: the wreck of Mandirac (IV th century, antique ports of Narbonne, France)

International audienceThe wreck of Mandirac (Narbonne, France, IV century) was excavated in 2013 and 2014 from waterlogged soil. A magnetic prospection campaign performed in 2014 revealed that the wood was abnormally magnetic. A plank extracted from the hull, containing an iron nail, was analysed using Environmental Scanning Electron Microscopy, micro-Raman spectroscopy, X-Ray diffraction and magnetic characterization methods in order to identify the mineral composition inside the wood and of the nail. Results revealed an accumulation of greigite and pyrite in the wood around the nail, where the pH was measured below 3. The nail was completely corroded into pyrite and siderite, with no metal left. Marcasite was also identified far from the nail, where the pH was measured around 5. Greigite was the only phase responsible of the magnetic signal emitted from the wood and proved to be present in varying amounts throughout the entire wreck. The iron sulfides were probably formed via anaerobic sulphidogenic bacteria influenced corrosion processes, which occurred on the nails. These results are very different from those obtained from more recent shipwrecks (XIX century). So the nature of these iron sulfides in wet archaeological woods is discussed

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

International audienceLes 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 (18 è s. 19 è 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

Application of ToF-SIMS for sulfur isotopic fractionation in sulfide phases of iron corrosion layers: determination of bacterial impact on the formation of these phases

International audienceTo a better understanding of the iron corrosion mechanisms, it is crucial to elucidate the role of bacteria. Thus, in order to have a diagnosis of the action of bacteria in the iron corrosion, the objective of this study is to determine by ToF-SIMS the isotopic sulfur fractionation δ 34 S in iron sulfides of (sub)micrometric size located in the corrosion product layers of the ferrous objects corroded in anoxic soils and marine environment. These iron sulfides may have two origins: an abiotic origin resulting in the dissolution/reprecipitation of sulfides from the surrounding medium (for example from pyrite in a soil) or a biotic origin by the action of the sulfate-reducing bacteria that reduce sulfate ions into sulfides leading to the formation of iron sulfides with ferrous ions issued from the aqueous dissolution of metal iron. A difference in the isotopic sulfur fractionation δ 34 S in the sulfur phases according to the abiotic or biotic origin of these phases is reported in the literature. Thus in this study, the isotopic sulfur fractionation δ 34 S in the iron sulfides formed in the corrosion product layers of iron was determined to identify the formation origin of these phases and the role of bacteria in the iron corrosion. After characterization of the distribution of the different iron sulfides within the layers (optical microscopy, SEM-EDS, μRaman spectroscopy), the local isotopic fractionation of sulfur is measured by the imaging and spectroscopy ToF-SIMS technique. Some important results have been obtained. First of all, the reproducibility and the accuracy of the method were established by the choice and the validation of a hydrothermal pyrite sample calibrated relatively to the international sulfur isotopic standard Canon Diablo Troilite. Secondly, it was observed that there was no or little variation in the isotopic sulfur fractionation δ 34 S with the degree of oxidation of sulfur. Finally, a noticeable difference in the isotopic sulfur fractionation δ 34 S between iron sulfides formed in laboratory under abiotic or biotic conditions was evidenced: δ 34 S is close to 0 in abiotic conditions whereas in biotic conditions it is shifted from 0 with values up to up to some tens per mil. These first results being promising, the study is actually in progress to determine the formation origin (abiotic/biotic) of the Fe-S present in the corrosion product layers of natural systems of iron corrosion, from soils, subaquatic and marine environments

Prediction of thermal spray coatings performance in marine environments by combination of laboratory and field tests

Cost-effective corrosion mitigation of offshore steel structures can be achieved by thermal spray coatings. These coatings, when comprised of Al, Zn and their alloys, provide a physical barrier against the environment when intact, and cathodic protection to underlying steel when damaged. Due to the complexity of marine environments, laboratory tests should be combined with field work in order to understand the corrosion protection offered by these coatings. The work presented here was carried out with thermal spray coatings of aluminum alloys (AA1050, AA1100, Al-5Mg) and Zn-15Al prepared by Twin Wire Arc Spray onto low carbon steel substrates. The resulting coatings were ~300 μm in thickness, and 5% of surface area defects were artificially machined in order to expose the steel substrate, simulating mechanical damage or erosion of the coating. Electrochemical data collected over a 90 days period showed a good correlation between laboratory and real marine environment results. Aluminum alloys showed better corrosion protection in fully immersed conditions, while zinc alloys performed better in atmospheric and splash zones. Overall, these results aim to improve design of thermal spray coatings to protect carbon steel in marine environments

La rouille verte 1 chloree: role dans les mecanismes de corrosion du fer en milieu aqueux chlores et chloro-sulfates, dans l'oxydation d'hydroxydes mixtes fer-nickel; sa structure cristallographique

SIGLEINIST T 77697 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Role of Al(III) and Cr(III) on the formation and oxidation of the Fe(II-III) hydroxysulfate Green Rust

International audienc

Analyses physico-chimiques d'encres ferrogalliques

LA ROCHELLE-BU (173002101) / SudocSudocFranceF

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

International audienc