In situ monitoring of corrosion processes by coupled micro-XRF/micro-XRD mapping to understand the degradation mechanisms of reinforcing bars in hydraulic binders from historic monuments

International audienceHistoric monuments have been partly built since antiquity with iron or steel reinforcements sealed in mortars or hydraulic binders. But the presence of chloride in the environment can weaken the structures due to the corrosion of these metallic parts, leading to the cracking of the binder. In this context, in order to better understand the first steps of these corrosion mechanisms a chemical cell was designed to operate in situ analyses of the phases precipitated when a chlorinated solution is introduced in the vicinity of the bar. The chemical and structural characterization (micro-XRF and micro-XRD respectively) was performed under synchrotron radiation at the SOLEIL-DiffAbs beamline. Moreover, complementary SEM-EDS analyses were carried out before and after the in situ cell experiment in order to determine the final localisation of the corrosion products inside the crack network. The results show that iron can spread up to 1 mm away from the metallic bar inside the pores of the binder after 44 h of corrosion. Moreover, in accordance with laboratory experiments conducted in solution in the presence of Fe2+ and Cl- ions the reaction pathways conduct to the successive formation of an intermediate Fe(ii)-Fe(iii) chlorinated green rust which transforms into ferric oxyhydroxides such as akaganeite or goethite depending on the local concentration of iron

Détermination de la composition isotopique du soufre pour l’étude de l’origine, biotique ou abiotique, des sulfures de fer en corrosion anoxique

The first goal of this project was to develop a methodology based on the study of the sulfur isotopic composition enabling the determination of iron sulfides origin, biotic or abiotic, within the corrosion products layers (CPL). Then, the aim was to apply this methodology to real corrosion systems in order to determine the mechanisms of iron sulfides formation.Sulfur isotopic analyses methodologies, adapted to micrometric iron sulfides layers observed in real corrosion systems, were developed in nanoSIMS and ToF-SIMS. The study of iron sulfides formed in anoxic carbonated medium with or without sulphate-reducing bacteria validated the use of these methods for the determination of iron sulfides origin.The application of these methods coupled with the precise characterization of irons sulfides formed in the real corrosion systems show two kind of corrosion pattern. In pattern 1, the iron sulfides are localized in the external part of the CPL. They result from the Fe2+ migration from the metal surface to areas rich in biotic S2-. In this pattern, corrosion rates are lower than 20 μm/year for laboratory systems, and lower than 5 μm/year for archaeological objects. In pattern 2, the large presence of conductive phases in the CPL results in the delocalization of electrons, and so a disequilibrium of the charges at the metal’s surface. That leads to the migration of biotic S2- in the CPL till the metal where they precipitate in iron sulphides. This pattern shows high corrosion rates (~100 μm/an) that might be resulting from the accumulation of biocorrosion and chloride corrosion mechanisms.Ce travail de thèse avait pour objectif de développer une méthode basée sur l’étude de la composition isotopique du soufre (δ 34S) permettant de déterminer l’origine, biotique/abiotique, des sulfures de fer au sein des couches de produits de corrosion (CPC). Puis, il s’agissait d’appliquer la méthodologie développée à des systèmes réels afin de déterminer les mécanismes de formation de ces sulfures de fer.Des méthodes d’analyse isotopique du soufre adaptées aux liserés de sulfures de fer micrométriques observés dans les systèmes réels ont été développées en nanoSIMS et ToF-SIMS. L’étude de sulfures de fer formés en milieu carbonaté anoxique en présence, ou non, de bactéries sulfato-réductrice a permis de valider l’emploi de ces méthodes pour la détermination de l’origine des sulfures de fer.L’application de ces méthodes isotopiques couplées à la caractérisation des sulfures de fer dans les systèmes réels a mis en évidence 2 faciès. Le faciès 1 pour lequel les sulfures de fer sont situés en externe de la CPC. Ils résultent de la migration des ions Fe2+ produits au niveau du métal jusqu’aux zones riches en ions S2- d’origine biotique. Les vitesses de corrosion y sont inférieures à 20 μm/an pour les systèmes de laboratoire et à 5 µm/an pour les objets archéologiques. Et le faciès 2 pour lequel la forte présence de phases conductrices dans la CPC entraîne une délocalisation des électrons, conduisant à la migration des ions S2- d’origine biotique vers le métal où ils précipitent sous forme de sulfures de fer. Ce faciès présente de fortes avancées de corrosion locales (200 µm) qui seraient dues à l’accumulation de phénomènes de corrosion par les chlorures et de biocorrosion

Determination of sulfur isotopic composition for the study of iron sulfides origin, biotic or abiotic, in anoxic corrosion

Ce travail de thèse avait pour objectif de développer une méthode basée sur l’étude de la composition isotopique du soufre (δ 34S) permettant de déterminer l’origine, biotique/abiotique, des sulfures de fer au sein des couches de produits de corrosion (CPC). Puis, il s’agissait d’appliquer la méthodologie développée à des systèmes réels afin de déterminer les mécanismes de formation de ces sulfures de fer. Des méthodes d’analyse isotopique du soufre adaptées aux liserés de sulfures de fer micrométriques observés dans les systèmes réels ont été développées en nanoSIMS et ToF-SIMS. L’étude de sulfures de fer formés en milieu carbonaté anoxique en présence, ou non, de bactéries sulfato-réductrice a permis de valider l’emploi de ces méthodes pour la détermination de l’origine des sulfures de fer. L’application de ces méthodes isotopiques couplées à la caractérisation des sulfures de fer dans les systèmes réels a mis en évidence 2 faciès. Le faciès 1 pour lequel les sulfures de fer sont situés en externe de la CPC. Ils résultent de la migration des ions Fe2+ produits au niveau du métal jusqu’aux zones riches en ions S2- d’origine biotique. Les vitesses de corrosion y sont inférieures à 20 μm/an pour les systèmes de laboratoire et à 5 µm/an pour les objets archéologiques. Et le faciès 2 pour lequel la forte présence de phases conductrices dans la CPC entraîne une délocalisation des électrons, conduisant à la migration des ions S2- d’origine biotique vers le métal où ils précipitent sous forme de sulfures de fer. Ce faciès présente de fortes avancées de corrosion locales (200 µm) qui seraient dues à l’accumulation de phénomènes de corrosion par les chlorures et de biocorrosion.The first goal of this project was to develop a methodology based on the study of the sulfur isotopic composition enabling the determination of iron sulfides origin, biotic or abiotic, within the corrosion products layers (CPL). Then, the aim was to apply this methodology to real corrosion systems in order to determine the mechanisms of iron sulfides formation. Sulfur isotopic analyses methodologies, adapted to micrometric iron sulfides layers observed in real corrosion systems, were developed in nanoSIMS and ToF-SIMS. The study of iron sulfides formed in anoxic carbonated medium with or without sulphate-reducing bacteria validated the use of these methods for the determination of iron sulfides origin. The application of these methods coupled with the precise characterization of irons sulfides formed in the real corrosion systems show two kind of corrosion pattern. In pattern 1, the iron sulfides are localized in the external part of the CPL. They result from the Fe2+ migration from the metal surface to areas rich in biotic S2-. In this pattern, corrosion rates are lower than 20 μm/year for laboratory systems, and lower than 5 μm/year for archaeological objects. In pattern 2, the large presence of conductive phases in the CPL results in the delocalization of electrons, and so a disequilibrium of the charges at the metal’s surface. That leads to the migration of biotic S2- in the CPL till the metal where they precipitate in iron sulphides. This pattern shows high corrosion rates (~100 μm/an) that might be resulting from the accumulation of biocorrosion and chloride corrosion mechanisms

Multi-scale physico-chemical characterization strategy to investigate the origin of sulfur phases in the corrosion product of iron corroded in long term anoxic conditions

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Multi-technique investigation of sulfur phases in the corrosion product of iron corroded in long term anoxic conditions: from micrometric to nanometric scale

International audienceThe study of anoxic corrosion process of ferrous metals is a matter of concern for industrial sector (pipelines, container for nuclear waste storage….) but also for cultural heritage objects conservation. Indeed, the formation and the presence of sulfide compounds in the corrosion products of buried objects, either in terrestrial or marine environments, can drastically change the corrosion mechanisms and, so, the conservation strategies for these objects. Particularly, in natural environment, the presence of microorganisms such as Sulfate-Reducing Bacteria (SRB) may influence the corrosion rate of ferrous objects by favoring the precipitation of iron sulfide phases and modifying then the initial corrosion process [1]. The determination of the iron sulfides nature and their distribution in the corrosion product layer is a crucial issue to address in order to anticipate the degradation of ferrous object during extraction, storage or conservation operations. In the present work, archeological ferrous samples, representative of long term corrosion systems, with or without bacteria exposition, have been considered. A multi-technique approach was developed to achieve an overall physico-chemical characterization and to cover the dimensions requirement of the corrosion systems. First, FE-SEM imaging coupled with EDS and µ-Raman spectroscopy were performed on the archeological ferrous samples enabling the localization and identification of the natural corrosion products. Mix of phases of greigite (Fe 3 S 4) and mackinawite (FeS) in a corrosion layer mainly constituted of iron carbonates were observed at a sub-micrometric scale, in consistency with the literature [2], showing the precipitation of greigite, mackinawite and/or pyrite (FeS 2) in the presence of bacteria or in sulfur environment. Then, Nano-Auger spectroscopy, owing to its local chemical characterization capability, was investigated to obtain a chemical diagnostic at a nanometric scale. Scanning Auger Microscopy (SAM) was performed to evaluate the ability of this technique to spatially discriminate different phases (iron sulfides, oxides and carbonates) at a local scale and extreme surface sensitivity (5nm escape depth). Then, thanks to µ-Raman mappings, specific areas presenting only one component were selected and identified for the acquisition of reference Auger spectra, and especially high energy resolution spectra of Fe-MVV and S-LVV regions. Finally, the spatial distribution of the different phases obtained with SAM could be compared with nano-SIMS experiments informing about the sulfur isotopic composition variations and the bio-origin of the sulfur phases

A trade-off between mucocytes and bacteriocytes in Loripes orbiculatus gills (Bivalvia, Lucinidae): a mixotrophic adaptation to seasonality and reproductive status in a symbiotic species?

International audienceIn this study, we investigated the composition of the gill tissue relative to the reproductive status of the lucinid clam Loripes orbiculatus (sensus Poli, 1791) according to seasonal as well as biological parameters to provide insights into the physiological variability of this symbiotic bivalve. Temporal variation in population density was also studied. The species was investigated in Zostera noltii seagrass beds in the Thau lagoon (43°26'52.27'' N, 3°39'6.25'' E) in the south of France in a monthly sampling study from May 2013 to July 2015. A total of 257 individual adults of different sizes were analysed according to water temperature and salinity variations. The findings revealed a very stable Loripes density over time, with one single reproductive period during late spring/early summer. We also found that bacteriocytes and mucocytes in the gills were negatively correlated and highly variable in their respective proportions. Bacteriocytes remained dominant during cold periods, whereas mucocytes appeared mainly in the gills of large individuals when the water temperature increased in the spring. As mucocytes were also related with gonadal maturation, we hypothesize that these may allow the host to increase the proportion of heterotrophy in its nutrition during spring primary production to face the metabolic demands required for reproduction. It is possible that mucocytes may also be involved in host immunity

Study of iron sulphides origin in archaeological artefacts by determination of sulphur isotopic ratio.

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Study of iron sulphides origin in archaeological artefacts by determination of sulphur isotopic ratio.

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Study of iron sulphides origin in archeological artefacts by determination of sulphur isotopic ratio

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Bio-corrosion detection by sulphur isotopic fractionation measurements using nanoSIMS

International audienceThe presence of Sulphate-Reducing Bacteria (SRB) may influence the corrosion rate of ferrous objects by inducing iron sulphides precipitation. The same phases are formed by biotic or abiotic ways. Yet, biotic iron sulphides are supposed to be depleted in heavy isotopes of sulphur relative to the starting sulphates[1]. So, sulphur isotopic composition analyses enable to determine the (a-)biotic origin of the iron sulfides. Previously, a single study [2] devoted to corrosion issues had used the sulphur isotopic composition to determine the origin of sulphides compounds formed on Cu/Ni steel. However, the sulphur isotopic fractionation was obtained by global mass spectrometry from the precipitation into BaSO4 of the remaining sulphates of the corrosion experiment. This method is not adapted to the iron sulphides formed in field samples, presents as strips of some micrometers size [3]. To fill this analytical gap, in the study presented here, nanoSIMS (nanoscale Secondary Ion Mass Spectrometry) is used to determine the local sulphur isotopic composition of the iron sulphides within the corrosion product layers oftwo kinds offield samples: a short term system consisting of a steel coupon buried for 24 months in the Andra (French National Radioactive Waste Management Agency) Underground Research Laboratory devoted to research onthe geological disposal of radioactive waste at Bure (Grand Est, France); and long term systems composed of iron nails buried in the water-saturated soil of the archeological site of Glinet (Normandie, France) during around 500 years. Thus, thanks to the methodology developed the iron sulphide bio-origin is proved in both corroded samples