Corrosion behavior of iron in cementitious solution at 80°C in anoxic condition

International audienceThe Belgian reference concept for high-level radioactive waste packaging proposed by ONDRAF/NIRAS is called Supercontainer. The design of the Supercontainer includes a stainless-steel liner, a concrete buffer and a carbon steel overpack containing one or several waste canisters. An objective of the concrete buffer is to maintain high alkaline conditions on the surface of the overpack during underground disposal of these wastes. In these conditions (alkaline and anoxic conditions), a passive film forms on the surface of the steel, resulting in very low and almost negligible uniform corrosion rates (passive dissolution). This film is generally composed of a double layer an inner layer, accounting for passivity, and a more or less porous outer layer. The latter is in contact with the environment and is formed by precipitation of elements in solution. The presence of silicon and cations from the cementitious environment could lead to neo-formed phases such as ferrous-silicates or phyllosilicates possessing corrosion inhibiting properties. The aim of this work is to study the impact of the cementitious materials during the corrosion at 80DC in anoxic media by characterizing the layer formed during the corrosion process. To ensure these measurements, iron plates were corroded in solution representative of a cementitious environment (at 80DC and under anoxic conditions). Evolution of the nature and growth of the corrosion layer is studied on samples after several duration tests. Corrosion products are characterized by means of several analytical techniques such as scanning electron microscopy, Raman micro-spectroscopy, X-ray diffraction, X-ray photoelectron spectrometry and transmission electronic microscopy. Results have revealed evolution of composition as a function of time. Layers are mainly composed of magnetite and others phases containing iron, calcium and silicon

Microscopic work function anisotropy and surface chemistry of 316L stainless steel using photoelectron emission microscopy

International audienceWe have studied the variation in the work function of the surface of sputtered cleaned 316L stainless steel with only a very thin residual oxide surface layer as a function of grain orientation using X-ray photo-electron emission microscopy (XPEEM) and Electron Backscattering Diffraction. The grains are mainly oriented [1 1 1] and [1 0 1]. Four distinct work function values spanning a 150 meV energy window are measured. Grains oriented [1 1 1] have a higher work function than those oriented [1 0 1]. From core level XPEEM we deduce that all grain surfaces are Cr enriched and Ni depleted whereas the Cr/Fe ratio is similar for all grains. The [1 1 1] oriented grains show evidence for a Cr 2 O 3 surface oxide and a higher concentration of defective oxygen sites

Corrosion behaviour of Fe-9Cr steels in O2_2 and CO2_2 containing media thick or thin oxide scale ?

International audienceIn order to better understand the corrosion behaviour of 9Cr steel in CO$_2$ rich gas phase environments and the possible effect of O2 molecules on the corrosion scale formation, a Gas Phase Analysis technique (GPA) was developed and used at CEA. This innovative device dedicated to the study of gas-solid interaction uses labelled gas molecules, mass spectrometer and pressure gaugesfor analysing the evolution of the gas phase composition. The use of this device combined to the analyses of the corrosion product by multiple techniques such as Raman spectroscopy, SIMS, XPS, SEM and TEM was very powerful to propose an entire story of the steel-gas interaction in CO$_2$ and O$_2$ rich environments

Ion beam modification of zinc white pigment characterized by ex situ and in situ µ-Raman and XPS

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Electrochemical behavior of mild steel in concrete: Influence of pH and carbonate content of concrete pore solution

International audienceThe increase of the rebars corrosion rate due to the concrete carbonation is the major cause of reinforced concrete degradation. The aim of this study was to investigate the transition from passive to active corrosion of mild steel rebars in carbonated concrete. For this purpose, electrochemical techniques (polarization curves, free corrosion potential measurements) and surface analyses (EDS, XRD, XPS) were used. Five different electrolytes, with pH ranging from 13 to 8.3, were chosen to simulate the interstitial concrete pore water at various degrees of carbonation. The results indicate that the transition pH is between 10 and 9.4. XPS results indicate a passivation of mild steel for pH values ranging from 13 to 10 due to the formation of a thin iron III oxide layer. Immersion tests highlight the importance of the buffering effect of the carbonate content. At the free corrosion potential in an aerated solution, a decrease of the carbonate content increases the corrosion rate. On the opposite, at low electrode potential, the kinetics of oxidation increases with the carbonate content

Proton beam modification of lead white pigments

Pigments and paint materials are known to be sensitive to particle irradiation. Occasionally, the analysis of paintings by PIXE can induce a slight or dark stain depending on the experimental conditions (beam current, dose, particle energy). In order to understand this discoloration, we have irradiated various types of art white pigments - lead white (hydroxycerussite and basic lead sulphate), gypsum, calcite, zinc oxide and titanium oxide - with an external 3 MeV proton micro-beam commonly used for PIXE experiments. We have observed various sensitivities depending on the pigment. No visible change occurs for calcite and titanium oxide, whereas lead white pigments are very sensitive. For the majority of the studied compounds, the discoloration is proportional to the beam current and charge. The damage induced by proton beam irradiation in lead white pigments was studied by micro-Raman and XPS spectroscopies. Structural modifications and dehydration were detected. Damage recovery was investigated by thermal treatment and UV-light irradiation. The discoloration disappeared after one week of UV illumination, showing that PIXE experiments could be safely undertaken for pigments and paintings

Mobilization of tungsten dust by electric forces and its bearing on tritiated particles in the ITER tokamak

International audienceExperimental investigations on the electric field strength required to overcome the adhesion forces of micron size tungsten metallic dust as well as silver and aluminum oxide in powdery form deposited on a conductive surface are presented. The results reveal a strong influence of particulate surface properties on the detachment threshold, especially for tungsten particles which exhibit a thin surface oxide layer that screens their electrical conductivity. Such tungsten particles makes possible that electrostatic self-charging occurs when tritiated because of their dielectric properties even if there are deposited on a conductive grounded surface. © 2017 Elsevier B.V

Etude des processus rédox aux interfaces solides-liquides par des techniques électrochimiques couplées à des méthodes in-situ et ex-situ : exemples des composés du fer

Conférence du 02 au 06 juillet 2007. Communication par affiche

Uptake of uranium and trace elements in pyrite (FeS₂) suspensions

International audiencePyrite dissolution and interaction with Fe(II), Co(II), Eu(III) and U(VI) have been studied under anoxic conditions by solution chemistry and spectroscopic techniques. Aqueous data show a maximal cation uptake above pH 5.5. Iron (II) uptake can explain the non-stoichiometric [S]aq/[Fe]aq ratios often observed during dissolution experiments. Protonation data corrected for pyrite dissolution resulted in a proton site density of 9 ± 3 sites nm−2. Concentration isotherms for Eu(III) and U(VI) sorption on pyrite indicate two different behaviours which can be related to the contrasted redox properties of these elements. For Eu(III), sorption can be explained by the existence of a unique site with a saturation concentration of 1.25 × 10−6 mol g−1. In the U(VI) case, sorption seems to occur on two different sites with a total saturation concentration of 4.5 × 10−8 mol g−1. At lower concentration, uranium reduction occurs, limiting the concentration of dissolved uranium to the solubility of UO2(s).Scanning electron microscopy and micro-Raman spectrometry of U(VI)-sorbed pyrite indicate a heterogeneous distribution of U at the pyrite surface and a close association with oxidized S. X-ray photoelectron spectroscopy confirms the partial reduction of U and the formation of a hyperstoichiometric UO2+x(s). Our results are consistent with a chemistry of the pyrite surface governed not by Fe(II)-bound hydroxyl groups, but by S groups which can either sorb cations and protons, or sorb and reduce redox-sensitive elements such as U(VI)