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Les analogues archéologiques ferreux pour la compréhension des mécanismes de corrosion multiséculaire en milieu anoxique

Abstract : Understanding the long term corrosion mechanisms of iron in an anoxic environment is of primary importance in the field of the radioactive wastes storage. In France, it is planned to store high level nuclear wastes in a a multibarrier system containing a glass matrix surrounding by a low carbon-steel container in compacted clay. This system would be placed in a deep geological repository, which would impose anoxic conditions. As it has been efficient for a period of several thousands of years, one should understand the alteration mechanisms that are expected to occur in such a long time. To this purpose, a specific approach is developed on archaeological analogues with thick corrosion layer formed in natural conditions. In this work, the corrosion mechanisms have been studied based on the study of nails aged of 400 years provided form the archaeological site of Glinet, selected as a reference site. The first point was to fine characterise the entire corrosion system metal/corrosion products/medium, through the use of coupled analytical tools, from the macrometric to the nanometric scale. The first results showed that the samples were corroded in an anoxic calco-carbonated environment Moreover, X-ray microdiffraction associated to Raman microspectroscopy and dispersive energy spectroscopy have allowed identifying three corrosion layouts composed of iron carbonate (siderite and chukanovite) and magnetite. Depending on the phase's layout in the system, its electronic resistance has been established. In a second stage, recorroding experiments in laboratory were performed. Firstly, the electrochemical behaviour of the corrosion system has shown that water reducing does not take place at the metallic interface. Furthermore, reaction tracing with copper and deuterium has allowed identifying the electrons consumptions mainly localised on the external part and the precipitation zones on the internal part of the corrosion layer. From the obtained results, long term corrosion mechanisms in anoxic media have been proposed. One is based on the occurrence of a nanometric non porous layer located at the metallic interface. The other one is based on a gel-like phase's formation.
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Submitted on : Thursday, September 9, 2010 - 2:31:46 PM
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Mandana Saheb. Les analogues archéologiques ferreux pour la compréhension des mécanismes de corrosion multiséculaire en milieu anoxique. Matériaux. Université Paris-Est, 2009. Français. ⟨tel-00516380⟩

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