Raman study of a deuterated iron hydroxycarbonate to assess long-term corrosion mechanisms in anoxic soils

What is it about?

In several contexts such as cultural heritage, oil and gas or nuclear waste disposal, the long-term corrosion mechanisms of iron in anoxic soils are studied. For this purpose, corrosion layers formed on ferrous archaeological artefacts from the site of Glinet (16th century, Normandy, France) were characterised. The main phases identified are siderite (FeCO3), chukanovite (iron hydroxycarbonate: Fe2(OH)2CO3 and magnetite (Fe3O4). In order to provide reliable Raman references for further studies on carbonated systems, the iron hydroxycarbonate (chukanovite) was synthesised on iron discs. The corrosion mechanisms were investigated by re-corroding the archaeological samples in a deuterated solution. Raman characterisation on cross sections inside the layer revealed the presence of deuterated chukanovite, allowing the deuterium tracing of the spreading of the corrosion. A set of chukanovite samples was synthesised with various D/H ratios. Using these reference data, the proportion of deuterated chukanovite in re-corroded artefacts was evaluated, and the corrosion rate was estimated as less than 1.6 µm/year.

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