A study on species transport in the corrosion products of ferrousarchaeological analogues - a contribution to the modelling of iron long termcorrosion behaviour

摘要

One of the main technological and environmental challenges for the next centuries is the safernstorage of nuclear wastes. For this purpose, the behaviour during several centuries of everyrnmaterial constituting the barrier between wastes and environment must be predicted. Inrnaddition to modelling and laboratory simulations, the only mean to study corrosion systemsrnformed during several centuries is to analyse archaeological ferrous artefacts buried in soil.rnPrecedent studies on this kind of artefacts have shown that the corrosion system is formed byrnthe metallic core, a dense corrosion product layer, a transformed medium constituted of a mixrnof corrosion products and soil compounds, and the soil itself. Moreover, analytical andrnelectrochemical studies seem to show that the corrosion mechanisms are driven by the speciesrntransport in the dense product layer (DPL) and especially by oxygen migration in the DPLrnpores. Thus, it seems necessary to precise the species transport properties in the DPL.rnA characterisation study on ferrous artefacts coming from the site of Glinet (16th AD) havernbeen carried out. The rust layers have been studied using several techniques. The compositionrnanalyses were performed with Energy Dispersive Spectroscopy (EDS) coupled to thernScanning Electron Microscope, and Electron Probe Microanalysis (EPMA). Structuralrninformation have been obtained by X-ray microdiffraction (μXRD) and microRamanrnspectroscopy.rnThe aim of this communication is to present the results of a study performed with markers inrnorder to better understand the species transport in the DPL. Experiments focus on anrnarchaeological artefact part from Glinet excavation.rnThe migration in the DPL of I and Na ions (which have roughly the same diffusion coefficientrnin water than oxygen) will be studied by immersion of an archaeological analogue with hisrnDPL in a saturated iodide (NaI) aqueous solution. After different immersion times (1h, 3h, 7hrnand 168h), the concentration profiles of Na and I in the DPL will be determinate usingrnspectral mapping by EDS. The obtained profiles allow proposing apparent diffusionrncoefficients and corrosion rates.