Long-term behaviour of iron in clay soils: a study of world war 1 remains by physico-chemical and electrochemical characterization

Iron archaeological analogues constitute a good way to contribute to the definition of the containers for high-level radioactive wastes. In the present study we considered objects from a battle field of world war 1. Visual and microscopic observations revealed 2 corrosion layers of similar thickness: an external layer that appeared orange-brown, about 200 μm to 1 mm thick and in contact with the metallic cores an internal layer which was dark-grey. The Raman spectroscopy testing showed that the external layer was made out of oxy-hydroxides, mixed with crystals from the soil, while the presence of oxides was always associated with the internal corrosion layer. Electrochemical measurements clearly illustrated a different behaviour between the 2 corrosion layers. Impedance spectroscopy measuring confirmed the porosity of the external layer. Polarization tests were performed in Evian water to better understand the behaviour of the internal corrosion layer, an indicative corrosion current was defined and its measurement confirmed the protective role of the internal layer against corrosion. Nevertheless the burial environment seems to play also a significant role in the slowdown of the corrosion. (A.C.)