Electrical properties of iron corrosion layers formed in anoxic environments at the nanometer scale

The electrical properties of the corrosion layers on archaeological iron artefacts were determined by Conductive Atomic Force Microscopy. Different corrosion products were studied: Fe-II carbonates, magnetite entrapped in the carbonate, and iron sulfides. The results indicate that the ferrous carbonate matrix is insulating, and that magnetite and iron sulfides have a conductive character, although these phases are not systematically connected to the metal. This suggests that electrons produced by the anodic dissolution of metal would be conducted to the external part of the corrosion product layer through a three-dimensional network of connected magnetite strips passing through the ferrous carbonate matrix.