5 - Electrochemical study of steel artefacts from World War I: Contribution of A.C. impedance spectroscopy and chronoamperometry to describe the behaviour of the corrosion layers

Abstract

Publisher Summary The chapter offers the observation that carbon steels excavated from a battlefield of World War I exhibited two thick and heterogeneous corrosion layers, formed during the subsequent long period of burial in the soil. Considering that their further corrosion was limited by the properties of the internal layer, the modeling proposed in the chapter lets us draw two distinct conclusions: (1) The first series of experiments, carried out by electrochemical impedance spectroscopy, confirmed that the internal layer was porous, as was previously attested for the external one. The impedance diagrams showed that the corrosion was controlled by transport phenomena of the species through this porous internal layer. In Evian water, which has poor conductivity, it was necessary to consider simultaneously two processes: a diffusion process in the liquid medium filling the pores and a solid-phase transport process in the electrode material. (2) In the second series of experiments, chronoamperometry tests revealed that the internal corrosion layer was protective, in spite of its porosity. This layer plays a significant role in hindering the further evolution of corrosion, leading to a large fall in the corrosion rate.