Integrated measuring approach for the study of corrosion mechanisms

The study of the corrosion mechanisms which affect iron artifacts is the first fundamental step for developing tailored and long-lasting conservation procedures. Unfortunately, such mechanisms are connected not only to the composition of the corrosion product layer, but also to its porosity and microstructure. μ-Raman spectroscopy can be used to assess the composition of the corrosion products, but the effect of the layer porosity requires a different approach. This paper investigates the combined use of μ-Raman and Electrochemical Impedance Spectroscopy (EIS) for the characterization of some iron reinforcements of the Metz Cathedral (France), with the final goals of understanding the corrosion mechanism and having a reliable assessment of the artifact stability. In particular, the proposed measuring approach has proved to be able to give useful data on the electrochemical reactivity of the surface, on the presence of cracks and on the porosity degree of the corrosion product layers. After a series of laboratory tests to characterize the surface, the EIS measurements can be employed also in-situ for a noninvasive assessment of the artifact corrosion behavior. This way it is possible to conceive long-lasting monitoring campaigns, which would allow one to identify artifacts apparently well-preserved, but in danger of possible corrosion due to the porous nature of their corrosion layers and the presence of active electrochemical species in contact to the metallic surface.