In Situ Electrochemical Impedance Spectroscopy Measurements and their Interpretation for the Diagnostic of Metallic Cultural Heritage: A Review

Protecting metallic cultural heritage from corrosion is a major challenge for metal conservators. Electrochemical techniques offer a great potential for monitoring the conservation condition of this type of heritage, providing a powerful tool for designing conservation strategies. For this reason, the application of techniques such as electrochemical impedance spectroscopy (EIS) has aroused increasing interest in recent years, although some difficulties in application and interpretation of the results still keep it from being routine practice. This Review aims to picture the state-of-the-art of using electrochemical impedance spectroscopy (EIS) for the insitu monitoring of metallic cultural heritage, focusing on spectra interpretation and different approaches that have been proposed to perform field measurements since the 1990's. In the first part of the Review, different cell designs based on the use of liquid or solid electrolytes for insitu measurements are reviewed. In the second part, a few general equivalent circuits are proposed as a basis for interpreting results on different metal surfaces after discussing different models proposed in literature. This overview intends to summarize and clarify the key points in the use of EIS, and encourage the use of this and other electrochemical techniques in the field of conservation science, for a better preservation of our cultural heritage.