The complex corrosion system of a medieval iron rebar from the Bourges’ Cathedral. Characterization and reactivity studies

• Study of complex atmospheric corrosion layers on an archaeological iron rebar.
• Methodology combining: μ-Raman maps, SEM–EDS, rust powder reductions.
• Identification/location of the corrosion phases.
• Characterization of the corrosion system reactivity.

Iron reinforcements used in many medieval monuments are submitted to centuries of corrosion, and a reliable prediction of long term corrosion is needed for their conservation and restoration. This study focuses on an iron rebar from the Bourges’ Cathedral (France). The corrosion product layers formed on the rebar have been investigated through SEM–EDS, Raman microspectroscopy and electrochemical measurements. Electrochemical reductions and composition results show reactive (oxyhydr)oxides-rich corrosion systems. As the location of these phases could influence the reactivity, these macroscopic results should be considered in the light of microscopic observations to propose corrosion mechanism hypotheses.