An analytic study permits us to characterize the altered surface of an archaeological bronze coin and to determine the structure and the composition of the patina covering the whole surface of this artefact. This patina could be interpreted at first sight as a type I patina, with copper product deposits on it, with some punctual and enlarged localized type II corrosion.To achieve the purpose of this work, we investigate the behaviour of an archaeological bronze in the presence of benzotriazole (BTA) in alkali medium with the intention of getting a better passivity while favouring the formation of a polymeric film on the surface of the working electrode. The behaviour of the considered interface is investigated by electrochemical impedance spectroscopy, in the presence and absence of an oxide layer, according to the immersion time.At pH ¼ 9, in the presence of 15 mmol/l of BTA, the optimum percentage of inhibition efficiency (IE%) is 67% obtained after 30 min of immersion. A pre-polarization of the bronze working electrode is realized in order to accommodate the preservation technique used in museums and to improve the formation of the Cu(I)-BTA polymeric film. The use of a pre-polarized electrode for 30 min at À35 mV/SCE carries an enhancement of the protection versus the non-polarized electrode. While comparing the result of our investigation with that obtained using the traditional preservation method, we can establish that using a concentration of BTA 15 times lower, important inhibitor efficiencies (%) of 92 and 97.4%, respectively, for 30 min and 96 h of immersion are reached.

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The aim of this work is to evaluate the behaviour of bronze in archaeological soil by gravimetric study, electrochemical research and analytic survey. Archaeological soil samples were collected from Jama that date back to the second Punic war. Mineralogical, micro‐structural, micro‐morphological and chemical analyses of soil constituents were performed. The bronze samples correspond to Cu‐9.4Sn (B1) and Cu‐7.7Sn with 1% of Pb (B2). The open circuit potential value recorded for B2/corrosion product/soil is stable after only 7 min due to its reactivity allowing to a rapid development of a protective corrosion layer. The B2 interphase is more developed and stable than B1. Under anodic polarisation, the B2 alloy corrodes less than the B1 alloy owing to its lower anodic current. Based on the EIS study, two evolution stages of the bronze alloy/corrosion product/soil interphase are detected. For the first stage, the interphase is equivalent to two R//C loops at high and medium frequencies, respectively related to the corrosion layer and charge transfer process, associated to mass transport phenomena. For the second stage, the resistance of corrosion layer decreases and the first loop vanishes. SEM‐EDS analysis demonstrate that the first stage (20 days of immersion) can be characterized by a well covered surface with a thin corrosion product, the external layer exhibits low tin content. However, after 310 days of immersion, the surface state is different with isolated particulates composed by Cu and soil compounds on a cracked layer with the presence of craters showing an internal layer.

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