Abstract
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 pHβ=β9, 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 preβpolarization 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)βBTA polymeric film. The use of a preβpolarized electrode for 30 min at β35 mV/SCE carries an enhancement of the protection versus the nonβpolarized 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.