An electrochemical impedance study of the corrosion protection of artificially formed patinas on recent bronze

The patina that covers bronze often has an aesthetic and/or historical value. It should therefore be protected from corrosion in aggressive urban environments. In the present study, two green chemically obtained bronze patinas were examined, as well as an electrochemical patina that resembles the natural patina. Different protective systems were applied to the samples: azole-based inhibitors in an ethanol solution, azole-based inhibitors in polymer coating or wax coating. The efficiency of these protective systems during immersion in simulated urban rainwater was monitored by electrochemical impedance spectroscopy. The results showed that the protection of patinated bronzes by the inhibitor/ethanol system was long-lasting and most effective for electrochemically patinated bronze. Protective properties of investigated inhibitor/Paraloid B44 systems were found to depend on inhibitor present in the coating as well as on properties of the patina layer on which it was applied. For all types of patina BTA/Paraloid B44 coating exhibited better protecting properties than MTI/Paraloid B44 coating. Carnauba wax was found to provide stabile and effective protection, especially for nitrate patinated bronze. (C) 2012 Elsevier Ltd. All rights reserved.