Inhibiting effect of 4-methyl-1-p-tolylimidazole to the corrosion of bronze patinated in sulphate medium

Bronze statues exposed to an urban area suffer corrosion processes induced by acid rainwater. Use of corrosion inhibitors is one of the most convenient and cost-effective techniques to mitigate it. In a previous work, it was found that 4-methyl-1-p-tolylimidazole (MTI) is non-toxic and efficient inhibitor of copper, and thus we will examine the anticorrosive effect of this substance to copper-tin bronze. First, with bare Cu-6Sn (wt%) bronze, inhibiting efficiency in artificial acid rainwater in urban environment was evaluated by Tafel extrapolation, polarization resistance, and electrochemical impedance spectroscopy (EIS) methods. This study showed that all three methods supply similar inhibiting efficiency validating thus the use of EIS, the least invasive method. This study was followed by the evaluation of inhibiting effect on patinated bronze in sulphate medium. A quntitative study about the inhibiting effect on patinated bronze is scarcely reported in the literature. EIS data revealed three capacitive loops. Comparison with EIS obtained in bare specimens allowed attributing the additional capacitive loop located at the highest frequency domain to the dielectric property of the patina layer. The impedance modulus determined in presence of MTI increased markedly with immersion time, revealing a protective effect of this non-toxic corrosion inhibitor. (C) 2011 Elsevier Ltd. All rights reserved.