engleski

Protection of bronze by an environment friendly corrosion inhibitor

Bronze is one of the oldest alloys which has been used for a very long time for sculptures and for building structures such as roofs and gutters. Many copper roofs have lasted for centuries on castles, churches and other monumental buildings. Because of the increasing air pollution all these artefacts are endangered by dissolving. In this work we propose the use of 4-methyl-1-p- tolylimidazole (TMI), an innoxious imidazole compound, as a corrosion inhibitor for bronze. The investigations were performed on Cu-6Sn bronze. To gain a condition similar to the urban environment the electrochemical measurements were performed in a solution consisting of 0.2 g L-1 Na2SO4 + 0.2 g L-1 NaHCO3 at pH 3 and 5, which simulate very strong and mild acid rain in urban environments. Corrosion studies were performed by potentiodynamic measurements and electrochemical impedance spectroscopy (EIS) to determine optimal concentrations of 4-methyl-1-p-tolylimidazole at both pH values. The results have shown that 4- methyl-1-p-tolylimidazole protects the bronze at both pH values. The adsorptive behaviour of TMI in the sulphate / carbonate solution may be approximated by the Langmuir type isotherm at pH 3 and by the Freundlich type isotherm at pH 5. The free energy of adsorption of bronze at pH 3 was found to be - 11 kJ/mol and at pH 5 it is - 21 kJ/mol. This indicates that the inhibitor adsorbs to the surface by physisorbtion at both pH values.

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