Two Imidazole Based Corrosion Inhibitors for Protection of Bronze from Urban Atmospheres

Two different imidazole based molecules were investigated as corrosion inhibitors for Cu-6Sn bronze in a sulphate/carbonate solution at pH 3 and 5 which simulate a mild and strong polluted urban environment. The tested corrosion inhibitors were 4-methyl-1-phenylimidazole (PMI) and 4- methy1-1-p- tolylimidazole (TMI). The difference between structures is in the additional para positioned methyl, -CH3, group in the phenyl ring of the TMI molecule. Their protective effect was investigated by different electrochemical methods: polarization in wide and narrow potential range and electrochemical impedance spectroscopy. The investigations have shown that both molecules give good protection to the bronze at pH 3, but only TMI showed a good effect at pH 5. Indicating that the para positioned methyl group serves as a link between the inhibitor molecule and substrate bronze.