Raman investigation of artificial patinas on recent bronze protected by different azole type inhibitors in an outdoor environment

Bronze surfaces, as well as prepatinated surfaces on bronze, undergo chemical and visual changes when exposed to humid and polluted environments. For this reason, it is important to study the effectiveness of corrosion inhibitors on patinated-bronze surfaces. The aim of this study was to investigate different protection systems for patinated bronze, which are based on the use of two azole type inhibitors: 2-mercaptobenzimidazole and benzotriazole. The results of our practice confirmed that these inhibitors were very effective when immersed in a corrosive solution containing inhibitor for 24h. The inhibited layers were then protected by a water-repellant layer. In the case of the studied patinas, green chloride and green nitrate patinas, applied over the brown artist's patina, were tested, as well as brown patina and the patina that develops on bare bronze. The study was performed after each chemical patination and the application of the two different inhibitors. The inhibition systems used on the different chemically achieved patinas were characterized by Raman spectroscopy and electrochemical techniques. The results of the Raman studies showed a chemical interaction of both inhibitors with copper and bronze but a versatile interaction between the inhibitors and the different patinas. The chemical interaction of benzotriazole was observed on the nitrate patina, whereas the mercaptobenzimidazole showed interaction also with the chloride-type patina. Electrochemical tests proved the interaction, which had been detected by Raman spectroscopy. Copyright (c) 2014 John Wiley & Sons, Ltd.