Inhibiting effects of some Schiff bases on the corrosion of bronze exposed to artificial acidic rain

Conservation of artistic heritage is of great importance for the future of the historical and cultural identity of a society. Both ancient and modern bronze artworks are an important part of this cultural heritage and the production of effective and environmentally satisfactory protective treatments is a central and still unresolved issue. The M-ERA.NET project named B-IMPACT (Bronze-IMproved non-hazardous PAtina CoaTings) operates in this context and aims at developing innovative, eco-friendly and non-hazardous protective coatings for bronze surfaces exposed to the outdoor environment. This research has the objective to identify new effective bronze corrosion inhibitors for the future entrapment in surface coatings so giving a contribution to the development of alternative efficient surface treatments. A number of organic compounds proved to be good corrosion inhibitors for copper [1-5], but mainly azoles, such as triazoles [6-8], tetrazoles [6,9], imidazoles [10] and thiadiazoles [6,9,11], were tested for bronze protection. Mostly benzotriazole (BTA) and triazole derivatives were used and applied in the conservation field [6,8], although there are toxicity and perhaps human carcinogenicity concerns due to their handling and leaching in the environment [12,13]. Some Schiff bases derivatives are claimed to be efficient [1,3,14,15] and environment friendly [1] inhibitors of copper corrosion in acid and neutral chloride solution. For these reasons, some specifically synthesized Schiff bases were tested by electrochemical methods, as BTA alternative inhibitors of bronze corrosion, during exposures to concentrated acidic rain. The inhibition mechanism of the most efficient substance was also studied by surface analyses methods (Scanning Electron Microscope (SEM) observations, Raman and X-Ray Photoelectron Spectroscopy (XPS).