Protective effect of inhibitor-containing nitrocellulose lacquer on artificially patinated bronze

Abstract

Abstract In the present work, the efficiency and time-degradation of new protective organic coatings for artificially patinated bronze based on nitrocellulose lacquer containing thiadiazole derivatives (2-mercapto-5-amino-1,3,4-thiadiazole and 2-mercapto-5-methyl-1,3,4-thiadiazole) as corrosion inhibitors were investigated. The samples were intermittently exposed to a solution simulating an urban rain (pH 5) and their behaviour was monitored for nearly three months by electrochemical impedance spectroscopy (EIS) measurements. Optical microscopy examination of cross sections of bronze samples covered with patina and nitrocellulose lacquer, without and with inhibitors, was used to determine the thickness of the coatings. Fourier transformed infrared spectroscopy (FT-IR) was employed to put on evidence the chemical interactions between the organic inhibitors and nitrocellulose lacquer functional groups. The best results were achieved in the presence of 2-mercapto-5-amino-1,3,4-thiadiazole into the nitrocellulose lacquer coating, which offers the highest long-lasting protection to patinated bronzes, without changing the visual appearance of the bronze surfaces covered with patina. This approach proved to be a promising alternative to benzotriazole in the development of highly protective coatings for patinated bronzes.