A LABORATORY STUDY OF CORROSION REACTIONS ON STATUE BRONZE

The initial stages of the atmospheric corrosion of statue bronze in the presence of sub-ppm concentrations of SO2 and NO2 were studied in the laboratory. Trace amounts of NaCl were added, ex situ, to the samples prior to exposure to the corrosive atmosphere. Polished and artificially patinated samples were studied. It was concluded from the laboratory studies that NO2 is more corrosive towards the bare bronze surface as compared with SO2. A large increase in the rate of corrosion of polished samples was observed upon exposure to an SO2 + NO2-containing atmosphere, as compared with exposure to the single gas atmospheres. A similar synergistic effect was seen on polished samples, pretreated with NaCl, exposed to NO2. Deposition rates of SO2 and NO2 were followed in real time by continuous monitoring of the inlet and outlet gas concentrations. HNO2(g) was evolved from the surface of polished samples exposed to NO2-containing atmospheres.