Characterization of atmospheric corrosion products of zinc exposed to SO2 and NO2 using XPS and GIXD

A complete characterization of corrosion products formed on zinc plates after exposure in a climatic chamber was conducted in this study. The dry deposition of NO2, SO2, and SO2 + NO2, at 25 °C and 35 °C, and relative humidity (RH) of 90% was simulated. Pollutant concentrations evaluated were selected to represent highly polluted industrial atmospheric levels. Analysis techniques included X-ray Photoelectron Spectroscopy (XPS) and Grazing Incidence X-ray Diffraction (GIXD). For tests conducted at 25 °C, the relative amount of sulfate was determined to be higher in the SO2 + NO2 atmosphere than in the SO2 atmosphere, and was associated with greater corrosivity in the former atmosphere. NO2 had an indirect role as a catalyst for SO2 reduction to sulfate, as evidenced by the greater proportion of sulfate ions detected and the lack of nitrogen compounds in corrosion products. At 35 °C, effect of NO2 was reduced, and was complicated by a greater tendency for drying so that it was more difficult to maintain the humidity layer. Therefore, no accelerating effect of exposure temperature was observed.