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.