A LABORATORY STUDY OF THE EFFECT OF OZONE, NITROGEN-DIOXIDE, AND SULFUR-DIOXIDE ON THE ATMOSPHERIC CORROSION OF ZINC

We report on a laboratory study of the role of O3, NO2, and SO2 in the sub-parts per-million range on the atmospheric corrosion of zinc. Each sample was exposed individually to synthetic atmospheres with careful control of pollutant concentrations, relative humidity, and flow conditions. In addition, we studied the interaction of the pollutants with zinc using time-resolved trace-gas analysis. NO2 and O3 accelerate the corrosion of zinc in humid air containing SO2. 03 oxidizes loosely bound four-valent sulfur on the zinc surface to sulfate while NO2 catalyzes the oxidation of SO2 on zinc. The increased formation of sulfate and hydrogen ions on the surface leads to the dissolution of solid corrosion products and to an increased rate of metal dissolution. The acceleration of SO2 oxidation and deposition on zinc by 03 becomes increasingly important as the concentration of SO2 and O3 decreases. The results suggest that O3 and NO2 may be important factors in the atmospheric corrosion of zinc.