Laboratory investigations of the impact of dry deposition of SO 2 and wet deposition of acidic species on the atmospheric corrosion of galvanized steel

Abstract

A series of short-term laboratory experiments were conducted in which galvanized steel samples were exposed to sub-ppm levels of SO 2. Dew was produced periodically on the test panels, and, at the end of some experiments, panels were sprayed with solutions of various pH levels. Both dew and rain rinse samples were analyzed for SO 3 2−, SO 4 2− and Zn. The laboratory results suggest that as a first approximation the damage to galvanized steel induced by the dry deposition of SO 2 can be calculated by equating the dry SO 2 flux to the Zn corrosion flux. SO 2 will deposit onto a fresh dry surface until an amount similar to that of a monolayer has formed. Under wet conditions, the dry deposition flux is controlled by the gas-phase resistance of the atmosphere. Wet deposition of ammonium bisulphate induces corrosion which depends not only on the pH of the incident rain, but also on the exposure history of the samples.