Atmospheric Corrosion of Copper and Silver

Abstract

The corrosion rate of copper in laboratory tests is shown to be a sensitive function of relative humidity, sulfur dioxide, hydrogen sulfide, ozone, hydrogen chloride, and chlorine concentrations. Observed indoor corrosion rates obey log normal statistics over the field population of this study. Also, the observed indoor rates correlate reasonably well with the measured reduced sulfur concentrations (, ). The corrosion rate of silver is shown not to be humidity dependent. Hydrogen sulfide, ozone, chlorine, and hydrogen chloride concentrations substantially influence its corrosion rate. The observed indoor rates obey log normal statistics and correlate well with the reduced sulfur gas concentration. In contrast to copper, where indoor rates are 1% of outdoor values, silver often corrodes faster indoors than outdoors. Its sensitivity to sulfur gases and insensitivity to relative humidity is proposed as a plausible explanation for these findings. It is proposed that metallic silver is stable in polluted acidic atmospheric environments and therefore is the dominant surface species while is present on the surface of copper. The thermochemistry and kinetics of these two surfaces will control the stability of silver and copper, respectively, in the presence of pollutants.