The Role of Sulfur in the Atmospheric Corrosion of Silver

Much emphasis has been placed on the role of chloride in the corrosion of silver, and although it is a leading contributor to the degradation process, it does not act alone. Recent surface analysis of field exposed silver has shown consistently that sulfur may be playing a larger part than previously thought. Here we report recent outdoor exposures from various sites including marine, urban and rural environments using X-ray Photoelectron Spectroscopy (XPS) to correlate atmospheric conditions to corrosion products, with emphasis on sulfide and sulfate differentiation. Although the high solubility of silver sulfate has made it an elusive product to study with typical electrochemical methods, this higher solubility likely leads to increased transport of silver away from the surface. Through XPS analysis, corrosion products on silver were identified as one or more of the following: AgCl, Ag₂S, and Ag₂SO₄. Results were highly dependent on atmospheric composition and weather conditions of the sampling sites.