Formation of Copper Sulfide in Moist Air-Sulfur Dioxide

Films formed on copper exposed to various sulfur-bearing environments were analyzed by XPS and electrochemical reduction to study the formation of copper sulfide. The S-2p photoelectron band showed the presence of copper sulfide in the film in addition to oxysulfur species. Coulometric reduction analysis of the film suggested that the sulfide was nonstoichiometric. The formation of copper sulfide was also noted on copper immersed in “sulfurous” acid and in sulfuric acid. The properties of the sulfide that formed reductively on copper from these oxysulfur environments were compared with those of copper sulfide that formed from a moist hydrogen sulfide environment. Formation of copper sulfide from the oxysulfur environments showed that sulfur could participate as a reducible species in the film-forming corrosion reactions.