X-Ray Photoelectron Spectroscopy Study on the Chemical Composition of Copper Tarnish Products Formed at Low Humidities

This work studies the chemical composition of copper tarnish products formed at 40, 60, and 80% relative humidity (RH) in an uncontaminated environment, for 21 days experimentation at 30°C. The experimental method used was X-ray photoelectron spectroscopy (XPS) in conjunction with -ion sputtering. The main compounds found were cuprite and copper hydroxide Differences were observed between 40, 60, and 80% RH. Copper specimens exposed to 40% RH show the thickest tarnish layers, while the thinnest correspond to the 80% RH specimens. The tarnish layer of the copper specimen exposed to 80% RH is constituted mainly by copper hydroxide. For the 40 and 60% RH copper specimens the tarnish layer is a mixture of copper hydroxide and cuprite.