X-ray photoelectron spectroscopic study on tarnishing mechanism of silver in sulphide solutions

Abstract

X-ray photoelectron spectroscopy (XPS) was used to examine the composition of the silversulphidefilm formed when silver sheets were immersed in sodium sulphide solutions at pH 12. Immersion of silver in 10⁻⁴ M sulphide solution for 0·5 and 3 h resulted in surfacefilms, the XPS spectra of which indicated the formation of two species of sulphur, assigned as AgSH and Ag₂S. For longer immersion times or when immersion wasin more concentrated (10⁻³ mol 1⁻¹) sulphide solutions no AgSH wasdetected in the film. This finding was explained by the fact that, under these conditions, Ag₂S builds up in three dimensions to form a relatively thick film to render the metal interface where AgSH originates far beyond the detection limit of the technique. On the other hand, the film formed during immersion in more dilute (<10⁻⁴ M) sulphide solution was so thin that it needed an analyser with a larger grazing anglefor detection, which was not available.