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AES and XPS study on the tarnishing of silver in alkaline sulphide solutions

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Abstract

Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to follow the changes that occur on the surfaces of silver sheets when reacting with sulphide solutions of pH 12. The results obtained enabled conclusions to be drawn about the nature of the Ag2S films. Immersion in dilute sulphide solutions (⩽ 3 × 10−4 M) resulted in highly irregular films that were interrupted by shallow depressions (cavities). Inside these cavities AES analysis proved the existence of massive carbon species, the presence of which delayed healing of the cavities by the formation of Ag2S film, thus allowing the silver metal interface to continue in contact with the solution oxygen. This explains why silver electrodes maintain the Ag/Ag2O potential while immersed in dilute sulphide solutions. Equilibration of silver with more concentrated sulphide solutions (5 × 10−4 to 5 × 10−3 M) effected healing of the cavities through the formation of a continuous Ag2S film. Once this continuous film is formed, the metal interface is no longer accessible to the solution oxygen. At this point the transition of potential from Ag/Ag2O to Ag/Ag2S occurs.

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References

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Saber, T.M.H., El Warraky, A.A. AES and XPS study on the tarnishing of silver in alkaline sulphide solutions. J Mater Sci 23, 1496–1501 (1988). https://doi.org/10.1007/BF01154622

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Keywords

  • Auger Electron Spectroscopy
  • Ag2S
  • Carbon Species
  • Silver Electrode
  • Metal Interface