Sulphide formation on the surface of binary AgPd alloys studied by XPS, AES, SEM/EDX

Abstract

AbstractFormation of a sulphide layer on the surface of AgPd alloys has been studied by XPS, AES, SEM/EDX and optical microscopy. In accordance with earlier studies of sulphidization of AuAgCuPd alloys, no palladium‐enrichment can be observed in the sulphide layer formed on AgPd samples treated in Na2S solutions. Strong Pd‐enrichment is observed underneath the sulphide layer on the surface of the metal substrate. The enrichment takes place rather quickly and is associated with a palladium‐deficient layer underneath the substrate surface, suggesting diffusion of palladium to the surface of the metal phase.In polycrystalline materials sulphidization also takes place along the grain boundaries. The sulphide phases on the grain boundaries seem to act as channels for the migration of the silver atoms to the sample surfaces. This process leads to further sulphidization of the whole sample surface and overlaps the direct sulphidization which eventually stops because of the formation of a palladium‐enriched layer. The grain boundary connected process is strongly influenced by the composition of the electrolyte in which the sample is immersed.