In situ X-ray diffraction study of tarnishing process of Ag and Ag-alloys

In presence of hydrogen sulphide and other sulphur compounds the tarnish layer occurs in building up insoluble sulphides of silver. Due to this reason the contact resistance of silver-plated contacts increases and the appearance of massive silver or silver coated objects is badly influenced. Either pure silver, high silver –content alloys and silver-rich microstructural phases are susceptible to discoloration from sulphides. In order to study the early stages of tarnishing and its subsequent evolution a different dry exposure method has been adopted, on the basis of some suggestions reported in aiming at antiquatening silver objects. The morphology, microstructure and chemical composition which develop on tarnished surface of Ag and Ag alloys during exposure were characterized by in-situ X-ray diffraction (XRD), and optical, electron and raman microscopies. The samples surface started to become tarnished after some minutes of exposure and the early stages as well the kinetics of the process were investigated by performing subsequent in-situ X-ray diffraction scans with short collection time.