The work presented in this paper describes the production of surface coatings on silver by inert and reactive sputtering. The application for the coated material is for use in the silversmithing industry. The surface should, therefore, be indistinguishable from silver and contain no more than 7.5% (by weight) of alloying addition in order to comply with the Sterling Standard. The initial part of the work comprises an investigation into the tarnish behavior of uncoated (pure) and sterling silver. Results indicated that the degree of sulphidation was a strong function of alloy content and also of surface preparation. Oxides of tantalum (Ta), hafnium (Hf), niobium (Nb), tin (Sn), zirconium (Zn), yttrium (Y), titanium (Ti) and aluminum (Al) were produced by reactive sputtering and deposited onto sputtered silver substrates. The degree of sulphidation was then assessed by Energy Dispersive X-ray Analysis (EDX). The corrosion resistance of the oxide film was related to film stress, thickness and sputter deposition conditions. Using a dual-target sputter system, alloys of Ag-Ti, Ag-Ta, Ag-Hf, Ag-Nb and Ag-Al were produced. Their tarnish behavior was investigated as a function of alloy composition. X-ray diffraction analysis was used to determine their crystallographic structures. Alloys were then selectively oxidized in order to determine whether improved corrosion resistance could be achieved. Some, such as Ag-Nb, showed a slight degree of improvement following the treatment while others were less protective.

Author: Helen Royal