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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The prevention of the tarnishing of silver

Royal, Helen January 1987 (has links)
The valuable properties of silver can be diminished or destroyed because the metal is susceptible to corrosion by certain atmospheric species. Particularly aggressive is H<SUB>2</SUB>S which 'tarnishes' the surface by reacting to form Ag<SUB>2</SUB>S. There have been many attempts in the past to produce a tarnish resistant silver either by surface coating or bulk alloying; none have so far proved to be entirely successful. This thesis describes the production of surface coatings on silver by inert and reactive sputtering for application in the Silversmithing Industry. They should, therefore, be indistinguishable from silver and contain no more than 7.5% (by weight) of alloying addition (to comply with the Sterling Standard). Initially, the tarnish behaviour of uncoated pure and Sterling silver was investigated. Results indicated that the degree of sulphidation is a strong function of alloy content and also of surface preparation. Oxides of tantalum, hafnium, niobium, tin, zirconium, yttrium, titanium and aluminium were produced by reactive sputtering and deposited onto sputtered silver substrates. Films were characterised by X-ray diffraction and tarnished in a controlled atmosphere. The degree of sulphidation was then assessed by Energy Dispersive X-ray Analysis. The protectiveness of the oxide films was related to film stress, thickness and sputter deposition conditions. Using a dual-target sputter system, alloys of silver-tantalum, silver-hafnium, silver-niobium, silver-titanium and silver-aluminium were produced. The tarnish behaviour of the alloys was investigated as a function of alloy composition. X-ray diffraction analysis demonstrated that the deposition technique was capable of producing non-equilibrium structures. For some of the alloys, selective oxidation resulted in a slight improvement in tarnish resistance. In order to establish whether selective oxidation might produce completely protective surfaces, further studies of the oxidation of such materials needs to be undertaken.

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