ABSTRACT
Silver, either as pure metal or in association with other metals such as copper or gold, has been used since ancient times in the fabrication of decorative and functional objects owing to its working properties and pleasant color and shine. Silver artifacts suffer tarnishing when exposed to a sulphur containg atmosphere. The experimental findings reveal that the SiOx deposition, performed in RF plasma fed with a tetraetoxysilane/oxygen/argon mixture, produces layers with excellent barrier effects against the aggressive agents. The protective effectiveness increases if the deposition is performed at increasing input powers and at decreasing tetraethoxysilane/oxygen ratios in feeding gas. Electrochemical impedance spectroscopy is usually used to assess the protective properties and stability of organic films, because it may provide direct information on the corrosion rate. The imaging based qualitative approach proposed for the tarnishing evolution assessment proved to be an effective diagnostic tool to evaluate the stability of films and onset of localised corrosion phenomena that modify the surface roughness.
