Aesthetic coatings for silver based alloys with improved protection efficiency

Ag-based alloy samples are submitted to innovative chemical and low pressure plasma treatments that lead to the deposition of aestheticcoatings with improved corrosion protection properties. The chemical treatments are carried out in alkaline dithionate solution in order to clean the surface and eventually remove the patina on aged samples, then the surface is protected by a Paraloid B72 coating containing different percentages of Al2O3 nanopigments. The plasma treatments are carried out by deposition of SiOx thin films in plasma fed with TEOS, Ar and O2. Before the PECVD deposition, a glow discharge in a low pressure hydrogen plasma eventually removes tarnishing, reducing the corrosion products layer back to silver. The coating protective effectiveness is assessed by means of electrochemical impedance spectroscopy and accelerated ageing tests. The corrosion mechanism of the coated samples is investigated by XRD analyses. Both the chemical and the plasma treatments show satisfactory results from an aesthetic point of view and good barrier effect against aggressive environmental agents