Silver Alloy Protection by Applying Nanomaterial Coat after Tarnish Removal

This research focuses on the tarnish removal and protection of silver alloy by using nanoalumina coating. In the presence of a high concentration of sodium sulphide (0.1 M Na₂S) at room temperature, a dark tarnish forms on the silver surface. Tarnish removal proceeds by coupling with aluminum sheets of various areas in a solution of 10% (1:1) sodium carbonate-bicarbonate at room temperature. Nanoalumina (Al₂O₃) is used to protect silver alloy. A silver alloy specimen was immersed in a suspension of nano-Al₂O₃, acetone and paraloid under an ultrasonic shaker. An efficient, invisible and protective layer against the tarnishing appearance was formed on the silver alloy surface. The protectiveness of the nanoalumina coating was tested by electrochemical measurement during immersion in a concentrated sulphide solution and by visual observation. The potential shifts to a more positive potential (anodic) in the presence of low concentrations of Na₂S and shifts to a more negative potential in the presence of high concentrations of Na₂S. The potential shifts to less negative values in the presence of the nanoalumina coating. This means that the nanoalumina coating increases the protective behaviour of the silver alloy. Visual observation indicates that the surface is bright and there is no tarnish formation,especially with the homogenous distribution of the nanoalumina layer on the surface.

Keywords:Silver alloy; Silver tarnish; Tarnish removal; Nanoalumina coating