Twin-jet electropolishing of cast sterling silver alloys using perchloric acid and potassium cyanide solutions

Abstract

Twin-jet electropolishing of Ag-4.87 wt%Cu-0.79 wt%Zn-0.09 wt%Si alloy was studied. Two electrolytes, i.e. potassium cyanide solution in distilled water and glycerol-perchloric acid solution in absolute ethanol, were used in the experiments. Effects of parameters including voltage and electrolyte concentration have been studied. Surface of polishing specimens and artifact formed were characterized by light microscopy and electron microscopy. In general, the potassium cyanide solution is a better electrolyte than the glycerol-perchloric acid solution. A more uniform polishing can be obtained from the potassium cyanide solution at the voltage higher than 5 V. Increasing of the potassium cyanide concentration reduced the electrical resistance of the electrolyte and polishing time. The concentration of 150 g KCN/L is recommended. By using the glycerol-perchloric acid solution, artifact as fine silver dendrites was found pronouncingly on the polished specimen. This artifact was considered as a major drawback and its mechanism of formation has been discussed.