Effects of Addition of Indium and/or Gold on Corrosion Resistance and Tarnish Resistance of Silver-Palladium Alloys

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Nine silver-palladium alloys (Ag+Au=58%, Pd=20%, Cu+In=18%, and Zn=4%) with three levels of indium content (0,9, or 18%) and three levels of gold content (0,10, or 20%) were characterized by tarnish test, electrochemical corrosion test, and mass loss test immersed in 0.1% Na_2S solution as well as in 1% NaCL solution. The following conclusions may be derived from this investigation about the alloys within the experimental range. 1. The color of alloy becomes darker, more chromatic, and more reddish, i.e., gold-like appearance to some extent regardless of gold content compared to the copper containing alloy when indium is added instead of copper. Increasing of gold content does not change the color of alloy very remarkably as long as indium content is the same. 2. The tarnish resistance of alloy is good in the sodium chloride solution, while it is poor in the sodium sulfide solution. Increasing of gold content increases the tarnish resistance of alloy as long as indium content is the same. If the alloy contains indium and copper equally, the tarnish resistance decreases dramatically compared to the alloy which contains either indium or copper. The latter effect is so remarkable that the tarnish resistance of 38%Ag-20%Au-20%Pd-9%Cu-9%In-4%Zn alloy is inferior to that of 58%Ag-20%Pd-18% (Cu or In) -4%Zn alloy. 3.The alloy appears to be corrosion prone in the sodium sulfide solution rather than in the sodium chloride solution. Increasing of gold content increases the corrosion resistance of alloy remarkably as long as indium content is the same. If the alloy contains indium and copper equally, the corrosion resistance decreases compared to the alloy which contains either indium or copper. 4.There is a positive correlation between the corrosion resistance and the tarnish resistance in the sodium chloride solution.