Effect of Platinum Content in 930Sterling Silver on Hardness and Tarnish Resistance

        In the jewelry industry, sterling silver has been widely used despite its resistance to tarnish. Silver is alloyed with other metals especially copper to enhance its mechanical properties with a drawback in tarnish resistance. Many alloying elements have been investigated to develop the sterling silver with anti-resistance [1-2]. In this study, 930 sterling silver alloyed with Pt was developed. The effects of platinum on microstructure, hardness and tarnish resistance of the as-cast sterling silver were investigated 0-7 wt.% platinum contents (Table 1). The samples were cast by an induction furnace with an investment casting process. The flask and pouring temperatures were set constant to investigate the solidification behavior of the alloys. Hardness of the as-cast sample was measured using Vickers microhardness testing. Tarnish test was performed in an environment of sodium sulfide vapor. Change of color every 15 minutes was measured using colorimeter in CIEL*a*b* system.
        Microstructural development of the as-cast samples was revealed using optical microscope (Figure 1). Dendrite structure developed with platinum contents indicating change of solidification rate. Hardness of the as-cast alloys was optimized from a contribution of phases and microstructure. Tarnish resistance obviously increased with platinum contents. With a compromise between hardness and tarnish resistance, the 930 sterling silver alloyed with 3wt.% Pt could be a promising candidate for anti-tarnish jewelry materials.