In vitro chloride corrosion behaviour of Dispersalloy

The in vitro chloride corrosion behaviour of Dispersalloy has been investigated by anodic polarization as a function of time after trituration (ageing) and compared with conventional dental amalgam. Dispersalloy is a commercial alloy containing a mechanical mixture of Ag-3-Sn and Ag-Cu eutectic in the ratio 2:1. From measurement of 1 h corrosion potentials it was observed that over a time period of 1 year Dispersalloy became appreciably more noble (potential shift from minus 500 mV to minus 350 mV Vs. SCE), whereas the corrosion potential of conventional amalgam remains unchanged. Initial anodic polarization profiles for Dispersalloy indicated presence of gamma2 and Cu-6-Sn-5 phases as evidenced by presence of the minus 250 mV peak. However, the current density associated with this peak was about three times less than that of conventional amalgam. As a function of ageing time the polarization profile is shifted in the direction of decreasing current density and after 1 year the minus 250 mV peak is absent. The anodic polarization profile of conventional amalgam is unchanges after 1 year. The improved corrosion resistance of Dispersalloy is attributed to the formation of Cu-3-Sn as a function of time due to solid state reaction between Ag-Cu eutectic and gamma2.