Corrosion of dental amalgams: Studies of individual phases

The corrosion resistance of commercial dental amalgam (Dispersalloy) and its component phases has been investigated. Electrochemical measurements were carried out in 0.9% NaCl which simulates the aggressivity of the oral cavity, using open circuit potential measurements, polarization curves and electrochemical impedance. The relative corrosion rates of the various phases, Ag-Cu, gamma(1)-Ag2Hg3, gamma-Ag3Sn and gamma(2)-Sn7Hg was investigated as a function of immersion time using Tafel analysis of polarisation curves and impedance at the open circuit potential. Impedance measurements in the region of the open circuit potential led to complex spectra with diffusional components and showed differences in the corrosion mechanism between the phases. The microstructure of Dispersalloy, after potentiodynamic polarization, showed that the corrosion attacked the Ag-Cu eutectic particles and reaction zone surrounding the grain boundaries of the gamma(1)-phase at the surface of the amalgam.