Electrochemical characterization and immersion corrosion of a consolidated silver dental biomaterial

A consolidated silver (CS) material, an alternative to dental amalgam, was studied for corrosion. Chemically precipitated silver particles were acid activated and pressure consolidated to a volume porosity of 25%. In selected tests comparisons were made between CS and melted and cast silver particles (MS), silver with a known mass fraction purity of 99.998% (FS), a silver-palladium alloy (SP). and a dispersed-phase amalgam (DA). Fusayama artificial saliva was used with controlled variations in pH, sulfide content, mucin content, and absorbed oxygen content. Electrochemical polarization, electrochemical impedance spectroscopy, and immersion methods were used. Results revealed differences in the zero current potentials E(I = 0) from forward polarization between CS and MS (or FS) in deaerated solution. By superposition of the cathodic polarization curves, the area for CS was increased by 7.3 times and was enclosed within an outer shell of material 5.5 microm thick. Polarization resistance was significantly the highest for SP, followed in order by MS (or FS) and CS or DA. With scanning electron microscopy, CS was shown to be significantly more susceptible than MS to long-term immersion corrosion. The modeled equivalent electrical circuits for CS and DA involved a double layer capacitance, a charge transfer resistance, and an element attributed to adsorption. The active pore depth for CS from the transmission line model for porous solids revealed satisfactory agreement with polarization results. It is concluded that the corrosion susceptibility of CS in Fusayama solution, while similar to that for DA, is greater than it is for MS.