Electrochemical Characterization and Immersion Corrosion of a Consolidated Silver Dental Biomaterial
H J. Mueller, R W. Hirthe
Precipitated silver particles acid activated and consolidated with pressure to a final volume porosity of 25 %, (CS) were investigated by electrochemical polarization, electrochemical impedance spectroscopy, and by continuous solution immersion. In selected tests, comparisons were made between CS and melted and cast precipitated silver particles (MS), pure silver foil, 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. Results revealed differences in the polarization between CS and MS in deaerated saliva. By superposition of the cathodic Tafel slopes, the active area for CS was increased due to the pore network by 7.3 times and corresponded to a reactive outer shell of material 5.5 υm thick. From mixed potential theory for corrosion and the corresponding graphical solution to the multi-electrode, differences in the corrosion potentials were attributed to different reduction reactions, which could have led to differences in the onset potential for the formation of soluble pre-state compounds, mainly AgCl. Differences also occurred between MS and CS polarizations in regard to sulfide- and mucin-interactions. Long term immersion tests also showed that CS was significantly more susceptible to corrosion than MS. Polarization resistance was significantly the highest for SP, followed in order by MS, CS and DA, with the latter two materials not significantly different. The modeled equivalent electrical circuits for both CS and DA involved a double layer capacitance, a charge transfer resistance, and an element attributed to adsorption. Calculation of the active pore depth for CS from the transmission line model for porous solids revealed good agreement with polarization results. It is concluded that the corrosion susceptibility of CS in Fusayama saliva, while similar to that for DA, is greater than it is for MS.