Multiscale electrochemical investigation of the corrosion resistance of various alloys used in dental prostheses

The electrochemical behaviour of Ag-Pd (Paliag), Ni-Cr (Heraenium NA), and Co-Cr (Heraenium CE) alloys used in dental prosthetics construction of crowns and bridges was studied in 0.9% NaCl solution at 25 ºC. The localized electrochemical characteristics related to corrosion resistance and eventual breakdown of the protecting oxide layers were investigated by scanning electrochemical microscopy (SECM), whereas potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed to establish oxide stability. When the corrosion resistance of the alloys was evaluated by means of the corrosion current value determined around their corresponding open circuit potential in 0.9% NaCl solution, good protection can be expected resulting from their spontaneous passivation (low current densities in the order of tenths of μA cm-2). The polarization resistance of all the samples increased with immersion time, in the sequence Ag-Pd < Heraenium NA < Heraenium CE. Yet, increased electrochemical activity was detected with SECM when the alloys were polarized at +0.40 VSCE, a value that may be eventually experienced in the human body. Though a passivation mechanism was still operating in the chromium-containing alloys, oxide dissolution and precipitation of corrosion products occurred on Ag-Pd instea