Several cobalt-chromium alloys such as MP35N are used for biomedical implants. The electrochemical behavior of these alloys in the passive range differs from that of other biomedical alloys. In particular, their cyclic potentiodynamic polarization curves exhibit an increase in current at a potential of about 0.4 V (SCE). This study examined the electrochemical behavior of MP35N in phosphate-buffered saline (PBS). Tests were performed on mechanically polished MP35N rod and electropolished MP35N wire using cyclic potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. In both cases, the surface oxide was shown to undergo two distinct changes as the potential is increased. The first change appears to be associated with solid-state oxidation reactions involving the conversion of Cr(III) to Cr(VI) and of Co(II) to Co(III) at similar potentials. The second change involves transpassive dissolution that results in the release of chromate and nickel ions. At potentials below where these reactions occur, the impedance spectra showed near-capacitive behavior, and the data could be fitted by a parallel resistance-capacitance (as a constant phase element) circuit associated with the passive oxide film. The thickness of the oxide was determined from the capacitance and found to be consistent with surface analytical results reported in the literature. Resistivities obtained from resistance values indicated changes in the film composition as the potential was increased, particularly after the onset of the solid-state reactions. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res 2010.

We have developed a high conductivity bilayered ceria/bismuth oxide anolyte/electrolyte that uses the Po gradient to obtain stability at the anolyte-electrolyte interface and reduced electronic conduction due to the electroly3te region. Results in terms of solid oxide fuel cell (SOFC) performance and stability are presented. These results include a 90 to 160 mV increase in open-circuit potential, depending on temperature, with the bilayered structure as compared to SOFCs fabricated from a single ceria layer. An open-circuit potential of >1.0 V was obtained at 500°C with the bilayered structuie. This increase in open-circuit potential is obtained without any measurable increase in cell resistance and is stable for over 1400 h of testing, under both open-circuit and maximum power conditions. Moreover, SOFCs fabricated from the bilayered structure result in a 33% greater power density as compared to cells with a single ceria electrolyte layer.

The electrochemical behavior of nitinol in simulated human bile and phosphate-buffered saline (PBS) was examined using electrochemical impedance spectroscopy. In addition, cyclic potentiodynamic polarization tests were performed in the simulated bile and salt-only bile, and the results compared with those obtained previously in PBS. The potentiodynamic tests showed that electropolishing was effective in providing nitinol with a high resistance to pitting corrosion in the bile solutions, as found in PBS. Differences between the breakdown potential and the corrosion potential indicated that mechanically polished nitinol should be more susceptible to pitting corrosion in simulated bile than in the salt-only bile and PBS. The impedance spectra showed near-capacitive behavior in both PBS and simulated bile, and the data could be fitted by a parallel resistance-capacitance (as a constant phase element) circuit associated with the passive oxide film. The thickness of the oxide was determined from the capacitive component and found to be consistent with surface analytical results reported in the literature. Resistivities obtained from resistance values indicated that compositional features of the oxide were similar for PBS and simulated bile.