Abstract
The objective of this study was to test the hypothesis that there is one model for the interface between the passive layer on the surface of an orthopaedic alloy and an electrolyte that has clinical relevance. To this end, electrochemical impedance spectroscopy measurements were made on mechanically-polished test specimens fabricated from three orthopaedic alloys [two Ti-based ones (Ti–6Al–4V and Ti–13Nb–13Zr) and a very-low-nickel austenitic stainless steel, Biodur® 108] while they were immersed in phosphate buffered saline (PBS) solution, at 37±1°C, over a period of 25 d. Through a statistical comparison between the experimental results (Nyquist and Bode plots) and those computed using seven different equivalent electrical circuits (each representing a different model of the aforementioned interface), it was found that one circuit (comprising an arrangement of three resistances and three capacitances in series with a resistor representing the solution resistance) provided the best-fit in all three alloy surface-PBS solution systems, thus providing support for the working hypothesis. The variation of each of the circuit elements with time of immersion of the specimen in the PBS solution and the study limitation are discussed.