Electrochemical characterisation of passive films on Ti alloys under simulated biological conditions

An electrochemical characterisation of the passive film on Ti, and its alloys Ti6Al4V and Ti6Al7Nb under simulated biological conditions is described. Electrochemical impedance spectroscopy and photoelectrochemistry were employed as in-situ techniques to monitor the evolution of the passive film on exposure to simulated body fluid environments. Of particular interest were the selective interactions of phosphate and calcium ions present in simulated body fluid with the oxide films, immediately after exposure. The effects of these ions on the TiO₂-electrolyte interface could be detected already within the first hour of exposure at 37 °C and were found to be the only ions present in simulated body fluid to interact with the titanium oxide surface. Photocurrent spectra showed no change in the semi-conductive properties of the passive films on Ti and the two alloys, but large variations on the intensity of the generated photocurrent indicated the presence of adsorbed ions on the surface. Different behaviour between the three metals investigated was also observed.