Electrochemical impedance spectroscopy characterization of passive film forme on Ti-Ta alloys

Abstract

Titanium derives its corrosion resistance from the stable oxide film that forms on its surface, which can reform at body temperature and in physiological fluid if damaged. Increased use of titanium alloys as biomaterials is occurring due to their lower modulus, superior biocompatibility and high corrosion resistance. These attractive properties were a driving force for the early introduction of Ti and Ti-6Al-4V as implantable materials. But Ti-6Al-4V has a potential cytotoxicity and adverse tissue reactions caused by vanadium and for this reason has been required the development of new titanium alloys with non-toxic elements (Nb, Zr, Ta, Mo, Fe etc.). The studied titanium tantalum alloys were Ti-15Ta and Ti-25Ta. The influence of potential on passive film of Ti-Ta alloys under simulated physiological conditions was investigated by Electrochemical Impedance Spectroscopy (EIS). All measurements were carried out in Ringer solution at 25 degrees C and at different potentials starting at -0.4V till +2V. Analysis of the impedance spectra was done by fitting these data using the Boukamp nonlinear least square fitting procedure. The EIS spectra exhibited two-time constant system suggesting the formation of a two-layer oxide film on the alloys surface, i.e. a porous outer oxide and a barrier inner oxide. The alloy Ti-25Ta has a higher corrosion resistance than Ti-15Ta, due to the inner layer and better osseointegration ability ascribed to the inner layer.