Passive film on orthopaedic TiAlV alloy formed in physiological solution investigated by X-ray photoelectron spectroscopy.

The passive film formed by electrochemical oxidation on TiAlV alloy in physiological solution was studied using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The alloy was polarised at different oxidation potentials in the electrochemical chamber attached to the spectrometer. Thus the composition of the layer formed by oxidation was analysed by XPS without prior exposure to air (quasi-in situ). The oxide layer was predominantly TiO2, which contained a small amount of suboxides TiO and Ti2O3 closer to the inner metal/oxide interface. With increasing potential the content of Ti4+ species increased and that of Ti3+ and Ti2+ decreased. The content of titanium in TiO2 was lower than theoretically predicted due to the incorporation of Al2O3 in TiO2 matrix. Vanadium oxide was not identified by XPS. Angular resolved XPS analysis confirmed that Al2O3 is located mainly at the outer oxide/solution interface. The thickness of the oxide layer was dependent on the oxidation potential and after oxidation at 2.5 V reached 9 nm. EIS measurements were used to in situ characterise electronic properties of passive films over seven decades of frequency. A link between electronic, electrochemical and physiochemical properties was established.