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 phys iological 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 t o the spectrometer. Thus the composition of the layer formed by oxidation w as 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 po tential the content of Ti4+ species increased and that of Ti3+ and Ti2+ dec reased. The content of titanium in TiO2 was lower than theoretically predic ted due to the incorporation of Al2O3 in TiO2 matrix. Vanadium oxide was no t 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 ele ctronic properties of passive films over seven decades of frequency. A link between electronic, electrochemical and physiochemical properties was esta blished. (C) 2000 Elsevier Science Ltd. All rights reserved.