Cobalt-based alloys for orthopaedic applications studied by electrochemical and XPS analysis
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- Kocijan, A., Milošev, I. & Pihlar, B. Journal of Materials Science: Materials in Medicine (2004) 15: 643. doi:10.1023/B:JMSM.0000030204.08616.3d
The composition of the passive layers formed by electrochemical oxidation at different passivation potentials on Co–Cr–Mo and Co–Ni–Cr–Mo alloys in simulated physiological solution (SPS), with and without the complexing agent EDTA, was studied by X-ray photoelectron spectroscopy. Composition as a function of depth, cationic fraction and thickness of the passive film was determined. Chromium oxide is shown to be the major constituent of the passive layer on both Co–Cr–Mo and Co–Ni–Cr–Mo alloys. The minor constituents of the passive layers, Co- and Mo-oxide in the case of Co–Cr–Mo alloy and Ni-, Co- and Mo-oxides in the case of Co–Ni–Cr–Mo alloy, are also located in the outer part of the layer. EDTA affects the formation of the passive layer on each alloy. The content of Co-, Ni- and Mo-oxide in the passive layer is lower in the presence of EDTA, thus indicating increased solubility associated with higher stability constants for complexes of metal cations with EDTA.