Influence of Phosphate Ions and Proteins on the Corrosion of CoCrMo Medical Grade Alloy: Electrochemical and XPS Characterization

The spontaneous formation of a thin (1-4nm) passive oxide film consisting of a mixture of cobalt, chromium and molybdenum oxides confers to CoCrMo alloys a good corrosion resistance in physiological medium and limits metal ions release. Unfortunately, this extremely thin film is susceptible to fracture under mechanical loading, resulting in exposure of the alloy to this medium. Subsequent electrochemical oxidation processes dissolve the alloy. Metal ions are released into the surrounding tissues3 causing tissue inflammations and diseases.
Several papers have been devoted to investigate the surface chemistry under various corrosion conditions using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy,4-6 Raman spectroscopy as well as by electrochemical means.
The aim of the present work is to understand the effect of surface modification in the presence of phosphate ions and calf serum proteins on the corrosion behavior of CoCrMo alloys. The interplay between the formation of chromium orthophosphate on CoCrMo surface and chromates dissolution is discussed as well as the adsorption of proteins.
XPS analyses are associated to electrochemical techniques to characterize the interface and its corrosion resistance. The evolution of CrO42-concentration with time and phosphate concentration is studied with an UV-Visible analysis.