Surface-enhanced Raman spectroelectrochemical studies of corrosion films on implant Co-Cr-Mo alloy in biosimulating solutions

Surface-enhanced Raman (SER) spectroelectrochemical studies were carried out to identify the surface species formed on Co–Cr–Mo alloy under different conditions. The surface films identified for the alloy in air include chromium(III) oxide, molybdate, molybdenum(VI) oxide and possibly cobalt(II) oxide. The air-formed molybdenum species disappear quickly in 0.15 M NaCl. In 0.15 M NaCl, part of the CoO and Cr2O3 might react with water to form Co(OH)2 and Cr(OH)3 , respectively. It is difficult to reduce these lower oxidation state oxides and hydroxides of Cr and Co. At high potentials, Co(OH)2 species remain at the interfaces. From electrochemical data, it appears that the alloy passivates very well, especially in artificial saliva. At lower potential, the Cr species play major roles in the passivation of the alloy, and at higher potential the Co species take on these roles. The dissolution rates of Mo from the Co–Cr–Mo alloy in NaCl and NaOH solutions are too low to be measured, indicating that the passive films of Cr and/or Co protect further oxidation of underlying Mo in the alloy.