XPS and EIS studies to account for the passive behavior of the alloy Ti-6Al-4V in Hank’s solution

The passivation mechanism of the film formed on the alloy Ti-6Al-4V was evaluated in Hank’s solution to infer the properties of this alloy as an implant material. Alloy passivation was found from electrochemical measurements and X-ray photoelectron spectroscopy (XPS) to strongly depend on the oxidation of Ti and Al, microstructural changes associated with the Al and V, and the formation of metallic hydroxides and oxyhydroxides that disrupt the TiO₂ matrix. Experimental impedance diagrams were fitted using the point defect model (PDM, transfer function) to describe the passive character of the alloy. According to this analysis, the transport of oxygen and hydroxide defects across the film on the alloy surface determines the adsorption of oxygen from water dissociation and/or phosphate and the precipitation of calcium phosphate. Therefore, osseointegration of the alloy Ti-6Al-4V occurs across the entire surface and strongly depends on the defects present in the film, Al incorporation, the penetration of hydroxide ions (hydration), and oxygen adsorption.