Electrochemical stability of TiO2 nanotubes with different diameters in artificial saliva

Recently, titanium and titanium alloys with nanotube layers by anodizing process have gained great interests as surgical implant materials. In this present paper, their electrochemical stability of self-organized TiO₂ nanotubue layers prepared by anodization of pure Ti in 0.5 wt.% hydrofluoric acid has been investigated in simulated biological environment by use of open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The electrochemical testing results indicate that the nanotubular Ti with the diameter of TiO₂ nanotube lower than 86 nm shows a better corrosion resistance in artificial saliva than that of the mechanically polished Ti. Moreover, the electrochemical stability of Ti nanotubes 22 to 59 nm in diameter is improved but that of Ti nanotubes larger than 86 nm decreases. Besides, the corrosion attack of the nanotubular Ti is shown by the collapse of TiO₂ nanotubue layer. The results suggest that the electrochemical corrosion behavior of nanotubular Ti in artificial saliva is related to the diameter of the nanotubes and thickness of the barrier layer.