Obtaining, structural and corrosion characterization of anodized nanolayers on Ti-20Zr alloy surface

Abstract

The binary Ti–20Zr alloy was elaborated with the aim to be used as small diameter implant placed in narrow edentulous ridge. The alloy surface was galvanostatically anodized in 1M H3PO4 solution to increase its corrosion resistance and bioactivity. The results of energy dispersive X-ray spectroscopy, Raman spectroscopy, Fourier-transform infrared and X-ray photoelectron spectroscopy showed that the alloy surface was covered by a quasi-amorphous TiO2 oxide based nanolayer with very small crystalline nuclei of rutile-type structure that incorporated phosphorous ions. The anodized nanolayer revealed submicron surface features and nanoscale roughness measured by atomic force microscopy, and flake-like platelets observed by scanning electron microscopy. The electrodeposited nanolayer acted as a barrier against the diffusion of ions through it and reduced very much (about ten times lower) the corrosion and ion release rates, a good indicator of increased long-term alloy biocompatibility in Ringer's solutions/simulated body fluids. The main electrochemical parameters evinced a nobler behavior of the anodized alloy in comparison with bare one. Electrochemical impedance spectroscopy indicated that the anodization treatment provided the formation of a more stable, resistant nanolayer. Long-term experiments denoted the improvement over time of the protective properties of the anodized nanolayer by its thickening. Immersion of the anodized alloy in neutral and alkaline Ringer's solutions resulted in the deposition of nanostructured coatings with a morphology of entangled acicular n-HA nanocrystallites, while brushite coatings deposited in acid Ringer's solution. The anodized nanolayer obtained on the Ti–20Zr alloy surface endowed the substrate both with protection and bioactivity.