Effect of Water and Fluoride Content of Anodizing Electrolyte on Morphology and Corrosion Behavior of ZrO₂-Nanotubes Developed on Zirconium Implant

Zirconium oxide nanotubes with inner diameter of 30-80 nm were fabricated by anodizing method in glycerol and DMF solution as organic electrolytes containing small amount of ammonium fluoride and water at room temperature. We investigated the effect of water content (1, 3, 5 wt.%) and ammonium fluoride concentration (0.5, 1, 2 wt.%) on the morphology, as well as the zirconia nanotubes diameter and their corrosion resistance in the artificial saliva solution as a biological medium at 37 ± 1 °C. Nanotubes morphology and structure were examined by field emission scanning electron microscopy (FE-SEM), energy dispersive x-ray and x-ray diffraction spectroscopy. The FE-SEM results show that the inner diameter of nanotubes rises with increasing the concentration of ammonium fluoride and water content in anodizing electrolyte solutions. The electrochemical impedance spectroscopy and Tafel polarization tests were used to study the corrosion behavior of zirconia NTs electrodes. The results show that the best concentration of ammonium fluoride and water content in anodizing electrolyte, which the samples demonstrated maximum corrosion resistance and regular structure, were at 1 wt.% H₂O and 2 wt.% NH₄F.