Comparative study of nanostructured titania grown by electrochemical anodization of α-Ti and β-TiNi substrates in organic electrolytes

The motivation of this work is to compare methods for nanotube formation in α-Ti with the results obtained in β-TiNi by electrochemical anodization at the same conditions. Both substrates were characterized by XRD to assure their phase constitution at room temperature. Samples were anodized in 0.2%m. NH4F and 1%v. H2O in ethylene glycol solvent at 5, 15, 25, 45, and 60 V. Each experimental condition had its current densities recorded as a function of time and the resultant anodic films were characterized by FE-SEM. All conditions lead to nanotube formation in Ti substrates. TiNi samples anodized at 5 V produced evenly spread nanotubes with similar diameters of those in Ti. As the potential increased, the nanotubular aspects of titania in TiNi were increasingly lost. At higher anodization potentials, tubular structures can be seen in a matrix of sponge-like oxide formed due to the increase of oxygen evolution as the potential increased. Examination of the metal/oxide interface indicates that, even though spongy oxide was formed in TiNi substrates, the mechanism of growth initiation is similar to Ti samples. It is possible to conclude that for the same anodization conditions β-TiNi is more reactive than α-Ti and requires milder conditions to produce nanotubular surfaces.