Publication date: 31st July 2014
In this paper, the synthesis of TiO2 porous nanostructures through electrochemical anodization of Ti foils at high voltage (60 V) in non-aqueous ethylene glycol (3% volume of DI H2O+ 0.25 Wt% NH4F) electrolyte solution during a time range from 11 to 14 hours, is reported. SEM analysis showed that at 14 hours of anodization, fibers of approximately 55µm long were observed, in which the presence of upper hollows was not distinguished. However, it was evident that the Ti foils without a previously formed oxide thick layer over its surface showed highly ordered and symmetric porous with an approximately 130 nm inner diameter, which evidences the previous existence of nanotubes, which were previously dissolved. At 11:30 hours, arrays of highly self-organized nanoporous with inner diameters between 75-80 nm were obtained, which suggests that the optimal anodization time in the formation of self-organized porous structures under the conditions above mentioned, was 11:30 hours.The electrochemical characterization was made under four different conditions: a) not anodized titanium samples (Ti foils), b) TiO2 plane layers, c) amorphous TiO2 nanoporous films, and d) crystalline TiO2 nanoporous films. The four samples were exposed to 1M Na2SO4 aqueous solution, applying two electrochemical approaches: potentiodynamic polarization curves and electrochemical impedance spectroscopy. Mechanical characterization was made using the nanoindentation technique, applying three different loads (1.0, 2.5, and 5.0 mN) on TiO2 amorphous and crystalline films. Through this technique the hardness, modulus of elasticity, and the maximum depth of penetration were obtained. In order to determine the differences and features of the different Ti/TiO2 samples, the electrochemical and nanoindentation results were analyzed and interpreted. It was observed that the amorphous and crystalline nanostructured films were electrochemically and mechanically more resistant than pure Ti and Ti+TiO2 planar film.
Key words: Potentiostatic anodization; Titanium Dioxide; TiO2 porous structures, Mechanical characterization.
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