Synthesis and Mechanical/Electrochemical Characterization of TiO2 Nanotubular Structures Obtained at High Voltage

Abstract

The synthesis of TiO2 nanotubular arrays obtained through anodization of Ti foils in ethylene glycol (3% volume DI H2O + 0.25 wt.% NH4F) at high voltage is reported. The physical, chemical, electrochemical, and mechanical characterization was made to the TiO2 nanotubular arrays. The morphological characterization showed a cylindrical geometry (112 nm inner diameter and 65 μm length), determining a rugosity factor of 1840 points. The electrochemical characterization was carried out exposing four samples: Ti, TiO2 amorphous, and two crystalline TiO2 nanotubular arrays (450 and 600°C) in two aqueous solutions of different pH: 1 M Na2SO4 and 1 M Na2SO4 + H2SO4, using the potentiodynamic polarization curves. The mechanical characterization was performed through the nanoindentation technique applying three different loads (2.5, 5.0, and 10 mN) on the amorphous and the two crystalline TiO2 nanotubular samples, obtaining the mechanical parameters such as the hardness, the elastic module, and the maximum penetration depth. The TiO2 nanostructured sample crystallized at 600°C had the best electrochemical stability in both media and presented an elastic modulus of 22.42 GPa when it was tested applying a load of 2.5 mN, whereas the amorphous sample presented the major hardness at the loads of 5 and 10 mN.