Synthesis of anodic TiO2-nanotubes in organic electrolyte and influence of voltage on corrosion properties of TiO2-NT

One dimensional nanostructures with their unique properties find their application in a variety of devices such as sensor, solar cell, batteries, etc. nanostructure titanium dioxide such as nanotube, nanofibers and nanowires has high surface to volume ratio compared to conventional microstructures[1]. Moreover TiO2-NTs are known to be chemically stable[2]. There are several synthesis methods for the TiO2 nanotubes growing such as seeded growth, hydrothermal process, sol-gel and electrochemical anodization[3], which among them anodization is one of the most common. Anodization was used for the first time to growth alumina (Al2O3) nanostructures by Masuda et al, and the Zwilling et al reported formation of the TiO2 nanoporous on Ti metal sheet by anodization in electrolyte containing HF. Anodization is a simple, low cost, an effective with a great degree of control on growth parameters (potential, PH, time, the chemistry of electrolyte solution)[4]. The present work reports on the effect of voltage on morphology and corrosion properties of selforganized TiO2 nanotube layers formed by anodization of Ti. The anodization process was performed at room temperature by electrolyze cell consist of the Ti substrate as anode and Pt as cathode, in electrolyte solution consist of ethylene- glycol, 0.5%wt NH4F and DI water 2.5 %wt. anodization process were performed at 20,30,40 V for 2h, using a constant voltage(DC) source. In order to enhance the crystal structure, they annealed at 450 C0 for 2h in air (heating rate: 5 C0/min). morphology and chemical composition of the coating were evaluated by field emission scanning 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 226 electron microscope (FESEM) and X-ray diffraction (XRD). Electrochemical corrosion behavior of the TiO2-NTs was determined by electrochemical impedance spectroscopy (EIS). Fig 1 Show FESEM images of TiO2-NT prepared by anodization in different voltage. When the potential is increased, rate of chemical dissolution and oxidation increase resulting in nanotube growth. Fig2 show XRD pattern for TiO2-NT after and before annealed at 450 C0. We showed that annealing TiO2-NT under oxidizing condition result in the formation of anatase crystal structure in the 450C0. The EIS result are shown in Figure3,a and the equivalent circuits used for fitting the TiO2-NT samples are illustrate in Fig 4. the coating which was formed in the 20 V had the highest corrosion resistance because this sample had lowest porosity, diameter and surface area.