Characterization of TiO2 nano-films obtained by anodic oxidation of Ti-6Al-4V

MARÍA LAURA VERA; ANGELES COLACCIO; DIEGO LAMAS; CARLOS SCHVEZOV; ALICIA ARES

Congreso; XXII IUCr Congress; 2011

IUCr

Anodic oxidation of Titanium and Titanium alloys produce a TiO2 coating with better mechanical properties and corrosion resistance than the substrate. In addition, this TiO2 coating is a film with biocompatible properties [1], [2]. In the present report, we determined and analyzed the effects of different acid electrolytes on the color, thickness, morphology and crystalline structure of the coating. The electrolytes used were sulfuric acid (H2SO4) 0.1M to 4M and phosphoric acid (H3PO4) 1M, and the substrates were plates of Ti-6Al-4V alloy; the oxidation voltages used ranged from 10V to 100V. The thicknesses of the films were determined by X-ray reflectometry with synchrotron radiation (D12A-XRD1 beamline of the Brazilian Synchrotron Light Laboratory, LNLS). The morphology of the films was observed using optical and scanning electron microscopy and the crystalline phases of the oxides formed were determined by the glancing incidence angle X-ray diffraction technique with a glancing angle of 1º. The oxide films produced different interference colors depending on the type of electrolyte and the voltage for oxidation applied. For both electrolytes, the fi lm thickness increased with the voltage applied. The concentration of the electrolyte produced minor shifts in color, negligible enough to establish a relation between color and thickness of the fi lm for each electrolyte as a way to have a quick method to determine thickness. The fi lms produced at low voltages were homogeneous, with low roughness and amorphous. At higher voltages, sparks discharges were observed and porous fi lms, with a degree of crystallinity, were produced. The voltage for spark discharge depended on the electrolyte. Using H2SO4 1M as electrolyte, the fi lms produced were compact, homogeneous and no crystalline phases of TiO2 were detected up to 60V. From 70V to 80V, the fi lms were porous and crystalline with the anatase phase formed, and above 80V, the rutile phase was formed. As the concentration of electrolyte increased, the conductivity increased and the homogeneous/amorphous to porous/crystalline transition was produced at lower voltages. In the case of the H3PO4 1M electrolyte, there were no spark discharges or crystalline phases up to a voltage of 100V, which was the highest voltage used.