| Titanium and its alloys are finding increasing application in the fabrication of surgical implants, such as artificial joints and dental implants. The excellent tissue response of titanium is attributed to the chemical and biochemical properties of titanium oxide films which form at the surface of titanium in the presence of oxygen.;In this work the fabrication of thick titanium oxide coatings (up to 40 $mu$m thick) on commercially pure titanium (cp Ti) and Ti-6Al-4V by anodization in methanolic electrolytes was studied. Formation of the oxide seems to occur in three steps: (1) anodic dissolution of titanium, (2) titanium methoxide formation, and (3) hydrolysis and condensation of titanium methoxide to form TiO$sb2.$ As the current density decreased, the growth rate decreased. Oxide growth was slower on Ti-6Al-4V substrates than on cp Ti substrates, due to the presence of aluminum in the coating which was detected by X-ray photoelectron spectroscopy (XPS). The crystal structure of the anodic titanium oxide coatings on cp Ti and Ti-6Al-4V were found to be amorphous, as a consequence of an oxygen deficiency, and the presence of OCH$sb3$ and OH groups in the oxide. Heat treatment resulted in crystallization of the oxide. This was accompanied by an increase in the oxygen content and removal of residual organics. The amorphous to anatase transformation occurred at 350$spcirc$C for oxides formed on cp Ti and 500$spcirc$C for oxides on Ti-Al-4V. Oxide coated samples were incubated for two weeks in a simulated body fluid (SBF) to study apatite formation on titanium oxide. Thick, carbonated apatite films (approximately 10$mu$m thick) formed on titanium oxide coated cp Ti samples which were heat treated at 400, 600, and 800$spcirc$C prior to incubation. |
