Oxides Formed on Titanium by Polishing, Etching, Anodizing, or Thermal Oxidizing

Photoelectrochemistry (PEC), glancing angle x-ray diffraction (GAXRD), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) in synthetic salt water were utilized to investigate the nature of different oxides formed on titanium by thermal oxidizing, polishing, acid-etching, and anodizing. This work demonstrated that at least four different types of titanium oxide were formed on the surface of titanium, depending on the surface treatment. Rutile titanium dioxide (TiO₂) was formed on thermally oxidized titanium, and rutile provided the lowest passive current in seawater, the lowest bandgap (3.0 eV), and the highest photocurrent quantum efficiency of all the surface treatments tested. A titanium oxide-hydroxide with a bandgap of 3.5 eV was found on polished, acid-etched, or step-anodized (to 1.5 V) titanium. This same oxide-hydroxide was also present on the surface of cubic titanium monoxide (TiO) immersed in salt water. A second titanium oxide-hydroxide with a bandgap of 3.35 eV was found on the surface of slow ramp anodized titanium (to 2.0 V). Previous work by others has shown the presence of anatase on the surface of thick anodized titanium (bandgap of 3.2 eV).