Surface analysis of anodic oxide films containing phosphorus on titanium

PURPOSE: To examine the effect of phosphoric acid solution on the anodic oxide film of titanium. MATERIALS AND METHODS: Commercially pure grade 2 titanium specimens were prepared and anodized in phosphoric acid solution at a constant current density (70 A/m2). Specimens were evaluated by means of scanning electron microscopy, x-ray diffraction analysis, electron probe microanalysis, energy-dispersive spectroscopy, profilometry, and atomic force microscopy. RESULTS: The anodic oxide film was observed to consist of a porous or non-uniform layer and a dense or uniform layer. X-ray diffraction and energy-dispersive spectroscopic analyses indicated that the film consisted of a mixture of anatase and amorphous oxide, with the incorporation of phosphorus. DISCUSSION: The degree of oxide crystallinity was observed to increase with an increase in voltage but decreased as the electrolyte concentration was increased. In addition, the concentration of phosphorus also increased as the electrolyte concentration and voltage increased. CONCLUSIONS: Electrolyte concentration and voltage play an important role in governing the anodic oxide thickness, composition, and degree of oxide crystallinity.