Sol–gel derived Ta-containing TiO₂ films on surface roughened NiTi alloy

Abstract

The surface of NiTi alloy was roughened by NaOH–HCl treatment, and the Ta-containing TiO₂ films were coated on the pretreated NiTi alloy by the sol–gel method. Thermal analyses indicate that the evaporation temperature of the organics decreases with the addition of tantalum ethoxide in the TiO₂ sol, but the crystallization temperature of anatase increases. The NaOH–HCl pretreatment improves the film integrity, but cracks still form in the films at high Ta contents (≥20 %, molar ratio) owing to the increasing film thickness. X-ray diffraction (XRD) confirms that the addition of Ta suppresses the crystallization of anatase. X-ray photoelectron spectroscopy (XPS) reveals that Ta exists as Ta₂O₅ in the film. With the increase of Ta content, the hydrophilic conversion of the films under UV illumination is impeded, but their corrosion resistance in 0.9 % NaCl solution increases, tested by the potentiodynamic polarization. The coating samples have acceptable hemolysis ratios for biomaterials (<5). The introduction of Ta improves the anti-aggregating function of the TiO₂ film in the platelet adhesion test.