Formation of titanium dioxide nanotubes on Ti–30Nb–xTa alloys by anodizing

Abstract

The goal of this study was to investigate the formation of titanium dioxide nanotubes on the surface of cast Ti–30Nb–xTa alloys by anodizing. The anodization technique for creating the nanotubes utilized a potentiostat and an electrolyte containing 1M H3PO4 with 0.8wt.% NaF. The grain size of the Ti–30Nb–xTa alloys increased as the Ta content increased. Using X-ray diffraction, for the Ti–30Nb alloy the main peaks were identified as α″ martensite with strong peaks of β phase. The phases in the Ti–30Nb–xTa alloys changed from a duplex (α″+β) microstructure to solely β phase with increasing Ta content. The nanotubes that formed on the surface of the Ti–30Nb–xTa alloys were amorphous TiO2 without an evidence of the crystalline anatase or rutile forms of TiO2. Scanning electron microscopy revealed that the average diameters of the small and large nanotubes on the Ti–30Nb alloy not containing Ta were approximately 100nm and 400nm, respectively, whereas the small and large nanotubes on the alloy had diameters of approximately 85nm and 300nm, respectively. As the Ta content increased from 0 to 15wt.%, the average lengths of the nanotubes increased from 2μm to 3.5μm. Energy-dispersive X-ray spectroscopy indicated that the nanotubes were principally composed of Ti, Nb, Ta, O and F. Contact angle measurements showed that the nanotube surface had good wettability by water droplets.