Anodised titania nanotubes prepared in a glycerol/NaF electrolyte

This paper discusses the preparation of titania nanotubes by anodisation of Ti in a glycerol-based electrolyte containing 0.5% wt of sodium fluoride (NaF). The influence of anodisation voltage and anodisation time on nanotube wall thickness, diameter and length has been investigated. The results indicate that nanotubes can be formed within a voltage range 10-40 V and that the tubular structure is lost when using a higher voltage. The diameter of the nanotubes is voltage dependent, with the widest tubes being obtained at the highest possible applied voltage of 40 V. An initial voltage ramp which increases at 100 mV/s to the anodisation voltage, rather than an instantaneous step, was observed to stabilise the metal-oxide interface. This enabled the growth of anodic films up to 5.5 microm in length by anodising for approximately 48 h. In the absence of a voltage ramp the films tended to collapse and become detached from the titanium electrode after 15-20 h. Electron microscopy observation suggests that the nanotubes in glycerol develop in a similar way to those produced in water-based media. The nanotubes formed using glycerol also exhibit ripples along the tube wall, although, growing at a slower rate, they are generally smoother than those formed in water.