Scan Rate and Fluoride Concentration Effect on the Anodic Growth of Self-Aligned Titanium Dioxide Nanotubes in Phosphates

Abstract

Formation of titania nanotubes at different scan rates of polarization during the first stage of anodizing titanium in 1M H3PO4 with the addition of various amounts of HF (0.2–0.4 wt.%) which consisted of a potential ramp to 20V with a scan rates of 400-600 mV/s. Insight into current/voltage curves allowed to identify the incubation of nanotubes by examination of current transient slope changes. The lowest values of the oxide layer breakdown time tbreak were observed at 500mV/s and 0.3%wt.HF, when the most homogenous titania nanotube, as observed with SEM and EDS, were obtained. Also the concentrations of phosphates and fluorine in titania nanotubes (XPS) were the highest for that conditions. These results suggest that to reach the equilibrium between oxidation/dissolution processes, transport of fluorides in oxide may be crucial.