Current characterization and growth mechanism of anodic titania nanotube arrays

Abstract

TiO 2 nanotube arrays were synthesized by anodic oxidation on a pure titanium substrate in solutions containing 0.175 M NH 4 F composed of mixtures with different volumetric ratios of DI water and glycerol. According to the results of the current curve recorded during anodization, the time of the first sharp current slope (corresponding to the initial oxide layer formation time) was found to vary from 8 to 171 s depending not only upon the water content in the electrolytes but also upon the voltage. The current curves exhibit oscillation with different amplitudes and periods. In combination with the scanning electron microscope (SEM) images, a growth mechanism, layer-by-layer model, of TiO 2 nanotube arrays was presented. Based on this mechanism, many phenomena that appeared during anodization can be reasonably explained. Our results would be helpful for the design of nanoarchitectures in related material systems.

Quantitative relationship between nanotube length and anodizing current during constant current anodization

“…J grow results from the ion migration across the barrier oxide, and J dis results from the field-assisted dissolution of barrier oxide and the field-assisted ejection of Ti 4+ ions into the electrolyte (i.e., Ti 4+ ions were ejected into the electrolyte without oxide formation) [8,18,19,21]. J grow will contribute to nanotube growth at the oxide/metal interface, meanwhile, J dis should also contribute to nanotube growth (deepening) at the electrolyte/oxide interface both on the top surface and at the nanotube bottom [10,19,29]. If it were true, both J grow and J dis will yield positive feedback and lengthen the nanotube length.…”

“…It must be emphasized that the complication of anodizing process arose from the complicated field-assisted dissolution current (J dis ) so that quantification of anodizing current and oxide growth rate were always difficult in the past decades [10,[15][16][17][25][26][27]29,31]. A challenge in this field of the metal anodization is how to separate the ionic current, dissolution current and electronic current [10,15,16,19].…”

Dependence of Nanotextured Titanium Orthopedic Surfaces on Electrolyte Condition

“…This facilitated ion transport causing a slight increase in anodic current [13]. The continued deepening of pores causes the inter-pore sites to become high surface energy regions which attracts more Fions leading to faster dissolution of oxides there [16]. Finally at stage III, a slowly decreasing current value was attained over the entire anodization time demonstrating steady state formation of nanostructures by field-assisted oxidation and dissolution of metal oxides into the electrolyte.…”

Simulation of anodizing current-time curves and morphology evolution of TiO2 nanotubes anodized in electrolytes with different NH4F concentrations

“…When the amount of NH 4 F in the electrolytes (0.6 wt% and 0.4 wt% NH 4 F) is not too low, the measured curves are similar to the typical current density-time curve of TiO 2 nanotubes, which include three stages: an initial exponential decay, an increase of current and a quasi-steady state. Based on the field-assisted dissolution and 'dissolution current' model, the increase and quasi-steady state of the current cannot be clearly explained [6,19,[38][39][40][41]. However, based on the conductivity of the oxide, Regonini et al [42,43] have given a reasonable explanation on current-time transient.…”