Growth orientation mechanism of TiO₂ nanotubes fabricated by anodization

Abstract

TiO 2 nanotubes (TNTs) fabricated by anodization have been extensively researched in recent years. However, the mechanism that controls the growth orientation of anodic TNTs is still not clear. Here, we firstly examine their growth orientation systematically. Combined with the previous literature, the results of anodization on rotated Ti foil and thin Ti wire confirm that almost all of the TNTs grow vertically to the local Ti substrate surface. Their growth orientation predominantly depends on the local electric field around the bottom of the nanotube. The distribution of the local electric field is regulated by the shape of the initial nano-scale local Ti substrate surface (INLTSS). Most of the INLTSS is nearly flat, which leaves vertical, circular, and straight TNTs. In terms of the evolution of TNTs fabricated on a micron-scale convex surface, the vertical growth of TNTs leads to a continuous decrease in the oxide/substrate (O/S) interface area, and a few TNTs are periodically crushed and detached from the O/S interface. For a micron-scale concave surface, due to the ever-increasing O/S interface area, Y-branched TNTs occurred periodically as a response to avoid a vacancy on the oxide/substrate interface.

Rearrangement of Oxide Scale on Ni-11Fe-10Cu-6Al Pre-Oxidized at 950 °C during Anodic Polarization in Molten Carbonate

“…The diffusion process of ions in oxide scale can be influenced by the opposite direction and stronger intensity of electric field, which will lead to the evolution and rearrangement of pre-formed oxide scale during anodic polarization in the melt. 3,4,[20][21][22][23][24][25] Before anodic polarization, alumina layer close to alloy substrate was mainly formed by inward diffusion of oxygen at 950 °C in air. However, Al exhibited higher outward diffusion rate during anodic polarization than that by oxidation in air which was attributed to the opposite electric field direction and stronger electric field intensity (Fig.…”

Modelling of simultaneously obtained small and wide angle synchrotron-radiation scattering depth profiles of ordered titania nanotube thin films

“…Then during the next 3-4 min current starts to decrease much slower (phase II), that represent the start of nanotubes formation within the Ti. This effect is much more pronounced (with additional plateau) for titanium foil anodization and corresponds to the formation of the porous structure [13]. After that follows a gradual current decrease (phase III) indicating that the formation of pores reach equilibrium with the dissolution, that phase persist up to moment when the titanium layer is completely etched (the electrolyte comes in direct contact with the ZnO coated glass substrate).…”

Synergy of Platinum Single Atoms and Platinum Atomic Clusters on Sulfur‐Doped Titanium Nitride Nanotubes for Enhanced Hydrogen Evolution Reaction

“…Then, TiO 2 nanotubes on titanium mesh (TiO 2 NTs/Ti) were synthesized by anodic oxidation of titanium mesh (3 × 1.5 cm 2 ) at a constant voltage of 30 V in an ethylene glycol (EG) electrolyte containing 0.3 wt% NH 4 F and 5 wt% H 2 O at room temperature in a two‐electrode system with a Pt foil as the cathode and the titanium mesh as the anode. [ 38 ] After anodization, the obtained grayish blue sample was rinsed with ethanol and water, dried at 60 °C in an oven to achieve amorphous TiO 2 NTs/Ti. To obtain TiN nanotubes on titanium mesh (TiN NTs/Ti), the amorphous TiO 2 NTs/Ti was nitrided in a NH 3 atmosphere at 750 °C for 2 h with a ramping rate of 2 °C min −1 .…”