Ideal Hexagonal Order: Formation of Self-Organized Anodic Oxide Nanotubes and Nanopores on a Ti–35Ta Alloy

Abstract

In this work, we report on the formation of highly aligned nanoporous or nanotubular oxide structures by anodization of Ti-Ta alloys in NH 4 F containing ethylene glycol electrolytes. We show that depending on the anodization conditions, either a hexagonally self-organized nanoporous layer or a nanotube array can be formed. Critical factors that decide on tube or pore formation are the water content of the electrolyte and the applied voltage. The present approach provides hexagonally packed oxide structures with an order comparable to that of the gold standard, anodized alumina. Layers of thicknesses Ͼ10 m and individual pore diameter in the range of 27-50 nm can easily be produced. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3490424͔ All rights reserved.Manuscript submitted August 13, 2010; revised manuscript received August 25, 2010. Published September 30, 2010 In the past few years, the electrochemical formation of selforganized nanoporous or nanotubular structures has attracted considerable attention from both the scientific and the technological community. Honeycomb-packed anodic Al 2 O 3 nanoporous films [1][2][3] represent one of the earliest and best-known examples for an almost ideal self-organizing electrochemical process. 1 More recently, by anodization of titanium in fluoride-containing electrolytes, it is possible to form a similar morphology, that is, self-aligned nanotube arrays. Some elements, upon anodization in aqueous fluoride electrolyte, tend to form nanotubular structures such as Ti, Zr, and Hf, whereas others, e.g., Ta, Nb, and W, tend to form nanoporous structures. Only very recently, first investigations were reported on the transition of the morphology from self-organized nanopore to nanotube structures depending on the specific anodization conditions. 12,17,23 In the present work, we investigate self-organizing anodization with an alloy that contains a typical tube formation element Ti and a typical pore formation element Ta. While in aqueous electrolytes, such an alloy forms only tubular structures, 22 we demonstrate in the present work that an organic electrolyte can induce transition to a porous structure with a virtually unprecedented degree of short-and longrange orders.Except for scientific interest in the feasibility of ordered oxide formation on these materials, Ti-Ta oxides are also of high technological significance. The oxide layers provide a very high corrosion resistance to surfaces, as Ta 2 O 5 is significantly more resistant than TiO 2 in almost any environment but particularly under cathodic reductive conditions. 24,25 Moreover, the alloy provides excellent biocompatibility but with a considerably lower average weight than pure Ta. Therefore, various Ti-Ta alloys are explored as candidates for biomedical implant materials. 26,27 In this context, the decoration of Ti implants with TiO 2 nanotubes has already shown a beneficial nature in view of cell response, 28,29 hydroxyapatite formation, 30 and for applications in drug delivery systems. 31,32 It is hence expe...

TiO2 Nanotubes: Synthesis and Applications

“…In this context, it is noteworthy that similar transition phenomena were reported on other valve metal alloys [36,124,161,162] and also on pure valve metals, such as zirconium and hafnium. [163][164][165][166] In each case it was found that a key parameter affecting the morphology is the concentration of H 2 O in the electrolyte.…”

WO3/TiO2 Nanotubes with Strongly Enhanced Photocatalytic Activity

“…[29,[39][40][41] Self-ordered oxide nanotubes cannot only be grown on pure Ti, but also on other transition metals such as Mo, W, Ta, Nb, and so forth, and a full range of Ti alloys including TiW, TiNb, TiAl, TiMo, TiTa. [30][31][32][33][34] In the present work, we demonstrate a very strong effect of tungsten addition to the TiO 2 nanotubes in terms of their photocatalytic activity. For this, different TiW alloys (Ti 0.2 at % W (Ti 0.2 W) and Ti 9 at %W (Ti 9 W)) as well as pure Ti were anodized to form % 2 mm-long self-organized tube layers as shown in Figure 1.…”

Doped TiO2 and TiO2 Nanotubes: Synthesis and Applications

“…[152] Under specific conditions, self-ordering at two length scales can be obtained. [153][154][155][156] The formation of these self-ordered structures in fluoride-containing electrolytes is not limited to Ti, but was also successfully demonstrated for other transition metals, such as Zr, [157][158][159][160] Hf, [161,162] W, [163,164] Nb, [165,166] and Ta, [167,168] and a full range of alloys, such as TiNb, [169] TiTa, [168,170] TiZr, [103,171] TiW, [172] TiMo, [173] and TiAl. [174] Recent reviews on the growth of these different systems are available.…”