Formation of Self‐Organized Zirconium Titanate Nanotube Layers by Alloy Anodization

Abstract

Self-organized nanoporous systems produced by using electrochemical processes have in the past decade attracted much interest owing to remarkable potential applications, for example, in high-density recording media, biological nanopatterning, optical devices, functional electrodes, and templates for nanoscale materials. Now, materials that exhibit self-organized anodic pore or tube growth include not only the wellstudied cases of aluminum oxide [1][2][3][4] and silicon [5][6][7] but a variety of metals and compounds. In our group, the fabrication of self-organized oxide nanotubes on valve metals has been investigated for titanium oxide, [8][9][10][11][12][13] zirconium oxide, [14,15] hafnium oxide, [16] niobium oxide, [17] tungsten oxide, [18] and tantalum oxide. [19] In these experiments, comparably thick layers consisting of oxide nanotubes with a diameter of ca. 20-100 nm were synthesized by anodizing metals in fluoride-ion-containing electrolytes. Oxide nanotubes grow as a result of a competition between electrochemical oxide formation and chemical dissolution of oxide by fluoride ions. In order to extend the functionality of the tubular materials by a new composition of oxides, one may target not only to produce binary oxide nanotubes but multicomponent oxide tubes by anodization of multielement alloys.[20] However, considerable difficulties can exist such as preferential dissolution due to chemical inhomogeneousness in the case of multiphase alloys. [20] In the present work, we demonstrate the direct formation of zirconium titanate (ZT) nanotube layers on a single phase Ti-Zr alloy. ZT is used as microwave resonant components and frequency-stable oscillators, [21][22][23] optical devices, [24,25] refractory ceramics, [26] and as a template for lead ZT (PZT). The Ti-Zr alloy system shows a solid solution behavior over the entire composition range.[27] This is particularly interesting as ZT complex oxides also show a solid solution behavior in the composition range between about X Ti = 0.4 and 0.7, including the compounds of ZrTiO 4 , Zr 5 Ti 7 O 24 , and ZrTi 2 O 6 . [28][29][30] The present work uses a (NH 4 ) 2 SO 4 + 0.5 wt % NH 4 F electrolyte for the growth of the nanotubular layers, that is, an electrolyte where nanotubes on elemental Ti and Zr could be successfully grown. Figure 1 shows the current density versus potential curve (Fig. 1a) and the current density versus time behavior during potentiostatic anodization at 20 V (vs. Ag/AgCl) (Fig. 1b) for the Ti-Zr alloy in 1 M (NH 4 ) 2 SO 4 + 0.5 wt % NH 4 F solution. During the potential sweep (Fig. 1a), the current first increases up to 7 mA cm -2 and then drops to a steady value of 4.5 mA cm -2 . This behavior has been found for pore formation on several valve metals including titanium [8][9][10][11][12][13] and zirconium. [14,15] In the initial stage with a current increase, an oxide layer is formed, which then becomes perforated and converted to a porous wormlike initial layers (the latter is combined with an increase in the active surface area). W...

Nanotubular surface modification of metallic implants via electrochemical anodization technique

“…31,36,38 It has been observed that F -ions may migrate at a rate twice as high as O 2-ions through oxide lattices. 31,36,47 As a result, a fluoride rice layer is formed at the metal-oxide interface. This layer is believed to be the origin of the nanotubular separation and formation.…”

“…47 Zirconium titanate nanotubular arrays were formed on Ti-50Zr alloys via anodization. 47 Similar to the TiO 2 nanotubular arrays formed on pure Ti, the formation of oxide nanotubular arrays on Ti alloys depends on the anodization parameters including anodic potential, anodization time, pH, and fluoride species concentration, as discussed in the Self ordering of TiO 2 nanotubular arrays section. However, due to the different chemical characteristics including selective dissolution of the oxide in fluoride and solubility of the respective metal fluorides in (41) …”

“…44,45 Further, remarkably, the self-ordering anodization approach is not only limited to Ti and Ti-based alloys but can also be applied to a large range of other transition metals or alloys to form highly ordered nanoporous or nanotubular oxide layers for potential biomedical applications. [46][47][48][49][50] For these reasons, this review focuses on up-to-date research that describes the synthesis of these nanotubular structures and the factors that influence the degree of self-ordering, tubular geometry, and crystal structure. Although previous publications have addressed the application of nanotubular arrays on photocatalytical applications, we mainly focus on the biomedical application of this interesting structure.…”

“…31,38 Anodization that forms nanotubular layers is usually carried out by ramping a potential step at a constant voltage normally between 1-30 V in aqueous electrolytes or 5-150 V in non-aqueous electrolytes containing approximately 0.05-0.5 M F -. 39,41,46,47 Crucial factors on fabrication of MO x nanotubular arrays are considered to be the applied potential, fluoride concentration, pH value, and anodization duration. 31,38 In general, the nanotubular diameter is reported to be linearly dependent on the applied anodic potential during growth.…”

Controllable Synthesis of Porous α-Fe2O3 Microtube and Tube-in-tube by Non-coaxial Electrospinning

“…3,4 Up to now, various methods have been developed for the synthesis of inorganic nanotubes and tube-intubes, such as the template method, 5 galvanic replacement reaction, 6 hydrothermal method, 7 nonequilibrium heat-treatment approach, 8 and multifluidic compound-jet electrospinning techniques. 9 Using these methods, some hollow and tube-in-tube structure nanomaterials have been fabricated successfully.…”