Formation Of Oxide Nanotubes Research Articles

Less known facts and findings about TiO2 nanotubes.

Anodic TiO2 nanotubes that are grown on Ti substrates by a simple anodization in various types of fluoride containing electrolytes have attracted scientific and technological interest due to their wide potential applications, and therefore, numerous research efforts have been dedicated to these self-ordered oxide structures in the past decade. The present mini-review highlights less known but important aspects, such as the formation of spaced nanotubes with adjustable interspacing that is achieved in a few specific organic electrolytes, and strong effects of the metallic Ti substrate which significantly affect the growth of the tubes. We discuss the formation of oxide nanotubes grown from adequately alloyed substrates and noble metal nanoparticle decoration of tubes. We describe how specific heat-treatment can introduce a nanotwinned boundary in the oxide tube walls of single-walled nanotubes obtained by a decoring process. All the facts and findings were studied in recent years and TiO2 nanotubes can be upgraded with more optimized functionalities for their applications.

Electrochemical synthesis of oxide nanotubes on Ti6Al7Nb alloy and their interaction with the simulated body fluid

The aim of the present work was to investigate electrochemical behavior of the Ti6Al7Nb alloy in the simulated body fluid (SBF) containing Ca2+, HCO3 −, and HPO4 2− ions. At first, optimal conditions necessary for oxide nanotube formation were determined. The experiments were conducted in the 1 M (NH4)2SO4 with 0.5 wt% NH4F electrolyte at room temperature. Anodization of the alloy samples was carried out under variable external voltage U in the range from 10 to 40 V at room temperature. Obtained surface morphology was examined by SEM and X-ray techniques. Nanotube diameter was calculated and correlated with the imposed voltage. Having control over the size of nanotubes, samples with the obtained nanostructures of a chosen diameter were immersed into SBF solution with pH = 7.4 for a fixed period of time. Then, they were removed from the fluid and subjected to the electrochemical investigation. Corrosion current and corrosion potential were determined, and it was found that the best anticorrosion properties were obtained for heat-treated nanotube layer: i corr = 39 nA/cm2 and E corr = −0.236 V vs Ag/AgCl. Finally, the interaction between the oxide surface and the solution was studied using polarization and electrochemical impedance spectroscopy (EIS) techniques.

Morphological and Chemical Relationships in Nanotubes Formed by Anodizing of Ti6al4v Alloy

Abstract The electrochemical formation of oxide nanotubes on the Ti6Al4V alloy has been so far difficult due to easy dissolution of vanadium reach β-phase of the two phase material. Due to the topographical heterogeneity of the anodic layer in nano and microscale at anodizing of the Ti6Al4V alloy we focused to establish the relationships between nanotube diameters on both phases of the alloy and fluorides concentration in electrolyte. We studied the effect of fluoride concentration (0.5-0.7 wt.%) in 99% ethylene glycol on morphological parameters of nanotube layer on the Ti6Al4V alloy anodized at 20V for 20 min. Nanotubes with diameter ~40-50 nm ±5nm on the entire Ti6Al4V alloy surface in electrolyte containing 0.6% wt. NH4F were obtained. Microscale roughness studies revealed that nanotubular layer on α-phase is thicker than on β-phase. The annealing of nanotube layers at 600°C for 2h in air, nitrogen and argon, typically performed to improve their electrical properties, influenced chemical composition and morphology of nanotubes on the Ti6Al4V alloy. The vanadium oxides (VO2, V2O3, V2O5) were present in surface nanotube layer covering both phases of the alloy and the shape of nanotubes was preserved after annealing in nitrogen.

New insights into the initial stages of Ta oxide nanotube formation on polycrystalline Ta electrodes

Ta oxide nanotubes (NTs) were formed by the anodization of Ta at 15 V in a solution of concentrated sulfuric acid containing 0.8-1.0 M hydrofluoric acid. To study the initial stages of NT formation, FESEM images of samples anodized for very short times were obtained. The results contradict the existing explanation of the current-time data collected during anodization, which has persisted in the literature for more than two decades. In addition to providing a first-time morphological study of Ta oxide NT formation at very early stages of anodization, we also propose a new interpretation of the i-t response, showing that pores are already present in the first few milliseconds of anodization and that NTs are formed well before present models predict. This behaviour may also extend to the anodization of other valve metals, such as Al, Ti, Zr, W, and Nb.

Electrochemical Oxide Nanotube Formation on the Ti-35Ta-xHf Alloys for Dental Materials

In this study, we investigated the electrochemical oxide nanotube formation on the Ti-35Ta-xHf alloys for dental materials. The Ti-35Ta-xHf alloys contained from 3 wt.% to 15 wt.% Hf were manufactured by arc melting furnace. The nanotube oxide layers were formed on Ti-35Ta-xHf alloy by anodic oxidation method in 1 M H3PO4 electrolytes containing 0.5 wt.% NaF and 0.8 wt.% NaF at room temperature. The surface characteristics of Ti-35Ta-xHf alloy and nanotube morphology were determined by FE-SEM, STEM, and XRD. The nano-porous surface of Ti-35Ta-xHf alloys showed in 0.5 wt% NaF solution and nanotubular surface showed in 0.8 wt% NaF solution, respectively. The highly ordered nanotube layer without regular knots was formed on the Ti-35Ta-15Hf alloy in the 0.5 wt% NaF solution compared to on Ti-35Ta-3Hf and Ti-35Ta-7Hf alloys in 0.8 wt% NaF solution. Also, the nanotube length of Ti-35Ta-xHf alloys increased as Hf content increased.

Effects of TiN coating on the corrosion of nanostructured Ti–30Ta–xZr alloys for dental implants

Electrochemical characteristics of a titanium nitride (TiN)-coated/nanotube-formed Ti–Ta–Zr alloy for biomaterials have been researched by using the magnetic sputter and electrochemical methods. Ti–30Ta–xZr (x=3, 7 and 15wt%) alloys were prepared by arc melting and heat treated for 24h at 1000°C in an argon atmosphere and then water quenching. The formation of oxide nanotubes was achieved by anodizing a Ti–30Ta–xZr alloy in H3PO4 electrolytes containing small amounts of fluoride ions at room temperature. Anodization was carried out using a scanning potentiostat, and all experiments were conducted at room temperature. The microstructure and morphology of nanotube arrays were characterized by optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The TiN coatings were obtained by the radio-frequency (RF) magnetron sputtering technique. The depositions were performed from pure Ti targets on Ti–30Ta–xZr alloys substrates. The corrosion properties of the specimens were examined using potentiodynamic test in a 0.9% NaCl solution by using potentiostat. The microstructures of Ti–30Ta–xZr alloys were changed from an equiaxed to a needle-like structure with increasing Zr content. The interspace between the nanotubes was approximately 20, 80 and 200nm for Zr contents of 3, 7 and 15wt%, respectively. The corrosion resistance of the TiN-coated on the anodized Ti–30Ta–xZr alloys was higher than that of the untreated Ti alloys, indicating a better protective effect.

Formation of Single-Walled Aluminosilicate Nanotubes from Molecular Precursors and Curved Nanoscale Intermediates

We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles.

Ultrafast oxide nanotube formation on TiNb, TiZr and TiTa alloys by rapid breakdown anodization

The present work demonstrates ultrafast formation of nanotube bundles on titanium-based alloys, namely TiNb, TiZr and TiTa, by so-called rapid breakdown anodization (RBA). In this process anodization is carried out in chloride–perchlorate based solution for a short period of time. Within seconds, initiation of tube growth appears randomly over the anodized surface, and within a few minutes the entire sample surface can be covered with bundles of nanotubes of several 10 μm in length and some 10 nm in diameter. For all three alloys, the tubes consist of mixtures of oxides of the alloying elements. In every case, the “as formed” oxide tubes are amorphous. By annealing, the oxide nanotube powders can be converted to crystalline mixed oxide in the case of TiNb and TiZr, and a mixture of the individual oxides in the case of TiTa.

Formation of Oxide Nanotubes and Bamboo-Like Structures via Oxidation of Cu, Fe and Ni Nanowires

The formation process of oxide nanotube via metal oxidation reaction was studied by transmission electron microscopy for Cu, Fe, and Ni nanowires. Cu2O and Fe3O4 nanotubes were formed after the oxidation of Cu and Fe nanowires with a diameter of 55 nm in air at 423 and 573 K for 3.6 ks, respectively. Both Cu2O and Fe3O4 nanotubes had a cylindrical interior pore with uniform diameter. On the other hand, Ni nanowires became bamboo-like structures of NiO with separate interior pores after oxidation at 673 K for 7.2 ks. The formation of the interior pores in Cu2O and Fe3O4 nanotubes and NiO bamboo-like structures can be explained by the rapid outward diffusion of metal ions through the oxide layers and the clustering of excess vacancies.

Controlled growth and monitoring of tantalum oxide nanostructures

Nanoporous metal oxide structures produced by the electrochemical anodization of valve metals, such as Zr, Ti, W, Nb, Al, and recently Ta, have attracted increasing interest because of their potential use as catalysts, waveguides, and three-dimensionally arranged Bragg-stack reflectors. Here we demonstrate the formation of either supported nanotubular Ta oxide films or free-standing Ta oxide membranes, produced by controlling the conditions of Ta anodization in organic-free aqueous HF/H(2)SO(4) solutions. The supported oxide nanotubes, which are at least 15 mum in length, are characterized by very good adhesion to the Ta substrate, and extremely smooth and homogeneous walls. It is also reported here, for the first time, that these nanotubular films can be removed as free-standing Ta oxide membranes that are easily transferable to other substrates, making them potentially useful in sensors, optics, and catalysis. We also show that, when the Ta oxide nanotubes detach to form the membranes, they leave behind an ordered array of dimples in the Ta surface, with the dimples having the identical distribution and size as the pores in the previously attached nanotubes. Finally, we demonstrate how the in situ electrochemical response during anodization can be used to determine which of these highly useful Ta surface morphologies (nanotubes vs. dimples) are formed, without the need for post factum microscopic analysis. Knowledge of the meaning of these in situ signals can now serve to accelerate the controlled formation of oxide nanotubes or dimpled surfaces using other combinations of metals and anodization conditions.

Formation of oxide nanotubes via oxidation of Fe, Cu and Ni nanowires and their structural stability: Difference in formation and shrinkage behavior of interior pores

Changes in the morphology of Fe, Cu and Ni nanowires with a diameter of 55 nm during oxidation at 423–923 K were studied by transmission electron microscopy. Oxide nanotubes with a cylindrical interior pore of uniform diameter were formed after the oxidation of Fe and Cu nanowires in air at 573 and 423 K, respectively, while the Ni nanowires became bamboo-like nanowires of NiO with separate interior voids after oxidation at 673–773 K. Oxide nanotubes of Fe and Cu and the bamboo structures of NiO showed a tendency to shrink into solid oxide nanowires after annealing at higher temperatures in air. In the shrinking process of Fe 3O 4 nanotubes, however, an array of additional nanovoids was observed along the inner wall of the nanotubes, suggesting the formation of a duplex porous nanostructure. This can be explained by the recombination of vacancies diffusing outward from the inner cylindrical pore.

Surface characteristics of HA coated Ti-Hf binary alloys after nanotube formation

Ti-Hf binary alloys contained 10%, 20%, 30% and 40% (mass fraction)Hf were manufactured in the vacuum furnace system. And then, specimens were homogenized for 24 h at 1 000 °C in argon atmosphere. The formation of oxide nanotubes was conducted by anodic oxidation on the Ti-Hf alloy in 1 mol/L H 3PO 4 electrolytes containing small amounts of NaF at room temperature. The hydroxyapatite (HA) coating made of tooth ash prepared by electron-beam physical vapor deposition (EB-PVD) method. The corrosion behaviors of the specimens were examined through potentiodynamic test in 0.9% NaCl solution by potentiostat. The microstructures of the alloys were examined by field emission scanning electron microscopy (FE-SEM) and x-ray diffractometer (XRD). It was observed that the lamellar structure translated to needle-like structure with Hf contents. Nanotube formed and HA coated Ti- xHf alloys had a good corrosion resistance.

Electrochemical Behaviors of a TiN-Coated/Nanotube-formed Ti-Zr Alloy

Ti-Zr (10, 20, 30 and 40 wt%) alloys were prepared by arc melting, followed by homogenization for 24 hr at 1000 C in an argon atmosphere. The formation of oxide nanotubes was achieved by anodizing a Ti-Zr alloy in H3PO4 electrolytes containing small amounts of uoride ions at room temperature. Electrochemical experiments were carried out using a conventional three-electrode con guration with a platinum counter electrode and a saturated calomel reference electrode. The anodization treatments were carried out using a scanning potentiostat (EG&G Co., Model 362, USA). All the experiments were conducted at room temperature. The microstructures of the alloys were examined by using optical microscopy (OM), eld-emission scanning electron microscopy (FE-SEM) and X-ray di ractometry (XRD). A TiN coating was deposited on the anodized titaniumoxide layer by reactive RF magnetron sputtering using a Ti target (99.99 %). The corrosion properties of the specimens were examined using potentiodynamic tests (potential range of 150

Template-directed gas-phase fabrication of oxide nanotubes

This paper describes a template-directed fabricating method of oxide nanotubes. Our approach combines gas-phase atomic layer deposition (ALD) of metal oxides with a micro-contact printing technique, allowing precise control over the dimensions of the nanotubes as well as one-step fabrication of free-standing oxide nanotubes. Nanotubes of TiO2, ZrO2, and Al2O3 with high aspect ratios of up to ∼300 have been fabricated. Notably, two different types of membranes are employed as templates: track-etched polycarbonate and anodic aluminium oxide (AAO). We have discussed the nanopore size effects in growing ALD layers as nanotube walls and the surface chemistry of selective ALD on the templates. Bundle formation of oxide nanotubes is proposed by strong capillary forces generated and exerted during dissolution of the surrounding AAO template.

Mechanistic Aspects of the Self-Organization Process for Oxide Nanotube Formation on Valve Metals

In this paper we address several key aspects to the formation mechanism of self-organized oxide nanotube layers grown by anodization of valve metals and their alloys in fluoride ion containing electrolytes. We suggest that the self-organized structure is produced as a result of an autocatalytic reaction, in which electrochemical oxidation and chemical dissolution of oxide accelerate each other; in the initial growth stage the competition for oxidizable area between neighboring initial growth spots is a key element in self-organization; and the diameter of the nanotubes on different materials and as a function of anodization voltage is strongly related with the anodic growth factor (nm/V) of the valve metal oxides. Additionally, for multilayer pore structure growth the present work provides insight into the sites of highest reactivity in repeated anodization experiments (bottom of the pores, in between pores).