High aspect ratio ordered nanoporous Ta2O5 films by anodization of Ta

Wei, Wei; Macák, Jan M.; Schmuki, Patrik

doi:10.1016/j.elecom.2008.01.004

Cited by 112 publications

(108 citation statements)

References 29 publications

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“…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. [4][5][6][7] Apart from Al and Ti, self-organized growth of nanoporous or nanotubular oxide structures have also been reported for other valve metals, such as Nb, 8,9 Zr, [10][11][12] Ta, [13][14][15] and W, 16 and alloys, such as TiAl, 17 TiNb, 18 TiZr, 19 TiW, 20 TiMo, 21 and TiTa. 22 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.…”

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

Wei

Berger

Shrestha

et al. 2010

J. Electrochem. Soc.

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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...

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

Wei

Berger

Shrestha

et al. 2010

J. Electrochem. Soc.

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“…[1][2][3] Recently, attention has been drawn to the formation of highly ordered nanoporous structures on aluminum, which are formed by the anodizing process, and their use in nanoscience and nanotechnology. 4 Furthermore, the formation of self-ordered nanoporous oxide films on a range of metals, including titanium, 5 zirconium, 6-8 niobium, 9 tantalum, 10 tungsten is also of interest. 11,12 Iron is the most widely used metal.…”

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Formation of Porous Anodic Films on Carbon Steels and Their Application to Corrosion Protection Composite Coatings Formed with Polypyrrole

Konno

Farag

Tsuji

et al. 2016

J. Electrochem. Soc.

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The growth behavior of nanoporous anodic films on carbon steel containing 0.213 mass% carbon has been examined. The films were grown by anodizing in an ethylene glycol (EG) electrolyte containing 0.1 mol dm −3 NH 4 F and 0.5 mol dm −3 H 2 O. The steel contains carbide precipitates with sizes in the range 50-800 nm. The anodic film formed on the carbide phase grew more slowly and was more chemically soluble during anodizing, resulting in submicrometer pits on the anodic film. The nanoporous morphology of the anodic films formed on an α-Fe matrix resembled those formed on iron. Heat treatment of the anodized specimens caused transformation of the chemically soluble fluoride-containing amorphous or poorly crystalline anodic films to crystalline oxide films containing α-Fe 2 O 3 and Fe 3 O 4 . Polypyrrole (PPy) was electropolymerized on the transformed surfaces to form a corrosion-protective composite coating. The resultant specimens coated with the composite coating showed improved durability compared to passivated steel with a PPy coating. Porous oxide films formed on aluminum and magnesium alloys by anodizing have been extensively studied for their ability to protect alloys from corrosion and wear; in addition, an anodizing process is of fundamental interest for the growth of self-ordered porous films. 1-3Recently, attention has been drawn to the formation of highly ordered nanoporous structures on aluminum, which are formed by the anodizing process, and their use in nanoscience and nanotechnology. 4 Furthermore, the formation of self-ordered nanoporous oxide films on a range of metals, including titanium, 5 zirconium, 6-8 niobium, 9 tantalum, 10 tungsten is also of interest. 11,12Iron is the most widely used metal. Recently, self-ordered nanostructured oxide films have been developed on iron using organic electrolytes containing fluoride and trace amounts of water. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] Depending upon the anodizing conditions, either nanoporous or nanotubular anodic films are formed on iron. 14,18,24,27 The as-formed anodic films are often amorphous and contain a relatively high concentration of fluoride species; however, such films are not chemically stable. Heat treatment of the anodized iron samples causes crystallization of the amorphous anodic film, forming mainly α-Fe 2 O 3 .16,17,21 α-Fe 2 O 3 is a promising material for solar-driven water splitting due to its low bandgap, low cost, abundance, and high chemical stability; consequently, nanostructured porous α-Fe 2 O 3 films formed by anodizing and subsequent heat-treatment have recently attracted much attention. 17,18 In addition to photocatalytic applications, porous anodic films on iron can be used to protect iron and steel from corrosion. Iron and steel alloys are often coated with paints to protect them from environmental corrosion. In addition, interest in the use of conducting polymer coatings has increased because they provide anodic protection due to their oxidizing ability; in addition, they act as a physical ba...

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“…While graded AAO templates were prepared in terms of porosity-and length-graded pores, it is expected that other materials such as porous Si 16 and porous metal oxides on various valve metals (Ti, 17 Hf, 18 Zr, 19 Ta, 20 Nb, 21 and W 22 ), which are formed by the anodization method, could be directly applied in the proposed strategy for the formation of laterally graded materials. Although we showed the laterally graded SNTs, it should also be noted that a variety of other elements and compounds could be fabricated into the graded AAO template by using electrochemical deposition, chemical vapor deposition, sol-gel method, etc., resulting in laterally graded nanotubes, nanowires, and nanodots.…”

Section: Resultsmentioning

confidence: 99%

Facile Route to Laterally Graded Nanotemplate

Kim¹,

Lee²,

Jung³

et al. 2009

Bulletin of the Korean Chemical Society

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Preparation of graded materials displaying gradients of desired properties is one of the important issues and less-developed areas in materials chemistry. For the first time we demonstrate facile control of porosity and length in the pores of AAO template in lateral directions by controlled dipping method. To demonstrate the versatility of the proposed method, laterally graded silica nanotubes are also prepared by using the laterally graded AAO templates. The method demonstrated here will open numerous possibilities for obtaining a variety of graded materials with lateral gradients of catalytic, electrochemical, mechanical and optical properties on the nanoscale. After chemically etching the first anodized AAO film, a lengthgraded AAO (a) was then obtained by slowly dipping the sample under the same conditions used in the first anodization process The dipping rate and time were 5.6 µm/sand 30 min, respectively. For the fabrication of porosity-graded templates (b), the two-step anodized sample was dipped into a pore widening solution at the rate of 4.8 µm/s for 35 min.

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High aspect ratio ordered nanoporous Ta2O5 films by anodization of Ta

Cited by 112 publications

References 29 publications

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

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

Formation of Porous Anodic Films on Carbon Steels and Their Application to Corrosion Protection Composite Coatings Formed with Polypyrrole

Facile Route to Laterally Graded Nanotemplate

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