Anodic Oxidation Of Aluminum Research Articles

Preparation and characteristics of large-area and high-filling Ag nanowire arrays in OPAA template

Highly ordered porous anodic aluminum oxide (OPAA) on aluminum substrate with an ultrathin barrier layer was prepared by a two-step aluminum anodic oxidation plus a step-by-step voltage decrement process. Ag nanowire arrays have been successfully electrodeposited into the OPAA template through constant current technique. The morphology, composition and structure of the nanowire arrays were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Ag nanowires possess smooth surface and high aspect ratio up to 330 with a diameter of 70–80 nm. Nearly 100% of the pores were filled by Ag nanowires, which have face center cubic structure and (111) preferential orientation. The branch of originally straight pores at the formation front was demonstrated and the branched pores favor the formation of several nucleation sites in each pore at the beginning of the electrodeposition.

Spontaneous Current Oscillations during Hard Anodization of Aluminum under Potentiostatic Conditions

AbstractNanoporous anodic aluminum oxide is prepared by hard anodization of aluminum under potentiostatic conditions using 0.3 M H2C2O4. Under unstirred electrolyte condition, spontaneous current oscillations are observed. The amplitude and period of these current oscillations are observed to increase with anodization time. As a consequence of the oscillatory behavior, the resulting anodic alumina exhibits modulated pore structures, in which the diameter contrast and the length of pore modulation increase with the amplitude and the period of current oscillations, respectively, and the current peak profile determines the internal geometry of oxide nanopores. The mechanism responsible for the oscillatory behavior is suggested to be a diffusion‐controlled anodic oxidation of aluminum.

Molecular‐selective adsorption property of chemically surface modified nanoporous alumina membrane by di(1‐naphthyl)silanediol to anthracenes

AbstractNano‐porous alumina membrane (NPAM) formed by the anodic oxidation of aluminum is an attractive composite as the base material for a functional filter, because of its honeycombed ordered structure with large surface area per weight and also high shape stability. In this work, we investigated the adsorption properties of the NPAM possessing π‐electron systems on the surface, which were produced through chemical surface modification by di(1‐naphthyl)silanediol, to aromatic compounds using anthracenes as typical aromatic compounds. The chemically surface‐modified NPAM exhibited strong affinity to anthracene molecules and the affinity was observed to be weakened remarkably with the introduction of methyl and phenyl substituents to anthracene, indicating a molecular‐selective adsorption property of the NPAM. Copyright © 2009 John Wiley & Sons, Ltd.

Synthesis and ultraviolet luminescence properties of half-wall Al2O3 nanotube arrays

The ordered half-wall alumina nanotubes (HWANs) were synthesized in an oxalic acid solution via a two-step aluminium anodic oxidation process. Their optical properties are closely associated with the annealing temperature and time. The emission peak of HWANs appears at about 302 nm, which has probably resulted from the 1B → 1A transition. Compared with the Al2O3 powders, a distinct blue shift in the as-prepared HWANs occurs. A schematic drawing of the possible formation of HWANs is proposed and two possible mechanisms for the blue shift are discussed. It can be concluded that the electron transitions to the excited states at 5.3, 4.5 and 4.4 eV (F+ centres) account for the photoluminescence of HWANs at high annealing temperatures.

Performance and Characterization of ALD Vanadium Oxide Catalytic Nanoliths

Supported vanadium oxide species are active catalysts for the selective, oxidative conversion of hydrocarbons to useful chemicals. Both the catalytic vanadium oxide and the supporting oxide were synthesized by ALD on high surface powders and anodic aluminum oxide (AAO) nanoliths. The nanoliths were prepared by anodic oxidation of aluminum. 1 nm of ALD aluminum oxide acts as the support for vanadium oxide loaded by 1 to 18 ALD cycles of vanadyltri-isopropoxide/H2O2. Ultraviolet-visible absorption edges red shift as the vanadia loading increases. The edge energy of 1-cycle ALD VOx corresponds to isolated, tetrahedral VO4 in agreement with Raman spectroscopy. V-O-V bonds form with additional cycles producing a gradual increase in VOx domain size. Reaction rate coefficients for the oxidative dehydrogenation of cyclohexane show increased overall activity in the high loading catalysts but a higher specific activity in the low loading catalysts for cyclohexene formation.

Porous Anodic Metal Oxides

Porous anodic aluminium oxide (AAO) and anodic titanium oxide (ATO) attracted an increased attention in the recent years due to their high potentials of application in nanotechnology. This article presents a brief review of some important developments of these smart materials including anodization methods, formation mechanisms of the pores, self-ordering processes and applications. Anodization of other metals are also highlighted.

Novel fabrication process using nanoporous anodic aluminum oxidation and MEMS technologies for gas detection

A class of nanoporous TiO2 gas sensors processed by novel anodic aluminum oxidation (AAO) of Al thin films and microelectromechnical systems (MEMS) techniques are presented. To enhance the sensitivity and reduce the sensing dimensions of a gas sensor, a nanoporous surface of the gas-sensitive material on the sensor is required. These sensors can be implemented on silicon or silicon dioxide substrate featuring a thin membrane of micro-hotplate structure featuring micro-heaters, thermometers and electrodes, and thus operate as chemoresistive devices. Combining the AAO method with dry-etch process, a homogeneous and nanoporous SiO2 surface of the sensor can be effectively configured by modulating various hole diameters and depth, hence replacing conventional photolithography and electrochemical etch. The process integration including AAO, reactive ion etch (RIE) and microfabrication is mainly developed and a feasibility study of PVD TiO2 thin film deposition upon the porous device is also provided. TiO2 thin films deposited on the nanoporous surface are investigated and compared with non-porous TiO2 films. It is encouraging that our fabrication process is able to provide relatively high surface area to enhance sensitivity of the sensor without additional doping steps. Our promising experimental results have revealed these miniature and cost-effective devices are not only compatible, but applicable to smart bio-chemical sensors of next generation.

The recovery of sulphuric acid from the waste anodic aluminum oxidation solution by diffusion dialysis

The recovery of H 2SO 4 from waste anodic aluminum oxidation solution using diffusion dialysis process was investigated by a series of batch, dynamic and pilot-scale tests. Experimental results from batch tests indicated that to some extent agitation could reduce concentration polarization phenomenon and CuSO 4 could enhance proton permeability throughout the DF120 anion exchange membrane. Dynamic experimental results showed that both acid recovery and H + concentration in recovered acid decreased with flow rate increase when the flow rate ratio of water to feed was kept at 1.0, and the optimal flow rate range of 3.0 × 10 −4 m 3/h to 5.0 × 10 −4 m 3/h (corresponding to the membrane flux of 9.4 × 10 −5 m 3/h m 2 to 1.56 × 10 −4 m 3/h m 2) was obtained. Although acid recovery efficiency could be improved by increasing the flow rate ratio, the recovered acid concentration decreased and metal leakage increased. And it is confirmed that the optimal flow rate ratio of water to feed should be controlled at 1.0–1.2. Pilot-scale tests performed very well when using the wastewater from a real anodic aluminum oxidation plant. H 2SO 4 recovery, recovered acid concentration and Al 3+ leakage in steady-state condition were 85.25%, 4.08 mol/L and 4.98%, respectively, suggesting that diffusion dialysis is a cost-effective technique for acid recovery from waste anodic aluminum oxidation solution.

Nonpolar Resistance Switching in Anodic Oxide Alumina Films

At an applied voltage, anodic oxide alumina (AOA) films exhibit reproducible resistance switching between two states: a high-resistance state with insulating properties and a metallic low-resistance state. This resistance switching does not depend on the polarity of the applied voltage. A reduction in photoluminescence signal intensity of points switched to the low-resistance state was observed. The filamentary electronic model was employed to explain the resistance switching in the AOA films, which assumed that rupture and recovery of filaments are caused by the migration of electrons from and to filaments, respectively.

Study on Molding of a Nanostructured Plastic Plate and Its Surface Properties

Plastic substrates with high-aspect-ratio surface nanostructures were fabricated by hot embossing using an anodic aluminum oxidation (AAO) membrane, and by injection molding using an AAO plate as a mold master with a very dense array of nanoholes on the surface. A new method of rapidly heating the AAO plate was used to injection-mold high-aspect-ratio nanostructures 120 nm in diameter and 1.5 µm high. The AAO plate was heated to over 150 °C to fill the nanoholes with melted polymer and then cooled to below 70 °C to release the molded nanostructures from the holes. Hot embossing was used to replicate surface nanostructures with an average diameter of 200 nm and a height of 60 µm. The contact angle and adhesive force of the hot-embossed textured surface were measured to estimate the effect of the surface nanostructures on the hydrophobicity and dry adhesiveness.

Study the effect of striping in two-step anodizing process on pore arrangement of nano-porous alumina

Two-step anodic oxidation of aluminum is generally employed to produce the ordered porous anodized alumina (PAA). Dissolving away (striping) the oxide film after the first anodizing step plays a key role in the final arrangement of nano-pores. In this work, different striping durations between 1 and 6 h were applied to the sample that was initially anodized at a constant voltage of 40 V at 17 °C for 15 h. The striping duration of 3 h was realized as the optimum time for achieving the best ordering degree for the pores. Scanning electron microscopy (SEM) was used during and at the end of the process to examine the cross section and finishing surface of the specimens. Linear-angular fast Fourier transform (LA-FFT), an in-house technique based on MATLAB software, was employed to assess the ordering degree of the anodized samples.

Anodic Oxidation of Aluminium in Oxalic Acid by Cyclic Voltammetry

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Injection molding of a nanostructured plate and measurement of its surface properties

This paper highlights recent research on the injection molding of a surface nanostructured substrate with super-hydrophobicity or dry adhesiveness. An anodic aluminum oxidation (AAO) membrane or layer on an Si wafer is used as a molding master for surface nanostructures. The AAO membrane or layer has closely packed nanoholes; depending on the AAO membrane used, the nanoholes have a diameter of around 200 nm and a depth that varies from a few hundred nanometers to 60 μm. This AAO master is installed directly in the injection molding tool, or the AAO holes are replicated on the nickel stamper by an electroforming process and installed in the injection molding tool. Either a high temperature (> T g of the molding material) mold or a rapid heating (up to 200 °C) and cooling (<70 °C) mold is used to fill the high aspect ratio nanoholes with thermoplastic melt for the injection molding. These high aspect ratio nanoholes are extremely difficult to fill with melt in a conventional injection molding process. This paper proposes a new simple and efficient rapid heating and cooling method that heats the stamper by means of the electrical resistance of the stamper itself. Depending on the aspect ratio of the structures and the type of master, a chemical etching or mechanical ejecting process is used to release the molded surface nanostructures. With the use of an AAO membrane and a high temperature mold, some polypropylene disks with a nanohairy surface and some polycarbonate plates with a nanopillar on the surface are injection molded at several different mold temperatures for the purpose of studying the replication of the surface nanostructures. In addition, the contact angle of the water and the adhesion force on the molded surfaces are measured to investigate the effect of the surface nanostructures on the hydrophobicity or dry adhesiveness.

Fabrication of Polymeric Nano-Batteries Array Using Anodic Aluminum Oxide Templates

Rechargeable nano-batteries were fabricated in the array pores of anodic aluminum oxide (AAO) template, combining template method and electrochemical method. The battery consisted of electropolymerized PPy electrode, porous TiO2 separator, and chemically polymerized PAn electrode was fabricated in the array pores of two-step anodizing aluminum oxide (AAO) membrane, based on three-step assembling method. It performs typical electrochemical battery behavior with good charge-discharge ability, and presents a capacity of 25 nAs. AFM results show the hexagonal array of nano-batteries' top side. The nano-battery may be a promising device for the development of Micro-Electro-Mechanical Systems (MEMS), and Nano-Electro-Mechanical Systems (NEMS).

Preparation and Visible Light Photocatalytic Properties of (Er, La, N)-Codoped TiO&lt;SUB&gt;2&lt;/SUB&gt; Nanotube Array Films

TiO2 nanotube array films were prepared by in-situ liquid phase transformation and deposition of anodic aluminum oxidation template films with (NH4)2TiF6 dilute solution; and the (Er, La, N)-codoped films were fabricated by impregnation with rare earth elements of Er and La following by heat treatment in flow ammonia. Obviously enhanced photocatalytic degradation of organic dye was obtained by codoped TiO2 under visible light irradiation compared with undoped TiO2 film, and the increase of photocatalytic performance of as-prepared TiO2 was attributed to the enlargement of light absorbency ranging from upconversed UV to red-shifted visible light up to 600 nm.

Resistance States and Photoluminescence in Anodic Oxide Alumina Films

Reproducible resistance switching behaviors induced by the external voltage were investigated in anodic oxide alumina (AOA) thin films. Electric-transport measurements showed that a low resistance state in the Ag/AOA/A1 structures might be caused by the formation of the conductive filaments. Switching to a high resistance state occurred due to the rupture of these filaments. Change in the photoluminescence properties of the AOA films depending on the resistance states was observed.

Fabrication of surface self-lubricating composites of aluminum alloy

Porous aluminum anodic oxide films fabricated by anodizing in phosphoric acid electrolyte containing organic acid were investigated. By controlling its microstructure, a macroporous and thick alumina template were obtained. Surface self-lubricating composites were prepared by taking ultra-sonic impregnation in PTFE latex and the relative subsequent heat treatment technology. The studies on the tribological behavior of the surface self-lubricating composite indicated that the tribological properties of aluminum surface can be improved obviously. Compared with the surface coating of hard-anodization, the friction coefficient of self-lubricating composite can be effectively reduced from the 0.575 to 0.166.

Ordered bulk heterojunction solar cells with vertically aligned TiO2 nanorods embedded in a conjugated polymer

Vertically aligned TiO2 nanorods were prepared by its sol-gel which is spun coat onto aluminum anodic oxide template pregrown on an indium tin oxide glass substrate. The poly(3-hexylthiophene) (P3HT), a conjugate polymer infiltrated into the nanorod arrays, and the combined system were used as the active layer. The nanorods/P3HT solar cell with cell size of 0.06cm2 demonstrated a power conversion efficiency of 0.512% while the bilayer TiO2 film/P3HT cell was 0.12%. The current work provides fabrication method for a stable well aligned nanorods/polymer hybrid solar cell production.

Deposition of Nanoscale Films on the Nanopore‐arrayed Template by an In‐situ Spinning‐precipitated Technique

A spinning‐precipitated technique is proposed to fabricate nanoscale films. In this study, the deposition of MnZn ferrite on the template of nanoporous anodic oxide alumina (AAO) is demonstrated. The liquid solutions for precipitating MnZn ferrite were citrated in turn in the center of the spin plate, and impinged on the target due to the applied centrifugal force. The MnZn ferrite is precipitated on the plane of AAO with the island growth mode at the initial stage. With increasing the precipitation time, the precipitated area would extend to cover the nanopores via the side growth. As a result, the thickness of the deposited thin film can be well controlled in the nanoscale by the island and side growth mode. On the other hand, the nanopores of the template are free from the deposition of the MnZn ferrite due to the spinning.

Investigation of the pore formation in anodic aluminium oxide

The mechanism accounting for the self-organization of nanoscale pores during anodic oxidation of aluminium is studied. Microstructural studies support the equifield strength model, which can be used to explain the formation of the hemispherical electrolyte/oxide and oxide/metal interfaces, uniform thickness of the oxide layer, as well as self-adjustment of the pore size and pore ordering. The fundamentals of the model are the electric field enhanced oxide dissolution rate and oxygen anion migration rate. The most important factor for determining the porosity of anodic alumina films with both ordered and disordered pores is the relative dissociation rate of water. The relationships between the porosity and anodization conditions, such as voltage, current density, and electric field strength, are also estimated.