Anodic oxide aluminum membranes

Ichimura, S., Tsuru, T., Nakao, S., and Kimura, S. (2000). Analysis of linear macromolecule transport through aluminum anodic oxide membranes by pore model. J. Chem. Eng. Jpn. 33 ... 

A completely different type of inorganic membrane also has its origin in the nuclear industry the asymmetric alumina membranes obtained by the anodic oxidation of an aluminum sheet were first developed for uranium enrichment... 

Figure 2.14. The structure of an anodized aluminum oxide membrane (Anopore) as shown in Anotec Separations (1986) (a) is a homogeneous membrane (b) an asymmetric membrane.

Figure 2.16. Production scheme of a anodic aluminum oxide membrane (Smith 1973,1974).

Fumeaux, R. C., W. R. Rigby and A. P. Davidson. 1989. The formation of controlled-porosity membranes from anodically oxidized aluminum. Nature 337 147-49. 

Smith, A. W. 1973. Porous anodic aluminum oxide membrane. J. Electrochem. Soc. 120(8) 1068-69. 

Fumeaux, R. C., A. P. Davidson and M. D. Ball. 1987. Porous anodic aluminum oxide membrane catalyst support. European Patent Appl. 0,244,970A1. 

Yamada, M., K. Fugii, H. Ham and K. Itabashi. 1988. Preparation and catalytic properties of special alumina membrane formed by anodic oxidation of aluminum. Proc. 9th Inti. Cong. Catal. 1945-1951. 

Alumina nanotubes have been prepared by the anodic oxidation of aluminum [41] the resulting tubes have one-dimensional channels with uniform diameters of 5nm and lengths of 50-100 nm. An alumina membrane with a highly ordered nanohole array in 50-100 nm diameter has also been synthesized by long-period anodization thus these local alumina nanotubes have been tried as a template for metal nanowire formation. 

Xiong G, Elam JW, Feng H, Han CY, Wang HH, Iton LE, Curtiss LA, Pellin MJ, Rung M, Kung H, Starr PC (2005) Effect of atomic layer deposition coatings on the surface structure of anodic aluminum oxide membranes. J Phys Chem B 109 14059... 

A very important recent application is to use aluminized membranes as a mask for physical vapor deposition. In these cases the membrane is either attached to the substrate or a film of aluminum (typically a few microns thick) is grown on a substrate such as Si. This is followed by the anodic oxidation process to convert the aluminum film to an anodized template. The growth process is either physical... 

This advantage can be used for growing nanowires (wires with nanometric diameter). Nanoporous membranes that can be fabricated by the anodic oxidation of aluminum are appropriate templates. This process leads to the formation of an alumina layer with parallel nanopores, as shown in Fig. 15A, which can then be filled by electrodeposition. Fig. 15B shows a schematic view of a multilayer nanowire and Fig.l5C a transmission electron microscopy image of a Cu/ CuCoNi layered nanowire grown in the nanopores. 

Evans PR, Yi G, Schwarzacher W (2000) Current perpendicular to plane giant magnetoresistance of multilayered nanowires electrodeposited in anodic aluminum oxide membranes. Appl Phys Lett 76 481 83... 

Membranes prepared via anodic oxidation possess a very regular morphology consisting of hexagonaUy close-packed cells with cyHndrical pores. They are formed by applying an aluminum foil as the anode in an add electrolyte. Depending on the experimental conditions, pore sizes can vary between 0.1 and 0.2 pm (Fig. 3.6-7). 

Figure 7.3 AFM images of anodic aluminum oxide membrane (a), and Zn-Ni alloy nanorods (b, c) obtained using double templates (liquid crystal and AAO). (b) and (c) were obtained with different deposition charges, 0.6 C and 0.9 C, respectively. The scale of each picture is 1.6 x 1.6 p,m. (Reprinted from A. Foyet et al. J. Electroanal. Chem. 2007, 604, 137. Copyright (2007) Elsevier. With permission.)...

Gold nanowire arrays were also used by Andreu and coworkers for DNA detection [45]. Anodic aluminum oxide membranes were used as templates for galvanostatic Au electrodeposition followed by treatment in base to dissolve away the template leaving freestanding gold nanowires 330 nm in diameter and 2 fim in length. [Ru(NH3)6] + was used to measure charge before and after... 

For template-based parylene, anodized aluminum oxide membranes with 100 nm of pore diameters and a thickness of 60 xm are placed into a deposition chamber. Using surface characterization techniques, both approaches have been compared. 

Figure 13.16 SEM image of a porous AAO membrane formed on ITO, manufactured by anodic oxidation of aluminum at 40 V in the presence ofO.3 M oxalic acid and a subsequent following pore widening for 60 min in phosphoric acid.

FIGURE 10.1.3 Pore structure of an anodic oxide aluminum membrane. 

One of the features of inorganic membranes is their controlled pore structure. Anodic aluminum oxide membranes have uniform cylindrical pores, and were applied to an investigation of the analysis of transport mechanism [ 12]. Another route involves the application of a micelle template to membrane preparation [44]. Cubic mesoporous silica (MCM48) membranes were prepared on a stainless steel supports [45] to possible applications for filtration membranes and membrane reactions. 

A novel one-sided NMR magnet has been developed for self-diffusion measurements in thin samples [7]. Using this technique, researchers have demonstrated measurements in bulk [BMIM][TFSI] and [BMIM][TFSI] confined in nanoporous anodized aluminum oxide membranes, as shown in Fig. 3. This operates at a proton Larmor frequency of 14.08 MFlz, and the expected appHcation is toward in situ measurements in portable energy devices. This method utilizes the fringe field to measure diffusion coefficients instead of conventional PFG-NMR. 

In addition, as a relatively mature technique, AI2O3 nanomembranes can be obtained by electrochemical anodic oxidation, and their thicknesses, pore diameters and densities adjusted by operational conditions such as electrolytes, voltages and temperatures. Under the assistance of porous aluminum, nanowires, nanotubes and more complex nanostructures can be prepared controllably [176], and this may open the door to the preparation of functional anisotropic NF membranes for high throughput in real applications. 

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