Alumina membrane mesoporous structures

Structural studies of mesoporous alumina membranes by small angle X-ray scattering... 

Figl Structural features of the mesoporous alumina membranes Schematic cross section (before removal of A1 backing) and schematic top view, together with an atomic force microscope AFM (Voltage) image for a membrane produced by anodisation at 40 V. 

In this section, reference is made to discrete approaches for the modeling of gas/condensate flow through mesoporous structures. Capillary network models are developed and evaluated by comparison with experimental results from the literature. Finally, experimental results obtained in our laboratory are presented on two mesoporous membranes, made by compaction of alumina microspheres, with porosities 0.41 and 0.48, respectively. 

Yao, B., Fleming, D., Morris, M.A. and Lawrence, S.E. (2004) Structural control of mesoporous silica nanowire arrays in porous alumina membranes. Chemistry of Materials, 16(24), 4851. 

Other methods to prepare porous membranes include pyrolysis for carbon membranes, heat treatment and leaching for mesoporous glass membranes, and anodization for alumina membranes. The microporous carbon membranes are prepared by coating a polymeric precursor such as polyfurfuril alcohol and polycarbosilane on porous substrates, followed by controlled pyrolysis under N2 atmosphere [15]. The carbon membrane structure is determined by the fabrication variables, including the polymeric solution concentration, solvent extraction, heating rate, and pyrolysis temperature [16]. 

Figure 34.1 (Left) Scanning electron microscopy (SEM) microstructure of state-of-the-art supported mesoporous y-alumina membrane structure. (Right) Idealized microstructure of supported zeolite membrane structure tbe intermediate layer is a reaction barrier and facilitates thin zeoUte membrane deposition. Only part of the support is shown its structure coarsens slightly toward the permeate side.

Thermoporometry is a method which measures cavity sizes and not inlet sizes. It has been mainly used for the characterisation of organic mesoporous membrane texture [70-73] but has been also applied to inorganic alumina symmetric membranes [73] with a good reliability. However the solidification of water in small pores may sometimes damage the membrane structure due to the expansion of the condensate and consequently different results can be obtained after several runs [74]. 

The most active areas of development for membrane materials are currently synthesis of supported thin Aims, and pore modification. The complete selectivity to one species provided by dense membranes is very attractive, but is accompanied by low permeation rates if the membrane is composed entirely of the dense material. To maintain structural stability, thinner dense films must be supported by materials that are strong but that offer no additional resistance to permeation. Similar principles apply to the use of microporous materials with high permselectivities or molecular sieving effects. Some examples of these developments are supported Pd films on porous aluminas,or on porous stainless steel, and supported zeolite films. Pore modification has been used to deposit materials inside mesoporous materials, an example being the deposition of SiOa films in porous glass. 

Martin CR (1994) Nanomaterials a membrane-based synthetic approach. Science 266 1961-1966 Martin CR (1996) Membrane-based synthesis of nanomaterials. Chem Mater 8(8) 1739-1746 Masuda H, Fukuda K (1995) Ordered metal nanohole arrays made by a two-step replication of honeycomb structures of anodic alumina. Science 268 1466-1468 Mishra JK, Bhunia S, Baneqee S, Baneqi P (2008) Photoluminescence studies on porous silicon/ polymer heterostructure. J Lumin 128 1169-1174 Moller K, Bein T (1998) Inclusion chemistry in periodic mesoporous hosts. Chem Mater 10(10) 2950-2963... 

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