Dense metallic membranes method

Thicker, self-supporting, dense metal membranes are known. These are tubular and are usually commercially successful palladium-silver hydrogen separation membranes were of this type.21 Currently, Power and Energy, Inc. also fabricates this type of membrane, although planar membranes are more common due to easier fabrication and a greater variety of fabrication methods. 

Based on the different compositions, structures and configurations, the dense metallic membranes can be prepared using various methods. As described earlier, the dense metallic hydrogen separation membrane can be... 

Because membranes appHcable to diverse separation problems are often made by the same general techniques, classification by end use appHcation or preparation method is difficult. The first part of this section is, therefore, organized by membrane stmcture preparation methods are described for symmetrical membranes, asymmetric membranes, ceramic and metal membranes, and Hquid membranes. The production of hollow-fine fiber membranes and membrane modules is then covered. Symmetrical membranes have a uniform stmcture throughout such membranes can be either dense films or microporous. 

The resulting metal membrane has a structure similar to the bulk pores of the anodic alumina but without the dense "skin layer and has straight through-pores. Nickel and platinum membranes having pore diameters in the 15 to 200 nm range can be produced this way. One of the critical steps of this method is depositing palladium catalyst on the surface, but not inside the pores, of the anodic alumina. The catalyst is used to facilitate the deposition of metal from the bottom to the surface of the cylindrical pores. 

Tong J, Suda H, Haraya K, Matsumura Y (2005) A novel method for the preparation of thin dense Pd membrane on macroporous stainless steel tube filter. J Memb Sci 260 10-18 Ryi SK, Park JS, Kim SH, Cho SH, Park JS, Kim DW (2006) Development of a new porous metal support of metallic dense membrane for hydrogen separation. J Memb Sci 279 439-445... 

Currently, the membranes incorporated in MMRs are mainly zeolite and Pd-based dense metal ones. Incorporation of these membranes in microreactors can be achieved using one of the preparation methods described in previous chapters. 

Different methods have been used to deposit microporous thin films, including solgel, pyrolysis, and deposition techniques [20], Porous inorganic membranes are made of alumina, silica, carbon, zeolites, and other materials [8], They are generally prepared by the slip coating method, the ceramic technique, or the solgel method (Section 3.7). In addition, dense membranes are prepared with metals, oxides, and other materials (Chapter 2). 

In the case of catalytic dense membranes such as palladium alloy sheets or tubes, a smooth membrane surface suffers from a small active surface area per unit volume of catalyst. This drawback can be remedied to some extent by adopting some conventional catalyst preparation methods to roughen the membrane suiface(s) to ensure that only the region near the surface is affected unlike the Raney metal catalysts where the entire matrix is leached. For example, Gryaznov [1992] suggested the use of thermal diffusion of a chemically active metal into a Pd alloy sheet followed by acid treatment to remove this metal. 

SEM photographs of sputtered films show that the layers are fairly dense and appear to crack into platelets when subjected to MEA fabrication. The dense films do not lend themselves to high surface areas therefore, there is substantial scope for enhancement of performance if the surface area can be increased. This may be achieved by producing porous 3-D Pt-Ru layered structures. One such method for creating such 3-D structures, that seem to be extremely promising, involves the pre-treatment of the membrane surface by ion-beam etching, which is then followed by sputter-deposition of the metal. This results in substantially enhanced surface area and very rough nanostructures. Next year s effort will include characterization of such films. 

Perovskite-structured membranes, in the form of thin films supported on porous ceramic or metal substrates, have been studied extensively in the past decade. Thin films offer several advantages including reduced material cost, improved mechanical strength and possibly higher H2 flux. Chemical vapor deposition (CVD) [99], electrochemical vapor deposition (EVD) [100] and sputtering [101] represent typical methods. However, dense films have been difficult to obtain by these methods. It was found that the continuity and gas-tightness of the deposited films were very sensitive to the morphologies and pore size of substrates. 

In the last decade, a variety of porous substrates were proposed for supporting the dense membranes, such as ceramics, metals, and alloys [42-44]. In those studies, special attention was paid to the LSCF coating on metallic substrates by using physical methods such as plasma spray physical vapor deposition and magnetron sputtering as an alternative to the wet chemical deposition methods [43,44]. When considering ceramic substrates, besides the elastic behavior and the thermal expansion of the perovskites, other properties such as toughness... 

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