Types of Dense Metallic Membranes

Early work focused on the application of unsupported dense Pd membranes prepared by conventional metallurgical processes. These self-supporting membranes are in the form of tubes or foils, and possess wall thicknesses greater than 50-100 pm to maintain sufficient mechanical strength. This leads to low hydrogen flux but a high cost of the membrane (precious Pd and Pd alloys), which limits their industrial applications. 

In order to meet the membrane performance targets of H2 flux exceeding Imol m s and H2 permeate purity of at least 99.99%, with a membrane cost target of 150/fT for commercial applications, the membrane thickness should be reduced to about 1-10 pm without the creation of cracks and pinholes [3]. This can be realized through supported composite membranes prepared by various techniques. The thin Pd membrane provides high hydrogen flux, while the porous support provides satisfactory mechanical strength. 

Palladium-based composite membranes consist of a thin dense layer of palladium or a palladium alloy on a porous support. Tubes or disks of porous glass, porous ceramics, or PSS can all be employed as supports. 

Usually, an intermediate layer of reduced porosity is used to improve the metallic membrane quality as well as the adhesion between the metal and the support. When metal supports (stainless steel, nickel, etc.) are used, the thermal mismatching between the Pd alloy films and the porous substrate can be reduced. 

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The cold-rolling technique has been applied to synthesize new types of dense metal membranes made of Nb-based alloys. In particular, Luo et al. verified that an Nb-Ti-Ni alloy consisting only of the primary phase and the eutectic phase exhibited high hydrogen permeability and good resistance to hydrogen embrittlement. ... 

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