Degradation of dense metallic membranes

H2 embrittlement is a consequence of H2/metal interactions. It has been established that severe mechanical degradation occurs and is manifested in a decrease of fracture resistance. From a materials-classification standpoint, one may distinguish between microstructurally stable materials, in which the metal and solute H2 interact, and those which require attention to phase stability. Stress-induced hydride formation and cleavage mechanism is the main H2 embrittlement mechanism for pure-metal H2 permeation membranes. The H2 permeation metals Pd, IVB (Ti, Zr, Hf) and VB (V, Nb, Ta) can all easily form hydride when exposed to H2 at relatively low temperatures (Buxbaum and Markerb, 1993 Buxbaum and Kinney, 1996). Alloying with other metals can stabilize the structure and improve the embrittlement effect (Yamaura et al, 2004 Yukawa et al, 2008). 

An oxide layer is commonly formed on the surface of the pure metals of IVB (Ti, Zr, Hf) and VB (V, Nb, Ta) due to being thermodynamically 

Preferential segregation of certain elements from dense alloy membranes can also result in degradation of the performance of H2 permeation membranes. For example, Pd-Ag films ( 2.4%Ag, 20-26 pm thick) were deposited by sequential electroless plating onto porous tubular stainless steel substrates with AI2O3 oxide layers to modify the substrate pore size and to prevent intermetallic diffusion of the stainless steel components into the Pd-Ag layer (Bosko et al., 2011). Composite membranes annealed at temperatures of 500-600°C were characterized for film structure (XRD), morphology (SEM), bulk and surface component distribution (EDS, XPS), and H2 permeance. Composition measurements within the Pd-Ag layer revealed preferential segregation of the Ag component to the top surface. This result is consistent with the lower surface free energy of Ag. 

24 Hydrogen and helium permeance (with the feed of 1 1 Hj and He mixture) through a 200 nm thick Pd-Ag membrane before and after being exposed to a carbon source at 600°C (Lin, 2001). Open symbols - before carbon poisoning closed symbols - after carbon poisoning. 

An example of the second process is furnished by Kulprathipanja et al. (2005), who hypothesize that the reduction of the performance was due to 

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