Simpson, George Innes (2012)
M.Res. thesis, University of Birmingham.
The development of a composite (Pd-alloy thin film / Porous stainless steel substrate)hydrogen separation membrane was investigated, that is able to operate at high temperatures (600°C), for use in a hydrocarbon reformation reactor for the production of pure hydrogen. An intermediated layer of tungsten powder was deposited onto the surface of macroporous 316L stainless steel (PSS) substrates. This layer served to create an interdiffusion barrier against iron diffusion and also to reduce the surface pore size of the PSS. The dual performance of this intermediate layer within a composite membrane was tested, in terms of surface pore size reduction and ability to prevent interdiffusion. The extent of the powder filling and surface pore reduction was calculated along with the effect on hydrogen transport through the modified substrate. The results showed that both one and three layers of tungsten powder were successful. Production of a defect-free membrane layer was also investigated, coating the tungsten modified PSS substrate with various thicknesses of stainless steel (SS) (as a low-cost proxy for a Pd-alloy thin film). The results showed that a more continuous defect-free membrane layer was achieved when the surface of the substrate was most uniform. The performance of both dense and powdered tungsten intermediate barriers on their ability to prevent iron diffusing into sputtered Pd/PdCu membrane layers, was also investigated. SEM-EDX analysis showed that dense tungsten was very successful at preventing iron diffusion while the powdered particles were also clearly preventing interdiffusion within the pores. It was concluded that a combination of both dense and powdered tungsten would need to be used to fully prevent iron diffusion.
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