Electroless plating metallic supports

The second method, i.e. electroless plating, has been used also to produce graphite - Sn, Sn02 composite materials. The chemical deposition of metals on the graphite supports is performed through two principal steps. 

This paper provides discussions on the hydrogen permeation through Pd membranes, methods of the formation of thin Pd and Pd/alloy films on porous supports with special emphasis on electroless plating, porous metallic supports, formation of intermetallic diffusion barrier and long term membrane stability at high temperatures. 

Thorough cleaning and the avoidance of any extraneous debris are essential in any membrane fabrication scheme. After EP, a composite membrane can be soaked in hot water or dilute ammonia to help remove any impurities trapped in the porous support that may be detrimental to the palladium film during high temperature operation [72, 73]. However, traces of impurities from the EP bath such as chlorine, sodium, and carbon, inevitably become incorporated into the metal film. Membrane defects can be a consequence of preparation conditions. Fabrication in a dean-room environment has resulted in increased permselectivity [140]. Porous stainless steel (PSS) must be cleaned and pickled before electrodeposition or else activated for electroless plating. 

Under properly controlled conditions all the above-mentioned methods produce good quality thin layers but electroless plating has the advantage of easy scale-up and the flexibility to coat the metal film on supports of diflerent geometry. 

Osmotic electroless plating An osmotic pressure is produced hy a concentration gradient between the two sides of the membrane the generated flux of solvent compresses the metal against the support... 

Composite membrane fabricated using metal supports can also use an intermediate layer for reducing the thermal mismatching between the support and the Pd-alloy film. For instance, ceramic layers have been positioned in between stainless steel porous supports and Pd-Ag and Pd films [62]. The ceramic interlayer also reduces intermetallic diffusion of the supports into the active Pd-based layers that could contaminate the membrane. Intermetallic film made of a porous Pd-Ag layer obtained through continuous electroless plating of alternating Pd and Ag baths has been used in the fabrication of composite Pd membranes, which consist of porous stainless steel plates with a selective Pd layer [63]. These membranes were successfully tested up to 500°C. Their effectiveness as diffusion barriers for Pd membrane deposited over porous stainless steel supports at 400°C was demonstrated by the presence of a zir-conia layer [64]. 

SEM images of Pd deposited on a metallic support via electroless plating (a) surface and (b) cross section. (Courtesy of RSE laboratories.)... 

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