Effects of osmosis on microstructure of Pd-composite membranes synthesized by electroless plating technique

Several issues related to preparation of dense thin Pd-composite membranes by the electroless plating technique with osmosis are investigated. The influence of osmosis on metal grain size and penetration into porous Vycor glass was studied, and in addition a new approach for substrate activation was developed. Quantitative image analyses of various micrographs, randomly chosen on the membrane surface, show that average Pd grain size gradually decreases from 350 without osmosis to 150 nm for osmosis with 9 M sucrose solution. The distribution of grain sizes is also narrower for membranes synthesized under higher osmotic flux conditions. Energy dispersive X-ray measurements reveal that under conditions of osmosis, Pd penetrates deeper into the porous substrate, forming intermediate zone with gradually changing Pd–SiO2 compositions. This enhances thermal stability and mechanical properties that depends on adhesion between film and substrate. Finally, it was shown that microstructure of the deposited film when seeded with osmosis is finer and more regular as compared to when osmosis is absent. It appears that use of osmosis during seeding contributes more to microstructural uniformity, while during plating it leads to finer grain size.