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

Several issues related to preparation of dense thin Pd-composite membranes by the electroless plating technique with osmosis are investigated. The inf luence of osmosis on metal grain size and penetration into porous Vycor gla ss was studied, and in addition a new approach for substrate activation was developed. Quantitative image analyses of various micrographs, randomly ch osen on the membrane surface, show that average Pd grain size gradually dec reases from 350 without osmosis to 150 nm for osmosis with 9 M sucrose solu tion. The distribution of grain sizes is also narrower for membranes synthe sized under higher osmotic flux conditions. Energy dispersive X-ray measure ments reveal that under conditions of osmosis, Pd penetrates deeper into th e porous substrate, forming intermediate zone with gradually changing Pd-Si O2 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 us e of osmosis during seeding contributes more to microstructural uniformity, while during plating it leads to finer grain size. (C) 2000 Elsevier Scien ce B.V. All rights reserved.