Structurally stable composite PdAg alloy membranes: Introduction of a diffusion barrier

Abstract

This work investigates the improvement of the structural stability of PdAg alloy membranes by introduction of a diffusion barrier. Asymmetric PdAg films were deposited on porous stainless steel (SS) substrate by electroless plating. The formation of these alloys was achieved by annealing the as-deposited membranes at temperatures higher than Tamman temperatures of the alloy components in a hydrogen atmosphere. The composite PdAg membranes were characterized using XRD and Auger electron depth profiling. The atomic interdiffusion of silver and palladium resulted in PdAg alloys in an fcc structure. To improve the structural stability of PdAg alloy/SS membranes, an ultrathin intermediate layer of titanium nitride being 0.1 μm thick was introduced as a diffusion barrier between PdAg and the SS substrate. The Auger electron depth profiling analysis indicated that the improved membranes were thermally stable at temperatures as high as 973 K, and practical for the catalytic membrane reactor use. An estimation of diffusion coefficients revealed that the presence of hydrogen in the annealing atmosphere favoured the PdAg interdiffusion and thus the formation of PdAg alloys.