Real-time monitoring of metal deposition and segregation phenomena during preparation of PdCu membranes

Abstract

The N 2 and H 2 evolution, respectively, were monitored during deposition of Pd and Cu from electroless plating baths to obtain in-process control of the composition during preparation of 3–7 μm thick PdCu membranes on tubular ceramic substrates. Compositions estimated by gas evolution compare favorably to those measured in post-mortem XRD and EDS analyses, mostly differing by not more than 1 at.%. This result suggests that use of gas evolution measurements to enable in-process control of composition to within 1 at.% is feasible. Annealing experiments in an H 2 atmosphere demonstrated that, at 893 K, only 48 h are needed to form a stoichiometrically homogeneous, 9.5 μm thick, face centered cubic (fcc) Pd 63Cu 37 membrane from sequentially deposited layers; at 723 K, the same transformation requires over 2 weeks. The appearance of transient body centered cubic (bcc) and fcc phases with lower Pd contents signaled compositional segregation in the initial stages of alloy formation at 723 and 773 K and could be a source of persistent stoichiometric heterogeneity particularly in bcc PdCu membranes. The H 2 fluxes of fcc Pd 58Cu 42 and Pd 70Cu 30 membranes were J H 2 = ( 1.6 ± 1.1 ) mol m − 2 s − 1 exp [ ( − 24.8 ± 0.4 ) kJ mo l − 1 / R T ] and J H 2 = ( 3.7 ± 0.6 ) mol m − 2 s − 1 exp [ ( − 21.3 ± 1.0 ) kJ mo l − 1 / R T ] , respectively, at 100 kPa H 2 pressure difference.