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

The N2 and H2 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 H2 atmosphere demonstrated that, at 893 K, only 48 h are needed to form a stoichiometrically homogeneous, 9.5 μm thick, face centered cubic (fcc) Pd63Cu37 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 H2 fluxes of fcc Pd58Cu42 and Pd70Cu30 membranes were JH2=(1.6±1.1) mol m−2 s−1 exp[(−24.8±0.4)kJ mol−1/RT]JH2=(1.6±1.1) mol m−2 s−1 exp[(−24.8±0.4)kJ mol−1/RT] and JH2=(3.7±0.6) mol m−2 s−1 exp[(−21.3±1.0)kJ mol−1/RT]JH2=(3.7±0.6) mol m−2 s−1 exp[(−21.3±1.0)kJ mol−1/RT], respectively, at 100 kPa H2 pressure difference.