Hydrogen permeation through Pd/Fe and Pd/Ni multilayer systems

Different sets of Pd/Fe and Pd/Ni multilayer systems, consisting of different numbers of individual layers, have been prepared on Pd substrates by ion-beam sputtering. The gas permeation of hydrogen through the multilayers was measured for various pressures and temperatures. After in situ surface cleaning the specimens, the permeation follows Sieverts' law indicating a diffusion-controlled process. Comparing the experimental results with the permeation calculated using the parameters obtained for bulk materials show, that the hydrogen permeation through Pd/Fe multilayers is suppressed, whereas, the permeation through Pd-Ni system is enhanced. In the case of the Pd-Fe system, the hydrogen atoms may additionally be trapped at dislocations lowering the permeation. For the Pd/Ni multilayers, the small grain size of the Ni layers leads to an enhanced permeation by grain boundary diffusion. For both multilayer systems, no strong influence of the interfacial layers was observed.