Inelastic neutron scattering study on different grades of palladium of varying pretreatment

The inelastic incoherent neutron scattering (IINS) technique has been utilized to study the way in which various kinds of palladium retain hydrogen after different pretreatments. Cold-rolled palladium foil, coarse palladium powder and finely divided palladium samples of different particle size and pretreatment were compared after controlled hydrogenation at room temperature and subsequent short-term dehydrogenation at 20, 50 and 70 degrees C. In a set of experiments under constant conditions, the incomplete decomposition of the beta- and alpha-hydride phases at the given temperatures were found to be uncorrelated to the morphology of the samples under investigation or to the presence of strongly adherent carbonaceous degradation products at the surface of some of the samples. The dominant factor was the effect of hydrogen trapping due to mechanical pretreatment. It was shown that this effect may also be of some relevance at elevated temperatures. It was also found that IINS is a suitable technique for the analysis of strongly adherent carbons at the surface of metals and metal hydrides and to discriminate between simple molecular structures and organic species of extended size. This is even the case for partial coverage of finely divided powders, the strong electromagnetic absorption and high electrical conductivity raises problems in utilizing other analytical techniques.