Study of the properties of hydrogen and deuterium in beta phase palladium hydride and deuteride

Work is underway in numerous countries around the world to design a viable nuclear fusion power station. It is hoped that this technology may one day provide a large amount of the world’s baseline power requirements. There are still numerous problems to be overcome in this field. The processing and refinement of hydrogen isotopes from mixed isotope sources is one such issue. Palladium already plays a part in existing infrastructure for this purpose. Existing work about the exact nature of the isotopic differences in the palladium hydride (/deuteride / tritide) system contains much conflicting evidence. This work is a study on the properties of the two lighter hydrogen isotopes (protium and deuterium) dissolved in palladium at high concentrations to form the well-established beta phase. Direct measurements of the tracer diffusion of these isotopes have been made for two sample geometries using quasielastic neutron scattering on Osiris at ISIS (Harwell, UK) and IN5 at The Institut Laue Langevin (Grenoble, France). Separate sorption measurements are also reported for each isotope to allow accurate determination of diffusion coefficients. Diffusion coefficients are reported for octahedral - octahedral jump diffusion in the beta phase for both isotopes. These results are used to calculate a temperature for the ‘crossover point’ in the diffusion rate of these isotopes (~730 K). This work also presents several unexpected results from these experiments: - A second diffusive motion, that does not appear to match any previously described, is reported for all samples and instruments. While it has not been possible to fully characterise this motion, its properties are investigated and discussed. - A high degree of ordering amongst the deuterium is inferred in the beta phase deuteride at temperatures between 433 and 500 K with around 55% of the available palladium interstitials occupied. This phenomenon has not previously been reported above 150 K. - Evidence for similar ordering and a possible transition in the ordered structure are reported for the beta phase hydride at similar temperatures and pressures