Publications

Separation factors for hydrogen isotopes in palladium hydride

Luo, Weifang; Cowgill, D.F.; Flanagan, Ted B.

This investigation examines how equilibrium pressures of single isotope metal-hydrogen systems can be used to determine the separation behavior of hydrogen isotopes in a mixed-isotope metal hydrogen system. The separation factor for a hydrogen-deuterium system, αHD, describes the equilibrium hydrogen isotope partition between the solid and gaseous phases. Very few values of αHD are reported for metals other than palladium, and the values for Pd are scattered with the origin of the scatter not fully understood. Wicke and Nernst and Trentin et al. have proposed models that relate αHD to the ratio of single isotope equilibrium pressures and the isotopic composition of the solid. The approaches of these models and the resulting equations appear to differ; however, as will be shown here, they are identical. It also will be shown that Raoult's law, employed by both models, is not needed. This puts the model derivation on a firmer theoretical basis. New measurements of αHD values are determined over a large temperature range and D/H ratio in β-phase Pd hydride, and they are compared with the model predictions, validating the model. Since experimental values for αHD are often not available for other systems, while single isotope equilibrium pressures are available, the model provides a valuable tool for predicting separation factors. Moreover, the model can also be used to estimate separation factors involving the third hydrogen isotope, tritium. © 2013 American Chemical Society.