Separation of Hydrogen Isotopes ELECTROLYTIC MIGRATION THROUGH A PALLADIUM MEMBRANE

With the increasing importance of “ heavy water” as a moderator in nuclear reactors there arises a pressing need for a more efficient method of separating hydrogen isotopes. In a report by 0. N. Salmon to the U.S. Atomic Energy Commission (AEC Research and Development Report KAPL 1272) a process is described which aims to improve the method of separation by the electrolysis of water. This process is based on the hypothesis that if a voltage drop is maintained across a palladium membrane in aqueous solution hydrogen ions will be discharged into thc palladium at the negative surface and will diffuse through the membrane to the positive surface. There they will combine with oxygen ions and re-enter the electrolyte as water. If the current density is sufficiently low a steady state will be reached where no hydrogen is evolved at the negative surface and no oxygen at the positive surface. Furthermore it is reasonable to expect that if hydrogen isotopes are present in the solution fractionation will occur at the palladium membrane with the lighter isotope being discharged preferentially at the negative surface. It was estimated that the separation factor would be equal to or slightly greater than that achieved by conventional electrolysis. To test these hypotheses and find the value of the separation factor, the cell shown here diagrammatically was found to be the most satisfactory. The palladium membrane, in the form of a thimble, and the two palladium electrodes were made from commercial palladium of 99.9 per cent purity. In saturating the palladium thimble with hydrogen expansion occurs due to an increase in the cubic lattice parameter on passing from a-phase palladium to ,&phase palladium Electrolytic cell for determining e$iciency and separation factor for the migration of hydrogen and deuterium