MEASUREMENT OF DIFFUSIVE AND SURFACE TRANSPORT RESISTANCES FOR DEUTERIUM IN PALLADIUM-COATED ZIRCONIUM MEMBRANES

Palladium-coated zirconium membranes are attractive choices for low pressure, high temperature hydrogen and hydrogen isotope extractions, e.g. from fission and fusion coolant fluids. Oxidizing the exiting hydrogen to water (oxidative extraction) is a good way of providing very low downstream hydrogen pressures that are sometimes needed to drive the extraction. We present here experimental data and a theoretical treatment of deuterium transport through Zr-Pd membranes at temperatures of 600-700 K and upstream deuterium pressures of 2.7 x 10(-2) to 6.7 x 10(-4) Pa. We also present a new technique for analyzing experimental flux measurements for calculating the effective permeation and sticking coefficients during such experiments. At very low pressures, transport is limited by molecular adsorption on the palladium surface; the sticking coefficient for this adsorption is log sigma = -0.676-0.0021(T - 273). At higher upstream pressures, permeability in zirconium limits transport; P(Zr) = 2.00 x 10(-6) exp(59/T) +/- 40% mol/msPa1/2. These permeability values are slightly higher than predicted. We find no evidence for additional transport resistance caused by zirconium surface oxidation, or from Zr-Pd interface effects. Membranes were used for several months without showing signs of deterioration.