X-ray diffraction study on the effects of hydrogen on Pd60Cu40 wt% foil membranes

Abstract

In-situ variable temperature X-ray diffraction analysis was performed on two as-received Pd 60 Cu 40 wt% foil samples containing the disordered face centred cubic (FCC) phase between 30 and 700 °C. One foil sample was exposed to 445 kPa of flowing helium and the other foil sample was exposed to 445 kPa of flowing hydrogen. Generally, it was found that 445 kPa of flowing hydrogen had the effect of expanding the temperature range over which the body centred cubic (BCC) phase in the foil sample was stable when compared to testing under 445 kPa of flowing helium. This is likely due to dissolved hydrogen shifting the BCC | FCC + BCC and FCC + BCC | FCC phase boundaries to relatively higher temperatures and Pd contents. An as-received Pd 60 Cu 40 wt% foil membrane had been cycled from 50 to 450 °C under a 445 kPa feed pressure and 100 kPa permeate pressure of hydrogen. In the third cycle, this membrane achieved a noticeably low hydrogen permeability of 5.59  10-9 mol m-1 s-1 Pa-0.5 at 450 °C. Moreover, the partial pressure exponent was found to deviate significantly from Sieverts' law between 400 and 450 °C. Subsequently, this membrane was cycled twice between 250 and 700 °C achieving a much higher hydrogen permeability of 1.19  10-8 mol m-1 s-1 Pa-0.5 which was measured at 450 °C. The activation energy for permeation reduced by more than 60% and the partial pressure exponent decreased to 0.52. The initial poor hydrogen permeability of the membrane was attributed to coring as evidenced by the presence of the disordered FCC phase in the as-received foil. The improvement in hydrogen permeability was linked to the homogenisation effect of hydrogen under the conditions used in this study.

Hydrogen solubility and diffusivity at Σ3 grain boundary of PdCu

“…Interestingly, some experimental studies reveal that hydrogen diffusion in GB of nickel is much faster than that in bulks due to a lower activation energy, 3,6 whereas the hydrogen diffusivity in GB of aluminum and nickel with ne grains is smaller than that in the bulks. 7,10,11,13 As to hydrogen diffusion in PdCu membranes, the reported experimental results are mainly concentrated on the polycrystalline phases, [19][20][21][22][24][25][26][27][28][29][30][31][32][33][34][35]37,39 while the theoretical investigations are all related to single crystals. 17,23,36,38,[40][41][42] It is therefore of importance to nd out the effect of GB on hydrogen diffusion of PdCu by means of rst principles calculation.…”

Influence of temperature and pressure on surface modified Pd-Cu alloy foils for hydrogen purification applications

“…Eq. (1) has been derived elsewhere [19] and has been used in this study to determine crystal lattice parameter of all foil samples.…”

Characterization of Pd60Cu40 Composite Membrane Prepared by a Reverse Build-Up Method for Hydrogen Purification

“…Cu has the additional advantages of resistance to H 2 S [29], higher durability in thermal cycling tests than PdAg alloys and other materials, and prevents H 2 embrittlement, which is a problem associated with pure Pd membranes [30]. In particular, the Pd 60 Cu 40 wt.% (Pd 47 Cu 53 at.%) alloy has the highest H 2 permeability at 350 • C among the PdCu alloys reported thus far [8,31]. For these reasons, H 2 -permeable membranes of Pd 60 Cu 40 alloy have been developed.…”