Journal of Membrane Science, Vol.545, 266-274, 2018
X-ray diffraction study on the effects of hydrogen on Pd60Cu40 wt% foil membranes
In-situ variable temperature X-ray diffraction analysis was performed on two as-received Pd60Cu40 wt% foil samples containing the disordered face centred cubic (FCC) phase between 30 and 700 degrees 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 Pd60Cu40 wt% foil membrane had been cycled between 50 and 450 degrees 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 x 10(-9) mol m(-1) s(-1) Pa-0.5 at 450 degrees C. Moreover, the partial pressure exponent was found to deviate significantly from Sieverts' law between 400 and 450 degrees C. Subsequently, this membrane was cycled twice between 250 and 700 degrees C achieving a much higher hydrogen permeability of 1.19 x 10(-8) mol m(-1) s(-1) Pa-0.5 which was measured at 450 degrees 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.