Abstract
Pd60Cu40 wt% (Pd47.3Cu52.7 at%) membranes were surface modified by depositing Pd thin films of three different thicknesses (~100, 800 and 1400nm) on to one side of a range of as-received Pd60Cu40 wt% cold-rolled foils via magnetron sputtering. The hydrogen permeability of the membranes was then measured and compared to the uncoated material. The Pd60Cu40 wt% membrane coated with a 1400nm thick Pd thin film positioned on the feed side (445kPa of hydrogen pressure) during hydrogen permeability measurements and cycled between 50 and 450°C achieved the highest hydrogen permeability of 1.09×10−8molm−1s−1Pa−0.5 at 450°C in the third cycle. This is a 58% increase on the value measured for the as-received Pd60Cu40 wt% membrane under the same conditions.This improvement can be attributed to a Pd-rich Pd–Cu face centred cubic (FCC) phase forming through interdiffusion between the Pd thin film and bulk Pd–Cu membrane as a result of the test conditions used during hydrogen permeability measurements. This introduces a larger hydrogen concentration gradient across the membrane due to the relatively high hydrogen solubility of the Pd-rich Pd–Cu FCC phase resulting in the observed increase in permeability.The Pd60Cu40 wt% membranes coated with a ~1400nm and ~800nm thick Pd thin film retained an almost pure Pd surface throughout cycling between 50 and 450°C with a feed and permeate hydrogen pressure of 445 and 100kPa, respectively. For the deposition technique and test conditions used throughout this work, these surface modified Pd–Cu membranes appear to stabilise the Pd thin films upon cycling across the critical temperature of 295 °;C.
Highlights
In the Pd–Cu system, diffusivity of hydrogen in the body centred cubic (BCC) phase is two orders of magnitude greater than in the FCC phase [14,15,18,19]
The aim of this work is to explore the possibility of creating a Pd-rich Pd–Cu FCC phase on the surface of a BCC Pd60Cu40 wt% membrane that is stable under typical operating conditions to determine the effects on hydrogen permeability
Eq 1 was determined from a line of best fit of the Fig. 2 data where xPd is the Pd concentration given in at%
Summary
In the Pd–Cu system, diffusivity of hydrogen in the BCC phase is two orders of magnitude greater than in the FCC phase [14,15,18,19]. At the Pd60Cu40 wt% composition, above 450 °C the disordered FCC phase begins to form and at temperatures higher than 600 °C only this phase exists. The Pd-rich Pd–Cu FCC phase with the composition Pd100ÀxCux wt% (0 r x r 20) has relatively high hydrogen solubility [20,21,22] and an enhanced resistance to H2S contamination over the BCC phase [10,12].
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