Rapid annealing of sequentially plated Pd-Au composite membranes using high pressure hydrogen

In this work, the time-consuming process of annealing Pd-Au alloy composite membranes, fabricated by sequential electroless plating, has been revisited. Composite Pd-Au/YSZ membranes approximately 5 mu m thick with compositions ranging from 8 wt% to 10 wt% Au were fabricated by the bi-layer fabrication technique. Using these membranes, we investigated the effect of changing the pressure of the annealing gas (H-2) on annealing time at temperatures between 450 degrees C and 550 degrees C. X-ray diffraction (XRD) was used to study the progress of annealing, where it was observed that a similar to 10 wt% Au membrane could be annealed in 9 h at 550 degrees C and 3 MPa H-2 whereas it took 120 h to anneal a similar membrane at 550 degrees C and 0.1 MPa H-2. Another similar to 10 wt% Au membrane was annealed in less than 2 days at 450 degrees C and 3 MPa H-2. Complete annealing was confirmed using energy dispersive x-ray spectroscopy (EDS) with multiple spot scans throughout the thickness of the membrane indicating a uniform Au composition. Additionally, it was found that the apparent activation energy for hydrogen permeation (Ear) could be used as an in situ parameter to judge the extent of annealing. In this technique, apparent Ear decreases as the membrane anneals, reaching a minimum value which is characteristic of its Au composition. Additional annealing time does not further change the apparent Ear for a membrane with a homogeneous Au distribution. (C) 2016 Elsevier B.V. All rights reserved.