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

• X-ray diffraction on a tubular substrate to study alloying process.
• Reduced Pd-10Au annealing time by an order of magnitude using high pressure H2.
• Annealed 5 µm, 10 wt% Au in Pd sequentially plated membrane in 9 h.
• Approximated activation energy of annealing process using transient diffusion model.
• Apparent Eact of H2 permeation as in situ parameter to judge extent of annealing.

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 µm 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 (H2) on annealing time at temperatures between 450 °C and 550 °C. X-ray diffraction (XRD) was used to study the progress of annealing, where it was observed that a ~10 wt% Au membrane could be annealed in 9 h at 550 °C and 3 MPa H2 whereas it took 120 h to anneal a similar membrane at 550 °C and 0.1 MPa H2. Another ~10 wt% Au membrane was annealed in less than 2 days at 450 °C and 3 MPa H2. 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 (Eact) could be used as an in situ parameter to judge the extent of annealing. In this technique, apparent Eact 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 Eact for a membrane with a homogeneous Au distribution.