Hydrogen permeability of palladium-copper alloy membranes

We are developing hydrogen permeable membranes for application to a membrane reformer. In this study, we have studied hydrogen permeability of palladium-copper (Pd-Cu) alloys that show beta-phase in certain composition and temperature ranges in the binary phase diagram. Three compositions of Pd-Cu alloys were prepared: Pd-30 mass%Cu, Pd-40 mass%Cu and Pd-45 mass%Cu. All these alloys were rolled to foils of 100 microns thickness, and only the Pd-40 mass%Cu alloy was re-rolled to 20 microns thick. As a result of X-ray diffraction analyses, the Pd-30 mass%Cu and Pd-40 mass%Cu membranes showed mostly alpha-phase, while the Pd-45 mass%Cu showed beta-phase mixed with minor alpha-phase at room temperature. Hydrogen permeability of the membrane samples was measured in the temperature range of 350-600 degrees C with 0.1-0.3 MPa hydrogen pressure difference. The permeability of both Pd-30 mass%Cu and Pd-45 mass%Cu were about one order of magnitude lower than that of Pd-23 mass% Ag, and it was found to monotonously increase with increasing temperature. The permeability of Pd-40 massy%Cu also increased with temperature to 1.2 X 10(-8) mol (.) m(-1) (.) s(-1) (.) Pa-1/2 at 450 degrees C, but it drastically decreased over 500 degrees C. And different permeability was obtained at the same temperature of 450 degrees C after different treatments: hydrogen introduction at 450 degrees C and hydrogen introduction at 350 degrees C followed by heating to 450 degrees C. This suggests that crystal structure and condition of phase transition change by the presence of hydrogen in the crystal or solid solubility of hydrogen in this alloy. It was also found that the existence of beta-phase was important to give the highest hydrogen permeability of Pd-Cu alloy.