Effects of fabrication technique upon material properties and permeation characteristics of palladium-gold alloy membranes for hydrogen separations

Abstract

This work highlights new research into the fundamental properties of palladium-gold alloy membranes. Two types of self-supported palladium-gold foils were studied; membranes produced by magnetron sputtering and membranes produced by cold-working. The cold-worked membranes had thicknesses of 25 microns and gold contents from 0-40 wt% Au, while the sputtered films ranged from 10-31 microns in thickness and 5-10 wt% Au. These films were characterized by single-gas permeation testing in the temperature range of 473-773K and at pressures of up to 772 kPa. Membranes were studied before and after testing by XRD, XPS, XRF, and SEM/EDS. Hydrogen permeability in the 0-20 wt Au% range was found to be a function of synthesis technique as much as alloy content, with no single alloy having superior permeability at all temperatures. Sputtered materials had generally higher permeability than cold-worked materials of equivalent composition, although the thicker sputtered membrane had reduced hydrogen permeability compared to its thinner counterparts. In this composition range, the addition of gold generally acted to reduce activation energy of hydrogen permeation. The differences in membrane permeability by fabrication technique are primarily attributed to preferential orientation effects. These effects also appear to contribute to other permeation phenomena, such as low-temperature hydrogen embrittlement, the dependence of flux on feed pressure, and the formation of long range ordered surface phases.