SYNTHESIS AND HYDROGEN PERMEATION PROPERTIES OF ULTRATHIN PALLADIUM-SILVER ALLOY MEMBRANES

The present work focuses on the synthesis and gas permeation properties of ceramic supported ultrathin palladium-silver alloy membranes. Pd-Ag films with a thickness ranging from 250 to 500 nm are coated on the surface of 3 nm pore sol-gel derived gamma-alumina support using an RF magnetron sputtering equipment. The coated Pd-Ag membranes exhibit the same composition and phase structure as those of the Pd-Ag foil used as the target in sputter deposition. The hydrogen to nitrogen separation factor of the ultrathin Pd-Ag membrane is 5.7 at 250 degrees C and increases with increasing temperature. Under proper preparation conditions, use of a pinhole-free gamma-alumina support is the key to ensure the gas-tightness and high-selectivity of the coated Pd-Ag membranes. A method is demonstrated for studying hydrogen permeation through ultrathin metallic films. Hydrogen permeation data at different hydrogen pressures and temperatures (100-250 degrees C) are reported to examine the mechanism of hydrogen permeation through the ultrathin metallic membranes. The experimental results clearly indicate the dominant role of surface reactions for hydrogen permeation through ultrathin metallic films at low temperatures.