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

The present work focuses on the synthesis and gas permeation propertie s 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 R F magnetron sputtering equipment. The coated Pd-Ag membranes exhibit t he same composition and phase structure as those of the Pd-Ag foil use d as the target in sputter deposition. The hydrogen to nitrogen separa tion factor of the ultrathin Pd-Ag membrane is 5.7 at 250 degrees C an d increases with increasing temperature. Under proper preparation cond itions, use of a pinhole-free gamma-alumina support is the key to ensu re the gas-tightness and high-selectivity of the coated Pd-Ag membrane s. A method is demonstrated for studying hydrogen permeation through u ltrathin metallic films. Hydrogen permeation data at different hydroge n pressures and temperatures (100-250 degrees C) are reported to exami ne the mechanism of hydrogen permeation through the ultrathin metallic membranes. The experimental results clearly indicate the dominant rol e of surface reactions for hydrogen permeation through ultrathin metal lic films at low temperatures.