Palladium-Diaphragm Hydrogen Pump

Abstract

It has been found possible to evacuate hydrogen from a container into the air by the use of a heated Pd or PdAg alloy diaphragm. This effect is not the expected diffusion of hydrogen from a region of high hydrogen pressure to a region of lower hydrogen pressure, but a true pumping from a region of low hydrogen concentration to a region of higher hydrogen concentration. This pumping occurs only if the region of higher hydrogen concentration is in an oxidizing atmosphere and the region of lower hydrogen concentration is in a reducing atmosphere or a good vacuum. Pumping speeds for hydrogen up to 0.25 liter/sec per cm² of diaphragm have been observed for Pd and Pd‐25% Ag alloy 0.004 in. thick while operating between 500 and 600°C. It has been found possible to pump down to a hydrogen pressure of 10⁻⁹ mm Hg while the hot Pd diaphragm was exposed to air. Ti and Ni diaphragms were found to exhibit similar pumping characteristics, but much lower pumping speeds were observed.