The interchange of hydrogen in the adsorbed film on tungsten

Source abstract

Abstract Films of tungsten have been prepared, by evaporation from a filament, which bring the reactions pH2=oH2 and H2+D2=2HD to equilibrium in a few minutes at 77° K. Their real surface area could be estimated as about 450 cm.2, from a measurement of the quantity of hydrogen which was rapidly and irreversibly adsorbed at 293° K. A WH film prepared by contacting the evaporated film with gaseous hydrogen showed a rapid interchange with deuterium gas at 193 and 293° K. From the interchange data a calculation of the surface area of the film was made, giving a value in good agreement with that cited above. An approximate treatment suggests that hydrogen and deuterium are equally strongly adsorbed on tungsten at 293° K. At 77° K the exchange equilibrium is displaced in favour of deuterium in the gas phase, so that no interchange could be detected between a WH film and gaseous deuterium . The interchange that was found to occur between gaseous hydrogen and a WD film was less than one would expect from results at 193° K. It was concluded that at 77° K only 20-40 % of the chemisorbed deuterium is sufficiently reactive to interchange with hydrogen gas, in the time of the experiment. A likely explanation for this is a slight variation over the tungsten, surface of the WD adsorption energy.