Adsorption of Oxygen and Carbon Monoxide on Tungsten

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Abstract
The adsorption of oxygen, carbon monoxide, and nitrogen on a tungsten ribbon filament at 300°K has been measured by means of the flash filament technique. An omegatron rf mass spectrometer has been used to measure pressure. It is shown that oxygen pressures cannot be measured satisfactorily with ionization gauges of the hot-tungsten-filament type. The total amounts of gases adsorbed by tungsten are 5.7×1014 molecules/cm2 for oxygen, 5.8×1014 for carbon monoxide, and 1.8×1014 for nitrogen. The sticking probabilities of these gases on the uncovered surface are 0.65 for oxygen, 0.62 for carbon monoxide, and 0.42 for nitrogen. All of the carbon monoxide and nitrogen desorb from the heated filament as the gases CO and N2; less than 1 percent of the oxygen desorbs as O2. The filament pumps oxygen at a rate of 9 liters/cm2 sec at temperatures above 2000°K.