INVESTIGATION OF THE ADSORPTION OF OXYGEN ON TUNGSTEN BY MASS SPECTROMETRY

Summary The deviations of the thermal ionization characteristics from the Langmuir slope have been examined, for metals on tungsten, by means of a 60° single-focusing mass spectrometer for temperatures below 2500°K. The deviations are caused by adsorption of gases, especially oxygen, on tungsten, which increases the work function. This is confirmed by measurements of the time taken to reach the adsorption equilibrium. The curves of ionization efficiency against temperature exhibit structures which indicate that there are different types of adsorption centres for oxygen. An adsorption theory has been developed which explains these curves as well as those of adsorption against time. The adsorption energies for oxygen on the different types of adsorption centre, and the relative abundance of these centres, is determined.