Analysis of the “Oxygen Pumping Effect” of Tungsten Cathodes in Ionization Gauges and Mass Spectrometers

Abstract

The quasiequilibrium treatment of gas-solid reactions (J. C. Batty and R. E. Stickney, J. Chem. Phys. 51, 4475 (1969)] is employed to develop a semiquantitative description of existing experimental data on the “pumping” of O2 by a hot tungsten filament [J. H. Singleton, J. Chem. Phys. 45, 2819 (1966)]. The results indicate that the present analysis provides a useful means for predicting the dependence of the O2 “pumping” speed on the operating conditions (e.g., O2 partial pressure, filament temperature) and on system design (e.g., conductance, pumping speed, wall material). The analysis is applied to estimate the error of an O2 partial pressure measured by a partial pressure analyzer or mass spectrometer having a tungsten cathode. It is also shown that the analysis provides a semiquantitative explanation of existing experimental data on the effects of O2 pressure and filament temperature on the rate of emission of ions (impurities) from a hot tungsten filament [H. F. Winters et al., J. Appl. Phys. 34, 1810 (1963)].