Work function variations of incandescent filaments during self-cooling in vacuum

A novel method of dynamic measurement of work function (WF) variations of hot metal filaments is described. It is essential in this method that electron emission current (Ie) is recorded during filament self-cooling when no heating power is supplied, thereby Ie is not disturbed by the potential gradient along the filament. WF shift due to the presence of a low-pressure gas, where the main active compounds are O2 and H2O, is calculated from an equation derived on the basis of the Richardson formula. The relative increase of WF found by this method was 5 times larger for tungsten than that for tantalum over the entire temperature range from 900 to 1800 K. Our method may be used in research studies of adsorption-related phenomena on metallic surfaces at high temperatures.