A study has been made of thermionic emission from tungsten filaments cataphoretically coated with alkaline earth oxides. It was found that the emission from the oxide-coated filament was not influenced by the variation of work-function with crystallographic direction of the base metal. A Richardson plot of emission at zero field yielded an apparent work function of 1.3 volts and an A value of 0.048 amp/cm2-deg2. In retarding potential data, the energy of thermionic electrons showed an apparent deviation from Maxwell-Boltzmann statistics. This deviation was interpreted as due to a potential drop through the coating. Such an interpretation led to a conductivity activation-energy of 1.3 volts. A strip theory of patches was used to explain the accelerating potential data. Satisfactory agreement with experiment was found with a patch amplitude of 0.2 volt and a period of 2×10−6 meter.
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C. P. Hadley (1953) studied this question.
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