The Effect of Impurity Migrations on Thermionic Emission from Oxide Cathodes

A comparison of thermionic emission from oxide cathodes with different base alloys showed the dependence of the work function on migrating impurities from tube parts other than the cathode. The effect of the base metal alone could be evaluated properly only by the use of a special diode structure which did not contribute any impurities toward the reduction of the oxide-coating. In the test method used, saturated emission was measured but the anode voltage was kept below the decomposition energies of most of the compounds apt to be found on the plate.