An investigation of the relationship between the thermochemistry and emission behavior of thermionic cathodes based on the barium oxide-scandia-tungsten trioxide ternary system.

摘要

It has been established that the addition of scandium to thermionic cathodes, both oxide and dispenser type, results in a reduction of work function. A number of experiments have been reported on various scandate cathode configurations, including those which incorporate scandium (or its oxide) into bulk and as a component of a surface layer. In addition, a number of scandium-containing compounds have been studied in various cathode designs. In order to understand the mechanism responsible for the improved emission properties displayed by scandate cathodes it is necessary to first gain an understanding of the thermochemistry of the cathode materials system.; In this investigation, two isothermal sections of the BaO{dollar}cdot{dollar}Sc{dollar}sb2{dollar}O{dollar}sb3cdot{dollar}WO{dollar}sb3{dollar} ternary system, one at 1100{dollar}spcirc{dollar}C and one at 950{dollar}spcirc{dollar}C, have been explored. The ternary system consists of eight binary compounds and one ternary compound, the existence of which was verified in this study. Electron emission and conductivity measurements were conducted on the nine compounds existing in the BaO{dollar}cdot{dollar}Sc{dollar}sb2{dollar}2O{dollar}sb3cdot{dollar}WO{dollar}sb3{dollar} ternary system. Emission and conductivity tests were also conducted on selected compositions within the ternary system. The emission data was analyzed utilizing a model developed by Wright and Woods describing emission from a semiconductor material. Furthermore, the current density and work function values obtained for the samples were examined for correlations with data reported for current scandate cathode configurations. Several samples were identified which correlated with the currently reported behavior for scandate cathodes and also displayed agreement with the Wright and Woods model. A reaction mechanism was identified which demonstrates how these materials are forming in current scandate cathode configurations.