Thermal Stability Calculation of Typical Phases in Tungsten Cathodes

Thermodynamic calculations were carried out on typical tungsten cathode materials using Factsage software within a temperature range of 1000-3400 degrees C. The relationship between the phase stability and electron emission performance of the cathode in a vacuum environment and under a protective atmosphere was investigated. The thermodynamic stability of tungsten cathodes doped with different proportions of carbides and oxides was calculated. It was found that when the doped phase (ThO2, La2O3, Y2O3, Lu2O3, Er2O3, Gd2O3, TiO2, ZrO2, HfO2, ThC2, LaC2, YC2, TiC, ZrC, and HfC) in the cathode starts to be consumed, the electron emission performance of the cathode will decline. Therefore, the high-temperature stability of the doped phase carbides and oxides also affects the operating temperature of the cathode. To verify these results, this study tested the electron emission performance of W-La2O3, W-ThO2, W-ZrO2, W-ZrC, and W-HfC, plotting their volt-ampere characteristic curves. The results indicated that the W-La2O3 cathode exhibits the best emission performance at low temperatures, while the W-ThO2, W-ZrO2, W-ZrC, and W-HfC cathodes showed better emission performance at high temperatures. The experimental results are in good agreement with the simulation results. The thermal stability of the doped phase is closely related to the high-temperature thermal stability of the cathode.