Evaporation of lanthanum on the surface of rare earth lanthanum-molybdenum hot cathode materials

• Mosten
• 19 Mar

The evaporation rate of lanthanum at different temperatures was calculated theoretically, and the effect of lanthanum evaporation on the thermal electron emission and stability of carbonized Mo-La₂O₃ thermal cathode material was analyzed. The results show that the diffusion rate of lanthanum in the cathode is higher than the evaporation rate of lanthanum on the cathode surface when the temperature is 1623~1700K. The formation and evaporation of elemental La on the surface of Mo-La₂O₃ cathode remain in balance, and the cathode emission is stable. When the operating temperature exceeds 1 700K, the evaporation rate of lanthanum on the cathode surface exceeds the diffusion rate, and the emission current decreases gradually. The emission performance of Mo-La₂O₃ cathode FU-6051 tube at different temperatures is tested. The thermodynamic calculation results are well interpreted.

1) When Mo-La₂O₃ cathode is emitted at high temperature, the diffusion rate and evaporation rate of lanthanum, the active substance in the material, increase exponentially with the temperature. When the temperature is lower than 1700K, the evaporation rate of lanthanum is less than the diffusion rate. When the temperature is higher than 1700K, the evaporation rate of elemental lanthanum on the cathode surface is greater than the diffusion rate of lanthanum in the cathode. 2) In the temperature range of 1623~1700K, the diffusion of lanthanum in the cathode and the evaporation of lanthanum on the surface balance, and the content of elemental lanthanum on the surface of the cathode remains unchanged during the operation of the cathode, and the cathode can emit stably with high current. When the temperature is higher than 1700K, the evaporation rate of La on the cathode surface is greater than the diffusion rate of La in the cathode, the active substance on the cathode surface decreases, and the emission decreases. However, when the temperature is lower than 1 623 K, the temperature is too low to maintain the activation state of the cathode surface, so the cathode emission decreases.