Scandium Tungsten Diffused Cathode Preparation by Spray Drying Method

Cathode is the electronic source and the core part of vacuum electronic devices. Electron emission cathode material is the core component of vacuum electronic devices. At present, the main thermal emission cathode material used in microwave vacuum devices is based on alkaline earth metal Ba.

The impregnated scandium tungsten diffused cathode can be spray dried. It includes the following steps:

Step 1: ammonium tungstate and scandium nitrate were dissolved in water solution respectively. Then, the scandium nitrate solution was added to the ammonium tungstate solution and mixed with a concentration of 20-40g/L. The precursor powder was prepared by spray drying. The feeding speed was 400ml/h, the blowing rate was 0.4m³ /min-0.6m3/min, the inlet temperature was 150 degrees, the outlet temperature was stable at 95 ℃. The mass is 1%-20%, and the residual is tungsten.

Step 2: the powder prepared by spray drying method was decomposed for 2 hours at atmospheric temperature for 500-550 hours, and the composite oxide powder was obtained.
Step 3: Reduction of composite oxide powders in hydrogen atmosphere is carried out in two steps: first, the temperature is kept at 500-600 ℃ for 1-2 hours, and then the temperature is raised to 800-950 ℃ for 1-2 hours to obtain scandium oxide doped tungsten powders.

Scandium oxide doped tungsten powder prepared by the above method was pressed at pressure of 1 t/cm2 and sintered in hydrogen furnace at 1500 ℃ for 1 minute. Porous bodies of 3*1.5mm were prepared. Scandium oxide doped tungsten matrix containing Scandium diffusion cathode was obtained after impregnated with calcium barium aluminate.

In addition to retaining the advantages of liquid phase doping technology, the spray drying method simplifies the preparation process of precursor powder compared with sol-gel method, avoids the introduction of impurity elements, and has high repeatability and is easy to scale production. The current density of impregnated Sc-W diffusion cathode material can reach 35A/cm² at 850 C b, which is much higher than that of barium-tungsten cathode at the same temperature, and meets the requirement of cathode current density for devices. The impregnated scandium doped tungsten matrix cathode materials prepared by spray drying method have wide application prospects in various military and civilian vacuum electronic devices.

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