Barium Strontium Tungstate Cathode Manufacturing Scheme

Barium strontium tungstate cathode as tungstate cathode first appeared in the form of compacted cathode in the 1960s. The cathode is made of barium strontium tungstate (Ba₅Sr (WO₆)₂) as an active material for emission. The synthesized barium strontium tungstate and activator, as well as tungsten powder with a certain size, are pressed and sintered in hydrogen at high temperature.

Because of the pressing process, the cathode is not suitable to be processed into various shapes, and the influence of sintering temperature and pressure, the cathode emitter is prone to shrink after sintering, which leads to the surface cracking of the cathode and other problems, which limits the application of the cathode. With the development of vacuum electronic devices in the direction of high power, high frequency, high reliability and long life, it is necessary to further improve the emission current density of cathode, reduce the working temperature of cathode, reduce the evaporation rate of cathode and prolong the life of cathode.

For this reason, some scholars have proposed a preparation method of impregnated barium strontium tungstate cathode to solve the difficult practical problems of traditional tungstate cathode. The main processes are as follows:

(1)After 72 hours of mixing BaCO₃, SrCO₃ and WO₆ massage with Erbi 5:1:2 ball mill, the mixed powder materials were pressed into small cakes with a diameter of 20 mm and a thickness of 2-3 mm under the pressure of 20 kg/cm².

(2)Put the pressed cake into the crucible and sinter in the muffle furnace with air atmosphere. The tungstate containing barium strontium tungstate (Ba₅Sr(WO₆)₂) was synthesized by heating for 30 minutes at 400 (+25) ℃, then gradually heating up to 800 (+50) ℃ for 1 hour, and then heating up to 1400 (+50) ℃ for 3-4 hours.

(3)The tungstate obtained by step (2) and ZrH₂ with a weight ratio of 12.5% were ground and mixed in an agate pot for 2 hours to obtain the active salt powder for impregnation.

(4)The cathode with tungsten sponge at the top is embedded in the salt powder obtained by step (3) and the system is heated in a hydrogen furnace to 1850 (+20 ℃) to melt tungstate and infiltrate into the sponge by capillary action. The diameter of the cathode is 2.5mm, and the porosity of the tungsten sponge is 24-26%.

(5)After the cathode cake is dipped in salt, the redundant salt on the cathode surface and the edge is removed by the cathode obtained in step (4) on the lathe to ensure the cleanliness and size of the cathode surface and complete the preparation of the cathode.

The new scheme enlarges the types of barium-tungsten cathodes and improves the emission current density. The tungstate with lower saturated vapor pressure reduces the evaporation rate of the active material and prolongs the cathode life, thus solving the difficult practical problem of the traditional pressed tungstate cathode.

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