Effect of Scandia on Tungsten Oxide Powder Reduction Process (b)

Vacuum electronic devices have a wide application in civil and military fields such as communication, radar and industrial heating. Cathode is an important component in the device since it provides the required electronic beam for the device. Among all the electron emitters, scandate cathodes have aroused great attention among all the cathodes due to their copious emission property.

It has been found in the previous work, the raw powder properties such as morphology, particle size and size distribution greatly affected the emission property of the cathode. The diffusion and distribution uniformity of rare-earth elements would be enhanced if the structure dimension of the emitter decreased from micrometer to sub-micrometer even to nanometer, i.e., the electron emission property of emitter would be improved with the diminution of the micro-structure dimension of cathode matrix.

Scandium oxide doped tungsten powders have been prepared by a new method of spray drying combined with two-step hydrogen reduction. Spray drying has some advantages such as the particle size can be controlled in the single step.

The addition of Sc2O3 shifted the hydrogen consumption peak to the lower temperature side. Namely, the reduction temperature of tungsten oxide decreased with Sc2O3 addition. Adding scandia could decrease the particle size of tungsten. The scandia doped tungsten powder prepared by spray drying method had sub-micrometer size in the range of 0.1μm to1μm in semispherical shape and scandium distributed evenly in the powder. Using scandia doped tungsten powder, sub-micro-structure cathode matrices with semispherical grains and homogenous distribution of scandium was obtained.

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