Binary Composite Tantalum Tungsten Cathode

Magnetron is currently the most efficient microwave device, and it has a huge application market in the fields of civil heating and radiology. In recent years, with the rapid growth of microwave application markets such as radiology and container inspection, magnetrons continue to develop in the direction of high power, high frequency, miniaturization and low cost.

When the magnetron is oscillating, the cathode is required to provide sufficient initial thermal emission current and as large a secondary electron emission coefficient as possible. At present, the tungsten-tungsten cathode widely used in magnetrons consumes too much enthalpy due to the strong re-bounce of electrons in the device, resulting in a decrease in lifetime, and the secondary electron-emitting capability is difficult to meet the requirements of high-power microwave devices.

In order to improve the cathode performance of the magnetron, on the basis of the rare earth oxide doped compacted thorium tungsten cathode, some scholars have developed a binary composite tantalum tungsten cathode (Y₂O₃-La₂O₃)_­­, which has no reduction in thermal emission. The secondary electron emission performance is better, and the manufacturing process of the cathode material includes:

(1) using ammonium metatungstate as raw material, adding cerium nitrate aqueous solution, cerium nitrate aqueous solution, cerium nitrate aqueous solution, aluminum nitrate aqueous solution and calcium nitrate solution to the ammonium metatungstate aqueous solution, and the rare earth oxide mixed by Y₂O₃ and La₂O₃ accounts for the cathode. 5-20% by weight of the total amount of the material, the ternary nitrate accounts for 5-15% by weight of the total weight of the cathode material, and then added to the citric acid solution, placed in a water bath of 70-90 ° C until a sol is formed, and then at 100-150 ° C Dry until a gel is formed;

(2) decomposing the gel at 500-600 ° C under atmospheric atmosphere for 2-4 h;

(3) The decomposed powder is reduced under a hydrogen atmosphere, the first reduction temperature is 450-550 ° C, and the temperature is 2-4 h; the second step is 750-950 ° C, and the heat preservation is 1-2 h, and the reduced powder is Pressing pressure is 1-3t/cm2, sintering temperature is 1450-1650 ° C, and sintering is performed for 1-5 min to form a cathode.

The Y₂O₃-La₂O₃ system is used to composite the rare earth binary composite yttrium-tungsten cathode. Due to the liquid phase doping technology, the rare earth elements lanthanum and cerium are uniformly distributed in the cathode, and the compact cathode preparation process is simple, the process repeatability is strong, and the scale is convenient. produce. The results of electron emission performance test show that the rare earth binary composite tantalum tungsten cathode material has a total rare earth content of 20% (including Y₂O₃: La₂O₃ quality ratio of 3:1), and the secondary emission coefficient is the highest when it is started at 1200 °C, which can reach 5.34. Significantly higher than barium.

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