Method for preparing pressed scandia-doped dispenser cathodes using microwave sintering

A method of preparing a pressed scandia-doped dispenser cathode using microwave sintering, the method comprising:

• preparing precursor powders by:
• dissolving ammonium metatungstate hydrate, scandium nitrate, aluminum nitrate, barium nitrate and calcium nitrate in water under a room temperature to obtain solutions, respectively;
• mixing a solution of the ammonium metatungstate hydrate and a solution of the scandium nitrate to obtain a mixture;
• mixing a solution of the barium nitrate, a solution of the calcium nitrate, and a solution of the aluminum nitrate to obtain a nitrate solution;
• adding the nitrate solution, while performing constant agitation, to the mixture;
• and
• obtaining precursor powder by spray drying, wherein a feeding rate is 200 ml/h-600 ml/h, a blast rate is 0.4 m3/min-0.6 m3/min, an inlet temperature is 150° C., and an outlet temperature is 90-96° C.;
• performing decomposition and reduction of the precursor powder by:
• decomposing the precursor powder in a muffle furnace for 3 hours to remove powder containing C and N in the precursor powder under a condition including a temperature of 550° C. and air or oxygen atmosphere to obtain oxide powder;
• and
• performing a reduction process of the oxide powder in a tube or furnace under hydrogen atmosphere by:
• keeping the temperature at 450-550° C. and maintaining it for 2-3 h;
• and
• raising the temperature to 800-850° C. and maintaining it for 2-3 h to obtain doped tungsten powder;
• and
• pressing and sintering a cathode by:
• pressing the decomposed powder under a certain pressure using molds;
• placing green bodies in an auxiliary heating and insulation combining device;
• placing the auxiliary heating and insulation combining device in a microwave cavity of a microwave source;
• turning on the microwave source and raising the temperature in the microwave cavity with a constant rate until 800-850° C.;
• maintaining the temperature for 5 minutes;
• raising the temperature with a rate of 10˜15° C./min until 1400-1500° C.;
• maintaining the temperature for 10-30 min;
• and
• obtaining the cathode after cooling the cathode to the room temperature.