New Scandate Type Dispenser Cathode

In this work, the matrix materials of impregnated scandate dispenser cathode are made by using Solid-Liquid doping method in which adding a small amount of rhenium compound. Meanwhile, scandia doped tungsten powder is made by using Liquid-Liquid doping method (Sol-Gel) in order to improve uniform distribution of scandia in tungsten matrix. The matrix of impregnated and pressed dispenser cathode is made by high temperature sintering under the protection of hydrogen. The properties of the doping powder and the microstructure of scandia doped tungsten matrix have been investigated by using modern analysis techniques, such as XRD, SEM, EDS and AES. At the same time, the emission capabilities of two kinds of cathodes are measured in UHV system. In this paper, the techniques on the preparation of impregnated cathode with sub-micron structure by using powder with sub-micron scale, the effect of added content of scandia on cathode emission and mechanism of cathode emission have been discussed. Moreover, the techniques on the preparation of the pressed cathode by using superfine powder have also been studied. The scandia doped tungsten powder is made by using Solid-Liquid doping method which scandium nitrate is doped into the blue tungsten powder and adding different amount of rhenium. It is indicated that the more the content of rhenium, the finer the scandia doped tungsten powder, even the size of this powder has reached the nanometer scale. In addition, scandium-tungsten powder which is made by using Liquid-Liquid doping method can improve the uniform distribution of scandia in tungsten powder. Based on a series of studies on the technique of pressing, sintering and impregnating, the new technique which is suitable for the preparation of cathode mixed by using the powder with sub-micron scale has been found out. The result indicated that the size of cathode matrix still remained sub-micron scale. The porosities and the content of impregnating of this cathode can meet the requirement of dispenser cathode. The microstructure of the cathode with uniform porosity will be favorable for cathode emission. The emission capability of impregnated dispenser cathode with sub-micron structure has been measured. The result showed that the current density at 850℃_b has reached 50 A/cm² by Jdiv, and the current density at 850℃_b has reached 100 A/cm² by J_10%. This result is the best emission level all over the world. Moreover, the life of this cathode has exceeded 5000 hours, and the life test is still continuing. It is also indicated that increasing amount of scandia can improve the cathode emission capability, and proper activation have an important role in improving the cathode emission capability.