Composite Rare Earth Doped Tungsten Matrix Dispenser Cathode

Scandate cathode has outstanding properties of high emission at low work temperature. It's the only thermionic cathode which can suffice to the development of new electronic device's requirement. Since non-uniform electronic emission, poor recovery after ion bombardment and too expensive of Sc2O3, scandate cathode has not been vastly used.In this dissertation, Eu2O3-Sc2O3, Y2O3-Sc2O3 co-doped tungsten powders and impregnated cathodes related to these powders have been prepared by pressing, sintering and impregnating for the first time. The properties of these doped powders, the microstructure and composition of these rare-earth co-doped tungsten matrices and cathodes have been investigated by size analysis, XRD, SEM and EDAX. The electronic emission performances of these cathodes are measured in UHV Electron Emission Surveyor. AES is adopted to analyze the atom composition and diffusion behavior of active elements on cathode surfaces. The relationship between emission capability and constitution of cathode surfaces has been studied.S2(5wt%Sc2O3), E1(1wt%Eu2O3-5wt%Sc2O3), E3(3wt%Eu2O3-3wt%Sc2O3), Y3(3wt%Y2O3-3wt%Sc2O3), Y4(4wt%Y2O3-2wt%Sc2O3) and Y6(6wt%Y2O3) doped tungsten powders have been synthesized by Sol-Gel and two-step hydrogen reduction methods. The effects of the technological parameters of pressing, sintering and impregnating on the porosity and content of impregnant in the cathode have been studied. The observation on the microstructures of matrices and cathodes indicate that EuScO3 exists in sintered matrices and cathodes of E3, while Sc2O3 and Y2O3 form a complete solid solution in matrices of Y3.The influence of microstucture to the emission properties of cathodes have been discussed.The emission properties of the six kinds of impregnated dispenser cathodes have been measured. Y3 cathode exhibits excellent emission performance. The current density Jdiv reaches 50 A/cm2 at 850℃b, which has reached the best emission level in the world while its Sc2O3.content reduced. The emission of E3 cathode is non-uniform and the emission capabilities of E1 and E3 cathode are lower than S2. Emission capability of Y4 and Y6 cathode is similar as that of normal Ba-W cathode. The influencing factors of emission properties have been analysed and found that emission capabilities of rare-earth co-doped cathodes are obviously related to the content of Sc2O3, the high content of Sc2O3 in some extent, the high emission capability can obtain.. Y3 cathode still has excellent emission capability though cheap Y2O3 partially substitutes for expensive Sc2O3, this has great significance for reducing the cost of cathode.The constitution of active elements on avtivated cathode surface is analysed by AES. It is found for the first time that only Sc,Ba and O can diffuse into surface for S2, E1, E3 and Y3 cathodes, but Y and Eu cannot diffuse into cathode surface.The relationship between emission capability and constitution of Sc, Ba and O is...