Study On The Microstructure And Emission Performance Of The Rare Earth-Molybodenum Cathode Materials

Based on the former study of our research group, the research on the propertiesof rare earth oxide-molybdenum cathode materials was done in this paper. Twelvekinds of rare earth oxide doped molybdenum powder were prepared for the first timeby sol-gel method. For comparison, the traditional method called as liquid-soliddoping method, was used to prepare rare earth oxide doped molybdenum powderwith the same composition. The rare earth oxide-molybdenum thermionic cathodeand secondary emission cathode were molded by isostatic press with pressure of 200MPa/cm2 and sintered by resistance furnace under a continuous flow of hydrogen. Inaddition, the thermionic and the secondary emission properties were measured,respectively. The composition, microstructure, particle size distribution, surfaceanalysis and the element analysis of these body materials were studied by TG-DTAXRD, SEM, AES and Laser particle analyzer. The rare earth oxide-molybdenumsecondary emission mechanism was discussed and a new model of electronmovement was proposed. The results showed that the average particle diameter of the powder prepared bysol-gel method was about 100nm, less than that made by solid- liquid doping method.TG-DTA result showed that rare earth oxide can react with Mo2C to producemolybdenum and the reaction temperature depends on the kinds of rare earth oxidereactant. The rare earth oxide doped molybdenum thermionic cathode prepared by sol-gelmethod had good thermionic properties and the emission current density of thecarbonized La2O3-Mo cathode could reach 7.96A/cm2 at 1500 . The SEMobservation displays that the rare earth oxide has particles about 80nm in size anddistribute evenly in the material which is favorable for the diffusion of rare earthfrom the inner to the surface to supply those evaporated from the surface. The resultalso showed that the carbonized La2O3-Mo cathode had good anti-exposure toatmosphere. The rare earth oxide-molybdenum secondary emission cathode prepared by sol-gelmethod also had the good secondary emission property. The maximum secondaryemission coefficient of Y2O3-Mo cathode was 2.63, higher than that of the cathodeprepared by solid- liquid doping method, which can meet practical magnetronneeds( >2.0). The secondary emission coefficients have relation with rare earthoxide content. The material showed the tendency that the secondary emission -III-北京工业大学工学硕士学位论文coefficients increase with the increase of the content of the rare earth oxide. Theresults also suggest that carbonization retards the secondary emission of the cathode. Based on a serial results, it can be deduced that the secondary emission of rareearth oxide-molybdenum originate from both rare earth oxide and molybdenum, andfree electrons show the trend to move from molybdenum to rare earth.