【作者】 崔颖；

【导师】 王金淑；

【作者基本信息】 北京工业大学 ， 材料学， 2004， 硕士

【摘要】 本论文在课题组前期研究的基础上对稀土钼阴极发射材料进行了更为深入的研究 用一种新的方法 溶胶凝胶法制备了多种稀土钼粉末材料 并与液固掺杂法制备的稀土钼粉末材料相比较 探索和改进了制备的工艺 采用冷等静压压制 氢气气氛烧结方法制成了稀土钼热发射和次级发射体材料 测试了其热发射及次级发射性能 利用 TG-DTA XRD SEM AES 和激光粒度测试仪研究了材料的成分 微观形貌 粒度分布 表面分析 并与用传统液固掺杂法制备的材料进行了发射性能的比较 对稀土钼次级发射材料的发射机理进行了初步的探讨 提出了一种稀土钼次级阴极电子输运的理论模型 研究了材料的结构与次级发射性能之间的关系 研究结果表明 溶胶凝胶法制备的稀土钼粉末颗粒较传统液固方法制备的颗粒细小 平均粒径约为 100nm 稀土氧化物可与碳化钼反应生成单质钼 稀土种类不同 二者的反应温度不同 用溶胶凝胶法制备的稀土钼热阴极材料具有良好的热发射性能 其中碳化La-Mo 阴极 1500 时的电流发射密度可达到 7.96A/cm2 通过对它们的微观结构的研究发现 溶胶凝胶法制备的烧结体材料中稀土分布及大小更加均匀 颗粒基本在 80nm 左右 这种均匀弥散分布的细小稀土粒子更容易在阴极体内扩散和补充 同时发现碳化的 La-Mo 阴极具有优良的抗暴露大气的性能 稀土氧化物在空气中的稳定性与其种类有关 其中 La2O3稳定性最差 及易与空气中的 H2O 和 CO2反应生成复杂稀土化合物 稀土氧化物可与碳化钼反应生成单质钼 稀土种类不同 二者的反应温度不同 溶胶凝胶法制备的稀土钼次级阴极材料也具有良好的次级发射性能 其中Y-Mo 次级阴极的最大次级发射系数达到 2.63 比传统液固方法制备的 Y-Mo 阴极的次级发射的发射系数有了很大的提高 满足了磁控管对阴极材料的次级发射系数 2.0 以上的应用要求 次级发射系数与材料表面的稀土含量有关 随着稀土含量的增加 材料的次级发射系数有增长的趋势 另外 通过对碳化的稀土钼次级阴极研究发现 碳化不利于次级发射 根据一系列的稀土钼次级发射现象推断稀土钼次级发射的电子输运模型为 - I -<WP=5>北京工业大学工学硕士学位论文稀土与钼共同发射电子的结果 其中自由电子有从金属向稀土补充的趋势更多还原

【Abstract】 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-<WP=7>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.更多还原