Mo-Y_2O_3阴极发射机理研究

采用热重分析、X射线衍射、扫描电镜及光电子能谱等方法对Mo Y2 O3阴极中钇的价态进行了研究 ,探讨了该阴极的发射机理。Y2 O3与Mo2 C在 1173K以上发生化学反应。Y2 O3与Mo2 C混合物经 1873K高温处理后 ,产物中含有两种价态的Y :Y0 和化合态的Y3 。Mo Y2 O3阴极的发射可用原子膜机理解释 ;在阴极工作过程中 ,Mo2 C将Y2 O3还原成单质钇 ,钇覆盖在钼基体表面 ,降低了基体钼的逸出功 ,促进了阴极的发射。

Study on Emission Mechanism of Mo-Y_2O_3 Cathode

The valence of element yttrium of Mo-Y2O3 cathode materials was studied by using thermal weight analysis, X-ray diffraction analysis, scanning electron microscopy and X-ray photoelectron spectrum. On the basis of experiment results, the emission mechanism of Mo-Y2O3 cathode was discussed. It is proved that yttrium oxide can be reduced by molybdenum carbide. The reaction between Y2O3 powder and Mo2C happens at 1173K. After the powder mixture of Y2O3 and Mo2C is heat-treated at 1873K, yttrium exists in two kinds of chemical state:yttrium of zero valence and yttrium of three valences. The emission of Mo-Y2O3 cathode can be explained by the following mechanism. A monoatomic layer of metallic yttrium at the surface forms and causes the emissivity of the cathode. The film can be created after yttrium oxide reduced to metal yttrium by molybdenum carbide during activating period and operation of the filament, and yttrium subsequently diffuses to the surface mainly along grain boundaries and migrates over the surface. Yttrium at the surface doesn′t give emission current, but the monoatomic active surface layer has a lower work function than clean molybdenum.