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为了提高磁控管用稀土难熔钇盐阴极的热发射能力，探索Sc2O3掺杂对稀土难熔钇盐阴极热发射性能的影响机理，采用Sc2O3掺杂稀土难熔钇盐来制备阴极，并测试该阴极的热发射性能。热发射测试结果表明，Sc2O3掺杂能够有效的提高稀土难熔钇盐阴极的热发射能力。其中，3wt%Sc2O3掺杂能够最大的提高阴极的热发射能力，当阳压为300V，温度为1600℃时，3wt%Sc2O3掺杂阴极可以支取3.85A/cm2的热发射电流。而在相同条件下，未掺杂Sc2O3阴极，即稀土难熔钇盐阴极仅可以支取1.66A/cm2的热发射电流，3wt%Sc2O3掺杂能够将该阴极的热发射能力提升132%。寿命试验结果表明，当负载电流为0.5 A/cm2，温度为1500℃时，3wt%Sc2O3掺杂阴极的试验寿命已经超过4200h，且没有明显的衰减迹象。最后，利用SEM、EDS、XRD及AES等对阴极进行了详细的分析。结果表明，热发射测试过程中，一方面，掺杂的Sc2O3和Y2Hf2O7发生了置换固溶反应，生成了ScxY(2-x)Hf2O[7+(3/2)x]固溶体，造成了Y2Hf2O7晶格畸变，导致晶格处于高能状态，降低了阴极表面的逸出功，与此同时，Sc2O3中的Sc置换掉了Y2Hf2O7晶胞中Y，被置换出来的Y以金属单质形式存在，改善了阴极表面的导电性。另一方面，ScxY(2-x)Hf2O[7+(3/2)x]固溶体中会产生一定数量的Vo2+氧空位和自由电子，也使得阴极表面的导电性能得到了改善。最终，在这两方面的共同作用下，阴极的热发射能力得到了显著的提高。To improve the thermionic emission performance of the rare-earth refractory yttrium salt cathode used in the magnetron, the influence of Sc2O3 doping on its thermionic emission properties was explored. Cathodes were fabricated by incorporating different weight percentages of Sc2O3 into the rare-earth refractory yttrium salt matrix, and their thermionic emission properties were systematically evaluated. The experimental findings revealed that the doping of Sc2O3 significantly enhances the thermionic emission capability of the cathode. Notably, a doping concentration of 3wt% Sc2O3 yielded the most pronounced improvement in emission performance. The 3wt% Sc2O3-doped cathode could achieve a thermionic emission current density of 3.85A/cm2 under a 300 V anode voltage at 1600℃. In contrast, the undoped cathode supplied a current density of merely 1.66A/cm2 under identical conditions, demonstrating a 132% enhancement in thermionic emission efficiency with 3wt% Sc2O3 doping. Utilizing the Richardson line method coupled with data-fitting algorithms, the absolute zero work functions for undoped and Sc2O3-doped cathodes (3wt%, 7wt%, and 11wt%) were determined to be 1.42, 0.93, 0.98, and 1.11 eV, respectively. Longevity assessments indicated that the 3wt% Sc2O3-doped cathode had been stable for over 4200 hours without significant degradation under an initial load of 0.5 A/cm2 at 1400℃. Finaly, those cathodes had been analyzed by the XRD, SEM, EDS, AES respectively. The analysis results showed that during thermionic emission testing, the Sc2O3 and Y2Hf2O7 had undergone substitutional solid solution reactions, forming the ScxY(2-x)Hf2O[7+(3/2)x] solid solution. This process induced lattice distortion in the Y2Hf2O7, placing it in a high-energy state and thereby reducing the work function on the cathode’s surface. Concurrently, Sc from Sc2O3 displaced Y within the Y2Hf2O7 unit cells, with the displaced Y existing in a metallic form, which enhanced the electrical conductivity of the cathode's surface. Additionally, the ScxY(2-x)Hf2O[7+(3/2)x] solid solution generated a substantial number of Vo2+ oxygen vacancies and free electrons, further augmenting surface conductivity. Collectively, these mechanisms contributed to a marked enhancement in the cathode's thermionic emission capacity.
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Keywords:
- Sc2O3 doping /
- thermionic emission /
- emission mechanism /
- magnetron
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