Y-Gd-Hf-O难熔稀土阴极制备技术及发射机理的研究

High-power (≥15kW) continuous wave magnetron tubes (HPCWMT) are widely applied in industrial heating. However, the output power and lifetime of a single magnetron cannot satisfy the needs of industry application. Cathode, as the heart of the magnetrons, its characteristics directly influence the output power and lifetime of the magnetron. In order to enhance the output power and prolong lifetime of the magnetron, developing high current density, low evaporation rate, good secondary electron emission yield (SEEY) and anti-electron-bombing ability (AEB), and long lifetime magnetron cathode is urgent and necessary. .In this project, a air plasma spraying method will be used to prepare the refractory rare-earth metal oxide Y-Gd-Hf-O emission coating of the directily-heated cathode, which has the good adhesion between the W base and the coating, the lower coating resistance, the lower metal-coating interface resistance and good anti-electron-bombing. The rare metal Re doped in the emission coating and W sponge will be studied in order to further enhance the anti-electron-bombing ability activity and prolong the lifetime of the cathode. The work function and its distribution on the emission surface of the cathode will be observed and counted by THEM, the surface state and structure of the cathode will be analyzed with SEM, and the ingredients on the emission surface and variation of the various elements in the cathode will respectively be analyzed with AES before and after the cathode activating, aging, lifetime and anti-electron-bombing ability test. Based on the thermionic emission lifetime, evaporation rate, and anti-electron-bombing ability testing results, the lifetime equation of the cathode in the actual magnetron tubes will be discussed and established.

针对我国微波能高效应用急需高功率长寿命连续波磁控管（15kW以上）对大电流密度、低蒸散、强耐电子轰击能力及长寿命阴极（寿命大于5000小时）的需求，开展低温、大电流密度、高次级电子发射系数、强耐电子轰击能力、长寿命Y-Gd-Hf-O难熔稀土直热式阴极的研究。本项目拟采用固相合成方法合成Y-Gd-Hf-O难熔稀土发射活性物质，采用一种大气等离子喷涂技术制备Y-Gd-Hf-O难熔稀土发射涂层，该涂层具有与阴极基金属粘接牢固、涂层密度高、涂层电阻小等特点，可提高阴极的热发射电流密度、次级电子发射系数及耐电子轰击能力。通过研究贵金属W、Re在阴极发射涂层、过渡层中的掺杂，进一步提高阴极涂层电导率及耐电子轰击能力，从而延长阴极寿命。结合阴极加速寿命试验、耐电子轰击能力及阴极蒸发率，建立阴极在实际大功率连续波磁控管中运用的寿命方程，填补我国大功率长寿命连续波磁控管中核心关键技术的空白。

针对我国微波能高效应用急需高功率长寿命连续波磁控管（15kW以上）对大电流密度、耐电子轰击能力强及长寿命阴极（寿命大于5000小时）的需求，开展工作温度低、热发射电流密度大、次级电子发射系数高、耐电子轰击能力强的长寿命Y-Gd-Hf-O系列难熔稀土直热式阴极的研究。本课题采用了固相合成方法合成Y-Gd-Hf-O难熔稀土系列发射活性物质，采用Sc2O3掺杂提高阴极的发射电流密度、延长阴极寿命，通过贵金属W、Re在阴极发射涂层、过渡层中的掺杂，进一步提高阴极次级发射系数及涂层电导率，通过涂层热压烧结等涂层改性技术提高阴极涂层与阴极基金属粘接牢固度和涂层密度，提高阴极的耐电子轰击能力。并通过对比阴极激活前后与寿命中发射表面与涂层内部发射物质的成分及含量变化对该阴极的发射机理进行了探讨。研究结果如下：.5wt.% Sc2O3掺杂Y-Gd-Hf-O直热式阴极在工作温度1400℃时，该阴极的发射电流达到6.3A/cm2，在1450-1500℃，支取电流0.6A/cm2，寿命达到9424小时。30%W粉掺杂Y-Gd-Hf-O直热式阴极在室温时的次级发射系数为3.24。实验表明Sc2O3掺杂及热压烧结涂层均能提高Y-Gd-Hf-O直热式阴极的耐电子轰击能力，5wt.% Sc2O3掺杂Y-Gd-Hf-O压制式阴极经过10 W电子连续轰击696 h后，发射电流仍保持为初始值的86%，表现出良好的耐电子轰击能力。 .阴极的发射机理：阴极激活后阴极发射表面活性物质分布均匀，表层孔隙结构良好，有利于活性物质在热发射过程中的传输和补充。激活后，表面元素Y与Hf的含量均高于激活前值，产生了一定量的n型缺氧型半导体Y2O3-x，而且发射活性层主要集中在距离表面50 nm深度内，在此范围内，Y、Hf含量变化较大且变化趋势一致，随着刻蚀深度的增加，Y/Hf的比例逐渐增加。高温稀土氧化Gd2O3的掺杂，提高了活性物质的高温相结构稳定性，提高了阴极高温工作稳定性。Sc2O3的掺杂，加速了阴极的热电子产生和和传输能力，提高了阴极的发射性能，延长阴极寿命。热压烧结后阴极表面呈陶瓷状结构形态，有利于提高阴极的耐电子轰击能力。