【作者】 王传璟；

【导师】 陈怀璧；

【作者基本信息】 清华大学 ， 核科学与技术， 2010， 硕士

【摘要】 阴极作为微波器件的发射源，直接决定着真空电子器件的性能和寿命。基于目前电真空器件对具有较低的工作温度，大的发射电流密度，均匀的发射电流和长的使用寿命的阴极的需求，混合金属基阴极日益成为研究的重点。本课题就是在这样的背景下确定的，围绕钨铱混合金属基阴极的制备工艺，性能测量，发射模型建立展开了广泛深入的实验和理论研究。论文采用溶胶凝胶法(sol-Gel)成功摸索出一套制备钨铱混合金属基阴极的工艺。该工艺稳定性和可重复性均达到了课题预期目标。利用粒度分析，x射线衍射，能谱分析等对阴极粉末的结构，形貌以及阴极的结构进行实验分析；测量了阴极的发射性能。特别是伏安特性，拐点电流密度等；探讨了激活温度，时间对阴极发射性能的影响。结果证实了利用溶胶凝胶法制备的W_IR混合金属基阴极的表面特征，内部形貌，发射性能均优于普通的固液掺杂法。在1100℃的工作温度下，其发射电流密度大于30A/cm2.为了能够定量的研究其特性的变化，建立能够描述这个过程的模型是至关重要。这个发射模型包括三方面：氧化钡的扩散消耗模型，低逸出功物质覆盖率模型，等离子体参数变化过程。氧化钡的扩散消耗模型，来源于bao-cao-al2o3三元体系的相关知识。建模时将Ba0的蒸发简化为一个由扩散系数来表示的简单反应。低逸出功物质覆盖模型主要包括沉积，低逸出功物质的热脱附和离子轰击脱附。这些过程均被分析和量化。其中得到最主要的导致脱附的机制是离子轰击。这也直接说明等离子参数是展示低逸出功物质的表面覆盖度的变化的关键参数。等离子体会被表面的发射所影响，因为低逸出功物质表面覆盖率的减小，将导致逸出功增加，随后导致热发射的减小，而这必然导致进入发射通道内的等离子体的电子数目减小。所以考虑到了这个影响，确定了可以计算等离子参数的半经验公式。更多还原

【Abstract】 The cathode is very important in the field of vacuum electronic device. Becauseof the low working temperature, high current density and long life, the Mixed MetalMatrix cathodes have been researched widely. So my issue is devoted to investigatingsteady technology and modelling for Mixed Metal Matrix cathodes.Because the general mixed metal matrix cathode can’t reach the emission perfor-mance we need, the research is focused on the W-Ir mixed metal-based cathode madewith Sol-Gel method successfully.The composition, microgram and granularity of the power and the surface andinner of the mixed metal-based cathode are studied by XRD, SEM and EDAX. Theemission performance of the mixed metal-based cathode has been measured. And thein?uence of activation temperature and time on the emission performance has beenresearched. The results show that the surface , inner structure and the emission perfor-mance of the mixed metal-based cathode made with Sol-Gel method are all better thanthe general mixed metal matrix cathode made with Solid-Liquid doping. The emissioncurrent density reaches more than 30A/cm2, when the work temperature is 1100 .The model has three parts: a BaO depletion model , a coverage model and aplasma model. The BaO depletion model comes from the knowledge of the BaO-CaO-Al203 system. And reduce the BaO evaporation to a single reaction. The lowwork function model includes deposition, thermal desorption and ion sputtering. theseparameters have been calculated and quantitative. The plasma characteristics is themost important in the evolution. If we have the temperature, the discharge current andthe plasma parameters we can predict the BaO depletion in everywhere of the insert.Because of the conservative estimate, the result is not accurate, but in the industrialapplications, this conservative estimate can increase the safety factor.更多还原