Preparation and emission performance of tungsten-osmium mixed matrix dispenser cathode by microwave sintering
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摘要:
采用固–液混合法制备出不同锇（Os）含量（原子数分数）的亚微米级钨锇混合粉体，通过微波烧结获得了孔道结构均匀的钨锇混合基扩散型阴极。电子发射测试结果表明，元素Os的加入使浸渍型钨基阴极的发射性能有明显提高。对比不同锇含量的混合基阴极，发现W–25Os阴极（Os原子数分数为25%）具有相对较低的逸出功和较高的发射电流密度，其在1100 ℃时脉冲发射电流密度为42.86 A·cm−2，斜率为1.40，发射电流密度是同等工作条件下传统钡钨阴极的1.7倍，达到了覆膜M型阴极的电子发射水平。W–25Os混合基阴极的有效逸出功最低为1.93 eV，有利于活性自由钡（Ba）的生成，表层元素摩尔比Ba:(W+Os)为0.83:1.00，比传统钡钨阴极中Ba:W（约为0.50:1.00）摩尔比有了明显提高。
Abstract:Submicron tungsten-osmium mixed powders with the different content of Os (atomic number fraction) were prepared by solid‒liquid mixing method. The tungsten-osmium mixed matrix disperser cathodes with the uniform pore structure were obtained by microwave sintering. The electron emission testing results show that, the addition of Os obviously improves the emission performance of the impregnated tungsten-based dispenser cathode. The W–25Os cathode (Os atomic number fraction is 25%) exhibits the relatively low work function and high emission current density. At 1100 ℃, the pulse emission current density of the W–25Os cathode is 42.86 A·cm−2 with the emission slope of 1.40, which is 1.7 times of the conventional barium-tungsten dispenser cathodes under the same working conditions and up to the electron emission level of M-type cathodes. The W–25Os cathode shows the low effective work function as 1.93 eV, which is conducive to the generation of active free barium source. The molar ratio of surface elements Ba:(W+Os) is 0.83:1.00, which is significantly higher than that of the traditional barium tungsten cathode (about 0.50:1.00).
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Keywords:
- microwave sintering /
- mixed-matrix cathode /
- osmium /
- electron emission /
- work function
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图 1 氢气还原W–Os混合粉末X射线衍射图谱
Figure 1. XRD patterns of the W–Os mixed powders after hydrogen reduction
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图 2 原始Os粉、氢气还原W粉末及W–Os混合粉末的扫描电子显微形貌：（a）原始Os粉；（b）氢气还原W粉；（c）W–15Os；（d）W–25Os；（e）W–50Os；（f）W–75Os
Figure 2. SEM images of the original Os powders, the hydrogen reduced W powders, and the W–Os mixed powders: (a) original Os powders; (b) hydrogen reduced W powders; (c) W–15Os; (d) W–25Os; (e) W–50Os; (f) W–75Os
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图 3 原始Os粉、氢气还原W粉末和W–Os混合粉末的粒度分布曲线：（a）原始Os粉；（b）氢气还原W粉；（c）W–15Os；（d）W–25Os；（e）W–50Os；（f）W–75Os
Figure 3. Particle size distribution curves of the original Os powders, the hydrogen reduced W powders, and the W–Os mixed powders: (a) original Os powders; (b) hydrogen reduced W powders; (c) W–15Os; (d) W–25Os; (e) W–50Os; (f) W–75Os
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图 5 不同温度微波烧结的W–25Os基体表面扫描电子显微形貌：（a）1450 ℃；（b）1500 ℃；（c）1550 ℃；（d）1600 ℃
Figure 5. SEM images of the W–25Os mixed matrix surfaces sintered by microwave sintering: (a) 1450 ℃; (b) 1500 ℃; (c) 1550 ℃; (d) 1600 ℃
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图 6 微波烧结W–25Os基体断面扫描电子显微形貌（a）~（c）及能谱面扫图（d）~（f）
Figure 6. SEM ((a)~(c)) and EDS mapping images ((d)~(f)) of the W–25Os mixed matrix in the cross section after microwave sintering
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图 7 W–Os混合基体X射线衍射图谱
Figure 7. XRD patterns of the W–Os mixed matrix with the different osmium concentrations
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图 8 W–Os混合基阴极表面扫描电子显微形貌：（a）W–15Os；（b）W–25Os；（c）W–50Os；（d）W–75Os；（e）Ba–W
Figure 8. SEM images of the W–Os mixed matrix dispenser cathodes with the different osmium concentrations: (a) W–15Os; (b) W–25Os; (c) W–50Os; (d) W–75Os; (e) Ba–W
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图 9 W–25Os混合基阴极能谱面扫图
Figure 9. EDS mapping images of the W–25Os mixed matrix dispenser cathode
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图 10 W–Os混合基阴极与钡钨阴极脉冲发射曲线和逸出功曲线：（a）W–15Os；（b）W–25Os；（c）W–50Os；（d）W–75Os；（e）Ba–W
Figure 10. Pulsed emission curves and work function curves of the W–Os mixed matrix dispenser cathodes and the barium impregnated tungsten cathodes: (a) W–15Os; (b) W–25Os; (c) W–50Os; (d) W–75Os; (e) Ba–W
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图 11 W–25Os混合基阴极表面活性元素X射线光电子能谱图：（a）W4f；（b）Os4f；（c）O1s；（d）Ba3d
Figure 11. Surface active element XPS spectra of the W–25Os mixed matrix dispenser cathodes: (a) W4f; (b) Os4f; (c) O1s; (d) Ba3d
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图 12 浸渍411活性盐Ba–W（a）和W–25Os阴极（b）充分激活后表面俄歇谱图
Figure 12. AES spectra of the activated Ba–W (a) and W–25Os dispenser cathodes (b) impregnated with 411 salt
表 1 W–Os混合基阴极与Ba‒W阴极逸出功
Table 1 Work functions of the W–Os mixed matrix dispenser cathodes and the barium impregnated tungsten cathodes
阴极编号 功函数 / eV W–15Os 1.97 W–25Os 1.93 W–50Os 1.96 W–75Os 1.94 Ba–W 2.03 
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