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Preparation and Properties Study on the Rare-Earth Molybdenum Secondary Electron Emission Material

Author: LiNa
Tutor: ZhouMeiLing
School: Beijing University of Technology
Course: Materials Science
Keywords: rare earth molybdenum secondary electron emission thermionic emission
CLC: TB331
Type: Master's thesis
Year: 2005
Downloads: 119
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Abstract


In order to obtain the secondary emission material which could meet the reqirement for practical application, the studies on the preparation technique and the composition of the rare earth molybdenum materials have been carried out in this paper. The doping methods (including solid-solid method, liquid-solid method and Sol-gel method) and the sintering temperature (including 1300℃, 1400℃and 1500℃) were researched. The effect of activation treatment on the property of La2O3-Y2O3-Mo was investigated. La2O3-Y2O3-Mo (LaYMo) and CeO2-Y2O3-Mo (CeYMo) samples were prepared by Sol-gel powder method followed by Spark Plasma Sintering method. The composition, microstructure, particle size distribution, surface analysis and the element analysis of these materials were studied by XRD, SEM, EDS and Laser particle analyzer etc. The studies on doping methods results showed that the grain size of the Sol-gel sample had the best property of secondary emission, the performance of the solid-solid sample was worst. The sample sintered at 1500℃exhibited better and stable secondary emission property, indicating that 1500℃was the suitable sintering temperature. Activation treatment can improve the secondary emission properties of the rare earth molybdenum cathode. The studies on LaYMo and CeYMo secondary emission materials indicated that the more the content of Y2O3, the finer the microstructure, the more uniform the elements distribution and the higher the micro-rigidity. Studied on the LaYMo samples displayed that due to the substitution of La3+ to Y3+ in Y2O3 lattice, La2O3 could not be found in the XRD pattern of the LaYMo4 and LaYMo5 samples. The lattice constant of Y2O3 in LaYMo4 was test. The result showed that the lattice constant of Y2O3 in LaYMo4 was bigger than the standard value. Emission results showed that the weight ratio of La2O3 /Y2O3 =1:3 will be beneficial to the emission properties. The CeYMo samples also showed the better performance in the secondary emission.δm of the CeYMo samples were higher than 3.50, and the CeYMo4 sample (the weight ratio of CeO2 and Y2O3 is 1:2) had the highest secondary emission coefficient among all the CeYMo samples. After activating in 1200℃, which δm can be as high as 11.11. Primary investigation on the thermionic emission properties of secondary emission materials was carried out.

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