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Microscopic study of the traveling wave tube cathode

Author: ZhangDeZheng
Tutor: BaoShengXiang
School: University of Electronic Science and Technology
Course: Materials Science and Engineering
Keywords: Traveling wave tube Cathode Scanning electron microscopy Secondary electron image Microscopic analysis
CLC: TN124
Type: Master's thesis
Year: 2010
Downloads: 68
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Abstract

The high-power broadband traveling wave tube as the heart of military electronic equipment, and plays an important role in modern high-tech warfare. Compared with foreign the domestic traveling wave tube have significant gaps in terms of longevity and reliability. Cathode as the key components that affect the life of the traveling wave tube, the relationship between performance and composition structure is the basic problem of developing high performance cathode must be clear. For the study of the cathode performance is usually from the cathode process, theory, materials and other aspects, rarely microstructure from the cathode to conduct a study. This work was supported by scanning electron microscopy and electron probe spectrometer with the traveling wave tube cathode developed technology, to carry out a comparative analysis of the raw material composition and structure, process comparative analysis of the test sample and Failure Analysis. Main tasks and results are summarized as follows. (1) secondary electron ingredients like. According to the difference of the atomic number of the substance constituent elements, there is proposed using a scanning electron microscope secondary electron image of a new method of analysis component, also studied the application of this method in the cathode as well as the possible problems, and the back scattered electron image of the phase ratio, the method can also be obtained while cathode component information morphology information. (2) a cathode substrate process comparative analysis. Using micro-analytical techniques to store long-term air oxidation of the tungsten powder, and compared with the hydrogen reduction of tungsten powder, the results show the before and after reduction of oxygen content, the effect of the reduction experiments. Tungsten powder micro-structural changes before and after reduction to explain the reasons for the decline of the cathode substrate binding force; Russia and China-made cathode surface microstructure analysis and comparison, in order to find ways to prepare the best substrate analysis results show that the selection of particle size of 5 to 5.5μm the reduced tungsten powder, porosity and microstructure can be prepared with the Russian cathode similar substrate. (3) cathode life is exhausted, for no poisoning gases within the tube and off the experiment after cathode VALID both cases, the use of micro-analysis techniques to analyze the cathode, results show that the life of the depletion in the microscopic structure of the cathode active material consumption do, the surface there is a hole;-off process does not cause significant changes of the microscopic structure of the cathode, but the component analysis showed that the active substance to the surface diffusion. (4) the use of micro-analytical techniques to study three types of cathode failure phenomenon. The results show that these three failure phenomenon is mainly due to the traveling wave tube memory of water vapor, oxygen and anode steam. Formation of the cathode surface and small spots of the tube memory in water vapor, lead to the phenomenon of \components changed; pollutant formation of the cathode surface is mainly due to the degree of vacuum in the tube is not high, the ignition plus a certain voltage to the anode and cathode, the anode, the anode material to cathode movement, and bombardment of the cathode surface at the same time destroy the film structure adhered to the cathode surface. (5) for the anode during the sintering process, the inner wall of the lehr newly generated the phenomenon of white deposits, using scanning electron microscopy and energy dispersive spectroscopy analysis of the structure and composition of the sediment, and lehr in the long-term annealing process in the inner wall The original dark sediment formed a comparative study. The results show that the morphology of white deposits on the charge is not obvious, the composition primarily to the elements such as C, N and O, the white sediment powdered because after the end of the pre-plating process does not clean the residual bath in volatile due to high temperatures. Improve the cleaning process, the results of the analysis to avoid the white deposits appear again. (6) the use of cathode emission performance degradation phenomena to study the heat shield tube Ta foil and a black substance of the surface of the copper anode in the cathode assembly, the analysis showed that the black substance to the cathode active material, and the the cathodic working temperature that, The phenomenon is due to the high temperature of the cathode work, a large number of active substances due to evaporation. The above results for the cathode raw materials selection, process optimization and failure analysis provides a microscopic basis for the life of the cathode and reliability study has an important supporting role.

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