Effect of Structural Parameters and Chemical Composition on the Polycrystalline LaB₆ Cathode Performance

The investigation considers how chemical composition and phase structure in a ceramic cathode material based on lanthanum hexaboride affect cathode performance during electron-beam welding. We chose to study polycrystalline cathodes from three different manufacturers (that is, different batches) in their initial state and after hot testing in an electron-beam welding facility. We used the test results to qualitatively evaluate cathode performance. A chemical composition analysis of the cathode material revealed that total impurity content in samples from all batches tended to change after hot testing. A qualitative phase analysis showed that the X-ray full width at half maximum for samples from all batches in the initial state differs from that after hot testing. This is how we detected changes in crystallite size on the emission surfaces of the cathodes. We used scanning electron microscopy and electron microprobe analysis to study grain size and morphology, porosity and element composition of contaminant phases in the cathode structure. These results enabled us to draw conclusions regarding the effect that impurity element content, grain size and morphology, as well as volumetric pore fraction in the LaB₆ material structure have on cathode performance during electron-beam welding

References

[1] Parshukov L.I., Gilmutdinov F.Z. Electron beam bonding and local heat treatment welded seams from hot strength alloys. Trudy VIAM [Proceedings of VIAM], 2017, no. 5. DOI: 10.18577/2307-6046-2017-0-5-3-3 Available at: http://www.viam-works.ru/ru/articles?art_id=1101

[2] Kablov E.N., Lukin V.I., Ospennikova O.G. [Welding and soldering in aerospace industry]. Vseross. nauch.-prakt. konf. «Svarka i bezopasnost» [Russ. Sci.-Pract. Conf. "Welding and safety"]. Yakutsk, IFTPS SO RAN Publ., 2012, pp. 21–30 (in Russ.).

[3] Istomin S.Ya., Antipov E.V. Cathode materials based on perovskite-like transition metal oxides for medium-temperature solid oxide fuel cells. Uspekhi khimii (Russian Chemical Reviews), 2013, vol. 82, no. 7, pp. 686–700 (in Russ.). DOI: 10.1070/RC2013v082n07ABEH004390

[4] Fomenko V.S. Emissionnye svoystva materialov [Emission properties of materials]. Kiev, Naukova dumka Publ., 1981. 339 p.

[5] Wang X., Jiang Y., Lin Z., Qi K., Wang B. Field emission characteristics of single crystal LaB6 field emitters fabricated by electrochemical etching method. Journal of Physics D: Applied Physics, 2009, vol. 42, no. 5, pp. 1–4. DOI: 10.1088/0022-3727/42/5/055409

[6] Samsonov G.V., Kondrashov A.I., Okhremchuk L.N., Podchernyaeva I.A. Thermal emission of complex alloys based on lanthanum hexaboride. Poroshkovaya metallurgiya [Powder Metallurgy], 1977, no. 1, pp. 21–28 (in Russ.).

[7] Bustani I., Byunker R., Khirsh G., Gurin V.N., et al. Field evaporation of lanthanum hexaboride and stability estimation of formed clusters. Pisma v ZhTF, 1999, vol. 25, no. 23, pp. 43–49 (in Russ.).

[8] Grashchenkov D.V. Strategy of development of non-metallic materials, metal composite materials and heat-shielding. Aviatsionnye materialy i tekhnologii [Aviation materials and technologies], 2017, no. S, pp. 264–271 (in Russ.).

[9] Vaganova M.L., Sorokin O.Yu., Osin I.V. Joining of ceramic materials by the method of spark plasma sintering. Aviatsionnye materialy i tekhnologii [Aviation materials and technologies], 2017, no. S, pp. 306–317 (in Russ.).

[10] Volkogon V.M., Paderno V.N., Martynenko A.N. Formation of lanthanum hexaboride structure during electric-pulse sintering under conditions of high pressure. Poroshkovaya me-tallurgiya [Powder Metallurgy], 1984, no. 2 (254), pp. 36–41 (in Russ.).

[11] Khasanov O.L., Dvilis E.S., Khasanov A.O., et al. Finding optimum regimes for producting heat-resistant ceramics from boron carbide powder by spark plasma sintering. Izvestiya Tomskogo politekhnicheskogo universiteta [Bulletin of the Tomsk Polytechnic University], 2012, vol. 320, no. 2, pp. 58–62 (in Russ.).

[12] Kablov E.N. Strategical areas of developing materials and their processing technologies for the period up to 2030. Aviatsionnye materialy i tekhnologii [Aviation materials and technologies], 2012, no. S, pp. 7–17 (in Russ.).

[13] Kablov E.N. Materials of a new generation. Zashchita i bezopasnost [Protection and Security], 2014, no. 4, pp. 28–29 (in Russ.).

[14] Chabina E.B., Alekseev A.A., Filonova E.V., Lukina E.A. The use of methods of analytical microscopy and X-ray diffraction analysis for the study of the structural phase state materials. Trudy VIAM [Proceedings of VIAM], 2013, no. 5 (in Russ.). Available at: http://viam-works.ru/ru/articles?art_id=37