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Low-Temperature Preparation of Lanthanum Hexaboride Fine Powder via Magnesiothermic Reduction in Molten Salt
K. Bao, C. Liu, B. Yazdani Damavandi, S. Zhang
College of Engineering, Mathematics & Physical Sciences (CEMPS), Harrison Building, University of Exeter, EXETER, EX4 4QF
received August 17, 2016, received in revised form September 20, 2016, accepted October 12, 2016
Vol. 7, No. 4, Pages 403-408 DOI: 10.4416/JCST2016-00057
Abstract
Lanthanum hexaboride (LaB6) fine powder was synthesized from La2O3 and B2O3 using a molten-salt-assisted magnesiothermic reduction technique. The effects of salt type, Mg amount, heating temperature and time on the synthesis were investigated, and the relevant reaction mechanisms discussed. Among the three chloride salts (NaCl, KCl and MgCl2) attempted, MgCl2 showed the best accelerating effect. When 20 mol% excessive Mg was used, phase-pure LaB6 particles of ∼ 200 and ∼ 100 nm were obtained respectively after 4 h heating at 1000 °C, and 5 h at 900 °C.
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Keywords
Lanthanum hexaboride, molten salt synthesis, cathode material.
References
1 Lafferty, J.M.: Boride cathodes, J. Appl. Phys., 22, [3], 299 – 309, (1951).
2 Buckingham, J.D.: Thermionic emission properties of a lanthanum hexaboride/rhenium cathode, Brit. J. Appl. Phys., 16, [12], 1821, (1965).
3 Leung, K.N.: Directly heated LaB6 cathodes for ion source operation, Vacuum, 36, [11], 865 – 867, (1986).
4 Herzig, P., Fojud, Z., Źogał, O.J., Pietraszko, A., Dukhnenko, A., Jurga, S., Shitsevalova, N.: Electric-field-gradient tensor and charge densities in LaB6: B11 nuclear-magnetic-resonance single-crystal investigations and first-principles calculations, J. Appl. Phys., 103, [8], 083534, (2008).
5 Goebel, D.M., Watkins, R.M.: Compact lanthanum hexaboride hollow cathode, Rev. Sci. Instrum., 81, [8], 083504. (2010).
6 Zhang, X.-H., Hu, P., Han, J.-C., Xu, L., Meng, S.-H.: The addition of lanthanum hexaboride to zirconium diboride for improved oxidation resistance, Scripta Mater., 57, [11], 1036 – 1039, (2007).
7 Jayaseelan, D.D., Zapata-Solvas, E., Brown, P., Lee, W.E.: In situ formation of oxidation resistant refractory coatings on SiC-reinforced ZrB2 ultra high temperature ceramics, J. Am. Ceram. Soc., 95, [4] 1247 – 1254, (2012).
8 Monteverde, F., Alfano, D., Savino, R.: Effects of LaB6 addition on arc-jet convectively heated SiC-containing ZrB2-based ultra-high temperature ceramics in high enthalpy supersonic airflows, Corros. Sci., 75, 443 – 453, (2013).
9 Shen, T.T., Xiao, D.H., Ou, X.Q., Song, M., He, Y.H., Lin, N., Zhang, D.F.: Effects of LaB6 addition on the microstructure and mechanical properties of ultrafine grained WC-10Co alloys, J. Alloy. Compd., 509, [4], 1236 – 1243, (2011).
10 Post, B., Moskowitz, D., Glaser F.W.: Borides of rare earth metals, J. Am. Chem. Soc., 78, [9], 1800 – 1802, (1956).
11 Hiebl, K., Sienko, M.J.: Chemical control of superconductivity in the hexaborides, Inorg. Chem., 19, [7], 2179 – 2180, (1980).
12 Hasan, M., Sugo, H., Kisi, E.: Low temperature carbothermal and boron carbide reduction synthesis of LaB6, J. Alloy. Compd., 578, [0], 176 – 182, (2013).
13 Hasan, M.M., Kisi, E., Sugo, H.: Preparation of lanthanum hexaboride cathodes for thermionic energy generation, pp. 1 – 5 in Informatics, Electronics & Vision (ICIEV), 2013 International Conference.
14 Hasan, M.M., Sugo, H., Kisi, E.H.: Low temperature synthesis of rare-earth hexaborides for solar energy conversion, MATEC Web of Conferences, 13 06005 (2014).
15 Sonber, J.K., Sairam, K., Murthy, T.S.R.C., Nagaraj, A., Subramanian, C., Hubli, R.C.: Synthesis, densification and oxidation study of lanthanum hexaboride, J. Eur. Ceram. Soc., 34, [5], 1155 – 1160, (2014).
16 Ağaoğulları, D., Duman, İ., Öveçoğlu, M.L.: Synthesis of LaB6 powders from La2O3, B2O3 and mg blends via a mechanochemical route, Ceram. Int., 38, [8], 6203 – 6214, (2012).
17 Ağaoğulları, D., Balcı, Ö., Öveçoğlu, M.L., Duman, İ.: Preparation of LaB6 powders via calciothermic reduction using mechanochemistry and acid leaching, KONA, (2016).
18 Dou, Z.-H., Zhang, T.-A., Zhang, Z.-Q., Zhang, H.-B., He, : Preparation and characterization of LaB6 ultra fine powder by combustion synthesis, T. Nonferr. Metal. Soc., 21, [8], 1790 – 1794, (2011).
19 Wang, L., Xu, L., Ju, Z., Qian, Y.: A versatile route for the convenient synthesis of rare-earth and alkaline-earth hexaborides at mild temperatures, CrystEngComm, 12, [11], 3923 – 3928, (2010).
20 Zhang, M., Yuan, L., Wang, X., Fan, H., Wang, X., Wu, X., Wang, H. Qian, Y.: A low-temperature route for the synthesis of nanocrystalline LaB6, J. Solid State Chem., 181, [2], 294 – 297, (2008).
21 Yuan, Y., Zhang, L., Liang, L., He, K., Liu, R., Min, G.: A solid-state reaction route to prepare LaB6 nanocrystals in vacuum, Ceram. Int., 37, [7], 2891 – 2896, (2011).
22 Lihong, B., Wurentuya, W. Wei, Tegus, O.: A new route for the synthesis of submicron-sized LaB6, Mater. Charact., 97, 69 – 73, (2014).
23 Selvan, R.K., Genish, I., Perelshtein, I., Calderon Moreno, J.M., Gedanken, A.: Single step, low-temperature synthesis of submicron-sized rare earth hexaborides, J. Phys. Chem. C, 112, [6], 1795 – 1802, (2008).
24 Szépvölgyi, J., Mohai, I., Károly, Z., Gál, L.: Synthesis of nanosized ceramic powders in a radiofrequency thermal plasma reactor, J. Eur. Ceram. Soc., 28, [5], 895 – 899, (2008).
25 Kelly, J.P., Kanakala, R., Graeve, O.A.: A solvothermal approach for the preparation of nanostructured carbide and boride ultra-high-temperature ceramics, J. Am. Ceram. Soc., 93, [10], 3035 – 3038, (2010).
26 Kanakala, R., Rojas-George, G., Graeve, O.A.: Unique preparation of hexaboride Nanocubes: A first example of boride formation by combustion synthesis, J. Am. Ceram. Soc., 93, [10], 3136 – 3141, (2010).
27 Portehault, D., Devi, S., Beaunier, P., Gervais, C., Giordano, C., Sanchez, C., Antonietti, M.: A general solution route toward metal boride nanocrystals, Angew. Chem. Int. Edit., 50, [14], 3262 – 3265, (2011).
28 Zhang, S., Khangkhamano, M., Zhang, H., Yeprem, H.A.: Novel synthesis of ZrB2 powder via molten-salt-mediated magnesiothermic reduction, J. Am. Ceram. Soc., 97, [6], 1686 – 1688, (2014).
29 Hayashi, H., Minato, K.: Stability of lanthanide oxides in LiCl-KCl eutectic melt, J. Phys. Chem. Solids, 66, [2 – 4], 422 – 426, (2005).
30 Zhang, M.-l., Cao, P., Han, W., Yan, Y.d., Chen, L.-j.: Preparation of Mg-Li-La alloys by electrolysis in molten salt, T. Nonferr. Metal. Soc., 22, [1], 16 – 22, (2012).
31 Zhang, S., Jayaseelan, D.D., Bhattacharya, G., Lee, W.E.: Molten salt synthesis of magnesium aluminate (MgAl2O4) spinel powder, J. Am. Ceram. Soc., 89, 1724 – 1726, (2006).
32 Li, Z., Zhang, S., Lee, W.E.: Molten salt synthesis of LaAlO3 powder at low temperatures, J. Eur. Ceram. Soc., 27, [10], 3201 – 3205, (2007).
33 Janz, G.J., Tomkins, R.P.T., Allen, C.B., Downey, J.R., Garner, G.L., Krebs, U., Singer, S.K.: Molten salts: Vol. 4, part 2, chlorides and mixtures—electrical conductance, density, viscosity, and surface tension data, J. Phys. Chem. Ref. Data, 4, [4], 871 – 1178, (1975).
34 Wypartowicz, J., Østvold, T., Øye, H.A.: The solubility of magnesium metal and the recombination reaction in the industrial magnesium electrolysis, Electrochim. Acta, 25, [2], 151 – 156, (1980).
35 Welham, N.J.: Formation of nanometric TiB2 from TiO2, J. Am. Ceram. Soc., 83, [5], 1290 – 1292, (2000).
36 Weimin, W., Zhengyi, F. Hao, W., Runzhang, Y.: Chemistry reaction processes during combustion synthesis of B2O3-TiO2-Mg system, J. Mater. Process. Tech., 128, [1 – 3], 162 – 168, (2002).
37 Nekahi, A., Firoozi, S.: Effect of KCl, NaCl and CaCl2 mixture on volume combustion synthesis of TiB2 nanoparticles, Mater. Res. Bull., 46, [9], 1377 – 1383, (2011).
38 Caravaca, C., Diaz Arocas, P., Serrano, J.A., Gonzalez, C., Bermejo, R., Vega, M, Martinez, A., Castrillejo, Y.: Solubilization studies of rare earth oxides and oxohalides. application of electrochemical techniques in pyrochemical processes, pp. 625 – 636, in 6th Information Exchange Meeting. Madrid, Spain, 2000.
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