Investigation of Boro/Carbothermic and Carbothermic Reduction Synthesized Calcium Hexaborides

Öz

In this study, crystal structure and powder morphologies of CaB₆ synthesized via different synthesis methods were investigated via Rietveld method and TEM studies. CaB₆ powders were synthesized via two different methods and to investigate the effect of the synthesis method on the crystal structure, synthesis temperature and dwell time were kept as constant for both method. In the first method, CaB₆ was synthesized via boro/carbothermal reduction of calcium carbonate by in-situ synthesized boron carbide. In the second method, CaB₆ powders were formed by carbothermal reduction of calcium hexaborate penthydrate by carbon obtained from pyrolysis of PVA in PVA-Borate gels. Phase analysis of powders were studied via X-Ray Diffraction (XRD) and crystal structure refinement was done using Rietveld method via Maud^TM software. Particle morphologies and size were studied with Transmission Electron Microscope (TEM) and crystal structure were analyzed via Selected Area Electron Diffraction (SAED). 

Anahtar Kelimeler

• CaB6,Hexaboride,Hexaborate,Borocarbothermic Reduction

Boro/Karbotermik ve Karbotermik İndirgeme Yöntemiyle Sentezlenen Kalsiyum Hekzaborürlerin İncelenmesi

Öz

Bu çalışmada, iki farklı yöntemle sentezlenen CaB₆ kristal yapısı ve toz morfolojisi incelenmiş ve sentez yönteminin, yapı üzerindeki etkisi Rietveld metodu ve TEM yardımıyla incelenmiştir. CaB₆ tozları iki farklı yöntem kullanılarak sentezlenmiş ve üretim yönteminin kristal yapı üzerindeki etkisinin incelenmesi için sentez sıcaklığı ve süresi her iki yöntem için sabit tutulmuştur. İlk yöntemde, CaB₆ tozları, kalsiyum karbonatın (CaCO₃) boro/karbotermik olarak yerinde indirgenmesiyle sentezlenmiştir. Diğer yöntemde ise kalsiyum pentaborat hekzahidrat (CaB₆O₁₀.5H₂O) tozları, PVA-Borat içeren jelin pirolizinden elde edilen karbonun indirgeyici olarak rol oynamasıyla ve boratın yerinde indirgenmesiyle sentezlenmiştir. Tozların faz analizi X-Işını Kırınım (XRD) tekniği ile, kristal yapıya ait detayların belirlenmesi ise Maud^TM yazılımı kullanılarak Rietveld analizi ve Elektron Kırınımı (SAED) yöntemi ile gerçekleştirilmiştir. Parçacık morfolojisi ve boyutu, geçirimli elektron mikroskobu (GEM) kullanılarak incelenmiştir.  

Anahtar Kelimeler

• CaB6,Hekzaborür,Hekzaborat,Borokarbotermik İndirgeme

Kaynakça

1. J.M. Lafferty, Boride cathodes, Journal of Applied Physics. 22 (1951) 299–309. doi:10.1063/1.1699946.
2. S.Q. Zheng, G.H. Min, Z.D. Zou, H.S. Yu, H.D. Han, Synthesis of calcium hexaboride powder via the reaction of calcium carbonate with boron carbide and carbon, Journal of the American Ceramic Society. 84 (2001) 2725–2727. doi:10.1111/j.1151-2916.2001.tb01083.x.
3. V.I. Matkovich, Boron and Refractory Borides, 1977. doi:10.1017/CBO9781107415324.004.
4. Z. Lin, M. Guanghui, Y. Huashun, Reaction mechanism and size control of CaB6 micron powder synthesized by the boroncarbide method, Ceramics International. 35 (2009) 3533–3536. doi:10.1016/j.ceramint.2009.05.032.
5. M. Takeda, M. Terui, N. Takahashi, N. Ueda, Improvement of thermoelectric properties of alkaline-earth hexaborides, Journal of Solid State Chemistry. 179 (2006) 2823–2826. doi:10.1016/j.jssc.2006.01.025.
6. H. Yin, D. Tang, X. Mao, W. Xiao, D. Wang, Electrolytic calcium hexaboride for high capacity anode of aqueous primary batteries, J Mater Chem A. 3 (2015) 15184–15189. doi:10.1039/C5TA03728J.
7. X. Huang, J. Zhong, L. Dou, K. Wang, Combustion synthesis of CaB6 powder from calcium hexaborate and Mg, International Journal of Refractory Metals and Hard Materials. 28 (2010) 143–149. doi:10.1016/j.ijrmhm.2008.11.009.
8. H. Razavi-zadeh, S.T. Mirdamadi, Deoxidizing Copper with CaB6, (1987).

9. S. Hanagiri, T. Harada, S. Aso, S. Fujihara, H. Yasui, S. Takanaga, et al., Effect of the addition of metal and CaB6 to magnesia carbon bricks for convertor, Refractories(Tokyo). 44 (1992) 490–498.
10. B.A. Galanov, V. V. Kartuzov, O.N. Grigoriev, L.M. Melakh, S.M. Ivanov, E. V. Kartuzov, et al., Penetration resistance of B4C-CaB6 based light-weight armor materials, Procedia Engineering. 58 (2013) 328–337. doi:10.1016/j.proeng.2013.05.037.
11. C.H. Chen, T. Aizawa, N. Iyi, A. Sato, S. Otani, Structural refinement and thermal expansion of hexaborides, Journal of Alloys and Compounds. 366 (2004) 2003–2005. doi:10.1016/S0925-8388(03)00735-7.
12. M.V. Stackelberg, F. Neumann, Die Kristallstruktur der Boride der Zusammensetzung MeB6., Zeitschrift Für Physikalische Chemie. 19 (1932) 314–320.
13. A. Akkoyunlu, R. Koç, J. Mawdsley, D. Carter, SYNTHESIS OF SUBMICRON-SIZE CaB6 POWDERS USING VARIOUS BORON SOURCES, in: M. Sanjay, S.S. Ray (Eds.), Nanostructured Materials and Nanotechnology V, The American Ceramic Society, 2011: pp. 127–135.
14. Ö. Balci, D. Aǧaoǧullari, I. Duman, M.L. Öveçoǧlu, Synthesis of CaB 6 powders via mechanochemical reaction of Ca/B 2O 3 blends, Powder Technology. 225 (2012) 136–142. doi:10.1016/j.powtec.2012.03.051.
15. S. Angappan, M. Helan, A. Visuvasam, L.J. Berchmans, V. Ananth, Electrolytic preparation of CaB6 by molten salt technique, Ionics. 17 (2011) 527–533. doi:10.1007/s11581-011-0531-9.
16. D. Yilmaz, N. Koç, S. Turan, Synthesis of Calcium Hexaboride Powder via Boro/ Carbothermal Reduction with a Gel Precursor, J Ceram Sci Tech. 356 (2016) 7–349. doi:10.4416/JCST2016-00044.
17. D. Yilmaz, U. Savaci, N. Koç, S. Turan, Carbothermic reduction synthesis of calcium hexaboride using PVA-calcium hexaborate mixed gels, Ceramics International. (2017) 8–13. doi:10.1016/j.ceramint.2017.11.050.