Vacuum-free electric arc synthesis and oxidation resistance of niobium diboride

Transition-metal-based ceramics possess a number of unique properties that make them suitable for various applications. One such material is niobium diboride (NbB₂), which is characterized by a high melting point, chemical resistance, and high thermal conductivity. In this study, the feasibility of synthesizing NbB₂ by a vacuum-free electric arc method was investigated. The method involved electric arc heating in ambient air using a direct-current arc discharge at atmospheric pressure. Based on a series of experiments, the recommended atomic ratio of niobium to boron was determined to be Nb:B = 1:2.6. The effect of milling time on the phase composition of the synthesized NbB₂ product was also investigated. The preferred conditions for homogenizing the starting powders in a planetary ball mill were established as a milling time of 3 h and a rotational speed of 400 rpm. The recommended electric arc treatment conditions  for producing phase-pure NbB₂ corresponded to a specific energy input of 59.41 kJ/g, an arc current of 200 A, and an arc duration of 40 s. A crystalline phase of hexagonal niobium diboride with lattice parameters a = 3.092 ± 0.004 Å and c = 3.303 ± 0.004 Å was identified in the samples. The oxidation resistance of the resulting powder was evaluated by heating it in a muffle furnace over the temperatures range of 25–800 °C. It was found that oxidation occurred at 600 °C, resulting in the formation of Nb₂O₅ and  NbO_0.76 oxide phases.

1. Ma T., Zhu P., Yu X. Progress in functional stu­dies of transition metal borides. Chinese Physics B. 2021;30(10):108103. https://doi.org/10.1088/1674-1056/ac1925

2. Jothi P.R., Yubuta K., Fokwa B.P.T. A simple, general synthetic route toward nanoscale transition metal borides. Advan­ced Materials. 2018;30(14):1704181. https://doi.org/10.1002/adma.201704181

3. Ramezanzadeh M., Ghamarpoor R., Dashan A., Fallah A., Soleimani S., Ramezanzadeh B. 2D-Transition Metal Borides (MBenes): A comprehensive review of the materials, chemistry, advances, and novel applications. Advanced Composites and Hybrid Materials. 2025;8(3):269. https://doi.org/10.1007/s42114-025-01311-3

4. Ma J., Du Y., Wu M., Li G., Feng Z., Guo M., Sun Y., Song W., Lin M., Guo X. A simple inorganic-solvent-thermal route to nanocrystalline niobium diboride. Journal of Alloys and Compounds. 2009;468(1-2):473–476. https://doi.org/10.1016/j.jallcom.2008.01.021

5. Buzea C., Yamashita T. Review of the superconducting properties of MgB2 . Superconductor Science and Techno­logy. 2001;14(11):115. https://doi.org/10.1088/0953-2048/14/11/201

6. Samsonov G.V., Vinitskiĭ I.M. Handbook of refractory compounds. N.Y.: Ifi/Plenum, 1980. 555 p.

7. Samsonov G.V., Vinitsky I.M. Refractory compounds. Moscow: Metallurgiya, 1976. 558 p. (In Russ.).

8. Carenco S., Portehault D., Boissiere C., Mezailles N., Sanchez C. Nanoscaled metal borides and phosphides: recent developments and perspectives. Chemical Reviews. 2013;113(10):7981–8065. https://doi.org/10.1021/cr400020d

9. Yao T., Wang Y., Li H., Lian J., Zhang J., Gou H. A universal trend of structural, mechanical and electronic properties in transition metal (M = V, Nb, and Ta) borides: First-principle calculations. Computational Materials Science. 2012;65:302–308. https://doi.org/10.1016/j.commatsci.2012.07.021

10. De la Mora P., Castro M., Tavizon G. Comparative study of the electronic structure of alkaline-earth borides (MeB2 ; Me = Mg, Al, Zr, Nb, and Ta) and their normal-state conductivity. Journal of Solid State Chemistry. 2002; 169(2):168–175. https://doi.org/10.1016/S0022-4596(02)00045-2

11. Li Y., Wang Z., Gu H., Jia H., Long Z., Yan X. Niobium boride/graphene directing high-performance lithium–sulfur batteries derived from favorable surface passivation. ACS Nano. 2024;18(12):8863–8875. https://doi.org/10.1021/acsnano.3c12076

12. Wang J., Liu C., Miao K., Zhang K., Zheng W., Chen C. Macroscale robust superlubricity on metallic NbB2 . Advan­ced Science. 2022;9(13):2103815. https://doi.org/10.1002/advs.202103815

13. Jafari M., Tajizadegan H., Golabgir M.H., Chami A., Torabi O. Investigation on mechanochemical behavior of Al/Mg–B2O3–Nb system reactive mixtures to synthesize niobium diboride. International Journal of Refractory Metals and Hard Materials. 2015;50:86–92. https://doi.org/10.1016/j.ijrmhm.2014.10.017

14. Maeda H., Yoshikawa T., Kusakabe K., Morooka S. Synthesis of ultrafine NbB2 powder by rapid carbothermal reduction in a vertical tubular reactor. Journal of Alloys and Compounds. 1994;215(1-2):127–134. https://doi.org/10.1016/0925-8388(94)90829-X

15. Iizumi K., Sekiya C., Okada S., Kudou K., Shishido T. Mechanochemically assisted preparation of NbB2 powder. Journal of the European Ceramic Society. 2006;26(4-5):635–638. https://doi.org/10.1016/j.jeurceramsoc.2005.06.012

16. Aydın H., Kurtan Ü., Üstün B., Koc S.N., Akgül E., Demir M. A preparation of niobium diboride (NbB2 ) via molten salt method: Impact of boron concentration on the structural and electrochemical performance. Materials Research Bulletin. 2024;180:113062. https://doi.org/10.1016/j.materresbull.2024.113062

17. Yeh C.L., Chen W.H. Preparation of niobium borides NbB and NbB2 by self-propagating combustion synthesis. Journal of Alloys and Compounds. 2006;420(1-2):111–116. https://doi.org/10.1016/j.jallcom.2005.10.031

18. Liu N., Dong L., Jin S., Wan R., Gu H., Li D. Significant impact of individual surface and modulation structure on mechanical properties of NbN/NbB2 multilayers. Journal of Alloys and Compounds. 2017;695:3225–3232. https://doi.org/10.1016/j.jallcom.2016.11.289

19. Motojima S., Sugiyama K., Takahashi Y. Chemical vapour deposition of niobium diboride (NbB2 ). Journal of Crystal Growth. 1975;30(2):233–239. https://doi.org/10.1016/0022-0248(75)90094-9

20. Tsuchida T., Kakuta T. Synthesis of NbC and NbB2 by MA-SHS in air process. Journal of Alloys and Compounds. 2005;398(1-2):67–73. https://doi.org/10.1016/j.jallcom.2005.01.049

21. He L., Fu J., Wang J., Wu Y., Wang J. Electrical and mechanical properties of SiC–NbB2 composite ceramics. Cera­mics International. 2025;51(28):59802–59810. https://doi.org/10.1016/j.ceramint.2025.10.207

22. Demirskyi D., Sakka Y. In situ fabrication of B4C–NbB2 eutectic composites by spark–plasma sintering. Journal of the American Ceramic Society. 2014;97(8):2376–2378. https://doi.org/10.1111/jace.13083

23. Demirskyi D., Sakka Y. Fabrication, microstructure and properties of in situ synthesized B4C–NbB2 eutectic composites by spark plasma sintering. Journal of the Ceramic Society of Japan. 2015;123(1433):33–37. https://doi.org/10.2109/jcersj2.123.33

24. Pak A.Y., Povalyaev P.V., Vlasov A.V., Gerasimov R.D., Bolatova Z.S., Svinukhova A.A., Spodina A.V., Vassil­yeva Y.Z. Synthesis of high-entropy diboride TiZrNbHfTaB2 by vacuum-free direct current arc plasma method. International Journal of Refractory Metals and Hard Materials. 2026;134:107417. https://doi.org/10.1016/j.ijrmhm.2025.107417

25. Vassilyeva Y.Z., Larionov K.B., Afonnikova S.D., Pova­lyaev P.V., Komkina U.S., Neklya Y.A., Mishakov I.V., Pak A.Y. Synthesis of Mo2C-based material in DC arc discharge plasma under ambient air conditions. Materials Chemistry and Physics. 2024;314:128805. https://doi.org/10.1016/j.matchemphys.2023.128805

26. Vassilyeva Y., Neklya Y., Lukanov M., Kvashnin A., Pak A. Vacuum-free arc synthesis and characterization of crystalline molybdenum borides as instrumental material. Thermal Science and Engineering Progress. 2025;67:104134. https://doi.org/10.1016/j.tsep.2025.104134

27. Xiong L., Jiang M., Miao F., Jiang S. The physical properties and mechanical behavior of NbB2 at high pressure. Solid State Communications. 2024;394:115706. https://doi.org/10.1016/j.ssc.2024.115706

28. Ran S., Sun H., Wei Y., Wang D., Zhou N., Huang Q. Low‐temperature synthesis of nanocrystalline NbB2 powders by borothermal reduction in molten salt. Journal of the American Ceramic Society. 2014;97(11):3384–3387. https://doi.org/10.1111/jace.13298

29. Kravchenko S.E., Kovalev D.Yu., Vinokurov A.A., Dremova N.N., Ivanov A.V., Shilkin S.P. Synthesis and thermal oxidation stability of nanocrystalline niobium diboride. Inorganic Materials. 2021;57(10):1005–1014. https://doi.org/10.1134/S002016852110006X