Contents lists available at ScienceDirect Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs NaF-assisted combustion synthesis of MoSi 2 nanoparticles and their densification behavior Hayk H. Nersisyan a,b , Tae Hyuk Lee a,b , Vladislav Ri a , Jong Hyeon Lee a,b, ⁎ , Hoyoung Suh c , Jin-Gyu Kim c , Hyeon Taek Son d , Yong-Ho Kim d a Graduate School of Department of Advanced Materials Engineering, Chungnam National University, 79 Daehak-ro, Yuseong-gu, Daejeon 305-764, Republic of Korea b RASOM, Chungnam National University, 79 Daehak-ro, Yuseong-gu, Daejeon 305-764, Republic of Korea c Division of Electron Microscopic Research, Korea Basic Science Institute (KBSI), 169-148 Gwahangno, Yuseong-gu, Daejeon 305-806, Republic of Korea d Korea Institute of Industrial Technology, 298 Beon-gil, Buk-gu, Gwangju 61012, Republic of Korea ARTICLE INFO Keywords: Molybdenum disilicide Nanoparticles Combustion synthesis Spark plasma sintering Hardness ABSTRACT The exothermic reduction of oxides mixture (MoO 3 +2SiO 2 ) by magnesium in NaF melt enables the synthesis of nanocrystalline MoSi 2 powders in near-quantitative yields. The combustion wave with temperature of about 1000–1200 °C was recorded in highly diluted by NaF starting mixtures. The by-products of combustion reaction (NaF and MgO) were subsequently removed by leaching with acid and washing with water. The as-prepared MoSi 2 nanopowder composed of spherical and dendritic shape particles was consolidated using the spark plasma sintering method at 1200–1500 °C and 50 MPa for 10 min. The result was dense compacts (98.6% theoretical density) possessing submicron grains and exhibiting hardness of 8.74–12.92 GPa. 1. Introduction Because MoSi 2 has attractive properties such as a high melting point, low electrical resistance, superior high-temperature stability and strength, and low density, it has already been used as a heating element and high-temperature protective coating, and has been studied for applications not only as high-temperature structural material, but also as gate electrodes, interconnects, and diffusion barriers in micro- electronic devices [1–6]. The commercial processes for producing MoSi 2 powders are arc melting or siliciding of molybdenum powders [7,8]. Mechanical alloy- ing of Mo-Si mixtures by energized ball-mill system [9–15] and combustion synthesis [16–21] can be considered alternative methods for MoSi 2 synthesis. Like for other intermetallics, the refinement of the grain size of MoSi 2 to nanometer dimensions is predicted [22,23] to improve ductility, fracture toughness, and strength by inducing funda- mental changes in the strengthening and deformation mechanisms. Therefore, MoSi 2 nanopowder is needed first as a precursor, for preparation of compact materials of fine grain size. Before the present work, MoSi 2 nanopowder was prepared using the sonochemical synthesis method [24]. With this method co-reduc- tion of MoCl 5 and SiCl 4 with NaK alloys in hexane was carried out using 600 W of irradiation at 20 kHz. The precipitate was annealed at 900 °C, and 16–31 nm size MoSi 2 nanoparticles was obtained. Preparation of nanocrystalline MoSi 2 using a chlorine-transfer reaction between MoCl 3 and Si at 500 °C has been reported to be useful for fabrication of dense compact with 95 wt% theoretical density [25].A known route to preparation of nanocrystalline MoSi 2 powder is the mechanical alloying of silicon and molybdenum [26,27]. In this technique α-MoSi 2 nanoparticles were obtained after more than 30 h of milling time. Each synthesis approach for nanocrystalline MoSi 2 synthesis is scientifically attractive, and each of them has particular advantages and disadvantages. Even do with a large variety of existing approaches, the development of a process that can produce good sinterability MoSi 2 nanopowders in a simple manner and a low-cost would be always welcomed. Recently we reported the synthesis of MoSi 2 fine powders using a combustion synthesis approach [28]. We investigated the synthesis of MoSi 2 powders from a MoO 3 +SiO 2 +Mg system diluted with NaCl. The MoSi 2 particle size produced by the combustion reaction was 100– 500 nm, and the specific surface area was 25–30 m 2 /g. A very similar investigation was performed by Vershinnikov et al. [29,30] who suggested basic principles for fabrication of fine MoSi 2 powders by SHS process with a reduction stage. Also investigated was the influence http://dx.doi.org/10.1016/j.jpcs.2016.11.003 Received 25 October 2016; Accepted 5 November 2016 ⁎ Corresponding author at: Graduate School of Department of Advanced Materials Engineering, Chungnam National University, 79 Daehak-ro, Yuseong-gu, Daejeon 305-764, Republic of Korea. E-mail address: jonglee@cnu.ac.kr (J.H. Lee). Journal of Physics and Chemistry of Solids 102 (2017) 34–41 Available online 11 November 2016 0022-3697/ © 2016 Elsevier Ltd. All rights reserved. MARK