Mechanochemical synthesis of NbC-NbB2 nanocomposite from the Mg/B2O3/Nb/C powder mixtures

摘要

An experimental study was conducted on the preparation and characterization of nanocrystalline niobium boride and carbide composite (NbB2-NbC) in the Mg-B2O3-Nb-C system via mechanochemical method. The thermodynamic appraisal indicated that the reduction and synthesis reactions were highly exothermic and should be self-sustaining. According to the differential thermal analysis (DTA) results, a pre-milling treatment of powder mixture up to 2 h not only reduced the reaction temperature, but also induced a different reaction path. In addition, the amount of Mg-3(BO3)(2), as a major by-product of the thermal synthesis, was significantly decreased by applying adequate mechanical activation. The phase analysis revealed that the NbB2 phase was achieved after 3 h high energy ball milling in self-stunning mode; meanwhile, the formation of NbC was progressively completed after a longer period of milling up to 7 h. According to the morphological evolutions, the range of particle size was within 100 nm. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.