Nanocrystalline VC y powders in the homogeneity range of a disordered cubic phase

Abstract

Nonstoichiometric vanadium carbide nanopowders ranging in average particle size from 20 to 40 nm have been prepared by high-energy milling and then vacuum-annealed at temperatures from 600 to 1200°C. The crystal structure, microstructure, morphology, and particle size distribution of the starting, milled, and annealed vanadium carbide powders have been studied by X-ray diffraction, laser diffraction, and scanning electron microscopy. The results demonstrate that vacuum annealing of the VCy nanopowders at temperatures from 600 to 800°C leads to partial carbon loss, compositional changes within the homogeneity range of the disordered cubic phase, and a slight increase in nanoparticle size. Vacuum annealing of the nanopowders at t ≥ 1000°C leads to a considerable carbon loss, the formation of the hexagonal phase V2C along with the cubic carbide VCy, and an appreciable increase in VCy particle size. Thus, vacuum annealing of the nanopowders at 800°C or a lower temperature allows one to vary their composition from VC0.70 to VC0.81, while maintaining the average particle size in the range 50 to 20 nm.