Preparation, microstructure and density of nanocrystalline powders of nonstoichiometric vanadium carbide VC

Nanocrystalline powders of VCy with different stoichiometry and the average particle size were produced by high-temperature solid-phase synthesis and subsequent milling. The crystal structure, phase composition, microstructure and particle morphology of initial and milled VCy powders, their specific surface area and density were studied using XRD, SEM, BET method and gas pycnometry. The anisotropy of microstrains in nanocrystalline VCy powders was experimentally studied by XRD. It was shown that the inclusion of microstrain anisotropy and inhomogeneous broadening in the analysis make it possible to more accurately describe experimental data on diffraction reflection broadening. It was found that microstrains mainly contribute to the broadening of diffraction reflections of VCy nanopowders produced by milling. The experimental dependence of the pycnometric density of VCy powders on the specific surface area was established and an expression describing it was obtained. It was shown that the main reason for pycnometric density reduction of the powders with increasing specific surface area is oxygen adsorption on the surface of carbide particles.