Density and particle size of cubic niobium carbide NbC$_y$ nanocrystalline powders

The density of coarse-crystalline and nanocrystalline powders of niobium carbide NbC$_y$ (0.77 $\le y\le$ 0.96) (with a different average particle sizes of 3–5 $\mu$m and 60–30 nm, respectively) was measured by helium pycnometry. The nanopowders were obtained via the high-energy ball milling of initial coarse-crystalline niobium carbide powders. The particle size of niobium carbide powders was estimated by X-ray diffraction and the Brunauer–Emmet–Taylor (BET) method. The nanopowder density measured by helium pycnometry was shown to be underestimated in comparison with the true density due to the adsorption of helium by the highly developed surface of carbide nanopowders.