W nanoparticles derived from WO3 during heating in H-2 were carburized at 900-1100 K in pure, Ar and H-2-diluted CH4 atmospheres. It was aimed to elucidate carburization behavior of pre-reduced W powders under various atmospheres and to establish optimal conditions for the synthesis of nanocrystalline WC. Weight measurements, XRD and SEM were used to characterize the products at various stages of the reaction. At 900 K, carburization was limited to the formation of W2C owing to slow C diffusion. At 1000 K, WC particles were obtained within similar to 75 min using the diluted gas mixtures, while under pure CH4 atmosphere carburization reaction practically stopped due to pyrolytic carbon skin formed on particle surfaces where C supply was more than consumed. WC powders with particle size 40-65 nm and grain size 15-25 nm were synthesized at 1100 K in a short time under the gas atmospheres studied. (C) 2010 Elsevier Ltd. All rights reserved.