A facile pathway to prepare ultrafine WC powder via a carbothermic pre-reduction followed by carbonization with CH4-H2 mixed gases.

In the present work, ultrafine tungsten carbide (WC) powder with a high purity has been prepared by first roasting yellow tungsten trioxide (WO 3) and carbon black powder under argon atmosphere followed by the further carbonization reaction with CH 4 -H 2 mixed gases. The effects of C/WO 3 molar ratio, CH 4 percentage in the CH 4 -H 2 mixed gases on the phase composition, morphology and particle size of the products were discussed. The results revealed that when the C/WO 3 molar ratios were 2.5 and 2.6, nano tungsten carbide powder with the average particle sizes of 93 nm and 77 nm could be prepared. Whereas, when the C/WO 3 molar ratio was in the range of 2.7–3.5, the finally prepared WC has the particle size of 446–192 nm, and became smaller with the increase of C/WO 3 molar ratio. The percentage of CH 4 should be <15% to prepare WC with a low free carbon content. From the results of thermodynamic calculation, X-ray diffraction (XRD), FE-SEM, and infrared carbon‑sulfur analyzer, it was concluded that ultrafine tungsten carbide powders with a high purity could be successfully prepared by this method. • A new process was proposed to prepare high purity and ultrafine WC powders. • Nano WC powder could be prepared when the C/WO 3 molar ratio was 2.5–2.6. • Particle size of WC decreased as increasingC/WO 3 ratio in ranges of 2.1–2.6 and 2.7–3.5. • The optimal CH 4 percentage of CH 4 -H 2 mixed gases for carbonization was 5–10%. [ABSTRACT FROM AUTHOR]