Phase and microstructure evolution during the synthesis of WC nanopowders via thermal processing of the precursor

Tungsten carbide (WC) nanopowders with granular particle of similar to 20-80 nm were prepared by a new precursor method at only 1000 degrees C. The process has two steps in which the amorphous WO3-C mixtures were first produced from salt solution containing tungsten and carbon elements by air drying and subsequent calcining at 400 degrees C for 1 h, and secondly treated at temperatures in the range of 500-1300 degrees C for 1-2 h. Reaction path of the WO3-C system was discussed by X-ray diffraction (XRD) and thermogravimetry-differential scanning calorimetry (TG-DSC), and microstructure of reaction products was studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that the phase evolution of WO3 follows mainly WO3 -> WO2.9 -> WO2.72 -> WO2 -> W -> WC and the incomplete carburization reaction occurs at low carburization temperature and short carburization time. In addition, the increase of carburization temperature contributes to the grain growth of WC powders which is relatively slow at 1000-1200 degrees C and enhanced significantly at 1200-1300 degrees C. (C) 2011 Elsevier B.V. All rights reserved.