Effect of precursor mass on product phase composition in plasma dynamic synthesis of tungsten carbide

Abstract

An interest in WC[1-x] cubic tungsten carbide results from its catalytic properties similar to those of platinum group metals and the synergistic effect between WC[1-x] and Pt in reactions of hydrogen evolution and hydrogen oxidation. However, according to the phase diagram of the W–C system, the cubic phase WC[1-x] only exists in a narrow range of temperature stability (about 2798–3058 K), which makes it difficult for being obtained. To date, there are different methods for synthesizing tungsten carbide powder with a low content of cubic phase that complicates the study of WC[1-x] properties. A direct plasma dynamic synthesis is known as one of the promising methods to produce WC[1-x]. The aim of this work is to find the optimal amount of tungsten precursor to obtain cubic tungsten carbide with a high purity by plasma dynamic method. The synthesized products were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns showed that the main phase was cubic tungsten carbide with negligible content of hexagonal tungsten carbide W[2]C and pure tungsten W. According to a quantitative analysis of synthesized products, which were obtained using masses of initial tungsten equal to 1.0, 0.7, 0.6 and 0.5 gram, the yield of WC[1-x] phase was 84, 89, 95 and 92 wt%, respectively. The results of TEM displayed that the synthesized powders consist of crystallites, having the size less than 100 nm (WC[1-x]), and a carbon matrix. This carbon was not detected in XRD due to its presence as an amorphous phase.