Mechanochemical synthesis of tungsten carbide powders induced by magnesiothermic reduction of WCl₆ and Na₂CO₃ raw materials

The present study explains the synthesis of tungsten carbide (WC and W₂C) powders from WCl₆ and Na₂CO₃ containing blends via magnesiothermic reduction induced by mechanochemical reactions. Mechanochemical synthesis (MCS) was conducted at room temperature in a high-energy ball mill (SPEX^TM 8000D Mixer/Mill) utilizing tungsten carbide vial/balls. A subsequent purification treatment using HCl and distilled water was applied on the mechanochemically synthesized (MCS'd) powders in order to leach out unwanted NaCl and MgO by-products. The optimum production conditions of tungsten carbide powders were examined in regard of MCS time and weight amounts of Na₂CO₃ and Mg reactants. Phase, microstructural and thermal characterizations of the MCS'd and leached powders were performed using x-ray diffractometer (XRD), stereo microscope (SM), scanning electron microscope/energy dispersive spectrometer (SEM/EDS), particle size analyzer (PSA), differential scanning calorimeter (DSC) and transmission electron microscope (TEM). Stoichiometric or 50 wt% excess Mg added WCl₆-Na₂CO₃-Mg mixtures resulted in the formation of both WC and W₂C powders with an amount of WCl₆, WO₂Cl₂ and W phases after MCS and leaching processes. However, WCl₆ and WO₂Cl₂ were disappeared, and only W₂C, WC and W phases were achieved from the 50 wt% excess Na₂CO₃ added WCl₆-Na₂CO₃-Mg mixtures. The best results were obtained for the WCl₆-Na₂CO₃-Mg mixtures with 70 wt% excess Na₂CO₃ which pure WC powders owning an 191 nm average particle size yielded after MCS for 5 h and leaching with 7 M HCl.