Preparation of Tungsten Carbide Powder by In Situ Electrolysis Utilizing Self-Consuming Graphite Anode

In this work, graphite was used as a self-consuming anode to synthesize WC nanopowders in situ in a molten salt containing Na2WO4 with Na2CO3. The effects of electrolysis voltage, W/C molar ratio, electrolysis temperature and time on the physical phase composition and morphology of the products were discussed. The intrinsic relationship between the carbon content in the molten salt during electrolysis and the electrolysis efficiency was revealed. The results show that WC powders with a particle size of about 100 nm can be prepared at a temperature of 800 °C and an electrolysis voltage of 3.5 V with a W/C molar ratio of 10:1. The carbon content in the molten salt increases and then decreases with time in the electrolytic process and the current efficiencies show a corresponding correlation. STEM results demonstrate that a single WC grain size can be up to 20 nm, which starts from a nucleation point on the carbon surface and grows along the initial grain spread. Cyclic voltammetry indicated that WO42− and CO32− were co-reduced and deposited to form the WC phase instantaneously. An analysis of the chronocurrent curves shows that the WC grains grow at the cathode in a transient nucleation mode.