A novel preparation process of tungsten carbide in molten salt: Carbon internal recycling

This study proposes a novel process for the clean production of tungsten carbide from the perspective of internal recycling of carbon. On the basis of NaCl-KCl-Na₂WO₄-Na₂O molten salts capturing and converting CO₂, the loss of graphite anode is fixed in the molten salt system. The clean production of nano-tungsten carbide and the internal recycling of carbon were realized. Firstly, the carbon transfer pathway from graphite anode to molten salt to electrolysis products was demonstrated by the characterization of each part of the electrolysis system. Subsequently, the effects of electrolysis voltage, temperature and Na₂O addition on carbon internal recycling were evaluated. It was found that the increase of Na₂O addition could effectively reduce the anode CO₂ gas spillage. When 0.9 wt% Na₂O was added, the amount of unfixed carbon could be reduced to 1.63 %. And the WC products with higher purity were obtained at a voltage of 3 V and a temperature of 800°C. Additionally, the average diffusion coefficient of CO₃²⁻ (6.91 × 10⁻⁹ cm²s⁻¹) was much larger than that of WO₄²⁻. It suggests that the first stage of electrolysis has a rapid carbon transfer rate, which provides a prerequisite for the nucleation of WC. The process provides a clean production route for the production of tungsten carbide nanoparticles in a low-carbon and environmentally friendly way.