Molten salt synthesis of continuous tungsten carbide coatings on graphite flakes

Continuous tungsten carbide (WC) coatings were prepared on graphite flakes (G_f) by molten salt synthesis (MSS) technique using NaCl and KCl as reaction medium. The effect of reaction temperature, dwelling times and WO₃/G_f molar ratio on the compositions and morphologies of resultant samples was investigated, and the related formation mechanism for the coatings was also discussed. The results show that continuous WC coatings can be prepared at 1100 °C for 60 min with a WO₃/G_f molar ratio ranging from 1/15 to 1/5. These coatings exhibit homogeneous and crack free features, and their thickness increases with the increase of molar ratio. With the WO₃/G_f molar ratio below or beyond the above range, discontinuous WC coatings or W/W₂C/WC flake-like particles without graphite are obtained, respectively. The varied compositions of the samples obtained with different WO₃/G_f molar ratio can be related to the detailed chemical reaction process between WO₃ and G_f in the molten salts. A “template-growth” mechanism is proposed to explain the formation of WC coatings in the MSS process.