Molten salt synthesis of continuous tungsten carbide coatings on graphite flakes

Abstract

Continuous tungsten carbide (WC) coatings were prepared on graphite flakes (Gf) by molten salt synthesis (MSS) technique using NaCl and KCl as reaction medium. The effect of reaction temperature, dwelling times and WO3/Gf 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 60min with a WO3/Gf 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/Gf 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/Gf molar ratio can be related to the detailed chemical reaction process between WO3 and Gf in the molten salts. A “template-growth” mechanism is proposed to explain the formation of WC coatings in the MSS process.