Thermodynamic, Kinetic, and Crystal Face Anisotropy Analysis of WC Coating on Diamond Surfaces

Through employing WO3 as a precursor, we successfully deposited a complete and continuous WC coating onto the surface of diamond particles by means of the salt bath method. Initially, a tungsten (W) layer forms on the diamond surface, which gradually transitions to a tungsten carbide (WC) coating as either the temperature is elevated or the duration of the process is prolonged. A thorough thermodynamic analysis was conducted to investigate this phase transition mechanism. At a lower synthesis temperature of 1000 °C, significant differences were observed in both the thickness and phase composition of the coatings formed on the (100) and (111) crystal planes of diamond. Specifically, the coating on the (100) plane exhibited earlier growth compared to that on the (111) plane, with WC phases appearing sooner within the coating’s composition. However, as the synthesis temperature increases, these differences in both thickness and phase composition between coatings on different diamond crystal faces tend to diminish, leading towards convergence. Furthermore, a detailed kinetic analysis of the coating growth process was conducted. It was found that the reduction reaction of carbon on WO3 led to the formation of the W coating, and the diffusion of carbon in the W coating resulted in the formation of the WC coating. The diffusion of carbon in the coating ensured its continuous growth, providing deeper insights into the mechanisms governing the deposition and transformation processes.