A simple and feasible method for preparing chromium carbide coating on graphite through binary NaCl-KCl molten salt

Due to excellent high temperatures resistance and wear resistance, graphite showed great potential apply in refractory materials. However, the porosity defects caused by the layered stacked structure of graphite would lead to easy permeability, which would result in reducing material's lifetime. Surface coating technology was considered to be an ideal method to solve the problems through a stable coating on the surface of graphite. But existing methods have some disadvantages, such as high-cost and complex processes. In this work, a simple, low-cost and green molten salt method was designed. This method successfully prepared a Cr7C3 coating on the graphite surface. The effect of reaction time and temperatures on the chromium carbide coating was investigated by SEM and EDS. The results showed that the thickness of the coating layer increased gradually with the increase in reaction time or reaction temperature, and finally stabilized at about 8 μm. In addition, the reasons behind the formation of Cr7C3 coatings were discussed in terms of both the molten salt reaction and Gibbs free energy, as well as the effect of the coating structure on adhesion. Based on this method, it could not only effectively address the structure defects of graphite, but also showed simple preparation processes and low cost, which would promote the development of graphite materials in high-temperature resistant materials.