Synthesis of graphite by chlorination of iron carbide at moderate temperatures

Abstract

Synthesis of graphite by extraction of iron from iron carbide by chlorine is reported in this work. This process is attractive because it can produce well-ordered graphite at temperatures as low as 600 °C, providing an opportunity for low-temperature solid-state synthesis. Thermodynamic simulation was used to determine the composition of the reaction products under equilibrium conditions and select the initial process parameters such as temperature and chlorine/carbide molar ratio. The interlayer spacing and crystal size of the produced graphite were calculated from X-ray diffraction measurements. The degree of orientation of the graphitic layers was determined by Raman spectroscopy. Three temperature regimes have been identified. At temperatures below 500 °C, amorphous or disordered carbon is formed as shown by Raman spectroscopy and TEM studies. Well-ordered graphite microcrystals are formed by solid-state growth between 600 and 1100 °C. Above the eutectic temperature in the Fe/Fe₃C system, 1130 °C, the growth of large graphite crystals occurs from the liquid phase, similar to the formation of kish graphite by precipitation of carbon at high temperatures from supersaturated molten iron. Iron chlorides, the main impurities in the material synthesized by the solid-state growth, can be removed by using excess chlorine gas or by a separate wet chemical purification step. Preparation of graphite doped with iron for catalytic purposes is also possible using this process.