Catalytic graphitization of coke carbon by iron: Understanding the evolution of carbon Structure, morphology and lattice fringes

Abstract

The catalytic graphitization process of coke carbon with iron was investigated in the temperature range of 1100 °C–1500 °C using X-ray diffraction, scanning electron microcopy, high-resolution transmission electron microscopy (HRTEM). The evolution of micro-crystal graphite lattice fringes was carefully analyzed by image processing of the HRTEM micrographs. A strong catalytic effect of iron on graphitization was observed at temperature above 1200 °C with an obvious increase of carbon structural orders. Iron was found to promote the decrease of d002 value and increase of Lc values of the turbostratic carbon, while the d002 value of the newly formed graphitic carbon is quite below that of the commercial graphite when it just forms at 1200 °C. The melting point of iron particles were decreased due to the significant carbon dissolution into iron, leading to the melting and aggregation of iron. The lattice fringe length and the stacking number of micro-crystal graphite were found to increase obviously, while no clear change of crystal orientation was observed. This indicates that the growth of micro-crystal graphite was along its original orientation. The carbon dissolution – graphite precipitation mechanism can be used to explain the catalytic graphitization process very well.