Characteristics of graphite-like crystallites in coal with increasing coalification

This paper presents a study on the characteristics of graphite-like crystallites (GCs) in coals with different maximum vitrinite reflectance (R-o,R-max) which can be used to describe the rank of coal. Laser Raman spectroscopy (LRS), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used in testing 17 coal samples with different ranks. Results show that the GCs in coal undertook through three consecutive processes including aromatisation, condensation and polymerisation. Five coalification upgrading yield to six stages that are corresponding to six different ranges of Ro,max. With the increasing coal rank, the GCs grow larger with improving quality and eventually evolve into graphite crystals. HRTEM observation also reveals that GCs in coal have undergone a graphitization process with increases in percentage, size, and order