Contrasting graphitization differences between vitrinite and inertinite based on high-temperature and high-pressure experiments

Abstract

It has been recognized that vitrinite and inertinite exhibit different evolutionary characteristics during coalification processs, but the study of their evolutionary differences after entering the graphitization process is limited. To investigate the graphitization differences, this study conducted high-temperature high-pressure (HT-HP) experiments under different temperature and pressure conditions. The precursor used in the HT-HP experiments was concentrated inertinite-rich samples and vitrinite-rich samples obtained through manual selection, and the parent coal is low volatile bituminous coal (Rmax (%) = 1.7). X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were employed to compare and analyze the graphite lattice evolution of the maceral. The experimental results indicated the following: (1) During the construction of the three-dimensional graphite lattice, vitrinite and inertinite exhibited differences in response to temperature and pressure conditions. Inertinite had a higher graphitization threshold compared to vitrinite, and once reached or exceeded, inertinite underwent rapid graphitization seen by the significant decrease of the interlayer spacing d002; (2) In terms of defect healing, under the same stress conditions, vitrinite was more sensitive to temperature compared to inertinite as observed by the Raman parameters R2 and R3; (3) By comparing the development of graphite structure under different temperature and pressure conditions, we found that both efficient graphitization process and development of the graphite structure require a synergistic combination of temperature and pressure, where an excessive or insufficient pressure can inhibit graphitization and even dismantle and damage the formed graphite structure.