Structural alterations of aromatic fringes by HRTEM for Xinjing Vitrinite-rich anthracite: Impact of low-temperature pyrolysis

Abstract

This study reports the evolution of aromatic lattice fringes of vitrinite-rich anthracite from the Xinjing mine upon slow pyrolysis in the range of 325-590°C using HRTEM. The distribution characteristics of fringe length, orientation, stacking, and curvature were quantified, revealing the thermal transformation processes and mechanisms of aromatic fringes in vitrinite-rich anthracite. The variations in fringe size exhibit stage properties with increasing temperature. Overall, fringe images showed an increased orderliness as temperature increased, and the fringes became highly ordered at high temperatures. The thermoplastic properties (rheological transition) of the coal are likely responsible for changes in orientation. The percentage of stacked layers increased significantly at higher temperatures, and layers of higher stacking numbers also appeared. However, the interlayer spacing did not change significantly (always within ∼4–4.75 Å). It is noteworthy that the curvature of fringes tended to decrease with increasing temperature at higher temperatures (>504°C).