Quantitative investigation on the structural characteristics and evolution of high-rank coals from Xinhua, Hunan Province, China

Abstract The structural features and evolution from anthracite to meta-anthracite were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM). All the high-rank coals (4.23%  C (64%–74%), followed by C–C/C–H, carbon–oxygen bonds, and π plasma. The lattice-fringe lengths of anthracites are mainly in the range of 0.6–1.5 nm examined by HRTEM, and trace amount of short aliphatic chains were detected in anthracite samples from micro-FTIR, whereas more aromatic rings condensed into larger polyaromatic clusters in the meta-anthracites and the residual aliphatic carbon atoms are in the form of quaternary aliphatic carbon forming Y-type dislocation. The Y-type dislocation and screw dislocation between edges of lattice-fringes are common in the meta-anthracite compared to anthracite; in addition, bent carbon layers are more frequent. Quantitative information of lattice-fringes was used to investigate the structural evolution of coal. The average diameter of local molecular-oriented domains increases with rank for the meta-anthracite samples, as does the degree of preferential orientation, but these local oriented domains are still distributed randomly at sub-micron scale and without stiff stacked graphene layers.