Coal graphitization:Structures and their differential evolution

As a strategic non⁃metal resource， graphite is extremely important to the economic development in China. Nevertheless， the graphite resource in China is limited. The preparation of graphite from coals as a carbon source has gradually become an important development trend at present and in the future. In the graphitization process of coals， with the release of heteroatoms， the aromatic layers are gradually connected and become to be orientation. The structure evolution of coal graphitization shows the characteristics of gradual change and drastic change， which is closely related to the evolution of the macromolecular structure of coals. Due to the heterogeneity of coal itself， such as the differences in maceral， aggregated structures， and molecular structures， different carbon types will be pro⁃ duced during the graphitization process， presenting some challenges for studying the evolution process from coals to graphite. Thus， by analyzing the theory of coal graphitization (including crystalline theory， turbostratic theo⁃ ry model， classification of graphitizable carbon and non⁃graphitizable carbon， as well as multi⁃defective statistical the⁃ ory)， the process of coal graphitization was proposed. Graphite microcrystals are formed continuously， and structural defects are also repaired continuously. Through studying the structural evolution of coal in the graphitization process， it is clarified that the coal graphitization process is characterized by gradual change and by drastic change. The different effects of coal macerals， internal and external coal particles and various coal aggregate structures on coal graphitization were systematically studied. Vitrinite is easier to be graphitized than inertinite. The graphitiza⁃ tion characteristics of different macerals are related to the difference in molecular structure. After coal particles be⁃ ing heated， the grain edges are easily aligned and develop toward graphitization. The difference between graphitiz⁃ able carbon and non⁃graphitizable carbon is reflected in the nanostructures. The existence of curvature in the non⁃graphitizable carbon inhibits the coal graphitization. Finally， considering the different carbon types in the products after coal graphitization， the prospect of future coal graphitization research was proposed.