Li Kuo, Liu Qinfu, Cheng Hongfei, Hu Mianshu, Zhang Shuai
College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China.
School of Earth Science and Resources, Chang'an University, Xi'an 710054, Shaanxi, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2021 Mar 15;249:119286. doi: 10.1016/j.saa.2020.119286. Epub 2020 Dec 3.
Low-weight components of coal macromolecule were subjected to pyrolysis and condensation when magmatic rock intruded into coal measure, eventually, the residual condensed aromatic components can transform into microcrystalline graphite (coaly graphite). To study the structural transformation from anthracite to natural coaly graphite, ten samples with different graphitization degrees from Xinhua and Lutang of Hunan Province, China were characterized by organic geochemical analysis, X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The geochemical parameters (proximate and ultimate analyses) and structural features (XRD, Raman, and HRTEM) of the series naturally graphitized coals exhibit a progressive change as the samples' locations closing to the intrusion. The series naturally graphitized coal samples were classified into four categories, including anthracite, meta-anthracite, semi-graphite, and coaly graphite. But, single parameter cannot classify the series metamorphosed coals well, multi parameters including ash free-basis volatile matter, petrographic features, and carbon structural parameters (based on XRD and Raman spectroscopy) should be considered, additionally, the lattice fringe change observed under HRTEM from anthracite to coaly graphite can verify for the classification. The relatively lower metamorphic grade samples (anthracite and meta-anthracite) have small crystalline sizes, prominent disorders, and amorphous carbon structure, whereas the crystallite structure of highest grade samples (coaly graphite) is three-dimensional crystalline order (testified by XRD and HRTEM), indicating a totally structural transformation from amorphous carbon of anthracite to highly ordered crystalline carbon of coaly graphite in the course of natural graphitization. The carbon structural evolution of coal under natural graphitization process will probably be helpful for synthetic graphite using coal to replace the expensive petroleum coke in the future.
当岩浆岩侵入煤系时，煤大分子的低重量组分发生热解和缩聚，最终，残留的缩合芳烃组分可转化为微晶石墨（煤质石墨）。为研究无烟煤向天然煤质石墨的结构转变，对来自中国湖南省新华和芦塘的十个不同石墨化程度的样品进行了有机地球化学分析、X射线衍射（XRD）、拉曼光谱和高分辨率透射电子显微镜（HRTEM）表征。随着样品位置靠近侵入体，该系列天然石墨化煤的地球化学参数（工业分析和元素分析）和结构特征（XRD、拉曼和HRTEM）呈现出渐进变化。该系列天然石墨化煤样品分为四类，包括无烟煤、半无烟煤、半石墨和煤质石墨。但是，单一参数不能很好地对该系列变质煤进行分类，应考虑包括无灰基挥发分、岩相特征和碳结构参数（基于XRD和拉曼光谱）在内的多个参数，此外，在HRTEM下观察到的从无烟煤到煤质石墨的晶格条纹变化可验证分类。变质程度相对较低的样品（无烟煤和半无烟煤）具有较小的晶体尺寸、明显的无序度和无定形碳结构，而最高等级样品（煤质石墨）的微晶结构是三维晶体有序的（由XRD和HRTEM证实），表明在天然石墨化过程中，从无烟煤的无定形碳到煤质石墨的高度有序晶体碳发生了完全的结构转变。天然石墨化过程中煤的碳结构演化可能有助于未来用煤替代昂贵的石油焦来合成石墨。
