College of Safety Science and Engineering, Anhui University of Science and Technology, Huainan 232000, China.
State Key Lab of Coal Mine Safety Technology, Shenyang Research Institute, China Coal Technology and Engineering Group, Fushun 113122, China.
Molecules. 2022 Jun 14;27(12):3810. doi: 10.3390/molecules27123810.
Contact metamorphism in coal is usually characterized by a rapid, brief, and exotherm reaction that can change the geothermal gradient. In this process, coal adjacent to the intrusive body can form thermally altered coal-based graphite (TACG). In order to further study the structural changes of TACG at different distances from the intrusive body, four TACG samples were collected in the Zhuji coal mine in the Huainan Coalfield, North China, and their vitrinite reflectance and Raman spectra were measured using polarizing microscopy and Raman spectroscopy. The results showed that: (1) affected by the temperature and stress of magmatic hydrothermal intrusion, the clay minerals in the coal seams appeared distributed in strips; the occurrence of ankerite and pyrite in the coal seams near the magmatic intrusions could be due to a late magmatic hydrothermal mineralization; (2) the R - R correlation for the TACG samples under study showed that thermal metamorphism was the main factor leading to the graphitization of the TACG samples, without an obvious pressure effect; (3) with the increase of the graphitization process, the D- and G-band showed some similar changes, specifically, their peak positions shifted to lower wave numbers, and the full width at half maximum (FW and FW) gradually decreased; the difference was that the intensity of the G-band increased, while that of the D-band decreased; (4) the graphitization degree of the TACG samples increased with the increase of the transverse size of the crystals, while the FW and FW values of the G- and D-band decreased; (5) in comparison to natural graphite, the TACG still presented structural defects.
接触变质作用通常以快速、短暂和放热反应为特征，这种反应会改变地热梯度。在这个过程中，侵入体附近的煤可以形成热变质煤基石墨（TACG）。为了进一步研究 TACG 在距侵入体不同距离处的结构变化，在华北淮南煤田朱集煤矿采集了四个 TACG 样品，使用偏光显微镜和拉曼光谱法测量了其镜质体反射率和拉曼光谱。结果表明：（1）受岩浆热液侵入的温度和应力的影响，煤层中的粘土矿物呈条带状分布；靠近岩浆侵入体的煤层中出现的铁白云石和黄铁矿可能是由于晚期岩浆热液成矿作用；（2）研究的 TACG 样品的 R - R 相关性表明，热变质是导致 TACG 样品石墨化的主要因素，没有明显的压力效应；（3）随着石墨化过程的增加，D-和 G-带表现出一些相似的变化，具体来说，它们的峰位向低波数移动，半峰全宽（FW 和 FW）逐渐减小；不同的是，G-带的强度增加，而 D-带的强度减小；（4）TACG 样品的石墨化程度随晶体横向尺寸的增加而增加，而 G-和 D-带的 FW 和 FW 值则减小；（5）与天然石墨相比，TACG 仍存在结构缺陷。
