The Characteristics Of Tectonic Coal’s Microstructure In Hancheng Mining Area

With the effect of tectonic stress, tectonic coal has similarities in thechanges of macroscopic and microscopic structure. The stronger the deformationis, the greater the damage to the native structure of coal will be. The deformationdegree increases from cataclastic coal to mylonite coal, with mechanicalproperties declined. The degree of fracture opening of coal decreases and part ofthe fracture is filled, resulting in bad connectivity. The deformation of coalpetrographical constituent is intensified, leading to indistinct boundary andreduced granularity of coal particles. Due to the squeezing action, coal particlesget squashed, presenting the characteristic of crumpled extrusion and causing asevere fracture filling. With the X-ray diffraction study of coal, themicrocrystalline structure parameters of coal are analyzed. It is found that thearomatic layer spacing（d002） presents fluctuated reduction with the increase ofcoal rank, and the packing layer and height increase. It shows the characteristicof polycondensation in the process of coal metamorphism and deformation, thusto some extent the analysis of microcrystalline parameter of coal can reflect theevolutionary characteristics of coal.The changing process of coal structure is accompanied by a series ofpolycondensation reactions, with the content of functional groups and thestructure changing. By means of nuclear magnetic resonance and infraredspectrum analysis, this change can be presented in a qualitative orsemi-quantitative way. The nuclear magnetic resonance spectrum displays arelatively consistent change. It is showed that the aromatic carbon spectrum hasthe absolute advantage with a relatively broad distribution, mainly concentrating in the110~140ppm. The overlapping phenomenon on the spectra refers to avariety of types of aromatic carbon, and the content of aromatic carbon increaseswith the increasing of coal rank. Between20~40ppm small peaks are distributed,mainly consisting of aryl methyl carbon, aliphatic carbon and methylene carbon,and different types of tectonic coal reveal some differences. Aromatic structurehas three absorption frequencies in the infrared spectra, respectively are750cm-1,800cm-1and875cm-1, corresponding to the benzene ring ortho-positiondi-substituted arene, ortho-position tri-substituted arene, benzene ringpenta-substituted arene. The absorption intensity of aromatic structure isenhanced from cataclastic coal, fragmented coal and mylonitic coal, amongwhich the change of mylonite coal is comparatively complex. Theoxygen-containing functional groups in coal decrease continuously with theincreasing of coal metamorphism and deformation degree. The study of aliphaticstructure indicates that the content of methylene of the coal is higher than that ofmethyl and the content of hydroxyl is lower, mainly exists in the form ofhydroxy-hydroxyl hydrogen bond.From the test result of XPS, it is observed that carbon mainly exists in theform of graphitized coal and C-H. Generally, the graphitized carbon increaseswith the increasing of coal metamorphism and deformation degree while thecontent of C-H is gradually decreasing. The existing forms of oxygen are C-O,COO, and C=O; the main existing forms of nitrogen are pyridine and pyrrole;sulphur exists mainly in the form of thiophene and sulfoxide and secondarilymercaptan phenol sulfur. By means of analyzing the tectonic coal frommacroscopic to microscopic aspects, the characteristics of coal can beunderstood comprehensively and it also provides research basis and theoreticalsupport for in-depth study of the structure of tectonic coal.