The effect of different deformation mechanisms on the chemical structure of anthracite coals

Abstract

To study the effect of different deformation mechanisms on the chemical structure of anthracite coals and further understand the correlation between changed chemical structures and coal and gas outburst, ten groups of sub-high-temperature and sub-high-pressure deformation experiments were performed. All samples maintained primary structure, which were collected from the Qudi Mine in the southern Qinshui Basin of China. The samples were analyzed by ultimate analysis, Vitrinite Reflection (VR), Fourier Transform Infrared spectroscopy (FTIR), and Raman spectroscopy both before and after deformation experiments for contrasting. The results showed that the VR values of all samples after experiments were significantly higher than before experiments, which suggested that the metamorphism degree of anthracite coals was increased by deformation. The results also indicated that both temperature and strain rate had significant effects on the chemical structure of anthracite coals. At a high strain rate of 4×10 5 s 1 , the deformation of the samples was mainly brittle in which the mechanical energy was transformed mainly into frictional energy. In this situation, all samples developed several distinct fractured surfaces and the change of chemical structures was not obvious. On the contrary, with the decrease of the strain rates, the ductile deformation was dominated and the mechanical energy was mainly transformed into strain energy, resulting in the accumulation of deformation energy confessed by increasing quantity of dislocation and creep in the coal's interior nucleus. The absorption in the aromatic ring groups increased; otherwise the absorption in the aliphatic structures and ether oxygen groups decreased rapidly. During these experiments, CO was collected from two experimental samples. The number of aromatic rings and the structure defects within the two generated gas samples increased and the degree of molecular structure orders decreased. anthracite coal, deformation experiment, VR, Vitrinite Reflection Indicating surface (VRI), secondary structure defect Citation: Xu R T, Li H J, Hou Q L, et al. 2015. The effect of different deformation mechanisms on the chemical structure of anthracite coals. Science China: Earth Sciences,

Geochemical Alteration and Mineralogy of Coals under the Influence of Fault Motion: A Case Study of Qi’nan Colliery, China

“…Frictional heat generated by fault motion could lead to early-metamorphism of coal containing the degradation of oxygen functional groups [41,130,131]. According to recent research, strong ductile deformation in zone I could also change the molecular structures of coal by transformation into strain energy [39,40,132]. Besides, the higher R o,max of sample 3 also indicated that the maturation degree of sample 3 was advanced by the influence of stress-induced dynamic metamorphism, including the stress degradation of functional groups (Table 1).…”

“…Moreover, it has been reported that there is early metamorphism of coal molecular structures in TDCs [37,38]. Side chains in TDCs including aliphatic structures and functional groups are disassociated by tectonic stress, which is followed by aromatic structures being collaged and rearranged (especially in ductile deformed coal) [39,40]. Furthermore, relevant studies have shown that coal molecular structures around faults are altered by strong deformation and frictional heat [41][42][43].…”

Novel super‐absorbent polymer‐grafted tea polyphenol composite inhibitor for the prevention of coal spontaneous combustion

“…8 Under the external force, coal breaks and a large number of cracks generated. Consequently, coal molecules would be destroyed, generating a large number of free radicals, [42][43][44][45] The new radical reacts with oxygen:…”

The impacts of stress on the chemical structure of coals: a mini-review based on the recent development of mechanochemistry

“…Using EPR, researchers found that more free radicals were induced through bond cleavages under stress/mechanical force [24,[44][45][46]. The FTIR and 13 C NMR results revealed that compared with the adjacent primary coals, tectonically deformed coals (TDCs) had lower aliphatic carbons and higher aromatic carbons [47][48][49][50][51]. Since TDCs and the primary coals were sampled from adjacent areas, they are assumed to have gone through the same thermal evolution, and the difference between them are thought to be the influence of stress.…”

“…The related work of Hou and co-workers has just been reviewed by Dong et al [66]. Different gases were collected in the experiments and corresponding chemical structure changes were revealed by elemental analysis [64], FTIR [51,64,65], and 13 C NMR [65] at temperatures lower than the pyrolysis needed. Though deformation experiments were performed by different researchers, they face the same problem how to prove the gases are generated during deformation and not from desorption.…”