Effects of Metamorphism and Deformation on the Coal

Subscriber access provided by Fudan University

Article

Effects of metamorphism and deformation on the coal macromolecular structure by laser Raman spectroscopy Jienan Pan, Minmin Lv, Heling Bai, Quanlin Hou, Meng Li, and Zhenzhi Wang Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02176 • Publication Date (Web): 16 Jan 2017 Downloaded from http://pubs.acs.org on January 17, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Effects of metamorphism and deformation on the coal macromolecular structure by laser Raman spectroscopy Jienan Pana,b∗, Minmin Lva,b ,Heling Baia,b, Quanlin Houc, Meng Lia,b, ZhenzhiWanga,b a. School of Resources & Environment, Henan Polytechnic University, Jiaozuo 454000, China b. Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region，Henan Province, China c. Key Lab of Computational Geodynamics, College of Earth Sciences, University of Chinese Academy of Sciences, Beijing 100049, China

Abstract: Metamorphism and deformation significantly affect the macromolecular structure of coal. In this study, experiments were conducted using coal samples with different metamorphic degree and deformation types from different regions of Hebei, Henan, Shanxi, and Anhui province, followed by laser Raman spectral analysis. The results indicated that the Raman spectrum of all coal samples consist of two characteristic peaks, namely the D and G peak, ranging from 1336.7 to 1360 cm-1 and from 1591.2 to 1600.6 cm-1, respectively. Simultaneously, with the metamorphic degree of coal increasing, certain change rules were observed in both strong and weak tectonically deformed coals: G and D peaks were gradually separated and the sharpness of these peaks was clearly enhanced. In addition, the D-peak position, FWHM-G and ID/IG decreased, but the G-peak position and d(G-D) values increased, while the analysis results indicated that the change trends in the d(G-D) values can serve as a measure of the change trends in the metamorphic degree of coal. Meanwhile, tectonic deformation can somewhat promote the order degree of the aromatic structure in the internal microscopic structure of coal, and the effects of tectonic

∗

Corresponding author at: School of Resources & Environment, Henan Polytechnic University, Jiaozuo 454000, China.

E-mail address: [email protected] (J. Pan)

ACS Paragon Plus Environment

Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

deformation on macromolecular structure of coal are even greater than those of high metamorphic stage in the low metamorphic stage. Keywords: Coal; Laser Raman spectrum; Tectonic deformation; Coal macromolecular structure

1. Introduction In 1928, an Indian physicist C V Raman

1

discovered Raman scattering, which is a type of inelastic

scattering; he reported a vibrational spectrum and attributed the signals to the vibration and rotation of molecules. In 1970, Tuinstra and Koenig 2 already reported the structural parameters of graphitic materials as measured from X-ray diffraction (XRD) are associated with the two main bands information in the Raman spectra in the very first paper. Since then, Raman spectroscopy opened a promising field in terms of study the microstructure of carbonaceous materials (CM)3.Raman spectra are very sensitive to the existence of defects in the crystal lattice structure of CM, and provide very reliable information about the order degree of the structure. Thus Raman spectroscopy has been attracting increasing attention for the study and applications of carbon structures. Reich and Thomsen

4

have reviewed the theory of double-resonant

Raman scattering on the Raman spectra of graphite and also conducted detailed relevant experimental work. Ferrari and Robertson 5 have comprehensively and critically evaluated the origin of the D and G peaks in the Raman spectra, which provide significance information about graphite and amorphous carbon. In addition, several studies

6-10

have reported the wide spread utility of Raman spectroscopy for the

characterisation of the structural features of CM (e.g. grapheme 11, 12, amorphous carbon films13, 14, carbon nanotubes (CNTs)15, 16 and coal17, 18). As compared to other instrumental techniques for molecular characterization, such as XRD 19, 20, Fourier transform infrared spectroscopy (FT-IR)20, micro-IR21, atomic force microscopy (AFM)22, 23, and


Page 2 of 38

Page 3 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

transmission electron microscopy(TEM)24, 25, Raman spectroscopy, as the main instrumental technique for exploring the microstructure of CM, demonstrates prominent advantages in that it provides abundant information about the structure, micro-domain, and heterogeneous states. It is also a rapid and non-destructive detection method. In the recent fifty years, the laser Raman microprobe technique, in particular, has been rapidly developed, making Raman spectroscopy a powerful tool for the characterization of the internal structure and qualitative identification of CM in the molecular spectrum micro-domain of analytical techniques26-30, because it is sensitive to not only crystal structures but also molecular structures (short-range order), as well as the degree of structural disorder. Especially, Raman spectroscopy has been widely used for the characterization of coal of geological interest. Coal, typically, which is a kind of organic matter with three-dimensional (3D) macromolecular network structures, is accepted to be a type of amorphous carbonaceous matter with long-range disorder and short-range order polycrystalline structure, heterogeneity, and different types of hierarchical structures 31, 32

. While with the aid of Raman spectroscopy, many researchers have extensively investigated the nature

and structure of coal with considerable success. For instance, Tsu et al.33 had found that Raman spectra of coals and disordered carbons are very similar. Wopenka and Pasteris 34 first suggested the D-band width as a sensitive maturity indicator for poorly ordered materials, such as low-rank coals and kerogens. However, no correlation analysis was performed between the spectral information contained in the G- and D-first-order carbon bands and the maturity of samples quantified by independent tracers (e.g. vitrinite reflectance)，while recent studies via a large series of samples revealed the high sensitivity of Raman spectroscopy to the maturity of coals and kerogens，and reported a correlation between the Raman spectral parameters and vitrinite reflectance or carbon content35-38 as well as structural parameters of XRD by in-depth analysis and research20, 39. In addition, a detailed comprehensive review on the application and


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 38

development of Raman spectroscopy for investigating coal has reported by Potgieter-Vermaak et al.3, and this paper was a valuable reference for the future research of Raman spectroscopy of coal. Thus far, although Raman spectroscopy has been successfully utilized for investigating aspects of coal with respect to the thermal evolution of organic matter structure 40-44, properties of organic macerals 28, and estimating coal rank 36, 39, 45, few papers investigated lager numbers of natural coal samples, not to mention the application of Raman spectroscopy in tectonically deformed coal. A tectonically deformed coal (TDC) 22, 46, 47

refers to a class of coal with obvious changes in the primary structure and texture of coal under the

effect of tectonic stress, which would inevitably result in changes in the pore structures and macromolecular structures. In addition, well-developed TDC not only controls coal and gas outbursts but also directly affects the occurrence state of coalbed methane (CBM)

46

; hence, it is of theoretical and

practical significance to investigate the structural change characteristics of TDC. In recent years, several researchers have been interested in the application of Raman spectral techniques for investigating the TDC structure, which was not only its metamorphism and deformation mechanism but also structural characteristics. For example, Lin et al.27 studied different types of TDC in the Huaibei Coal Basin by laser Raman spectroscopy, detailing the changes in the structural constituents of TDC under different deformation mechanisms; this in turn provided a new idea about the deformation mechanism of TDC and the generation and occurrence state of CBM at the molecular level. Li et al.48 further analysed the same characteristics, taking into account that the secondary structural defect of the coal macromolecular structure produced by tectonic deformation, which is the primary reason for the varied structural evolution of TDC compared with primary structure coal, and the leading role of degradation and condensation polymerization are different under different deformation mechanisms; furthermore, the secondary structural defect can be easily generated in ductile deformation as compared to generation in


Page 5 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

brittle deformation. Nevertheless, the TDC structure by Raman spectroscopy has not been sufficiently investigated and has not attracted sufficient attention. While notably in these papers, the samples selected for experiments were all pre-treated by two treatments, demineralisation and vitrinite centrifugation, before conducting other tests, which possibly might result in damage to the macromolecular structure of coal. A large amount of the tectonically deformed coal has been found in China. However, their structural characteristics are largely unknown. The objective of this study was to apply Raman spectroscopy to characterization of the macromolecular structure of coal and to probe the effects of metamorphism and deformation on the coal macromolecular structure.

2. Sample selection and experiments 2.1 Sample selection In this study, coal samples were selected from the Fengfeng coal field in Hebei province, Pingdingshan, Xinmi, Hebi, Yongxia coal field in Henan province, and Huaibei coal field in Anhui province of North China. These coal fields had gone through multi-period superposition of tectonic movements since the Paleozoic and led to complicated tectonic with well-developed folds and faults in these regions. Furthermore, Fault zone and Collision zone had obviously destroyed on coal seam, and the coal structure was subjected to varying degrees of tectonic deformation and formed different types of tectonically deformed coal. As well as the coal field in Shanxi province, which was situated in the Qinshui depression point of Lvliang - Taihang fault block in North China block region, and geological structure was relatively simple. The coal samples analyzed in this study were obtained from Carboniferous-Permian (C-P) coal-bearing strata, and the maximum vitrinite reflectance (Ro, max/%) (Reflectance measurements of coal were performed on the polished sections of the samples using a standard polarizing microscope (OPTONⅡMPV-3) in accordance with the specification of coal petrology.) ranged from 0.88% to 3.80%.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Consequently, the maximum vitrinite reflectance can be used to represent the metamorphic rank of coal but it was also slightly affected by the ‘deformation’ factor. In addition, two types of tectonically deformed coals were selected with the degree of coal deformation: weak tectonically deformed coal (weak TDC) and strong tectonically deformed coal (strong TDC) (Figure 1 and Table 1). In this study, all coal samples passed a 200 mesh sieve and weighed 10g to conduct the laser Raman spectroscopy experiments. Table 1 summarizes the basic information of the coal samples.

2.2 Experiments Raman experiments were performed with a Renishaw inVia (Reflex) Raman Microscope (UK) equipped with RenCam Series of electrically cooled CCD-detector and Research level microscope. The instrument was equipped with a Spectra Physics argon ion laser (excitation wavelengths (λ0) =514.5nm; source power: 20 mW), the laser power of the incident beam on the sample surface was kept at 0.8 mW (which can avoid some irrevocable thermal damage), with data acquisition time of 30s, the spectral resolution was 2 cm-1, receiving slit width was 25µm. And silicon wafer to be used for wave number calibration of Raman spectroscope. Each measurement was taken at three different spots on the samples due to the heterogeneous nature of the coal. In the meantime, all samples of wavenumber were scanned range from100 to 3200cm-1. Concerning the fitting Raman spectra procedure，Hinrichs et al.45 compiled a detailed instructions about the choice of analytical functions as well as the number of fitting lines to be used. In addition, the accuracy and relevance of the different parameters obtained by the decomposition of spectra by conventional fitting procedure, has been reviewed by Beyssac et al.29 By comparing different fitting approaches of Hinrichs et al. and Beyssac et al., as well as others literatures,6, 9, 20, 49, 50 so, in the following, only the Raman parameters of the D and G bands were discussed


Page 6 of 38

Page 7 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

for all the spectra of coals in order to eliminate the excessive amount of parameters. Based on that, a simple curve-fitting procedure was performed within the range of 500-2000 cm−1 (this region spectrum could provide more valuable data about the microstructure of coals) with a linear baseline correction was used, due to this spectral window seemed broad enough to allow the fitting software to estimate the linear baseline, as well as the corresponding fit curves was the multi-peak fit, which needed to select two Lorentzian functions and was done using the Levenberg–Marquardt algorithm as implemented.

3. Results and discussion Figure 2 shows the laser Raman spectral curves of some coal samples. As can be observed in the figure, two obvious Raman vibration peaks, which provide complex, rich micro-structural information of coals, were recorded ranging from 1300 to 1700cm-1; the generation of these two characteristic bands is closely relate to the composition of the molecular internal structure and the order degree of molecular structure27, 51. Generally, the Raman spectra of graphite and CM are commonly divided into first-order and second-order regions

2, 10, 35, 52, 53

; however, for coals, the first-order Raman spectrum is mainly analysed.

The single crystals of graphite in the first-order Raman spectrum, shows one narrow band at ~1580cm−1 (e.g. 1581cm-1,5, 51, 53 1575cm-1,2 1578cm-1,37), corresponding to the graphite peak (G peak), which is attributed to the stretching vibration of the graphite lattice ‘in-plane’ C = C bonds; this vibration is associated to the E2g mode of the graphite aromatic layer. On the other hand, with respect to coal, a high disorder degree is observed, with two typically characterised peaks recorded in the Raman spectrum

35, 36

.

As can be seen in the figure, an additional peak is also located at 1336.7 -1360cm-1 (so-called defect peak or D peak, D for disordered), in addition to the omnipresent G (graphite) peak located at 1591.2~1600.6cm-1. The D peak（corresponding to the main influence of the D1 band of the literature）was


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 38

attributed to the A1g vibration mode of the irregular hexagon lattice structure in amorphous graphite; this mode is typically called the ‘disorder induced’ or the D mode, attributed to the defects between the molecular structure units; in addition, Raman scattering was mainly induced by the primary or secondary structural defects and disordered carbon bond of crystal grain boundaries 52, 54, 55. Nevertheless, the D peak, which was the secondary structural defect peak generated by tectonic stresses, was mainly analysed in this paper. However, previously reported studies have produced considerable debate about the origin of the D peak

5, 10, 56

. For example, some researchers have hypothesised that the D peak is attributed to in-plane

defects between the basic structural units (BSUs) or the occurrence of hetero atoms

57

, while others have

hypothesised that it is put down to double-resonant Raman scattering12, 58, 59. Lespade et al.60 investigated various CM (including graphitizing and nongraphitizing) by Rama n spectroscopy and extracted four parameters called the ‘graphitization indices’ from the Raman sp ectra of all recorded samples. Whilst by comparison with the Raman spectral parameters for coals in other literatures

36, 37, 49

，the following parameters were finally chosen for analysis and discussi

on herein: (1) Band position: WG and WD, represents the Raman shift of the νE2gband (G peak) and νA1g band (D peak) 52

, respectively. The Raman shift is a general term representing the difference between the frequency of the

Stokes or anti-Stokes scattered light and that of the excitation light source. The Raman shift depends on the change in the molecular vibrational levels, where different chemical bonds or ground states exhibit different vibration modes and determines the energy variation between the energy levels. Therefore, the corresponding Raman shift is characteristic, and Raman spectroscopy demonstrates theoretical foundation for the qualitative analysis of molecular structure. (2) Full width at half maximum: FWHM-G and FWHM-D. FWHM-G, i.e. full width at half maximum of


Page 9 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

G band, represents the degree of graphitization. FWHM-D, i.e. full width at half maximum of D band, reveals the defect degree of coal. (3) The ratio of D peak intensity to the G peak intensity, i.e. ID/IG. Which indicate the order degree of the coal internal microscopic molecular structure. (4) Raman band separation: the difference between the G peak position and D peak position, i.e. d (G-D), to some extent, which could be expressed as a measure of the change trends in the metamorphic degree of coal. Then, a series of curve-fitting procedure (had discussed in Section 2.2) were conducted for the measured Raman spectra, structural parameters were calculated for each spectrum and then mean value was calculated for each sample. See the following specific decomposition process (take XTM10 as an example). The Raman spectra were analyzed by curve-fitting the three peaks (D, D3 and G) using Gaussian functions as shown in Figure 3(a). We tried to fit all the spectra with five Gaussian functions and a linear baseline, accounting for all main features expected in this region, namely G, D1, D2, D3, and D4 bands as shown in Figure 3(b). To sum up, the two results were very disappointing, so it was chose the simple fitting method of this paper. See the following Figure 3(c). And Table 2 summarizes the Raman spectral data of each coal sample obtained. The Raman spectral characteristics of coals depend on the structural characteristics of the internal structure of coal molecules; hence, the Raman spectra as well as parameters vary with structural change of coals with different metamorphic degrees and deformation types. In this study, the variation rules of the Raman spectra parameters of coals with different metamorphic degrees and deformation types were mainly investigated in term of two factors, metamorphic degree and deformation, and the change relationships in


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 38

the structural composition of the coal molecules were explored; the results indicated that tectonic deformation and metamorphism affect the molecular structure of coal.

3.1 Variation of Raman peak positions of coals with different metamorphic degrees and deformation types As can be observed in Figure 4, with the change of metamorphic grade, the two typically characteristic peaks (D-peak position (WD) and G-peak position (WG), respectively) exhibited different variation rules. The D-peak positions of strong and weak TDC linearly decreased with increasing reflectance of vitrinite (Figure 4(a)). The relationship between the D-peak positions of strong TDC and vitrinite reflectance can be expressed as follows: Y1=-7.098X1+1366, Rଶଵ =0.899

（1）

Here, Y1 is the D-peak position, cm-1; X1 is the vitrinite reflectance, %. In addition, the relationship between the D-peak positions of weak TDC and vitrinite reflectance can be expressed as follows: Y2=-6.039X2+1361, Rଶଶ =0.866

（2）

Here, Y2 is the D-peak position, cm-1; X2 is the vitrinite reflectance, %. The G-peak positions of strong TDC and weak TDC linearly increased with increasing vitrinite reflectance (Figure 4(b)), where the relationship between the G-peak positions of strong TDC and vitrinite reflectance can be expressed as follows: Y3=2.831X3+1589, Rଶଷ =0.809

（3）

Here, Y3 is the G-peak position, cm-1; X3 is the vitrinite reflectance, %. In addition, the relationship between the G-peak positions of weak TDC and vitrinite reflectance can


Page 11 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

be expressed as follows: （4）

Y4=2.964X4+1590, Rଶସ =0.865 Here, Y4 is the G-peak position, cm-1; X4 is the vitrinite reflectance, %.

Moreover, from Figure 4, with the increase of coal metamorphic degree, the WD of strong and weak TDC exhibited the same change trend of shifting to low wave numbers,

35-37, 45, 61

and the WD gradient of

strong TDC was less than that of weak TDC. Still, WD was obtained between 1336.7 and 1360cm-1, and the peak position changed 23.3cm-1 by combining the results shown in Table 2, indicating that the metamorphism of coal exerts a certain effect on the change of WD. Then, by fitting the relationship formula of WD—Ro, max, when Ro, max=1, the WD difference between strong and weak TDC was 3.9cm-1; when Ro, max =2,

its difference was 2.9cm-1; when Ro,

max=3,

its difference was 1.8cm-1; when Ro,

max=3.5,

its

difference was 1.3cm-1. This result reveals that tectonic deformation significantly affects the WD values of coals, and the generated D peak is simply inducted by discontinuity and structural defect in a ‘similar crystal lattice’. That is, the secondary structural defects 52 produced by tectonic stress can make the path of WD change. On the other hand, a previous study

27

has provided another explanation to this problem:

tectonic stress not only enhances the extent of coal deformation, but also promotes the improvement of coal rank to some extents. However, with increasing metamorphic grade, the WG both of strong and weak TDC exhibited the same tendency to shift to high wave numbers, ranging from 1591.2 to 1600.6cm-1, and the peak position changed 9.4cm-1; hence, the metamorphism of coal exerts a specific effect on the change of WG. In addition, at the same metamorphic degree, the WG of strong TDC on average was less than 1.4 cm-1 as compared with that of weak TDC, attributed to the obvious slip caused by the strong tectonic deformation (‘similar crystal lattice’ in the coal macromolecular structure) and with increasing accumulation of the


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 38

dislocation (energy), the disintegration of aromatic ring can occur, following which, the aromatic fused rings of BSU can rearrange, thereby enhancing ring condensation. This results in the vibration peak positions being relatively lower than those of weak tectonic deformation. The high peak positions in weak TDC caused by dislocation (energy) in the coal structure did not cause the disintegration of aromatic rings or the dissociation of aromatic ring numbers of the side-chain groups. Therefore the increased aromatisation was still greater than the forced dissolution of aromatic ring numbers.

3.2 Variation of the difference values of Raman peak positions of coals with different metamorphic degrees and deformation types From Figure 5, with increasing metamorphic grade of coal, the d(G-D) values of strong and weak TDC both presented linear increasing trends. Kelemen et al.37 have reported that this increasing trend attributed to the width of amorphous peaks becomes narrow in the organic matter, where the relationship between the d(G-D) values of strong TDC and vitrinite reflectance can be expressed as follows: Y5=9.930X5+222.5, Rଶହ =0.911

（5）

Here, Y5 is d(G-D), cm-1; X5 is the vitrinite reflectance, %. In addition, the relationship between the d(G-D) values of weak TDC and vitrinite reflectance can be expressed as follows: Y6=9.274X6+228.6, Rଶ଺ =0.911

（6）

Here, Y6 is d(G-D), cm-1; X6 is the vitrinite reflectance, %. From the above analysis, good relationships (R2>0.9) exist between the Ro, max and d(G-D) values of strong and weak TDC. In addition, in this study, the change trends of d(G-D) values are expressed as a measure of the change trends in the metamorphic degree of coal based on the change rule of d(G-D) values:


Page 13 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

d(G-D) values increased with increasing metamorphic grade. That is, the higher the d(G-D) values, the higher the metamorphic grade of coal and the condensation degree of aromatic rings and the stronger the order degree. By contrast, it indicates that the lower the coal rank and the condensation degree of aromatic ring, the weaker the order degree. Moreover, the d(G-D) values of coals with different metamorphic degree and deformation types were subjected to statistical analysis, and the d(G-D) mean values were obtained for coals with different metamorphic grades and deformation types(Table 3). As can also be observed in Table 3, both d(G-D) mean values of strong TDC and weak TDC increased with increasing metamorphic grade, mainly attributed to the fact that the non-crystalline structure in coal gradually becomes structurally stable and ordered after condensation polymerization. This result also indicated that metamorphism increasingly strengthens the impact of d(G-D). At different metamorphic stages, the d(G-D) mean values of strong TDC were less than those of weak TDC, and the data suggested that the impact of tectonic deformation on the d(G-D) values at the low metamorphic stage was the most obvious, followed by the medium and high metamorphic stages.

3.3 Variation of FWHM values of Raman peaks for coals with different metamorphic degrees and deformation types From Figure 6(a), with increasing coal rank, the FWHM-D values did not exhibit obvious change trends 35; however, a change rule between the FWHM-D values and the metamorphic degree of coal has reported in other studies 36, 49, 62 , which might be correlated to the selection of excitation light power or the maturity of coal. Moreover, as can be observed in Figure 2, the D and G peaks in the Raman spectra exhibited regular changes with changes in the metamorphic grade. At low metamorphic grade, because the size of crystallite


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

carbons in coal samples were too small, the FWHM-D and FWHM-G were broad, and the two lines considerably overlapped; however, with increasing metamorphic grade, the D peaks and G peaks gradually separated, and the sharpness of their peaks significantly increased, especially, the sharpness of the G peaks of high metamorphic coal was the most obvious, also indicating that the size of crystallite carbons in coal increases and becomes more ordered. As shown in Figure 6(b), significant changes between the FWHM-G values of coals with different coal ranks and deformation types were observed: the FWHM-G values gradually decreased with increasing coal rank. Furthermore, the FWHM-G varied from 33.3 to 55.5 cm-1 as shown in Table 2, where the maximum of falling range is 22.2 cm-1 with increasing metamorphic grade. What's more, by the comparison of FWHM-G values of both coals and CNTs, the FWHM-G values of coals are reported to be far greater than those of CNTs

63

; hence, coal presents a low crystallisation

degree. In other words, FWHM-G is associated with the degree of graphitisation in coal, as well as reflects the changes in the degree of coal metamorphism and the degree of order of the ‘crystal structure’ in coals 39

. In addition, the FWHM-G values for coals with different metamorphic degree and deformation types

were subjected to statistical analysis, and the FWHM-G mean values were obtained for coals with different metamorphic degree and deformation types (Table 4). From Figure 6 and Table 4,with increasing metamorphic degree, the FWHM-G values of strong and weak TDC present the same significant decreasing trend 36, 37, 39, attributed to the decrease in the interlayer spacing in the macromolecular structure of coal

39

, also implying that the crystalline degree of

graphitization in coal constantly increases. Besides, from low to high metamorphic grade, tectonic deformation affected the changes in the FWHM-G values, such that these values decreased in Table 4, but


Page 14 of 38

Page 15 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

for the most part, the FWHM-G values of strong TDC were typically less than those of weak TDC, indicating that tectonic deformation slightly promotes the process of crystalline degree of graphitization in coal, that is, it affects the increase of the coal metamorphism degree27. Finally, a negative correlation was observed between the change of FWHM-G and lattice dimension in coal by the comprehensive analysis of deformation and metamorphism and changes of FWHM-G.

3.4 Variation in the Raman peak intensity ratio of coals with different metamorphic degree and deformation types Previous studies have reported that the order degree of the internal molecular structure of CM is typically characteristic by the ratio of the intensities of the D peak (representing disordered structures) to the G peak (representing graphite structures) 17, 64; hence, the D to G peak intensity in the Raman spectrum can reflect the order degree of aromatic structures within the coal internal microscopic molecular structure. In summary, the essence of the whole evolution process in the coal was the increase of the order degree of internal molecular structure. Zheng et al.52 have reported that areas with non-regular carbon atoms exist between the graphitic carbon layers during graphitisation of coal, in which ‘defect areas’ are present in the structure, while during the graphitisation coal, structural defect areas are constantly reduced until they disappear. From previous studies employing XRD20 and high-resolution transmission electron microscopy (HRTEM)65 for coal samples with different metamorphic degree and deformation types, the metamorphism and deformation of coal indeed result in increasing elongation and stacking height of the aromatic macromolecules, as well as decreasing lamellar spacing, namely, there is an ever-increasing performance in the overall order degree. In addition, the ID/IG values of coal samples with different metamorphic degrees and deformation types were statistically analyzed, and ID/IG mean values were obtained for coal samples with different


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

metamorphic degree and deformation types (Table 5). Considering the results obtained from both Figure 7 and Table 5, the ID/IG values of strong and weak TDC decreased with increasing coal metamorphic grade, indicating that the order degree of the aromatic structure in the internal microscopic molecular structure of coal increases. Meanwhile, as shown in Table 5, the ID/IG mean values of strong TDC were no greater than those of weak TDC from a low metamorphism grade to a high metamorphism grade, indicating that tectonic deformation exerts a certain promoting effect towards the increase in the order degree of the aromatic structure in the internal microscopic molecular structure of coal.

4. Conclusions The following conclusions are obtained. (1) The Raman spectrum of coal is a characteristic depending on the internal molecular structure and molecular order degree of coal. With increasing metamorphic grade of coal, two characteristic peaks (respectively, D peak and G peak),in the laser Raman spectrum exhibit different change rules for coal samples with different deformation degree, these peaks are also characteristic of the metamorphism and deformation, which produce different effects on the macromolecular structure of coal. (2) The data obtained from Raman spectra, indicate that with increasing metamorphic grade, some change rules shown from Raman parameters, WD shifts to low wave numbers, while WG shift to high wave numbers; FWHM-G values decrease, but there is no obvious relationship between the FWHM-D values and the metamorphic degree of coal; furthermore, the ID/IG values decrease. Hence, it can be obtained from the Raman parameters that metamorphism significantly contributes to the arrangement in the order degree of the carbon network within BSU and between BSU in the internal microscopic molecular structure of coal. Meanwhile, metamorphism gradually strengthens d(G-D) values, so the change trend of d(G-D) can


Page 16 of 38

Page 17 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

be employed as a measure of the change trend in the metamorphism degree of coal. (3) In addition, tectonic deformation plays an important role in the ultra-structure of coal. Because tectonic deformation not only transforms the macrostructure of coal and enhances the coal deformation degree, but also slightly improves the degree of coal metamorphism and significantly affects the macromolecular structures of coal, the secondary structural defect can make the path of WD change, as well as significantly affect d(G-D) in low metamorphic grade coal; in addition, tectonic deformation also slightly promotes the increase in the order degree of the aromatic structure in the internal microscopic molecular structure of coal. Finally, analysis of the various characteristics of the macromolecular structure of tectonically deformed coal with different metamorphic degree and deformation types can aid in researching an efficient approach for studying coal and gas outburst as well as the mechanism for the occurrence of CBM in detail.

Acknowledgment This study was sponsored by the National Natural Science Foundation of China (Grant No. 41372161), the Program for Innovative Research Team (in Science and Technology) in University of Henan Province (17IRTSTHN025) and the Program for Innovative Research Team of Henan Polytechnic University (T2015-1). Special thanks are given to the three anonymous reviewers for their valuable advice and comments on the manuscript.

References (1) Raman, C.V.; Krishnan, K.S. A new type of secondary radiation. Nature 1928, 121(3048), 501-502. (2) Tuinstra, F.; Koenig, J.L. Raman spectrum of graphite. J. Chem. Phys. 1970, 53(3), 1126-1130.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(3) Potgieter-Vermaak, S.; Maledi, N.; Wagner, N.; Van Heerden, J.H.P.; Van Grieken, R..; Potgieter, J.H. Raman spectroscopy for the analysis of coal: a review. J. Raman Spectrosc. 2011, 42(2), 123-129. (4) Reich, S.; Thomsen, C. Raman spectroscopy of graphite. Philos. Trans. R. Soc. Lond. A 2004, 362(1824), 2271-2288. (5) Ferrari, A.C.; Robertson, J. Interpretation of Raman spectra of disordered and amorphous carbon. Phys. Rev. B 2000, 61(20), 14095-14107. (6) Sheng, C. Char structure characterised by Raman spectroscopy and its correlations with combustion reactivity. Fuel 2007, 86(15), 2316-2324. (7) Zaida, A.; Bar-Ziv, E.; Radovic, L.R.; Lee, Y-J. Further development of Raman Microprobe spectroscopy for characterization of char reactivity. P. Combust. Inst. 2007, 31 (2), 1881-1887. (8) Rodrigues, S.; Marques, M.; Suárez-Ruiz, I.; Camean, I.; Flores, D.; Kwiecinska, B. Microstructural investigations of natural and synthetic graphites and semi-graphites. Int. J. Coal Geol. 2013, 111(6), 67-79. (9) Zickler, G.A.; Smarsly, B.; Gierlinger, N.; Peterlik, H.; Paris, O. A reconsideration of the relationship between the crystallite size La of carbons determined by X-ray diffraction and Raman spectroscopy. Carbon 2006, 44 (15), 3239-3246. (10) Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U. Raman microspectroscopy of soot and related carbonaceous materials: Spectral analysis and structural information. Carbon 2005, 43(8), 1731-1742. (11) Ferrari, A.C.; Basko, D.M. Raman spectroscopy as a versatile tool for studying the properties of graphene. Nature Nanotech. 2013, 8(4), 235-246. (12) Das, A.; Chakraborty, B.; Sood, A.K. Raman spectroscopy of graphene on different substrates and


Page 18 of 38

Page 19 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

influence of defects. B. Mater. Sci. 2008, 31(3), 579-584. (13) Wang, Y.J.; Li, H.X.; Ji, L. et al. Microstructure, mechanical and tribological properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering. Surf. Coat. Tech. 2011, 205 (8–9), 3058-3065. (14) Wang, S.; Zhu, J.Q.; Wang, J.Z. et al. Raman spectroscopy and mechanical properties of multilayer tetrahedral amorphous carbon films. Thin Solid Films 2011, 519 (15), 4906-4909. (15) Tyborski, C.; Herziger, F.; Gillen, R.; Maultzsch, J. Beyond double-resonant Raman scattering: UV Raman spectroscopy on graphene, graphite and carbon nanotubes. Phys. Rev. B 2015, 92 (4). (16) Costa, S.; Borowiak, E. Characterization of carbon nanotubes by Raman spectroscopy. Mater. Sci.-Poland 2008, 26(2), 433-441. (17) Pusz, S.; Borrego, A.G.; Alvarez, D.; et al. Application of reflectance parameters in the estimation of the structural order of coals and carbonaceous materials. Precision and bias of measurements derived from the ICCP structural working group. Int. J. Coal Geol. 2014, 131, 147-161. (18) Su, X.B.; Si, Q.; Song, J.X. Characteristics of coal Raman spectrum. J. China Coal Soc. 2016, 41(5), 1197-1202. (19) Lu, L.; Sahajwalla, V.; Kong, C.; Harris, D. Quantitative X-ray Diffraction Analysis and Its Application to Various Coals. Carbon 2001, 39(12), 1821-1833. (20) Sonibare, O.O.; Haeger, T.; Foley, S.F. Structural characterization of Nigerian coals by X-ray diffraction, Raman and FTIR spectroscopy. Energy 2010, 35(12), 5347-5353. (21) Hacura, A.; Wrzalik, R.; Matuszewska, A. Application of reflectance micro-infrared spectroscopy in coal structure studies. Anal. Bioanal. Chem. 2003, 375(2), 324-326. (22) Pan, J.N.; Zhu, H.T.; Hou, Q.L.; et al. Macromolecular and pore structures of Chinese tectonically


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

deformed coal studied by atomic force microscopy. Fuel 2015, 139, 94-101. (23) Pan, J.N.; Zhu, H.T.; Bai, H.L.; et al. Atomic force microscopy study on microstructure of various ranks of coals. Journal of Coal Science & Engineering (China) 2013, 19(3), 309-315. (24) Sharma, A.; Kyotani, T.; Tomita, A. A new quantitative approach for microstructural analysis of coal char using HRTEM images. Fuel 1999, 78(10), 1203-1212. (25) Smędowski, Ł.; Krzesińska, M. Molecular oriented domains (MOD) and their effect on technological parameters within the structure of cokes produced from binary and ternary coal blends. Int. J. Coal Geol. 2013, 111, 90-97. (26) Smędowski, Ł.; Krzesińska, M.; Kwaśny, W.; Kozanecki, M. Development of Ordered Structures in the High-Temperature (HT) Cokes from Binary and Ternary Coal Blends Studied by Means of X-ray Diffraction and Raman Spectroscopy. Energy Fuels 2011, 25(7), 3142–3149. (27) Lin, H.; Ju, Y.W.; Hou, Q.L.; Li, X.S. et al. Laser Raman spectra of tectonically deformed coals in brittle and ductile deformation mechanisms and its response to structural components. Prog. Nat. Sci. 2009, 19(10), 1117-1125. (in Chinese) (28) Morga, R. Micro-Raman spectroscopy of carbonized semifusinite and fusinite. Int. J. Coal Geol. 2011, 87(3–4), 253-267. (29) Olivier, B.; Bruno, G.; Jean-Pierre, P.; Emmanuel, F.; Myriam, M.; Jean-Noël, R. On the characterization of disordered and heterogeneous carbonaceous materials by Raman spectroscopy. Spectrochim. Acta A 2003, 59(10), 2267-2276. (30) Baysal, M.; Yürüm, A.; Yıldız, B.; Yürüm, Y. Structure of some western Anatolia coals investigated by FTIR, Raman, 13C solid state NMR spectroscopy and X-ray diffraction. Int. J. Coal Geol. 2016,163, 166-176.


Page 20 of 38

Page 21 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(31) Levine, J.R.; Davis, A. The relationship of coal optical fabrics to Alleghanian tectonic deformation in the central Appalachian fold-and-thrust belt, Pennsylvania. Geol. Soc. America Bull. 1989, 101(10), 1333-1347. (32) Given, P.H.; Marzec, A.; Barton, W.A.; Lynch, L.J.; Gerstein, B.C. The concept of a mobile or molecular phase within the macromolecular network of coals: A debate. Fuel 1986, 65(2), 155-163. (33) Tsu, R.; Jesus, G.H.; Isaac, H.C.; Luengo, C.A. Raman scattering and luminescence in coal and graphite. Solid State Commun. 1977, 24(12), 809-812. (34) Wopenka, B.; Pasteris, J.D. Structural characterization of kerogens to granulite-facies graphite; applicability of Raman microprobe spectroscopy. Am. Mineral. 1993, 78(5-6), 533-557. (35) Guedes, A.; Valentim, B.; Prieto, A.C.; Rodrigues, S.; Noronha, F. Micro-Raman spectroscopy of collotelinite, fusinite and macrinite. Int. J. Coal Geol. 2010, 83(4), 415-422. (36) Quirico, E.; Rouzaud, J.N.; Bonal, L.; Montagnac, G. Maturation grade of coals as revealed by Raman spectroscopy: Progress and problems. Spectrochim. Acta A 2005, 61(10), 2368-2377. (37) Kelemen, S.R.; Fang, H.L. Maturity Trends in Raman Spectra from Kerogen and Coal. Energy Fuels 2001, 15(3), 653-658. (38) Liu, D.H.; Xiao, X.M.; Tian, H.; et al. Sample maturation calculated using Raman spectroscopic parameters for solid organics： Methodology and geological applications. Chinese Science Bulletin 2013, 58(11), 1285-1298. (39) Marques, M.; Suárez-Ruiz, I.; Flores, D.; Guedes, A.; Rodrigues, S. Correlation between optical, chemical and micro-structural parameters in high-rank coals and graphite. Int. J. Coal Geol. 2009, 77(3-4), 377-382. (40) Dong, S.; Alvarez, P.; Paterson, N.; Dugwell, D.R.; Kandiyoti, R. Study on the effect of heat treatment


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

and gasification on the carbon structure of coal chars and metallurgical cokes using fourier transform Raman spectroscopy. Energy & Fuels 2009, 23(3), 1651-1661. (41) Li, X.J.; Hayashi, J.; Li, C.Z. FT-Raman spectroscopic study of the evolution of char structure during the pyrolysis of a Victorian brown coal. Fuel 2006, 85(12-13), 1700-1707. (42) Liu, X.F.; You, J.L.; Wang Y.Y.; et al. Raman spectroscopic study on the pyrolysis of Australian bituminous coal. Journal of Fuel Chemistry & Technology (China) 2014, 42(3), 270-276. (43) Smędowski, Ł.; Duber, S.; Matuszewska, A. An effect of igneous intrusion on the structure, texture and microtexture of coal from the Sośnica coal mine, Upper Silesian Coal Basin, Poland. Geological Quarterly 2015, 59(3), 507–516. (44) Matuszewska, A.; Pusz, S.; Duber, S. Evaluation of the structure of bituminous coal from Sośnica mine in the Upper Silesian Coal Basin (Poland) using reflectance indicating surface (RIS) parameters. Int. J. Coal Geol. 2015, 152, 177-188. (45) Hinrichs, R.; Brown, M.T.; Vasconcellos, M.A.Z.; Abrashev, M.V.; Kalkreuth, W. Simple procedure for an estimation of the coal rank using micro-Raman spectroscopy. Int. J. Coal Geol. 2014, 136, 52-58. (46) Hou, Q.L.; Li, H.J.; Fan, J.J.; et al. Structure and coalbed methane occurrence in tectonically deformed coals. Science China Earth Sciences 2012, 55(11), 1755-1763. (47) Pan, J.N.; Hou, Q.L.; Ju, Y.W.; et al. Coalbed methane sorption related to coal deformation structures at different temperatures and pressures. Fuel 2012, 102(6), 760-765. (48) Li, X.S.; Ju, Y.W.; Hou, Q.L.; et al. Spectra response from macromolecular structure evolution of tectonically deformed coal of different deformation mechanisms. Science China Earth Sciences 2012, 55(8), 1269-1279.


Page 22 of 38

Page 23 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(49) Zhou, Q.; Xiao, X.M.; Pan, L.; Tian, H. The relationship between micro-Raman spectral parameters and reflectance of solid bitumen. Int. J. Coal Geol. 2014, 121, 19-25. (50) Morga, R.; Jelonek, I.; Kruszewska, K. Relationship between coking coal quality and its micro-Raman spectral characteristics. Int. J. Coal Geol. 2014, 134, 17-23. (51) Green, P.D.; Johnson, C.A.; Thomas, K.M. Applications of laser Raman microprobe spectroscopy to *

the characterization of coals and cokes . Fuel 1983, 62(9), 1013-1023. (52) Zheng, Z.; Chen, X.H. Raman spectra of coal-based graphite. Science in China, Ser: B 1995, 38(1), 97-106. (53) Nemanich, R.J.; Solin, S.A. First- and second-order Raman scattering from finite-size crystals of graphite. Phys. Rev. B 1979, 20(2), 392-401. (54) Nakamizo, M.; Kammereck, R.; Walker, P.L. Laser raman studies on carbons. Carbon 1974, 12(3), 259-267. (55) Zerda, T.W.; John, A.; Chmura, K. Raman studies of coals. Fuel 1981, 60(5), 375-378. (56) Matthews, M.J.; Pimenta, M.A.; Dresselhaus, G.; Dresselhaus, M.S.; Endo, M. Origin of dispersive effects of the Raman D band in carbon materials. Phys. Rev .B 1999, 59(10), R6585-R6588. (57) Rouzaud, J.N.; Oberlin, A.; Beny-Bassez, C. Carbon films: Structure and microtexture (optical and electron microscopy, Raman spectroscopy). Thin Solid Films 1983, 105(1), 75-96. (58) Saito, R.; Jorio, A.; Filho, A.G.S.; Dresselhaus, G.; Dresselhaus, M.S.; Pimenta, M.A. Probing phonon dispersion relations of graphite by double resonance Raman scattering. Phys. Rev. Lett. 2002, 88(2), 237-257. (59) Thomsen, C.; Reich, S. Double Resonant Raman Scattering in Graphite. Phys. Rev. Lett. 2000, 85(24), 5214-5217.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(60) Lespade, P.; Marchand, A.; Couzi, M.; Cruege, F. Caracterisation de materiaux carbones par microspectrometrie Raman. Carbon 1984,22(4–5), 375-385. (61) Nestler, K.; Dietrich, D.; Witke, K.; Rößler, R.; Marx, G. Thermogravimetric and Raman spectroscopic investigations on different coals in comparison to dispersed anthracite found in permineralized tree fern Psaronius sp.. J. Mol. Struct. 2003, 661(25), 357-362. (62) Quirico, E.; Montagnac, G.; Rouzaud, J-N. et al. Precursor and metamorphic condition effects on Raman spectra of poorly ordered carbonaceous matter in chondrites and coals. Earth Planet. Sci. Lett. 2009, 287(1–2), 185-193. (63) Kastner J, Pichler T, Kuzmany H, Curran, S.; Blau, W.; Weldon, D.N.; Delamesiere, M.; Draper, S.; Zandbergen, H. Resonance Raman and infrared spectroscopy of carbon nanotubes. Chem. Phys. Lett. 1994, 221(1), 53-58. (64) Ferrari, A.C. Raman Spectroscopy of Graphene and Graphite: Disorder, Electron-Phonon Coupling, Doping and Nonadiabatic Effects. Solid State Commun. 2007, 143(1-2), 47-57. (65) Pan, J.N.; Wang, S.; Ju, Y.W.; et al. Quantitative study of the macromolecular structures of tectonically deformed coal using high-resolution transmission electron microscopy. J. Nat. Gas Sci. Eng. 2015, 27, 1852-1862.


Page 24 of 38

Page 25 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Figure Captions Figure 1. Photomicrographs (A, B, C, D) and hand specimens (a, b, c, d) of coal samples. Weak tectonically deformed coal: A, a; B, b. Strong tectonically deformed coal: C, c; D, d. Figure 2. Raman spectra of coals with different metamorphic degree. Figure 3. The curve-fitting diagram of Raman spectrum from coal sample (XTM10). (a) Three Gaussian functions and linear baseline. (b) Five Gaussian functions and linear baseline. (c) Two Lorentzian functions and linear baseline Figure 4. Variation in the D and G peak positions of coals with different metamorphic degrees and deformation types:(a) D-peak position; (b) G-peak position. Figure 5. Variation of d(G-D) values in the Raman peaks of coals with different metamorphic degree and deformation types. Figure 6. Variation of FWHM-D and G for coals with different metamorphic degrees and deformation types: (a) FWHM-D; (b) FWHM-G Figure 7. Variation of ID/IG for coals with different metamorphic degree and deformation types.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table Captions Table 1. Information of the experimental coal samples Table 2. Raman parameters of coals with different metamorphic degrees and deformation types. Table 3. Mean values of d(G-D) of coals with different metamorphic degrees and deformation types. Table 4. Mean FWHM-G values for coals with different metamorphic degree and deformation types. Table 5. ID/IG mean values of coals with different metamorphic degree and deformation types.


Page 26 of 38

Page 27 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(A)

(a)

(B)

(b)

(C)

(c)

(D)

(d)

Figure 1. Photomicrographs (A, B, C, D) and hand specimens (a, b, c, d) of coal samples. Weak tectonically deformed coal: A, a; B, b. Strong tectonically deformed coal: C, c; D, d.


Energy & Fuels

High rank

FHM03 XZM03 HBM01 SJZM06

Low rank

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 38

500

1000

1500

Wavenumber

2000

/cm-1

Figure 2. Raman spectra of coals with different metamorphic degree.


2500

Page 29 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(a)

(b)

(c) Figure 3. The curve-fitting diagram of Raman spectrum from coal sample (XTM10). (a) Three Gaussian functions and linear baseline. (b) Five Gaussian functions and linear baseline. (c) Two Lorentzian functions and linear baseline.


Energy & Fuels

Weak TDC

1365

1602

Strong TDC

Weak TDC

Strong TDC

1600 y = -7.0987x + 1366.6 R² = 0.8999

1355 1350

WG/cm-1

1360

WD/cm-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 38

y = 2.9647x + 1590 R² = 0.8656

1598 1596

y = 2.8314x + 1589.1 R² = 0.8096

1594

1345 y = -6.3095x + 1361.4 R² = 0.8669

1340

1592 1590

1335 0.5

1.5

2.5

3.5

0.5

1.5

2.5

3.5

Ro,max/%

Ro,max/%

(a)

(b)

Figure 4.Variation in the D and G peak positions of coals with different metamorphic degrees and deformation types: (a) D-peak position; (b) G-peak position


Page 31 of 38

270

Weak TDC

Strong TDC

265 260 d(G-D)/cm-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

y = 9.2741x + 228.63 R² = 0.911

255 250 245 240

y = 9.9301x + 222.56 R² = 0.9113

235 230 225 0.5

1

1.5

2 2.5 Ro,max/%

3

3.5

4

Figure 5.Variation of d(G-D) values in the Raman peaks of coals with different metamorphic degree and deformation types


Energy & Fuels

Weak TDC

270

Strong TDC

Weak TDC

60

260

55

250

50

FWHM-G/cm-1

FWHM-D/cm-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

240 230 220 210 200

Page 32 of 38

Strong TDC

R² = 0.8405

45 40 35

R² = 0.863

30 25

190

20 0.5

1.5

2.5

3.5

0.5

1.5

Ro,max/%

(a)

2.5

3.5

Ro,max/%

(b)

Figure 6. Variation of FWHM-D and G for coals with different metamorphic degrees and deformation types: (a) FWHM-D; (b) FWHM-G


Page 33 of 38

0.9

Weak TDC

0.85 0.8

Strong TDC R² = 0.8217

0.75

ID/IG

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.7 0.65

R² = 0.7586

0.6 0.55 0.5 0.5

1

1.5

2

2.5

3

3.5

4

Ro,max/% Figure 7. Variation of ID/IG for coals with different metamorphic degree and deformation type.


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Page 34 of 38

Table 1. Information of the experimental coal samples Sample ID

Location

Vitrinite

Proximate analysis, ω/%

Ultimate analysis, ωdaf/%

Extent of

The characteristics of tectonically deformed

Ro, max

deformation

coal

/%

0.71

Weak tectonically deformed coal presents a

0.93

/%

Mad

Ad

Vdaf

FCd

C

H

O

N

S

7.32

78.50

61.70

2.42

34.85

0.32

XTM09

Xutuan Colliery

60.40

7.65

7.65

SJZM04

Shenjiazhuang Colliery

86.38

0.53

12.29

25.79

65.23

87.19

4.96

5.48

2.03

0.34

weak tectonic stress on the coal body; thus,

1.11

8.26

26.14

67.76

88.16

4.88

4.97

1.61

0.34

the overall structure is relatively intact, and

1.18

9.23

23.81

69.15

88.40

4.57

5.24

1.49

0.27

the primary structure of coal almost can be

1.26

SJZM02


86.51

0.74

SJZM06


75.50

0.77

HBM01

Hebi Colliery

93.51

0.98

8.52

16.69

76.21

89.55

4.33

4.16

1.67

0.27

2.04

11.18

87.01

89.22

3.76

5.17

1.47

0.36

12.16

11.97

77.41

83.05

3.75

11.30

1.57

0.33

TLM01

Tunliu Colliery

94.00

2.93

ZZM01

Zhaozhuang Colliery

94.57

0.69

Weak tectonic deformation

observed. The coal has high mechanical strength and is difficult to separate by hand with present a larger fragmental. The structure of fractures and joints are common,

1.91 2.09 2.16

XZM05

Xinzhuang Colliery

92.03

1.28

15.61

14.67

72.01

88.20

3.22

6.64

1.37

0.49

XZM04

Xinzhuang Colliery

89.14

1.38

6.95

7.39

86.18

91.77

3.38

3.12

1.22

XZM03

Xinzhuang Colliery

93.31

1.25

8.98

7.58

84.12

91.43

3.35

3.62

1.09

FHM03

Fenghuangshan Colliery

91.70

0.81

13.79

6.55

80.62

70.16

2.57

25.14

0.84

XTM07

Xutuan Colliery

56.60

5.80

7.95

6.72

80.45

54.76

1.77

42.42

0.28

0.77

0.88

6.97

16.69

72.40

64.57

2.64

30.87

1.46

0.46

0.90

and cracks may occur along the fracture or

2.37

0.48

joint plane with a flat fracture surface. In

2.53

0.47

addition, the gloss of coal is from light to

2.73

1.28

semi-bright.

3.77

XTM06

Xutuan Colliery

56.00

6.13

XTM10

Xutuan Colliery

54.00

14.90

5.85

18.80

64.35

69.89

2.64

26.82

0.36

0.29

Strong tectonically deformed coal presents

0.96

SJZM01

ShenjiazhuangColliery

78.65

0.48

13.91

27.18

62.82

76.51

4.53

16.79

1.85

0.32

strong tectonic stress on the coal body; thus,

1.12 1.14 1.21

PMBK05 LHM14 LHM03 CHM07

th

Pingdingshan 8 Colliery

92.25

1.20

7.09

21.02

73.38

88.19

4.40

5.63

1.45

0.30

the primary structure of coal has been

Linhuan Colliery

70.00

1.71

3.70

22.01

75.10

87.56

4.56

5.88

1.50

0.47

obviously destroyed, and the coal bedding

Linhuan Colliery Chaohua Colliery

67.70

1.51

1.68

22.98

75.73

87.24

4.58

6.32

1.45

0.41

88.40

1.13

8.05

14.27

78.83

90.01

4.05

3.74

1.74

0.42

2.64

10.01

87.27

79.25

3.97

14.76

1.58

0.43

16.18

69.36

88.94

4.29

5.05

1.29

0.35

CHM05

Chaohua Colliery

91.77

0.08

CHM04

Chaohua Colliery

83.20

0.89

17.25

CHM03

Chaohua Colliery

90.40

0.70

13.98

16.83

71.66

76.42

3.85

17.58

1.49

8.06

15.49

77.70

90.24

4.33

3.41

1.61

Strong tectonic deformation

has almost disappeared due to stronger tectonism. The coal forms irregular crumb structures with subangular or subrounded particles and Mylonite structure of some coal

1.33 1.49 1.56

low

1.78

0.66

strength and can be turned into fine grains or

1.86

0.37

powder by hand. Besides, the whole gloss of

1.86

coal is dim.

2.50

is

developmental,

which

exhibits

HBM06

Hebi Colliery

91.69

1.12

HZM10

Haizi Colliery

74.20

0.64

5.68

13.19

81.35

80.83

2.83

14.44

1.27

0.63

XZM01

Xinzhuang Colliery

93.62

0.99

2.29

8.66

88.35

82.10

3.24

12.23

1.48

0.95

2.57

FHM04

Fenghuangshan Colliery

89.86

0.76

18.27

6.19

76.72

74.33

2.56

20.97

0.83

1.32

3.80


Page 35 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 2. Raman parameters of coals with different metamorphic degrees and deformation types Sample ID

Ro, max%

D peak /cm-1

G peak /cm-1

d (G-D) /cm-1

FWHM-D /cm-1

FWHM-G /cm-1

ID/IG

XTM09 SJZM04 SJZM02 SJZM06 HBM01 TLM01 ZZM01 XZM05 XZM04 XZM03 FHM03

0.93 1.11 1.18 1.26 1.91 2.09 2.16 2.37 2.53 2.73 3.77

1355.2 1355.2 1351.5 1351.5 1353.2 1351.2 1349.2 1344.1 1344.1 1344.1 1336.7

1592.2 1592.8 1593.8 1592.8 1595.5 1596.6 1596.2 1599.2 1598.2 1598.5 1599.5

237 237.6 242.3 241.3 242.3 245.4 247 255.1 254.1 254.4 262.8

255.9 257.3 260.2 259.3 255.5 248.6 240.8 246.6 227.7 243.2 216.6

52.8 53.4 53.5 51.8 55.5 49.2 48.2 44.4 43.7 42.5 33.3

0.85 0.84 0.81 0.77 0.74 0.75 0.76 0.72 0.72 0.7 0.69

XTM07 XTM06 XTM10 SJZM01 PMBK05 LHM14 LHM03 CHM07 CHM05 CHM04 CHM03 HBM06 HZM10 XZM01 FHM04

0.88 0.90 0.96 1.12 1.14 1.21 1.33 1.49 1.56 1.78 1.86 1.86 2.5 2.57 3.80

1360 1359.8 1358 1358.9 1356.2 1357 1357 1354.2 1356.5 1357.2 1356.5 1354.2 1351.2 1347.8 1336.7

1592.2 1591.2 1592.2 1593.1 1592.2 1593.2 1591.2 1593.5 1593.5 1594.5 1594.5 1594.5 1593.2 1597.9 1600.6

232.2 231.4 234.2 234.2 236 236.2 234.2 239.3 237 237.3 238 240.3 242 250.1 263.9

248.6 236.9 229.6 235.1 251.6 249.3 235 249.2 239 234 234.9 254.5 230.2 231.9 207.1

52.1 53.2 48 48.1 50.5 52.8 48 48.1 44.4 44.4 48.1 48.1 40.2 40.7 33.3

0.84 0.84 0.82 0.75 0.73 0.78 0.79 0.7 0.71 0.72 0.73 0.69 0.66 0.65 0.63


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 38

Table 3. Mean values of d(G-D) of coals with different metamorphic degree and deformation types. Metamorphic grade

d(G-D) mean value of weak-TDC/cm-1

d(G-D) mean value of strong-TDC/cm-1

Low metamorphic grade

237

232.6

Middle metamorphic grade

240.9

236.9

High metamorphic grade

253.1

252.0


Page 37 of 38

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 4. Mean FWHM-G values for coals with different metamorphic degree and deformation types

Metamorphic grade

FWHM-G mean value of weak-TDC /cm-1

FWHM-G mean value of strong-TDC /cm-1

Difference of FWHM-G mean value of weak and strong TDC /cm-1


52.8

51.1

1.7


53.6

48.1

5.5


43.6

38.1

5.5


Energy & Fuels

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 38

Table 5. Mean ID/IG values of coals with different metamorphic degree and deformation types Metamorphic grade

ID/IG mean values of weak-TDC

ID/IG mean values of strong-TDC


0.85

0.83


0.79

0.73


0.72

0.65


Effects of Metamorphism and Deformation on the Coal

Recommend Documents