The differences of nanoscale mechanical properties among coal maceral groups

Hou, Chenliang; Jiang, Bo; Liu, Hewu; Song, Yu

doi:10.1016/j.jngse.2020.103394

Cited by 18 publications

(22 citation statements)

References 57 publications

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“…Furthermore, its deformation behavior is believed to be influenced by the distribution of various maceral groups with different mechanical properties, as has been demonstrated in recent studies (Anmin Hou et al, 2020). The aforementioned studies on the properties of coal macerals utilized depth-sensing nanoindentation technology (DSNI), which allows the mechanical properties of coal maceral groups to be precisely measured (Kossovich et al, 2019;Anmin Wang et al, 2020;Hou et al, 2020). In contrast to traditional centimeter-scale tests of coal mechanical properties (for example, uniaxial compression, triaxial compression, and tension tests etc.…”

Section: Introductionmentioning

confidence: 88%

“…Coal, being mainly composed of different types of maceral groups, is a highly heterogeneous material at different length scales and cannot be treated as uniform (Sun et al, 2020a). Furthermore, its deformation behavior is believed to be influenced by the distribution of various maceral groups with different mechanical properties, as has been demonstrated in recent studies (Anmin Hou et al, 2020). The aforementioned studies on the properties of coal macerals utilized depth-sensing nanoindentation technology (DSNI), which allows the mechanical properties of coal maceral groups to be precisely measured (Kossovich et al, 2019;Anmin Wang et al, 2020;Hou et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulation of the Nanoindentation of Coal Vitrinite

2022

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Coal deformation is closely correlated with the distribution of organic maceral groups, however, molecular dynamics (MD) simulations of vitrinite nanoindentation have rarely been conducted. In this study, the vitrinite substrate for indentation was constructed utilizing polymer consistent force field (PCFF), and a spherical ghost indenter was used for loading. The results showed that: 1) In the indentation process, some of the vitrinite atoms overcame the energy barrier to move, with the most important deformation mechanism including the sliding, bending, and reorientation of vitrinite molecular chains, leading to the formation of a shearing transformation zone (STZ), which was also found to contain structural defects and stacking of aromatic structures. 2) The distribution of atomic displacements in the vitrinite substrate could be subdivided into distinct regions, with slippage at the region boundaries producing shear bands. 3) The surface morphology and mechanical properties obtained from the nanoindentation simulation were similar to experimental results from the literature, indicating that MD simulations are a powerful tool for studying coal nanoindentation. The results from this study increase the current scientific understanding of the mechanical properties of vitrinite by providing a new perspective that elucidates the nanoscale structural evolution occurring during the indentation process.

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Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of the Nanoindentation of Coal Vitrinite

2022

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“…The correlation between the brittleness index and macerals in the primary structure coal is better than that of the cataclastic and granulate structure coal (Figures 4(a) and 4(b)). Previous studies have shown that different components of coal have different effects on brittleness, grindability, and breakability of coal, and the brittleness of the coal structure rather than its hardness dominates coal grindability [19,27,28]. The vitrinite is the brittleness component in coal, and the inertinite is the hardness component in coal.…”

Section: Influence Of Macerals On Coalmentioning

confidence: 99%

Brittleness Index of High-Rank Coal Reservoir and Its Influencing Factors in Mabidong Block, Qinshui Basin, China

et al. 2021

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Brittleness index is an important mechanical index to evaluate the fracturability of conventional oil and gas reservoirs. However, the brittleness index of an organic coal reservoir is more complex. In this study, based on array sonic logging and density logging data, coal brittleness index is calculated using an elastic parameter method in the Mabidong coalbed methane (CBM) block in southern Qinshui Basin. In combination with coal-body structure observation, the maceral analysis, and proximate data of coal cores, a comprehensive study of geological influencing factors of coal brittleness index has been carried out. According to coal fragmentation degree, the coal-body structure of coal seams can be divided into primary, cataclastic, and granulate structure. The average interval of brittleness index of primary, cataclastic, and granulate structural coals is 63.3-71.48, 73.01-74.85, and 77.41-82.77, respectively. The results indicate that generally the order of brittleness index is primary structural coal < cataclastic structural coal < granulate structural coal. Young’s modulus and the brittleness index have a good positive correlation. Poisson’s ratio and the brittleness index are negatively correlated in No. 3 coal seam but are positive correlated in No. 15 coal seam. The vitrinite content is positively correlated with brittleness index, and the inertinite content is negatively correlated. For the primary and cataclastic structure coal, the ash and volatile is positively correlated with the brittleness index. The correlation of brittleness index, macerals, and coal quality parameters in the primary structure coal is better than that of the cataclastic and granulate structure coal. The research results are helpful to guide the coal brittleness index and coal-body structure prediction in fracturing of CBM wells.

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“…The pressure-loading/unloading process of the experiment was recorded by a sensor and the load-displacement curve of the nanoindentation was obtained ( Figure 3). Because the TDC is extremely soft, it must be conglutinated by epoxy resin so that the TDC can be tested, which is a common approach by many researchers because the "side-effect" of glue to the measurement results can be negligible [21]. The experimental equipment is a nanoindentation tester produced by Swiss CSM Instrument Co., Ltd, Peseux, Switzerland, with a minimum load of 25 μN, a maximum load of 350 mN and a maximum indentation depth of 3100 μm, with a displacement resolution of 0.0004 nm.…”

Section: Nanoindentation Experimentsmentioning

confidence: 99%

“…Pan et al [20] revealed that the coal strength and Young's modulus are strongly related to coal rank and composition by comparing coals of different vitrinite reflectances and compositions. Hou et al [21] determined that the hardness and elastic modulus are in the order of exinite < vitrinite < inertinite by employing depth-sensing nanoindentation. Kožušníková [22] revealed that the Vickers microhardness and elastic modulus of coal sample with higher coalification were lower than of coal sample with lower coalification and also, Godyńand et al [23] found that micro-hardness value decreases with metamorphism degree using Vickers hardness test in Silesian Coal Basin, Poland.…”

Section: Introductionmentioning

confidence: 99%

Macromolecular Structure Controlling Micro Mechanical Properties of Vitrinite and Inertinite in Tectonically Deformed Coals—A Case Study in Fengfeng Coal Mine of Taihangshan Fault Zone (North China)

et al. 2020

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In order to study the evolution of the mechanical properties and macromolecular structures in different macerals of tectonically deformed coal (TDC), vitrinite and inertinite samples were handpicked from six block TDCs in the same coal seam with an increasing deformation degree (unaltered, cataclastic, porphyroclast, scaly and powdery coal). The micro mechanical properties were tested by the nanoindentation experiment and the macromolecular structures were measured using 13C nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The results show that the range of hardness and elastic modulus of inertinite is 0.373–1.517 GPa and 4.339–12.158 GPa, respectively, which is significantly higher than that of vitrinite with values of 0.278–0.456 GPa and 4.857–7.810 GPa, respectively. From unaltered coal to powdery coal, the hardness of vitrinite and inertinite gradually decreases, with the difference between these macerals becomes smaller and the elastic modulus of vitrinite shows an increasing trend, while that of inertinite was more variable. Both the NMR and FITR results reveal that the macromolecular structure of inertinite has similar structural transitions as vitrinite. As the degree of deformation increases, the aliphatic side chains become shorter and the aromaticity is increasing. Macromolecular alterations caused by tectonic stress is expected to produce defects in the TDCs, therefore there should be more interspacing among the macromolecular groups for the extrusion of macromolecules caused by the indenter of the nanoindentation experiment, thereby reducing the hardness. The elastic modulus of coal is believed to be related to intermolecular forces, which are positively correlated to the dipole moment. By calculating the dipole moments of the typical aromatic molecular structures with aliphatic side chains, the detachment of the aliphatic side chains and the growth of benzene rings can both increase the dipole moment, which can promote elastic modulus. In addition, the increasing number of benzene rings can create more π-π bonds between the molecules, which can lead to an increase in the intermolecular forces, further increasing the elastic modulus.

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The differences of nanoscale mechanical properties among coal maceral groups

Cited by 18 publications

References 57 publications

Molecular Dynamics Simulation of the Nanoindentation of Coal Vitrinite

Molecular Dynamics Simulation of the Nanoindentation of Coal Vitrinite

Brittleness Index of High-Rank Coal Reservoir and Its Influencing Factors in Mabidong Block, Qinshui Basin, China

Macromolecular Structure Controlling Micro Mechanical Properties of Vitrinite and Inertinite in Tectonically Deformed Coals—A Case Study in Fengfeng Coal Mine of Taihangshan Fault Zone (North China)

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