A Multiscale Structural Analysis of Soft and Hard Coal Deposits in Deep High-Gas Coal Seams

In recent years, with the increases in coal mining depths, the risk of coal seam outburst occurrences has increased. Therefore, it is of major significance to study the multiscale structures of soft and hard coal deposits in order to prevent and control the coal and gas outbursts. In this research investigation, soft and hard coal multiscale structures were comprehensively examined using various laboratory methods. The results revealed the following: (1) From a macrostructural aspect, the physical and mechanical properties of the soft coal were weaker than those of the hard coal. It was found that the majority of the examined specimens were characterized by scaly structures without blocks larger than 50 mm. The hard coal was observed to be mainly massive with only a small part being clastic. Therefore, the structural characteristics were considered to be stable. (2) From a microstructural perspective, the surfaces of the soft coal specimens were observed to be rough. The pores were found to be more developed, with the edge of pores being mainly hackly. At the same time, fractures were also relatively developed, showing good connectivity. (3) From a micropore structural perspective, it was found that the BET-specific surface areas and BJH-specific surface areas of the soft coal specimens were higher than those of the hard coal specimens, which indicated that the gas adsorption and diffusion migration abilities of the soft coal were greater than those of the hard coal. (4) It was suggested from the study results that the ventilation and gas extraction processes should be strengthened in the mining activities of coal seams with high, soft stratification content. At the same time, the methods used for water injection modification should be enhanced in order to improve the mechanical stability of soft coal. Consequently, the instantaneous released gases will be decelerated, and the occurrences of coal and gas outburst events in mine working faces can be prevented.

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A Study of the Differences in the Gas Diffusion and Migration Characteristics of Soft and Hard Coal in High Gas Coal Seams

Advances in Civil Engineering ◽

10.1155/2020/8825625 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Anying Yuan

Keyword(s):

Coal Particle ◽

Gas Diffusion ◽

Hard Coal ◽

Coal Seams ◽

Surface Areas ◽

Soft Coal ◽

Gas Desorption ◽

Major Significance ◽

Specific Surface Areas ◽

And Migration

At the present time, it is of major significance to examine the differences in the gas diffusion and migration characteristics of soft and hard coal in order to prevent and control safety hazards in high gas coal seams. In this study, the differences in the gas diffusion and migration characteristics between soft coal and hard coal were examined in detail using macrostructural, mesostructural, and microstructural research methods. The root causes of the differences in the gas diffusion and migration between soft coal and hard coal were revealed in the obtained research results. The study shows that, in terms of the macrostructures, the soft coal particle grains were flakey and with shapes resembling fingernails. Meanwhile, the hard coal particle grains were observed to be in the shapes of complete blocks. In addition, in terms of the mesostructures of the different coal types, it was found that the proportion of granular coal below the particle size limit of 6 mm in the soft coal was much higher than that of the hard coal. Also, from the aspect of the characteristics of the microstructures, the pores and fissures on the soft coal surfaces were observed to be better developed, and the BJH specific surface areas of the soft coal were more than twice those of the hard coal. That is to say, the gas diffusion and migration conditions of the soft coal were better than those of the hard coal. At the same time, the increments of the specific surface areas and volumes of the pores of soft coal were above 100 nm, which provided channels for gas diffusion and migration at rates of more than twice those of the hard coal. Therefore, the soft coal was more conducive to gas emissions. This study conducted gas desorption experiments on both soft and hard coal samples and found that the initial gas desorption speed of the soft coal was significantly higher than that of the hard coal. Since the instantaneous gas emissions of the soft coal were significantly higher than those of the hard coal, it was considered to be more likely that gas outbursts and transfinite accidents could potentially occur in the soft coal layers of a project site. This study’s results provided a foundation and basis for effective gas control measures in coal seams composed of soft coal layers, which will be of major significance to the safety of coal mining activities in the future.

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Electrospun structures with controlled specific surface areas and pores

57th International Astronautical Congress ◽

10.2514/6.iac-06-c2.4.07 ◽

2006 ◽

Author(s):

Vasana Maneeratana ◽

Wolfgang M. Sigmund

Keyword(s):

Specific Surface ◽

Surface Areas ◽

Specific Surface Areas

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Ultrafine porous boron nitride nanofibers synthesized via a freeze-drying and pyrolysis process and their adsorption properties

RSC Advances ◽

10.1039/c5ra23426c ◽

2016 ◽

Vol 6 (2) ◽

pp. 1253-1259 ◽

Cited By ~ 42

Author(s):

Jing Lin ◽

Lulu Xu ◽

Yang Huang ◽

Jie Li ◽

Weijia Wang ◽

...

Keyword(s):

Boron Nitride ◽

Specific Surface ◽

Freeze Drying ◽

Adsorption Properties ◽

Pyrolysis Process ◽

Surface Areas ◽

Aspect Ratios ◽

Large Pore ◽

Specific Surface Areas

Ultrafine porous boron nitride nanofibers with high aspect ratios, high specific surface areas and large pore volumes has been synthesized in large quantity via a freeze-drying and post pyrolysis process.

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Experimental Investigation of Coal Dust Wettability Based on Surface Contact Angle

Journal of Chemistry ◽

10.1155/2016/9452303 ◽

2016 ◽

Vol 2016 ◽

pp. 1-8 ◽

Cited By ~ 15

Author(s):

Gang Zhou ◽

Han Qiu ◽

Qi Zhang ◽

Mao Xu ◽

Jiayuan Wang ◽

...

Keyword(s):

Surface Tension ◽

Contact Angle ◽

Specific Surface ◽

Coal Dust ◽

Single Point ◽

Contact Angles ◽

Critical Surface ◽

Volume Percentage ◽

Surface Areas ◽

Specific Surface Areas

Wettability is one of the key chemical properties of coal dust, which is very important to dedusting. In this paper, the theory of liquid wetting solid was presented firstly; then, taking the gas coal of Xinglongzhuang coal mine in China as an example, by determination of critical surface tension of coal piece, it can be concluded that only when the surface tension of surfactant solution is less than 45 mN/m can the coal sample be fully wetted. Due to the effect of particle dispersity, compared with the contact angle of milled coal particle, not all the contact angles of screened coal powder with different sizes have a tendency to increase. Furthermore, by the experiments of coal samples’ specific surface areas and porosities, it can be achieved that the volume of single-point total pore decreases with the gradual decreasing of coal’s porosity, while the ultramicropores’ dispersities and multipoint BET specific surface areas increase. Besides, by a series of contact angle experiments with different surfactants, it can be found that with the increasing of porosity and the decreasing of volume percentage of ultramicropore, the contact angle tends to reduce gradually and the coal dust is much easier to get wetted.

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Facile Method To Synthesize Mesoporous Multimetal Oxides (ATiO3, A = Sr, Ba) with Large Specific Surface Areas and Crystalline Pore walls

Chemistry of Materials ◽

10.1021/cm903303v ◽

2010 ◽

Vol 22 (4) ◽

pp. 1276-1278 ◽

Cited By ~ 39

Author(s):

Xiaoxing Fan ◽

Ying Wang ◽

Xinyi Chen ◽

Ling Gao ◽

Wenjun Luo ◽

...

Keyword(s):

Specific Surface ◽

Surface Areas ◽

Specific Surface Areas

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Carbon Microspheres Prepared by High Internal Phase Emulsion Polymerization

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.239-242.3105 ◽

2011 ◽

Vol 239-242 ◽

pp. 3105-3108

Author(s):

Ming Xian Liu ◽

Li Hua Gan ◽

Jun Hu ◽

Hong Lai Liu ◽

Long Wu Chen

Keyword(s):

Electron Microscopy ◽

Specific Surface ◽

Aqueous Phase ◽

Apparent Density ◽

Tween 80 ◽

Carbon Microspheres ◽

High Internal Phase Emulsion ◽

Surface Areas ◽

Internal Phase ◽

Specific Surface Areas

In this paper, we present a novel approach for the synthesis of carbon microspheres via the polymerization of a high internal phase emulsion (HIPE). By using Span 80 and Tween 80 as emulsifiers, 1iquid paraffin as oil phase, and the mixture of resorcinol/formaldehyde (R/F) solution as aqueous phase, an O/W emulsion was obtained. This emulsion phase inverted to a W/O HIPE induced by ammonia which served as the polymerization catalyst. Carbon microspheres (CMs) were prepared by polymerization of the HIPE, followed by drying and carbonization. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) analyzer were used to characterize as-prepared CMs. The results indicate that, in case of 0.25 wt% ammonia of the HIPE, the diameters of CMs decreased from about 2 to 1 μm when the mass fraction of aqueous R/F decreased from 0.714 to 0.357; the apparent density and the specific surface areas of the CMs, however, did not change obviously, which are about 0.6 g/cm3and 200 m2/g, respectively. The dosage of ammonia has a significant influence on the morphology and properties of CMs. With increasing of the ammonia mass to 1 wt% of the HIPE, the resultant carbon materials comprise not only CMs, but also some carbon sheets; the apparent density of which increased to 0.9 g/cm3and the specific surface areas of which decreased to below 100 m2/g. In addition, the other parameters for CMs preparation were also investigated. It was found that the proper conditions were controlling the temperature of 303-333 K and the oil/aqueous phase mass ratio of 2.5:7.

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The Experimental Study on Grinding Properties of Gas Quenching Steel Slag

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.189-193.612 ◽

2011 ◽

Vol 189-193 ◽

pp. 612-617

Author(s):

Hong Wei Xing ◽

Yue Long ◽

Xiu Li ◽

Gao Liang Li ◽

Yu Zhu Zhang ◽

...

Keyword(s):

Specific Surface ◽

New Technology ◽

Steel Slag ◽

Economic Benefits ◽

Surface Areas ◽

Mineral Phases ◽

Quenching Process ◽

Gas Quenching ◽

Specific Surface Areas ◽

Better Than

A gas quenching process to deal with steel slag and its characteristics of the new technology was briefly introduced. The grinding characteristics, mineral phases of gas quenching steel slag and the potential economic benefits of using it as cement mixing material was studied by compared to heat-stew steel slag. The results indicated that the specific surface areas (S) and grinding times (t) of the gas quenching steel slag showed a first order exponential decay relationship. With the extension of time, the specific surface areas of heat-stew steel slag was tending to balance earlier than that of gas quenching steel slag; The energy consumption of gas quenching steel slag was much lower than that of heat-stew steel slag. Gas quenching steel slag was comprised of C2S, C3S, a certain amount of (Ca2(Al, Fe)2O5）and RO phase, but the content of RO phase was relatively low, which increased the grindability of the quenching steel slag, so that the grindability of gas quenching steel slag was much better than that of heat-stew steel slag. Gas quenching steel slag prepared for cement addictives would bring great economic benefits.

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Photocatalytic activity of CaTaO2N nanocrystals obtained from a hydrothermally synthesized oxide precursor

10.31219/osf.io/qdgam ◽

2019 ◽

Author(s):

Roberto Köferstein

Keyword(s):

Photocatalytic Activity ◽

Methyl Orange ◽

Specific Surface ◽

Morphological Properties ◽

Soft Chemistry ◽

Co Catalyst ◽

Surface Areas ◽

Oxide Precursor ◽

Photocatalytic Activities ◽

Specific Surface Areas

Highly crystalline CaTaO2N nanoparticles possessing large specific surface areas were investigated as photocatalysts for the decomposition of methyl orange. Two different Ca2Ta2O7 precursors were synthesized by classical solid state synthesis and a hydrothermal soft-chemistry approach, respectively. In both cases, nitridation was carried out by thermal ammonolysis. The obtained CaTaO2N samples were compared with respect to their optical, thermal and morphological properties as well as their photocatalytic activities. In particular, the influence of ammonolysis temperature on the photocatalytic properties was studied. Using hydrothermally synthesized Ca2Ta2O7, phase pure CaTaO2N was obtained already at a relatively low ammonolysis temperature of 860 °C. Morphological investigations show that the CaTaO2N samples from the hydrothermally synthesized precursor consist of single-crystalline particles of 45 to 70 nm diameter with high specific surface areas between 12 and 19 m2 g-1, depending on ammonolysis temperature. A considerable photocatalytic activity for methyl orange degredation was found for the nanoscaled CaTaO2N particles prepared at lower ammonolysis temperatures. Using CoOx as co-catalyst, a further strong enhancement of the methyl orange decomposition by a factor 5-10 was achieved.

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