CONNECTIONS BETWEEN MICRO/NANO SCALE HETEROGENEITY OF MECHANICAL PROPERTIES OF COALS AND THEIR PROPENSITY TO OUTBURSTS AND CRUSHING
The outbursts of coal and gas is one of the main coal mining hazards, therefore, for the coal mining industry, studying of mechanisms and predisposing factors for these events is of the utmost importance. It is demonstrated here that the micro/nano scale structure of coal samples is one of predisposing factors for the coal propensity to outburst. The same is related to the coal propensity to crushing and formation of fine powder (dust). The results of micro/nanoindentation experimental studies of heterogeneity of spatial distribution brittleness and mechanical properties of coals at micro/nano scales are presented for samples taken from both hazardous (outburstprone) and non-hazardous strata (packs) of the same coal seam. The experiments were performed on both ‘as received’ coal samples and ones after sorption treatment by dimethylformamide. The latter treatment allowed to partially discharge the internal stresses that exist in the coal samples. The mapping the indentation results enabled us to reveal the actual heterogeneity of distribution of mechanical properties at nanoscale. It has been confirmed that hardness of coals at microand nanoscale is not an informative parameter for characterization of their propensity to destruction. It was established that higher heterogeneity of stiffness could be a reason to formation of multiple cracks at coals after microhardness tests. The part of energy spent for the irreversible changes in the material structure within the total work of indentation is the parameter indicating clearly the propensity of coal samples to crushing and formation of fine powder (dust). Coal samples from the non-hazardous packs have a low ratio of inclusions prone to irreversible changes of the structure and those prone to keeping their structural integrity, while the ratio is about a unity for samples from the hazardous packs. Thus, there is a natural distinction of the mechanical properties between two coal samples having similar origin and rank but different in their proneness to instantaneous outbursts.
Acknowledgements: This work was supported by the Russian Science Foundation (grant # 18-7710052).
For citation: Kossovich E. L., Epshtein S. A., Borodich F. M., Dobryakova N. N., Prosina V. A. Connections between micro/nano scale heterogeneity of mechanical properties of coals and their propensity to outbursts and crushing. Gornyy informatsionno-analiticheskiy byulleten'. 2019;5:156-172. [In Russ]. DOI: 10.25018/0236-1493-2019-05-0-156-172.
: Kossovich E. L., Epshtein S. A., Borodich F. M., etc.
E.L. Kossovich (1), Ph.D., senior researcher, e-mail: firstname.lastname@example.org,
S.A. Epshtein (1), D.Sci. (Engineering), Head of Laboratory, e-mail: email@example.com,
F.M. Borodich, D.Sci. (Physics and Mathematics), Professor,
School of Engineering, Cardiff University, Cardiff, UK,
N.N. Dobryakova (1), Ph.D. (Engineering), Leading Engineer,
V.A. Prosina1, Engineer,
1) Scientific and Training Laboratory of Physics and Chemistry of Coals,
National University of Science and Technology «MISiS», 119049, Moscow, Russia.
Corresponding author: E.L. Kossovich, e-mail: firstname.lastname@example.org.Key words
Сoal, mechanical properties, heterogeneity, fine dust, brittleness, sorption-induced strength degradation.References
1. Rout T. K., Masto R. E., Padhy P. K., George J., Ram L. C., Maity S. Dust fall and elemental flux in a coal mining area. Journal of Geochemical Exploration, 2014. Vol. 144, no PC, pp. 443—455. DOI: 10.1016/j.gexplo.2014.04.003.
2. Tang Z., Chai M., Cheng J., Jin J., Yang Y., Nie Z., Huang Q., Li Y. Contamination and health risks of heavy metals in street dust from a coal-mining city in eastern China. Ecotoxicology and Environmental Safety, 2017. Vol. 138, pp. 83—91. DOI: 10.1016/j.ecoenv.2016.11.003.
3. Shepherd J., Rixon L. K., Griffiths L. Outbursts and geological structures in coal mines. A review. International Journal of Rock Mechanics and Mining Sciences and, 1981. Vol. 18, no 4, pp. 267—283. DOI: 10.1016/0148-9062(81)91192-X.
4. Lama R. D., Bodziony J. Management of outburst in underground coal mines. International Journal of Coal Geology, 1998. Vol. 35, no 1—4, pp. 83—115. DOI: 10.1016/S01665162(97)00037-2.
5. Fedorova G. G., Sidorov I. N., Afanas’ev K.M. Dispersion of coal in a gaseous medium under the influence of physicochemical processes, and methods of dust suppression. Soviet Mining Science, 1974. Vol. 10, no 4, pp. 498—503. DOI: 10.1007/BF02501444.
6. Johann-Essex V., Keles C., Rezaee M., Scaggs-Witte M., Sarver E. Respirable coal mine dust characteristics in samples collected in central and northern Appalachia. International Journal of Coal Geology, 2017. Vol. 182, no March, pp. 85—93. DOI: 10.1016/j.coal.2017.09.010.
7. Organiscak J. A., Page S. J. Airborne Dust Liberation During Coal Crushing. Coal Preparation, 2000. Vol. 21, no 5—6, pp. 423—453. DOI: 10.1080/07349340108945630.
8. An F. H., Cheng Y. P. An explanation of large-scale coal and gas outbursts in underground coal mines: The effect of low-permeability zones on abnormally abundant gas. Natural Hazards and Earth System Sciences, 2014. Vol. 14, no 8, pp. 2125—2132. DOI: 10.5194/ nhess-14-2125-2014.
9. Fisne A., Esen O. Coal and gas outburst hazard in Zonguldak Coal Basin of Turkey, and association with geological parameters. Natural Hazards, 2014. Vol. 74, no 3, pp. 1363—1390. DOI: 10.1007/s11069-014-1246-9.
10. Ding Y., Dou L., Cai W., Chen J., Kong Y., Su Z., Li Z. Signal characteristics of coal and rock dynamics with micro-seismic monitoring technique. International Journal of Mining Science and Technology, 2016. Vol. 26, no 4, pp. 683—690. DOI: 10.1016/j.ijmst.2016.05.022.
11. Wang S., Elsworth D., Liu J. Rapid decompression and desorption induced energetic failure in coal. Journal of Rock Mechanics and Geotechnical Engineering, 2015. Vol. 7, no 3, pp. 345—350. DOI: 10.1016/J.JRMGE.2015.01.004.
12. Wen Z., Wang X., Tan Y., Zhang H., Huang W., Li Q. A Study of Rockburst Hazard Evaluation Method in Coal Mine. Shock and Vibration, 2016. Vol. 2016, pp. 1—9. DOI: 10.1155/2016/8740868.
13. Li X., Wang C., Zhao C., Yang H. The propagation speed of the cracks in coal body containing gas. Safety Science, 2012. Vol. 50, no 4, pp. 914—917. DOI: 10.1016/j.ssci.2011.08.004.
14. Beamish B. B., Crosdale P. J. Instantaneous outbursts in underground coal mines: an overview and association with coal type. International Journal of Coal Geology, 1998. Vol. 35, no 1—4, pp. 27—55. DOI: 10.1016/S0166-5162(97)00036-0.
15. Molchanov O., Rudakov D., Soboliev V., Kamchatnyi O. Destabilization of the hard coal microstructure by a weak electric field. E3S Web of Conferences, 2018. Vol. 60, pp. 00023. DOI: 10.1051/e3sconf/20186000023.
16. Bobin V. A., Malinnikova O. N., Odintsev V. N., Trofimov V. A. Analysis of the connection between the microstructure and gas-dynamic fracture susceptibility in coal. Gornyi Zhurnal, 2017, pp. 22—27. DOI: 10.17580/gzh.2017.11.04.
17. Epshtein S. A., Kossovich E. L., Prosina V. A., Dobryakova N. N. Features of sorption-induced strength degradation of coals originated from potentially prone to outburst and non-hazardous packs. Gornyi Zhurnal, 2018, no 12, pp. 18—22. DOI: 10.17580/gzh.2018.12.04.
18. Sergejev F., Kimmari E., Viljus M. Residual Stresses in TiC-based Cermets Measured by Indentation. Procedia Engineering, 2011. Vol. 10, pp. 2873—2881. DOI: 10.1016/j.proeng.2011.04.477.
19. Vatulyan A. O., Lyapin A. A., Kossovich E. L. Studying of Elastoplastic Properties of Coal Specimens Using Indentation Technique. Izv. Saratov Univ. (N. S.), Ser. Math. Mech. Inform., 2018. Vol. 18, no 4, pp. 412—420. DOI: 10.18500/1816-9791-2018-18-4-412-420.
20. ASTM D7708-14, Standard Test Method for Microscopical Determination of the Reflectance of Vitrinite Dispersed in Sedimentary Rocks. West Conshohocken, PA, 2014, www.astm. org: ASTM International. DOI: 10.1520/D7708-14.
21. Kossovich E. L., Epshtein S. A., Shkuratnik V. L., Minin M. G. Perspectives and problems of modern depth-sensing indentation techniques application for diagnostics of coals mechanical properties. Gornyi Zhurnal, 2017. Vol. 2017, no 12, pp. 25—30. DOI: 10.17580/gzh.2017.12.05.
22. Kossovich E., Epshtein S., Dobryakova N., Minin M., Gavrilova D. Mechanical Properties of Thin Films of Coals by Nanoindentation. Physical and Mathematical Modeling of Processes in Geomedia, Moscow: IPMech RAS, 2018, pp. 45—50. DOI: 10.1007/978-3-319-77788-7_6.
23. GOST 21206-75 Coals and anthracite. Determination method for microhardness and microbrittleness. Moscow: Standards publishing, 1977. Russian p.
24. ASTM. ASTM E384: Standard Test Method for Microindentation Hardness of Materials. Annual Book of ASTM Standards, PA: ASTM International, West Conshohocken, 2016. 1-42 p. DOI: 10.1520/E0384-10.2.
25. Khrushchov M. M., Berkovich E. S. Devices PMT-2 and PMT-3 for microhardness testing. Moscow, Izdatelstvo AN USSR, 1950. 66 p.
26. Kossovich E. L., Borodich F. M., Epshtein S. A., Galanov B. A., Minin M. G., Prosina V. A. Mechanical, structural and scaling properties of coals: depth-sensing indentation studies. Applied Physics A, 2019. Vol. 125, no 3, pp. 195. DOI: 10.1007/s00339-018-2282-1.
27. Sakai M. Energy principle of the indentation-induced inelastic surface deformation and hardness of brittle materials. Acta Metallurgica Et Materialia, 1993. Vol. 41, no 6, pp. 1751— 1758. DOI: 10.1016/0956-7151(93)90194-W.
28. Argatov I. I., Borodich F. M., Epshtein S. A., Kossovich E. L. Contact stiffness depth-sensing indentation: Understanding of material properties of thin films attached to substrates. Mechanics of Materials, 2017. Vol. 114, pp. 172—179. DOI: 10.1016/j.mechmat.2017.08.009.
29. Baumgart F. Stiffness — an unknown world of mechanical science?. Injury, 2000. Vol. 31, pp. S-B14-S-B23. DOI: 10.1016/S0020-1383(00)80040-6.
30. Borodich F. M. The Hertz-Type and Adhesive Contact Problems for Depth-Sensing Indentation. Advances in Applied Mechanics, 2014. Vol. 47, pp. 225—366. DOI: 10.1016/B978-0-12800130-1.00003-5.
31. Bulychev S. I., Alekhin V. P., Shorshorov M. K., Ternovskij A. P., Shnyrev G. D. Determination of Young modulus by the hardness indentation diagram. Zavodskaya Laboratoriya, 1975. Vol. 41, no 9, pp. 1137—1140.
32. Oliver W. C., Pharr G. M. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. Journal of Materials Research, 1992. Vol. 7, no 06, pp. 1564—1583. DOI: 10.1557/JMR.1992.1564.
33. Oliver W. C., Pharr G. M. Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology. Journal of Materials Research, 2004. Vol. 19, no 01, pp. 3—20. DOI: 10.1557/jmr.2004.19.1.3.
34. Galanov B. A., Dub S. N. Critical comments to the Oliver—Pharr measurement technique of hardness and elastic modulus by instrumented indentations and refinement of its basic relations. Journal of Superhard Materials, 2017. Vol. 39, no 6, pp. 373—389. DOI: 10.3103/ S1063457617060016.