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Volume 45 | Copyright
Adv. Geosci., 45, 73-83, 2018
https://doi.org/10.5194/adgeo-45-73-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

  07 Aug 2018

07 Aug 2018

Nanoindentation study of macerals in coals from the Ukrainian Donets Basin

Sanja Vranjes1,2, David Misch1, Thomas Schöberl3, Daniel Kiener2, Doris Gross1, and Reinhard F. Sachsenhofer1 Sanja Vranjes et al.
  • 1Department Applied Geosciences and Geophysics, Montanuniversitaet Leoben, Leoben, 8700, Austria
  • 2Department Materials Physics, Montanuniversitaet Leoben, Leoben, 8700, Austria
  • 3Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, 8700, Austria

Abstract. This article discusses the mechanical properties of macerals in Carboniferous coals from the Ukrainian Donets Basin, covering a maturity range from 0.62 to 1.47%Rr (vitrinite reflectance). The inherent inhomogeneity of geological samples requires characterization at the micro-/nanoscale, and hence material parameters, such as hardness H and reduced elastic modulus Er, were obtained from twelve coal specimens via nanoindentation tests. Different material properties and maturity trends were acquired for the individual maceral groups (vitrinite, inertinite, liptinite). The results indicate that apart from maturity, multiple factors like microstructural features and depositional environment control the mechanical properties of macerals in coals. H and Er of vitrinites show a complex relationship with maturity due to additional influence of microstructural features such as nanoporosity or mineral inclusions and complex changes in the organic matter structure with increasing rank. The mechanical behaviour of inertinites is mainly controlled by the prevailing conditions (temperature, exposure) during paleo-wildfires. Er and H of liptinites are strongly influenced by transformational processes related to devolatilization at low to medium rank, as well as later hydrocarbon generation. Variations in the depositional environment (e.g. increased organic S content due to marine influence) might play an additional role.

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Macerals are the constituents of coal and usually have a small size (e.g. micro-scaled). Therefore, we used nanoindentation to determine material parameters like hardness and reduced elastic modulus from macerals in well examined coals from the Ukrainian Donets Basin. Our main goal was to study the relationship of these parameters with increasing rank of coal. The results indicate that multiple factors control the mechanical properties of macerals (e.g. microstructure, depositional environment).
Macerals are the constituents of coal and usually have a small size (e.g. micro-scaled)....
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