Microhardness of Coal from Near-Fault Zones in Coal Seams Threatened with Gas-Geodynamic Phenomena, Upper Silesian Coal Basin, Poland

Abstract

Near-fault coal displays some specific structural and textural features. As the distance to the fault diminishes, one can observe ever stronger, gradual degradation of coal, demonstrated by the emergence of structural distortions exogenic in their origin, visible under a microscope. The process of gradual degradation of coal—manifested by the appearance of structural distortions exogenic in their origin—takes place. This can be observed under a microscope. The measurements of the microhardness of structurally altered coal carried out using the Vickers hardness test. For the purpose of this research, a microhardness tester by the CSM Instruments was used. The microhardness of particular structural types of coal was measured. The procedure encompassed both structurally unaltered and altered coal. The tested objects were exogenically fractured fragments, cataclastic, and mylonitic structures. Each of the analyzed structural types displayed a different range of the microhardness, with the highest values confirmed for the structurally unaltered coal. In the case of fractured coal, the microhardness values were somewhat lower. Finally, the lowest values were ascertained for cataclastic coal. Mylonitic coal, in turn, displayed microhardness values similar to those found in the unaltered coal. It was also observed that, in the case of the unaltered, fractured, and cataclastic coal, cracks propagated in the manner typical of brittle materials, whereas the mylonitic coal revealed some degree of elasticity. The analyzed microhardness parameters expose the structural–textural features of coal, particularly when it comes to the degree and character of destruction of the rock’s original matrix. The specific structural–textural composition of particular types of near-fault creations influences both their sorption parameters and the compactness of coal in a seam.

Synergy of Parameters Determining the Optimal Properties of Coal as a Natural Sorbent

“…Micro-hardness parameters change with the metamorphism degree and with the structural and textural characteristics of coal. This relationship, described by many authors [52][53][54][55][56], can also be seen in the coals from the USCB area described in this work.…”

Sorption and Micro-Scale Strength Properties of Coals Susceptible to Outburst Caused by Changes in Degree of Coalification

“…The degree of coalification is a parameter determining several coal properties. A higher degree of coalification results in a higher gloss, changes to microscopic properties (e.g., colour or structure), along with changes to strength properties [ 23 , 30 ], accumulation properties [ 24 ], etc. Therefore, assessment of the degree of coalification is the key and the starting parameter required for further studies of coal.…”

“…Therefore, researchers are trying to identify the important properties of coal that contribute to the increased outbursts hazard [ 17 , 18 , 19 , 20 , 21 ]. All the properties are closely related to the coalification degree of the organic matter [ 22 , 23 , 24 , 25 , 26 ].…”

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)

“…TDC can be classified in different types with increasing deformation, such as cataclastic, porphyroclast, scaly, powdery, heterogeneous structure and mylonitic coal [14]. Godyńand and Kožušníková [15] studied the microhardness of TDC using the Vickers hardness test in Silesian Coal Basin, Poland and found the lowest values in cataclastic coal and the highest values in unalerted coal, which was a valuable discovery for TDC research. Therefore, there should be more quantitative descriptions for studies of TDC with different degrees of deformation.…”