Mechanical Properties of Thin Films of Coals by Nanoindentation

In the current work, depth-sensing indentation tests were applied at different coals microcomponents in order to characterize their mechanical properties. To this end, three coals were chosen differing by their rank and properties. Thin transparent films of such coals were prepared as samples in order to use transmitted light microscopy to achieve exact positioning of indent probe in the zone occupied by specific coal microcomponent. Experimental procedures allowed obtaining load-displacement curves at different microcomponents. These curves revealed differences between microcomponent vitrinite behavior among coals of different types. Measured values of elastic moduli and hardness also proved that they variate with coal rank. It was concluded that matrix of coals (vitrinite microcomponent) transforms its mechanical properties with rank, whereas the inclusions properties do not change as significantly.