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Chemical composition of coal surface as derived from micro-FTIR and its effects on contact angle Liu, Jie


In this study, in-situ image analysis, contact angle measurements, micro-FTIR spectroscopy and SEM are used to obtain information on the surface composition of coal. The heterogeneous coal surface is investigated with regard to the distribution of the chemical functional groups and its effect on hydrophobicity as derived from contact angle measurements. Contact angles obtained from sessile drop and captive bubble techniques are correlated with the semi-quantitative ratios from micro-FTIR spectroscopy. As part of the new methodology, image analysis and SEM are also applied in order to characterize and analyze for the petrographic composition of areas that are subjected to these measurements. An opposite trend between high rank coal and low rank coal is found in relation to the micro-FTIR semi-quantitative ratios versus contact angle. For lower rank coal, the increase in Aromaticity 1 and 2 led to an increase in the contact angle, while the increased quantity of aliphatic groups decreased the contact angle values. For high rank coal, the rising aliphatic groups increased the contact angle values and the increase in Aromaticity 1 and 2 led to smaller contact angle values. The newly introduced CHal/C=O was used to assess the abundance of aliphatic groups and oxygenated groups. The increased content of oxygenated groups in the high rank coal samples led to a decrease in the contact angle, which is consistent with the findings of previous studies. For low rank coal samples, although the correlation was less distinct, an opposite trend was observed.

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