Abstract

Samples of 25-30 mgs of various coals and their constituents were analyzed by vacuum differential thermal analysis using a heating rate of 20 degrees C per minute. Exothermic and endothermic peaks obtained by this technique provide graphic representations of the net thermal effects from the physical and chemical changes that take place during carbonization. Replicate analyses show that both peak temperature and the area under a peak can be reproduced readily.Thermograms of vitrains selected from a number of coals of widely different rank show an increase in peak temperature with increasing rank. Similar correlation is obtained between peak temperatures and fixed carbon values using vitrains from coals of the bituminous A group.A study of samples of known petrographic composition reveals that neither exinite nor opaque matter exerts any evident control on the peak temperature. Peak temperatures of average samples of coal from different intervals in a column sample show no correlation with the percentages of fixed carbon. The peak temperatures are relatively constant for average samples taken from a given column sample, but the fixed carbon values show considerable spread. It is concluded that the fixed carbon of a vitrain provides a better index of rank than the fixed carbon of an average sample.Further conclusions are that thermographic analysis is a useful method for the detection of cellulose in lignites and that the chemical fraction of the coal extractable with pyridine gives rise to the peaks. The suggestion is made that future investigators should consider the possibilities of relating the thermographic curves to the coking properties of coal.

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