Observation of First- and Second-Order Transitions During the Heating of Argonne Premium Coals

Abstract

Differential scanning calorimetry (DSC) has been used to investigate the thermal transitions occurring for a series of Argonne Premium Coals. Two sets of experiments were conducted using different heating profiles to further examine a second-order transition which had previously been observed for Illinois No. 6 coal. Thermogravimetric analysis (TGA) was also conducted on the samples to support the DSC data. The DSC results show that on initial heating a first-order transition is observed which is a function of the cooling cycle and that subsequent scanning shows a clear and reproducible second-order process with the characteristics of a glass transition process. TGA shows that no mass loss is associated with either of these transitions.

LeBoeuf's Comment on “Evaluation of the Glassy/Rubbery Model for Soil Organic Matter”

“…For a low-rank coal such as Leonardite, the glass transition would likely appear between 307 °C and 320 °C (although report of secondary relaxation processes observed in Illinois no. 6 and other coals may suggest that Tg's may occur at temperatures as low as 110 °C (11)). This is obviously different than the Tg for humic acid derived from Leonardite coal.…”

Evaluation of coal swelling‐controlled CO2 diffusion processes

“…In the standard excess sorption isotherms that assume a constant void volume, the effects of the free volume may reveal themselves in the form of local maxima and minima. There is a dramatic decrease in the coal softening temperature under supercritical CO 2 , and changes in the solubility of CO 2 in coal due to density fluctuations near the critical isochore could play a role in either sorption or excess volume changes . The structural changes and phase transition of coal lead to anomalous CO 2 desorption and adsorption from Yaojie coal.…”

“…Unswollen coal is in a glassy state (not in the lowest energy state) under typical reservoir conditions. The temperature required to cause a transition in coal from the glassy to rubbery state is the glass transition temperature . Analysis of the effects of high‐pressure CO 2 on the macromolecular structure of coal shows that the glass transition temperature of coal decreases significantly with CO 2 pressure, indicating that high‐pressure CO 2 diffuses through the coal matrix, causing significant plasticization effects and changes in the macromolecular structure of coal.…”

Sorption irreversibility of 1,4‐dichlorobenzene in two natural organic matter–rich geosorbents

“…By contrast, a glassy solid lying on the fixed‐pore side of the apex would show increasing hysteresis with increasing degree of plasticization. BZL is harder than PP, as indicated by the T (115°C for BZL [43] and 52°C for PP [44]). It is therefore suggested that unloaded PP lies on the rubbery side while BZL lies on the fixed‐pore side of the apex.…”