Effects of glass formation by solvents in differential scanning calorimetry investigations of solvent swollen coals

The behavior of solvents under conditions of rapid cooling is investigated. It is demonstrated that certain coal solvents form glasses on quenching at 60 K/min whereas others form crystals. In swollen coals, most free solvents tend to go into glassy states. An important exception is pyridine. The formation of glasses by free solvents has two effects on differential scattering calorimetry results. At temperatures below the solvent melting point, exotherms are produced. This is probably due to cold recrystallization. At high solvent weight fractions, second-order phase transitions may occur, which are not a feature of the coal. It is concluded that investigations of phase transitions in swollen coals should preferably be performed at the ''gel'' point, with no free solvent present. It is shown that low-temperature second-order phase transitions for quenched solvents occur at the same temperature as in coal gels formed with the same solvents. This suggests that phase changes in the solvents determine the form and temperature of the glass transitions.