Kinetics of “Melting” of Sucrose Crystals

Kinetics of “melting” of sucrose crystals has been examined by conventional differential scanning calorimetry (DSC) and fast-scan calorimetry in terms of the possibility of a clear distinction between physical melting and chemical decomposition processes by fast scan up to 10 000 K s –1 . On the basis of a modeling of the crystal melting kinetics with superheating and the possible influence of thermal lag, the heating rate dependence of “melting” was carefully examined. The equilibrium melting point T M of sucrose crystals at a zero heating rate was estimated to be T M = 188.9 ± 1.2 °C by fast-scan calorimetry, and the heat of fusion of 46 kJ mol –1 was determined by conventional DSC, which is in agreement with the reported values in the literature. The Kissinger plot of the peak temperatures by heating runs and the plot of characteristic times of isothermal runs against the inverse of absolute temperature suggested a kinetic diagram, in which the “melting” behaviors above and below T M are qualitatively different with purely physical melting above T M and “melting” initiated by chemical decomposition at active sites below T M .