Kinetic Study on the Isothermal Transition of Bromovalerylurea Polymorphs in the Solid State at High Temperature

Abstract

The kinetics of the solid-state isothermal transition of bromovalerylurea polymorphic forms (I, II and III) at high temperature were investigated by means of differential scanning calorimetry. Kinetic analysis according to the method of Hancock and Sharp indicated that the transition of form I to form II follows the one-dimensional diffusion mechanism. The activation energy for this transition calculated from the Arrhenius plots was 826.2 kJ/mol. On the other hand, it was found that the transition of form III to form I conforms with the mechanism of random nucleation and two-dimensional growth of nuclei (Avrami-Erofeev equation). This activation energy was estimated to be 185.2 kJ/mol. It was concluded that the mechanism and the value of activation energy were both different between the two kinds of isothermal transitions of bromovalerylurea polymorphic forms.