Kinetics of the Thermal Transition of Carbamazepine Polymorphic Forms in the Solid State

Abstract

The thermal transition of carbamazepine polymorphic forms (forms I, II, III) in the solid state was investigated by X-ray powder diffractometry. From the kinetic analysis according to the method of Hancock-Sharp, it appears that the transition of form I to form III follows the mechanism of random nucleation and two-dimensional growth of nuclei (Avrami-Erofeev equation). The activation energy for the transition from form I to form III was calculated to be 54.7 kcal/mol from the slope of the Arrhenius plots. On the other hand, the transition of form II to form III will proceed by the mechanism of the two-dimensional diffusion. The activation energy for this transition was calculated to be 31.6 kcal/mol.