Kinetics of non-isothermal cold-crystallization of carbamazepine in the glassy state studied by DSC

Abstract

Kinetics of non-isothermal cold-crystallization of quench-cooled carbamazepine (CBZ) was investigated under different heating rates using Differential Scanning Calorimetry. Relevance of Johnson-Mehl-Avrami, Kissinger, Augis-Bennett, Ozawa, Mo and Matusita models to describe the mechanism of nucleation and growth was thoroughly discussed. Some assumptions of Johnson-Mehl-Avrami and Kissinger models were showed to be inadequate when describing kinetics of cold-crystallization of quench-cooled CBZ. Augis-Bennett, Ozawa and Mo models correctly outlined the nucleation and growth mechanism, however they were not able to distinguish between surface and bulk crystallization. Matusita model was the only one which properly described these two mechanisms and consequently was considered as the most versatile one. Quench-cooled CBZ displayed two different crystallization mechanisms for lower and higher heating rates. In the first case, surface crystallization was dominant, whereas in the second case – the bulk one. Activation energy was noticed to be heating rate, temperature and fractional extent of crystallization dependant.