학술논문
Kinetics of the (solid + solid) transformations for the piracetam trimorphic system: Incidence on the construction of the p–T equilibrium phase diagram.
Document Type
Article
Author
Source
Subject
*SOLID-solid transformations
*CHEMICAL kinetics
*PIRACETAM
*PHASE diagrams
*THERMAL analysis
*TRANSITION temperature
*POLYMORPHISM (Crystallography)
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Language
ISSN
0021-9614
Abstract
The three common polymorphs of piracetam have been characterized by associating thermal analysis, X-ray diffraction and densimetry. DSC experiments showed that the (solid + solid) transition temperature between Forms II and I and between Forms III and I is scan-rate dependent. The transition temperatures decrease when the DSC scan rate decreases and the thermodynamic temperatures were confirmed by isothermal X-ray diffraction. These new results in terms of temperature and enthalpy of transition allow us to propose a new equilibrium phase diagram establishing the relative thermodynamic stability of the three common polymorphs of piracetam as a function of the temperature and the pressure. The diagram suggests that Form II presents a small stability domain located just above the stability domain of Form I. As a consequence, Form I should transform into Form II, which itself can turn into Form III when placed under pressure. [ABSTRACT FROM AUTHOR]