Crystallization from solution: Methods for the study of solubility, kinetics and phase transitions.

摘要

The purpose of this study has been to understand the crystallization process including solubility, crystal growth kinetics and phase transformations from a practical as well as a thermodynamic point of view.; In the development, analysis and control of crystallization processes, knowledge of solubility data and kinetics is essential. It is often found that the data is not available for the conditions of interest. In the present work, simple and fast techniques for the measurement of solubility and crystal growth kinetics using a Differential Scanning Calorimeter (DSC) are presented. Seeded isothermal growth experiments were performed at temperatures ranging from 0 to 200°C and high pressures utilizing sealed pans to obtain the growth kinetics from the desupersaturation curve. For the measurement of solubility, the questions to be answered are the accuracy and sensitivity of this method. The technique introduced is useful in estimating solubility and growth kinetics in a relatively short period, under conditions of high pressure and temperature or when only small amounts of material are available. Results obtained employing this method are reported for a number of systems and are in reasonable agreement with those in the literature.; The driving force for crystallization has been examined from a thermodynamic perspective and combined with the Burton Cabrera Frank (BCF) crystal growth model to obtain a simplified and consistent method to analyze crystal growth data and obtain kinetics with only a single constant. This method is applied to a number of systems employing kinetic data obtained from the literature and thermodynamic data measured in this laboratory. The results demonstrate the simplicity and utility of the method.; The phase transformation of anhydrous and hydrated l-phenylalanine has been studied using x-ray powder diffractometry. Experiments were performed to determine the effect of additives on the transformation rates of anhydrous to hydrate form below the transition point (37°C). Results show that the anhydrous form is not the stable form, as previously thought, but only a metastable form that will eventually transform to a more stable form and that certain additives slow the rate of transformation of the anhydrous form.