A Fully Automatic Apparatus for Thermal Analysis of Crystallization from Solution and Metastable Zone Width Determinations

Abstract

This work describes the development of a fully automatic apparatus to perform crystallization studies and metastable zone width (MSW) determinations using the polythermal method. Heating and cooling ramps, and isothermal steps can be carried out, while continuously monitoring the mixture inside the crystallization vessel, with temperature and turbidity sensors. These allow the onsets of crystallization or of complete dissolution of the solute to be detected. Programmed dilutions of the mixture under study can also be automatically performed, so that different concentrations can be studied in a given experiment. The apparatus was tested by using the ammonium chloride–water system. The results indicated that it is capable of reproducing the equilibrium solubilities of ammonium chloride in water, independently determined by the residue mass method, with an average deviation of 0.6 K. The obtained MSW and the kinetic parameters for the crystallization process showed deviations from the literature data, which are typical of these studies when nucleation is not induced by the addition of crystalline seeds.

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