Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Process Engineering, Biotechnology, Nutrition Technology
Normal freezing of several organic systems exhibiting simple eutectic behavior has been studied experimentally, and the occurrence of constitutional subcooling has been clearly established. This phenomenon, previously observed in systems of metallurgical interest, results in the instability of a planar solid-liquid interface and leads to solute trapping. This trapping mechanism quantitatively explains why eutectic forming systems exhibit solid phase concentration profiles identical to those expected of systems which form solid solutions. The onset of constitutional subcooling can be correlated and reliably predicted by theoretical equations.Although the process of normal freezing with no liquid phase agitation would appear to be well described by a diffusion model, free convection induced by concentration gradients renders a boundary-layer model more appropriate when the liquid density of the solvent exceeds that of the solute and freezing is in an upward direction.
Type of Medium: