Investigation of metastable zone width of ammonium oxalate aqueous solutions

Abstract

AbstractThe metastable zone width of pure ammonium oxalate aqueous solutions, as represented by maximum supercooling ΔTmax, is investigated as functions of cooling rate R and saturation temperature T0 by the polythermal method. The experimental results are discussed by using two recently advanced approaches: (1) self‐consistent Nývlt‐like approach based on a power‐law relationship between nucleation rate J and maximum supersaturation lnSmax, and (2) a novel approach based on the relationship between J and lnSmax described by the classical three‐dimensional nucleation theory. Analysis of the experimental data revealed that both approaches describe the experimental data on metastable zone width by the polythermal method reliably and provide useful information about the physical processes and parameters involved in nucleation kinetics. The values of various physical quantities predicted by both of these approaches are reasonable for a fairly‐soluble compound. A careful examination of the data on ΔTmax as a function of T0 obtained by polythermal method and from density measurements showed that ΔTmax has a slight tendency to decrease with increasing saturation temperature T0. The values of lnSmax at saturation temperature 303 K suggest that the metastable zone width of ammonium oxalate aqueous solutions is determined by primary nucleation in the polythermal method and by secondary nucleation during density measurements. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)