Recent developments in understanding of the metastable zone width of different solute−solvent systems

During the last four decades voluminous literature has emerged on the metastable zone width, as determined by the maximum supercooling ΔTmax using the conventional polythermal method, of various compounds in different solvents. The experimental data of maximum supercooling ΔTmax for solute−solvent systems have traditionally been analyzed until now as a function of cooling rate R using Nývlt's equation, proposed in 1968, which contains two empirical parameters (i.e. nucleation order m and nucleation constant k). However, the physical significance of these parameters in Nývlt's equation has remained obscure until now. Since 2008 several papers have been devoted to the understanding of the effect of various experimental factors on the metastable zone width. The aim of this communication is to review these recent developments in the understanding of metastable zone width of solute−solvent systems. Finally, some general features of the dependence of ΔTmax/T0 on saturation temperature T0 for different systems, the maximum supersaturation for isothermal crystallization and the effect of impurities are briefly discussed.