Determination of the metastable zone and induction time of thiourea for cooling crystallization

The solubility, metastable zone width (MSZW), and induction time of thiourea for cooling crystallization were experimentally determined in the temperature range of 283–323 K. The solubility data could be well described by the Apelblat equation model as lnx = -99.55 + 1071.66/T + 16.27lnT. The determinations of the effects of various stirring and cooling rates indicated that the MSZW increased with increasing and decreasing cooling and stirring rates, respectively. Furthermore, the induction times at various temperatures and supersaturation ratios were also measured. The results indicated that homogeneous nucleation could occur at high supersaturation, whereas heterogeneous nucleation was more likely to occur at low supersaturation. Based on the classical nucleation theory and induction period data, the calculated solid–liquid interfacial tensions of thiourea in deionized water at 302.46 and 312.58 K were 2.86 and 2.94 mJ·m^-2, respectively.