Determination of Solubility and Metastable Zone of Sodium Hypophosphite and Nucleation Kinetics

To obtain thermodynamic and kinetic data of sodium hypophosphite, such as solubility and metastable zone, respectively, the solubility data for sodium hypophosphite in the temperature range of 298.15–373.15 K were obtained using a dynamic method. These data were then fitted to the Apelblat and Van't Hoff equations, and the corresponding model parameters were determined. The effects of stirring intensity and cooling rate on the width of the metastable zone of sodium hypophosphite in water were studied. The findings indicated that an increase in stirring intensity reduced the width of the metastable zone, whereas an increase in cooling rate resulted in its widening. The self-consistent NýVlt and Sangwal metastable zone models were employed to calculate nucleation dynamic parameters in conjunction with classical nucleation theory. The results showed that the nucleation order was 2.311–3.361 over the investigated temperature range. 316.15 K is the critical temperature point at which sodium hypophosphite transforms into a dominant nucleation mode. The solid–liquid interface tension decreased rapidly with the increase of saturation temperature, and the solid–liquid interface tension is 1.167–2.638 mJ m⁻².