Study on the supercooling and crystallization mechanism of saline soil based on thermodynamic framework

Quantifying the supercooling characteristics of saline soil-water systems is essential for engineering and agriculture in cold regions. However, the crystallization mechanism of supercooling remains unclear. We conducted experimental observations to investigate the impact of salinity on the soil supercooling properties. Additionally, a freezing nucleation thermodynamic model for saline soil was established based on the Negentropic Nucleation Framework (NNF). Statistical analysis methods were employed to analyze the sensitivity of the parameters and interpret the supercooling microscopic mechanism. The results indicated that the supercooling degree distribution of saline soil is best described by a normal distribution (hypothesis testing statistic Dn= 0.176). The nucleation rate was primarily controlled by water activity and activation energy of water molecules. The concentration of salt solution played a crucial role in promoting the formation and growth of crystal nuclei. However, the promoting effect decreased with increasing solution concentration when the concentration was below 0.3 mol/L. Moreover, the nucleation potential energy barrier increased with salt concentration, with NaCl environment exhibiting a higher nucleation potential energy barrier compared to Na2SO4 environment at the same salt concentration. In summary, this research provides a theoretical reference for revealing the freezingthawing hysteretic mechanism and improving the accuracy of numerical calculation models in cold regions.