Electrochemical characteristics of phase transition process in sodium chloride saline soil during cooling

Chlorine saline soil is a typical type of saline soil in the cold and arid regions of northwest China, and its electrochemical characteristic is crucial for understanding of the corrosion mechanism of saline soil. To explore the relationship between the phase transition of pore solution in saline soil and its electrochemical characteristics, sodium chloride saline silty clay was taken as the research object, and its electrochemical impedance spectra were measured under different salt content and temperature conditions. The results revealed that the impedance of sodium chloride saline soil gradually decreases with the increase of frequency, and reaches stable state at high frequency condition. The logarithm of the impedance modulus of sodium chloride saline soil increases linearly with temperature decreasing before freezing, while the generation of ice crystals and salt crystals leads to a significant increase in the impedance modulus of the soil after freezing. Sodium chloride saline soil exhibits a capacitive impedance arc before freezing, while the migration of soil water and salt caused by phase transition results in a diffusion impedance of the soil after freezing. Based on the conductivity path of the soil before and after freezing, the equivalent circuit model of the soil before and after freezing were established, and the relationship between the phase transition of the soil pore solution and the corresponding circuit components were analyzed. It is of great significance for understanding the electrochemical characteristics of saline soil and the phase transition process of pore solution.