Experimental Study of Phase Transition Effects on Electrochemical Impedance Spectroscopy of Sodium Sulfate Soil

The durability of engineering buildings in saline soil is often disturbed by corrosion problems, which are closely related to the electrochemical characteristics of saline soil. To explore the electrochemical characteristics of saline soil at different temperatures, the electrochemical impedance characteristic of sodium sulfate soil was investigated by electrochemical impedance spectroscopy (EIS) tests. The results revealed that the impedance modulus of sodium sulfate soil decreases with the increase in frequency and tends to stabilize at high frequencies; its variation is mainly driven by the water–salt phase transition in sodium sulfate soil. Mirabilite and the second phase transition decrease the liquid water content and then increase the impedance modulus of the saline soil. There is a section of capacitive reactance arc in the Nyquist plot before the second phase transition, and another section of diffusion impedance appears in the second phase transition stage. According to the conductivity path of saline soil at different temperatures, the equivalent circuit models of sodium sulfate soil were established (Q1R1(Q2R2)) and (Q1(R1W)(R2Q2)) are the equivalent description codes before and after the second phase transition, respectively. In addition, the relationship between equivalent resistance and phase transition is discussed. These results could provide a theoretical reference for investigating the corrosion mechanism of saline soil in cold regions.