Electrical impedance analysis of NaCl and CaCl2 solutions based on equivalent electric circuit

Abstract

Abstract In this paper, we report the behaviour of electrical impedance of sodium chloride (NaCl) and Calcium chloride (CaCl2) with the concentration of 1.25 to 100 mM/L in frequencies ranging from 10 mHz to 1 MHz. The complex electrical impedance (real and imaginary parts) is obtained using the electrical impedance spectroscopy (EIS) technique. The experimental data had been fitted with three models of equivalent electrical circuit (EEC), model-a is Randles circuit, model-b consist of R solution (Rs) in series with constant phase element (CPE) and model-c consist of Randles circuit in series with CPE. Best fit data is obtained from model-c with goodness of fit less than 0.005. The CPE in this circuit associated with the electric double-layer. As expected from the experimental and fitting spectra, even for a low concentration for both salts, an inverse relationship was observed between impedance and salt concentration. The number of ions contains in CaCl2, which are more than NaCl is estimated to be the cause that CaCl2 impedance is lower than NaCl. The total impedance influenced by the CPE component increased significantly at frequencies about 100 Hz, indicating that the equivalent electric circuit used can estimate the effect of double-layer on the measurement.