Concentration dependance of the capacitive to inductive transition observed in electrolytic solutions

We investigate, in a systematic way, the electric response of KCl, NaCl, CaCl2 and MgCl2 aqueous solutions as function of salt concentration. Our experimental data show that the cell's reactance transits from capacitive to inductive regime at a well defined frequency. The transition depends critically on the salt concentration. The present work is motivated from published data in the literature showing deviations of the impedance spectra from the expected behavior, at high enough frequency as salt concentration increases. These data were interpreted by means of a mechanical model. We propose an alternative interpretation of the observed transition from capacitive to inductive regime, which is based on the parasitic inductance of the coaxial cables used in the experimental set-up. The dependence of the transition frequency on the concentration is investigated, and approximated formulae are obtained. A critical concentration where the capacitive to inductive regime transition jumps from a high to a low frequency region has been both experimentally located and theoretically deduced. Ion generation-recombination effects are shown to be important and taken into account. Solutions of divalent ions present a lower critical concentration than solutions of monovalent ions.