Extrapolation Methods for AC Impedance Measurements Made with a Concentric Cylinder Cell on Solutions of High Ionic Strength

Abstract

Different extrapolation methods of AC impedance spectra measured in a conductance cell with concentric cylinder geometry have been evaluated at room temperature. This was undertaken because previous high temperature studies showed that the extrapolation method was one of the largest contributors to the uncertainty for molar conductivities at high concentrations: these high concentrations are needed to determine ion-pairing formation constants under hydrothermal conditions. This was done by measuring the impedance spectrum of sodium chloride solutions with ionic strengths up to 0.49 molÁkg -1 and comparing different extrapolation methods to accurate molar conductivity results reported by other authors using cells designed for concentrated solutions at ambient conditions. The most accurate extrapolation method at high concentrations was found to be the method based on the expression Z Re x ð Þ ¼ R s þ b 0 Á x Àb 1 , where Z Re (x) is the real component of the angular frequency-dependent impedance, and R s , b 0 and b 1 are fitting parameters.

Electrical conductances of aqueous electrolytes at high temperatures: Limiting mobilities of several ions including the proton and HCl dissociation constant

“…The performance of the two-electrode cell in EIS measurements showed non-standard featurea presence of an inductance element. Similar behavior of this cell was reported in [9] . The cell inductive response was described by constant phase element with inductance (LCPE).…”

“…The measurements of HCl electrical conductivity were carried out in Wood's laboratory in a flow apparatus described in more detail elsewhere [9,14]. Electrochemical impedance spectroscopy (EIS) data were obtained in a two-electrode flow cell at the range 100 -20,000 Hz for aqueous solutions of HCl (10 -5 -10 -3 mol kg -1 ) at 298 -673 K and up to 28 MPa.…”

“…The electrical conductance of aqueous electrolyte solutions in this region were studied by many authors starting from [1]. To demonstrate the research horizon we list the important contributions by Franck, Marshall, Ho, Wood and coworkers [2][3][4][5][6][7][8][9][10]. The present temperaturepressure (TP) field comprises of the region of equilibrium water vapor and the region of supercritical water near its critical point.…”

“…The simplified EIS conductivity data treatments published in [14] and [9] have the same limitation. However, if the ratio ct R / sol R is constant under all experimental conditions, the above error is canceled for the resulting conductivity because the same error is included in cell constant, determined by the EIS measurements of reference electrolyte solutions [14].…”

Ion-pair formation in aqueous strontium chloride and strontium hydroxide solutions under hydrothermal conditions by AC conductivity measurements

“…The details of the frequency-dependent measurements and the experimental uncertainty limits in Z Re (o) and Z Im (o) are discussed in ref. 16 and 18-22. Our previous studies 16,18,22 showed that, for our type of cell, an extrapolation of Z Re (o), according to the expression…”