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Electrochemistry J Electrolyte Solutions J Ion-Pair Formation J Relative Permittivities f Spectroscopy, MicrowavesThe low-frequency relaxation process contributing to the complex permittivity spectra of aqueous solutions of MgS04, CdS04, Na2S04, CdCI2, and CuCI2 is investigated. The dispersion amplitudes are analysed with the help of model calculations, based on a modified Cavell equation for ellipsoidal bodies. It is shown that ion pairs are responsible for the low-frequency relaxation process with solvent separated ion pairs dominating for the sulfates, whereas contact ion pairs are formed by the chlorides. Thc observed relaxation time is analysed as the superposition of chemical and reorientational relaxation. For the ion pairs the effective volumes of rotation and the rate constants of formation are determined. The results are compared with information from the literature.

Abstract

Complex permittivity measurements on aqueous solutions of CdCl2, CuCl2, MgSO4, CdSO4, Na2SO4, Cd(ClO4)2, and MgCl2 in the frequency range from 0.9 to 90 GHz are reported. The data analysis reveals the superposition of 2 Debye dispersion steps for the solvent thus supporting multi‐step relaxation mechanisms discussed for water in the literature. An additional low frequency process is found for CdCl2, CuCl2, MgSO4, CdSO4, and Na2SO4 solutions due to solute relaxation, but not for Cd(ClO4)2 and MgCl2 solutions. – The decrease of the static solvent permittivity at increasing electrolyte concentrations is interpreted in terms of irrotational bonding and kinetic depolarization and is used to determine effective solvation numbers. The dependence of the main (low frequency) relaxation time of water on electrolyte concentration is explained with the help of the reorientation and residence times of water in the hydration spheres of ions and in the bulk. The high frequency relaxation time is approximately concentration independent, whereas the dispersion amplitude of the process increases with electrolyte concentration.

A system of computer controlled transmission lines based on the method of travelling waves is presented, permitting the precise determination of complex permittivities of medium to high loss liquids at 8.5 to 90 GHz. It consists of a newly developed apparatus for the E‐band region (60 ≤ v/GHz ≤ 90), which is described in detail, together with existing X‐ (8.5 ≤ v/GHz ≤ 12.4), Ku‐ (12.4 ≤ v/GHz ≤ 18), and A‐band (26.4 ≤ v/GHz ≤ 40) set‐ups now appropriately adapted for computer control. Consistency and accuracy of the equipment are evidenced with the help of permittivity data for water, methanol, N‐methylformamide (NMF), and N,N‐dimethylformamide (DMF).