Structural Relaxation and Ultrasonic Absorption in Aqueous Solutions of Alkali Halides

Abstract

The ultrasonic absorption in aqueous solutions of a number of alkali halides has been measured in the frequency range 5–100 MHz. Lower as well as higher ultrasonic absorption than in pure water has been found depending on type and concentration of the ions present. A kinetic model of the structural relaxation processes in ionic solutions is presented with which the absolute values of the structural absorption as a function of ion concentration and temperature for different types of ions can be described quantitatively. The analysis of the ultrasonic absorption data of the alkali halide solutions with this model yields information concerning the kinetic properties as well as the number of solvent molecules at different distances from the ions. The relaxational parameters obtained are consistent with other experimental data of water and of the solutions.