Ultrasonic Study of Aqueous Solutions of ZnCl2: From Dilute Solutions to Hydrated Melts

Publisher Website
Google Scholar
Abstract
Longitudinal sound absorption and velocity measurements for aqueous solutions of ZnCl2 in the concentration range 0.5–12M between − 15 and 25°C and in the frequency range 5–250 MHz are reported. A single relaxation process is noticed throughout the entire concentration range. These results are interpreted as due to a chemical relaxation caused by rearrangement between various complex forms of the type ZnCln2−n in accord with findings by Raman spectra. A phenomenological treatment in terms of the compressional moduli adapted for the case of a chemical relaxation and for the condition τυ ≫ τs, τυStr, is applied to the data corresponding to the composition ZnCl2·5H2O, ZnCl2·4H2O, and ZnCl2·2.3H2O. The condition τυ ≫ τs is confirmed by shear velocity measurements on the most concentrated solution. Measurements by changing the ratio Zn:Cl and the nature of the anion prove the specificity of Cl− for the observed relaxation and indicate that probably ZnCl4−2 is the species always involved in the observed process.