Dispersion and Absorption of Ultrasonic Waves in Molten Zinc Chloride

Abstract

Among the inorganic molten salts, liquid zinc chloride is unusual in that it has a high shear viscosity which makes it possible to study its viscoelastic properties by high-frequency sound-propagation techniques. Longitudinal ultrasonic-absorption and velocity measurements were made in the frequency range 5–95 and 5–45 Mc, respectively. Shear-elasticity measurements were obtained in the frequency range 43–118 Mc. The viscosity range covered was 3 60 poise. A single relaxation time was observed for the absorption at each temperature investigated. The data demonstrate the existence of a volume viscosity and the simultaneous presence of both shear and structural-relaxation processes. The ratio of the compressional viscosity to the shear viscosity is 0.8 and was found to be nearly independent of temperature. The activation energies for the shear and compressional flows are approximately equal. Both the longitudinal and sear-dispersion data can adequately be described by a single and the same relaxation time at a given temperature. The variation of the relaxation time with temperature is in accordance with the rate theory. The shear modulus and the relaxational part of the compressional modulus increase exponentially with decreasing temperature. (This work supported by the U. S. Atomic Energy Commission.)