Absorption of Ultrasonic Waves in Molten ZnCl₂-MCl (M=Li, Na, K, Cs) Binary Systems

Abstract

Absorption coefficients of ultrasonic waves in the molten ZnCl₂-MCl (M=Li, Na, K, Cs) binary systems were measured with a U.S. spectrometer by the double-transducer method over the frequency range of 5 to 55 MHz. Bulk viscosity coefficients of these systems were determined from the measured absorption data.
The results obtained are summarized as follows:
(1) Absorption coefficient is greatest in pure ZnCl₂ and decreases with increasing content of MCl for all these systems. The absorption coefficient of pure ZnCl₂ shows the greatest negative temperature gradient. The temperature dependence of absorption coefficients for the mixtures decreases with increasing MCl content and becomes constant within the experimental error in the composition range of more than 70 mol%MCl for all these systems.
(2) Bulk viscosity of pure ZnCl₂ has an extremely large value and a large negative dependence on temperature. For all the systems, bulk viscosity coefficients on the ZnCl₂-rich side decrease markedly with increasing MCl content and the extent of decrease increases in the order of LiCl<NaCl<KCl<CsCl.
(3) Composition dependences of the apparent activation energies of bulk viscosity, E_ηB, and the ratio of apparent activation energies of bulk and shear viscosities, E_ηB⁄E_ηS were determined. It is found that the ratio E_ηB⁄E_ηS is nearly equal to unity on the ZnCl₂-rich side except the ZnCl₂-CsCl system. This fact may indicate that the mechanism of bulk viscosity is analogous to that of shear viscosity on the ZnCl₂-rich side.
(4) Bulk viscosity coefficients of alkali metal chlorides obtained in the present work are much smaller than those reported by other investigators. Compared with the organic liquids and the calculated values by the two state model combined with the hole theory, it is suggested that the present results are more reasonable than the others.