Thermophysical properties of molten salts: Hypersonic velocities of molten alkali nitrates and their mixtures

By means of Brillouin scattering spectroscopy, hypersonic velocities in NaNO₃-KNO₃ binary melts have been measured at temperatures from the liquidus temperatures of the melts to 200 K above them over the entire range of compositions. The light beam scattered by the melt is analyzed with a pressure-scanned Fabry-Perot spectrometer. The hypersonic velocities obtained are about the same as the ultrasonic velocities reported at compositions rich in NaNO₃, but are markedly larger than those at compositions rich in KNO₃, indicating the occurrence of structural relaxation. Thermodynamic values such as adiabatic and isothermal compressibilities, constant-volume heat capacity, and internal pressure calculated from the sound velocity obtained show that the melt can be treated as a typical ionic liquid, though it contains a certain amount of associated species.Paper presented at the Japan-United States Joint Seminar on Thermophysical Properties, October 24–26, Tokyo, Japan.