Ultrasonic velocity for an equimolar mixture of molten AgI and NaCl in the biphasic region

The ultrasonic velocities of a molten stratifying mixture composed of 0.5 AgI and 0.5 NaCl (the composition corresponding to the top of the miscibility gap) were measured along the saturation line for a wide temperature range via the pulse method to establish the characteristics of mixing salts with different chemical bonds. We show that the difference, Δu, between the magnitudes of the sound velocities for the coexisting phases decreases with increasing temperature and becomes zero at 1064 K. This temperature corresponds to the critical phase transition point, Tc. The temperature dependence of the sound velocity difference, Δu, is described by the equation Δu ≈ (Tc − T)Θ, where Θ = 0.896, which is less than that found for alkali halide melts (Θ = 1.02), in which long-range Coulomb forces between ions prevail. The results are discussed in terms of the peculiarity of the chemical bond in silver iodide.

► The sound velocity in the 0.5 AgI–0.5 NaCl melt is measured depending on temperature.
► The system is biphasic between the melting point and 1064 K.
► The sound velocities for the coexisting phases converge when the temperature increases.
► The temperature coefficient of difference in the velocities for phases is less than that for the alkali halide melts.