An anion effect on the separation of AgI-containing melts using sound waves

• The sound velocity in the (AgI + LiBr) and (AgI + LiF) melts was measured as a function of the temperature.
• The system (AgI + LiBr) is biphasic between the melting point and 984 K.
• The sound velocities for the coexisting phases converge when the temperature increases.
• The (LiF + AgI) melt remains biphasic at all temperatures investigated up to 1218 K.

Sound velocities in molten ((LiF + AgI)) and ((LiBr + AgI)) mixtures have been measured to investigate the relationship between the sound velocity and the temperature and the role of the anion in the (liquid + liquid) phase transition. Our results show that the ((LiBr + AgI)) system is biphasic between the melting point and T = 984 K and becomes monophasic above this temperature. We show that the upper consolute critical temperature for the AgI-containing melts increases with decreasing anion size in the series F− > Cl− > Br−. The ((LiF + AgI)) melt remains biphasic at all temperatures investigated up to T = 1218 K. The temperature coefficients for the sound velocities in the upper and lower phases of the ((LiBr + AgI)) system have opposite signs because of the superposition of the temperature and composition factors. The difference between the magnitudes of the velocities for the coexisting phases decreases exponentially with increasing temperature and is described by a critical exponent of 0.85 for the ((LiBr + AgI)) melt near the critical temperature. This value is 15% less than that found for alkali halide melts, in which long-range Coulomb forces between ions prevail. This difference may result from the fact that silver halides are intermediate between the typical ionic salts and the fully covalently bonded ones.

Figure optionsDownload as PowerPoint slide