V. P. Stepanov, N. K. Тkаchev, N. P. Кulik, K. G. Peshkina
molten salts, immiscibility, critical properties, adiabatic compressibility
The adiabatic compressibility, β, of the immiscible liquid mixture 0.5 NaCl + 0.5 AgI in the range of immiscibility was investigated as experimentally as using the charged hard spheres model with different diameters. Experimentally, the compressibility was studied by means of the sound velocity values, u, measured by the pulse method, and the density quantities, ρ, which were determined using the hydrostatic weight procedure based on the relationship β = 1/u2ρ. The compressibility of the upper phase were determined to decrease, but that of the lower phase increases at temperature rise, because of the intensity superposition of the ions thermal motion and change in the composition of the phases. The difference, Δβ, in the magnitudes of the compressibility for the equilibrium phases decreases with temperature elevation. The temperature dependence of the compressibility difference was described using the empirical equation Δβ = (Tc – T)0.442, which is close to the mean-field theoretical description. The results of the model calculations sufficiently reproduce the experimentally observed temperature dependence of the coexisting phases compressibility. However, the theoretically predicted critical exponent (1/2) was different from the one determined experimentally by 13%. The results were discussed in terms of the chemical bond nature of AgI.