Estimation of the Thermodynamic Properties of Mixing Binary Systems Based on Silver Nitrate and Alkali Nitrates using Ionic Model

This work was devoted to the formulation of thermodynamic properties of binary systems of molten salts by using an ionic model which requires three physical parameters for each salt : the crystal lattice energy, the latent heat of melting and the sum of the ionic radii. This formulation, whose adjustable parameters have been obtained by smoothing from the experimental mixing properties available in the literature, allowed us to calculate the molar enthalpies of mixing for twelve (12) binary systems of alkali nitrate and silver nitrate. The different results obtained show satisfactory general agreement between calculation and experiment with regression coefficients within the range 0.992 and 0.999 and relative uncertainties between experimental and calculated values of less than 6% throughout the compositional range for all systems studied. The present formulation more accurately determines the enthalpies of mixing of binary systems with a volume effect (without intermediate compounds) predominating over the chemical effect (formation of intermediate compounds) ; Furthermore, we were able to show that in binary systems of alkali nitrates based on lithium nitrate and sodium nitrate, the solutions are strictly regular and that the deviation from regularity increases as one goes down in the alkali metal family namely from lihium to caesium.