Physicochemical Investigation of the Ternary (LiF + MgF₂)_eut + LaF₃ Molten System

Abstract

The physicochemical properties of the (LiF (1) + MgF 2 (2)) eut + LaF 3 (3) molten system have been investigated. The phase equilibria, density and volume properties, electrical conductivity, and surface tension have been selected for investigation. The phase equilibria have been measured by thermal analysis method, and the CALPHAD method for optimizing of the phase diagram has been used in order to interpret the obtained experimental data. Calculated values of the eutectic point of the binary system (LiF (1) + MgF 2 (2)) eut have the following coordinates: eutectic temperature T eut = 998 K and x 2 = 0.3095 and calculated composition of the ternary eutectic, according to the thermodynamic model, are at x 1 = 0.6627, x 2 = 0.2718, and x 3 = 0.0655. The Archimedean method of hydrostatic weighing was used for density measurements, a method based on the principle of phase shift measurement was used for electrical conductivity measurements, and the maximum bubble pressure method was used for surface tension measurements. The calculated concentration dependencies of particular physicochemical properties showed increasing character for density, partial molar volume, and electrical conductivity, while decreasing character was observed for surface tension. These data have been compared with corresponding physicochemical properties of two other molten systems: (LiF + CaF 2 ) eut + LaF 3 and (LiF + NaF) eut + LaF 3 .

Assessment of Molten Eutectic LiF-NaF-KF Density through Experimental Determination and Semiempirical Modeling

“…Equation shows the density of the molten salt mixture. The ideal behavior term (ρ id ) comes from the additive nature of the volume as a physical property, whereas ρ ex is the term to account for the deviation from the ideal density behavior. Similar equations to eq were used in the past, where an ideal term was determined directly from volume. ,, Ideal density is calculated as the ratio of average molecular weight to the molar volume of the liquid where MW i is the molecular weight and x i is the molar fraction of component i . The excess behavior of the density of molten salts is defined using the RK expansion .…”

“…Similar equations to eq 2 were used in the past, where an ideal term was determined directly from volume. 35,52,53 Ideal density is calculated as the ratio of average molecular weight to the molar volume of the liquid…”

Densities and Volume Properties of the Melts of the Systems (LiF + NaF)eut + SmF3, (LiF + NaF)eut + GdF3, and (LiF + NaF)eut + NdF3

“…Due to the almost complete absence of reports on the volume properties of the ternary system, we focused on the systematic investigation of certain systems that could be compared after appropriate accumulation of data. The volume properties of the systems (LiF + MgF 2 ) eut + LnF 3 , , (LiF + CaF 2 ) eut + LnF 3 , , (Ln = La, Nd, Sm and Gd), and (LiF + NaF) eut + LaF 3 have already been reported; thus, it made sense to examine the systems (LiF + NaF) eut + LnF 3 (Ln = Nd, Sm, and Gd) to complete a set of data suitable for drawing comparisons between systems. It must be noted that although these systems are in principle ternary systems, we evaluated them as quasi-binary ones in which the eutectic component is considered as one component.…”