Thermodynamic Properties of Sr–Sn Alloys via Emf Measurements and Thermal Analysis

Abstract

The thermochemical properties of Sr-Sn alloys were determined by electromotive force (emf) measurements to evaluate liquid tin as an interacting electrode material for separating alkaline-earth elements from molten salt solutions. A Sr(s)|CaF 2 -SrF 2 |Sr(in Sn) cell was used to measure emf values for twelve Sr-Sn alloys at mole fractions x Sr = 0.02-0.43, allowing the determination of thermochemical properties such as activity and partial molar quantities of Gibbs energy, entropy, and enthalpy of Sr at 730-1110 K. Activity values of Sr in liquid Sn were as low as 6.9 × 10 -12 at 800 K and x Sr = 0.02 indicating highly non-ideal solution behavior between Sr and Sn. Phase transitions were also determined from the emf data and were validated via differential scanning calorimetry (DSC). Through the combination of emf measurements for thermochemical properties, X-ray diffraction (XRD) for phase constituents, and DSC measurements for phase transitions, this work established more complete thermodynamic properties of the Sr-Sn binary system.

Electrochemical Separation of Alkaline-Earth Elements from Molten Salts Using Liquid Metal Electrodes

“…and Lichtenstein et al clearly illustrates inconsistencies in the assessment of liquid Bi for alkaline-earth recovery as well as in γ Ba by nine orders of magnitude, inviting scrutiny into the capability of liquid metals for alkaline-earth recovery from molten salts. Thermodynamic properties of eight binary (Ba, Sr)–(Bi, Sb, Sn, Pb) alloys were investigated via emf measurements (Δ G̅ = – 2FE = RT ln a ) using a solid CaF 2 –BaF 2 /SrF 2 electrolyte, as shown in Figure for selected Ba/Sr mole fractions ( x Ba/Sr = 0.03–0.07). − A large emf value of these liquid metals (i.e., low γ) indicates strong chemical interactions between alkaline-earth and liquid metals; the degree of interactions is strongest for Sb followed by Bi, Sn, and Pb for both Ba and Sr.…”

“…Emf as a function of temperature for (a) binary Ba–(Sb, Bi, Sn, Pb) alloys and (b) binary Sr–(Sb, Bi, Sn, Pb) alloys at selected mole fractions, where solid lines represent linear or curved fits. − …”