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Hojong Kim, Nathan Smith and Timothy Lichtenstein
Pennsylvania State University, USA
Posters & Accepted Abstracts: J Phys Chem Biophys
The thermodynamic properties of Ba-Bi and Sr-Bi alloys were determined by electromotive force (EMF) measurements to evaluate the viability of liquid bismuth metal as a medium for separating alkaline-earth species from molten salt electrolyte. EMF values of various Ba-Bi and Sr-Bi alloy compositions were measured at ambient pressure as a fuction of temperature between 700 K and 1050 K at mole fractions xBa or xSr=0.05-0.80. Binary solid-state electrolytes (CaF2-BaF2 or CaF2-SrF2) were employed to fabricate two types of electrochemical EMF cells: Ba(s)|CaF2-BaF2|Ba-Bi and Sr(s)|CaF2-SrF2|Sr-Bi. Reproducible EMF values within �?±5 mV were obtained during cooling-heating cycle at dilute alloy compositions (xBa or Sr<0.35), as shown in Figure 1a; increased thermal hystesis was apparent for higher alloy compositions (xBa or Sr>0.35) due to the formation of meta-stable phases. For each alloy composition, reported are the measured activity, the excess partial molar Gibbs energy, and temperature-independent partial molar entropy and enthalpy of alkaline-earths (Ba and Sr) in Bi, as well as the phase transition temperatures. Combining the high liquid-state solubility of Ba and Sr in Bi and the strong chemical interactions with Bi metal (e.g., aSr as low as 1.2ï�?´10â�?�?13), Bi shows promise as an electrode material for separating alkaline-earth species from molten salt electrolytes (e.g., LiCl-KCl-SrCl2). The EMF measurements were further corroborated using power X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to determine the relevant crystal structures and phase transition temperatures for each alloy composition. These data were used to construct revised binary phase diagrams over a wide range of composition range.