Fundamentals of liquid metal displacement reactions: Emf measurements of Na-Sn, Li-Sn, Mg-Sn, and Ca-Sn

Abstract

The driving force of spontaneous displacement reactions between Na-Sn alloys and molten LiCl, MgCl2, and CaCl2 salts stems from the difference of chemical potential between Na and Li, Mg, or Ca in liquid Sn. However, fundamental thermodynamic data are absent. Herein, electromotive force (emf) values of Na-Sn, Li-Sn, Mg-Sn, and Ca-Sn alloys (electrodeposition of Na, Li, Mg, and Ca in liquid Sn via the coulometric titration) were measured in NaF-NaCl-NaI, LiF-LiCl, MgCl2-NaCl-KCl, and CaCl2-LiCl-NaCl salts respectively at 650 °C. The measured emf values of these alloys were normalized with respect to the Cl−/Cl2 potential that −3.14 V to −3.35 V for Na-Sn (mole fractions xNa = 0.02–0.30) alloy, −2.90 V to −3.21 V for Li-Sn (xLi = 0.02–0.30) alloy, −2.38 V to −2.45 V for Mg-Sn (xMg = 0.01–0.15) alloy, and −2.90 V to −3.06 V for Ca-Sn (xCa = 0.01–0.15) alloy. And Li20Sn, Mg10Sn, and Ca10Sn alloys were successful prepared by displacement reactions between Na20Sn alloys and LiCl-NaCl, MgCl2-NaCl, and CaCl2-NaCl salts, which offers theoretical guidelines for s-block elements extraction and separation.