Thermodynamic and Kinetic Properties of Mg(II) in LiCl-KCl Melt and the Formation of Zn-Mg Alloy on Liquid Zn Electrode

Abstract

Thermodynamic and kinetic properties of Mg(II) in LiCl-KCl eutectic melt were investigated by electrochemical techniques. The diffusion coefficients of Mg(II) in the melt at various temperatures were studied by cyclic voltammetry, and the activation energy of Mg(II)/Mg was calculated to be (48.5 ± 3.7) kJ mol−1. The exchange current densities and reaction rate constants of Mg(II)/Mg at different temperatures from 773 K to 873 K were calculated by testing polarization curves on Mo electrode, and results showed that the exchange current densities became larger as the temperature increased. Equilibrium potentials of Mg(II)/Mg on Mo electrode and liquid Zn electrode were also tested by open circuit potential method. Subsequently, the apparent standard potential of Mg(II)/Mg, apparent standard Gibbs energy for the formation of MgCl2 and activity coefficients of Mg in the liquid Zn were calculated. Finally, metallic Mg was extracted in the form of Zn-Mg alloys by galvanostatic electrolysis on liquid Zn electrode. The deposit was analyzed by X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and Mg2Zn11 was detected in the deposit.