Study on the electrochemical behavior of Mg and Al ions in LiCl-KCl melt and preparation of Mg-Al alloy

Abstract

The electrochemical behavior of Mg2+ and Al3+ in LiCl-KCl (mass 4: 1) melt at 973 K was studied on a Mo electrode systematically by cyclic voltammetry, square wave voltammetry and chronopotentiometry. The results showed that the reductions of Mg2+ and Al3+ were reversible processes controlled by the rate of the mass transfer. When Mg2+ and Al3+ coexisted in LiCl-KCl melt, they had no significant effect on the reduction potential of each other. The equilibrium potentials of Mg2+/Mg and Al3+/Al were obtained by open circuit potential method. Their apparent standard potentials were also calculated in this system and the values were −2.52 V vs Cl2/Cl−, −1.66 V vs Cl2/Cl−, respectively. Correspondingly, the apparent Gibbs free energies of Mg2+/Mg and Al3+/Al were −485.71 kJ/mol, −480.78 kJ/mol. Finally, potentiostatic electrolysis was performed on a Mo electrode in LiCl-KCl-MgCl2-AlCl3 (the mass ratio of MgCl2 to AlCl3 was 10:1) melt at different potentials. The components of the deposits were characterized by scanning electron microscope and energy dispersive spectroscopy. The study revealed that the content of Al in the deposit decreased as the overpotential increased and Al tended to segregate at the grain boundaries.

Keywords

• Electrochemical behavior
• Thermodynamic properties
• Mg-Al alloy
• Electrolysis