Phase diagrams for electrodeposition of alloys from molten chlorides

Abstract

The optimization of the electrochemical co-deposition of alloys from molten salts can be facilitated by CALculation of PHase Diagrams (CALPHAD) using appropriate software and databases. An electrochemical phase diagram (EPD) is a phase diagram in which the ordinate is the electrical potential relative to a reference electrode and the abscissa is a composition variable; it can be used to predict the deposited phases under potentiostatic conditions. The electrochemical diagram (ECD), recently introduced by Kaptay [Electrochim. Acta 484 (2024) 144,002], relates the salt composition to the composition of the electrodeposited alloy under galvanostatic conditions in the limit of vanishing current. In this study, we develop a method to calculate both types of diagrams for electrodeposition from chloride salts using CALPHAD software, compatible with any CALPHAD-type model for the participating phases, including the molten salt. We also establish the relationship between the phase diagram and ECD. The electrodeposition of Co-Ni, Ce-La, Al-Sc and Co-Sn alloys on inert cathodes from a KCl-LiCl eutectic melt is analyzed and compared with experimental results reported in the literature. For Ce-La containing salts, electrodeposition on a reactive nickel cathode is also considered. Additional potential applications of EPDs and ECDs are discussed.