The conversion of phase diagrams of solid solution type into electrochemical synthesis diagrams for binary metallic systems on inert cathodes

A method has been developed to convert equilibrium phase diagrams into equilibrium electrochemical synthesis diagrams (EESDs) using the same Calphad (Calculation of the Phase Diagrams) type of information behind them. The method is developed for binary (A–B) metallic systems electrodeposited from an electrolyte containing cations A+n and B+m on inert cathodes in a galvanostatic regime at very low cathodic current densities, i.e. close to equilibrium. The EESD shows the equilibrium composition of different phases in the equilibrium cathodic product at fixed values of temperature and pressure as a function of parameter ΔEB, being the deposition potential of one of the components (B) relative to another (A). The key to construct the EESD is a new equation derived for the synthesis potential of the alloy as a function of ΔEB, the charges the ions n and m in the electrolyte and the Gibbs energy of the cathodic product (alloy) as a function of its composition, temperature and pressure. The general method of phase diagram construction (i.e. the Gibbs energy minimization) is converted during the construction of the EESDs into the method of synthesis potential maximization. The given EESD is generally valid for the corresponding binary metallic A–B system, independent of the electrolyte (for the given values of n and m). The EESD can be used to design electrochemical synthesis of alloys if parameter ΔEB is known as a function of the composition of the given type of electrolyte (ionic liquid, aqueous solution, molten salt, etc.) at given temperature and pressure. In the present paper the method is developed to construct EESDs for phase diagrams of solid solution type.