Electrochemical and calorimetric investigations of some thermodynamic properties of EuCl3 and EuCl2 dissolved in alkali chloride melts

The electroreduction of EuCl3 in alkali chloride melts (NaCl-KCl, KCl, CsCl) was studied in the temperature range 973-1123 K by different electrochemical methods. It was determined that electrochemical reduction of Eu(III) in alkali chloride molten salts occurs via two successive reversible stages involving transfer of one and two electrons. The formal standard potentials of EEu(II)/Eu∗, EEu(III)/Eu∗ and formal redox potentials of EEu(III)/Eu(II)∗ were determined from open-circuit potentiometry and linear sweep voltammetry data. The thermodynamics of formation dilute solutions of europium di-and tri-chloride in alkali chloride melts was determined. The relative partial molar enthalpies of mixing EuCl2 with alkali chloride melts when dilute solutions are formed have been measured previously by direct calorimetry in a Calvet type calorimeter using of ampoule break-off technique. It was shown that the values determined from electrochemical measurements are in a good agreement with those data obtained by calorimetric method.