Potentiometric study of the interaction of Sm3+ and O2− ions: thermodynamic properties of samarium compounds in molten NaCl–2CsCl eutectic.

The reactions of oxygen and samarium ions in molten NaCl–2CsCl eutectic in the temperature range of 823–913 K have been investigated by potentiometric titration in an inert gas atmosphere. The activity of oxygen ions in the studied melts was monitored using a standard YZME (indicator) electrode based on Y2O3-stabilized ZrO2 with a solid–electrolyte membrane. The titration of Sm3+ by O2− ions demonstrated the formation of insoluble SmOCl compounds in the investigated region. The mechanism of formation of SmOCl and Sm2O3 was established by the analysis of potentiometric titration curves. Subsequently, the solubility of SmOCl and Sm2O3 in the melt was calculated using the material balance equation and solubility constant equation. Finally, the basic thermodynamic properties of SmOCl and Sm2O3 in molten NaCl–2CsCl eutectic were calculated, and the properties of samarium in the melt were summarized using the Pourbaix-type (E-pO2−) diagram to determine the kinds of stabilized samarium compounds. Furthermore, the optimal chlorination conditions can be obtained from the E-pO2− diagram of Sm. [ABSTRACT FROM AUTHOR]