Stability of lanthanide oxides in LiCl-KCl eutectic melt

Some lanthanide oxides form oxychlorides (LnOCl) in the chloride melts, according to the reaction, Ln2O3+2Cl−=2LnOCl+O2−. Equilibria of the reaction for Ln=La, Nd, Gd in LiCl-KCl eutectic melt were examined. Entire La2O3 and a part of Nd2O3 were converted to LaOCl and NdOCl, respectively, though Gd2O3 remained unchanged after adding 2 wt% of Ln2O3 in LiCl-KCl eutectic melt at 723 K. The equilibrium depends on the free energies of formation of the solid compounds, Ln2O3 and LnOCl, and that of oxide ion (O2−) in the melt. The standard chemical potential of the oxide ion in LiCl-KCl eutectic melt at 723 K has been calculated to 154 kJ mol−1<μ0(O2−)<168 kJ mol−1 from the equilibria using the reported thermochemical data of Ln2O3 and LnOCl.