Stability of lanthanide oxides in LiCl-KCl eutectic melt

Some lanthanide oxides form oxychlorides (LnOCl) in the chloride melts, according to the reaction, Ln(2)O(3) + 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 Ln(2)O(3) in LiCl-KCl eutectic melt at 723 K. The equilibrium depends on the free energies of formation of the solid compounds, Ln(2)O(3) 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) < mu(0)(O2- < 168 kJ mol(-1) from the equilibria using the reported thermochernical data of Ln(2)O(3) and LnOCl. (c) 2004 Elsevier Ltd. All rights reserved.