High-temperature Study of Phase Equilibria in the Systems CsCl-LnCl3 (Ln=Ce, Nd) by Knudsen Effusion Mass Spectrometry

The vaporization of samples of different chemical and phase compositions in the systems CsCl-LnCl3 (Ln=Ce, Nd) was investigated in the temperature range between 850 and 1050 K by the use of Knudsen effusion mass spectrometry. The gaseous species CsCl, Cs2Cl2, LnCl3, Ln2Cl6 and CsLnCl4 were identified in the vapour and their partial pressures were determined. The thermodynamic activities of CsCl, and LnCl3 and the free enthalpies of formation for the phases Cs3LnCl6(s) were determined at 950 K in the two phase fields {liquid+Cs3LnCl6(s)}. The correlations between the condensed phase equilibria and the partial pressures of the vapour components at the phase boundaries are discussed and illustrated with the present experimental data.