Mass spectrometric investigations of thermodynamic properties of the RbCl/GdCl3 system

The vaporization of pure RbCl, GdCl3, and RbCl-GdCl3 samples of different phase compositions was investigated in the temperature range between 666 K and 982 K by use of the Knudsen effusion mass spectrometry. The gaseous species RbCl, Rb2Cl2, GdCl3, and RbGdCl4 were identified in the equilibrium vapours and their partial pressures were determined. The enthalpy of dissociation of RbGdCl4(g), Delta(diss)Hdegrees(859 K) = 263.1 +/- 7.7 kJ mol(-1), was evaluated by second law treatment of the equilibrium partial pressures. The thermodynamic activities of RbCl and GdCl3 were obtained at 800 K in the two-phase fields {Rb3GdCl6(S) + liquid} and {RbGd2Cl7(S) + GdCl3(s)}. The Gibbs free energies of formation of the pseudo-binary phases Rb3GdCl6(s), Delta(f)Gdegrees(800 K) = -75.1 +/- 2.5 kJ mol(-1) and RbGd2Cl7(S), Delta(f)Gdegrees(800 K) = -40.6 +/- 1.2 kJ mol(-1), were evaluated from the thermodynamic activities of the components. The results are compared with the available literature data.