THERMODYNAMICS OF CAO-AL2O3-SIO2 AND CAF2-CAO-AL2O3-SIO2 MELTS

Exchange reactions, occurring in CaF2-CaO-Al2O3-SiO2 liquid solution, and reactions between CaF2-CaO-Al2O3-SiO2, or CaO-Al2O3-SiO2 melts and Ta, Nb or Mo have been studied, using Knudsen effusion mass spectrome try. SiF3+, SiF2+, SiF+ CaF2+, CaF+, Ca+, Al2F5+ , AlF3+, AlF2+, AlF+, Al+, AlOF+, SiO+, MO+, MO2+ (M = Nb, Ta, Mo) and MoO3+ were detected in the mass spectra of the saturated vapour. SiF4, AlF3, AlOF, SiO, Ca F2 and MO2 were found to be the main vapour species and their partial vapour pressures were measured and used for calculation of the compone nts' activities. The activities, computed in different ways, were in g ood agreement. Representative files of experimental data comprising ca . 3500 activities of all components in the CaF2-CaO-Al2O3-SiO2 liquid solution and more than 350 values of (SiO2) in the CaO-Al2O3-SiO2 melt at various temperatures and concentrations were obtained. The thermod ynamic functions of the liquid solutions were described by the associa ted-solution model under the assumption that binary and ternary associ ates and SiO2 polymer complexes exist in the melts. The model and the thermodynamic functions of solid compounds were applied for the comput ation of phase equilibria in the CaO-Al2O3-SiO2 and CaF2-CaO-Al2O3-SiO 2 systems. The computed coordinates of the ternary invariant points ar e shown to agree with the available experimental data.