Thermodynamic modeling of the miscibility gaps and the metastability in the R 2O 3–SiO 2 systems (R=La, Sm, Dy, and Er)

Abstract

A range of compositions and temperatures below the monotectic temperature exists where there are thermodynamic restrictions that prevent the equilibrium solid from forming directly from the undercooled homogeneous liquid. In this region the solid can form only after liquid–liquid phase separation has occurred. As suggested by earlier research, the thermodynamic restrictions on the crystallization process may be useful to control the crystallized grain structure in glass–ceramic systems. Thus, understanding the thermodynamic limitations on the formation of the solid in monotectic systems could have commercial significance. In the present paper, the metastable liquidus boundaries, liquid miscibility gaps, and spinodal curves in the binary La 2O 3–SiO 2, Sm 2O 3–SiO 2, Dy 2O 3–SiO 2, and Er 2O 3–SiO 2 systems were calculated using analytical expressions for the Gibbs free energies of the liquid phases.