Thermodynamic modeling of the miscibility gaps and the metastability in the R2O3-SiO2 systems (R=La, Sm, Dy, and Er)

A range of compositions and temperatures below the monotectic temperature e xists where there are thermodynamic restrictions that prevent the equilibri um solid from forming directly from the undercooled homogeneous liquid. In this region the solid can form only after liquid-liquid phase separation ha s occurred. As suggested by earlier research, the thermodynamic restriction s on the crystallization process may be useful to control the crystallized grain structure in glass-ceramic systems. Thus, understanding the thermodyn amic limitations on the formation of the solid in monotectic systems could have commercial significance. Ln the present paper, the metastable liquidus boundaries, liquid miscibility gaps, and spinodal curves in the binary La2 O3-SiO2, Sm2O3-SiO2 Dy2O3-SiO2, and Er2O3-SiO2 systems were calculated usin g analytical expressions for the Gibbs free energies of the liquid phases. (C) 2001 Elsevier Science B.V. All rights reserved.