Thermodynamic Modeling of the Miscibility Gaps and the Metastable Liquidi in the MgO‐SiO₂, CaO‐SiO₂, and SrO‐SiO₂ Systems

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 binary MgO-SiO 2 , CaO-SiO 2 , and SrO-SiO 2 systems are calculated by using analytical expressions for the Gibbs free energies of the liquid phases. Calculating the metastable liquidus rather than using a simple extrapolation as originally proposed in the aforementioned previous research provides greater control of the heat-treatment processes and, thus, greater control over the resulting microstructure.

On the rigid to floppy transitions in calcium silicate glasses from Raman scattering and cluster constraint analysis

“…Even if this mode is broader than the preceding ones, these parameter evolutions are sufficiently large to be unambiguous. This frequency downshift and line narrowing upon increasing Ca content is different from high-frequency modes (6,9). This softening and narrowing is an uncommon behaviour and can be qualitatively explained only by a significant change of eigenvectors.…”

“…Several studies have stressed the special role played by the calcium atom which acts as a modifier in the silicate networks [6] and leads to a global increase of the density from 2.75 g cm À3 at x ¼ 0.38 to 2.97 g cm À3 at x ¼ 0.60 pyrosilicate composition [7,8]. Extensive studies have been performed to understand the miscibility limits in this system and in other alkaline earth silicates [9,10].…”

Thermodynamic Assessment of the Miscibility Gaps and the Metastable Liquidi in the B2O3–RO Systems (R = Mg, Ca, Sr, and Ba)

“…This value is much larger than that of the silicate systems (20%-25%). 18,19 The liquidi for these intermediate compounds also were calculated and included in Figs. 2-5.…”

“…Using experimental liquid miscibility data, the interaction parameters in Eqs. (10a,b) can be optimized through a multiple linear regression method 18,19,[25][26][27][28] , which is based on least squares. And then the metastable liquidus as well as the equilibrium miscibility gap can be assessed as a function of temperature and composition.…”

“…Yu et al 15 11,12 their results of liquid miscibility gaps showed a reasonable agreement on the B 2 O 3 -CaO system 15 but a large difference in the B 2 O 3 -BaO system 16 because they tried to optimize the large scattered experimental data, which result from the change of local glass structure around boron with heat-treatment temperature. 17 Recently Kim et al 18,19 developed a reasonable model to describe the liquid miscibility gaps in the binary silicate systems. In the present work, the recent experimental data of Hageman and Oonk 12 were chosen and used to describe the liquid miscibility gaps in the B 2 O 3 -MgO, B 2 O 3 -CaO, B 2 O 3 -SrO, and B 2 O 3 -BaO systems.…”