Phase equilibria of the CaO-BaO-SiO2-12mol pct. Al2O3-13mol pct. MgO system with a wide substitution range of CaO with BaO have been experimentally determined at 1623 K (1350°C) and 1573 K (1300°C) using high-temperature equilibration followed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) analysis. The (Ca,Ba)3MgSi2O8, BaAl2O4, BaAl2Si2O8 and Ca2(Al0.46Mg0.54)(Al0.46Si1.54)O7 phases have been designated within the phase diagram. The liquidus temperature initially decreased and then increased for the samples substituting CaO with BaO at a constant (C + B)/S ratio between 1.50 and 1.86. For samples with a constant BaO/CaO ratio, the liquidus temperature showed similar trends with a lower (C + B)/S ratio from 1.22 to 0.67. The volume fraction of crystal phases of the samples as-quenched from 1573 K (1300°C) correlated well with the variation of liquidus and the primary phases. In addition, the change in the Gibbs free energy of the reactions and the bond parameter (Xp × Z/Rk) of the cations were analyzed, where the maximum change in the Gibbs free energy was found for the formation of Ca3MgSi2O8; furthermore, the stronger basic tendency of Ba2+ than Ca2+ facilitates Ba2+ substitution for Ca2+ and bonding with acidic tendency cations to form Ba-containing phases.
All Science Journal Classification (ASJC) codes
- Ceramics and Composites
- Materials Chemistry