Experimental determination of phase equilibria in the CaO‐BaO‐SiO 2 ‐12 mol pct. Al 2 O 3 ‐13 mol pct. MgO system at 1573 K and 1623 K

Phase equilibria of the CaO‐BaO‐SiO 2 ‐12mol pct. Al 2 O 3 ‐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) 3 MgSi 2 O 8 , BaAl 2 O 4 , BaAl 2 Si 2 O 8 and Ca 2 (Al 0.46 Mg 0.54 )(Al 0.46 Si 1.54 )O 7 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 (X p  × Z/R k ) of the cations were analyzed, where the maximum change in the Gibbs free energy was found for the formation of Ca 3 MgSi 2 O 8 ; furthermore, the stronger basic tendency of Ba 2+ than Ca 2+ facilitates Ba 2+ substitution for Ca 2+ and bonding with acidic tendency cations to form Ba‐containing phases.