Calculation of metastable immiscibility region in the Al₂O₃–SiO₂ system

Metastable liquid-liquid immiscibility region in the Al₂O₃–SiO₂ system was calculated by a regular solution model using three sets of liquidus data from the stable phase diagrams reported. These calculations indicated that the immiscibility region was richer in Al₂O₃ composition than those reported before. A miscibility gap calculated using the liquidus data reported by Klug et al. [F. J. Klug, S. Prochazka, and R. H. Doremus, J. Am. Ceram. Soc. 70, 750 (1987)] (model A) ranged from 2.6 to 71 mol % Al₂O₃ at around 1000 °C, which was the most compatible result with the idea that metastable pseudotetragonal mullite crystallized at around 1000 °C became Al₂O₃-rich composition due to the immiscibility phase separation before mullitization among three sets of liquidus data.