Phase Equilibria and Thermodynamics in the Al2O3-SiO2 System-Modeling of Mullite and Liquid

The Al2O3–SiO2 system has been reassessed using a solution model for mullite extending from sillimanite to a hypothetical state of alumina. The property of sillimanite, to be used to describe one of the end‐members, was extracted from an analysis of the T–P phase diagram for Al2SiO5 polymorphs. It was possible to represent the information on the range of stability of mullite, including some showing that mullite extends to higher SiO2 contents than represented by the composition of 3:2 mullite. An attempt was made to model the liquid with the ionic two‐sublattice model using a new species AlO2−1. The pressure dependence of Al2SiO5 polymorphs was optimized by a new model recently implemented in Thermo‐Calc.