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

The Al 2 O 3 –SiO 2 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 Al 2 SiO 5 polymorphs. It was possible to represent the information on the range of stability of mullite, including some showing that mullite extends to higher SiO 2 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 AlO 2 −1 . The pressure dependence of Al 2 SiO 5 polymorphs was optimized by a new model recently implemented in Thermo‐Calc.