Revised phase equilibrium relationships in the system Al2O3ZrO2SiO2

Current research on the mechanical behaviour of ceramic matrices reinforced by zirconia particles, and on the processing of mullite-zirconia composites via reaction sintering, has brought about the need to update the phase diagram of the system Al2O3ZrO2SiO2, whose available version dates back to 1956. In the present work selected compositions in this system were prepared from reagent-grade oxides, uniaxially pressed into 6 mm cylindrical pellets, fired at temperatures between 1550 and 1750°C for 6 to 24 h, water-quenched, and observed by X-ray diffraction and SEM, the composition of some of the phases identified being evaluated by EPMA. These experiments led to the relocation of the boundary curves neighbouring the ternary eutectic involving alumina, zirconia and mullite. This eutectic was found to occur between 1700 and 1710°C, a temperature significantly lower than previously reported, and at a composition c. 11SiO2+58Al2O3+31ZrO2 (wt%).