Preparation of zirconia–mullite composites by an infiltration route

In order to improve the mechanical properties of pure mullite ceramics, a process has been developed that incorporates Zr(Y)O2 into mullite by infiltrating partially reaction sintered (porous) mullite compacts with mixed ZrOCl2·8H2O and YCl3·6H2O solutions, corresponding to ZrO2/Y2O3 = 97/3 (mol.%). The infiltration of small amount (∼7.2 wt.%) of Zr(Y)O2 significantly improved the densification behavior and mechanical properties of mullite bodies sintered at 1620 °C, for 10 h. The mocrostructure contained a few elongated mullite crystals (aspect ratio > 6) which were embedded in a fine-grained matrix. The relatively large Zr(Y)O2 inclusions were mainly dispersed intergranularly in the matrix, but small (<0.7 μm) inclusions were present in the grains. During sintering, the liquid phase having higher Al2O3 content than that of stoichiometric mullite composition formed at triple points of the mullite/mullite grains.