Effect of TiO2 addition on the stability of t-ZrO2 in mullite–ZrO2 composites prepared from various starting materials

Mullite–zirconia composite materials were prepared by reaction sintering of α-alumina and aluminium nitrate as alumina sources, and zircon powder. Different effects were observed on sintering, densification and microstructure of composites prepared by various alumina sources by adding TiO2. The formation temperature and retention of tetragonal zirconia phase were found to differ in composites with and without TiO2. The more fraction of t-ZrO2 was retained from the reaction sintering of alumina nitrate and zircon without TiO2 addition. The same trend was observed for the combination of α-alumina and zircon containing 3.5 wt.% TiO2 below 1550 °C. The microstructural analysis show enlarge ZrO2 particles in compositions containing TiO2; that is the reason for the reduction of t-ZrO2 concentration.