Effects of fine reactive alumina powders on properties of alumina-magnesia castables with TiO2 additions

The design of alumina-magnesia castables was optimized based on the action mechanism of raw materials. In this study, the effects of fine reactive alumina powders on the properties of alumina-magnesia castables with TiO₂ additions were investigated. The phase composition and microstructure of castables with different contents of TiO₂ and two fine reactive alumina powders were characterized by X-ray diffraction and scanning electron microscopy. The results of these studies showed that the Na₂O/SiO₂ ratio of reactive alumina affected on the phase evolution and properties of castables. The changes in the spinel and CA₆ content and their solid solubility could account for the comprehensive effect of TiO₂ and reactive alumina on the castables. The difference in the expansion of castables with 1 wt% TiO₂ addition after calcination at 1350 °C was significant. The permanent linear changes and the apparent porosity of castables first increased and then decreased with increasing the calcination temperature. Castables containing reactive alumina with lower Na₂O/SiO₂ ratio had higher cold moduli of rupture.