Effects of TiO2 addition on the expansion behavior of alumina–magnesia refractory castables

Abstract

Cement-bonded alumina–magnesia refractory castables present excellent properties because of the in situ spinel and calcium hexaluminate formation. However, controlling the expansion derived from in situ reactions is essential for keeping the integrity of castables. The present work addresses the effects of TiO2 addition on the expansion behavior of alumina–magnesia refractory castables by the assisted sintering technique. The mechanism was discussed by comparing the apparent porosity, phase composition and the resultant microstructure. The change of the expansion with the temperatures for castables containing 0–2 wt% of TiO2 presented a trend of first increase and then decrease. The expansion level of alumina–magnesia refractory castables after firing at 1500 °C for 5 h decreased gradually with TiO2 amount from 0.5 to 2 wt%. The results indicated that TiO2 acted in a greater extent in accelerating the spinel and CA6 formation at 1300 °C, while the effect of TiO2 was reduced with the increase of the temperature. The microstructure development of alumina–magnesia castables with TiO2 addition was more complex. The more liquid phase with lower viscosity formed by adding TiO2, resulted in the drastic decrease of the overall expansion for alumina–magnesia refractory castables.