Influence of the Characteristics of Spinels on the Slag Resistance of Al 2 O 3 –MgO and Al 2 O 3 –Spinel Castables

The XRD patterns at ambient temperature and at 1500°C showed that the spinel in the Al 2 O 3 –MgO castables fired at 1500°C for 3 h has the higher peak intensity, compared to those in Al 2 O 3 –spinel castables; the interplanar distance in the set (311) is 2.43 Å for the spinel in Al 2 O 3 –MgO castables as well as the spinels in Al 2 O 3 –spinel castables using spinels containing 73, 90, and 94 wt% Al 2 O 3 , respectively. The corresponding alumina contents of the spinels in these castables were estimated to be around 75 wt%. The smaller grain size of the spinel in Al 2 O 3 –MgO castables compared to that in Al 2 O 3 –spinel castables is evidenced by the recrystallization of the in situ spinel only occurring in Al 2 O 3 –MgO castables as revealed by the XRD patterns at ambient temperature and at 1500°C. The larger amount and smaller grain size of the in situ spinel in the matrix mostly account for the better slag resistance of Al 2 O 3 –MgO castables, compared to Al 2 O 3 –spinel castables.