Influence of the Characteristics of Spinels on the Slag Resistance of Al2O3–MgO and Al2O3–Spinel Castables

The XRD patterns at ambient temperature and at 1500°C showed that the spinel in the Al₂O₃–MgO castables fired at 1500°C for 3 h has the higher peak intensity, compared to those in Al₂O₃–spinel castables; the interplanar distance in the set (311) is 2.43 Å for the spinel in Al₂O₃–MgO castables as well as the spinels in Al₂O₃–spinel castables using spinels containing 73, 90, and 94 wt% Al₂O₃, 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 Al₂O₃–MgO castables compared to that in Al₂O₃–spinel castables is evidenced by the recrystallization of the in situ spinel only occurring in Al₂O₃–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 Al₂O₃–MgO castables, compared to Al₂O₃–spinel castables.