Alumina hollow castable material SL-1.3 SL-1.6 AL2O3 % ≥95 ≥95 Fe2O3 % ≤0.8 ≤0.8 bulk density g/cm3 ≤1.3 ≤1.6 cold compressive strength Mps ≥5 ≥8 highest service tempreture ℃ >1600 >1600