Thermal Shock Resistance Enhancement of Alumina-Based Castables by Incorporating Porous Alumina Spherical Aggregates

Chrome-containing corundum–spinel castables are the preferred materials for ladle purging plugs due to their excellent slag resistance, high mechanical strength, and good volume stability. However, their poor thermal shock resistance often leads to transverse cracking or thermal spalling, thereby limiting their service life improvement. Since aggregates typically constitute 70 wt% of castables, modifying the aggregates may be an effective strategy to enhance the thermal shock resistance. To this end, alumina spherical aggregates were prepared via a pan granulation technique using α-Al2O3 powders as the raw material and a ZnCl2 solution as the binder. The effects of the firing temperature on the physical properties and the microstructure of the as-fabricated aggregates were investigated, followed by an evaluation of their impact on castable performance. After firing at 1400 °C for 3 h, the resulting alumina spherical aggregates exhibited a porous interior and a dense exterior structure, with an apparent porosity of 27.21%, a water absorption capacity of 9.38%, and a crushing rate of 51.3%. When these aggregates were incorporated into castables, their apparent porosity increased, while the bulk density and the cold strength showed slight reductions; however, their thermal shock resistance was notably improved. Among the formulations tested, the castable containing 4% of 0.2–0 mm spherical aggregates exhibited the best thermal shock resistance, with a residual strength of 7.96 MPa and a strength retention rate of 27.85%.