A comparative study on microstructures and slag resistance of Al2O3–MgO castables with dense and lightweight aggregates

Lightweight Al₂O₃–MgO refractory castables were prepared using microporous corundum–spinel aggregate, which was fabricated using the Kirkendall effect. The physical properties, microstructure, thermal conductivity, and slag resistance of the castables were analyzed using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and thermodynamic calculations. A comparative analysis was carried out between these findings and the corresponding ones for dense aggregates of Al₂O₃–MgO castables. Compared with dense aggregates, the reaction between microporous aggregate and matrix results in a smaller pore size in lightweight aggregate castables. The less soluble spinel in the microporous aggregate contributes to the reduced solubility of lightweight castables in slag, thus enhancing their corrosion resistance. Porous aggregates could absorb more Fe²⁺/Mn²⁺ ions from slag than dense aggregates, resulting in an increased viscosity of the slag. This, combined with the small pore size of the matrix, contributes to the superior penetration resistance of the lightweight aggregates castable compared with the dense aggregates castable. Consequently, lightweight aggregate castables exhibit superior corrosion and penetration resistance compared with dense aggregate castables. In contrast to dense aggregates castables, lightweight aggregates castables exhibit a 16.3% reduction in bulk density, an 8.2% decrease in thermal conductivity, and a notable enhancement in slag corrosion resistance.