Effect of solid solution of magnesia-alumina spinel on the microstructure and mechanical properties of CAC-bonded corundum castables

Magnesia-alumina spinel undergoes a solid solution reaction during firing, which potentially impact the microstructure as well as the mechanical properties of the CAC-bonded corundum castables. Moreover, spinels possessing the same chemical composition yet produced via different methods may exhibit diverse solid solution behaviors. Consequently, this study firstly compares the solid solution behaviors of sintered and fused spinel powders, both of which have an identical alumina content of 72 wt%, and then investigates the effect of solid solution on the microstructure and mechanical properties of CAC-bonded corundum castables. The results indicate that both sintered and fused spinel powders experience solid solution reactions during the firing process, leading to the formation of spinel-calcium hexaluminate (CA₆) connection structures. This transformation alters the fracture behavior from intergranular to transgranular mode, thereby enhancing the mechanical properties of castables. When the spinel content is 10 wt%, the cold crushing strength of the castables containing sintered spinel reaches 235.9 MPa, which is 28.6 % higher than that of the castables without spinel. The spinel-CA₆ connection structures increase with the elevation of the spinel content. Additionally, due to its smaller grain size, sintered spinel undergoes higher degree of solid solution reaction, forming tighter connection structures, which contributes to the improvement of the overall mechanical properties.