Corrosion of a high alumina concrete with synthetic spinel addition by ladle slag

A high alumina concrete with synthetic spinel (MgAl2O4) addition, conformed as a brick, has been tested in the slag line of a secondary steel ladle. A post-mortem study allowed to establish the elements diffusion profile inside the refractory as well as its microstructural evolution. This study was carried out by means of X-ray diffraction, reflected optical light microscopy and scanning electron microscopy coupled with energy dispersive X-ray analysis. From the analysis of the obtained results, making use of the Al-2,O-3-MgO-CaO-SiO2 quaternary system, it has been possible to establish the mechanism of corrosion, justifying, at the same time, the role that spinel and calcium hexaluminate (CaAl12O19) play. The spinel, that is the only stable solid phase in the slag - refractory interface, admits in its structure large amount of bivalent and trivalent elements (e.g. M2+, Fe2+, Fe3+, Cr3+...). Therefore, the slag becomes silica-rich and highly viscous, as CaAl12O19 is precipitated, decreasing the corrosion. The calcium hexaluminate grows from coarse and medium-sized grains of alumina to form a network of interlocked crystals that act as unions among the alumina grains. This microstructure together with that the CaAl12O19 also admits in solid solution large quantities of Fe2+ and Fe3+, provide a smaller, slower and more uniform wear of the refractory material.