Microstructural analysis of corroded alumina-spinel castable refractories

Microstructural analysis indicates that the corrosion of alumina-spinel castables by a liquid steel ladle slag involves initial reaction of CaO in the slag with alumina fines in the refractory bond. The slag becomes saturated in CaO and Al2O3 and CA(2) is precipitated from it along with other calcium aluminates. The spinel fines and grains in the refractory take up the MnO/FeO/Fe2O3 from the slag, which becomes silica-rich as CA(2) is precipitated and highly viscous. The thickness of the remnant slag layer on the corroded samples indicates the viscosity of the liquid slag under the test conditions. Further into the refractory CA(6) is formed, firstly crystallized with a tabular morphology in dense regions and then with a similar morphology in more porous regions. Deeper still in the refractory CA(6) takes a whisker/needle habit suggesting some vapour-phase reaction. MgO-rich spinel-alumina castables undergo less corrosion under these conditions as dissolution of MgO leads to a viscous MgO-rich slag which is less corrosive to the Al2O3 components of the refractory. (C) 1996 Elsevier Science Limited.