Reaction Mechanism of MgAl₂O₄ Refractories in Contact with a Liquid Ferromanganese Metal

A reaction mechanism is suggested for two types of MgAl₂O₄ refractories; a MgAl₂O₄ and a MgO-rich MgAl₂O₄, which were reacted with a liquid ferromanganese metal. The finger rotating test (FRT) technique was adopted and experiments were carried out at 1873 K. After the experiments, each refractory was analyzed by X-ray computed tomography, field emission scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. When the MgAl₂O₄ was in contact with the liquid ferromanganese metal, complex (Mg,Mn)(Mn,Al)₂O₄ layers were formed at the surface of the refractory. It acted as a passive layer since manganese ions did not penetrate into the bulk of the refractory with increasing reaction time. However, when the MgO-rich MgAl₂O₄ was in contact with liquid ferromanganese metal, manganese ions selectively penetrated through the MgO grains, which led to the formation of a (Mg_xMn_1-x)O solid solution. The penetration depth increased both with increasing reaction time and rotating speed. The characteristics of the reaction layers were analyzed by XRD and EDX and, a possible mechanism to form these layers was suggested based on thermodynamic consideration.