Penetration and corrosion of magnesia grain by silicate slags

Penetration and corrosion resistance of high purity sintered and fused magn esia grain by model EAF (CaO/SiO2 =1.38) and BOF 'late' slags (CaO/SiO2 = 3 .29) at 1600 and 1700 degreesC were investigated by SEM, EDS, and XRD analy sis. Thermodynamic calculations were performed to assist interpretation of the reaction processes involved. At the test temperatures, Fe and Mn ions f rom both model slags diffused into the magnesia grain to form a magnesiowus tite, (Mg, Fe, Mn)O. The magnesiowustite directly adjacent to the slag had a much larger crystal size than that of the bulk MgO far from the MgO/slag interface. The large magnesiowustite grains limit the potential for grain b oundary penetration into the sintered magnesia. The magnesiowustite layer f ormed with the EAF slag took up more FexO from the slag than that formed wi th the BOF slag, which was partially responsible for a lower slag penetrati on into sintered magnesia grain since the remaining silica rich local liqui d was rendered more viscous. The EAF slag was not saturated with respect to MgO, so the magnesiowustite which did form later reacted with Ca and Si io ns remaining at MgO/EAF slag interface to form low melting phases such as m erwinite, C3MS2, and then dissolved into the slag, rendering the dissolutio n process essentially indirect. The BOF late slag was already oversaturated with respect to MgO, so slag penetration only occurred in the sintered mag nesia grains. BCT/411.