Phase Reactions Between Refractory and High-Acidic Synthetic CaO-Ferronickel Slag

Interactions between high melting synthetic ferronickel slags with acidic character and MgO as refractory were investigated. In order to facilitate the complex composition of real ferronickel slag, a synthetic slag of SiO2-MgO-Fe2O3-CaO was used. The practical corrosion tests of the MgO refractory were performed in a hot-stage microscope at temperatures of 1650°C under a CO/CO2 atmosphere for process-oriented conditions. The formed phases between slag and magnesia substrate were analyzed by scanning electron microscope analysis. The results show that, by penetrating the slag into the refractory, the melt dissolves the magnesia and forms Mg- and Ca silicates. Furthermore, a diffusion of Fe from the slag into the magnesia grains can be observed and a transformation to magnesiowustite occurs. Thermodynamic phase calculations using FactSage software confirmed the generation of these minerals. The combination of practical testing and thermodynamic calculations should ultimately provide a path for improving the refractory lifetime and performance.