The effect of in-situ phase formation on the infiltration and chemical degradation of magnesia-chromite bricks in contact with a synthetic non-ferrous slag

To have a robust smelting process it is essential to be able to rely on a long refractory life. In case of Cu-smelters, life times of two and more years can be obtained. In these processes a fayalite slag is used. However, in processes operated with a PbO slag, the refractory life time is often lower. A major difference between both slags lies in the infiltration behavior of the slag; PbO slags can infiltrate the porous lining much deeper, attacking a larger part of the lining. In this paper the chemical degradation of magnesia-chromite refractory material in contact with a deeply infiltrating synthetic PbO-SiO₂-Al₂O₃-"Fe₂O₃" based slag is investigated. The results indicate the formation of two new phases inside the refractory sample: (1) a new spinel phase, rich in aluminum and iron, forming near the contact surface with the bath and (2) a forsterite (Mg₂SiO₄)phase forming deeper inside the sample. Unlike forsterite, the new spinel phase forms a dense protective layer, limiting the dissolution of the MgO into the liquid slag. The main dissolution of the lining does therefore not occur at the first contact area between the refractory lining and the unsaturated slag but deeper inside the sample when the protective layer is no longer formed.