Interaction between MgO–C-bricks and ladle slag with a 1:1 CaO/Al2O3 ratio and varying SiO2 content

Abstract

The interaction between the industrial ladle lining bricks (carbon = 5-13 mass%) and secondary metallurgical slag (CaO/Al2O3 ratio = ~1; SiO2 = 1–20 mass%) was evaluated under laboratory conditions using finger testing between 1550 and 1650 °C. The thermophysical properties, including viscosity, density, and surface tension of the three slags were measured and compared with previously reported data. The experimental investigations were supported by thermochemical modelling (Factsage 7.2). The three lining materials exhibited different wear behaviour when in contact with each of the three slags at different temperatures. The slag with 1 mass% SiO2 was MgO-saturated and had a low viscosity compared to the slags with 10 and 20 mass% SiO2. This slag effectively infiltrated the lining without dissolving it at 1550 °C. With increasing temperature, the MgO saturation in the slag decreased, which led to the dissolution of the MgO grains from the mining bricks into the slag. Further, the carbothermal reaction began to dominate at higher temperatures, which led to carbon oxidation and the formation of new MgO. A solid spinel phase was observed in the slag with 10 mass% SiO2 below 1600 °C and in the slag with 20 mass% SiO2 at all investigated temperatures. Interaction with the lining materials intensified this spinel formation, which slowed or stopped slag infiltration. The high content of impurities in the lining material (e.g. SiO2, CaO, and Fe2O3) led to the formation of a liquid slag phase on the grain boundary, which compromised the strength of the material and caused the loss of MgO grains.