Thermal Properties of Magnesia-Chromite Refractories in a Precious Metals Top-Blown Rotary Converter

The aim of this study is to evaluate the effect of slag infiltration on the thermal properties of magnesia-chromite refractories. The samples studied in this work were obtained from a precious metals top-blown rotary converter. The bricks were collected from three locations inside the furnace. The structure, slag infiltration, and porosity of the bricks were studied using X-ray computed tomography (XCT), after which the thermal diffusivities of slag-infiltrated and as-delivered MgO–Cr₂O₃ refractory bricks were measured using laser flash analysis (LFA). The diffusivities were obtained as a function of temperature, from 20 to 700 °C. After LFA, the sample microstructures were analyzed with scanning electron microscope-energy dispersive X-ray spectrometer to investigate changes in the microstructure and degradation of the bricks. Changes in thermal diffusivity were evaluated in relation to structural changes and degradation. XCT imaging showed that the brick samples from the bottom and cylinder contained notable amounts of infiltrated slag throughout their length, but the slag infiltrated to a lesser extent in the cone. The porosity of the samples decreased significantly after slag interaction, and the structure was densified towards the hot face. Changes in the microstructure occurred through chemical dissolution, slag penetration, and hot erosion. The MgO was corroded by the reaction between MgO and SiO₂ in the slag, consequently forming a new phase, forsterite. The slag infiltration causes changes in the thermal diffusivities in comparison to an unused refractory. These changes, however, are rather slight. The highest increase in diffusivities was observed in samples near the cold face, but the differences in the slag volume at that penetration depth showed a surprisingly small impact on the diffusivity.