Thermodynamic calculation and microscopic examination of liquid phase formation in MgO–C refractories contain calcium magnesium aluminate

Abstract

MgO-CMA-C refractories contain calcium magnesium aluminate (CMA) to increase the corrosion and penetration resistance due to the increase of the alumina and lime content of the infiltrating slag leading to a reduced reactivity. It is expected, that the addition of CMA to MgO–C may also result in the in situ formation of a small amount of high viscous liquid phase, which may affect the high-temperature properties. Hence, thermodynamic calculations, as well as EBDS analysis, were performed to gain insight into the effect of CMA on the liquid phase formation in MgO. Thermodynamic calculations identified liquid phase formation even in sintered and fused magnesia without CMA. By adding CMA, the increase in liquid phase portion, especially due to increase in Al2O3 portion, is only marginal (approx. 0.7 wt.-%) and the liquid phase formation is retarded up to 1500 °C. By means of EBSD analysis, an amorphous phase composed of Ca, Fe, P, Al, and Mg within the MgO-CMA matrix could be identified, which also indicates a liquid phase formation and assists the findings of the thermodynamic calculations.