The phase composition and microstructural evolution of a novel MgO-C-Al-Si refractory used in bottom-blowing elements at high temperatures in flowing nitrogen

A novel MgO-C-Al-Si refractory with low carbon content used in bottom-blowing elements was prepared, and its phase composition and microstructural evolution were investigated by XRD, SEM and EDS after being treated at 1200–1600°C in flowing nitrogen. Results show that the samples are composed of MgO, Al4C3, SiC, Al4SiC4, MgAl2O4, Mg3Al2N4 and Al2O3 at 1200–1400°C, while the samples are composed of MgO, Al4C3, SiC, Al4SiC4, Al4Si2C5, MgAl2O4, Mg3Al2N4 and Al2O3 at 1500–1600°C. Al and Si present gradient reactivity at high temperatures and Al has priority over Si to react with MgO, forming MgAl2O4. Based on the microstructure analysis, we find that the higher the temperatures are, the more abundant the products. Al(g), Al2O(g), SiO(g), Mg(g) and CO(g), as the gas–gas reaction substances, react to form many of Al4SiC4 flakes containing Mg, O and N within pores or gaps of the refractory, along with trace amounts of SiC whiskers and MgAl2O4 spinel whiskers. In addition, the surface morphology of the magnesia aggregates is modified by the MgAl2O4 spinels and Al4SiC4 flakes, owing to the synergistic effect of Al and Si. Further, some physical properties are also characterized.