Effect of calcium magnesium aluminate on microstructural distribution of SiO ₂ impurity in magnesia

Abstract The effect of calcium magnesium aluminate (hereinafter referred to as CMA) on the microstructural distribution of the main impurity SiO 2 in magnesia was investigated in this research. The XRD, SEM, and EDS analyses were used in this work. It can be seen from the result that SiO 2 in low‐grade sintered magnesia diffused into CMA area at high temperature and the distribution of SiO 2 in sintered magnesia was significantly reduced. The main mineral phase of sintered magnesia was periclase and monticellite, and impurities in sintered magnesia mainly existed in the form of monticellite, which was completely decomposed into liquid phase and periclase above 1400°C, SiO 2 in the liquid phase in the sintered magnesia migrated into the liquid phase that formed in the CMA. Furthermore, the adsorption energy of CaO on SiO 2 is stronger than that of MgO on SiO 2 , so the SiO 2 in sintered magnesia diffused into CMA due to its relatively higher CaO content compared with the sintered magnesia. The SiO 2 content in fused magnesia was lower than that of sintered magnesia and the dicalcium silicate (C 2 S) content in fused magnesia was higher than that of sintered magnesia, so the influence of CMA on microstructural distribution of SiO 2 in fused magnesia was obviously different than that with low grade sintered magnesia.