Effect of La2O3 addition on the microstructural evolution and thermomechanical property of sintered low-grade magnesite

Abstract

The rich mineral resources of magnesite have been decreasing rapidly, while the low-grade magnesite is abandoned, and the requirement on utilization of low-grade magnesite is causing much attention. La2O3 has been introduced as an additive in this study, considering its positive role in the modification of the magnesia matrix. Low-grade magnesite containing 0–3 wt% La2O3 was fired at 1550 °C for 3 h. The effect of La2O3 on the microstructural evolution and thermomechanical property of sintered low-grade magnesite was investigated. The results showed that La2O3 markedly improve the microstructure of sintered low-grade magnesite. The distribution state of the low melting monticellite phases among the periclase grains evolved from distribute continuously to concentrate in isolation at the triple-point junction of the periclase grains, and the generated CaO·3SiO2·2La2O3 based dendrites phases interlaced in the magnesia matrix. The hot modulus of rupture (HMOR) was significantly enhanced with increasing addition of La2O3 due to the low-melting monticellite phases were transformed to CaO·3SiO2·2La2O3 phases based dendrites with large aspect ratio, effectively reducing the availability of monticellite. Besides, the bridging phenomenon resulting due to the dendritic phase exhibited an optimal toughening effect, attributing to the increase in crack deflection and resistance to crack propagation.