Pore evolution of microporous magnesia aggregates with the introduction of nano-sized MgO

Microporous refractories applied in the working-lining of metallurgical furnaces have been rapidly developed in recent years owing to the outstanding mechanical properties, thermal insulation performance and slag resistance, the pore structure of which plays a critical role in the variation of service performance. Meanwhile, the microporous magnesia aggregates were prepared in our previous research with the introduction of nano-sized particles to overcome the shortcomings of high thermal conductivity, poor thermal shock resistance and slag penetration resistance, however, the pore evolution during sintering still remains to be investigated. Hence, in this study, the pore evolution of microporous magnesia aggregates is explored specifically and the effect of nanosized MgO on pore structure and sintering is simultaneously discussed. The sintering model of microporous magnesia was built for analyzing the pore structure evolution process. The results revealed that a micro-nano double-scale sintering model developed by the introduction of nano-sized MgO dramatically promoted the sintering kinetic force and boundary migration velocity. The sintering pressure discrepancy and free energy change per unit mole of specimens were respectively increased by -43 times and -48 times, which effectively improved the closed porosity and pore distribution homogeneity, while reduced the pore size. Meanwhile, the high sintering diving force lead to the significant improvement of direct bonding degree and grain size of microporous magnesia. With the addition of 3 wt% nano-sized MgO, the optimal sintering properties with closed porosity of 6.4%, bulk density of 3.23 g/cm3 and median equivalent pores diameters of 4.07 mu m were achieved. The exploration of pore evolution in microporous magnesia aggregates contributed to the fabrication and industrialization development of microporous refractories.

Automated summary

This study focuses on the pore evolution of microporous magnesia aggregates and discusses the effect of nanosized MgO on pore structure and sintering. The results show that the introduction of nano-sized MgO dramatically improves the sintering kinetic force and boundary migration velocity, leading to increased sintering pressure discrepancy and free energy change per unit mole of specimens. This effectively improves the closed porosity and pore distribution homogeneity, while reducing the pore size. The addition of 3 wt% nano-sized MgO achieves optimal sintering properties.