Effect of Al2O3 nano/micro powder ratio on microstructures and properties of microporous MgO-MgAl2O4 refractory aggregates

Abstract

In this work, the microporous MgO-MgAl2O4 refractory aggregates were prepared by in-situ decomposition synthesis method. The effect of Al2O3 nano/micro powder ratio on the microstructures and properties was studied under the premise that the fixed total content of Al2O3 was 15wt%. The results demonstrated that the aggregates were composed of microporous MgO microparticles with nano pores as well as MgAl2O4 grains located among them. The ratio not only influenced the volume expansion through changing the lattice constant of in-situ MgAl2O4, but also affected the formation of two different positions of MgAl2O4 bonds, thereby influencing the microstructures and properties. When the ratio was 4:6, the combined effect of the shrinkage of MgO microparticles and the expansion of in-situ MgAl2O4 grains promoted the formation of the bonds between MgAl2O4 grains and MgO microparticles, as well as among the MgAl2O4 grains, which resulted in the best comprehensive properties of the microporous MgO-MgAl2O4 refractory aggregates, characterized by micro-nano pores, an apparent porosity of 26%, a flexural strength of 23.2 MPa, a flexure strength after thermal shock of 20.4 MPa and a low thermal conductivity of 2.99 W/(m·K) at 800°C.