High-strength microporous corundum-mullite refractory aggregates with sub-micron pores using vacuum impregnation treatment

Abstract

A novel route was proposed to decrease the pore size and enhance the strength of microporous corundum-mullite refractory aggregates, which were fabricated by using the vacuum impregnation treatment of porous Al2O3 powder with silica sol. The effect of the SiO2 content (0–23.6 wt. %) on the phase composition, microstructures and physical properties of the refractory aggregates was studied. It was found that the sub-micron pore structure inside the pseudomorph particles was effectively preserved due to the volume expansion effect of mullite and the mullite sintering neck formation between the α-Al2O3 microcrystallites. With the SiO2 content increasing from 0 to 13.0 wt. %, the pseudomorph particles containing a large number of sub-micron pores formed in the refractory aggregates resulting from the introduction of silica sol. This resulted in the decrease of intra-particle pore size as well as the development of mullite sintering necks between the pseudomorph particles. The strength of the refractory aggregates was therefore enhanced. With a further increase of SiO2 content to 16.4 and 23.6 wt. %, the inter-particle pore sizes increased due to the mullite volume expansion between the pseudomorph particles, which was responsible for the decrease of strength. Overall, the optimized product is the microporous corundum-mullite refractory aggregates with the addition of 13.0 wt. % SiO2, which showed an apparent porosity of 45.4% and a high compressive strength of 56.4 MPa. Significantly, it also had a median pore size of only 1.24 μm and contained a large number of sub-micron pores.