Vacuum impregnation treatment of microporous Al2O3-MgAl2O4 refractory raw materials with sub-micron pores and high strength

Abstract

In the present work, we propose a novel method to decrease the pore size as well as to enhance the strength of microporous Al2O3-MgAl2O4 refractory raw materials, which were prepared by the vacuum impregnation treatment of porous Al2O3 powders with at MgCl2 solution. The effect of the MgCl2 content (0–32.5 wt%) on the phase distribution, microstructures, and physical properties of the refractory raw materials was thoroughly investigated. The results demonstrated that the sub-micron pore structure inside the pseudomorph particles was effectively preserved due to the volume expansion effect of spinel and the spinel sintering neck formation between Al2O3 microcrystallites. With the MgCl2 content increasing from 0 to 11.9 wt%, the pseudomorph particles contained many sub-micron pores resulting from the introduction of the MgCl2 solution, resulting in the decrease of the intra-particle pore size as well as the development of spinel sintering necks between pseudomorph particles. The strength of the aggregates was therefore enhanced. With a further increase of MgCl2 content to 24.2 and 32.5 wt%, the inter-particle pore sizes increased due to the volume expansion and Kirkendall effect associated with the spinel formation between pseudomorph particles, which were responsible for the progressive decrease of the strength. Overall, the optimized samples were microporous Al2O3-MgAl2O4 refractory aggregates with the addition of 11.9 wt% MgCl2, which exhibited an apparent porosity of 45.0%, a high compressive strength of 45.6 MPa, a median pore size of only 1.49 µm, and a high sub-micron pore volume content of 42.5 vol%. Meanwhile, it is possible to obtain the porous Al2O3-MgAl2O4 powders with a large number of sub-micron pores by crushing and sieving the optimized aggregates.