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The microstructures of the reaction interfaces between slag and corundum aggregates, microporous corundum produced in the laboratory and tabular corundum were observed after slag resistance experiments, and their associated slag resistance mechanisms were investigated. A continuous isolation layer was observed around the microporous corundum, which showed a significantly better slag resistance than tabular corundum. The formation of columnar crystals of CaAl 12 O 19 (CA 6 ) and CaAl 4 O 7 (CA 2 ) in the isolation layer was the main reason for the difference in slag resistance. With respect to the nucleation and growth of second phase, the slag resistance mechanism of lightweight microporous corundum was explored by thermodynamic and kinetic analysis. Due to its smaller pore size, the second phase is more likely to achieve supersaturation, and large quantities of crystal nuclei are generated for microporous corundum. The critical dissolved depths of the microporous and tabular corundum in saturated slag were calculated to be 0.14 and 0.27 lm, respectively. Additionally, the small pore sizes lead to an increase in the Ostwald ripening rate of the second phase, and the Ostwald ripening rate of microporous corundum was 12 times that of the tabular corundum based on Ardell's theory. †

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In this study, lightweight alumina containing nanoscale intracrystalline pores was fabricated by introducing zirconia sol and alumina sol into α‐Al2O3 micropowder. The effects of zirconia sol on the sintering behavior of lightweight alumina were also investigated. With the introduction of zirconia sol, the grain growth and phase transformation of nano‐alumina are delayed. Therefore, the structure of the nanoscale pores between nanoparticles can be stabilized during heat treatment, and numerous nanoscale intracrystalline pores with diameters in the range of 50‐300 nm are trapped in the alumina grains. Because of the existence of these nanoscale intracrystalline pores, the thermal conductivity of lightweight alumina decreases significantly. Lightweight alumina with the addition of 0.75 wt% zirconia sol exhibits 31% lower thermal conductivity compared to alumina without zirconia sol.