Effect of microporous Al2O3–MgAl2O4 content on the thermal shock resistance and molten steel purification performance of β-SiC whisker-reinforced Al2O3–MgAl2O4–C ceramic filters

This study investigates the effect of microporous Al 2 O 3 –MgAl 2 O 4 content on the phase composition, microstructures, mechanical properties, and purification performance for molten steel of Al 2 O 3 –MgAl 2 O 4 –C filters, conducted through XRD, SEM, EDS, immersion test with molten steel, and so on. The results indicate that the microporous Al 2 O 3 –MgAl 2 O 4 raw material significantly promotes the formation of in-situ β-SiC whiskers within the filters, which intertwine among the particles and grow within the microporous structure, working synergistically with the MgAl 2 O 4 phase to improve the strength and thermal shock resistance. Regarding molten steel purification, on the one hand, the microporous structure of Al 2 O 3 –MgAl 2 O 4 particles enhances the filter's contact area with molten steel, imparting a higher physisorption efficiency to the filter. On the other hand, MgAl 2 O 4 has a greater tendency for carbothermal reactions, generating Mg vapor that has a strong chemisorption capability for [Al], [O], and Al 2 O 3 inclusions in the molten steel. The microporous structure and MgAl 2 O 4 facilitate the formation of a MgAl 2 O 4 reaction layer at the interface during immersion test, contributing to the purification of the molten steel. The filter AM60, prepared with 60 wt% microporous Al 2 O 3 –MgAl 2 O 4 powder, not only exhibits excellent thermal shock resistance (with a cold compressive strength of 0.54 MPa and a strength of 0.59 MPa after three thermal shock tests), but also demonstrates a high purification efficiency (reducing inclusions in steel by 68 %, and lowering the total oxygen content from 56.3 ppm to 13.5 ppm). Finally, the formation mechanism of in-situ β-SiC whiskers, the role of microporous Al 2 O 3 –MgAl 2 O 4 raw material in purification function, and the comprehensive molten steel purification mechanism were proposed.