Thermal Shock Performance of Refractories for Application in Steel Ingot Casting

This study investigates the thermal shock performance of carbon-free and low-carbon-containing refractories, with and without nanoscale additives, based on alumina, mullite, and alumina doped with zirconia and titania (AZT). For this purpose, the porosity and cold modulus of rupture of the refractories before and after a single thermal shock by compressed air were determined. The mullite-matrix materials exhibited the highest porosities owing to restrained densification during sintering, but exhibited the lowest strength losses of the carbon-free materials. In general, the carbon-containing materials had very low strengths because the carbon content was only 4 wt%. The matrix strength was therefore quite low. However, the additions of nanoadditives increased the strength of the carbon-containing alumina. Meanwhile, in the carbon-containing mullite, the nanoadditives caused an enhanced reaction of the used mullite raw material, while in the carbon-containing AZT, the nanoadditives resulted in enhanced decomposition of the aluminum titanate phase leading to reduced strengths after thermal shock. Nevertheless, all alumina-based compositions as well as the carbon-free mullite-matrix materials seem very promising for application in steel ingot casting.