Kinetics of Oxidation of an Al2O3–SiC–C-Based Blast Furnace Trough Refractory in Air

During tapping of liquid hot-metal from the blast-furnace, the blast-furnace main trough gets exposed to air and the blast-furnace-trough refractory becomes prone to oxidation. In this work, isothermal oxidation kinetics of an Al₂O₃–SiC–C-based BFT (Blast-Furnace-Trough) refractory castable using a high-temperature vertical tubular furnace equipped with a microbalance is investigated. Herein, it is observed that up to about 800 °C, carbon only oxidizes, resulting in weight loss in the refractory. Around 900 °C, SiC also starts to oxidize via the passive-oxidation mechanism, leading to the formation of a mullite phase as a result of the reaction between SiO₂ generated via passive oxidation and Al₂O₃ already present in the refractory. This causes a volume expansion and weight gain, both having a beneficial effect on the refractory performance, which is further validated from apparent porosity measurements. Thus, above 900 °C, simultaneous oxidation of C and passive oxidation of SiC occurs, which eventually stabilizes the weight of the refractory. Around 1100 °C, the oxidation process of the refractory is practically complete, with no further increase in the oxidation rate beyond 1100 °C. The activation energy for the oxidation process is obtained as 37.2 ± 5 kJ mol⁻¹ in the temperature range 600–1150 °C.