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 degrees C, carbon only oxidizes, resulting in weight loss in the refractory. Around 900 degrees 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 degrees C, simultaneous oxidation of C and passive oxidation of SiC occurs, which eventually stabilizes the weight of the refractory. Around 1100 degrees C, the oxidation process of the refractory is practically complete, with no further increase in the oxidation rate beyond 1100 degrees C. The activation energy for the oxidation process is obtained as 37.2 +/- 5 kJ mol-1 in the temperature range 600-1150 degrees C.