Rahul Sarkar

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 Al ₂ O ₃ –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 SiO ₂ generated via passive oxidation and Al ₂ O ₃ 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.

Interaction of alumina (Al₂O₃) refractory with FeO–SiO₂ and FeO–SiO₂–CaO slags relevant to the flash ironmaking technology (FIT) is investigated in this work. It is shown that for slags relevant to FIT, the interaction process can be described by a kinetic model based on counter diffusion of only Fe²⁺ and Al³⁺ cations through hercynite (FeAl₂O₄) formed as a result of the interaction. The diffusion of Si⁴⁺ and Ca²⁺ ions through FeAl₂O₄ can be neglected, and the only effect these cations have is that they affect the activity of iron oxide (FeO) at the slag–FeAl₂O₄ boundary. Analyses of reacted samples using X‐ray diffraction (XRD), scanning electron microscopy–energy dispersive X‐ray spectroscopy (SEM–EDX), and electron probe microanalyzer (EPMA) show that the proposed model appropriately describes the growth of FeAl₂O₄ with the parabolic rate law being obeyed for both FeO–SiO₂ and FeO–SiO₂–CaO slags in the temperature range of 1200–1400 °C. The values of effective diffusivity () are calculated independently from experiments with FeO–SiO₂ and FeO–SiO₂–CaO slags agreed with each other, with the activation energy values in the two cases being 246 and 253 kJ mol⁻¹, respectively. These values of and activation energy are in good agreement with the corresponding values obtained previously from Fe–Al₂O₃ and FeO–Al₂O₃ systems.