Reduction behavior of refractory exposed to hydrogen at high temperature

Abstract To realize direct reduction by hydrogen in iron and steel making industry, hydrogen resistance of refractory bricks should be sufficient. However, the effects of hydrogen on refractory bricks have not been studied intensively. In this study, the physical and chemical changes in mullite‐based refractory bricks were investigated for use in a hydrogen atmosphere. After exposure to hydrogen at 1100°C for 72 h, the mechanical strength was reduced by up to ∼ 15%, with a change in color. Multi‐aspect analysis indicated possible causes: the reduction of SiO 2 , that is, SiO(g) formation, for the strength degradation, and the reduction of Fe 2 O 3 and/or TiO 2 for the optical changes. Both were identified from defects at the interface of the mullite particles observed using scanning electron microscopy and the lower‐valence states detected via X‐ray photoelectron spectroscopy. In addition, thermodynamic analysis revealed that the dominant reduction mechanism of the oxides was direct reduction due to the hydrogen reaction rather than indirect reduction due to low oxygen partial pressure.