Microstructural evolution during H2 corrosion of Al2O3–SiO2 based refractory aggregates

Abstract

Hydrogen-based direct reducing iron production (H-DRI) has caused more and more attention in metallurgical industry owing to the near-zero carbon emission. However, the strong reducibility of H2 at elevated temperature can possibly cause serious corrosion to the lining refractories of furnaces. In this study, four types of Al2O3–SiO2 based aggregates (brown corundum, bauxite, mullite and quartz) with various SiO2/Al2O3 mass ratios were utilized for the H2 corrosion test at 1673 K with a soaking time of 8 h. Based on the analysis of weight-loss ratios, phase-composition variation and reduction thermodynamics, the microstructure evolution during H2 corrosion was investigated in detail. The results indicates that the SiO2 impurity of brown corundum was partly reduced by H2 which led to the formation of rod-like or flaky intergranular grains. For bauxite, a porous structure was produced by the accumulation of rod-like or elongated grains owing to the significant reduction of intergranular silicon compounds. Nevertheless, due to the high sintering activity between the Al2O3 products from the reduction of mullite, a high densification structure was realized to effectively prevent the further H2 penetration, hence, mullite inversely obtained the better H2 corrosion resistance than bauxite in spite of its higher S/A ratio. The accumulation of SiO and H2O gases due to the high reduction rate of SiO2 led to the formation of a great deal of SiO2 fiber on the surface of quartz aggregates. The [O] provided by the phase-transformation from α-quartz to cristobalite could be partially captured by the H2 for the reduction, which caused the deterioration of corrosion. With this study, we aim to provide theoretical assistance for the refractory selection applied in hydrogen metallurgy.