| The steel industry accounts for about 8%of global final energy demand and about 7%of CO2 emissions（including process emissions）from the global energy system.In 2020,China’s crude steel production has reached 56.49%of the world’s total crude steel production,and China’s steel industry is facing huge environmental pressure.Hydrogen metallurgy technology is a technology that uses hydrogen to partially or completely replace carbon as a reducing agent for iron ore to realize the deoxidation process of iron ore.The breakthrough of refractory materials for hydrogen metallurgy is directly related to the development of low-carbon metallurgy in the steel industry and the localization of related process equipment,which is of great significance to help achieve the"dual carbon"goal of the steel industry.Hydrogen has the characteristics of high reducing activity,strong penetration ability,easy leakage and safety accidents,and there are few related studies on the reaction between refractories and hydrogen.A core premise of the research on refractory materials for hydrogen metallurgy is that refractories should be able to resist the reduction erosion of high-temperature pure H2.Among them,the resistance of refractory raw materials to the reduction and erosion of high-temperature pure H2 is very important for the selection of refractory materials.In this paper,aiming at the selection of refractory materials for hydrogen metallurgy,the commonly used Al2O3-SiO2/Ca O refractory oxide raw materials are subjected to high-temperature corrosion treatment under flowing H2 conditions.In different temperature ranges（873 K-2073 K）,the mass changes of siliceous raw materials,mullite raw materials,bauxite raw materials and corundum raw material powders after high temperature H2 corrosion were studied,and the changes of microstructure of aggregates of different materials after high temperature H2 corrosion were compared.The changes of chemical composition,microstructure and impurity oxide distribution of brown corundum raw materials before and after high-temperature H2 corrosion were explored.From the perspectives of thermodynamics and actual high-temperature pure H2 reduction experiments,the valence state transformation and microstructure evolution of iron oxides,which are widely present in refractory raw materials,were studied.The evolution of phase and microstructure of Al2O3-based high-purity raw material white corundum under high-temperature H2 corrosion conditions was studied.CA6 was used as the research object to explore its high-temperature H2 corrosion behavior under the coexistence of iron ore.As a result of the work in this thesis the following conclusions can be drawn.（1）The change trend of powder weight loss rate of aluminum-silicon refractory raw materials and the change law of microstructure of four typical refractory aggregates after H2 corrosion show that the ratio of Al2O3/SiO2 in raw materials will have a decisive influence on their stability under high temperature H2 conditions.The stability order of its phase against high-temperature H2 corrosion is:Corundum>>Mullite>Quartz.Compared with the corrosion behavior of sintered mullite raw material（70 wt%Al2O3）and bauxite clinker（88 wt%Al2O3）,it was found that sintered mullite with a much more uniform and dense microstructure had better corrosion resistance,and the presence of some SiO2 in bauxite in the form of intergranular glass phase accelerated its erosion under high temperature H2 conditions.After corrosion by 1673 K×8h high temperature H2,the weight loss rate of silica raw material reaches about 4%,and a large number of SiO2 fibers are generated on the surface.（2）Furthermore,Al2O3 wt%>92.5%brown corundum was used as the research object to explore its high-temperature H2 corrosion behavior,and the results showed that the impurity oxide composition had an effect on the mass change and microstructure before and after corrosion.The thermodynamic stability of oxide components in brown corundum under 1673 K and H2 atmosphere conditions was ordered as Ca O>Al2O3>Mg O>SiO2>TiO2>Fe2O3.At the same time,after corrosion by 2073 K×8 h H2,the impurity Ca O in brown corundum reacts with Al2O3to form a plate-like CA6 intergranular phase,and CA6 reacts under H2 conditions to form Ca（g）and H2O（g）with low equilibrium pressure,which speculates that Al2O3/CA6-based refractories have good prospects in the field of hydrogen metallurgy.（3）In-depth investigation of the valence transformation pattern of iron-containing impurities widely present in refractory materials under pure H2 conditions shows that excess H2 contributes to the final step of the Fe O→Fe reduction reaction,and that Fe3O4can be reduced to a higher degree than Fe2O3 under the same conditions.reduction temperatures above 837 K help to weaken the disproportionation reaction(Fe3++Fe=2Fe2+),thus driving the Fe O→Fe conversion.Moreover,the transformation of iron oxides to metallic iron is accompanied by a large bulk effect,so the presence of iron oxides in the refractory is very detrimental to its stability under H2 atmosphere conditions.（4）The mass change,microstructure and impurity composition of white corundum raw materials（Al2O3 wt%>99%）after corrosion by pure H2 at high temperatures indicate that white corundum is more stable than brown corundum under pure H2 at high temperatures,and the results of EDS spectroscopy show that the impurities in white corundum tend to be enriched towards the particle edges from scattered random distribution with the increase of reduction temperature.The interfacial region rich in impurity oxides will be the key area for the corrosion of white corundum-based refractories under pure H2 conditions.（5）The mass change,microstructure and intergranular phase composition evolution pattern of CA6 raw material after high temperature pure H2 corrosion showed that the mass of CA6 remained stable and the mineral composition was basically the same as the raw material in the temperature range of 873 K-1873 K.When the corrosion temperature continued to rise to 2073 K,CA6 reacted with Si O（g）and H2O（g）to form corundum and yoshiokaite(Ca5.35Al10.70Si5.30O32.00),and the porous CA6 was transformed into a dense Corundum-Yoshiokaite-Calcium Hexaaluminate composite. |
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