Comprehensive study on the competitive mechanisms of oxidation and nitriding reactions in ferrosilicon alloys under high-temperature air condition: reaction mechanism, product properties, and kinetics

As a key additive in steelmaking, ferrosilicon alloy significantly improved steel performance through deoxidation and nitrogen control during refining. However, the competitive reaction mechanism between oxidation and nitriding of ferrosilicon alloy in the high-temperature air environment post molten steel tapping remained unclear. This study conducted a systematic investigation via a combination of experiments, kinetic analysis, and density functional theory (DFT) simulations: high-temperature air experiments were performed to reveal the evolution law of the alloy's physicochemical properties during reaction; the reaction mechanism was evaluated by integrating kinetic analysis and product characterization; a DFT-based adsorption model was established to clarify the competitive mechanism at the microscopic level. The results demonstrate that after reacting in an air atmosphere, ferrosilicon alloy forms a reaction layer characterized by a layered structure, surface collapse, and cracks. For samples with particle size 0.075–0.1 mm reacted at 1673.15 K for 120 min, shows that silicon-related compounds consist of 2 wt% Si 3 N 4 and 52 wt% SiO 2 , while iron-related compounds comprise 1 wt% Fe 4 N and 9 wt% Fe 2 O 3 . In the kinetic analysis, the one-dimensional diffusion model exhibits the best fitting performance, suggesting that the reaction is significantly influenced by the diffusion rate of gas molecules. Using this model, the apparent activation energies for Group S, Group M, and Group L are calculated to be 105.75 kJ∙mol −1 , 119.63 kJ∙mol −1 , and 127.54 kJ∙mol −1 , respectively. Furthermore, the co-adsorption model reveals that the average adsorption energies of Si(111) and β -FeSi 2 (220) are −8.047 eV and −5.142 eV, respectively. Additionally, the significant change in the bond length of O 2 and the negligible change in the bond length of N 2 further confirm that the oxidation reaction dominates the entire reaction process. • The reaction products of ferrosilicon alloys in an air environment are primarily layered oxides. • It is verified that the optimal kinetic fitting model for the reaction of ferrosilicon alloy in an air atmosphere is a one-dimensional diffusion model. • It was verified that the co-adsorption effect of O 2 and N 2 in Si(111) was stronger than that of β -FeSi 2 (220). • During co-adsorption, O 2 exhibits significantly greater bond length and average charge transfer than N 2 .