Thermodynamic analysis of strontium deoxidizing ability in liquid iron at presence of aluminum

Phase diagram of the ternary oxide system FeO - SrO -Al₂O₃ was constructed for the first time. In this system, the following compounds can be formed: hercynite FeAl₂O₄ and five strontium aluminates - Sr₄Al₂O₇ , Sr₃Al₂O₆ , SrAl₂O₄ , SrAl₄O₇ , SrAl₁₂O₁₉ . According to the calculations performed, solid solutions of oxides are not formed in the system, as it is confirmed by the literature data. In the course of modeling, the optimal energy parameters of the theory of subregular ionic solutions were selected for the components of the oxide melt (FeO, SrO, Al₂O₃ ). Thermodynamic analysis of strontium deoxidizing ability in liquid iron at presence of aluminum was carried out using the technique for constructing the surface of solubility of strontium and aluminum in metal for steelmaking temperatures (1550 and 1600 °C) and carbon concentrations of 0.1 and 0.4 %. The equilibrium constants of the reactions of formation of strontium aluminates Sr₃Al₂O₆ and SrAl₂O₄ from the components of the metal melt were calculated for the temperature range of 1550 - 1650 °C. It was found that the rest of strontium aluminates can be formed in liquid metal only at temperatures above 1750 °C. The base of thermodynamic data for the studied systems is given: temperature dependences of equilibrium constants for reactions occurring between components; values of interaction parameters of the first order (according to Wagner) for elements in liquid iron; values of energy parameters of the theory of subregular ionic solutions (for oxide melt). It follows from the calculations that the formation of strontium monoaluminate SrAl₂O₄ and corundum Al₂O₃ is most probable as the interaction products in Fe -Al - Sr - O and Fe -Al - Sr - C - O systems.

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