Transition of Blast Furnace Slag from Silicate-Based to Aluminate-Based: Structure Evolution by Molecular Dynamics Simulation and Raman Spectroscopy

To determine the effect of Al₂O₃ content and Al₂O₃/SiO₂ mass ratio on the structure of molten aluminosilicate systems, CaO-SiO₂-Al₂O₃-MgO-TiO₂ systems were investigated by conducting molecular dynamics (MD) simulation and Raman spectroscopy. The capabilities of different elements to attract O on the basis of bond length are ranked as follows: Si > Al > Ca. The CN_Si-O (approximately 4) and the average CN_Al-O (approximately 4.09) demonstrate that the [AlO₄] tetrahedron is not as stable as the [SiO₄] tetrahedron and that some highly coordinated Al units exist in the slags. Non-bridging oxygen prefers to be coordinated with Si, and Al tends to be localized in polymerized environments as a network intermediate phase. In addition, Ca²⁺ is more energetically active than Mg²⁺ as the charge compensation ion. MD results and Raman analysis show that an increase in Al₂O₃ content complicates the structure at a fixed CaO/SiO₂ ratio. In addition, the viscosity of the sample may increase with increasing Al₂O₃ content but is also influenced by polymerization strength. The substitution of Al₂O₃ for SiO₂ simplifies the structure of the slag at a fixed CaO concentration when Al₂O₃/SiO₂ is less than 0.92, as indicated by the (Q⁴ + Q³)/(Q² + Q¹) ratio of Al and the structure complexity. The results of MD and Raman analysis agree with those of viscosity measurement.