In-Situ Study of the Crystallization Behavior of CaO–SiO2–Al2O3–MgO–FeOx Melts

The crystallization behavior of steel slag determines its mineral phase composition, which is of key importance for the resource utilization of steel slag. It is difficult to characterize the evolution behavior of crystals and melts accurately by ex-situ analysis techniques, and experimental findings are often inconsistent with the results of thermodynamic analysis. In this study, in-situ analysis was employed to investigate the evolution behavior of crystals and the molten phase during the cooling process of a CaO–SiO ₂–Al ₂O ₃–MgO–FeO _x melt. Real-time observation revealed that crystal growth requires a continuous supply of growth components. If the supply is insufficient, the movement of the melt not only causes displacement or detachment of the precipitated crystals but also promotes their aggregation or separation through parallel or vertical rotation and flow-induced motion, leading to their reintegration into the melt. At 1600 °C, in-situ Raman analysis reveals significant depolymerization of the silicate melt structure. This is evidenced by intensified Q ₀ (841 cm ⁻¹) and Q ₁ (900 cm ⁻¹) bands attributed to C ₃S-like and C ₂S-like structural motifs, along with a weakened Q ₂ band indicative of meta-silicate chain dissociation. Concurrent enhancement of the Q ₃ band suggests localized ordering or vitrification. These spectral shifts reflect structural reorganization toward less-polymerized units at high temperature, elucidating the melt’s evolution prior to crystallization during cooling. This work provides experimental evidence for the dynamic behavior and structural evolution of high-temperature melts to support slag resource utilization.