Phase Stability of SFCA and Liquid Phase on the CF₆–C₄S₃–CA₆ Plane at 1573 K Under Variable Oxygen Partial Pressures

Abstract

This study investigates the phase stability and decomposition behavior of SFCA (Silico-Ferrite of Calcium and Aluminum) at 1573 K under varying oxygen partial pressures. SFCA, a key mineral phase in sintered ore, plays a critical role in enhancing the mechanical strength and reducibility of sinter. Understanding its stability under different conditions is essential for optimizing sinter production processes. Equilibrium and decomposition experiments were conducted under oxygen partial pressures ranging from atmospheric levels to 10^-6 atm. The results revealed that SFCA remains stable up to 5×10^-3 atm, while it decomposes at lower oxygen partial pressures. The decomposition products include magnetite, melilite, and other SFCA groups, indicating that SFCA undergoes a stepwise transformation rather than direct breakdown. Additionally, the liquid phase in equilibrium with SFCA shifts toward the CA₆ (CaAl₆O₁₀) region of the CCC plane as oxygen partial pressure decreases, resulting in an expansion of the liquidus-only region. The findings highlight the narrow stability range of SFCA, with an estimated oxygen partial pressure limit around 10^-3 atm. These results provide valuable insights into the formation and transformation of SFCA under sintering conditions, where local oxygen partial pressures fluctuate due to coke combustion.