A Structural Study on the Foaming Behavior of CaO-SiO₂-MO (MO = MgO, FeO, or Al₂O₃) Ternary Slag System

The foaming index of the CaO-SiO₂-MO (MO = MgO, FeO, or Al₂O₃) ternary slag system with a fixed CaO/SiO₂ ratio is measured to understand the effect of the ionic structure. At 1773 K (1500 °C), the foaming index of the slag increases with Al₂O₃ addition and decreases with MgO or FeO addition at a fixed CaO/SiO₂ ratio. It is verified that the previous correlation between the foaming index and the physical properties could also be valid for the CaO-SiO₂-(MgO or Al₂O₃) system. Raman spectroscopy for the CaO/SiO₂ = 1.0 slag is applied to explain the foaming behavior from an ionic structural perspective. From the ionic structural viewpoint, the fractional change in each silicate anion unit is identified by de-convoluted Raman spectra. The Raman spectra indicate that the silicate network structure is polymerized with Al₂O₃ as an aluminosilicate structure; in contrast, de-polymerization occurs by MgO or FeO addition. Furthermore, the relationship between the silicate structure and the thermodynamic stability function is discussed. Since the ionic structure of the molten slag affects various physical/thermodynamic properties, the foaming behavior could be successfully interpreted from the ionic structural viewpoint.