Phase Equilibrium Studies of CaO-SiO₂-MgO-Al₂O₃ System with Binary Basicity of 1.5 Related to Blast Furnace Slag

Slags play an important role in blast furnace operation, and their compositions are based on the CaO-SiO₂-MgO-Al₂O₃ quaternary system in many steel companies. The binary basicity (CaO/SiO₂ weight ratio) of blast furnace slags, especially primary slag and bosh slag, can be as high as 1.5 or higher. Phase equilibria and liquidus temperatures in the CaO-SiO₂-MgO-Al₂O₃ system with binary basicity of 1.50 are experimentally determined for temperatures in the range 1723 K to 1823 K (1450 °C to 1550 °C). High temperature equilibration, quenching, and electron probe X-ray microanalysis techniques have been used in the present study. The isotherms are obtained in the primary phase fields of Ca₂SiO₄, melilite, spinel, periclase, and merwinite related to blast furnace slags. Effects of Al₂O₃, MgO, and binary basicity on liquidus temperatures have been discussed. In addition, extensive solid solutions have been measured for different primary phases and will be used for development and optimization of the thermodynamic database.