Phase Equilibrium Studies in the CaO–SiO2–Al2O3–MgO System with MgO/CaO Ratio of 0.2

Abstract

With the raw materials for ironmaking are becoming increasingly complex, more accurate control of blast furnace operation is essential to reduce the energy cost and CO2 emission. CaO–SiO2–Al2O3–MgO is a basic system of ironmaking slag in which CaO and MgO are mainly come from the flux, SiO2 and Al2O3 are mainly from the raw materials. Effect of raw material composition on phase equilibrium of the slag can be described by a pseudo-ternary system (CaO + MgO)–SiO2–Al2O3 at a fixed MgO/CaO ratio of 0.2. High-temperature experiments have been carried out in this system, and the quenched samples were analyzed by an electron-probe microanalyzer. The results are presented in a pseudo-ternary phase diagram (CaO + MgO)–SiO2–Al2O3 with a fixed MgO/CaO weight ratio of 0.2. Dicalcium silicate (Ca2SiO4), Melilite (2CaO·MgO·2SiO2–2CaO·Al2O3·SiO2), spinel (MgO·Al2O3), merwinite (3CaO·MgO·2SiO2), and anorthite (CaO·Al2O3·2SiO2) are the major primary phases in the composition range investigated. A series of pseudo-binary phase diagrams have been constructed to demonstrate the applications of phase diagram on blast furnace operation. CaO-rich cordierite solid solution has been first time reported with the accurate compositions and microstructure. The liquidus temperatures and solid solution compositions are compared between the experimental data and FactSage predictions to provide useful information for optimization of the thermodynamic database.