Phase equilibria studies of CaO-SiO2-Al2O3-Fe2O3-MgO system using CALPHAD

A detailed CALPHAD (CALculation of PHAse Diagram) based thermodynamic study on CaO- SiO2-Al2O3-Fe2O3-MgO system (C-A-S-F-M) has been carried out to study the evolution of phases during heating and to investigate the effects of individual oxides. The important phases present at high temperature in the system are tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), dicalcium ferrite (C2F) and a liquid phase. The evolution of liquid phase and other important phases predicted by CALPHAD closely matches with the experimental results. It was observed that in C-A-S-F-M system, there is a critical percentage of CaO and SiO2 at which C3S is maximum. Both Fe2O3 and Al2O3 significantly increase the amount of liquid phase. Both Fe2O3 and Al2O3 reduce C3S and increase C2S in the system. Up to 1.5 wt%, MgO also helps in increasing liquid phase. A mathematical model to predict phases has been developed as an alternative to the Bougue's equation which is very effective in predicting phase fractions.