Experimental Determination of CaO-CrO-Cr2O3-MgO-SiO2 and Thermodynamic Modeling of the CrO-Cr2O3-MgO-SiO2 System

This article focuses on the CaO-CrOx-MgO-SiO2 system at low CaO contents, providing quantitative phase relation data, and improving the thermodynamic description. The observed liquidus data are compared with literature data and state-of-the-art thermodynamic calculations (FactSage 5.5). The experimental phase diagram measurements are performed under various conditions: (1) liquidus of CaO-CrOx-MgO-SiO2 at a basicity CaO/SiO2=0.5 (by weight), at 1500 degrees C and at a partial oxygen pressure pO(2)=10(-11.04) atm, (2) liquidus of CaO-CrOx-MgO-SiO2 at 1600 degrees C and pO(2)=10(-9.36) atm with constant molar ratio Mg/Cr of 1/2 and varying basicity, (3) phase equilibria of the CrO-Cr2O3-MgO-SiO2 system at 1600 degrees C and pO(2) ranging from air to equilibrium with metallic chromium. In the experiments, equilibrium samples of crystalline phases and melts are analyzed by electron probe microanalysis using wavelength dispersive spectroscopy to determine both solid and liquid compositions. Some discrepancies from previous literature data and calculations are found. In order to improve the thermodynamic calculations, a new thermodynamic model of the CrO-Cr2O3-MgO-SiO2 system is also developed using the Modified Quasichemical Model for the liquid and the compound energy formalism for the solid solution phases. The newly optimized model parameters can describe the present experimental data and literature data more accurately.