Effect of Oxygen Partial Pressure on Phase Equilibria and Liquidus in CaO-Al2O3-FeOx System

A high temperature equilibration experiment was carried out to investigate the effect of oxygen partial pressure on the phase equilibria and liquidus in CaO-Al2O3-FeOx system with the intermediate oxygen partial pressures of 10. 13 Pa and 1. 01 × 10−3 Pa. The equilibrated phases and their compositions of the quenched samples were analyzed by using SEM/EPMA (Scanning Electron Microscope/Electron Probe Micro-Analysis) and XRD (X-Ray Diffraction). The phase equilibrium results include two cases, the two-phase coexistence and the three-phase coexistence in the high Al2O3 region with oxygen partial pressure of either 10. 13 Pa or 1. 01 × 10−3 Pa. Effects of oxygen partial pressure and temperature on the liquidus along the primary phase fields of CaO · Al2O3 and CaO · 2Al2O3 were notable. With the decrease of oxygen partial pressure, the liquid area expands and the liquidus of CaO · Al2O3 and CaO · 2Al2O3 primary fields moves to the Al2O3-FeOx region. On the other hand, the liquid area of CaO-Al2O3-FeOx system extends extremely to the high Al2O3 region with the temperature increasing from 1400 to 1500 °C, especially at lower oxygen partial pressure. The present experiment results are in good agreement with the calculated ones by FactSage.