Experimental study of “CuO0.5”-“FeO”-SiO2 and “FeO”-SiO2 systems in equilibrium with metal at 1400–1680 °C

Abstract

The phase equilibria of the “CuO0.5”-“FeO”-SiO2 slag system in equilibrium with metallic copper and tridymite/cristobalite (SiO2), and the “FeO”-SiO2 slag system in equilibrium with metallic iron and tridymite/cristobalite (SiO2) were investigated between 1400 and 1680 °C. High temperature equilibration in closed silica ampoules, followed by quenching and the direct measurement of the phase compositions with the electron probe X-ray microanalysis (EPMA) was used. The liquidus isotherms in the tridymite and cristobalite (SiO2) primary phase fields were measured, and the shape of the two liquid slags miscibility gap over cristobalite was determined for the “CuO0.5”-“FeO”-SiO2 and “FeO”-SiO2 systems in equilibrium with metallic copper and iron respectively. The two liquid slags miscibility gap over cristobalite was found to be present at all Cu/(Cu+Fe) molar ratios in the slag. However, the difference in the SiO2 concentration between the low- and high-SiO2 slag was found to decrease as the Cu/(Cu+Fe) molar ratio in slag approached 0.5, with the minimal difference assessed to be approximately 4 mol.%. Additionally, new phase equilibria data obtained for the “FeO”-SiO2 subsystem in equilibrium with metallic iron suggested that the monotectic temperature of the subsystem is 1673 ± 3 °C, and that the low- and high- SiO2 slags contain 59.7 mol.% and 96.4 mol.% SiO2 respectively. The present study was a continuation of previous investigations by the authors into the Cu-Fe-Si-O multicomponent slag system, aimed at providing information for improving the thermodynamic models for all phases in this system.