Phase equilibria and preliminary viscosity studies of 'Cu2O'-SiO2-Al2O3 systems in equilibrium with metallic copper

Present study is a part of an overall program on development of the accurate viscosity model of the complex multi-component slag (molten oxide) for Cu production. Copper converting slag, in which contain high concentrations of Cu2O and SiO2 with some other components such as Al2O3 and iron oxides, need to be carefully investigated. Very limited phase equilibrium information and no viscosity data were found in literature in 'Cu2O'-SiO2-Al2O3 system at Cu saturation condition. In the present study, the phase diagram of 'Cu2O'-Al2O3-SiO2 system at metallic copper saturation condition has been constructed parallel to the development of viscosity measurement technique. High temperature equilibration and rapid quenching techniques were used to study the phase equilibria. The primary phases and liquidus temperature between 1423 K (1150 °C) and 1573 K (1300 °C) have been determined. The experiments were carried out in Ar gas atmosphere using different substrates (Al2O3, SiO2, and etc.) as containment material. The compositions of all phases present in the slag were measured accurately using electron probe X-ray micro-analysis (EPMA). Under experimental conditions, there are both Cu+ and Cu2+ presented in the samples. However, only the metal cation concentrations can be measured using EPMA, so the phase compositions are usually recalculated to 'Cu2O' on the assumption that all copper is presented as Cu+. The following primary phase fields were identified in the system: SiO2 (tridymite), Cu2O (cuprite), Cu2O.Al2O3 (delafossite), Al2O3 (corundum) and 3Al2O3.2SiO2 (mullite). The ratio of Al2O3/SiO2 was found almost fixed along the liquidus lines at high 'Cu2O' concentration in 'Cu2O'-SiO2-Al2O3 system