Integrated experimental phase equilibria study and thermodynamic modeling of the PbO–SnO–SnO2–SiO2 system in air and in equilibrium with Pb–Sn metal

Highlights: • Phase equilibria of the Pb-Sn-Si-O slags with solids in air or in equilibrium with Pb-Sn metal studied at 800–1730 °C. • Experimental data used to obtain thermodynamic parameters for all phases in this system using FactSage. • Modified Quasichemical model used for the liquid slag phase, while all solid phases were described as stoichiometric. • Detailed review done to evaluate the properties of SnO and SnO₂ slag endmembers and the melting point of cassiterite in air. -- Abstract: Phase equilibria of the PbO-SnO-SnO₂-SiO₂ slags with solid phases (cristobalite, tridymite and quartz SiO₂, cassiterite SnO₂, massicot PbO, lead stannate Pb₂SnO₄, and lead-tin silicate Pb₃Sn₂SiO₉) were studied at 800–1730 °C in air and in equilibrium with Pb-Sn metal. High-temperature equilibration on silica, platinum or platinum–iridium foil, or on MgO substrates, followed by quenching and direct measurement of Pb, Sn and Si concentrations in the phases using electron probe X-ray microanalysis (EPMA) was used to accurately characterize the system. Present experimental data were used to obtain a self-consistent set of parameters of the thermodynamic models for all phases in this system using FactSage computer package. The modified quasichemical model with two sublattices (Pb²⁺, Sn²⁺, Sn⁴⁺, Si⁴⁺)(O^2-) was used for the liquid slag phase, while all solid phases were described as stoichiometric. A detailed review was done to reevaluate the properties of SnO and SnO₂ slag endmembers and the melting point of cassiterite in air. Present study was a part of research program on the characterization of the multicomponent Pb–Zn–Cu–Fe–Ca–Si–O–S–Al–Mg–Cr–As–Sn–Sb–Bi–Ag–Au–Ni system.