Experimental phase equilibria studies of the PbO-SiO2 system

Phase equilibria of the PbO-SiO2 system have been established for a wide range of compositions: (i) liquid in equilibrium with silica polymorphs (quartz, tridymite, and cristobalite) between 740 degrees C and 1580 degrees C, at 60-90 mol% SiO2; (ii) with lead silicates (PbSiO3, Pb2SiO4, and Pb11Si3O17) and lead oxide (PbO) between 700 degrees C and 810 degrees C. A high-temperature equilibration/quenching/electron probe X-ray microanalysis (EPMA) technique has been used to accurately determine the compositions of the phases in equilibrium in the system. Significantly, no liquid immiscibility has been found in the high-silica range, and the liquidus in this high-silica region has been accurately measured. The phase equilibria information in the PbO-SiO2 system is of practical importance for the improvement of the existing thermodynamic database of lead-containing slag systems (Pb-Zn-Fe-Cu-Si-Ca-Al-Mg-O).