Experimental phase equilibria studies of the PbO–SiO₂ system

Abstract

Phase equilibria of the PbO-SiO 2 system have been established for a wide range of compositions: (i) liquid in equilibrium with silica polymorphs (quartz, tridymite, and cristobalite) between 740°C and 1580°C, at 60-90 mol% SiO 2 ; (ii) with lead silicates (PbSiO 3 , Pb 2 SiO 4 , and Pb 11 Si 3 O 17 ) and lead oxide (PbO) between 700°C and 810°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-SiO 2 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).

Experimental liquidus study of the binary PbO-ZnO and ternary PbO-ZnO-SiO2 systems

“…The composition ranges of solid phases observed in the present study as well as in [7] before and after correction using eq. (1-4) are presented in Table 2.…”

“…Experimental points on the liquidus surface with compositions of phases in the PbO-ZnO-SiO 2 and PbO-ZnO systems in air. [7] 66.0-66.3 -33.7-34.0 66.5-66.8 -33.2-33.5…”

“…Over two hundred experimental liquidus points over the composition range 0-75 mol.% SiO 2 and 0-52 mol.% ZnO in all primary phase fields (except cristobalite) were obtained. The liquidus includes cristobalite, tridymite, quartz (SiO 2 ), willemite (Zn 2 SiO 4 ), zincite (ZnO), larsenite (PbZnSiO [7]), and massicot (PbO) primary phase fields, and a two-liquid immiscible range close to the ZnO-SiO 2 binary at x(SiO 2 )>60 mol.% that does not reach the PbO-SiO 2 binary. None of the solid phases were reported to form any significant range of solid solutions in the PbO-ZnO-SiO 2 system; however, several solids form wide ranges of multicomponent solutions in the Pb-Zn-Fe-Cu-Ca-Si-O system, including (Zn,Fe The previous experimental study [6] did not involve the high-temperature, low-PbO parts of tridymite/cristobalite, willemite and zincite primary phase fields; present study, therefore, is focused on these in the temperature range 1473-1898 K (1200-1625°C).…”

“…The dataset [6] has been acquired while the information about systematic deviations of the JEOL 8200 EPMA ZAF correction for the PbO-SiO 2 and ZnO-SiO 2 systems [7][8][9] was not systematically characterized yet. For certain slag compositions, these deviations reach 1.5 mol.% overestimation of SiO 2 concentrations.…”

Experimental Liquidus Studies of the ZnO-“CuO0.5” and ZnO-“CuO0.5”-SiO2 Liquidus in Equilibrium with Cu-Zn Metal

“…The standard ZAF correction was further improved following an approach similar to the one previously described. [11][12][13] The accuracy of ZAF correction for the ''CuO 0.5 ''-SiO 2 system has been checked recently, [14] using dehydrated natural dioptase (CuSiO 3 ) as a reference material of fixed composition; overestimation of SiO 2 concentration by 1.8% was observed. In the ZnO-SiO 2 system, willemite Zn 2 SiO 4 was used as a reference material.…”