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I. INTRODUCTION

THE complex sinters and slags formed during lead and zinc smelting contain alumina. This alumina is introduced into these systems through the impurities present in the ore feedstocks and coke ash, and from the dissolution of refractory materials. Recent studies of zinc-smelting slags under reducing conditions[1,2,3] have shown that even relatively small alumina concentrations can have significant effects on the phase stabilities. To be able to predict and analyze the behavior of the complex lead and zinc industrial slags and sinters, it is necessary to develop accurate thermodynamic databases and models of the Pb-containing systems. The subsystem PbO-Al2O3-SiO2 has yet to be fully characterized. The aim of the present study is to provide accurate experimental data on the liquidus and the phase relations in this ternary system.

formed. Subsequently, however, only the compounds, PbSiO3, Pb2SiO4, and Pb4SiO6 were confirmed by other researchers.[13,14,15] Jak et al.[16] reviewed the thermodynamic and phase equilibria data and developed the thermodynamically optimized phase diagram for the PbO-SiO2 system. In this binary system, PbSiO3 and Pb2SiO4 are congruently melting compounds, and Pb4SiO6 decomposes through an incongruent reaction. Experimental studies on the PbO-Al2O3 system have been reported by a number of researchers[14,17,18] who have identified three incongruently melting compounds: PbAl2O4, Pb2Al2O5, and PbAl12O19. Using thermodynamic computer package F*A*C*T[19] Dessureault[20] has optimized and calculated the PbO-Al2O3 phase diagram.

B. Ternary System II. PREVIOUS WORK A. Binary Systems The Al2O3-SiO2 system has been investigated by a number of researchers.[4–9] Mullite (Al6Si2O13) is the only binary compound stable in the Al2O3-SiO2 system at atmospheric pressure. In this binary system, mullite has been reported to decompose by incongruent[4–7] and congruent[8,9] reactions. It has been suggested[10] that these differences in observed behavior are due to kinetic factors. Eriksson and Pelton[11] reviewed the thermodynamic properties of the system and concluded that mullite melts congruently at chemical equilibrium in the Al2O3-SiO2 system. Experimental studies of the PbO-SiO2 system by Smart and Glasser[12] indicated that a series of compounds with PbO:SiO2 mole ratios of 4:1, 3:1, 2:1, 1:1, and 5:8 were

S. CHEN, Postgraduate Research Scholar, B. ZHAO, Postdoctoral Research Fellow, P.C. HAYES, Associate Professor, and E. JAK, Research Director, are with PYROSEARCH, Pyrometallurgy Research Centre, School of Engineering, The University of Queensland, Queensland 4072, Australia. Manuscript submitted June 12, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS B

Geller and Bunting[17] systematically characterized phase relations in the PbO-Al2O3-SiO2 system in the composition region containing over 80 wt pct of PbO. Three ternary compounds (Pb4Al2Si2O11, Pb6Al2Si6O21, and Pb8Al2Si4O19) were reported. Subsequently, Haensel et al.[21] observed and characterized these three compounds and another te