Experimental study of phase equilibria in the system PbO-ZnO-SiO 2
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I.
INTRODUCTION
THE overall research program combines experimental investigations with computer-aided thermodynamic modeling to develop a self-consistent thermodynamic database for the six-component system PbO-ZnO-SiO2-CaO-FeOFe2O3 with the computer package FACT.[1] The research methodology and some results of this overall research program have already been described by the present authors in previous publications,[2–11] including work on the systems PbO-CaO-SiO2,[2,3,4] PbO-ZnO-SiO2,[5,6] Ca-O-Pb,[2,4] PbOSiO2,[6,7] Fe-O-Zn,[7] and six-component slag system PbOZnO-SiO2-CaO-FeO-Fe2O3.[7–11] In the present study, critical evaluations of all phase diagrams and thermodynamic data for the PbO-SiO2, ZnOSiO2, and PbO-ZnO binary systems have been initially conducted. During that initial thermodynamic optimization of the PbO-ZnO-SiO2 ternary system using the computer package FACT, it was found that there were significant inconsistencies between the data previously reported on binary subsystems and this ternary system.[12,13] The liquidus temperature data reported by Umetsu et al.[12] and lead oxide activity measurements by Toivonen and Taskinen[13] could not be reproduced simultaneously with one set of thermodynamic parameters with the FACT package. This indicated that either liquidus data[12] or lead oxide activity data[13] were not accurate. To resolve these discrepancies, this present new experimental investigation was initiated. II.
EXPERIMENTAL PROCEDURE
The experimental procedure in general is similar to that described in detail previously.[2,3,5,7,8,10,11] In brief, binary glassy lead and zinc silicate master slags were prepared from pure oxide powders, then mixed in the desired proportions with the addition of pure ZnO, SiO2, and PbO powders where required, pelletized, and equilibrated in air
EVGUENI JAK, Research Fellow, BAOJUN ZHAO, Postgraduate Student, and PETER C. HAYES, Associate Professor, are with the Department of Mining, Minerals and Materials Engineering, The University of Queensland, St. Lucia, Queensland, 4072, Australia. NAIGANG LIU, Associate Professor, is with the Department of Metallurgical and Materials Engineering, Metallurgical Branch, Tianjin University, Tianjin, 300400, People’s Republic of China. Manuscript submitted November 4, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
in shallow-bottomed platinum crucibles first at higher temperature to homogenize the melt, and then at the final experimental temperature. The total equilibration time varied from a few hours to a few days. The temperature accuracy was estimated to be within 55 K. After equilibration, the samples were quenched in air or in water, mounted, and analyzed using optical and scanning electron microscopy. The compositions of liquid and solid phases were measured with electron probe X-ray microanalysis (EPMA) using a JEOL* 8800L electron probe microanalyzer with wavelength *JEOL is a trademark of Japan Electron Optics Ltd., Tokyo.
dispersive detectors. Lead-silicate glass standard** (Pb 5 **Office of Standard Reference M
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