High-temperature isopiestic studies on the ternary slag PbO-SiO 2 -B 2 O 3 at 1273 K
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I.
INTRODUCTION
AN improved high-temperature isopiestic technique has been proposed and applied to comparative investigations for several binary molten alloys m21 having one volatile component. The method has also been used for direct measurement of the entire isoactivity curve for the volatile component in ternary molten alloys, f3,41 It was recently suggested as an extended form of the isopiestic method for aqueous solutions, tSj Isopiestic measurements have also been made for binary t6~ and ternary[~l molten salt mixtures. In this study we extend the technique to molten slags, taking as examples the ternary system PbO-SiO2-B203 and its binary subsystems PbO-SiO2 and P b O - B 2 0 3 at 1273 K. One reason for choosing this particular ternary slag is that an entire isoactivity curve of one component in a ternary molten slag is a basic thermodynamic quantity. Scientists always display and report measured and calculated activity data in ternary slags in the form of entire isoactivity curves, t8~ It was therefore of interest to see whether entire isoactivity curves could be measured directly in ternary slags, especially since the activity data for the ternary slag PbO-SiOz-B203 are not currently available. Also, different values have been reported for measured activity data of PbO in both binary slags PbOSiO2 I9-19] and PbO-B203 ~2~ 23j at 1273 K, as shown in Figures 1 and 2. These data are also compared with different theoretical models, t24-281 For example, Gaskell t291 recently compared various theoretical models only with Richardson-Webb's experimental data, tl~ Turkdogan t81 selected only Kapoor-Frohberg's data,[16] while Bjorkman e t a l . p~ modeled only Charette-Flengas' data tI41 for the binary slag PbO-SiO2. We undertook to make a comparative isopiestic investigation between the two binary slags and to compare the isopiestic results with the literature data mentioned above. On the other hand, activity coefficients of SiO2 in the binary slag SiO2-B203 have been calculated by Charles Z.C. WANG, Professor, Department of Chemistry, and Y.W. TIAN, Associate Professor, and H.L. YU, Senior Engineer, Department of Nonferrous Metallurgy, are with Northeastern University, Shenyang, 110006, Liaoning, China. X.H. ZHANG, Research Associate, and J.K. ZHOU, Research Assistant, are with the Shanghai Institute of Nuclear Research, Academia Sinica, Shanghai 201800, China. Manuscript submitted August 5, 1992. METALLURGICAL AND MATERIALS TRANSACTIONS B
and Wagstaff t31l from its phase diagram, assuming constant partial molar enthalpy of silica at given composition and nearly ideal behavior of the system at high temperature. Furthermore, a partial ideal solution model has been proposed by one of the authors [3,32-351 for describing the thermodynamic behavior of the ternary nonideal system A-B-C whose binary subsystem B-C is classically ideal. This solution model has recently been further verified t361by using the literature data for organic mixtures, organic-inorganic mixtures, and aqueous solutions at room temperature and fo
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