Activities of Cu, Pb and S in the Ternary Cu-Pb-S System at 1473K

Abstract

Thermodynamic activities of Cu, Pb and S in the miscibility gap region of the ternary Cu-Pb-S System are calculated at 1473K. From a knowledge of the tie-line distribution in the region recently determined in the authors' lab, it is found that the method developed by Choudary and Chang is not applicable to the whole miscibility gap region and, therefore, the ternary suffix Margules equations are also employed in the calculation.
The activity values obtained by the method of Choudary and Chang are proved to be thermodynamically consistent, which confirms the applicability of the method and the correctness of the tie-line distribution adopted in this study. On the other hand, the values calculated from the Margules equations are partly, for the activity of Pb, contradictory to thermodynamics, which may be attributed to lack of information on limiting activity coefficients of Cu and Pb in sulfur at high temperatures, and also to the unsymmetrical nature of the ternary system, since the equations are considered useful for cases of relatively small unsymmetry.