2009 Volume 50 Issue 7 Pages 1820-1823
Distributions of Sn, Sb, and Bi between Ag-Pb alloy and PbO based melt were investigated at 1273 K. A chemical equilibrium technique was used in order to measure the distributions. The oxygen partial pressure equilibrated with the melts was measured by an EMF method. The distribution ratios were defined as the weight ratios of Sn, Sb, and Bi in PbO divided by those in the Ag-Pb phase. The obtained distribution ratios were plotted against the logarithm of the oxygen partial pressure. The plots showed that the distribution ratios of Sn, Sb, and Bi increased with an increase in the oxygen partial pressure. Taking the slope of these plots, the oxide forms of the minor elements dissolved in the PbO based melt could be estimated. Sn dissolves in PbO based melts as SnO2 in the oxygen partial pressure range, PO2=10−7.5–10−4. Depend on the concentration of Sn in PbO and that in Ag, the activity coefficient of SnO2 in the PbO based melt at 1273 K was determined to be 62,000. The activity coefficient of BiO1.5 decreases with increasing oxygen partial pressure and that of SbO1.5 increases with increasing oxygen partial pressure. The distribution behavior of such minor elements was compared with that of Ag, and the efficiency of oxidation in the removal of such impurities from Ag was investigated.