DISTRIBUTION OF BISMUTH IN LIQUID Pb AND PbO-SiO2 SYSTEM.

The equilibrium distribution of bismuth in the liquid Pb and PbO-SiO//2 system was investigated by using the EMF method. The oxygen pressure in an equilibrium state was determined from e. m. f. of the following cell: Ni-NiO / ZrO//2( plus CaO) / Slag-Metal-Gas System. Slag composition ranged in N//P//b//O/N//S//i//O//2 from 1. 35 to 1. 86, and atomic fraction of bismuth in metal ranged from 0. 03 to 0. 12. Equilibrium temperature was 900 degree C. The experimental results show that bismuth solubility in the slag increased with the increase of bismuth content in metal and PbO content in slag. The distribution coefficients of bismuth defined as wt. % in slag / wt. % in metal were of the order of 10** minus **3. These data were associated with the measured oxygen pressures and it was found that, if the activity of bismuth in metal was kept constant, the solubility of bismuth in slag increased in proportion to P//O//2**3**/**4. This result shows that bismuth in such slag exists as trivalent ion. Based on the experimental results and available thermochemical data, the activity of Bi//2O//3 and BiO//1//. //5 in the molten Pb-Bi-Si-O system were calculated. The activity of Bi//2O//3 was found to have a considerably negative deviation from Raoult's law and not to obey Henry's law even in such a dilute solution, while the activity of BiO//1//. //5 nearly obeyed the Henry's law and the deviation from Raoult's law was only a little. These results show that bismuth in such slag exists as mono-nuclear trivalent ion. The activity coefficient of BiO//1//. //5 was 1. 6 similar 2. 2 and increased a little with the increase in SiO//2 content.