THERMODYNAMIC PROPERTIES OF LIQUID TE-PB ALLOYS BY EMF METHOD

A study of thermodynamic properties of the liquid Te-Pb alloys has been carried out by the galvanic cells of -W/Pb (1) \PbCl2(KCl, LiCl)\Te-Pb (1)/W+ for N(pb)=0.10-0.20 at 689 to 1079 K). and -W/Pb (1) \PbCl2(NaCl, KCl)\Te-Pb (1)/W+ (for N(Pb)=0.30-0.90 at 950 to 1268 K). The reliable values of E.M.F. were obtained for the alloys. Activities of lead at 1210 K show remarkably negative deviations from Raoult's law in the wide concentration range and abruptly increase from negative to positive around N(Pb)=0.45-0.65 and show slightly positive deviations on the lead-rich side. Activities of tellurium at 1210 K exhibit significantly negative deviations from Raoult's law over the whole concentration range. a(Pb) values agree well with the data measured by Moniri and Petot but a(Te) values differ from those of Predel et al. The gamma(Pb)degrees and gamma(Te)degrees, values are estimated to be 6.4 x 10-3 and 3.1 x 10(-2) at 1210 K. From the features of alpha functions of lead for the system, the alloys are not considered as regular solutions. The minimum values of the heat of mixing for the system are -27.2 kJ/mol at about N(Pb)=0.48. It is observed that the anomalous behaviors in heats of mixing, xi function, entropy of mixing and concentration fluctuation at long wave length limit at the composition of PbTe are affected by the stable compound in the liquid state.