THE PD-PB SYSTEM - EXCESS FUNCTIONS OF FORMATION AND LIQUIDUS LINE INTHE RANGE-0-LESS-THAN-X(PD)LESS-THAN-0.60 AND 600-LESS-THAN-T-LESS-THAN-1200-K

Using a galvanic cell with liquid electrolyte, the activity of lead in the Pd-Pb system has been investigated in the molar fraction range 0. 10<x(Pd)<0.60 between 600 and 1200 K. With a second technique, high te mperature calorimetry, the molar enthalpy of mixing has been measured at 952, 1108 and 1170 K and the coordinates of the extremum of Delta(m ix)H(m)(o)=f(x(Pd)) have been found (Delta(mix)H(m)(o)=-38+/-2 kJ mol( -1) with x(Pd)=0.66). From these experiments, on one hand, the molar p artial free energies, entropies and enthalpies of lead were obtained a nd, on the other hand, the molar integral enthalpy was calculated and the limiting molar partial enthalpies of liquid palladium (Delta H-m(o )(Pd(liq.) in infinity liquid Pb)=-78+/-3 kJ mol(-1)) and liquid lead (Delta H-m(o)(Pb(liq.) in infinity liquid Pd)=-272+/-10 kJ mol(-1)) we re extrapolated. Similarly to the liquid Pd-Ga and Pd-In systems, the enthalpy of formation of the Pd-Pb alloy is exothermic and the Delta(m ix)H(m)(o)=f(x(Pd)) curve is asymmetrical. These data indicate strong interatomic bands in the liquid state. Moreover, the coordinates of se veral (liq.<->liq.+PbxPd1-x(sol.)) equilibrium points (liquidus points ) have been deduced in this concentration range.