The PdPb system: excess functions of formation and liquidus line in the range O < XPd < 0.60 and 600

Abstract

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 temperature calorimetry, the molar enthalpy of mixing has been measured at 952, 1108 and 1170 K and the coordinates of the extremum of Δ mix H o m= f( x Pd) have been found ( Δ mix H o m= −38±2 kJ mol −1 with x Pd=0.66). From these experiments, on one hand, the molar partial free energies, entropies and enthalpies of lead were obtained and, on the other hand, the molar integral enthalpy was calculated and the limiting molar partial enthalpies of liquid palladium ( ΔH o m(Pd(liq.) in ∞ liquid Pb)=−78±3 kJ mol −1) and liquid lead ( ΔH o m(Pb(liq.) in ∞ liquid Pd) = −272± 10 kJ mol −1) were extrapolated. Similarly to the liquid PdGa and PdIn systems, the enthalpy of formation of the PdPb alloy is exothermic and the Δ mix H o m= f( x Pd) curve is asymmetrical. These data indicate strong interatomic bonds in the liquid state. Moreover, the coordinates of several (liq.↔ liq. + Pb x Pd 1− x (sol.)) equilibrium points (liquidus points) have been deduced in this concentration range.