CALORIMETRIC DETERMINATION OF THE ENTHALPIES OF FORMATION OF LIQUID AND SOLID YB-PB ALLOYS

The enthalpies of formation of liquid and solid Yb-Pb alloys have been deter mined by using high-temperature calorimetry and direct calorime try, respectively. The enthalpies of mixing of liquid Yb-Pb alloys hav e been measured in the temperature range 960-1100K and the results are discussed on the basis of the association model. Formation and meltin g enthalpies have been measured for the intermetallic compounds Yb2Pb, Yb5Pb3, YbPb and YbPb3. The formation enthalpies of the solid phases are in agreement with the presence in the alloys of divalent Yb. Typic ally for the formation, in the solid state at 300K, of Yb2Pb the follo wing values were obtained: -66.0 +/- 5 kJ (mol at.)(-1) by solution ca lorimetry and -67.0 +/- 3 kJ (mel at).(-1) by direct calorimetry.