Calorimetric investigation on the Pb-Sm and Sn-Sm alloys

The integral enthalpy of formation of the Sm-Pb and Sm-Sn melts at 1203 K, h(f), was determined by direct reaction calorimetry (drop method) in the Pb and Sn rich sides with the help of a high-temperature Tian-Calvet calorimeter. The results can be fitted respectively with reference to the mole fraction of samarium, x, as follows: h(f)/kJ mol(-1) = x(1-x)(-109.8-372.0.7x) with 0 < x(Sn) < 0.27 and h(f)/kJ mol(-1) = x(1-x)(-277.0 + 105.4x) with 0 < x(Sn) < 0.32 for the Sm-Pb and Sm-Sn melts respectively. They yield the following partial enthalpies of samarium at infinite dilution: -109.8 and -277.0 kJ mol(-1) respectively. Such negative values suggest the existence of a strong short-range order in the liquid state. The stoichiometry and the thermal stability of these associations needs additional thermodynamic determinations concerning mainly the free enthalpy of formation. It will be determined by Knudsen-effusion combined with mass spetrometry in a further work. (C) 1997 Elsevier Science S.A.