Standard enthalpies of formation of ThAl2, ThSi2, ThGe2 and Th5Sn3, determined by high-temperature direct synthesis calorimetry

The standard enthalpies of formation of ThAl2, ThSi2, ThGe2 and Th5Sn3 have been determined by direct synthesis calorimetry at 1473+/-2 K. The followi ng values of DeltaH(f)(o), in kJ(mol atom)(-1), are reported: ThAl2, -46.8/-2.1; ThSi2, -55.6+/-2.0, ThGe2, -72.2+/-1.4, and Th5Sn3, -63.8+/-2.0. The results are compared with predicted values from the Miedema model and with an earlier calorimetric value for ThSi2. For systematic reasons the result s are also compared with earlier values of DeltaH(f)(o) for the equivalent Ce and U compounds. (C) 1000 Elsevier Science B.V. All rights reserved.