Standard enthalpies of formation of some 5d transition metal gallides by high-temperature direct synthesis calorimetry

The standard enthalpies of formation of some 5d transition metal gallides h ave been measured by high-temperature direct synthesis calorimetry at 1373/-2 K. The following results (in kJ/mol of atoms) are reported: LaGa2 (-69. 2+/-2.4); HfGa3 (-42.4+/-2.7); Hf5Ga3 (-45.4+/-2.1); Ta5Ga3 (-28.3+/-2.2); OsGa3 (-27.4+/-1.6); IrGa3 (-41.2+/-1.9); IrGa (-43.3+/-1.8); Pt3Ga (-41.3/-2.2); PtGa (-57.3+/-2.3). The results are compared with some earlier valu es obtained by solution calorimetry or derived item EMF measurements. They are also compared with the predicted values of Miedema and coworkers. We co mpare the enthalpies of formation of 3d, 4d and 5d transition metal gallide s and the heats of formation of the 5d gallides with available values for t he 5d transition metal aluminides and germanides. (C) 2000 Elsevier Science S.A. All rights reserved.