Standard enthalpies of formation of some 4d transition metal gallides by high temperature direct synthesis calorimetry

The standard enthalpies of formation of some 4d 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) rue reported: YGa (-71.4 +/-1.7); YGn(2) (-68.1+/-2.3); Zr2Ga (-53.4+/-2.1); Nb5Ga3 (-26.5+/-1.7); M o3Ga (-16.6+/-2.5); RuGa (-35.4+/-2.3); RuGa2 (-41.0+/-1.6); RhGa3 (-44.9+/ -1.2); RhGa (-73.2+/-2.3). The results are compared with some earlier value s obtained by solution calorimetry or derived from emf measurements. They a re also compared with predicted values from the semi-empirical model of Mie dema and coworkers. We compare the enthalpies of formation of the 3d and 4d gallides and the heats of formation of the 4d gallides with available valu es for the 4d transition metal aluminides and germanides. (C) 2000 Elsevier Science S.A. All rights reserved.