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

The standard enthalpies of formation for some 5d transition metal silicides have been measured by high temperature direct synthesis calorimetry at 1473+/-2 K. The following results in kJ/mole of atoms are reported: HfSi (-70.9+/-2.0); Ta(5)Si(3) (-38.1+/-1.7); TaSi(2) (-46.0+/-2.5); WSi(2) (-27.3+/-2.0); Re(2)Si (-12.7+/-2.5); Os(2)Si(3) (-30.5+/-2.1); IrSi (-64.4+/-2.6); PtSi (-59.6+/-2.1); Pt(2)Si (-63.3+/-2.3). In addition to the values for the 5d silicides we are also reporting results for three additional compounds. These are: LaGe(1.6) (-75.4+/-2.2); Re(3)Ge(7) (2.1+/-2.7); OsAl(2) (-44.9+/-2.2). The results are compared with some earlier values obtained by calorimetry or derived from EMF or vapor pressure measurements. They are also compared with predicted values from the semiempirical model of Miedema and coworkers and with available enthalpies of formation for 3d and 4d transition metal silicides and with values for 5d germanides and aluminides. (C) 1998 Elsevier Science S.A. All rights reserved.