STANDARD ENTHALPIES OF FORMATION FOR SOME SAMARIUM ALLOYS, SM-TEMPERATURE DIRECT SYNTHESIS CALORIMETRY(ME (ME = NI, RH, PD, PT), DETERMINEDBY HIGH)

The standard enthalpies of formation of eight samarium alloys with lat e transition metals have been determined by direct synthesis calorimet ry at 1273 +/- 2 K. The following values of Delta H-f(o), in kJ.(mole atom)(-1), are reported: SmNi5, -27.4 +/- 0.5; Sm5Rh4, -66.5 +/- 1.0; SmRh2, -65.5 +/- 1.2; SmPd, -82.4 +/- 2.0; Sm3Pd4, -87.2 +/- 2.5; SmPd 3, -82.9 +/- 2.5; SmPt, -108.7 +/- 3.5; and SmPt2, -100.2 +/- 2.6. The results are compared with predicted values from the Miedema model, wi th available literature data for SmNi5, SmPd, and SmPt, and with earli er values for similar compounds formed by other lanthanide metals repo rted by this laboratory. The observed relationships between the enthal pies of formation and the number off-electrons in the considered binar y alloys RE,Me, (RE = lanthanide elements; and Me = Group VIII element s) are discussed.