Article

Thermodynamics of the Ni-Yb system

Università degli Studi di Genova, Genova, Liguria, Italy
Journal of Phase Equilibria 02/2002; 23(1):51-56. DOI: 10.1361/105497102770332207

ABSTRACT The experimental description of the Ni-rare earth systems is incomplete, with many gaps and uncertainties remaining in both
the phase diagram and the thermochemical information. No thermodynamic information is available for the Ni-Yb system, except
for an estimation of the enthalpy of formation of the Ni5Yb compound. In this work, we investigated the thermochemistry of the Ni-Yb intermediate phases by means of tensimetric measurements
and, on a few compositions, calorimetric measurements. The equilibrium vapor pressures over two solidphase regions were measured
by Knudsen effusion-mass spectrometry and Knudsen effusion-weight loss, and the data were analyzed by the second- and the
third-law methods in order to derive the enthalpy changes for the HT decomposition reactions. Furthermore, the enthalpy of
formation of the NiYb compound was preliminarily determined by direct reaction calorimetry (DRC). The heats of formation of
the five intermediate phases was finally obtained by a combined analysis of all the collected data. The values are as follows:
Ni17Yb2, −13.9±0.3 kJ/mol atoms; Ni5Yb, −20.9±4.4 kJ/mol atoms; Ni3Yb, −26.0±4.8 kJ/mol atoms; Ni2Yb, −32.0±4.6 kJ/mol atoms; and NiYb, −28.0 ± 2 kJ/mol atoms. The results are compared with those estimated by the Miedema’s
model.

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