Thermodynamics of intermetallics through emf measurements under effusion conditions

A general treatment is performed for a complete description of the thermodynamics of galvanic cells PtMe″, Me″zF jCaF2s.c./MehMe′k, Me lMe′m,MexFyPt type working under effusion conditions where the vaporization of Me″ is considered. The treatment has been applied to three Me2Ni17Ni ss systems with Me ≡ Eu, Tb, Ho and Me hMe′k is the solid solution, Niss, produced by the eutectic reaction L ↔ Me2Ni 17s+Niss. From the emf vs T experimental data, ΔfH298θ and Δ fST̄θ have been calculated. The ΔfH298θ values for Tb 2Ni17(s) and Ho2Ni17(s) are, respectively, -16.76±0.06 and -18.8±0.1 kJ/mol atoms. In the same order, the ΔfST̄θ values are -1.27±0.06 and -1.81±0.09 JK-1/ mol atoms, respectively, at T = 1023 and 1085 K. For Eu2Ni17(s), ΔfHT̄θ and Δ fST̄θ are, respectively, -48±4 kJ /mol atoms and 2.0±0.2 JK-1/mol atoms, both the values at T = 910 K. The latter results should be considered unexpected and the reason for this is extensively discussed. © 2003 Elsevier Ltd. All rights reserved.