Thermodynamics of intermetallics through emf measurements under effusion conditions

Abstract A general treatment is performed for a complete description of the thermodynamics of galvanic cells Pt Me″ , Me″ z F j CaF 2 s.c. Me h Me′ k , Me l Me′ m ,Me x F y Pt type working under effusion conditions where the vaporization of Me ″ is considered. The treatment has been applied to three Me 2 Ni 17 Ni ss systems with Me ≡ Eu, Tb, Ho and Me h Me ′ k is the solid solution, Ni ss , produced by the eutectic reaction L ↔Me 2 Ni 17 s +Ni ss . From the emf vs T experimental data, Δ f H 298 θ and Δ f S T θ have been calculated. The Δ f H 298 θ values for Tb 2 Ni 17 (s) and Ho 2 Ni 17 (s) are, respectively, −16.76±0.06 and −18.8±0.1 kJ/mol atoms. In the same order, the Δ f S T θ values are −1.27±0.06 and −1.81±0.09 JK −1 / mol atoms, respectively, at T =1023 and 1085 K. For Eu 2 Ni 17 (s) , Δ f H T θ and Δ f S T θ 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.