High Temperature Thermodynamics of Solutions of Hydrogen and Deuterium in Palladium and its Alloys

Abstract

The solutions of hydrogen in palladium and its alloys are classical examples of interstitial metallic solutions. Although these alloys have been studied for a very long time, a good deal of new information has become available in recent years, partly as a result of the application of the combined calorimetric-equilibrium approach. This experimental method, which was developed in our laboratory about 10 years ago, allows essentially simultaneous determinations of the Gibbs energies, the enthalpies and the entropies of solution. This approach has been particularly useful in throwing new light on the temperature dependence of the thermodynamic properties, and also on their dependence on the alloying constituents. Special interest is attached to the new information on the partial entropies of hydrogen, which points strongly toward a temperaturedependent, non-random distribution of the hydrogen atoms among the available interstitial sites.

Thermodynamics of Hydrogen Solution and Hydride Formation in Binary Pd Alloys

“…DS H°v alues are then obtained by extrapolation of DS H°( r) values to r = 0. Flanagan and Lynch [5] and Kleppa and co-workers [1] have concluded that for alloys such as Pd-Ag, Pd-Au and Pd-Cu there is selective occupation of interstices as r fi 0. If the nonconfigurational contributions to DS H are the same for the alloys as for Pd, then the entropy differences between Pd and the alloys must be configurational in origin.…”

“…An earlier review covering this type of research was published by Kleppa [1] in 1983 for a large series of Pd-rich alloys. Most data were obtained at T ‡ 555 K, where the H 2 solubilities are small and hydride phases do not form.…”

“…They did, however, carry out measurements for Pd-H at relatively high pressures over the temperature range, 518-623 K, where thermodynamic data for hydride phase formation was determined calorimetrically. [2] The research to be reviewed here uses the same dual approach employed by Kleppa and co-workers, [1] where thermodynamic parameters are determined using calorimetry and equilibrium p H 2 measurements. This dual approach has advantages as compared to the usual technique of employing only equilibrium p H 2 measurements at a series of temperatures because the calorimetric data are unaffected by hysteresis in the dilute M hydride two-phase region [3] and it is more accurate in the phase transition regions while the equilibrium p H 2 measurement method is more accurate in the dilute phase.…”

“…[4] Based on entropy changes it is generally agreed that some octahedral interstitial sites must be preferred to others. [1,5,6] Wagner and coworkers [7,8] have shown directly from Mössbauer measurements that H avoids interstices with Fe, Sn, Au, Pt, Co, etc., as nearest neighbors, however, it does not avoid interstices with Rh nearest neighbors.…”

Determination calorimetrique des enthalpies de formation en metallurgie

“…On mesure donc l'enthalpie de la r6action : La m~thode directe de chute peut ~tre utilis~e non seulement pour les syst~mes condens~ mais aussi pour les rb, actions gaz-solide. Gerdanian et al [23,24] ont de cette fafon drtermin6 les enthalpies partielles de l'oxyg~ne dans des syst~mes mrtaloxyg~ne en fonction de la composition pour des phases non-stoechiom~triques et Kleppa et al [25][26][27][28][29] ont appliqu~ la m~me mrthode aux syst~mes mrtal-hydrog~ne.…”