Thermodynamics of Solution of Hydrogen in Pd  Cu and Pd  Cu  Au Solid Solution Alloys

Abstract

Hydrogen in Metals J Pd -Cu Binary and Pd -Cu-Au Ternary Solid Solution Alloys p-c Isotherms J ThermodynamicsThermodynamic quantities for absorption of hydrogen by Pd-Cu alloys with up to atom fraction of Xc, = 0.2, and by Pd -Cu-Au ternary alloys with up to (Xc, + XAu) = 0.2, where X,, = XAu, have been determined at temperatures between 273 K and 423 K and hydrogen pressures up to 1000 Torr by measurements of the pressure-composition isotherms. The hydrogen absorption characteristics of these alloys have been compared with that of the previously reported Pd -Au binary alloys. The room temperature lattice parameters of hydrogen-free Pd -Cu -Au alloys increases with the solute content, albeit by a small amount. The relative partial molar enthalpy, AH!, at infinite dilution in Pd-Cu-Au alloys increases in exothermicity with increasing (Cu + Au) content, and the alloy composition dependence of the AH! value falls near the mid-points between those of each Pd-Cu and Pd-Au binary alloy. The relative partial molar entropy, Ash, at infinite dilution in Pd -Cu -Au alloys decreases with the solute content, and the AS! values at the same alloying content are larger than that of Pd-Au alloys, but are smaller than that of Pd -Cu alloys. The [H -Cu + H -Au] pair interaction energies between the dissolved hydrogen and the substitutional solute atoms in the ternary alloys have been evaluated according to a quasi-chemical model with zeroth order approximation by taking into account the "constant pressure" to "constant volume" correction. The hydrogen solubility behaviour at low hydrogen concentration in Pd-Cu-Au ternary alloys can be described as due to the counteraction of the repulsive H-Cu pair interaction and the attractive H -Au pair one in the Pd host lattice. The stability of the P-phase hydride at a given temperature in Pd-Cu-Au alloys decreases with the solute content, and the alloy composition dependence of the stability is also placed near the mid-points between those for each Pd-Cu and Pd-Au binary alloy.

Rationally Designed PdAuCu Ternary Alloy Nanoparticles for Intrinsically Deactivation-Resistant Ultrafast Plasmonic Hydrogen Sensing

“…Furthermore, also in the α-phase region at low hydrogen pressure, H solubility is reduced for increasing Cu content (Figure 1c) in agreement with the bulk 54,55 but in contrast to the PdAu alloy system where it is found to increase. This lower H-solubility in PdCu alloys stems from repulsive Cu-H pair interactions, as well as from the Pd host lattice contraction induced by addition of Cu due to its smaller atomic radius (i.e.…”

“…α Pd = 3.89 Å, α Cu = 3.61 Å). 54 Consequently, for the hysteresis-free Pd 70 Cu 30 system, the sensitivity in the α-phase is reduced by a factor of 4 compared to pure Pd (i.e. 0.34 nm/mbar 0.5 compared to 0.08 nm/mbar 0.5 -inset Figure 1c).…”

Low-temperature H2 and N2 transport through thin Pd66Cu34Hx layers

“…3 consists of three components: H 2 diffusing through the metal lattice, H 2 passing through defects in the Pd 66 Cu 34 H x or the Pd 66 Cu 34 layer, and N 2 permeating through those defects. The intake of H leads to an expansion of the metal lattice [1,21]. Consequently microscopic pinholes in the layer become smaller and the gas transport through them drops off in the Pd 66 Cu 34 H x phase as can be seen in Fig.…”

“…Partial molar enthalpies and entropies of hydrogen dissolution in fcc-PdCu alloys with up to 40 at.% Cu were determined by several groups [13,14,21,25]. Fisher et al carried out the most comprehensive study and reported DH 0 H ¼ À8:3 and À7.7 kJ mol À1 for alloys with 29 and 40 at.% Cu, respectively [13].…”

Verifying Larché–Cahn elasticity, a milestone of 20th-century thermodynamics

“…The wide miscibility gap of Pd-H at room temperature ( 31 ) implies that Pd-H alloys with intermediate hydrogen fraction cannot be obtained as homogeneous, single-phase states. Yet, alloying coinage metals atom fractions in the order of few 10% reduces of the gap to room temperature ( 31 – 35 ). There is then a wide range of solubility for H.…”