Thermodynamics of Hydrogen Dissolved in Palladium‐rich PdErAg(Au,Cu) Ternary Solid Solution Alloys

Abstract

AbstractUsing a volumetric method, pressure‐composition hydrogen absorption isotherms have been determined for the ternary face centered cubic solid solution alloys (Pd1‐xMx)1‐yEry (M = Ag, Au, Cu; xAg = xAu = 0.079; xCu = 0.08; yEr = 0.00‐0.08) within 10 ≤ PH2/mbar ≤ 1000 and 473 ≤ T/K ≤ 873. The lattice constants a0 of the ternary alloys increase with increasing yEr and the increase in a0 with a given erbium and noble metal content is in the order ao[(Pd1‐xAux)1‐yEry] > ao[(Pd1‐xAgx)1‐yEry] > a0[(Pd1‐xCux)1‐yEry], as in the erbium free binary Pd1‐xMx (M = Au, Ag, Cu) solid solution alloys. The hydrogen solubility r increases with increasing yEr in the (Pd1‐xMx)1‐yEry ternary solid solution alloys; the increase in r with a given erbium and noble metal content is in the order r[(Pd1‐xAgx)1‐yEry] > r[(Pd1‐xAux)1‐yEry] > r[(Pd1‐xCux)1‐yEry], a trend noted in the erbium free binary alloys Pd1‐xMx (M = Ag, Au, Cu). The partial molar enthalpy of hydrogen solution at infinite dilution (ΔH0H) becomes more exothermic with yEr and the increase of exothermicity of hydrogen absorption at given yEr and xM is in the order (ΔH0H[(Pd1‐xAgx)1‐yEry] > (ΔH0H[Pd1‐xAux)1‐yEry] > (ΔH0H[Pd1‐xCux)1‐yEry]. The partial molar excess entropy of hydrogen solution at infinite dilution (ΔSE,0H) and the chemical potential of dissolved hydrogen at infinite dilution (Δ0H), both, decrease with yEr. The hydrogen solubility and the exothermicity of hydrogen absorption in Pd0.903Cu0.078Er0.019 alloy are higher than those in pure palladium, even though a0 of Pd0.903Cu0.078Er0.019 alloy is less that of pure palladium, due to the larger metal‐hydrogen attractive interaction in Pd0.903Cu0.078Er0.019 alloy than in pure Pd. As in Pd1‐yREy‐H (RE = Er, Y, Dy, Gd, and Sm) and Pd1‐xMx‐H systems, a correlation between ΔH0H and ΔSE,0H exists in (Pd1‐xMx)1‐yErx‐H systems.