Thermodynamics of hydrogen solution in Pd-Y alloys

Equilibrium hydrogen isotherms (343-523 K) have been determined for some low Y content fcc Pd-Y alloys. At a given pH(2) <= 1 bar, the hydrogen solubilities increase with atom fraction Y, X-y. Partial thermodynamic parameters, Delta H-H and Delta S-H, have been determined from these isotherms over a range of H contents. Extrapolation of Delta H-H and Delta S-H to infinite dilution of H, give Delta H-H degrees and Delta S-H degrees for 1/2H(2)(g, 1 bar) absorption where the superscript zero indicates infinite dilution of H in the solid phase and 1 bar for H-2 in the gaseous phase. These parameters become increasingly negative with atom fraction Y. Thermodynamic factors, (partial derivative lnp(H2)(1/2)/partial derivative lnr)(r) where r = H-to-metal, mol ratio, are needed for the interpretation of diffusion parameters. From equilibrium isotherms, lnp(H2)(1/2) vs lnr, the slopes give the thermodynamic factors over a range of H contents and temperatures. Plots of the thermodynamic factors as a function of r exhibit minima which suggests that Fick's diffusion constants should also exhibit minima. (C) 2017 Elsevier B.V. All rights reserved.