M. Yoshihara

The thermodynamics of dilute solutions of hydrogen in palladium and its substitutional alloys

Abstract A review has been given of the thermodynamic and kinetic behavior of hydrogen in dilute solid solution in palladium and in binary solvents consisting of palladium containing a substitutional solute element. The properties of the binary Pd-H system can be understood in terms of simple mixing statistics and classical rate theory. The situation with respect to the ternary systems is not so unequivocable. A large volume of thermodynamic and kinetic data has been analyzed in terms of the cell model for such ternary solid solutions. In some cases the statistical theory is in impressive agreement with both sets of experimental data. In other cases, although the diffusion and thermodynamic behavior of the H-atoms can be described by modified forms of the cell theory, the modifications required are somewhat arbitrary in nature. Modern developments in fundamental calculations of the interactions between H-atoms and both ideal crystals and lattices containing defects have been briefly reviewed. Impressive agreement between the calculated H-atom binding energies to lattice defects and experimental values have been achieved.

The high-temperature elastic properties of palladium single crystals

Abstract A thin-line acoustic method has been utilized to measure the single-crystal elastic moduli of palladium in the temperature range 30–1200 K. The single-crystal constants behave, at high temperatures, in a classical manner in contrast to a large modulus defect observed in polycrystalline palladium. The latter effect has been interpreted as a result of grain boundary relaxation.

The diffusivity of hydrogen through Pd-based solid solutions containing rhodium and platinum

Abstract An electrochemical technique has been used to measure the diffusivity of hydrogen in Pd-based solid solutions containing up to 60 at.% Pt and 33 at.% Rh in the temperature range 280–360 K. The results show that the addition of either substitutional solute to the Pd-lattice decreases the diffusivity of hydrogen in the f.c.c. matrix. The diffusion data have been discussed in terms of the cell model for solid solutions. In the case of the Pd-Pt-H system, the kinetic data are in accord with the predictions of the cell model and interaction parameters derived from independent thermodynamic studies.

The thermodynamics of PdAgH ternary solid solutions

The solubility of hydrogen in PdAgH ternary solutions in equilibrium with H2 gas at atmospheric pressure has been measured in the temperature range 625–1111 K and in PdAg “binary solvents” containing up to 93 at.% of Ag. Concomitant elastic measurements have provided data which enable the partial thermodynamic functions of the H-atoms deduced from the solubility measurements to be converted so as to refer to a hypothetical PdAg lattice of constant specific volume. The resulting “volume corrected” functions have been discussed in terms of the cell model for ternary solutions and have been shown to vary with temperature and Ag-concentration in a manner in accord with this model.

Volume effects in the thermodynamics of ternary austenites

Abstract Elastic measurements have been made as a function of temperature and composition on a series of Fe-based substitutional solid solutions containing Mn, Ni and Cr. These data have been used to calculate the degree of error involved in applying statistical models to ternary carbon or nitrogen austenites when such models ignore the dilation of the substitutional lattice as a function of its composition. The results show that the error in the partial thermodynamic quantities and in the isothermal variation of the activity of the interstitial species with composition is of the order of scatter found in experimental thermodynamic data measured at constant pressure.

The thermodynamics of hydrogen in palladium-yttrium solid solutions

Abstract An equilibrate-quench-analyze technique has been used to measure solubility isobars at 10 5 N/m 2 in the Pd-Y-H system over the temperature span 625–1250 K. These data have been used to derive the dependence upon Y-content and temperature of the partial molar enthalpy and excess entropy of dissolved H-atoms. The partial enthalpy decreases at all temperatures rapidly as the concentration of Y increases. Virtually all of the large variation is ascribable to the effects of lattice dilation in the Pd-Y matrix as the Y-concentration increases.

Thermodynamics of ternary PdPtH solid solutions

Abstract The solubility of hydrogen in PdPtH ternary solutions in equilibrium with hydrogen gas at atmospheric pressure was measured in the temperature range 625–1250 K and in PdPt binary solvents containing up to 61 at.% Pt. Concomitant elastic measurements provided data which enable the partial thermodynamic functions of the hydrogen atoms, deduced from the solubility measurements, to be converted to refer to a hypothetical PdPt lattice of constant specific volume. The resulting volume-corrected functions are discussed in terms of the cell model for ternary solutions and are shown to vary with temperature and platinum concentration in a manner in accord with this model. In contrast with Pd(Au, Ag, Cu)H solid solutions, the isobars for the PdPtH system always show a decreasing hydrogen solubility at any given temperature as the platinum content of the PdPt matrix increases, whereas isobars for the Pd(Au, Ag, Cu)H solutions show well-defined solubility maxima. This marked difference in thermodynamic behavior is almost entirely due to volume effects caused by changes in the host lattice and not to differences in the hydrogen-metal interactions in a rigid lattice system.

The thermodynamics of ternary palladium-based solid solutions containing nickel and hydrogen

Abstract The solubility of hydrogen in Pd-Ni-H ternary solutions in equilibrium with H gas at atmospheric pressure has been measured in the temperature range 625–1250 K and in Pd-Ni “binary solvents” containing up to 80 at.% of Ni. Concomitant elastic measurements have provided data which enable the partial thermodynamic functions of the H-atoms, deduced from the solubility measurements, to be converted so as to refer to a hypothetical Pd-Ni lattice of constant specific volume. The resulting “volume corrected” functions have been discussed in terms of the cell model for ternary solutions and have been shown to vary with temperature and Ni-concentration in a manner in accord with this mode. The usual linear form of cell interaction energy spectrum has been modified by including supplemental contributions to the cell interaction energy which occur when substitutional solute atoms occupy adjacent sites on the f.c.c. Pd-Ni lattice.

Palladium-cerium-hydrogen solid solutions—I. Thermodynamic properties

Abstract Solubility isobars in the temperature range 625–1250 K have been measured at an H 2 -pressure of 1.01 × 10 5 Nm −2 for solutions of H in Pd-Ce matrixes containing up to 12at.% Ce. The partial enthalpies of the H-atoms at any temperature exhibit minima as a function of Ce-concentration. The ternary solid solutions have been analyzed by a cell model in which the cells (interstitial sites) encompass two coordination shells of lattice atoms. This model is shown to be consistent with the enthalpy behavior measured, i.e. with the generation of trapping sites by the inclusion of Ce-atoms into the Pd-lattice.

Thermodynamic study of the palladium-yttrium-hydrogen system

Abstract Equilibrium isobars for the ternary solid solution Pd-Y-H have been measured in the temperature range 625–1250 K and the composition range 0–13 at. % Y. The maximum H content was 1.5 at.%. The isobars were determined at six different pressures ranging from 1.01 × 10 3 to 1.01 × 10 5 N m 2 . The resulting partial thermodynamic functions for H atoms in the solid solution are in good accord with the predictions of the cell model for such systems.