R.B. McLellan

Solid solutions of hydrogen in gold, silver and copper

Abstract The temperature variation of the hydrogen solubility of copper, silver, and gold in equilibrium with H2-gas at atmospheric pressure has been measured. Values for the relative partial enthalpy and partial excess entropy of the interstitially dissolved hydrogen atoms have been estimated from the solubility data. The experimental data are compared with those of previous investigations. The partial entropy values obtained for, copper and silver show a ‘regular’ behavior when compared with partial entropies for other cubic metals having a small occludive capacity for hydrogen. The gold-hydrogen system is, however, anomalous and has a partial excess entropy which is essentially zero.

The solubility of carbon in palladium and platinum

Saturation solubility of carbon in solid Pd and Pt obtained by equilibrating excess graphite at various high temperatures

Carbon diffusivity in B.C.C. iron

Abstract All the available data sets for the diffusivity of C in b.c.c. iron have been analyzed statistically. The data may not be represented by a single linear Arrhenius expression. The high-temperature data, predominantly generated by mass-flow techniques, are significantly greater than an extrapolation of data from below 360 K, which is predominantly generated by mechanical and magnetic relaxation techniques. This effect has been discussed in terms of the effects of magnetic spin ordering on the diffusion jump energy.

Hydrogen-induced vacancies on metal surfaces

Abstract Statistical mechanical calculations have been carried out in order to determine the vacancy concentration C 1v in bulk nickel crystals containing dissolved hydrogen. As expected the C 1v concentrations are enhanced with respect to the H-free crystal due to the formation of H-vacancy clusters. Corresponding calculations on the {111} surface have shown that the presence of H-atoms also results in an enhancement of the surface vacancy concentrations. The energy level spectra for the H-decorated bulk and surface vacancy calculations were taken from effective medium calculations.

The diffusion of boron in f.c.c. iron

Abstract Lattice parameter and solute diffusion data suggest that the solid solutions of boron in f.c.c. iron constitute a hybrid system, where the B-atoms simultaneously occupy both interstitial and substitutional sites. A thermodynamic and kinetic analysis based on first-order cluster statistics indicates that, although the substitutional solution mode dominates, solute transport is almost entirely due to interstitial hopping.

The diffusion of hydrogen through palladium-titanium and palladium-vanadium solid solutions

Abstract An electrolytic method has been used to measure the diffusivity of hydrogen through substitutional Pd-alloys containing Ti and V in atomic fractions up to about 10 At.% in the temperature range 273–350K. In all cases the diffusivities obeyed the Arrhenius relation. Both Ti and V atoms create trapping sites for hydrogen and the mobility of hydrogen decreases as the concentration of substitutional solute increases. However, the trapping sites are shallow in comparison to trapping sites created by dislocations and the thermodynamic and kinetic properties of the system can be described adequately by using classical Boltzmann statistics.

Thermodynamics of dilute platinum-hydrogen solid solutions

Abstract The temperature dependence of the solubility of hydrogen in a superpure platinum single crystal in equilibrium with H2 gas at atmospheric pressure has been determined in the temperature range 833 −-1466 K. The atomic ratio of dissolved hydrogen varies from 0.95 × 10−4 to 0.23 × 10−4. The solid solution shows no departure from simple quasi-regular mixing statistics. The partial molar enthalpy and excess entropy of hydrogen are −171.8 kJ mol−1 and 3.25 k .

Cumulant expansion treatment for ternary solid solutions

Abstract The free energy of a ternary solid solution in which one dilute component occupies interstitial sites, and one component is dissolved substitutionally has been investigated by the semi-invariant cumulant technique. The first two moments have been derived and the corresponding thermodynamic functions have been discussed.

The calculation of polyvacancy concentrations in rigid disk and hard sphere solids using cell cluster techniques

Abstract Formal expressions for the concentrations of monovacancies and for equilibrium constants for higher order vacancies are derived for v -dimensional hard sphere solids near close packing. The concentration of monovacancies is found to be P 1.1 = K 1.1 exp ⁡ [ D – v ] exp ⁡ [ – v / ( т – 1 ) ] where P 1.1 is the fraction of lattice sites occupied by monovacancies, K 1.1 is a ratio of free volumes, τ is the reduced volume for the system and D is a constant due to the curvature of the accessible regions of the spheres. Cell cluster theory is discussed and used to evaluate numerically expressions for the concentrations of mono- and divacancies in the f.c.c. and h.c.p. lattices of hard spheres. The significance of the results is discussed in relation to cell cluster theory and experimental results for the concentration of, and free energy of formation of vacancies.

The thermodynamics of hydrogen–vacancy interactions in aluminum

Abstract The thermodynamic properties of Al–H solid solutions containing lattice vacancies have been discussed using an approach in which the grand canonical ensemble is used to elucidate the behavior of the Al–VAC–H system in Fermi–Dirac statistics. Calculations have been presented and compared for specific models in which H-atoms act both as a simple interstitial species and forms either decorated vacancies or substitutional defects. Vacancy concentrations concomitant to different levels of hydrogenization are calculated and approximate penetration curves for the ingress of vacancies from the metal surface are presented.