James F. Lynch

The absorption of hydrogen by binary vanadium-chromium alloys

Abstract The thermodynamic parameters of the solution of hydrogen in binary vanadium-chromium alloys (to 20 at. % Cr) have been determined. The partial molar enthalpy at infinite dilution increases with increasing Cr content (values range from −7615 cal/H in pure vanadium to −5891 cal/H in V/19.96 at. % Cr). The partial molar entropy of solution is unaffected by the presence of Cr. It is suggested that this behavior indicates that Cr atoms do not block potentially available interstitial sites for occupation by hydrogen. The apparent H-H interaction is diminished by the presence of Cr. The stability of the dihydride is decreased by Cr additions, to the point that V/19.96 at. % Cr does not form a dihydride (−78°C, 68 atm). X-ray data indicate that the structural characteristics of the alloy hydrides are similar to those observed in vanadium/hydrogen.

An x-ray diffraction examination of the FeTi-H2 system

The alpha , beta 1, beta 2, and gamma phases exhibited by the FeTi-H2 system are shown to be isostructural with the corresponding phases of the FeTi-D2 system. Evidence is presented suggesting that the phases exhibited by a given FeTiHx specimen depend not only upon the hydrogen content but also upon the sample history and the method of preparation.

Irreversible effects in the FeTi-H system☆

The equilibrium hydrogen absorption isotherm using annealed strain-free FeTi exhibits only one plateau up to a composition of FeTiH1.95. However, the desorption isotherm exhibits the usual two plateaux. X-ray diffraction results of samples with compositions within the absorption plateau limits indicate the major phases present to be α and γ, although a small amount of β phase was always detected. Apparently the absorption isotherm represents the direct α → γ conversion and β phase precipitation is almost completely suppressed. The results are attributed to the influence of lattice strain upon the behavior of the β1 and β2 phases. A practical consequence of the effect is the distortion of the pressure-composition isotherm in the β-γ region as a function of hydriding-dehydriding cycles.

Lattice expansion as a measure of surface segregation and the solubility of hydrogen in α-FeTiHx

The lattice expansion of α-FeTiHx as a function of hydrogen content was found to be anomalously small. Samples of α-FeTiHx were prepared by absorbing hydrogen in previously activated strain-relieved FeTi with a specific surface area of 0.5 m2 g−1. The apparent partial molar volume VH of hydrogen was 0.1± 0.1 cm3 (g atom)−1 (FeTiH < 0.03); this is much lower than the accepted range of 2.2-1.4 cm3 (g atom)−1 previously reported for hydrogen-metal solutions. This behavior is attributed to preferential occupation by hydrogen of titanium-rich sites produced by surface segregation effects which are known to occur in activated FeTi. The α-(α + β) phase boundary is estimated to occur at an overall composition equivalent to FeTiH≈0.04. At this composition about 85% of the total hydrogen content is estimated to be associated with surface layers approximately 100 A in depth. Unactivated (low surface area) FeTi behaved quite differently and it is clear that, in the low dilution region, surface segregation effects play a dominant role in the behavior of the system. We also present evidence that strain and dislocations produced by a hydriding-dehydriding cycle increase the hydrogen solubility and shift the phase boundary towards higher hydrogen contents.

The dilute solution of hydrogen and deuterium in β-titanium☆

Recent work in this Laboratory concerning the solution of hydrogen and deuterium in ..beta..-stabilized binary titanium alloys (1) has led to our interest in the properties of hydrogen in pure ..beta..-Ti (T > 1155 K). Examination of the literature reveals that data regarding the dilute solution of hydrogen in ..beta..-Ti are scarce. The reported results are somewhat scattered, as is evident in the available thermodynamic data which we have collected in Table 1. An independent examination of the solution of H in ..beta..-Ti was made and the results are presented.

Hydrogen vibrations in the α, β1, β2 and γ phases of FeTiHx

The local hydrogen vibrations are measured by inelastic neutron scattering techniques in the FeTiHx system for x=0.06 ( alpha phase), 0.94 ( beta 1 phase), 1.4 ( beta 2 phase) and 1.86 ( gamma phase) as well as a function of temperature in the gamma phase. The spectra exhibit both sharp and broad peaks in the energy range of 60-110 meV and are strongly dependent upon H concentration and temperature.

Proton NMR and magnetic susceptibility study of TiCr1.8Hitx

Abstract Electronic properties of the hexagonal (C-14) and cubic (C-15) allotropes of the TiCr 1.8 -hydrogen system have been examined via magnetic susceptibility and proton NMR. Both methods indicate an unusual increase in N(E F ) with increasing H/M. Proton Knight shifts indicate that the N(E F ) increase is due to changes in the d-electron states, although a high concentration of s-electron states at E F is also present.

Magnetic susceptibility of the TaV2/H2 system

Abstract The magnetic susceptibility exhibited by the ordered (C-15) and random bcc allotropes of TaV 2 decreases linearly with increasing hydrogen content. However, the susceptibility exhibited by the (C-15) form is about four times more sensitive to hydrogen than that exhibited by the bcc form. The results are in qualitative accord with the thermodynamics of hydrogen solution.

Novel Interpretations of Carbon Oxide Reductions

The manufacture of petrochemicals utilizing nonconventional hydrocarbon sources such as coal has suddenly become recognized as having great potential. Coal, which comprises over 80% of the known recoverable fossil fuel reserves in the United States, is the “chemical resource material of the future.” Of the general routes to convert coal to chemicals, the production of petrochemicals from synthesis gas (a mixture of hydrogen and carbon monoxide produced by the steam gasification of coal) heterogeneously catalyzed by transition metals, has attracted considerable attention since its discovery. Practically the full range of petrochemicals and oil products can be obtained from these syntheses.

Magnetic Susceptibility and Proton NMR Study of TiCr1.8Hx

The electronic properties of the hexagonal (C-14) and cubic (C-15) allotropes of the TiCr1.8+0.1/H2 system have been examined via magnetic susceptibility and proton NMR studies. The results indicate an increase in N(EF), the electron density of states at the Fermi level, with increasing H/M for both allotropes; the trend extends into the α′-hydride phase. The results suggest a basis for thermodynamic anomalies reported for the solution of hydrogen in TiCr1.8.