The absorption or removal of hydrogen from various materials is often affected by the presence of palladium.

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Title: The influence of electronic structure on hydrogen absorption in palladium alloys
Author(s): Xuezhi Ke, Gert Jan Kramer and Ole Martin Løvvik
Publication date: 1 September 2004 Volume: 16 Start page: 6267
Publication: Journal of Physics: Condensed Matter
URL: http://stacks.iop.org/0953-8984/16/6267

Abstract: The influence of the electronic structure and the lattice constant on hydrogen absorption in bulk Pd 3M 1 (M = Cd, Ag, Au, Pd, Cu, Ni, Pt, Pb, Sn, Fe, Rh, Ru) has been studied by density-functional calculations. We have assumed face-centred cubic structure for all the alloys, and hydrogen has been placed in the octahedral site surrounded by six Pd atoms. We have calculated the absorption energy of hydrogen in the alloys, and found that the influence of the electronic structure is much more important than that of the lattice constant. The results demonstrate that Miedema's empirical rule is also satisfied in this system, i.e., the higher the binding energy of the host alloy, the less stable the hydride. We have also calculated the detailed electronic structures of the alloys and their hydrides. We found that more stable hydrogen absorption is correlated with the hydrogen 1s electrons, palladium s electrons, palladium s-like electrons and the palladium d electrons moving higher in energy towards the Fermi level. The two latter relations have previously been described for bulk systems and surfaces respectively, while this study is apparently the first to point out the correlation between the position of the hydrogen band and the stability of the hydride, i.e., the deeper the hydrogen band, the less stable the hydride.

Title: Continuum modelling of transformation hysteresis in a metal hydride system
Author(s): C R Krenn
Publication date: July 2004 Volume: 12 Start page: S415
Publication: Modelling and Simulation in Materials Science and Engineering
URL: http://stacks.iop.org/0965-0393/12/S415

Abstract: Charging many metal films or powders with hydrogen results in the growth of second-phase metal hydride particles. A large volume difference between hydride and metal can induce plastic deformation and result in a significant hysteresis upon removal of the hydrogen. For a palladium hydride system (with an 11% volume change), we estimate this hysteresis with calculations of the elastic and plastic works of multiple forward and reverse transformations using a two-dimensional finite-element model and find reasonable agreement between finite-element estimates and experimental observations. We also use a three-dimensional phase-field model to determine the effects of particle interactions, but for the isotropic dilation in the Pd/PdH system, these interactions do not apparently have a significant effect.

Title: Influence of hydrogen on the thermoelectric power of palladium alloyed with neighbouring elements: I. Pd/Ru/H and Pd/Rh/H alloys
Author(s): A W Szafranski
Publication date: 4 June 2003 Volume: 15 Start page: 3583
Publication: Journal of Physics: Condensed Matter
URL: http://stacks.iop.org/0953-8984/15/3583

Abstract: Pd/Ru and Pd/Rh alloys have been loaded with hydrogen in high-pressure conditions. The resulting hydrogen contents were close to the stoichiometric composition, H/(Pd + Me) &equal; 1. Lower hydrogen contents have been obtained by successive partial desorptions. The thermoelectric power and electrical resistance of one- and two-phase alloys have been measured simultaneously in the temperature range between 80 and 300 K. A Nordheim–Gorter type correlation of the two quantities has been observed in many cases and the partial thermopowers corresponding to electron–phonon scattering and lattice disorder could be determined. The observed anomalous behaviour of the total and partial thermopowers is attributed to virtual bound states of ruthenium or rhodium.

Title: Surface plasmon resonance hydrogen sensor using an optical fibre*
Author(s): X Bévenot, A Trouillet, C Veillas, H Gagnaire and M Clément
Publication date: January 2002 Volume: 13 Start page: 118
Publication: Measurement Science and Technology
URL: http://stacks.iop.org/0957-0233/13/118

Abstract: An optical fibre surface plasmon resonance (SPR) sensor has been developed for the detection of hydrogen leakages. A thin palladium layer deposited on the bare core of a multimode fibre was used as the transducer. In this device, modification of the SPR is due to variation in the complex permittivity of palladium in contact with gaseous hydrogen. This effect is enhanced by using selective injection of high-order modes in the fibre via a collimated beam with non-normal incidence on the input end of the fibre. Measurements of concentrations as low as 0.8% of hydrogen in pure nitrogen have been found to be possible. The response time varies between 3 s for pure hydrogen and 300 s for the lowest concentrations. Such a large range can be explained by the two different crystallographic phases of the palladium-hydrogen system. Moreover, the response of the sensor is dependent on the length of the sensing area. In preliminary experiments, it has been possible to split the sensing area in order to achieve a two-point detection device.

Title: Inelastic neutron scattering study on different grades of palladium of varying pretreatment
Author(s): P Albers, M Poniatowski, S F Parker and D K Ross
Publication date: 22 May 2000 Volume: 12 Start page: 4451
Publication: Journal of Physics: Condensed Matter
URL: http://stacks.iop.org/0953-8984/12/4451

Abstract: The inelastic incoherent neutron scattering (IINS) technique has been utilized to study the way in which various kinds of palladium retain hydrogen after different pretreatments. Cold-rolled palladium foil, coarse palladium powder and finely divided palladium samples of different particle size and pretreatment were compared after controlled hydrogenation at room temperature and subsequent short-term dehydrogenation at 20, 50 and 70†∞C. In a set of experiments under constant conditions, the incomplete decomposition of the β- and α-hydride phases at the given temperatures were found to be uncorrelated to the morphology of the samples under investigation or to the presence of strongly adherent carbonaceous degradation products at the surface of some of the samples. The dominant factor was the effect of hydrogen trapping due to mechanical pretreatment. It was shown that this effect may also be of some relevance at elevated temperatures.

It was also found that IINS is a suitable technique for the analysis of strongly adherent carbons at the surface of metals and metal hydrides and to discriminate between simple molecular structures and organic species of extended size. This is even the case for partial coverage of finely divided powders, the strong electromagnetic absorption and high electrical conductivity raises problems in utilizing other analytical techniques.

Title: Ultrasonic and resistive hydrogen sensors for inert gas-water vapour atmospheres
Author(s): S Lomperski, M Anselmi and I Huhtiniemi
Publication date: May 2000 Volume: 11 Start page: 518
Publication: Measurement Science and Technology
URL: http://stacks.iop.org/0957-0233/11/518

Abstract: Hydrogen concentration measurements were developed for a series of experiments in which a molten oxide is mixed with water to study vapour explosion phenomena. The gas mixture to be analysed consisted of hydrogen with water vapour and either helium or argon. Two types of sensor have been developed for these tests. The first is an ultrasonic sensor, which detects variations in the acoustic velocity within a 0.4 mm-diameter palladium wire. The sensor measures hydrogen concentrations in the range 0.1-100%, at atmospheric pressure, over an operating temperature range of 200-400 ∞C. The response time (for 0-90% of the final response) is about 30 s at 180 ∞C and 8 s at 380 ∞C. The second sensor consists of a palladium coil, constructed with 0.05 mm-diameter wire that is wound around a ceramic tube. Measurements of wire resistance were used to detect partial pressure of hydrogen. This sensor operates at 150-300 ∞C and measures hydrogen concentrations of 1-100%. The response time is short, 1-2 s for a temperature of 300 ∞C.

Title: Development of a tritium fuel processing system using an electrolytic reactor for ITER
Author(s): T. Yamanishi, Y. Kawamura, Y. Iwai, T. Arita, T. Maruyama, T. Kakuta, S. Konishi, M. Enoeda, S. Ohira, T. Hayashi, H. Nakamura, K. Kobayashi, T. Tadokoro, H. Nakamura, T. Ito, M. Yamada, T. Suzuki, M. Nishi, T. Nagashima and M. Ohta
Publication date: March 2000 Volume: 40 Start page: 515
Publication: Nuclear Fusion
URL: http://stacks.iop.org/0029-5515/40/515

Abstract: A system composed of a palladium diffuser and an electrolytic reactor has been proposed and then developed for the fuel cleanup system of ITER. The performance of the system has been studied in detail in a stand-alone test. A fuel simulation loop of ITER was constructed by connecting the fuel cleanup and hydrogen isotope separation systems developed; and the function of each system in the loop has been demonstrated. For tritium recovery from the exhaust gas during helium glow discharge cleaning of the vacuum chamber of ITER, a cryogenic molecular sieve bed system has been proposed and demonstrated.

Title: Hydrogenation studies in p-GaAs
Author(s): U P Singh and P C Srivastava
Publication date: October 1998 Volume: 13 Start page: 1219
Publication: Semiconductor Science and Technology
URL: http://stacks.iop.org/0268-1242/13/1219

Abstract: Hydrogenation studies in p-GaAs have been performed by fabricating Pd/p-GaAs devices. The devices have been studied by I-V and C-V measurements. Hydrogenation has been found to improve the ideality factor of the diode. The forward C-V characteristics have shown the presence of interfacial deep donors at and , the density of which decreased on hydrogenation. The content of hydrogen in Pd/p-GaAs has been measured both in the semiconducting substrates and the palladium thin film by ERDA using 55 MeV Si ions.

Title: Hydrogen adsorption on the (100) surfaces of rhodium and palladium: the influence of non-local exchange - correlation interactions
Author(s): A Eichler, J Hafner and G Kresse
Publication date: 7 October 1996 Volume: 8 Start page: 7659
Publication: Journal of Physics: Condensed Matter
URL: http://stacks.iop.org/0953-8984/8/7659

Abstract: We report ab initio investigations of the adsorption of atomic hydrogen on the (100) surfaces of Rh and Pd in the local-density-functional and generalized-gradient approximations. Our calculations have been performed using a plane-wave basis, using optimized ultrasoft pseudopotentials for describing the electron - ion interactions. Detailed results are reported for the adsorption energies, the stabilities of various adsorption geometries, and the adsorption-induced changes in the surface relaxations and in the work-functions. We find that the adsorption of a monolayer of hydrogen changes the inward relaxation of the top layer of the substrate into an outward relaxation. However, the change of the substrate relaxation has only a very small influence on the adsorption energy and geometry. For both metals the stable adsorption sites are the fourfold hollows. The site preference has its origin in a maximum gain of covalent bonding energy resulting from the overlap of the hydrogen s and the metal orbitals and from a minimal Pauli repulsion. Non-local exchange - correlation corrections have only a small influence on the atomic adsorption process and on the relaxation of the substrate, but influence the adsorption energy through corrections to the binding energy of the hydrogen molecule. Relativistic effects, however, turn out to be quite important.

Title: Electrical resistance measurements as a function of composition of palladium - hydrogen(deuterium) systems by a gas phase method
Author(s): Y Sakamoto, K Takai, I Takashima and M Imada
Publication date: 6 May 1996 Volume: 8 Start page: 3399
Publication: Journal of Physics: Condensed Matter
URL: http://stacks.iop.org/0953-8984/8/3399

Abstract: The simultaneous measurement of both the relative electrical resistance and the equilibrium hydrogen and deuterium pressure as a function of composition of Pd - H and Pd - D systems have been carried out at temperatures between 273 and 323 K at pressures up to about 3.3 MPa. The relative resistance, , in the two-phase region for the absorption processes shows a very small and almost linear increase with increasing H(D) content, especially for the Pd - H system, compared to the larger changes previously observed by the electrolysis method. The resistance behaviour is quite similar to the shape of p - c isotherm relationships. The relative resistance increments per unit change of H(D)/Pd content at 298 K, , in the two-phase region are about 1.5 and 2.1 times larger for the Pd - H and Pd - D systems, respectively, compared to the changes in the relative lattice parameters with H(D)/Pd content, , within the two-phase region, where is the lattice parameter of H(D)-free Pd and r is the atom ratio. On the other hand, the resistance increment in the single solid solution phase and single phase, except for the higher-H(D)-content region, is significantly larger compared to the changes of the lattice expansion due to dissolved hydrogen and deuterium. Thus, the variation in resistance with hydrogen and deuterium content in the two-phase region may be mainly associated with an incoherent formation of hydride within the phase. The relative resistance for the subsequent desorption processes from the absorption up to about 3.3 MPa at 298 K in both Pd - H and Pd - D systems exhibits almost the same maximum as that of the absorption processes, i.e. at about and at about , and then the values decrease gradually with decreasing H(D) content up to the phase boundary composition; on entering the two-phase region, the values remain almost constant, i.e. for the Pd - H system and for the Pd - D system. This large hysteresis of resistance can be attributed to the creation of `lattice strain deformations' accompanied by dislocation formation from hydride (deuteride) formation and by further highly dissolved hydrogen and deuterium in the phase region.

Title: Calorimetric enthalpies for palladium - hydrogen (deuterium) systems at H(D) contents up to about [H]([D])/[Pd] = 0.86
Author(s): Y Sakamoto, M Imoto, K Takai, T Yanaru and K Ohshima
Publication date: 29 April 1996 Volume: 8 Start page: 3229
Publication: Journal of Physics: Condensed Matter
URL: http://stacks.iop.org/0953-8984/8/3229

Abstract: The enthalpies for the reaction of gaseous hydrogen and deuterium with palladium have been measured as a function of [H]/[Pd] and [D]/[Pd] atomic ratios up to 0.865 and 0.85, respectively, in the temperature range 298 - 194.5 K using a differential-heat-flow low-temperature calorimeter; pressure - concentration isotherms have been measured simultaneously. The calorimetric two-phase enthalpies for the Pd - H and Pd - D systems at 298 K are and , and the corresponding entropies determined from the calorimetric enthalpies and the absorption plateau pressures are and . These - and -values are in agreement with the previously reported values and also with values determined in the literature from van't Hoff plots of the plateau pressures.

The calorimetrically determined enthalpies for solution in the -phase regions of both systems become less exothermic in an almost linear fashion with increasing H(D) content, independently of temperature. At the same H(D) content, the -values for the Pd - H system are slightly more exothermic than the -values for the Pd - D system. Enthalpies of almost the same magnitude are obtained from the desorption data. The corresponding entropies, for solution in the -phase region of both systems have a tendency to decrease gradually with increase in H(D) content independently of temperature; however, there is no marked difference between the magnitudes of the -values of the two systems. The dependences of the calorimetric enthalpies for hydrogen (deuterium) solution on H and D contents in the ranges and can be expressed by the temperature-independent relations , and . The variations in -values with H(D) content are in agreement with that calculated from van't Hoff plots of the previously reported relative chemical potentials of hydrogen and deuterium at low temperatures. The present calorimetric data determined by gas-phase measurements do not offer support for the generation of any ‘excess heat’ up to [D]/[Pd] = 0.85, beyond that which is expected from the chemical reaction because the values determined calorimetrically are almost the same as those derived from van’t Hoff plots.