The configuration-based approach for 3d impurities in palladium and platinum

It is suggested that the magnitude and variation of the characteristic temperature associated with 1st transition series impurities in Pd and Pt could be interpreted within the framework of configurational phase stability criteria.     

Calculation of the Knight shift in palladium

The direct and the exchange core polarization (ECP) contributions of the conduction electrons to the Knight shift of palladium are evaluated. To obtain the wave functions for the conduction electrons and the partial densities of states at the Fermi surface a KKR energy band calculation was performed. The contributions of the core electrons to the Knight shift were determined by using the moment perturbation method (MP). Electron-electron interactions are taken into account by individual enhancement factors for thed ands electrons. The agreement between the theoretical results and the available experimental data is quite satisfactory.     

Calculation of the Knight shift in palladium

The direct and the exchange core polarization (ECP) contributions of the conduction electrons to the Knight shift of palladium are evaluated. To obtain the wave functions for the conduction electrons and the partial densities of states at the Fermi surface a KKR energy band calculation was performed. The contributions of the core electrons to the Knight shift were determined by using the moment perturbation method (MP). Electron-electron interactions are taken into account by individual enhancement factors for thed ands electrons. The agreement between the theoretical results and the available experimental data is quite satisfactory.     

X-ray photoemission of small platinum and palladium clusters

X-ray photoemission of the Pt(4f) and Pd(3d) core-levels of small Pt and Pd metal clusters have been investigated. As cluster size decreases, there is a reduction in the lineshape asymmetry, a broadening in the linewidth, and a shift of the core-level toward the higher binding energies. The changes in the linewidth and line asymmetry can be interpreted in terms of the final state effects — the changes in the response of the valence electrons to the core-hole as a function of the cluster size. The decrease in the lineshape asymmetry is due to the reduction in the low-energy electron-hole screening and the linewidth broadening is due to the damping of the plasmons by the boundary surface of the cluster.     

Electroless polymerization of aniline on platinum and palladium surfaces

Aniline was found to polymerize slowly and spontaneously on the platinum and palladium metal surfaces in an aqueous acid solution of the monomer. The phenomenon was thus equivalent to an “electroless polymerization” process. The polyaniline (PANI) so-deposited were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The chemical state of the electroless deposited PANI film was near to that of the 75% intrinsically oxidized nigraniline (NA) state of PANI. The electrolessly deposited PANI films exhibited similar protonation–deprotonation behavior as that of the aniline homopolymer. The amount of the PANI deposited on the metal surface was affected by the monomer concentration, the nature of the acid medium, and the oxygen content in the reaction medium.     

Evidence for multiple states of hydrogen on palladium

Adsorption of hydrogen on polycrystalline palladium has been investigated using ESD techniques. Although a single thermal desorption peak is observed for H₂ and Pd, total ESD cross section measurements suggest the existence of four distinct sources for desorbing H⁺ and H^? species. The very large cross section associated with the H^? signal along with its behavior during sample heating suggests the possible existence of a molecular precursor state.     

Diffusivity permeability and solubility of hydrogen in platinum

The permeability time-lag method has been used to measure the temperature dependence of the diffusivity of hydrogen in platinum in the temperature range 558–936°C. In this temperature range the diffusivity D was found to be represented by the Arrhenius relation,

$\text{D = (6.47±1.73) × 10}{}^{\mathrm{?7}}\text{exp}\text{?}\text{Q}\text{RT}\text{m}{}^2\text{sec}$

where $\text{Q =}\text{26.3 ± 2.3}\text{kJ}\text{mol}$.Measurements of the absolute permeation flux in the steady state condition yield values for the permeability coefficient and the solubility. The solubility values obtained from the permeability flux determinations show discrepancies when compared to solubilities determined by direct equilibration techniques. This discrepancy is briefly discussed.     

XPS-valence bands of iron,cobalt, palladium and platinum

XPS valence band spectra of iron, cobalt, palladium and platinum are reported. They show good agreement with theoretical density of states curves that have been corrected for instrumental resolution, electron-hole interaction, matrix element modulation, lifetime of the photohole and inelastic electron electron scattering.     

Synthesis of vanadium-doped palladium nanoparticles for hydrogen storage materials

Palladium–vanadium (Pd/V) alloy nanoparticles stabilized with n-pentyl isocyanide were prepared as new hydrogen storage materials by a facile polyol-based synthetic route with tetraethylene glycol and NaOH at 250 °C. The size distribution of the nanoparticles thus obtained featured two peaks at 4.0 ± 1.1 and 1.4 ± 0.3 nm in diameter, which were the mixture of Pd/V alloy and Pd nanoparticles. The ratio between the number of Pd/V and that of Pd nanoparticles was 51:49, and the Pd:V ratio of the overall product was 9:1 in wt%, indicating that the 4.0 nm Pd/V nanoparticles were composed of 81% Pd and 19% V. The inclusion of vanadium caused the increase in the d-spacing and thus expansion of lattice constant. A rapid increase in hydrogen content at low H₂ pressures was observed for the Pd/V nanoparticles, and a 0.47 wt% H₂ adsorption capacity was achieved under a H₂ pressure of 10 MPa at 303 K. Hydrogen storage performances of Pd/V alloy nanoparticles was superior compared with Pd nanoparticles.     

Raman studies of hydrogen vibrational modes in palladium

The phonon density of states of substoichiometric polycrystalline Pd-H(D) was investigated by Raman Scattering above and below the 50 K anomaly. The Raman spectra for hydrogen and deuterium were found to be asymmetric and peaked at 58.5 meV and 39.7 meV respectively, in near agreement with inelastic neutron scattering data. The scattering mechanism appears to require hydrogen-hydrogen interactions. No major changes in the optical spectra were observed in going through the 50 K anomaly.     

A search for superconductivity in platinum and nickel films with adsorbed hydrogen

The adsorption of hydrogen onto the surfaces of thin films of platinum and nickel at low temperature decreases their electrical conductance slightly. This effect is smaller for platinum than for nickel. The films do not undergo a superconducting transition when cooled down to 1.11 K for the platinum and 1.32 K for the nickel.     

Adsorption of hydrogen and carbon monoxide on platinum

TDS spectra and ESD ion energy distributions have been measured for coadsorption of H₂ and CO on recrystallized platinum. Sample exposure to a 90% H₂?10% CO gas mixture results in appearance of structurein both TDS spectra of H₂ and CO. Coadsorption also results in an O⁺ ion energy distribution which is much narrower compared to the distribution resulting from pure CO adsorption. These results are interpreted as evidence for the formation of an HCO surface complex.     

Structure and effective interionic potential of liquid palladium,platinum and zirconium

The structure of palladium, platinum and zirconium in the liquid state has been studied by X-ray diffraction near the melting point. In all the cases the structure factor looks similar to those of liquid metals such as copper and silver in contrast to mercury, tin and bismuth which show the small hump or the large asymmetry of the first peak maximum in the structure factor. The atomic radial distribution function was evaluated from the structure factor and the interatomic distance and coordination number of each liquid metal were also obtained. The effective interionic potential was derived from the structural data obtained in this work using the Born-Green equation and applied to the estimation of self-diffusion coefficient and viscosity coefficient in these liquid metals by the kinetic theory of fluids.     

Nuclear magnetic resonance of hydrogen sorbed by powdered palladium metal and alumina-supported palladium.

Hydrogen in 0.2 micron beta-palladium powder and in an alumina-supported palladium catalyst was investigated by NMR spectroscopy. The dependence of the shift on hydrogen pressure and the hydrogen-to-palladium (H/Pd) ratio in beta-palladium hydride was determined for 273 K < T < 368 K. The activation energy for the process affecting the hydrogen shift is 9.4(+/- 0.5) kcal mol-1, similar to the enthalpy of transition from the alpha- to beta-phase. NMR measurements of hydrogen in alumina-supported palladium show a similar behavior, which may allow one to use NMR shifts as a barometer of the state of the hydrogen in the metal.     

Calculation of the energy-momentum tensor of the vacuum in an anisotropic universe

Subtractive methods (N-wave and adiabatic) which are applicable to the calculation of the energy-momentum tensor of quantum fields in curved space-time are in need of a foundation in terms of renormalizations. In the example of a scalar field in an anisotropic universe of Bianchi type I it is shown that the Pauli-Villars scheme, in which the renormalization is in fact realized separately in each mode, provides such a foundation. The technical difficulty obstructing the explicit regularization of divergent integrals in momentum space is shown. We calculate the polarization of the vacuum of a scalar field with arbitrary coupling to the curvature in a weakly anisotropic universe.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 93–98, July, 1986.