Phase Of Pd Research Articles

The defect structure with superabundant vacancies to be formed from fcc binary metal hydrides: Experiments and simulations

The process of formation of defect hydrides containing a large number of metal-atom vacancies was studied experimentally in the fcc phase of Fe, Co, Ni and Pd, under different conditions of hydrogen pressure and temperature. Two distinctly different behaviors were observed: In metals with small formation energies of Vac–H clusters, both H and vacancies readily enter the metal lattice to attain the ultimate composition M 3VacH 4, whereas in metals with relatively large formation energies, the formation of this ultimate structure may become appreciable only at H concentrations exceeding some critical value. This general trend was confirmed by a model calculation including a long-range elastic interaction and short-range interatomic interactions between H atoms and vacancies.

Magnetism of two-dimensional defects in Pd: Stacking faults, twin boundaries, and surfaces

Careful first-principles density functional calculations reveal the importance of hexagonal versus cubic stacking of closed packed planes of Pd as far as local magnetic properties are concerned. We find that, contrary to the stable face centered cubic phase, which is paramagnetic, the hexagonal close-packed phase of Pd is ferromagnetic with a magnetic moment of 0.35 $\mu_{B}$/atom. Our results show that two-dimensional defects with local hcp stacking, like twin boundaries and stacking faults, in the otherwise fcc Pd structure, increase the magnetic susceptibility. The (111) surface also increases the magnetic susceptibility and it becomes ferromagnetic in combination with an individual stacking fault or twin boundary close to it. On the contrary, we find that the (100) surface decreases the tendency to ferromagnetism. The results are consistent with the magnetic moment recently observed in small Pd nanoparticles, with a large surface area and a high concentration of two-dimensional stacking defects.

An ab Initio Periodic Study of NiO Supported at the Pd(100) Surface. Part 2: The Nonstoichiometric Ni3O4 Phase

The present computational study describes the structure and properties of a substoichiometric 2D monatomic in the height phase of nickel oxide, c(4 x 2)-Ni(3)O(4), which has been newly found to epitaxially grow under special deposition conditions on the (100) face of palladium. A slab model is adopted where palladium is simulated by a thin film covered on both sides by epilayers, in combination with a DFT hybrid-exchange Hamiltonian; to make convergence of the SCF procedure easier, a thermal smearing technique is used, whose consequences on the results are critically analyzed. Three adsorbed systems are considered and characterized: (i) RH, that is, the c(4 x 2)-Ni(3)O(4) phase with a rhombic distribution of Ni vacancies, as is experimentally observed; SQ, or p(2 x 2)-Ni(3)O(4), which differs from the previous one for a square, instead of a rhombic distribution of vacancies; (iii) OX, or p(2 x 2)-O, that is, a surface oxidized phase of Pd(100) which is believed to be the precursor for the formation of RH. For a better understanding of the interaction of the metal with the adlayers, the isolated substoichiometric oxides, i-RH and i-SQ, have also been studied. It is shown that RH is more stable than SQ by a few tenths of electronvolts per Ni(3)O(4) unit, which justifies its preferential formation and that the surface reaction, OX + 3NiO(ads) --> RH, is thermodynamically possible. Special attention has been devoted to characterize RH from an energetic, geometric, electronic, and magnetic viewpoint. The strong bond which is formed between surface Pd and O ions in the adlayer is responsible for some peculiar aspects of the electronic and magnetic structures of that phase.

Supersaturation and hydride formation in the dilute phase of Pd–H and Pd–Mn–H alloys

Annealed Pd exhibits supersaturation of the dilute phase before the hydride phase forms and this is characterized here by measurements of both |Δ H H| and equilibrium p H 2 . Dilute phase |Δ H H| and p H 2 values were determined for annealed Pd for both absorption and desorption of H 2 and the |Δ H H| were the same for both and the dilute phase H 2 isotherms were also the same, i.e., absorption/desorption was reversible. Pd, which has a high dislocation density, however, does not exhibit supersaturation, and its |Δ H H| values are a continuous function of H/Pd in contrast to annealed Pd where there is a discontinuity at the phase boundary. In addition, absorption/desorption of H 2 is irreversible for this “cycled” Pd. The same phenomena were examined for several substitutional fcc Pd–Mn alloys; supersaturation was also observed for the three alloys: X Mn = 0.01, 0.05 and 0.075.

Supersaturation and hydride formation in the dilute phase of Pd–H

Annealed Pd exhibits supersaturation of the dilute phase before the hydride phase forms and this is characterized here by measurements of both ∣ΔHH∣ and pH2. Pd, which has a high dislocation density, however, does not exhibit supersaturation, and its ∣ΔHH∣ values are a continuous function of H/Pd, in contrast to annealed Pd where there is a discontinuity at the phase boundary.

Spin fluctuations, electron–phonon coupling and superconductivity in near-magnetic elementary metals––Fe, Co, Ni and Pd

An investigation of possibilities for superconductivity mediated by spin fluctuations in some elementary metals is motivated by the recent discovery of superconductivity in the hcp high-pressure phase of iron. The electronic structure, the electron–phonon coupling ( λ ep) and the coupling due to spin fluctuations ( λ sf) are calculated for different phases and different volumes for four elementary metals. The results show that such possibilities are best for systems near, but on the non-magnetic side of, a magnetic instability. Fcc Ni, which show stable magnetism over a wide pressure range, is not interesting in this respect. Ferromagnetic and anti-ferromagnetic fluctuations in hcp Fe contribute to a relatively strong coupling in the pressure range where superconductivity is observed. The absence of fluctuations at large q-vectors makes fcc Pd only moderately interesting despite its large exchange enhancement for q=0. Fcc Co at high pressure (∼0.5 Mbar) behaves as an improved version of Pd, where the fluctuations extend to larger q. The estimations of T C, which reproduce the experimental situation in Fe quite well, suggest a measurable T C for the high-pressure phase of fcc Co, while the estimate is lower for the ambient-pressure phase of fcc Pd.

Genetics of Parkinson's disease and biochemical studies of implicated gene products: Commentary

Parkinson's disease was thought, until recently, to have little or no genetic component. This notion has changed with the identification of three genes, and the mapping of five others, that are linked to rare familial forms of the disease (FPD). The products of the identified genes, α-synuclein (PARK 1), parkin (PARK 2), and ubiquitin-C-hydrolase-L1 (PARK 5) are the subject of intense cell-biological and biochemical studies designed to elucidate the underlying mechanism of FPD pathogenesis. In addition, the complex genetics of idiopathic PD is beginning to be unraveled. Genetic information may prove to be useful in identifying new therapeutic targets and identifying the preclinical phase of PD, allowing treatment to begin sooner.

Tetragonal states of palladium II. Experiment

The goal of this work is to try and stabilize by constrained pseudomorphic epitaxy the body-centered-tetragonal (bct) phase of Pd that was revealed by the epitaxial Bain path (EBP) at the axial ratio $c/a\ensuremath{\sim}0.9.$ The substrate chosen is W{001}, and Pd is deposited on it in ultrahigh vacuum at room temperature. The films obtained are pseudomorphic with the substrate, but quantitative low-energy-electron diffraction (QLEED) analysis suggests that they do not consist of pure Pd. The analysis provides strong evidence for the fact that Pd and W interdiffuse, producing an alloy of Pd and W. In order to avoid alloy formation, and yet maintain conditions for pseudomorphism, a diffusion barrier is introduced in the form of a pseudomorphic film of Mn on W{001}. A Pd film with thickness of about 19 \AA{} is then grown pseudomorphically on top of the Mn film and analyzed by QLEED. The film is highly strained and defective, allowing only mediocre agreement between theory and experiment, but the analysis shows that its structure is probably a strained state of the bct phase found on the EBP.

PENGARUH PENAMBAHAN PALADIUM TERHADAP PERILAKU THERMAL AMALGAM TEMBAGA TINGGI TIPE LATHE CUT

Effects of additing 1 percent (w/o) palladium (Pd) on the thermal behavior of a lathe cut type high copper amalgam (13 w/o copper) were studied. The identical alloys, with and without 1% Pd were fabricated. X-ray diffraction studies of the amalgams revealed the elimination of the γ 2 -phase by Pd addition DSC thermogram of non-Pd containing amalgam indicated the existence of two γ 1 -phaseone with the transition temperature (endothermic peak) at 88 ◦ C and the other at 109 ◦ C. The thermogram data of the Pd containing amalgam showed an endothermic peak at 110.7 ◦ C. The transition temperature of the n phase of the palladium containing amalgam is 4.9 ◦ C lower than the transition temperature of the n phase of the non Pd containing amalgam. This result indicates that the n phase of the Pd containing amalgam includes more of Tin (Sn) than the non-Pd containing amalgam. The thermogravimetri diagram showed that the phase decomposition occurred at about 390 ◦ C for the non-Pd containing amalgam and at about 410 ◦ C for the Pd containing amalgam. It is concluded that the addition of 1% Pd into a lathe cut type of high copper amalgam (13%) could eliminate the formation of γ 2 phase as well as an unstable γ 1 phase, promoting strong mercury bonding to Silver.

On hydrogen solubilities in Pd/alumina composites prepared by internal oxidization of Pd/Al alloys

Internal oxidation of a Pd–Al alloy results in a composite consisting of Al 2O 3 precipitates within a Pd matrix. In accord with earlier studies (Huang et al., 1988. Scripta Met. 22, 1114), H dissolved in the Pd matrix becomes strongly and weakly trapped by the alumina precipitates. It is shown that the extent of strong H trapping is only weakly dependent on the Al content from X Al=0.005 to 0.06. H can be removed from the strong traps by evacuation at 573 K (2 h) but not at 473 K. After evacuation at 973 K, the strong traps themselves disappear but when the alloys are hydrided/dehydrided (cycled) at 323 K, traps reappear along with weak-dislocation traps due to dislocation formation resulting from the cycling. Although the former traps, which appear after cycling, are deep enough so that the corresponding P H 2 ( equil) cannot be readily measured (273 K), they are not as deep as the initial ones produced after internal oxidation since H can be removed from them by evacuation at 323 K. The number of weak-dislocation traps due to cycling the composite formed from internal oxidation (1073 K) is greater than for cycled pure Pd. A higher temperature is needed to anneal out the weak-dislocation traps arising from cycling the composites as compared to Pd; thus the alumina precipitates hinder the movement and annihilation of the dislocations. The enthalpies for H 2 solution in the dilute phase of the internal oxidation Pd–Al alloys have been determined directly by reaction calorimetry and they have a spectrum of trapping enthalpies.

Solubility and kinetic properties of deuterium in single crystal Pd

The pressure–composition (PC) behavior of deuterium in single crystal Pd has been measured over a temperature range extending from room temperature to 393 K. These data allow the determination of (i) relative partial molar enthalpy and entropy, without the contribution of the configuration entropy, for the dilute solid solution phase, (ii) enthalpy and entropy change characterizing the α→α′ phase transformation, and (iii) Gibbs free energy loss associated with the PC thermodynamic hysteresis. Comparison of these quantities with published data for polycrystal Pd and with our own polycrystal Pd measurements show good agreement, indicating grain boundary interfaces and second phase inclusions known to exist in polycrystalline Pd do not influence these thermodynamic properties. The time dependence of deuterium absorption and desorption from the gas phase has been measured in both single and polycrystal Pd as well. The activation energy and diffusion constant of deuterium in the solid solution phase of Pd agree with published values. The time dependence of deuterium absorption and desorption within the miscibility gap are reduced by approximately two orders of magnitude compared to solid solution behavior. The two-phase kinetic data exhibit an Arrhenius behavior with a factor of two increase in the activation energy compared to diffusion. This is attributed to the phase transformation process controlling the deuterium absorption/desorption kinetic behavior when the Pd–D system is within the miscibility gap.

On the Re-Entrant State of the Pd11Co50Al39 Alloy

The re-entrant state in the Pd 11 Co 50 Al 39 alloy is investigated by dc and ac magnetization measurements. A dynamic scaling analysis of ac susceptibility data indicates a true spin-glass state below 5.6 K. Magnetic aging, characteristic of spin-glass dynamics, persists well into the re-entrant ferromagnetic phase of Pd 11 Co 50 Al 39 . Borders of the re-entrant spin-glass and ferromagnetic behaviour are established for this allov.

Formation of a palladium carbide with a palladium-silicide-like structure in fullerene-C 60/Pd multilayers

We present structural studies of C 60/Pd multilayer films. A new phase of a layered structure with a sixfold (or threefold) axis, which is similar to the metastable phase in Pd–Si alloys, has been observed by means of transmission electron microscope and X-ray diffraction in the C 60/Pd multilayer films after annealed at 470 K 60 min. This new phase, which is believed to be one metastable phase of Pd–C, is a hexagonal structure with the lattice constant a = 0.438 nm. The reciprocal lattice points become continuous spikes in the direction c∗ of the reciprocal lattice, which indicates the Pd–C phase consists of layers.

Intracellular punctures by the adult whitefly Bemisia argentifolii on DC and AC electronic feeding monitors

AbstractOne of the most biologically important electrical penetration graph (EPG) waveforms recorded from aphids on DC EPG systems is the potential drop (pd), which is correlated with intracellular punctures by the stylet tips. In this study, pds of the adult female Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae), recorded on a DC EPG, are characterized and compared to pds of aphids. Whitefly pds consisted of 3 phases similar to those recorded from probing aphids. The major difference between aphid pds and whitefly pds was that whitefly pds lacked any observable subphases within the second phase of the pd. In addition, whitefly pds differed from aphid pds in that they: (1) did not occur frequently during stylet penetration, (2) did not occur early within probes, (3) did not occur during brief probes (<1 min). Pds produced by probing whiteflies always were preceded by a variant of waveform C which we named the pre‐pd. The differences between pds of aphids and whiteflies are discussed in terms of their implications for virus transmission and host selection. Using a technique where EPG recordings can be switched back and forth between DC and AC systems, we demonstrated that the AC EPG pseudotransition waveform (Pt) was equivalent to the DC pd, and thus was correlated with intracellular punctures. Previously, intracellular punctures by whiteflies had not been detectable on AC EPG systems. The AC Pt consisted of three distinct phases (Pt1, Pt2, and Pt3) and our observations suggest that AC Pt1 correlates with the pre‐pd waveform in DC EPGs and that AC Pt 2 and 3 correlate with the intracellular phase of the DC pd. AC Pts (n = 47) and DC pds (n = 43) were recorded on three separate plant species and were similar on all plant species.

Preparation of Palladium Ultrafine Particles in Reverse Micelles

The preparation of palladium ultrafine particles by the reduction of Pd(NH3)4Cl2with hydrazine in AOT/isooctane reverse micellar solutions has been studied. By the analyses of high-resolution electron microscope, electron diffraction pattern, and XRD, the resultant particles have been found to be pure fcc palladium. Their sizes were observed to increase first and then approach constant values with increases in the molar ratio of water to AOT (ω0) and in the concentration of Pd(NH3)4Cl2, but were not significantly affected when the concentration ratio of hydrazine to Pd(NH3)4Cl2was above 10, the AOT concentration increased from 0.1 to 1.0 M, the temperature varied from 15 to 35°C, and the pH of aqueous phase of Pd(NH3)4Cl2was between 7 and 12. In addition, the kinetic study of particle formation indicated that the nucleation time needed several minutes. After nucleation, the particles grew to their final sizes within several to tens of minutes. The formation rates were found to be faster at larger ω0values and higher AOT and Pd(NH3)4Cl2concentrations.

Combustion of methane over palladium/zirconia: effect of Pd-particle size and role of lattice oxygen

The catalytic combustion of methane over palladium/zirconia catalyst prepared by oxidation and subsequent reduction of Pd/Zr glassy metals has been investigated with special emphasis on the influence of the catalyst structure (particle size and specific surface area) on the catalytic performance and the impact of a redox mechanism on the product formation. The reaction of 1% methane and 4% oxygen (balance of He) in a fixed-bed microreactor was found to be strongly dependent on the particle size of palladium, which was controlled by appropriate reduction before catalytic testing. Pre-reduction of PdO resulted in an enhanced activity compared to the unreduced catalysts. The structural changes induced upon reduction were accompanied by altered physico-chemical properties, evidenced by different behaviors in the decomposition of PdO and the reduction of PdO by methane. The correlation established between catalytic performance and the rate of reduction of PdO by methane led to the postulation of a redox mechanism, involving the reaction of methane with the active palladium oxide phase and subsequent reoxidation of metallic Pd by oxygen, which was independently confirmed by the use of 18 O labeled catalysts and pulse methods.

Search for Nuclear Products of The D+D Nuclear Fusion

Nuclear products which were caused by the D + D nuclear fusion reaction were searched in electrolytic cells and in gas phase of Pd + D systems. Measurements of nuclear products were made for gamma-ray, neutron, tritium and helium. To detect neutron, liquid scintillation and 3 He counters were used. For gamma-ray measurement, a NaI detector was used. For tritium concentration measurement in gas phase, a gas proportional chamber was fabricated and operated in low background level. The signals of those detectors were fed to Pulse Height Analyzer and recorded as energy spectra which were carefully compared with background spectra. A different type of neutron hunting was also tried in the instants of pressurizing and depressurizing the deuterium gas in crystal. A large size crystal of tungsten bronze was prepared for the experiment.

XAFS characterization of supported PdCl2−CuCl2 catalysts for CO oxidation

A heterogenized Wacker catalyst system in which pores of a high surface area alumina were filled with an aqueous solution of PdCl2−CuCl2 was active for the oxidation of CO near room temperature. The structure of thecatalyst was studied by XRD and XAFS. The active phase of Pd was a molecular Pd species whose structure was similar to PdCl2, probably modified by a carbonyl ligand. The active phase of copper was found to be solid Cu2Cl(OH)3 particles. The presence of Cu was essential to keep the Pd in the Pd(II) state during the reaction.

Supported PdCl2[sbnd]CuCl2 catalysts for carbon monoxide oxidation II. XAFS characterization

A heterogenized Wacker catalyst system in which pores of a high surface area alumina were filled with an aqueous solution of PdCl2CuCl2 was active for the oxidation of CO near room temperature. The structure of the catalyst was studied by X-ray absorption fine structure (XAFS). The active phase of Pd was a Pd11 species containing chlorine and, probably, carbonyl ligands. Direct interaction of PdPd or PdCu was not detected. The active phase of copper was found to be solid Cu2Cl(OH)3 particles in agreement with the X-ray diffraction (XRD) results. The presence of Cu was essential to keep the Pd in the Pd11 state during the reaction. The rates of CO oxidation measured at temperatures of 30–70°C showed a minimum at 40°C, which was attributable partly to an unusual structure change of the active palladium species during the reaction at this temperature.

Quantitative measurements of helium-4 in the gas phase of Pd+D2O electrolysis

Abstract A method for the mass spectrometric quantitative determination, down to the sub-ppb level, of the 4 He content in the gaseous products of cold fusion Pd+D 2 O electrolytic cells is described. The data collected in an experiment lasting over 1000 h provided a time picture of the phenomena. Measurements of the 20 Ne content have also been performed in order to check air contamination. The methods and controls employed are suitable for use with non-dedicated mass spectrometers which cannot be operated in vacuum static conditions.