The effects of fabrication and annealing on the structure and hydrogen permeation of Pd–Au binary alloy membranes

The addition of gold to palladium membranes produces many desirable effects for hydrogen purification, including improved tolerance of sulfur compounds, reduction in hydride phase formation, and, for certain compositions, improved hydrogen permeability. The focus of this work is to determine if sequential plating can be used to produce self-supported alloy membranes with equivalent properties to membranes produced by conventional metallurgical techniques such as cold-working.Sequential electroplating and electroless plating were used to produce freestanding planar Pd–Au membranes with Au contents ranging from 0 to 20 wt%, consisting of Au layers on both sides of a pure Pd core. Membranes were characterized by single-gas permeation measurements, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), and high temperature, controlled-atmosphere XRD (HTXRD). Sequentially plated foils tested without any prior annealing had significantly lower H₂ permeabilities than either measured or literature values for homogeneous foils of equivalent composition. This effect appears to be due to the formation of stable gold-enriched surface layers. Pretreatment of membranes to 1023 K created membranes with hydrogen permeabilities equivalent to literature values, despite the fact that trace amounts of surface gold remained detectable with XRD.     

An elliptic system with bifurcation parameters on the boundary conditions

In this paper we consider the elliptic system Δu=a(x)upvq, Δv=b(x)urvs in Ω, a smooth bounded domain, with boundary conditions , on ∂Ω. Here λ and μ are regarded as parameters and p,s>1, q,r>0 verify (p−1)(s−1)>qr. We consider the case where a(x)?0 in Ω and a(x) is allowed to vanish in an interior subdomain Ω₀, while b(x)>0 in . Our main results include existence of nonnegative nontrivial solutions in the range 0<λ<λ₁?∞, μ>0, where λ₁ is characterized by means of an eigenvalue problem, and the uniqueness of such solutions. We also study their asymptotic behavior in all possible cases: as both λ,μ→0, as λ→λ₁<∞ for fixed μ (respectively μ→∞ for fixed λ) and when both λ,μ→∞ in case λ₁=∞.     

Magnetic Resonance Imaging of Water Content and Flow Processes in Natural Soils by Pulse Sequences with Ultrashort Detection

Magnetic resonance imaging is a valuable tool for three-dimensional mapping of soil water processes due to its sensitivity to the substance of interest: water. Since conventional gradient- or spin-echo based pulse sequences do not detect rapidly relaxing fractions of water in natural porous media with transverse relaxation times in the millisecond range, pulse sequences with ultrafast detection open a way out. In this work, we compare a spin-echo multislice pulse sequence with ultrashort (UTE) and zero-TE (ZTE) sequences for their suitability to map water content and its changes in 3D in natural soil materials. Longitudinal and transverse relaxation times were found in the ranges around 80 ms and 1 to 50 ms, respectively, so that the spin echo sequence misses larger fractions of water. In contrast, ZTE and UTE could detect all water, if the excitation and detection bandwidths were set sufficiently broad. More precisely, with ZTE we could map water contents down to 0.1 cm³/cm³. Finally, we employed ZTE to monitor the development of film flow in a natural soil core with high temporal resolution. This opens the route for further quantitative imaging of soil water processes.     

Substitutional and positional disorder in Sr2.88Cu3.12(PO4)4

The title compound, a hydrothermally synthesized strontium copper(II) phosphate(V) (2.88/3.12/4), is isotypic with Sr₃Cu₃(PO₄)₄, obtained previously by solid‐state reaction, but not with Sr₃Cu₃(PO₄)₄, obtained previously by the hydrothermal method. A surplus of copper was observed by both structural and chemical analysis, and the formula obtained by the structural analysis is in full agreement with results of the EDX (energy‐dispersive X‐ray diffraction) analysis. The structure consists of layers of Cu₃O₁₂ groups which are linked via the PO₄ tetrahedra. The Cu₃O₁₂ groups are formed by one Cu1O₄ and two Cu2O₅ coordination polyhedra sharing corners. The central Cu1 atom of the Cu₃O₁₂ group is located at an inversion centre (special position 2a). The unique structural feature of the title compound is the presence of 12% Cu in the Sr1 site (special position 2b, site symmetry ). Moreover, disordered Sr2 atoms were observed: a main site (Sr2a, 90%) and a less occupied site (Sr2b, 10%) are displaced by 0.48 (3) Å along the b axis. Such substitutional and positional disorder was not observed previously in similar compounds.     

Large solutions to an anisotropic quasilinear elliptic problem

In this paper we consider existence, asymptotic behavior near the boundary and uniqueness of positive solutions to the problem ${\rm div}_x (|\nabla_x u|^{p-2}\nabla_xu)(x,y) + {\rm div}_y (|\nabla_y u|^{q-2}\nabla_y u) (x, y) = u^r(x, y)$ in a bounded domain ${\Omega \subset \mathbb{R}^N \times \mathbb{R}^M}In this paper we consider existence, asymptotic behavior near the boundary and uniqueness of positive solutions to the problem

divx (|?x u|p-2?xu)(x,y) + divy (|?y u|q-2?y u) (x, y) = ur(x, y){\rm div}_x (|\nabla_x u|^{p-2}\nabla_xu)(x,y) + {\rm div}_y (|\nabla_y u|^{q-2}\nabla_y u) (x, y) = u^r(x, y)      137. Electromechanical properties of laminated piezoelectric composites      Reinaldo Rodriquez Ramos  Jose A. Otero Hernandez  Julian Bravo Castillero  Federico J. Sabina 《Mechanics of Composite Materials》1996,32(3):286-291 The general expressions for the effective elastic, piezoelectric, and dielectric coefficients of a laminated piezocomposite composed of laminates in parallel connection are shown. By means of the asymptotic averaging method [12] these effective coefficients are calculated. The effective coefficients as well as physical properties such as electromechanical piezoelectric coupling coefficients, acoustic impedance, and wave velocity for a two-phase composite, where one phase is ceramic and the other one is polymer, are analyzed. A comparison with another results is shown.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 410–417, May–June, 1996.      138. Quenching of superoxide ions by curcumin. A mechanistic study in acetonitrile      Toniolo R  Di Narda F  Susmel S  Martelli M  Martelli L  Bontempelli G 《Annali di chimica》2002,92(3):281-288 The quenching of superoxide ions, O2.-, by curcumin has been studied by electrogenerating this anion radical from oxygen dissolved in acetonitrile solvent (that is, at best, a mimic of the lipofilic layer of biological membranes), containing known amounts of curcumin. Voltammetric tests, combined with coulometric and spectrophotometric measurements, pointed out that each mol of curcumin is able to react with six mols of such anion radical, through a process initiated by an acid-base step, which provides the perhydroxyl radical, HO2.; that disproportionates rapidly to the anionic form of hydrogen peroxide, HO2-, and oxygen, which is thus partially regenerated. At the same time, curcumin is converted to the corresponding three-charged anion. The strict resemblance existing between the mechanism of the rapid superoxide radical decay caused by curcumin and that involved in the presence of the superoxodismutase enzyme (SOD) is also underlined.      139. Oriented attachment and membrane reconstitution of His-tagged cytochrome c oxidase to a gold electrode: in situ monitoring by surface-enhanced infrared absorption spectroscopy      Ataka K  Giess F  Knoll W  Naumann R  Haber-Pohlmeier S  Richter B  Heberle J 《Journal of the American Chemical Society》2004,126(49):16199-16206 A novel concept is introduced for the oriented incorporation of membrane proteins into solid supported lipid bilayers. Recombinant cytochrome c oxidase solubilized in detergent was immobilized on a chemically modified gold surface via the affinity of its histidine-tag to a nickel-chelating nitrilo-triacetic acid (NTA) surface. The oriented protein monolayer was reconstituted into the lipid environment by detergent substitution. The individual steps of the surface modification, including (1) chemical modification of the gold support, (2) adsorption of the protein, and (3) reconstitution of the lipid bilayer, were followed in situ by means of surface-enhanced infrared absorption spectroscopy (SEIRAS) and accompanied by normal-mode analysis. The high surface sensitivity of SEIRAS allows for the identification of each chemical reaction process within the monolayer at the molecular level. Finally, full functionality of the surface-tethered cytochrome c oxidase was demonstrated by cyclic voltammetry after binding of the natural electron donor cytochrome c.      140. Palladium(II) complexes of (t-butyl salicylidene) diphenyl disulfide diamine: synthesis,structure, spectral characterization and catalytic properties      Bhowon  Minu G.  Jhaumeer Laulloo  Sabina  Hosten  Eric C.  Elaheebacus  Sumayya  Dowlut  Mounisha R. 《Transition Metal Chemistry》2021,46(7):537-545 The hexadentate N2S2O2 donor ligand N,N’-bis(3,5-tert-butylsalicylidene) diphenyl disulfide-2,2’-diamine was synthesised by the condensation of 2-aminophenyl disulfide and 3,5-di-tert-butyl-2-hydroxybenzaldehyde and its molecular structure was confirmed by X-ray studies. One of the tert-butyl groups in the Schiff base has rotational disorder around the C–C bond with ratio 0.56:0.44. The palladium complexes were prepared by the direct reaction of PdCl2(CH3CN)2 and Schiff base ligands N,N’-bis (5-tert-butylsalicylidene) diphenyl disulfide-2,2’-diamine and N,N’-bis(3,5-tert-butylsalicylidene) diphenyl disulfide-2,2’-diamine, respectively. The structure of the metal complexes was characterized by physico-chemical and spectroscopic methods. Palladium is in square-planar geometry bonded to imine nitrogen and phenolic O in both the complexes. The catalytic efficiency of the palladium complexes was evaluated in the cross-coupling reactions; Heck-Mizoroki reaction of iodobenzene and methyl acrylate and the Suzuki-Miyaura reaction of phenylboronic acid and iodobenzene, which gave low to moderate yields. Higher conversions were obtained for 2a as catalyst due to the increase in the number of bulky tertiary butyl groups in the structure.       [首页] « 上一页 [9] [10] [11] [12] [13] 14 [15] [16] [17] [18] [19] 下一页 » 末  页»

Electromechanical properties of laminated piezoelectric composites

The general expressions for the effective elastic, piezoelectric, and dielectric coefficients of a laminated piezocomposite composed of laminates in parallel connection are shown. By means of the asymptotic averaging method [12] these effective coefficients are calculated. The effective coefficients as well as physical properties such as electromechanical piezoelectric coupling coefficients, acoustic impedance, and wave velocity for a two-phase composite, where one phase is ceramic and the other one is polymer, are analyzed. A comparison with another results is shown.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, October, 1995.Published in Mekhanika Kompozitnykh Materialov, Vol. 32, No. 3, pp. 410–417, May–June, 1996.     

Quenching of superoxide ions by curcumin. A mechanistic study in acetonitrile

The quenching of superoxide ions, O2.-, by curcumin has been studied by electrogenerating this anion radical from oxygen dissolved in acetonitrile solvent (that is, at best, a mimic of the lipofilic layer of biological membranes), containing known amounts of curcumin. Voltammetric tests, combined with coulometric and spectrophotometric measurements, pointed out that each mol of curcumin is able to react with six mols of such anion radical, through a process initiated by an acid-base step, which provides the perhydroxyl radical, HO2.; that disproportionates rapidly to the anionic form of hydrogen peroxide, HO2-, and oxygen, which is thus partially regenerated. At the same time, curcumin is converted to the corresponding three-charged anion. The strict resemblance existing between the mechanism of the rapid superoxide radical decay caused by curcumin and that involved in the presence of the superoxodismutase enzyme (SOD) is also underlined.     

Oriented attachment and membrane reconstitution of His-tagged cytochrome c oxidase to a gold electrode: in situ monitoring by surface-enhanced infrared absorption spectroscopy

A novel concept is introduced for the oriented incorporation of membrane proteins into solid supported lipid bilayers. Recombinant cytochrome c oxidase solubilized in detergent was immobilized on a chemically modified gold surface via the affinity of its histidine-tag to a nickel-chelating nitrilo-triacetic acid (NTA) surface. The oriented protein monolayer was reconstituted into the lipid environment by detergent substitution. The individual steps of the surface modification, including (1) chemical modification of the gold support, (2) adsorption of the protein, and (3) reconstitution of the lipid bilayer, were followed in situ by means of surface-enhanced infrared absorption spectroscopy (SEIRAS) and accompanied by normal-mode analysis. The high surface sensitivity of SEIRAS allows for the identification of each chemical reaction process within the monolayer at the molecular level. Finally, full functionality of the surface-tethered cytochrome c oxidase was demonstrated by cyclic voltammetry after binding of the natural electron donor cytochrome c.     

Palladium(II) complexes of (t-butyl salicylidene) diphenyl disulfide diamine: synthesis,structure, spectral characterization and catalytic properties

The hexadentate N₂S₂O₂ donor ligand N,N’-bis(3,5-tert-butylsalicylidene) diphenyl disulfide-2,2’-diamine was synthesised by the condensation of 2-aminophenyl disulfide and 3,5-di-tert-butyl-2-hydroxybenzaldehyde and its molecular structure was confirmed by X-ray studies. One of the tert-butyl groups in the Schiff base has rotational disorder around the C–C bond with ratio 0.56:0.44. The palladium complexes were prepared by the direct reaction of PdCl₂(CH₃CN)₂ and Schiff base ligands N,N’-bis (5-tert-butylsalicylidene) diphenyl disulfide-2,2’-diamine and N,N’-bis(3,5-tert-butylsalicylidene) diphenyl disulfide-2,2’-diamine, respectively. The structure of the metal complexes was characterized by physico-chemical and spectroscopic methods. Palladium is in square-planar geometry bonded to imine nitrogen and phenolic O in both the complexes. The catalytic efficiency of the palladium complexes was evaluated in the cross-coupling reactions; Heck-Mizoroki reaction of iodobenzene and methyl acrylate and the Suzuki-Miyaura reaction of phenylboronic acid and iodobenzene, which gave low to moderate yields. Higher conversions were obtained for 2a as catalyst due to the increase in the number of bulky tertiary butyl groups in the structure.