Showing papers on "Nickel published in 1994"

Magnetism from the Atom to the Bulk in Iron, Cobalt, and Nickel Clusters

Abstract: Molecular beam deflection measurements of small iron, cobalt, and nickel clusters show how magnetism develops as the cluster size is increased from several tens to several hundreds of atoms for temperatures between 80 and 1000 K. Ferromagnetism occurs even for the smallest sizes: for clusters with fewer than about 30 atoms the magnetic moments are atomlike; as the size is increased up to 700 atoms, the magnetic moments approach the bulk limit, with oscillations probably caused by surface-induced spin-density waves. The trends are explained in a magnetic shell model. A crystallographic phase transition from high moment to low moment in iron clusters has also been identified.

The Chemistry of Metal Cvd

Abstract: CVD of aluminium tungsten copper from Cu(II) percursors copper from Cu(I) precursors gold and silver platinum, pallaium, and nickel assorted metals.

Biomimetic Chemistry of Nickel

Abstract: Methyl-Scoenzyme-M Methylreductase and Factor 430 A. Methyl-Scoenzyme-M Methylreductase B. Isolated F430 Structural and Functional Models for Factor 430 A. Structural and Electrochemical Investigations of Nickel Tetrapyrroles i. Redox Studies ii. Structural and Conformational Studies B. C-S and C-X (X = Halide) Bond Cleavage by Nickel Complexes Carbon Monoxide Dehydrogenase A. Introduction B. Acetykoenzyme A Synthesis and Center A C, Carbon Monoxide Oxidation and Center C Model Systems for Carbon Monoxide Dehydrogenase A. Mixed NilFelS Clusters and Related Species B. Redox Reactions of Nickel Complexes with CO and COZ C. Thioester Formation Mediated by Nickel Centers Hydrogenase A. Introduction B. Redox Chemistry of [NiFe] Hydrogenases C. Structural Properties of [NiFe] Hydrogenases D. The Mechanism of H2 Oxidation and H + O

Semiconductor, semiconductor device, and method for fabricating the same

Abstract: Method of fabricating semiconductor devices such as thin-film transistors by annealing a substantially amorphous silicon film at a temperature either lower than normal crystallization temperature of amorphous silicon or lower than the glass transition point of the substrate so as to crystallize the silicon film. Islands, stripes, lines, or dots of nickel, iron, cobalt, or platinum, silicide, acetate, or nitrate of nickel, iron, cobalt, or platinum, film containing various salts, particles, or clusters containing at least one of nickel, iron, cobalt, and platinum are used as starting materials for crystallization. These materials are formed on or under the amorphous silicon film.

Stabilized α ‐ Ni ( OH ) 2 as Electrode Material for Alkaline Secondary Cells

Abstract: Hydrotalcite-like compounds of formula Ni1-xAl(x)(OH)2(CO3)x/2 . nH2O (x = 0.1 to 0.25), having the same structure as that of alpha-Ni(OH)2, have been synthesized by substituting nickel hydroxide with aluminum. Of these, the compounds of compositions x greater-than-or-equal-to 0.2 are found to have prolonged stability in strong alkaline medium. The electrodes comprising stabilized alpha-Ni(OH)2 of x = 0.2 composition are rechargeable with discharge-capacity values of 240 (+/- 15) mAh-g-1 and are attractive for applications in various alkaline secondary cells employing nickel-positive electrodes.

Study of Electrodeposited Nickel‐Molybdenum, Nickel‐Tungsten, Cobalt‐Molybdenum, and Cobalt‐Tungsten as Hydrogen Electrodes in Alkaline Water Electrolysis

Abstract: Electrodeposited nickel-molybdenum, nickel-tungsten, cobalt-molybdenum, and cobalt-tungsten were characterized for the hydrogen evolution reaction (HER) in the electrolysis of 30 w/o KOH alkaline water at 25 C. The rate-determining step (rds) of the HER was suggested based on the Tafel slope of polarization and the capacitance of electrode-solution interface determined by ac impedance measurement. The HER on the nickel- and cobalt-based codeposits was enhanced significantly compared with that o the electrolytic nickel and cobalt with comparable deposit loadings. The decrease in the HER overpotential was more pronounced on the molybdenum-containing codeposits, particularly on cobalt-molybdenum which also showed a high stability. The enhancement of the HER was attributed to both the synergetic composition and the increased active surface of the codeposits. The real electrocatalytic activity of te electrodes and the effect of their and the increased active surface of the codeposits. The real electrocatalytic activity of the electrodes and the effect of their surface increase were distinguished quantitatively. The linear relations between HER overpotential and surface roughness factor of the electrodes on a Y-log(X) plot were obtained experimentally and interpreted based on the Tafel law.

The structure of small nickel clusters. I. Ni3–Ni15

Abstract: The geometrical structure of small nickel clusters is probed via molecular adsorption of nitrogen on their surfaces. Nitrogen uptake patterns can be rationalized with the proposed structures if it is assumed that N2 binds to every exposed nickel atom, that the binding energies decrease with increasing metal—metal coordination, and that atoms that are four or less coordinate can bind two nitrogen molecules. In some cases nitrogen adsorption causes a change in cluster structure, usually to one that can accommodate more nitrogen molecules. Cluster structures are proposed for all clusters (bare and nitrogenated) in the 3–15‐atom size range except Ni4 and Ni11. The nitrogen uptake for Ni4 is consistent with virtually any structure, and the data for Ni11 could not be interpreted in terms of a specific structure. In general, nickel cluster structures are different from those found for rare gas clusters as well as those derived from bulk packing. A comparison of the experimental results with existing theoretical ...

Preparation of Nickel Pattern Electrodes on YSZ and Their Electrochemical Properties in H 2 ‐ H 2 O Atmospheres

Abstract: To study the reaction kinetics at the anode of solid-oxide fuel cells, a nickel stripe pattern was prepared on the surface of yttria-stabilized zirconia (YSZ) [8 mole percent (m/o) Y 2 O 3 -doped ZrO 2 ] by an ionized cluster beam (ICB) method and photolithography. Due to grain growth of nickel film at high temperatures, the minimum possible width of the stripes was found to be ca. 5 μm. By impedance measurements in H 2 -H 2 O atmospheres at 100 to 850 o C, it was shown that the reaction proceeds through the triple-phase boundary (TPB) of H 2 -H 1 O/Ni/YSZ and the mechanism of the rate-determining reaction is different from that at the TPB of H 2 -H 2 O/Pt/YSZ

Borohydride Reduction of Nickel and Copper Ions in Aqueous and Nonaqueous Media. Controllable Chemistry Leading to Nanoscale Metal and Metal Boride Particles

Abstract: The reduction of Ni 2+ (aq), Ni 2+ (diglyme), Cu 2+ (aq), and Cu 2+ (diglyme) by NaBH 4 has been studied with mechanistic and stoichiometric factors as the focus

On the Mechanism of Electroless Ni‐P Plating

Abstract: The electroless deposition mechanism of nickel, in a chloride‐based solution, using hypophosphite ion as reducing agent was examined using potentiodynamic method and open‐circuit potential measurements. The results indicate that the mixed potential theory is unable to describe this system. This is due to the nature of the involved mechanism. It is assumed that the process is initialized by adsorption of hypophosphite ions, followed by the homolysis of primary reductant species, resulting in the formation of atomic and ionic radicals which promote nickel and hypophosphorous acid reduction to originate the Ni‐P deposit. The initial deposition stages of Ni‐P were observed, revealing that the substrate induction, which leads to an increase in the catalytic activity, is not related to a galvanic displacement process, but rather to the establishment of the electrochemical conditions which allow the adsorption/breakdown of the hypophosphite ions. The experimental results are in good agreement with the proposed mechanism.

Decoration of Nickel and Magnesium Oxide Crystallites with Spinel-Type Phases

Abstract: The structure of the Al promoted magnesium and nickel oxides obtained by calcination of hydrotalcite-type coprecipitates was investigated by X-ray diffraction, 27 Al MAS-NMR, EXAFS, and alkaline leachings. In addition to the reflections of the MgO rock-salt type structure, the diffraction patterns of the Al modified MgO exhibited an additional, well-defined reflection at d=0.253 nm, attributable to cations on tetrahedral sites. The tetrahedrally coordinated cations were likely to belong to a nonstoichiometric spinel-type phase including an excess of magnesium. The same behavior was observed when Ga(III) were substituted for Al(III) ions in the materials

Ethylene Hydrogenation on Ni(111) by Bulk Hydrogen

Abstract: We report that bulk H atoms, upon moving out from the bulk metal to the surface, readily hydrogenate C[sub 2]H[sub 4] adsorbed on Ni(111) to form C[sub 2]H[sub 6], while surface-bound H atoms have no hydrogenation activity under the conditions of these experiments. This result is the first observation of the role of bulk H specifically as a reactant in the hydrogenation of an unsaturated hydrocarbon on a transition metal and calls into question the generality of the Horiuti-Polanyi mechanism for catalytic hydrogenation reactions. This results is also a plausible molecular level basis for the correlation between the hydrogenation activity of a Raney Ni catalyst and the H content in the catalyst. 17 refs., 2 figs.

Reduction of model steam reforming catalysts : NiO/α-Al2O3

Abstract: The effect of NiO loading (5–21 wt-%) on the reduction of NiO/α-A 2 O 3 catalysts, prepared by multiple impregnation of nickel nitrate solution followed by calcination at 650°C has been characterized usingtemperature-programmed reduction, isothermal hydrogen consumption, magnetization, X-raydiffraction, and electron microscopy X-ray diffraction analysis of fresh catalysts indicated normal NiO crystallites about 30 nm in size Studies from 270°C to 350°C show hydrogen consumption at lower temperatures is faster than the subsequent growth of nucleated clusters of nickel atoms into crystallites, with the rates of the two processes approaching each other at higher temperatures As NiO loading increases, chemical reduction becomes more difficult but nickel crystallite growth is not affected This decreased reducibility is believed due to Al 3+ ion incorporation into NiO surface layers during impregnation Isothermal hydrogen consumption from 270°C to 450°C follows a shrinking core model with NiO crystallites decreasing progressively in size Magnetic measurements show crystallite growth is dependent on diffusion-controlled nucleation Decreasing hydrogen flow has a profound effect on chemical reduction and nucleation but not on growth Similar results are found with added water vapor X-ray diffraction and transmission electron microscope measurements reveal 23 nm nickel crystallites with some evidence for Al-Ni alloy formation A mechanism is proposed in whichadsorbed water inhibits chemical reduction and nucleation, and foreign ions such as A1 3+ increase this effect

Catalytic reduction of Iodoethane and 2-Iodopropane at Carbon Electrodes Coated with Anodically Polymerized Films of Nickel(II) Salen

Abstract: In acetonitrile containing tetramethylammonium tetrafluoroborate, nickel(II) salen undergoes antic polymerization onto a carbon electrode. Nickel(II) in the polymer film exhibits reversible one-electron reduction to form nickel(I), which can catalytically reduce iodoethane or 2-iodopropane to form an ethyl or 2-propyl radical respectively, and to regenerate nickel(II). Kinetics studies with the aid of hydrodynamic voltammetry indicate that the catalytic reduction of iodoethane belongs to the EB regime of Saveant and co-workers, whereas catalytic reduction of 2-iodopropane is of the S classification. Controlled-potential electrolyses of iodoethane and 2-iodopropane at nickel-(II) salen-coated reticulated vitreous carbon cathodes give product distributions in accord with the relative importance of radical coupling and disproportionation

Voltammetry and anodic stability of a hydrous oxide film on a nickel electrode in alkaline solution

Abstract: A hydrous oxide film on a nickel electrode was formed electrolytically by square-wave cycling in 1 mol dm-3 NaOH solution. The reproducibility of a second scan in a voltammetric experiment depended on holding the potential at a negative value (−1.1 V vs SCE) and on the positive potential limit. The hydrous oxide film, with a charge enhancement factor of 19, exhibited two stages of oxide reduction. Coulometric data showed that the majority of the oxide (80-90%) was reduced in Ni(III)/ Ni(ii) transition almost reversibly at potentials where the higher oxide was formed while, depending on the potential of formation, about 10–20% of the NiOOH was irreversibly reduced in the potential region of the hydrogen evolution reaction. An anodic stability test in the oxygen evolution reaction was carried out at 0.1 A cm−2 The hydrous oxide layer was stable over 14 days of electrolysis with an unchanged charge enhancement factor. The electrocatalytic activity of the electrode, however, expressed through the overpotential at the same current density, was not maintained.

Influence of the preparation method and the nature of the support on the stability of nickel catalysts

Abstract: The influence of the preparation method and the nature of the support on the stability of the metal dispersion in nickel catalysts was studied Three different preparation methods, incipient wetness, ion exchange and precipitation-deposition using three different commercial supports, silica, alumina and silica-alumina were used The metallic dispersion stability was evaluated by hydrogen adsorption measurements after high-temperature calcination of the samples before and after reduction Results have shown that the behaviour of the samples depends on the balance between positive and negative effects in the metal-support interaction, ie, the increase of the initial metal dispersion and its resistance against sintering and, the loss of nickel in the form of difficult to reduce interaction compounds Interaction depends on the preparation method, but can be considerably modified during catalyst life The reactivity of the support towards nickel plays an important role in these changes The catalyst prepared by precipitation-deposition over silica showed the best metallic dispersion and stability

Nickel release from nickel-plated metals and stainless steels.

Abstract: Nickel release from nickel-plated metals often induces allergic contact dermatitis, but, for nickel-containing stainless steels, the effect is not well-known. In this paper, AISI 304, 316L, 303 and 430 type stainless steels, nickel and nickel-plated materials were investigated. 4 tests were performed: patch tests, leaching experiments, dimethylglyoxime (DMG) spot tests and electrochemical tests. Patch tests showed that 96% of the patients were intolerant to Ni-plated samples, and 14% to a high-sulfur stainless steel (303), while nickel-containing stainless steels with a low sulfur content elicited no reactions. Leaching experiments confirmed the patch tests: in acidic artificial sweat, Ni-plated samples released about 100 micrograms/cm2/week of nickel, while low-sulfur stainless steels released less than 0.03 microgram/cm2/week of nickel, and AISI 303 about 1.5 micrograms/cm2/week. Attention is drawn to the irrelevance of the DMG spot test, which reveals Ni present in the metal bulk but not its dissolution rate. Electrochemical experiments showed that 304 and 316 grades remain passive in the environments tested, while Ni-plated steels and AISI 303 can suffer significant cation dissolution. Thus, Ni-containing 304 and 316 steels should not induce contact dermatitis, while 303 should be avoided. A reliable nitric acid spot test is proposed to distinguish this grade from other stainless steels.