Showing papers on "Nickel published in 1985"

High-temperature ordered intermetallic alloys

Abstract: This book contains over 50 selections. Some of the titles are: Order-disorder behavior of grain boundaries in a two-dimensional model ordered alloy; Dislocation reactions at grain boundaries in Ll/sub 2/ ordered alloys; Creep cavitation in a nickel aluminide; Effects of elastic anisotropy on the anomalious yield behavior of cubic ordered alloys; and Processing technology for nickel aluminides.

Surface reactions of metal clusters. II. Reactivity surveys with D2, N2, and CO

Abstract: Reactions on the surface of a variety of transition metal clusters have been studied in the gas phase at near room temperature using a newly developed fast-flow reaction device. Initial examples of the use of this device are provided by survey studies of the reactivity of iron, cobalt, nickel, copper, and niobium clusters in contact with low concentrations of D2, N2 and CO. Dissociative chemisorption of D2 is found to occur with dramatic sensitivity to cluster size in the cases of iron, cobalt, and niobium clusters, the detailed pattern of reactivity differing markedly for each metal. The corresponding reaction is also observed with nickel clusters, but here the reactivity shows only a slow, steady increase with cluster size. Copper clusters are found to be completely unreactive to H2 chemisorption under these conditions. Molecular nitrogen is found to chemisorb readily to clusters of cobalt and niobium, with a reactivity pattern very similar to that observed with D2. Iron clusters are found to show slight reactivity with N2; only a small amount of chemisorption is observed on the most reactive clusters at high N2 concentration, but the pattern of this reactivity with cluster size is consistent with that observed in D2 chemisorption. In contrast to these highly structured reactivity patterns of D2 and N2, carbon monoxide is found to show only a slow, monotonic increase in reactivity with cluster size. It is suggested that these dramatic reactivity patterns for chemisorption on metal clusters provide stringent tests for future theories as to the nature of chemisorption on metal surfaces at a detailed, molecular level.

The Formation of Filamentous Carbon on iron and Nickel Catalysts

Abstract: The microstructure of primary carbon filaments formed on supported iron and nickel catalysts has been investigated using transmission electron microscopy, dark-held imaging, and (selectedarea) electron diffraction. It has been established that the filaments consist of cone-shaped graphite layers, stacked with their c-axes in a direction normal to the metal-carbon interface. A growth mechanism is proposed involving the excretion of cone-shaped graphite layers. To explain the constancy of the filament diameter, slippage of these layers over one another is invoked. Edge dislocations are brought about by differences in the rate of carbon excretion.

Evidence that an iron-nickel-carbon complex is formed by reaction of CO with the CO dehydrogenase from Clostridium thermoaceticum.

Abstract: The interaction between carbon monoxide and the CO dehydrogenase from Clostridium thermoaceticum was studied by electron spin resonance (ESR) techniques. When the enzyme reacts with CO, a paramagnetic complex is formed which previously was shown, by isotope substitution, to be due to a nickel-carbon species. In this paper, we demonstrate that iron is also a component of this ESR-detectable complex. When the iron in the enzyme is replaced with 57Fe, a broadening of 18 G in the g parallel and 7 G in the g perpendicular region is seen. This hyperfine interaction is probably due to more than one iron atom in the complex. Coenzyme A influences this ESR spectrum. In the absence of CoA, the ESR spectrum consists of two superimposed signals, which were simulated using the following ESR parameters: signal 1, with g = 2.074 and g = 2.028, and signal 2 with gx = 2.062, gy = 2.047, and gz = 2.028. CoA converts signal 2 into signal 1. Since iron, nickel, and carbon all are part of this ESR-detectable complex, we propose that these atoms exist in a spin-coupled complex with net spin = 1/2, analogous to other iron-sulfur centers in which the metals are bridged by acid-labile sulfide.

Stabilization of the monovalent nickel complex with 1,4,8,11-tetraazacyclotetradecane in aqueous solutions by N- and C-methylation. An electrochemical and pulse radiolysis study

Abstract: Les complexes de Ni(II) avec le tetraaza-1,4,8,11 cyclotetradecane (L 1 ), les tetramethyl-1,4,8,11-, hexamethyl-5,7,7,12,14,14- et decamethyl-1,4,5,7,7,8,11,12,14,14-tetraazacyclotetradecane sont reduits par des reactions avec e aq − et CO 2 − et par reactions electrochimiques en solutions aqueuses. Estimation des potentiels redox

Analysis of Passive Films on Stainless Steel by Cyclic Voltammetry and Auger Spectroscopy

Abstract: Anodic passivation of Type 316L stainless steel in a borate-boric acid buffer solution was studied using cyclic voltammetry and Auger spectroscopy. Based on a comparison with the results obtained on the metals (iron, chromium, and nickel), the reduction peaks appearing in the voltammograms for the steel were attributed to the reductive dissolution of a ferric oxide and to valence transitions associated with chromium and nickel in the oxide. It is shown that cyclic voltammetry in the buffer solution provides a qualitative and semiquantitative analysis of the passive film growth. Okamoto's model of formation of two types of films, determined by the anodization potential, is found to be applicable; the mechanism of oxide growth is related to selective enrichment of iron or chromium, which is based on solubility relationships predicted by thermodynamic considerations. 12 references, 8 figures.

Die Sattelkonformation der hydroporphinoiden Nickel(II)‐Komplexe: Struktur, Ursprung und stereochemische Konsequenzen

Abstract: The Saddle Conformation of Hydroporphinoid Nickel(II) Complexes: Structure, Origin, and Stereochemical Consequences Thirteen crystal structures document the general phenomenon of coordination-hole contraction in hexahydro- and tetrahydroporphinoid ligands of complexes with small metal ions such as low-spin Ni(II). The contraction is characterized by a deformation of the ligand system towards a saddle-shaped, ruffled conformation of approximate S4 symmetry. The central metal ion is coplanar with the four coordinating N-centers whereas the four C(meso)-atoms are situated alternately above and below this coordination plane. Increasing steepness of the saddle (parameter dm) is associated with decreasing metal-N distances. For metal pyrrocorphinates, dm increases in the order Cu(II) < (pyridine) Co(II) < Ni(II), for Ni(II) complexes it does so in the order porphyrin < chlorin < bacteriochlorin < isobacteriochlorin < pyrrocorphin. In the saddle conformation of hydroporphinoid Ni(II) complexes, the hydropyrrole rings assume half-chair conformations whereby the individual half-chairs are conformationally constrained in such a way that the inclination of their peripheral single bond parallels the inclination of the ligand saddle (W-conformation of the ensemble of 5-membered ring half-chairs). There are only two such conformations available for a given complex; they interrelate by saddle inversion with concomitant inversion of the ensemble of half-chairs. The coordination-hole contraction of hydroporphinoid ligands is expected and observed experimentally to exert control on the stereochemistry and reactivity of the ligand periphery as well as on the axial electrophilicity of the central metal ion. Tetracoordinate nickel(II) pyrrocorphinates are found to favor the tctct configuration of substituents at the ligand periphery, nickel(II) isobacteriochlorinates the tct configuration, whereas nickel(II) bacteriochlorinates are expected to favor the ttt configuration. Relative rates and regioselectivities of autoxidation of nickel(II) pyrrocorphinates to corresponding bacterio-and isobacteriochlorinates depend on the configuration and conformation of the ligand periphery. The residual axial electrophilicity of the metal ion in tetracoordinate Ni(II) complexes of the octaethyl series appears to increase in the order chlorin < isobacteriochlorin ≲ bacteriochlorin < pyrrocorphin. All hydroporphinoid metal complexes used in the X-ray structure studies were prepared as part of exploring the porphyrinogen pyrrocorphin tautomerization, a novel structural transformation of porphyrinogens.

Interaction between nickel and the ligand groups carbonyl, water, and phosphine

Abstract: The interaction between nickel and three different types of ligands are studied at the CASSCF (Complete Active Space Self-Consistent Field) and contracted CI (Configuration Interaction) level. The carbonyl group is used as a model for a strong ..pi.. acceptor and water as a ligand without ..pi.. bonding. The phosphine group has an intermediate character. The effect on the binding of adding one, two, and in the case of carbonyl four ligands is studied in detail. For water and phosphine the binding energy per ligand is larger with two ligands than with only one ligand. There are also inductive effects on nickel which are quadratic in the field strength of the ligand field. Large near-degeneracy effects are found for all studied systems except Ni(H/sub 2/O). When ..pi.. bonds are formed involving the metal 3d orbitals, the corresponding antibonding orbital will always have a high occupation. Even more critical for the binding is the fractional distribution of the two electrons among the pair of (4s,3d/sub sigma/) hybrid orbitals. Depending on the interaction, the occupation of the hybridized orbitals ranges from 1.27, 0.73 for Ni(H/sub 2/O) to 1.94, 0.06 for NiCO. These near-degeneracy effects in general lead to very poor results for relativemore » energies in the SCF approximation. 33 references, 4 figures, 3 tables.« less

Heterogeneous distribution of nickel in hydrous silicates from New Caledonia ore deposits

Abstract: Four nickel-bearing clay minerals from New-Caledonia belonging to the lizardite-nepouite and the kerolite-pimelite series have been investigated in order to study the mechanisms of Ni-Mg substitution. Local order around Ni was determined by optical absorption spectroscopy and X-ray absorption spectroscopy at the Ni-K edge. Optical spectra have been reinterpreted through the Kubelka and Munk formalism which lead us to reject the optical evidences for the trigonal distortion of the octahedral Ni site. New data were also obtained concerning Mg-Ni ordering in these minerals. Analysis of the Extended X-ray Absorption Fine Structure (EXAFS) indicates that the intracrystalline distribution of nickel is not random: Ni atoms are segregated into discrete domains, the minimal size of which have been calculated and are interpreted differently depending on whether the mineral belongs to the 7A (solid state transformed) or to the loA (solution precipitated) structure type. This departure from ideal behavior of the Mg-Ni substitution is compared to the chemical and structural variations involving modulated structures. These heterogeneities seem to be quite common in low temperature formation conditions.

Triangular platinum and nickel clusters: the "tinker-toy" construction of chains with high nuclearity

Abstract: The triangular metal carbonyls formed from the Ni group transition metals are remarkable in their propensity to form high nuclearity clusters just by associating into chains. Such chains are typified by the compounds [Pt3(w2-CO),(CO),]?( n = 2, 3 , 4, 5 , 6, 10). However, there is a characteristic structural difference between the “tinker-toy” construction of stacks using Ni rather than Pt; the Ni carbonyl chains have a screw axis along the main axis, whereas the Pt chains have a simple threefold axis. Reasons for stacking and the requirements of the 2charge for all chain lengths as well as the structural differences between Ni and Pt chains are discussed in terms of the calculated electronic structure of the dimer. As well as a necessary electron count for oligomerization, there exist monomers which have specific valence electron counts. For 42 valence electrons and acceptor ligands as bridges (e.g., Pt,(CNR),) an equilateral triangle of metals is expected. When an extra two electrons are added, calculations show that distortion to an isosceles triangle or to a larger equilateral triangle is favored. Differences in electron count of various monomers are related to the types of bridging and terminal ligands present. For instance for bridging phosphido, PR2, trimers the 44-electron species should be the stable one. The reasons for further deformation in such 44-electron trimers are addressed. In addition to oligomers, intercalation complexes are also known. For Ni there is the series [NiI2(CO),,H,,]“ where n = 2,3,4 and for Pt there are the compounds [Pt3(fi2-CNR)3(CNR)3]2Hg where R = 2,6-dimethylphenyl and [Pt(p2-CO)3(PPh-i-Pr2)3]2Hg2. The reasons for the stability of these compounds are discussed in terms of the electronic structure of the Pt dimers at large monomer-monomer separation. On the basis of the known monomers, intercalates, and oligomers the existence of long-chain polymers is postulated. For [Pt3(C0)6] the calculated bond structure indicates that oxidation or reduction of the neutral chain should result in stabilization. In many ways it is similar to the tetracyanoplatinate chains discussed previously in the literature. Partially occupied bands may result in Peierls distortions leading to structures similar to those observed for the pentamer and presumably the decamer. The band structure of ‘[Pt,(CO),Hg], shows a valence band with much greater dispersion than the other bands. Partial occupation of this band (by replacing Hg with Cu, Ag, or Au) will most likely result in a pairing distortion to give a semiconductor. The attention paid to polyhedral, multinuclear metal clusters derives both from the aesthetically pleasing act of creating polyhedral clusters with increasingly higher nuclearity and also from the desire to use these clusters as models of crystalline metal surfaces. Many reactions catalyzed on metallic surfaces are also seen to occur on smaller metal complexes.’ The smallest multinuclear metal cluster which can be considred as a model (albeit a highly simplistic one) of a metal surface is a triangular, trinuclear cluster. This unit forms the basis of many polyhedral clusters, indeed three out of the five platonic solids can be built up from this simple unit, viz., tetrahedron, octahedron, and icosahedron. Triangular units can be recognized in polyhedra having 4-12 vertices, and for each of these molecular examples are known.2 Once the polyhedra (closo structures) have been enumerated, more open frameworks having the same number of vertices can be found (nido, arachno, and hypho structures). A beautiful example of the opening of a closed structure is given by Lewis, Johnson, and co-workers in their discussion of the raft-like os6(co)17[P( O M e ) 3 1 ~ ~ There are still further ways to construct high nuclearity clusters from the basic “tinker-toy”, triangular building block. If the building block is flat, and the M3(k2-L’)3(L)3 unit 1 is particularly suited for this, then it can be simply stacked in one dimension. Two layers if eclipsed lead to a trigonal prism and if staggered to an octahedron of metals. The extension to oligomers and to a one-dimensional polymer is obvious. And not only on paper. These are real systems. We have discussed elsewhere4 the beautiful CSIRO Division of Applied Organic Chemistry. * Cornell University. t Osaka University. $The Institute of Physical and Chemical Research. 0002-7863 /85 /1507-5968$01.50/0 L

Effect of nickel and silver ions on survival, growth, carbon fixation and nitrogenase activity in Nostoc muscorum: Regulation of toxicity by EDTA and calcium.

Abstract: The effects of different concentrations of nickel (2.1, 4.2, 5.04μM) and silver (0.013, 0.026, 0.052μM) on survival, growth, carbon fixation and acetylene reduction of Nostoc muscorum has been studied. All concentrations of the heavy metals except 2.1μM Ni were inhibitory. At 2.1μM, nickel chloride stimulated carbon fixation and nitrogenase activity. Silver seems to be much more toxic than nickel because concentrations as low as 0.026μM silver chloride inhibited approximately 90% of the carbon fixation. EDTA protected carbon fixation and calcium ameliorated the nitrogenase activity in the test alga. However, none of these ameliorative agents were so effective against silver toxicity. This study suggests that (i) calcium plays an imporatnt role in nitrogen fixation, (ii) like hydrogen production and uptake hydrogenase, nickel seems to have some role in regulating nitrogenase activity, and (iii) carbon fixation is a more sensitive parameter than growth and nitrogensase in evaluating metal toxicity.

Dopant Effect of Yttrium and the Growth and Adherence of Alumina on Nickel‐Aluminum Alloys

Abstract: The atom superposition and electron delocalization molecular orbital theory and large cluster models have been employed to study cation vacancy diffusion in alpha-Al2O3 and the bonding of alpha-Al2O3 to nickel, aluminum, and yttrium surfaces. Al(3+) diffusion barriers in alpha-Al2O3 by the vacancy mechanism are in reasonable agreement with experiment. The barrier to Y(3+) diffusion is predicted to be much higher. Since addition of yttrium to transition metal alloys is known to reduce the growth rate and stress convolutions in protective alumina scales, this result suggests the rate-limiting step in scale growth is cation vacancy diffusion. This may partially explain the beneficial effect of yttrium dopants on scale adhesion. The theory also predicts a very strong bonding between alumina and yttrium at the surface of the alloy. This may also be important to the adhesion phenomenon. It is also found that aluminum and yttrium atoms bond very strongly to nickel because of charge transfer from their higher lying valence orbitals to the lower lying nickel s-d band.

Corrosion of stainless steels in chloride solution: An XPS investigation of passive films

Abstract: Five commercial steels ranging from the martensitic stainless steel containing 12% chromium to the superferrite containing 29% chromium, 4% molybdenum, and 2% nickel have been studied by XPS. In addition, a pure iron-chromium alloy containing 7% chromium has been investigated. Armco iron and pure chromium (99.99%) were included as references. The formation of the passive films (or corrosion) occurred in deoxygenated 0.1 M NaCl solution (pH=5.6), from which the samples were transferred directly to the XPS chamber under controlled atmosphere (Ar). Concentration profiles (at.-%) of the alloy constituents in their oxidized and metallic states have been determined separately from the measured XPS depth profiles. Forc≳= 12% chromium the passive films have the following structure: there is a depletion of Cr in the inner region, followed by an enrichment (concentration maximum) in the central region of the films. The height of this maximum increases, and its position shifts towards the surface with increasing chromium content in the alloy. The outermost monolayers are rich in water and hydroxyl groups. Various significant properties of the films change drastically at the critical chromium concentration of about 12%. This behaviour is rather independent of the other components (Mo, Ni, Cu) present in the alloys and is discussed in terms of a phase transition in the films which is controlled by the chromium concentration.