Showing papers on "Cobalt published in 1988"

Oxygen complexes and oxygen activation by transition metals

Abstract: Opening Remarks- Dioxygen Complexes with Transition Metals- Bonding of Dioxygen to Transition Metals- Oxygen Binding by the Metalloproteins Hemerythrin, Hemocyanin, and Hemoglobin- Metal Oxo Complexes and Oxygen Activation- Kinetics of Formation of Biological Oxygen Carriers- Synthetic Dioxygen Carriers for Dioxygen Transport- Formation and Degradation of Cobalt Dioxygen Complexes- Reversible Complexes for the Recovery of Dioxygen- Summary - Dioxygen Complexes with Transition Metals- Oxygen Activation by Transition Metals- Summary - Oxygen Activation by Transition Metals- The Chemistry and Activation of Dioxygen Species (02, 02-, and H00H) in Biology- Oxygen Activation by Neutrophils- Mechanisms of Dioxygen Activation in Metal-Containing Monooxygenases: Enzymes and Model Systems- Radical Cation Pathways for Selective Catalytic Oxidation by Molecular Oxygen- Vanadium Catalyzed Autoxidation of Hydrogen Sulfide- Copper Catalyzed Oxidative Carbonylation of Methanol to Dimethyl Carbonate- Dependence of Reaction Pathways and Product Distribution on the Oxidation State of Palladium Catalysts for the Reactions of Olefinic and Aromatic Substrates with Molecular Oxygen- Oxygen Activation and Oxidation Reactions on Metal Surfaces- Methane Oxidation at Metal Oxide Surfaces- The Activation of Oxygen by Metal Phosphorus Oxides - The Vanadium Phosphorus Oxide Catalyst- The Oxidation of Organic Compounds by Metal Complexes in Zeolites- Abstracts of Posters- Kinetics and Mechanisms of Degradation of Binuclear Cobalt Dioxygen Complexes- Methane Activation over Lanthanide Oxides- Dioxygen Affinities of Some Synthetic Cobalt Schiff Base Complexes- Temporal Analysis of Products (TAP): A Unique Catalyst Evaluation System with Sub-Millisecond Time Resolution- Dioxygen Insertion into Metal-Carbon Bonds of Metalloporphyrins: Formation and Characterization of Alkylperoxy Metalloporphyrins- Iron Porphyrin Catalyzed Air Oxidation of Aldehydes and Alkenes- Oxidative Dimerization of Methane over Sodium-Promoted Calcium Oxides- Synthesis and Metal Ion Affinities of a Binucleating Polyamine: Reversible Formation of a Cobalt Dioxygen Complex- Potentiometric Determination of Stabilities of Cobalt(II) Complexes of Polyamine Schiff Bases and Their Dioxygen Adducts- Catalysis of Cobalt Schiff Base Complexes for the Oxygenation of Olefins Mechanisms for the Ketonization Reaction- Selective Oxidation of Saturated Hydrocarbons by the Gif and Gif-Orsay Systems- The Formation, Characterization, and Reactivity of the Oxene Adduct of Tetrakis(2,6-dichlorophenyl)porphinato-Iron(III) Perchlorate in Acetonitrile- Preparation and Characterization of a Binuclear Iron(III)- Hydroxo-y-hydroperoxy Complex [(Ph3PO)4(HO)FeIII(HOOH)FeIII(OH)(OPPh3)4](C1O4)4- Autoxidation of FeII(dihydroxyphenanthroline)3- Phosphine-Ruthenium(II)-Aquo Redox Chemistry: The Aerobic Catalytic Oxidation of Cyclohexene- The Oxidation of Organic Substrates by Molecular Oxygen Catalysis by Ru(III) and Ru(III)-EDTA- Oxygenation of Tryptophane Catalyzed by Polyamine Cobalt Dioxygen Complexes- Resonance Raman Spectroscopy of the Fe(IV)=0 Group in Peroxidase Intermediates- Reaction of Dioxygen with Synthetic Copper(I) Compounds of Biological Relevance- Thorough Elucidation of Oxygenation- and Oxidation-Mechanisms of Iron(II) Porphyrin on the Basis of a New Hypothesis for an Electron-Transfer Pathway- IUCCP Description

Cobalt in ferromanganese crusts as a monitor of hydrothermal discharge on the Pacific sea floor

Abstract: Ferromanganese oxide crusts, which accumulate on unsedimented surfaces in the open ocean1–6, derive most of their metal content from dissolved and particulate matter in ambient bottom water7,8, in proportions modified by the variable scavenging efficiency of the oxide phase for susceptible ions9. They differ in this respect from abyssal nodules, much of whose metals are remobilized from host sediments. Here we present maps of cobalt concentration and inferred accumulation rate of ferromanganese crusts from the Pacific Ocean. We propose that depletion of cobalt in Pacific crusts measures the location and intensity of submarine hydrothermal discharge. Use of the 'cobalt chronometer', an algorithm inversely relating cobalt content and crust growth rate, permits mapping of the accumulation rate of ferromanganese crusts with only indirect recourse to radioactivity-based dating methods. These maps show that crusts in hydrothermal areas grow from two to more than four orders of magnitude faster than in the Central Pacific Ocean. Cobalt-enriched crusts are found where water masses are most isolated from continental-coastal and hydrothermal sources of metals, now and in the past. This relationship can resolve the problem of cobalt enrichment in crusts without recourse to hypotheses invoking special cobalt sources or enrichment mechanisms.

Direct determination of dissolved cobalt and nickel in seawater by differential pulse cathodic stripping voltammetry preceded by adsorptive collection of cyclohexane-1,2-dione dioxime complexes

Abstract: A highly sensitive voltametric technique was developed for the direct determination of cobalt and nickel in seawater at picomolar and nanomolar concentrations, respectively. Cyclohexane-1,2-dione dioxime (nioxime) complexes of Co(II) and Ni(II) were concentrated from 10 mL of sample onto a hanging mercury drop electrode by controlled adsorption and the current resulting from reduction of Co(II) and Ni(II) was measured by differential pulse cathodic stripping voltametry. Detailed experiments were conducted to determine the optimal ligand type and concentration, buffer type and concentration, pH, and adsorption potential. Maximum sensitivity was obtained by using a nioxime concentration of 1 x 10/sup -4/ m, a HEPES buffer concentration of 0.03 m, a solution pH of 7.6, and an adsorption potential of -0.6 V. Replicate analyses of seawater reference materials yielded excellent agreement with certified values. Analytical precision for Co and Ni at coastal and open ocean concentrations was approximately +/-5% relative standard deviation. Detection limits for Co and Ni depend upon reagent blanks and are 6 pM and 0.45 nM, respectively, for 15-min adsorption periods.

Some effects of the addition of cobalt to the nickel hydroxide electrode

Abstract: The action of cobalt upon the characteristics of the nickel hydroxide electrode has been investigated by constant current, linear potential sweep and EDAX methods. It was found that cobalt raises the oxygen overpotential and promotes greater utilization of the active material, although major additions of cobalt were observed to lower the working potential of the electrode. It was also found that cobalt prevented any significant loss of electrode capacity when the system was poisoned with iron.

Fourier transform infrared studies of atomic titanium, vanadium, chromium, iron, cobalt, nickel and copper reactions with carbon dioxide in low-temperature matrices

Abstract: Titanium, vanadium, chromium, iron, cobalt, nickel, and copper metal atoms were cocondensed with CO/sub 2/ in neat matrices at 15 K. Even though a large proportion of atoms do not react, new complexes with CO/sub 2/ are characterized by using FTIR techniques and their infrared absorption bands are assigned. It is clearly shown that CO/sub 2/ is highly bent in these complexes. The behavior of oxophile metals is different from that of other metals which spontaneously form 1:1 complexes with CO/sub 2/. For Ti, V, and Cr, the authors observe first an insertion of metallic atom into a CO bond, leading to the formation of the intermediate (O)M(CO) molecule, followed by the CO/sub 2/ fixation on this complex, to form (O)M(CO)(CO/sub 2/). The other identified products in the matrices are CO, M(O), M(CO)/sub n/, and possibly a few carbonates. Most complexes are thermally unstable and decompose above 60 K. Only Fe and Ni compounds give rise upon annealing above 80 K to CO/sub 2/ reduction to CO along with the simultaneous formation of metal carbonyl complexes. Isotopic experiments with /sup 13/CO/sub 2/ and C/sup 18/O/sub 2/ allow them to conclude that the geometry of complexes is both metal and matrixmore » dependent: in neat CO/sub 2/ matrices, Fe and CO lead to a C coordination, the others being fixed in a side-on and end-on manner.« less

The effect of plasma‐sprayed calcium phosphate ceramic coatings on the metal ion release from porous titanium and cobalt‐chromium alloys

Abstract: Bone tissue ingrowth in porous materials is enhanced by the deposition of bioactive calcium phosphate ceramic linings onto the pore walls. These bioactive coatings can be deposited using several methods which yield a variety of coating efficiencies and thereby influence the mechanisms and kinetics of ion release from the metal. We analyzed the effect of plasma-spraying hydroxyapatite onto titanium and cobalt-chromium alloys by measuring the release of Ti, Al, V, Co, and Cr in vitro. Plasma-sprayed coatings significantly reduced the Ti and Al release from titanium-based alloy specimens. The tendencies of release from the cobalt-based specimens are less pronounced. The data substantiate that neither localized enhanced passive dissolution of metal ions nor ceramic shielding of the metal occurs. The Scanning Auger Electron Microprobe Spectroscopic data suggest that the dissipation of thermal and kinetic energy of the ceramic particle at the time of impact can produce compositional and structural changes in the metal surfaces. The resulting effects are significant for the titanium alloy but less significant for the Co-Cr alloy system.

Synthesis and characterization of metal-free and metal derivatives of a novel soluble crown-ether-containing phthalocyanine

Abstract: A straightforward and generalizable synthesis of metal-free and metal (Cu, Co, Ni, or Fe) derivatives of a symmetrically tetrasubstituted phthalocyanine derived from 15,16-dicyano-2,3,5,6,8,9,11,12-octahydro-benzo[1,4,7,10,13]pentaoxacyclopentadecine is described. The new compounds have been characterized by elemental analyses, and i.r., 1H n.m.r., u.v.–visible, and fast atom bombardment mass spectra. The alkali metal ions (sodium and potassium) bound to crown ether groups of the metal complexes force dimerization of the phthalocyanine units in solution as observed in the electronic spectra by the broadening of the Q-band transition at ca. 630 nm. The solubilities of the metal phthalocyaninates in chloroform were determined to be ca. 10–3 mol dm–3. The thermal stabilities of the compounds were determined by thermogravimetric and differential thermal analysis. The high affinity of the cobalt(II) derivative for the potassium ion was observed in solvent extraction experiments.

Anodic polarization and corrosion of cemented carbides with cobalt and nickel binders

Abstract: The polarization of pure cobalt, nickel and tungsten, and hardmetals based on WC/Co and WC/Ni, in a solution of 001 M H2SO4 + 099 M Na2SO4 (pH 255), has been investigated using potentiodynamic and metallographic techniques Pure cobalt dissolved rapidly, nickel had an excellent passivity, while tungsten had a high degree of passivity over the whole potential range up to 2O V (SCE) Extensive dissolution of WC was observed metallographically at potentials in the range 06 to 14V (SCE) The polarization of WC/Co hardmetals reflected mainly the behaviour of the binder phase modified by the presence of tungsten in the binder and passivating film The effects of the carbon in the binder are discussed in relation to the tungsten in the binder Tungsten carbide grain size, and the presence of TaC and TiC, had no noticeable effects Hardmetals with nickel binders had a superior performance compared with cobalt binders Chloride in the solution had a relatively small effect

Characterization of haze-forming precipitates in silicon

Abstract: The defects leading to haze formation after diffusion of the transition metals cobalt, nickel, copper, and palladium have been studied by means of transmission electron microscopy and preferential etching. In all cases crystalline metal silicide particles have been observed. Both cobalt and nickel form disilicide particles of different morphologies in the surface regions of silicon wafers, whereas copper and palladium form metal‐rich silicide particles causing a supersaturation of Si self‐interstitials or undersaturation of vacancies and leading to the formation of extrinsic dislocation loops.

Carbon dioxide activation: thermodynamics of CO2 binding and the involvement of two cobalt centers in the reduction of CO2 by a cobalt(I) macrocycle

Abstract: The interaction of CO/sub 2/ with the cobalt (I) macrocycle, CoL/sup +/ L = (14)diene = 5,7,7,12,14,14-hexamethyl-1,4,8,11-reversible binding of CO/sub 2/ to CoL/sup +/ in CH/sub 3/CN as characterized by uv-visible spectroscopy, a CO/sub 2/ reduction in the solid state, of a binuclear species containing the Co-C(OH)-O-Co moiety are described in this article 22 references, 2 figures

Catalyst for production of hydrocarbons

Abstract: A catalyst for converting synthesis gas composed of hydrogen and carbon monoxide to hydrocarbons. The catalyst includes cobalt in catalytically active amounts up to about 60 wt % of the catalyst, rhenium in amounts of about 0.5 to 50 wt % of the cobalt content of the catalyst and an alkali in amounts ranging from about 0.5 to 5 atom percent of the cobalt content of the catalyst, supported on alumina. A metal oxide promoter may be added.

Directional catalyst alloy sweep through process for preparing diamond compacts

Abstract: Disclosed is an improved method for making a polycrystalline diamond compact comprising subjecting a mass of diamond particles, which mass is adjacent a cemented metal carbide mass containing a catalyst, to a high pressure/high temperature process which results in a compact characterized by diamond-to-diamond bonding. The improvement in such process comprises placing a second catalyst source adjacent the diamond mass, said second catalyst having a melting point which is lower than the melting point of the catalyst of the carbide; and subjecting said mass to high pressure/high temperature sintering at a temperature above the melting point of the second catalyst, but below the melting point of the carbide catalyst, for causing said second catalyst to selectively diffuse through said mass for forming said polycrystalline diamond compact. The preferred catalyst is a mixture of cobalt and boron.

Charge-transfer satellites in the 2p core-level photoelectron spectra of heavy-transition-metal dihalides.

Abstract: We extend the charge-transfer model with the core-hole--3d-electron Coulomb attraction [van der Laan et al., Phys. Rev. B 23, 4369 (1981)] to the 2p core-level photoemission satellite structures of cobalt, iron, and manganese dihalides. This model was found to account for the positions and intensities of satellites and main peaks very well with reasonable values of parameters. These parameter values show the expected trends not only along the ligand series from fluorine to bromine but also along the transition-metal series from copper to manganese. This gives us confidence that the charge-transfer mechanism is responsible for the satellite structures in the 2p core-level photoemission spectra of heavy-transition-metal compounds, and that the screening response is important even for insulators in the presence of a core hole. It also suggests the core-level photoemission spectra, if properly understood, can be used to obtain parameters on the valence-electronic structures.

Electrochemistry of metalloporphyrins and viologens at zeolite Y-modified electrodes: evidence for electron trapping by monomolecular porphyrin layers

Abstract: Cyclic voltammetric data are presented for electrodes coated with zeolite Y powder containing porphyrins and viologens. Half-wave potentials for viologen cations (methylviologen, benzylviologen, or N,N'-(1,3-propenyl)-2,2'-bipyridinium) do not change significantly when they are exchanged into zeolite Y, whereas the reduction potentials for cobalt and zinc tetrakis(N-methyl-4-pyridyl)porphyrins shift (relative to aqueous solution) by + 200 mV. When a viologen cation is ion exchanged into the bulk of the zeolite, and cobalt tetrakis(N-methyl-4-pyridyl)porphyrin is adsorbed onto its outer surface in monolayer quantities, current rectification and charge trapping reactions are observed. The charge untrapping reactions are similar to those previously observed at redox polymer bilayer electrodes and are attributed to a kinetically fast cross reaction between double reduced viologens inside the zeolite and cobalt(II)porphyrin on the outer surface. Rotating disk experiments show that the porphyrin monolayer effectively seals up the zeolite against exchange of encapsulated viologens with solution-phase cations.