Showing papers on "Cobalt published in 1986"

Cobalt-catalyzed evolution of molecular hydrogen

Abstract: Solutions of chromium(II), europium(II), or vanadium(II) chloride in hydrochloric acid evolve molecular hydrogen rapidly in the presence of trace concentrations of the cobalt(II) macrocycle Co(dmgBF/sub 2/)/sub 2/. The stoichiometry for Cr(II) corresponds to the net reaction Cr/sup 2 +/ + Cl/sup -/ + H/sup +/ = CrCl/sup 2 +/ + 1/2H/sub 2/. The kinetics are described quite adequately by the Michaelis-Menton scheme. Kinetic studies of the reaction were during the pre-steady-state phase, during which an intensely absorbing intermediate forms, and also at longer times during the steady-state phase when the pseudo-steady-state concentration of the intermediate slowly declined as the substrate was consumed. Arguments are given in support of the intermediate being ((H/sub 2/O)/sub 5/Cr-Cl-Co(dmgFB/sub 2/)/sub 2/)..mu... Its dissociation leads, in acidic solution, to the hydridocobalt complex HCo(dmgBF/sub 2/)/sub 2/, which is responsible for H/sub 2/ formation. Bromide ions, but not perchlorate, also give catalytic H/sub 2/ production, whereas iodide forms a ternary complex that does not decompose. 27 references, 8 figures, 1 table.

Photogeneration of Carbon Monoxide and of Hydrogen via Simultaneous Photochemical Reduction of Carbon Dioxide and Water by Visible‐Light Irradiation of Organic Solutions Containing Tris(2,2′‐bipyridine)ruthenium(II) and Cobalt(II) Species as Homogeneous Catalysts

Abstract: CO and H2 are photogenerated simultaneously by visible-light irradiation of systems containing a photosensitizer, the [Ru(bpy)3]2+ complex, Co(II) species as homogeneous catalysts, which mediate CO2 and H2O reduction by intermediate formation of Co(I), a tertiary amine as electron donor, which provides the electrons for the reduction, and an organic solvent which also facilitates dissolution of CO2. The efficiency of (CO + H2) gas production and the selectivity CO/H2 markedly depend upon the composition of the medium, the nature of the tertiary amine, the solvent, and the ligand of the Co ions. 2,9-Dimethyl-1,10-phenanthroline is particularly effective in promoting CO and H2 formation, giving a quantum yield of 7.7% in (CO + H2) (1.2% for CO and 6.5% for H2). The process consists of two catalytic cycles: a photocatalytic cycle for the Ru complex and a double dark reaction pathway for the Co species; oxidative and/or reductive quenching of the excited state of the photosensitizer lead to the formation of Co(I) species which reduce either CO2 or H2O to CO or H2, respectively.

Marine cobalt resources.

Abstract: Ferromanganese oxides in the open oceans are more enriched in cobalt than any other widely distributed sediments or rocks. Concentrations of cobalt exceed 1 percent in ferromanganese crusts on seamounts, ocean ridges, and other raised areas of the ocean. The cobaltrich crusts may be the slowest growing of any earth material, accumulating one molecular layer every 1 to 3 months. Attention has been drawn to crusts as potential resources because they contain cobalt, manganese, and platinum, three of the four priority strategic metals for the United States. Moreover, unlike abyssal nodules, whose recovery is complicated by their dominant location in international waters, some of the most cobalt-rich crusts occur within the exclusive economic zone of the United States and other nations. Environmental impact statements for crust exploitation are under current development by the Department of the Interior.

Cobalt(II) chelates as chain transfer agents in free radical polymerizations

Abstract: Free radical polymerization processes employing cobalt(II) chelates of vicinal iminohydroxyimino compounds, diazadihydroxyiminodialkyldecadienes and -undecadienes, tetraazatetraalkylcyclotetradecatetraenes and -dodecatetraenes, N,N'-bis(salicylidene)ethylenediamines and dialkyldiazadioxodialkyldodecadienes and -tridecadienes as catalytic chain transfer agents for controlling the molecular weight of the homopolymers and copolymers produced.

Mixed alcohols production from syngas

Abstract: Mixed alcohols are produced from carbon monoxide and hydrogen gases using an easily prepared catalyst/co-catalyst metal catalyst. The catalyst metals are molybdenum, tungsten or rhenium. The co-catalyst metals are cobalt, nickel or iron. The catalyst is promoted with a Fischer-Tropsch promoter like an alkali or alkaline earth series metal or a smaller amount of thorium and is further treated by sulfiding. The composition of the mixed alcohols fraction can be selected by selecting the extent of intimate contact among the catalytic components.

Sorption and desorption of cobalt by soils and soil components

Abstract: SUMMARY The sorption of Co by individual soil components was studied at solution Co concentrations that were within the range found in natural soil solutions. Soil-derived oxide materials sorbed by far the greatest amounts of Co although substantial amounts were also sorbed by organic materials (humic and fulvic acids). Clay minerals and non-pedogenic iron and manganese oxides sorbed relatively little Co. It is considered that clay minerals are unlikely to have a significant influence on the sorption of Co by whole soils. Cobalt sorbed by soil oxide material was not readily desorbed back into solution and, in addition, rapidly became non-isotopically exchangeable with solution Co. In contrast, Co was relatively easily desorbed from humic acid and a large proportion of the Co sorbed by humic acid remained isotopically exchangeable. Cobalt sorbed by montmorillonite was more easily desorbed than that sorbed by soil oxide but less easily than that sorbed by humic acid. Cobalt sorption isotherms for whole soils at low site coverage were essentially linear and the gradients of isotherms increased with pH. A comparison of isotherm gradients for whole soils and individual soil components supported the suggestion that Co sorption in whole soils is largely controlled by soil oxide materials.

A self‐aligned cobalt silicide technology using rapid thermal processing

Abstract: The feasibility of a self‐aligned silicide technology based upon cobalt has been investigated. Silicidation reactions were performed by means of rapid thermal processing. Phase sequence, layer morphology, and reaction kinetics were studied by XRD, SEM, RBS, AES, and TEM. Extremely smooth, highly conductive (16 μΩ cm) CoSi2 films were formed by direct reaction of Co on Si, without significant lateral silicide formation at oxide edges. Shallow arsenic junctions were successfully silicided and low contact resistances were obtained on n+ and p+ Si.

Quantitative microanalysis of carbide/carbide interfaces in WC–Co-base cemented carbides

Abstract: Carbide/carbide boundaries in WC–Co-base cemented carbides containing 6–20 wt-%Co were studied with two high resolution microanalytical techniques: atom probe field ion microscopy and analytical transmission electron microscopy. All boundaries studied, i.e. WC/WC boundaries and, in materials containing cubic carbides (γ-phase), WC/γ and γ/γ boundaries, were found to contain about half a monolayer of cobalt, localized to a zone of monolayer thickness. The carbide/carbide boundaries may thus be described as grain (phase) boundaries to which cobalt has segregated. The carbide skeleton model for WC–Co is thereby confirmed. In WC–Co materials which contain Cr3C2 as a grain growth inhibitor, chromium segregates to WC grain boundaries.MST/354

Synthesis, stereochemistry, and oxygenation of cobalt(II)-pyridoxal model complexes. A new family of chiral dioxygen carriers

Abstract: Preparation de complexes Co(Sal-L-aa) et Co(pdx-L-aa) (aa=ala, Val, phe, his). Ils peuvent fixer O 2 ; les derives d'histidine reagissent rapidement sans solvant, ceux d'aminoacides a chaines laterales non polaires necessitent la presence de molecules basiques supplementaires

Coloured coatings prepared by the sol-gel process

Abstract: Homogeneous clear transparent coloured coatings can be produced by using sol-gel processes. Transition metal elements are incorporated into the glass network as ions showing a certain valence and coordination. The oxidation-reduction equilibrium moves towards the oxidized state in these low temperature glassy films. It was found that cobalt exists as Co 2+ in tetrahedral coordination, chromium as Cr 6+ in tetrahedral symmetry and manganese as Mn 3+ in octahedral coordination. Crystalline segregations of Co 3 O 4 , Mn 2 O 3 , CuO and Cr 2 O 3 were also observed. The spectra for iron and copper coatings change with coating thickness. Both light scattering and absorption mechanism exist. These thin coating films give absorption colours which are too weak for application. Only colours due to light scattering (manganese, iron and copper ruby) were effective.

Cobalt-catalyzed one-step assembly of B-ring aromatic steroids from acyclic precursors

Abstract: Because of their varied physiological activity, steroids are important testing grounds on which to explore the utility of novel synthetic methodology In this study cobalt, in the form of CpCo(CO)/sub 2/ is used as a matrix around which to assemble natural and unnatural polycyclic products, including the steroid nucleus In this way, the total synthesis of A-ring aromatic systems of the estrone type was achieved via the D --> ABCD and A --> ABCD strategies An approach is reported here in which all four rings are assembled (0 --> ABCD) in one step to give B-ring aromatic derivatives with complete control of the crucial stereochemistry of the C,D-ring juncture This strategy has been accomplished previously only by employing biomimetic cyclizations and not en route to the rate target class of compounds which has never been constructed by total synthesis 13 references, 1 table

Kinetics of hydrodesulfurization on a cobalt-molybdenum/.gamma.-alumina catalyst. 1. Kinetics of the hydrogenolysis of thiophene

Abstract: The hydrogenolysis of thiophene on a commercial hydrodesulfurization CoMo/..gamma..-Al/sub 2/O/sub 3/ catalyst was studied in a bench-scale tubular reactor. The experimental conditions were varied over the following range: total pressure, 2-30 bar; temperature, 533-623 K; molar hydrogen to hydrocarbon ratios, 4-9. The experimental rate data were described by a set of Hougen-Watson rate equations for both the hydrogenolysis of thiophene into butene and the hydrogenation of butene into butane. The surface reactions between thiophene or butene and competitively adsorbed hydrogen were found to be the rate-determining step. Models with active site concentrations determined by the gas-phase conditions were also derived and comparisons were made with the data.

Respiratory diseases in hard metal workers: an occupational hygiene study in a factory.

Abstract: A hygiene study of a hard metal factory was conducted from 1981 to 1984. All workers exposed to hard metal were medically examined and their exposure to cobalt measured. Eighteen employees had occupational asthma related to exposure to hard metal, a prevalence rate of 5.6%. Nine had a positive bronchial provocation test to cobalt and reactions of the immediate, late, or dual type were elicited. Exposure measurements suggest that asthma may be caused by cobalt at a mean time weighted average concentration below 0.05 mg/m3. Only two of the nine individuals with cobalt asthma had a positive patch test to cobalt. Chest radiographs of three workers showed diffuse shadows of category 1 or over. X ray microanalysis of lung biopsy specimens from two of these three workers showed the presence of tungsten, titanium, cobalt, nickel, and some minerals. One of the two was diagnosed as having pneumoconiosis due to exposure to silica in a steel industry and the other was suspected of having pulmonary fibrosis caused by dust generated from the carborundum wheels used to grind hard metal. There were no cases with interstitial pneumonitis in the factory.

Novel cobalt(II)-catalyzed oxidative cleavage of a carbon-carbon double bond

Abstract: Oxydation de l'isoeugenol en presence de [bis (salicylideneamino-3 propyl) methyl amine] cobalt(II)

Mechanisms of transition metal interferences in hydride generation atomic absorption spectrometry. Part 4. Influence of acid and tetrahydroborate concentrations on interferences in arsenic and selenium determinations

Abstract: An increase in the hydrochloric acid concentration from 0.5 to 5 mol l–1 improves the range of interference-free determination for arsenic and selenium in the presence of cobalt, copper or nickel by factors of 5–100. Decreasing the sodium tetrahydroborate(III) concentration from 3 to 0.5%m/V increases the range of interference-free determination for both elements further by factors of 4–50. The only exception is the interference of copper on selenium, which is slightly more pronounced with the less concentrated tetrahydroborate(III) solution. The proposed mechanism is that both in higher acid and with lower tetrahydroborate(III) concentrations the interferent is reduced to a lesser extent to the metal (the interfering species) owing to (i) better solubility of the metal in the more concentrated acid, (ii) the formation of chloro complexes, thus reducing the concentration of free ions, and (iii) a larger percentage of the tetrahydroborate(III) being consumed by the acid. Copper, however, interferes with selenium in the ionic form.