Showing papers on "Cobalt published in 1981"

Study of nickel-molybdenum-.gamma.-aluminum oxide catalysts by x-ray photoelectron and Raman spectroscopy. Comparison with cobalt-molybdenum-.gamma.-aluminum oxide catalysts

Abstract: Several series of nickel (or Co) molybdenum oxide catalysts supported on ..gamma..-Al/sub 2/O/sub 3/ have been studied by X-ray photoelectron and Raman spectroscopy. The combination of these two techniques is a complementary approach to the alumina coverage, the nature of the deposited species, and the interaction between these species. In particular, the characteristics of the monolayer coverage by the nickel species appear somewhat different from cobalt in systems without molybdenum. When molybdenum is present, formation of a phase similar to (a) NiMoO/sub 4/ is observed. No bulk NiO or Ni(OH)/sub 2/ phases are detected. Comparison with Co-Mo or Ni-Mo-..gamma..-Al/sub 2/O/sub 3/ industrial catalysts is also presented.

Adsorption of lead, copper, zinc, cobalt, and cadmium by soils that differ in cation-exchange materials

Abstract: Summary The adsorption of Zn2+, Pb2+, Cu2+, Co2+, and Cd2+ (M2+) by soils was measured at concentrations ranging from 10-7 to 10-2 M in 10-3 to 10-2 M CaCI2. Exchange between Ca2+ and M2+, and solubility products [M2+][OH−]2 indicate that M2+ is not precipitated as hydroxide but is adsorbed on cation-exchange sites. The proportion of selective adsorption sites with specified values of the selectivity coefficient calculated using Ca as reference ion, increased in the order montmorillonite 10 000. The formation of the coordination complexes of heavy metal with deprotonoted OH and COOH groups as ligands is suggested as a possible mechanism of selective adsorption.

Hydrogenation of carboxylic acids

Abstract: A process is provided for the vapor phase hydrogenation of carboxylic acids to yield their corresponding alcohols in the presence of steam and a catalyst comprising the mixed oxides of ruthenium, at least one of cobalt, nickel, and optionally one of cadmium, zinc, copper, iron, rhodium, palladium, osmium, iridium and platinum. A process is further provided for the preparation of carboxylic acid esters from carboxylic acids in the absence of steam utilizing the above-identified catalysts.

The toxicity of metals used in orthopaedic prostheses. An experimental study using cultured human synovial fibroblasts.

Abstract: Some of the component metals of the alloys used for total joint prostheses are toxic and dissolve in the body fluids. It is important to establish how toxic these metals are and to assess the risk of localised tissue necrosis around the prostheses. This has been investigated by incubating primary monolayer cultures of human synovial fibroblasts with various preparations of metals for periods up to 18 days. Morphological changes were evident after exposure to cobalt chloride at a concentration of 50 nanomoles per millilitre and to nickel chloride at 200 nanomoles per millilitre. Chromic chloride, ammonium molybdate and ferric chloride produced no changes up to 500 nanomoles per millilitre. Cultures exposed to particulate pure metals were poisoned by cobalt and vanadium but were not affected under the same conditions by nickel, chromium, molybdenum, titanium or aluminium. Particulate cobalt and vanadium were probably toxic due to their relatively high solubility (four and one micromoles per millilitre respectively after seven days incubation). Particulate nickel also dissolved (three nanomoles per millilitre after seven days) but not in sufficient quantities to be toxic. It appears, therefore, that potentially the most harmful components are cobalt from cobalt-chromium alloy, nickel from stainless steel, and vanadium from titanium alloy. As far as can be estimated, the only combination of materials which is likely to give rise to toxic levels of metal under clinical conditions, is cobalt-chromium alloy articulating against itself to produce relatively high levels of cobalt.

Mechanism of the Electrodeposition of Zinc Alloys Containing a Small Amount of Cobalt

Abstract: Corrosion resistant Zn‐Co alloys were electrodeposited on the steel sheet cathode from an acid galvanizing bath containing a small amount of cobalt sulfate. Under most of the plating conditions studied, the anomalous codeposition and, hence, the preferential deposition of electrochemically less noble Zn occurred. The electrodeposition process of the alloy including the Zn hydroxide formation resulting from the rise in pH in the vicinity of the cathode was estimated by electrochemical and spectroscopic studies.

Activation of Molecular Oxygen: Kinetic Studies of the Oxidation of Hindered Phenols with Cobalt-Dioxygen Complexes.

Abstract: : Mechanistic studies of the oxidation of various substituted phenols by Co(II) bis(salicylidene-gamma-iminopropyl)methylamine, CoSMDPT are reported. The reaction is first order in (O2), (substrate) and (Co). A series of experiments are reported to provide strong support for a mechanistic scheme that involves reaction of coordinated dioxygen. Coordination of O2 to this cobalt(II) complex enhances the ability of the dioxygen to abstract hydrogen atoms and to react with phenoxy radicals. The mechanism provides a rationale for the influence of several variables on the reaction and suggests steps that were taken to retard catalyst deactivation. (Author)

Effects of Nickel, Cobalt, and Molybdenum on Performance of Methanogenic Fixed-Film Reactors

Abstract: The conversion of acetic acid to methane and carbon dioxide by a mixed methanogenic population from an anaerobic fixed-film digestor was stimulated by the addition of nickel (100 nM) and cobalt (50 nM) and especially by the addition of these elements in combination. Molybdenum addition (50 nM) was only slightly stimulatory when added in combination with both nickel and cobalt. The addition of these trace metals to anaerobic fixed-film digestors, which treat food processing waste, greatly enhanced reactor performance. Total gas and methane productions were increased 42%, greater volumes of waste could be effectively treated, and reactor residence time was shortened. However, the lag period for reactor start-up was not reduced. Tests showed that reactor performance was increased because trace nutrient addition allowed accumulation of a thicker methanogenic fixed film.

Spectral studies of cobalt (II)- and Nickel (II)-metallothionein.

Abstract: The zinc and cadmium of native rabbit metallothionein-1 were replaced stoichiometrically with either cobalt (II) or nickel (II). The electronic, magnetic circular dichroic (MCD), and electron spin resonance spectra of Co (II)-metallothionein reflect distorted tetrahedral coordination of the cobalt atoms. Both the d-d and charge-transfer spectral regions closely resemble those of simple cobalt-tetrathiolate complexes, implying that their coordination chemistry is analogous. Ni (II) complex ions and Ni (II)-metallothionein similarly exhibit analogous MCD bands in the d-d region. The circular dichroic bands associated with ligand-metal charge-transfer transitions in the non-d-d region of Co (II)- and Ni (II)-metallothionein afford additional evidence for the similarity in tetrahedral microsymmetry of the two metal derivatives. The known ratio of 20 thiolate ligands to 7 metal ions, in conjunction with the spectral evidence for tetrathiolate coordination in metallothionein, represents good evidence that these metal thiolates are organized in clusters.

Impact of fossil fuel combustion on the sediments of Lake Michigan.

Abstract: A study was conducted to determine the relationships between metal and mineral contents of the Lake Michigan sediments and fluxes of charcoal, whose morphologies and surface characteristics are indicative of different combustion processes. Sediments deposited during 1930-1968 showed increasing concentrations of chromium, nickel, iron, aluminum, zinc, cobalt, lead, cadamium, and copper. After 1968, these concentrations decreased slightly. A similar profile was found for total charcoal concentration.

Ion beam studies of the reactions of atomic cobalt ions with alkanes: determination of metal-hydrogen and metal-carbon bond energies and an examination of the mechanism by which transition metals cleave carbon-carbon bonds

Abstract: An ion beam apparatus is employed to study the reactions of singly charged cobalt positive ions with hydrogen and 17 alkanes. Reaction cross sections and product distributions as a function of kinetic energy are determined. Exothermic carbon-carbon bond cleavage reactions are observed for all alkanes but methane and ethane. A mechanism involving oxidative addition of C-C and C-H bonds to cobalt as a first step is demonstrated to account for all major reactions at all energies. Interpretation of several endothermic processes allows the extraction of thermochemical data. The bond dissociation energies obtained are D/sup 0/(Co/sup +/-H) = 52 +- 4 kcal/mol, D/sup 0/(Co-H) = 39 +- 6 kcal/mol, D/sup 0/(Co/sup +/-CH/sub 3/) = 61 +- 4 kcal/mol, and D/sup 0/(Co-CH/sub 3/) = 41 +- 10 kcal/mol.

Magnetic and transport properties of granular cobalt films

Abstract: Simultaneous magnetization and magnetoresistance measurements have yielded the magnetic phase diagram of the granular Co-Si${\mathrm{O}}_{2}$ system. The superparamagnetic-to-ferromagnetic transition temperature changes gradually with composition from \ensuremath{\sim}80 K at 20 vol% Co to \ensuremath{\sim}280 K at 43 vol% Co. The results confirm the theory of spindependent tunneling in granular magnetic metals and yield the value of $JP=(1.0\ifmmode\pm\else\textpm\fi{}0.3)$ meV. Here $P$ is the spin polarization of the tunneling electrons and $J$ their exchange-coupling constant. This quantity has not been measured previously for cobalt. A quantitative comparison shows that the molecular-field theory does not provide an adequate description of the magnetization of granular cobalt.

Cobalt silicide metallization for semiconductor integrated circuits

Abstract: In order to form MOSFET structures, a cobalt layer (16) is deposited and sintered, at about 400° C. to 500° C., on a patterned semiconductor wafer having exposed polycrystalline (14) or monocrystalline (11) silicon portions, as well as exposed oxide (15 or 25) portions. The cobalt reacts with exposed surfaces of the silicon portions and forms thereat such compounds as cobalt monosilicide (CoSi) or di-cobalt silicide (C02 Si), or a mixture of both. The unreacted cobalt is selectively removed, as by selective etching in a suitable acid bath. A heat treatment at about 700° C. or more, preferably in an oxidizing ambient which contains typically about 2 percent oxygen, converts the cobalt compound(s) into relatively stable cobalt disilicide (CoSi2). Subsequently, deposition of an in situ doped layer (33) of polycrystalline silicon (polysilicon) on the cobalt disilicide contacting the monocrystalline silicon portions--followed by gettering, deposition of a layer (34) of aluminum, and standard etch-patterning of the aluminum and polysilicon layers--completes the metallization of the desired MOSFET structures on the silicon wafer.

The oxidation of cobalt in air from room temperature to 467°C

Abstract: The oxidation of cobalt in air is investigated for times ranging over three orders of magnitude up to 1000 hr and for temperatures ranging from room temperature up to 467°C. Three different growth processes are observed. When a clean surface is exposed to air at room temperature, an 8–10 Afilm of Co(OH)2forms in seconds or less. For temperatures of 50–100°C, very little additional film forms for times up to 1000 hr. For temperatures of 100–225°C, a film of CoO grows in a manner which can be described empirically with a fourth root rate law with an activated rate constant. Between 225 and 325°C there is a transition to a quadratic rate law. At 425°C the film appears to be a mixture of CoO and Co3O4.

Energy levels of cobalt, Co I through Co XXVII

Abstract: The energy levels of the cobalt atom in all of its stages of ionization, derived from analyses of atomic spectra, have been critically compiled. In cases where only line classifications are reported in the literature, level values have derived. Electron configurations, term designations, J‐values, experimental g‐values, leading percentages and ionization energies are included.