Showing papers on "Cobalt 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.

Relation between metal electronic structure and morphology of metal compounds inside carbon nanotubes

Abstract: SEVERAL attempts have been made to fill carbon nanotubes1 with metals or metallic compounds to obtain nanocomposite materials with potentially interesting properties. Capillary action, predicted2 to be a filling mechanism, has been used3'4 to encapsulate lead and bismuth in open tubes. Compounds of yttrium5, manganese6 and gadolinium7 have also been encapsulated by formation of the nano-tubes in an arc discharge with the metals present in situ. Very recently, Tsang et al.8 showed that oxides of nickel, cobalt, iron and uranium can be encapsulated by opening the tubes and deposit-ing the filling material using wet chemical techniques. Here we report a search for general principles relating to the nature and structure of the filling material, using the arc-discharge method to fill tubes with fifteen metals and/or their compounds: Ti, Cr, Fe, Co, Ni, Cu, Zn, Mo, Pd, Sn, Ta, W, Gd, Dy and Yb. We find that the propensity for forming continuous 'nanowires' throughout the length of the tubes seems to be strongly correlated with the existence of an incomplete electronic shell in the most stable ionic state of the metal. We also find that the interplay between growth of the nanotube and growth of the filling results, in one case, in the formation of an unusual helical filling morphology.

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.

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.

Effects of cobalt on plants

Abstract: Cobalt, a transition element, is an essential component of several enzymes and co-enzymes. It has been shown to affect growth and metabolism of plants, in different degrees, depending on the concentration and status of cobalt in rhizosphere and soil. Cobalt interacts with other elements to form complexes. The cytotoxic and phytotoxic activities of cobalt and its compounds depend on the physico-chemical properties of these complexes, including their electronic structure, ion parameters (charge-size relations) and coordination. Thus, the competitive absorption and mutual activation of associated metals influence the action of cobalt on various phytochemical reactions. The distribution of cobalt in plants is entirely species-dependent. The uptake is controlled by different mechanisms in different species. Biosorption involves ion-exchange mechanism in algae, but in fungi both metabolism-independent and -dependent processes are operative. Physical conditions like salinity, temperature, pH of the medium, and presence of other metals influence the process of uptake and accumulation in algae, fungi, and mosses. Toxic concentrations inhibit active ion transport. In higher plants, absorption of Co2+ by roots involves active transport. Transport through the cortical cells is operated by both passive diffusion and active process. In the xylem, the metal is mainly transported by the transpirational flow. Distribution through the sieve tubes is acropetal by complexing with organic compounds. The lower mobility of Co2+ in plants restricts its transport to leaves from stems. Cobalt is not found at the active site of any respiratory chain enzymes. Two sites of action of Co2+ are found in mitochondrial respiration since it induces different responses toward different substrates like α-keto glutarate and succinate. In lower organisms, Co2+ inhibits tetraphyrrole biosynthesis, but in higher plants it probably participates in chlorophyll b formation. Exogenously added metal causes morphological damage in plastids and changes in the chlorophyll contents. It also inhibits starch grain differentiation and alters the structure and number of chloroplasts per unit area of leaf. The role of cobalt in photosynthesis is controversial. Its toxic effect takes place by inhibition of PS2 activity and hence Hill reaction. It inhibits either the reaction centre or component of PS2 acceptor by modifying secondary quinone electron acceptor Qb site. Co2+ reduces the export of photoassimilates and dark fixation of CO2. In C4 and CAM plants, it hinders fixation of CO2 by inhibiting the activity of enzymes involved. Cobalt acts as a preprophase poison and thus retards the process of karyokinesis and cytokinesis. The action of cobalt on plant cells is mainly turbagenic. Cobalt compounds act on the mitotic spindle, leading to the formation of chromatin bridges, fragmentation, and sticky bridges at anaphase and binucleate cells. High concentrations of cobalt hamper RNA synthesis, and decrease the amounts of the DNA and RNA probably by modifying the activity of a large number of endo- and exonucleases. The mutagenic action of cobalt salts results in mitochondrial respiratory deficiency in yeasts. In cytokinesis-deficient mutant of Chlamydomonas it increases the amount of sulfhydryl compounds. Cobalt has been shown to alter the sex of plants like Cannabis sativa, Lemna acquinoclatis, and melon cultivars. It decreases the photoreversible absorbance of phytochrome in pea epicotyl and interferes with heme biosynthesis in fungi. Low concentration of Co2+ in medium stimulates growth from simple algae to complex higher plants. Relatively higher concentrations are toxic. A similar relationship is seen with crop yield when the metal is used in the form of fertilizer, pre-seeding, and pre-sowing chemicals. Toxic effect of cobalt on morphology include leaf fall, inhibition of greening, discolored veins, premature leaf closure, and reduced shoot weight. Being a component of vitamin B12 and cobamide coenzyme, Co2+ helps in the fixation of molecular nitrogen in root nodules of leguminous plants. But in cyanobacteria, CoCl2 inhibits the formation of heterocyst, ammonia uptake, and nitrate reductase activity. The interaction of cobalt with other metals mainly depends on the concentration of the metals used. For example, high levels of Co2+ induce iron deficiency in plants and suppress uptake of Cd by roots. It also interacts synergistically with Zn, Cr, and Sn. Ni overcomes the inhibitory effect of cobalt on protonemal growth of moss, thus indicating an antagonistic relationship. The beneficial effects of cobalt include retardation of senescence of leaf, increase in drought resistance in seeds, regulation of alkaloid accumulation in medicinal plants, and inhibition of ethylene biosynthesis. In lower plants, cobalt tolerance involves a cotolerance mechanism. The mechanism of resistance to toxic concentration of cobalt may be due to intracellular detoxification rather than defective transport. In higher plants, only a few advanced copper-tolerant families showed cotolerance to Co2+. Tolerance toward Co2+ may sometimes determine the taxonomic shifting of several members of Nyssaceae. Due to the high cobalt content in serpentine soil, essential element uptake by plants is reduced, a phenomenon known as “serpentine problem,” for New Caledonian families like Flacourtiaceae. Large amounts of calcium in soil may compensate for the toxic effects of heavy metals in adaptable genera grown in this type of soil. The biomagnification of potentially toxic elements, such as cobalt from coal ash or water into food webs, needs additional study for effective biological filtering.

Method for producing an unsaturated carboxylic acid

Abstract: A method for producing an unsaturated carboxylic acid, which comprises subjecting an alkane to a vapor phase catalytic oxidation reaction in the presence of a catalyst containing a mixed metal oxide comprising, as essential components, Mo, V, Te, O and X wherein X is at least one element selected from the group consisting of niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium and cerium, wherein the proportions of the respective essential components, based on the total amount of the essential components exclusive of oxygen, satisfy the following formulas: 0.25

Radical superexchange in semiquinone complexes containing diamagnetic metal ions. 3,6-Di-tert-butyl-1,2-semiquinonate complexes of zinc(II), cobalt(III), gallium(III), and aluminum(III)

Abstract: The tris(3,6-di-tert-butylsemiquinonato)gallium(III), -aluminum(III), and -cobalt(III) complexes have been studied structurally, spectrally, and magnetically. Complexes of the three diamagnetic metals have octahedral structures of D 3 symmetry (Ga(3,6-DBSQ) 3 , monoclinic, C2/c, a=22.069(6) A, b=19.365(5) A, c=10.163(3) A, β=94.90(2) o , V=4327(2) A 3 , Z=4; Co(3,6-DBSQ) 3 , monoclinic, C2/c, a=21.799(6) A, b=19.376(8) A, c=10.167(3) A, β=94.99(3) o , V=4278(3) A 3 , Z=4

Structure of a linear unsymmetrical trinuclear cobalt(II) complex with a localized COII–COII bond: dichlorotetrakis[µ3-bis(2-pyridyl)amido]tricobalt(II)

Abstract: The synthesis and X-ray crystal structure of a linear unsymmetrical trinuclear cobalt(II) complex with a syn–syn bis(2-pyridyl)amido ligand, possessing a short, localized CoII–CoII bond and a spin crossover square-pyramidal CoII ion, is described.

Selectivity and mechanism of Fischer-Tropsch synthesis with iron and cobalt catalysts

Abstract: The Fischer-Tropsch CO-hydrogenation has been comparatively performed on iron and cobalt in a gradientless tank reactor. Kinetic coefficients of elementary reactions and their dependence on pH 2 , Pco' ph 20 and T were determined with the help of a model for chain growth-, branching- and termination reactions. Changes of reaction rates of CO consumption, of methane formation, of chain propagation and chain branching are presented and discussed in terms of elemental surface reactions and characteristics of the catalyst base metals.

Zeolite encapsulated cobalt(II) and copper(II) perfluorophthalocyanines. Synthesis and characterization

Abstract: Synthetic faujasite type zeolites have been modified with cobalt(II) and copper(II) hexadecafluorophthalocyanines (MF 16 Pc) by synthesizing zeolite NaX around the MF 16 Pc complexes and by the template synthesis of the complexes inside NaY zeolites ion exchanged with Co 2+ and Cu 2+ . Mid FT-IR and UV-vis spectroscopy as well as X-ray powder diffraction and elemental analysis provide evidence for the encapsulation of the MF 16 Pc complexes inside the zeolites. The redox properties of the intrazeolite metal complexes were investigated by cyclic voltammetry

Catalytic Synthesis of Single-Layer Carbon Nanotubes with a Wide Range of Diameters

Abstract: We have synthesized single-layer carbon nanotubes by co-vaporizing cobalt with carbon in an arc fullerene generator and have identified conditions that lead to high yields. The diameter distribution of the tubes and their morphologies are studied using transmission electron microscopy. For nanotubes produced using cobalt and carbon, the tube diameters range from 1 to 2 nm with distribution peaks at 1.3 and 1.5 nm. When sulfur is added to the carbon and cobalt, production of single-layer nanotubes is enhanced and the tubes have a wider range of diameters (from 1 to 6 nm). The diameter distribution for these nanotubes shows prominent peaks at 1.3 and 1.5 nm and additional maxima at 2.7 and 3.6 nm. Cobalt-containing crystallites, some encapsulated in graphitic polyhedra, are produced with the nanotubes and are found in the soot away from the cathode.

Collision‐induced dissociation of Co+n (n=2–18) with Xe: Bond energies of cationic and neutral cobalt clusters, dissociation pathways, and structures

Abstract: The kinetic energy dependence of collision‐induced dissociation (CID) of Co+n (n=2–18) with xenon is studied by using a guided ion beam mass spectrometer. Examination of the general dissociation behavior over a broad collision energy range shows that cobalt cluster cations dissociate exclusively by loss of single atoms (cluster ‘‘evaporation’’), with no evidence found for elimination of molecular cluster fragments. Bond dissociation energies for cobalt cluster cations, Co+n (n=2–18), are determined from measurements of the CID thresholds. Bond energies for neutral cobalt clusters, Con (n=4–18), are derived by combining these cationic bond energies with ionization energies for Con from the literature. The dependence of binding energy on cluster size is similar to that observed for iron clusters, and inspires some speculation regarding cluster ion structures.

Oxidation induced lifetime limits of thin walled, iron based, alumina forming, oxide dispersion strengthened alloy components

Abstract: The long term oxidation resistance of most high temperature alloys depends on the ability to form protective alumina or chromia surface scales during service. Scale growth and scale rehealing after spalling leads to depletion of the scale forming element, aluminium or chromium, in the bulk alloy. If the concentration of this element decreases below a critical level, oxidation of the base elements, e.g. iron, nickel, or cobalt, occurs leading to catastrophic oxidation and destruction of the metallic component. Using iron based, alumina forming, oxide dispersion strengthened alloys as an example, a model is presented which allows the calculation of the time at which the catastrophic breakaway oxidation for a given component occurs. The calculated data are presented as oxidation diagrams in which the time to breakaway is plotted as a function of component wall thickness. Experimental data for the oxidation of the oxide dispersion strengthened alloys MA 956, PM 2000 and ODM 751 in air in the temperat...

ESR Study of Cobalt(II) Tetrakis(N-methyl-4-pyridiniumyl)porphyrin and Cobalt(II) Tetrasulfophthalocyanine Intercalated in Layered Aluminosilicates and a Layered Double Hydroxide

Abstract: The orientation, hydration state, and electronic properties of Co(II) tetrakis(N-methyl-4-pyridiniumyl)porphyrin (CoTMPyP) cation and Co(II) tetrasulphophthalocyanine (CoPcTs) anion, intercalated in crystalline negatively charged layered aluminosilicates and positively charged layered double hydroxide (LDH), respectively, were studied in the presence and absence of water by electron spin resonance (ESR), electron absorption spectroscopy, and X-ray diffraction (XRD). When intercalated on the low charge density clay hectorite, CoTMPyP orients with the plane of the porphyrin parallel to the clay layers. The g tensors, in both the wet and dry states (g∥=1.88, g⊥=3.10), are indicative of CoTMPyP interacting with charge-deficient siloxane oxygens on the hectorite surface and having no water in axial coordination sites

Importance of cobalt for individual trophic groups in an anaerobic methanol-degrading consortium.

Abstract: Methanol is an important anaerobic substrate in industrial wastewater treatment and the natural environment. Previous studies indicate that cobalt greatly stimulates methane formation during anaerobic treatment of methanolic wastewaters. To evaluate the effect of cobalt in a mixed culture, a sludge with low background levels of cobalt was cultivated in an upflow anaerobic sludge blanket reactor. Specific inhibitors in batch assays were then utilized to study the effect of cobalt on the growth rate and activity of different microorganisms involved in the anaerobic degradation of methanol. Only methylotrophic methanogens and acetogens were stimulated by cobalt additions, while the other trophic groups utilizing downstream intermediates, H2-CO2 or acetate, were largely unaffected. The optimal concentration of cobalt for the growth and activity of methanol-utilizing methanogens and acetogens was 0.05 mg liter-1. The higher requirement of cobalt is presumably due to the previously reported production of unique corrinoid-containing enzymes (or coenzymes) by direct utilizers of methanol. This distinctly high requirement of cobalt by methylotrophs should be considered during methanolic wastewater treatment. Methylotroph methanogens presented a 60-fold-higher affinity for methanol than acetogens. This result in combination with the fact that acetogens grow slightly faster than methanogens under optimal cobalt conditions indicates that acetogens can outcompete methanogens only when reactor methanol and cobalt concentrations are high, provided enough inorganic carbon is available.

Magnetic properties of microemulsion synthesized cobalt fine particles

Abstract: Two microemulsion systems, the ternary system H2O/AOT/isooctane and the binary system DDAB/toluene, were used to prepare metallic cobalt particles by borohydride reduction of a cobalt salt. The particles prepared in the AOT system were extremely small and superparamagnetic with magnetic moment per particle of 11.5μB, a blocking temperature of 2 K, and σs=146 emu/g at 1.7 K. The magnetic moment and σs combined imply a particle size of about 5.4 A. However, the particles made in the DDAB system were relatively large, ∼10 nm. They were ferromagnetic at room temperature but with no coercivity.

Catalytic decomposition of nitrous oxide on “in situ” generated thermally calcined hydrotalcites

Abstract: Catalytic decomposition of nitrous oxide to nitrogen and oxygen has been carried out on “in situ” generated thermally calcined hydrotalcites of the general formula MAlCO3HT, where M stand for Ni, Co and Cu, in the temperature range 140–310°C at 50 Torr (1 Torr=133.3 Pa) initial pressure of the gas. All the catalysts showed first-order dependence on nitrous oxide without any inhibition by oxygen. Among the catalysts studied, NiAlCO3HT was the most active, followed by the cobalt and copper catalysts. These catalysts are more active in comparison with earlier reported Cu-ZSM-5, Co-ZSM-5 and Rh-ZSM-5 catalysts based on their conversion for the decomposition. The enhanced activity can be attributed to non-stoichiometry and dispersion of the active mixed metal oxides. Prior to the kinetic runs, the catalytic precursors were characterised by X-ray diffraction, thermogravimetry-differential scanning calorimetry measurements, IR, transmission electron microscopy and nitrogen adsorption measurements.

Metal filaments for electromagnetic interference shielding

Abstract: A material including filaments, which include a metal and an essentially coaxial core, each filament having a diameter less than 6 μm, each core being essentially carbon, displays high effectiveness for shielding electromagnetic interference (EMI) when dispersed in a matrix to form a composite material. This matrix is selected from the group consisting of polymers, ceramics and polymer-ceramic combinations. This metal is selected from the group consisting of nickel, copper, cobalt, silver, gold, tin, zinc, nickel-based alloys, copper-based alloys, cobalt-based alloys, silver-based alloys, gold-based alloys, tin-based alloys and zinc-based alloys. The incorporation of 7 percent volume of this material in a matrix that is incapable of EMI shielding results in a composite that is substantially equal to copper in EMI shielding effectiveness at 1-2 GHz.

The Synthesis and Structure of Encapsulating Ligands: Properties of Bicyclic Hexamines

Abstract: Template syntheses based on tris (ethane-1,2-diamine)cobalt(III) lead to cobalt(III) complexes of cage hexamines of the ' sarcophagine ' type ( sarcophagine = sar = 3,6,10,13,16,19- hexaazabicyclo [6.6.6] icosane ) rapidly and in high yield. Reduction of these species to their cobalt(II) forms enables the ligands to be removed in concentrated acids at elevated temperatures, and in hot aqueous solutions containing excess cyanide ion. The free sarcophagine and 1,8-diaminosarcophagine [(NH2)2sar or diamsar] ligands are strong bases, accepting up to four and five protons, respectively, in aqueous solution. In chloride medium, I = 1.0, at 298 K, pK1 = 11.95, pK2 = 10.33, pK3 = 7.17, pK4 ≈ 0 for sarcophagine , and pK1 = 11.44, pK2 = 9.64, pK3 = 6.49, pK4 = 5.48, pK5 ≈ 0 for diaminosarcophagine , with very similar values being found for triflate medium. Crystal structure determinations for both free bases, the chloride, sulfate, perchlorate and nitrate salts of diamsar , the complex of zinc chloride with sar, and the magnesium nitrate complex with diamsar show remarkably small variations in the cavity defined by the bicyclic ligands, though relatively subtle bond length and bond angle changes can be rationalized in terms of the effects of proton and metal ion binding. Exhaustive methylation of sarcophagine produces the highly lipophilic, hexatertiary base hexamethylsarcophagine , which, in the solid state, adopts quite different conformations and nitrogen-atom configurations to those of sar itself. All the ligands rapidly form metal ion complexes of generally exceptional kinetic and thermodynamic stability.