Showing papers on "Cobalt published in 1990"

Rhenium-containing protective coating with high corrosion and oxidation resistance

Abstract: The present invention relates to a corrosion-resistant or oxidation-resistant coating for metallic components, in particular gas turbine components of superalloys based on nickel or cobalt. By adding rhenium, the life of protective coatings, in particular of the MCrAlY type, under corrosive or oxidising conditions can be increased. The protective coating according to the invention contains, in addition to certain selected components and impurities, the following components (in percent by weight): 1 - 20%, prefeably 4 - 10%, of rhenium, 22 - 50% of chromium, 0 - 15% of aluminium, the amount of chromium and aluminium together being at least 25% and not more than 53%, 0.3 - 2% of yttrium and 0 - 3% of silicon, the remainder mainly being at least one of the elements selected from iron, nickel and cobalt, preferably one of the elements selected from nickel and cobalt. Protective coatings qualified for certain applications can be considerably improved with regard to the life under corrosive conditions by adding even smaller amounts of rhenium.

The Structure and Activity of Pt‐Co Alloys as Oxygen Reduction Electrocatalysts

Abstract: This paper reports on carbon-supported Pt-Co (3:1 atom ratio) catalysts prepared in both acid and alkaline aqueous media, followed by heat-treatments to promote alloy formation. both preparations began with a commercial 10% Pt-on-carbon catalyst, with Pt particle sizes of 15--30 {Angstrom}. Significantly greater alloying was observed in the catalyst prepared in the acid medium. X-ray diffraction studies of the acid-prepared catalyst demonstrated lattice parameters tending away from Pt (3.927 {Angstrom}) and forward that for Pt{sub 3}Co (3.831 {Angstrom}), greatly increased particle sizes, and significant ordering evidenced by the presence of super-lattice reflections. In all cases, catalysts prepared in the alkaline medium were alloyed to a lesser extent, were of moderately increased particle size, and gave no indication of alloy ordering. Activity testing under phosphoric acid fuel cell conditions demonstrated that the most highly alloyed catalysts were not significantly more active than pure Pt catalyst of comparable crystallite size. Loss of cobalt in the phosphoric acid environment was the lowest in catalysts which were the most alloyed, and were the Pt{sub 3}Co ordered phase was present.

Aqueous ferrofluids based on manganese and cobalt ferrites

Abstract: Synthesis of two new aqueous ferrofluids is performed chemically according to Massart's procedure. Manganese and cobalt ferrite magnetic particles are precipitated and treated in order to obtain colloidal sols by creating a charge density on their surface. Such “ionic” ferrofluids can be prepared in an acidic (after a treatment by ferric nitrate) or in an alkaline medium at a concentration as high as 17moll−1, i.e. a volumic fraction of 0.26. This result makes these new compounds of great interest.

X‐ray photoelectron spectroscopic studies of thin film oxides of cobalt and molybdenum

Abstract: Surface oxidation reactions of cobalt, molybdenum and mixed cobalt–molybdenum metals have been investigated using x-ray photoelectron spectroscopy (XPS). The oxide stoichiometries have been determined from XPS intensity measurements. Such quantification has been important in identifying oxide compositions with characteristic XPS spectra. A number of discrete binary molybdenum oxides have been characterized after reactions at 200°C and pressures ranging from 1 atm to 10−6 Pa. At the lowest pressure, the Mo 3d spectra and O/Mo ratios suggest the formation of a molybdenum–oxygen structure with a stoichiometry near unity. By contrast, at higher pressures, oxides that are predominantly MoO2 and MoO3 appear, but other intermediate oxide structures are also identified. Well-defined binary oxides of cobalt can be prepared from cobalt metal after heating in oxygen at different pressures. New binary oxides of cobalt and molybdenum have been generated by the reaction on MoO3 or Co3O4 substrates. Oxidation of a thin film of molybdenum on a Co3O4 substrate has been shown to produce a nearly stoichiometric surface layer of CoMoO4. The procedure could be useful for the production of other ternary oxides of possible interest for use as XPS reference materials.

Evidence for multinuclear metal-ion complexes at solid/water interfaces from X-ray absorption spectroscopy

Abstract: METALS dissolved in natural waters often become sorbed onto oxide or clay minerals, so that prediction of their chemical behaviour and transport properties requires knowledge of the structure and bonding of metal species at the solid/water interface1. For many sorption systems, X-ray absorption spectroscopy (XAS) can be used to determine the identity and number of nearest-neighbour atoms and interatomic distances in aqueous complexes on solid surfaces, and thus to identify the dominant type of surface complex and the partitioning mechanism2. Here we describe an XAS study of divalent cobalt (Co(II)) complexes sorbed on three different solids, γ-Al2O3, rutile (TiO2) and kaolinite (Al2Si2O5(OH)4). We find direct evidence for the presence of multinuclear sorption complexes at surface coverages below one monolayer of Co(II) atoms. Our spectroscopic data reveal distinct differences in the number of coordinating atoms and interatomic distances in the surface complexes formed on each of the solids at the same sorption density. These results suggest that different oxide and clay surfaces influence the structure and properties of aqueous surface complexes, and therefore must be accounted for in models of metal-ion sorption.

A transmission electron microscopy study of low‐temperature reaction at the Co‐Si interface

Abstract: An efficient preparation method, which provides wedge‐shaped cross‐section transmission electron microscopy samples, has been developed. It was then used to investigate the structure of as‐deposited cobalt multilayers on silicon substrates by rf plasma sputtering. It was found that an extended reaction takes place between Co and Si probably during the deposition. The cobalt atoms react with the silicon substrate to form an amorphous silicide layer. When the deposited layer is <3 nm thick, it entirely reacts with the substrate and can form an amorphous silicide as large as 5 nm. Above 4–5 nm thickness, growth of Co crystallites comes in competition with the formation of the amorphous silicide and limits it to 2 nm. The composition of this amorphous silicide is estimated to be Co2Si. In Co/C multilayers, the reactivity between the two materials is negligible, and the coalescence thickness of cobalt is 2–3 nm. At 2 nm, the cobalt layers are noncontinuous and very rough, whereas at 3 nm the critical thickness...

Fourier-transform infrared study of the surface properties of cobalt oxides

Abstract: The surface properties of cobalt oxide after two different pretreatments have been investigated by means of Fourier-transform infrared (FTIR) spectroscopy of adsorbed carbon monoxide, methanol and ammonia. The surface of evacuated Co3O4 exposes CO3+ cations that react rapidly with CO, producing Co2+ and probably CO+, together with carbonate ions. This surface is extremely reactive, and decomposes at room temperature both ammonia and methanol. After mild reduction in hydrogen, CoO is produced. After this treatment the surface exposes Co2+ and even more reduced sites that by contact with CO give small polycarbonyl clusters. This surface adsorbs methanol dissociatively and ammonia molecularly at room temperature.

Effect of particle size on carbon monoxide hydrogenation activity of silica supported cobalt catalysts

Abstract: Two series of silica supported cobalt catalysts were prepared by incipient wetness impregnation, one by varying the calcination temperature (200-400{degree}C, 3 wt % Co) and the other by changing the cobalt loading (1-10 wt % Co). Examination by ESCA, XRD, and H{sub 2} chemisorption showed that Co{sub 3}O{sub 4} is the dominant phase. The cobalt phase is reduced to cobalt metal at 400{degree}C. The cobalt particle sizes obtained from ESCA correlated well with those derived from H{sub 2} chemisorption and XRD line broadening. The turnover frequency of Co/SiO{sub 2} for CO hydrogenation was invariant with cobalt dispersion in the range of 6-20% dispersion.

Preparation, structure, and properties of pseudotetrahedral, D2d complexes of copper(II), nickel(II), cobalt(II), copper(I), and zinc(II) with the geometrically constraining bidentate ligand 2,2'-bis(2-imidazolyl)biphenyl. Examination of electron self-exchange for the Cu(I)/Cu(II) pair

Abstract: The bidentate ligand 2,2'-bis(2-imidazolyl)biphenyl (3=L) has been synthesized and used to prepare perchlorate complexes. X-ray structure analysis reveals pseudotetrahedral, MN(imH) 4 chromophores, each with approximate D 2d point symmetry. The ligand 3 experts an unprecedented degree of geometric control of the coordination spheres for complexes of this type

Pre-concentration of copper, cobalt and nickel with 3-methyl-1-phenyl-4-stearoyl-5-pyrazolone loaded on silica gel

Abstract: 3-Methyl-1-phenyl-4-stearoyl-5-pyrazolone loaded on to silica gel was used as a pre-concentration reagent for copper, cobalt and nickel prior to atomic absorption spectrometric determination. Both batch and column methods were used for the concentration of the above metals. These metals are quantitatively retained on the proposed adsorbent above pH 4. The adsorption-elution cycle can be repeated ten times with no observable decline in the efficiency of the adsorbent. As there are no observable effects due to changes in the volume of sample solution up to a volume of 1 l, a concentration factor of 40 can be achieved. The method has been applied to samples of sodium chloride solution and tap water.

Structure, Reactivity, Spectra, and Redox Properties of Cobalt(III) Hexaamines

Abstract: Publisher Summary This chapter discusses the effect of structural properties of cobalt (III) hexa-amines on their other properties. The chapter discusses complexes ranging from cobalt hexa-ammine, to complexes composed of three secondary and three tertiary amine donors. The chapter discusses only those coordination compounds, having a complete CoN 6 core, thus excluding the enormous number of CoN 6 - x L x complexes. Ammonia and organic amines with an aliphatic skeleton are described in the chapter. The chapter discusses complexes, containing just one kind of ligand—that is, homoleptic complexes. Structural properties and their relationship to kinetic stability (toward hydrolysis and racemization), electronic structure, reduction potentials, and electron transfer processes are explained in this chapter. The standard preparative procedure for the Co(III)–amine complexes consist of the reaction of an aqueous or alcoholic solution of a Co(II) salt with the free base of the amine. Oxidation in the solution is achieved by air, oxygen, H 2 0 2 , or other oxidants. In this chapter, the term molecular mechanics describes a method used frequently to predict structures and relative energies of related complexes (usually isomers). The method involves summing the potential energy of all the interatomic interactions in terms of bond deformation, valence angle deformation, torsion angle deformation, and nonbonded interactions. The chapter discusses the effects of structure on the other properties of the amine complexes predominantly in terms of the steric effects.

Pressure dependence and isotope effect of self-diffusion in a metallic glass.

Abstract: The pressure dependence and isotope effect of cobalt diffusion have been measured in amorphous Co 76.7 Fe 2 Nb 14.3 B 7 and fcc Co. Within experimental accuracy no pressure dependence and an isotope effect E=(Dα/Dβ−1)/[(mβ/mα) 1/2 −1]=0.1 were found in Co 76.7 Fe 2 Nb 14.3 B 7 . These results show that diffusion in the metallic glass is not mediated through quasivacancies in thermal equilibrium similar to crystalline Co. Diffusion rather occurs via a direct mechanism involving about ten atomic masses

Low‐Temperature Operation of Solid Electrolyte Oxygen Sensors Using Perovskite‐Type Oxide Electrodes and Cathodic Reaction Kinetics

Abstract: The lowest limit of operation temperature for the oxide solid electrolyte oxygen sensors was affected by the electrode materials. The sensors with silver and cobalt‐based perovskite‐type oxide electrodes exhibited theoretical EMF's at lower temperatures than those with Pt electrodes. In particular, the sensor with attained theoretical EMF even at 200°C. The electrode materials operative at low temperatures tend to have low cathodic over‐potential. From the kinetic analysis of the exchange current, the rate‐determining step is expected to be the dissociative adsorption of oxygen molecules at high temperatures and the charge transfer process at low temperatures.

Mutagenicity, carcinogenicity and teratogenicity of cobalt metal and cobalt compounds.

Abstract: Cobalt metal and cobalt compounds are extensively used for the production of high-temperature alloys, diamond tools, cemented carbides and hard metals, for the production of various salts used in electroplating and as catalysts, drying agents in paints, additives in animal feeds and pigments. Cobalt oxides are used not only in the enameling industry and for pigments, but also in catalytic applications. There is no indication that cobalt metal and cobalt compounds constitute a health risk for the general population. Allergic reactions (asthma, contact dermatitis) can be induced by certain cobalt compounds. Interstitial fibrosis has also been observed in workers exposed to high concentrations of dust containing cobalt, tungsten, iron, etc., mainly in the cemented carbides and the diamond-polishing industries. Several experiments have demonstrated that single or repeated injections of cobalt metal powder or some forms of cobalt salt and cobalt oxide may give rise to injection site sarcoma in rats and in rabbits but the human health significance of such data is questionable. Intratracheal administration of a high dose of one type of cobalt oxide induces lung tumors in rats but not in hamsters. In the latter long-term inhalation of cobalt oxide (10 mg/m3) did not increase the incidence of lung cancer. The human data are too limited to assess the potential carcinogenic risk for workers. Co2+ interacts with protein and nucleic acid synthesis and displays only weak mutagenic activity in microorganisms. Some cobalt salts have been reported to enhance morphological transformation of Syrian hamster embryo cells. Cobalt chloride displays some limited mutagenic activity in yeast and some cobalt compounds are able to produce numerical and structural chromosome aberrations in plant cells. Cobalt and its salts appear to be devoid of mutagenic and clastogenic activity in mammalian cells. Cobaltous acetate and cobaltous chloride have not been found to be teratogenic in hamsters and rats respectively.

Perchlorinated phthalocyanines: spectroscopic properties and surface electrochemistry

Abstract: : The electronic spectroscopic data for zinc, cobalt and iron perchlorinated phthalocyanines in several oxidation states are discussed. The magnetic properties of the iron(II) and cobalt(II) derivatives from ambient temperature to 5 K are reported. The electrochemical behavior of these three species is reported in solution and as surfaces on highly oriented pyrolytic graphite. The pH dependence of the surface data is analysed in detail. The first clearly defined reduction process corresponds with M(I)(Cl16Pc(-2))(-)/M(I) (cl16Pc(-3))(2-) for M = Co, Fe. The iron and cobalt species M(II)Pc(-2)/(M(I) pc(-2))(-) redox process are broad or ill-defined on the surface, and absent from solution. The Fe(III)(Cl16Pc(-2))(+)/Fe(II)Cl16Pc(-2) redox process has a typical pH dependence. The data are explained in terms of the acceptor nature of the chlorine substitution. Oxygen reduction data, catalysed by these species, are also reported. Keywords: Electrochemistry surfaces.

Process for eliminating mercury and possibly arsenic in hydrocarbons

Abstract: Process for elimination of mercury in hydrocarbon charges wherein said charge is contacted, under hydrogen, with a catalyst containing at least one metal from the group consisting of nickel, cobalt, iron and palladium followed by--or mixed with--a capture mass containing sulfur or a metal sulfide.

Slurry-phase Fischer-Tropsch synthesis and kinetic studies over supported cobalt carbonyl derived catalysts

Abstract: This paper reports the preparation characterization, and performance of cobalt carbonyl cluster based catalysts for use in slurry-phase Fischer--Tropsch (FT) technology investigated. Using metal carbonyls as active metal precursors allows for the control of metal particle size on the support surface, thus offering the potential for better control of activity and selectivity of the FT reaction. Silica as the support provided the highest catalyst activities. A Co{sub 2}(CO){sub 8}/Zr(OPr){sub 4}/SiO{sub 2} catalyst (3.5% cobalt, 6.6% zirconium) was developed as the most active system in the FT slurry reactor and also gave the best liquid fuel selectivity. Selectivity patterns correlated to the Schulz--Flory prediction. These catalysts exhibited low water/gas shift activity. Diesel fuel product produced by this catalyst was high quality. A kinetic expression that took water inhibition into account was verified, yielding an activation energy of 97 kJ/mol for syngas conversion ranging from 34% to 71% at 240--280{degrees} C.

Highly selective partial oxidation of methane to methyl trifluoroacetate

Abstract: Methane has been oxidized stoicheiometrically by cobalt(III) trifluoroacetate in CF3CO2H solution at 150–180 °C and 10–40 atm to give methyl trifluoroacetate in 90 ± 10% yield based on CoIII, which is reduced to CoII; in the presence of O2(1–5 atm) the reaction becomes catalytic with respect to the cobalt(III) salt, giving methyl trifluoroacetate as the sole product of the oxidation of methane by dioxygen.

Process for formation of a self aligned titanium nitride/cobalt silicide bilayer

Abstract: A process for the formation of a titanium nitride/cobalt silicide bilayer for use in semiconductor processing. Titanium and then cobalt are deposited on a silicon substrate by sputter deposition techniques. The substrate is then annealed. During this process the titanium first cleans the silicon surface of the substrate of any native oxide. During the anneal, the titanium diffuses upward and the cobalt diffuses downward. The cobalt forms a high quality epitaxial cobalt silicide layer on the silicon substrate. The titanium layer diffuses upward to the surface of the bilayer. The anneal is carried out in a nitrogen or ammonia ambient, so that a titaniun nitride layer is formed. The resulting structure can be used in self aligned silicide technology, as a contact fill material for contact to electrical regions of the device, and as a diffusion barrier preventing the diffusion of aluminum from a subsequently deposited aluminum layer or the diffusion of dopants from a subsequently grown doped selective silicon layer into the silicon substrate.

Electrodeposition of cobalt from aqueous chloride solutions

Abstract: In this paper, the kinetics of nucleation and crystal growth of cobalt in chloride aqueous solutions are studied by means of single-cycle voltammetry and potentiostatic current-time transient techniques. The influence of the concentration of Co 2+ ions on the mechanism of nucleation and crystal growth will be studied. Kinetic analysis of the cathodic current responses on the reverse sweep in the voltammetric curves has also been carried out

Platinum alloy electrocatalyst

Abstract: Disclosed are a platinum alloy electrocatalyst having high activity and a long life comprising an electrically conductive carrier and dispersed in, and deposited on it, a platinum-iron-cobalt-copper quaternary ordered alloy composed of 40 to 70 atomic % of platinum, 9 to 27 atomic % of iron, 9 to 27 atomic % of cobalt and 9 to 27 atomic % of copper, and an electrode for an acid electrolyte fuel cell which electrode comprises the platinum alloy electrocatalyst, a water-repellent binder and a conductive and acid-resistant supporting member, the electrocatalyst and the water-repellent binder being bonded to.