252,930 research outputs found
Cobalt toxicity in anaerobic granular sludge: influence of chemical speciation
The influence of cobalt speciation on the toxicity of cobalt to methylotrophic methanogenesis in anaerobic granular sludge was investigated. The cobalt speciation was studied with three different media that contained varying concentrations of complexing ligands [carbonates, phosphates and ethylenediaminetetraacetic acid (EDTA)]. Three fractions (nominal added, dissolved and free) of cobalt were determined in the liquid media and were correlated with data from batch toxicity experiments. The average concentration of cobalt that was required for 50% inhibition of methanogenic activity (IC50) for free Co2+ in the three sets of measurements was 13 mu mol/L with a standard deviation of 22% and a similarity of 72% between the data obtained in the three different media for the range of cobalt concentrations investigated. The standard deviation of the IC50 for the other two fractions was much higher, i.e. 85 and 144% for the added cobalt and dissolved cobalt, respectively, and the similarity was almost 0% for both fractions. Complexation (and precipitation) with EDTA, phosphates and carbonates was shown to decrease the toxicity of cobalt on methylotrophic methanogenesis. The free cobalt concentration is proposed to be the key parameter to correlate with cobalt toxicity. Thus, the toxicity of cobalt to granular sludge can be estimated based on the equilibrium-free cobalt concentration
Two electrodeposition strategies for the morphology-controlled synthesis of cobalt nanostructures
In this contribution, two different strategies are discussed to synthesize cobalt nanostructures: direct cobalt electrodeposition on a planar aluminum electrode and cobalt electrodeposition into nanoporous alumina templates generated by aluminum anodization (template electrodeposition). In the direct electrodeposition of cobalt on aluminum, cobalt nanoparticles are formed during the early stage of electrodeposition, which causes the depletion of cobalt ions near the electrode. Water reduction then takes place catalyzed by electrodeposited cobalt nanoparticles, which increases the pH near the electrode and can induce cobalt hydroxide precipitation. By varying the electrode potential and the cobalt ion concentration, the interplay between electrochemical growth of cobalt and water reduction could be controlled to induce transition from cobalt hexagonal nano-platelets to nanostructured films composed of cobalt nanoparticles and cobalt hydroxide nano-flakes. Cobalt nanowires can be synthesized by electrodeposition into nanoporous alumina templates generated by aluminum anodization. This approach typically involves the application of alumina templates produced by a two-step anodization procedure: the alumina nanoporous layer generated by a first anodization is dissolved in a chromic acid solution while a very ordered alumina nanoporous layer is produced by a second anodization stage. In accordance with previous studies, this procedure is fundamental to achieve uniform filling of the nanopores in the subsequent electrodeposition stage. In the present study, uniform filling of the nanoporous alumina generated by one-step anodization could be achieved by the electrodeposition of cobalt nanowires. This result was made possible by the application of a novel pulsed electrodeposition strategy
Role of charge carriers for ferromagnetism in cobalt-doped rutile TiO2
Electric and magnetic properties of a high temperature ferromagnetic oxide
semiconductor, cobalt-doped rutile TiO2, are summarized. The cobalt-doped
rutile TiO2 epitaxial thin films with different electron densities and cobalt
contents were grown on r-sapphire substrates with laser molecular beam epitaxy.
Results of magnetization, magnetic circular dichroism, and anomalous Hall
effect measurements were examined for samples with systematically varied
electron densities and cobalt contents. The samples with high electron
densities and cobalt contents show the high temperature ferromagnetism,
suggesting that charge carriers induce the ferromagnetism.Comment: 14 pages, 12 figure
Synthesis and antibacterial effects of cobalt–cellulose magnetic nanocomposites
© The Royal Society of Chemistry. Green synthesis is employed to prepare cobalt/cellulose nanocomposites with cubic (α-cobalt) cobalt as a main component with antibacterial and magnetic properties. An in situ reduction of aqueous solutions of cobalt ions on a model cellulose substrate surface using hydrogen gas affords spherical, cellulose-stabilised cobalt nanoclusters with magnetic properties and an average diameter of 7 nm that are distributed evenly over the surface of the cellulose fibres. These cobalt/cellulose nanocomposites exhibit good antibacterial action against opportunistic pathogens both Gram-positive (S. aureus) and Gram-negative (E. coli, A. baumannii and P. aeruginosa), with zones of inhibition up to 15 mm, thereby encouraging the deployment of these advanced materials for the treatment of wastewater or within medical dressings. This method of preparation is compared with the analogous in situ reduction of cobalt ions on a cellulose surface using sodium borohydride as reducing agent
Heat treatment for superalloy
A cobalt-free nickel-base superalloy composed of in weight % 15 Cr-5 Mo-3.5 Ti-4 Al-0.07 (max) C-remainder Ni is given a modified heat treatment. With this heat treatment the cobalt-free alloy achieves certain of the mechanical properties of the corresponding cobalt-containing nickel-base superalloy at 1200 F (650 C). Thus, strategic cobalt can be replaced by nickel in the alloy
Using a dual plasma process to produce cobalt--polypyrrole catalysts for the oxygen reduction reaction in fuel cells -- part II: analysing the chemical structure of the films
The chemical structure of cobalt--polypyrrole -- produced by a dual plasma
process -- is analysed by means of X-ray photoelectron spectroscopy (XPS), near
edge X-ray absorption spectroscopy (NEXAFS), X-ray diffraction (XRD),
energy-dispersive X-Ray spectroscopy (EDX) and extended x-ray absorption
spectroscopy (EXAFS).It is shown that only nanoparticles of a size of 3\,nm
with the low temperature crystal structure of cobalt are present within the
compound. Besides that, cobalt--nitrogen and carbon--oxygen structures are
observed. Furthermore, more and more cobalt--nitrogen structures are produced
when increasing the magnetron power. Linking the information on the chemical
structure to the results about the catalytic activity of the films -- which are
presented in part I of this contribution -- it is concluded that the
cobalt--nitrogen structures are the probable catalytically active sites. The
cobalt--nitrogen bond length is calculated as 2.09\,\AA\ and the
carbon--nitrogen bond length as 1.38\,\AA
Technique for manufacturing nickel electrodes
A method of manufacturing nickel electrodes distinctive for its use of a composite material for the electrode made up of nickel compound, electrode material, cobalt in metal form or cobalt in compound form is investigated. The composite is over-discharged (same as reverse charging) in an alkaline solution. After dealkalization, synthetic resin adhesive is added and the electrode is formed. Selection of the cobalt compound is made from a group consisting of cobalt oxide, cobalt hydroxide, cobalt carbonate and cobalt sulfate. The method upgrades plate characteristics by using an active material in a non-sintered type nickel electrode, which is activated by electro-chemical effect
Temperature dependence of spin resonance in cobalt substituted NiZnCu ferrites
Cobalt substitutions were investigated in Ni0.4Zn0.4Cu0.2Fe2O4 ferrites,
initial complex permeability was then measured from 1 MHz to 1 GHz. It appears
that cobalt substitution led to a decrease in the permeability and an increase
in the \mus\timesfr factor. As well, it gave to the permeability spectrum a
sharp resonance character. We also observed a spin reorientation occurring at a
temperature depending on the cobalt content. Study of the complex permeability
versus temperature highlighted that the most resonant character was obtained at
this temperature. This shows that cobalt contribution to second order
magnetocrystalline anisotropy plays a leading role at this temperature
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