Percentage Of Cobalt Research Articles

Investigation on Mechanism of Catalysis by Pt−LiCoO2 for Hydrolysis of Sodium Borohydride Using X-ray Absorption

The synthesis of platinum nanoparticle loaded LiCoO2 (Pt-LiCoO2) was carried out successfully by an impregnation method followed by sintering at different temperatures. The catalytic role of Pt-LiCoO2 composite in hydrogen generation during hydrolysis of sodium borohydride (NaBH4) was studied for fuel cell applications. X-ray diffraction (XRD), transmission electron microscopy (TEM), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) have been used to elucidate the structural and catalytic properties of Pt-LiCoO2. It was found that the 15 wt % of Pt nanoparticles on LiCoO2 sintered at 450 degrees C support showed the maximum efficiency for the catalysis reaction of hydrogen production. X-ray absorption near edge structure (XANES) analysis and extended X-ray absorption fine structure (EXAFS) analysis using a synchrotron radiation source were performed to carry out ex situ measurements in order to understand the mechanism of the catalytic process for the production of hydrogen during the hydrolysis of NaBH4. Co K-edge XANES showed a small percentage of cobalt in the metallic form after hydrogen generation which suggests the reduction of the cobalt during the hydrolysis of NaBH4.

Effects of thiourea and urea on zinc–cobalt electrodeposition under continuous current

The effect of thiourea and urea on zinc-cobalt alloys obtained from chloride baths under continuous current deposition are described and discussed. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and an X-Ray Diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. The use of additives does not refine the grain size of the Zn–Co alloy and an especially porous alloy was produced in the presence of urea. The preferred crystallographic orientations of zinc–cobalt alloys do not change in the presence additives. Zinc–cobalt alloys were without texture in the presence and absence of additives. Also, in the absence of additive and in the presence of urea, the XRD lines of the Zn–Co alloys are slightly shifted with respect to the pure zinc XRD lines, whereas, in the presence of thiourea, the XRD lines are not shifted. The alloy composition was examined using Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases slightly from 1.04 to 0.91 wt.% in the presence of urea and in the presence of thiourea it increases from 1.04 to 7.70 wt.%. Voltammetric studies show that thiourea increases the reduction rate of cobalt. This explains the increase in cobalt percentage in the alloy in the presence of thiourea.

Electrodeposition of Co–Ag films and compositional determination by electrochemical methods

An electrolytic bath containing silver(I), cobalt(II) and different complexing agents to electrodeposit Co–Ag coatings over vitreous carbon and silicon/seed-layer substrates is proposed. In situ electrochemical characterization of thin deposits is performed by means of stripping (potentiodynamic or galvanostatic) methods. These techniques allow detecting the heterogeneous codeposition of cobalt and silver. Electrochemical ex situ methods (polarographic and voltammetric methods) are implemented to quantify the silver and cobalt percentage in the coatings. Optimal analytical parameters for voltammetric method are established.

Electrodeposition and characterization of zinc–cobalt alloy from chloride bath; influence of coumarin as additive

Zinc–cobalt alloys were electrodeposited from chloride bath under continuous current and in the presence and absence of coumarin. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. Zinc–cobalt alloys was without texture in the absence of coumarin whereas, the preferred crystallographic orientations was (103) at 65% in the presence of coumarin. The presence of coumarin yields deposits with a finer grain size. The alloy composition was examined using the Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases from 1.04 wt.% to 0.69 wt.% in the presence of coumarin. Voltammetric studies show that coumarin affects the reduction of zinc but it was without effect on cobalt reduction. That explains the decrease of cobalt percentage in the alloy in the presence of coumarin.

Survey of the quasi-ternary system La0.8Sr0.2MnO3–La0.8Sr0.2CoO3–La0.8Sr0.2FeO3

An overview on the variation of the thermal expansion, the electrical conductivity as well as non-stoichiometry of the oxide content as a function of composition within the quasi-ternary system La 0.8 Sr 0.2 MnO 3− δ –La 0.8 Sr 0.2 CoO 3− δ –La 0.8 Sr 0.2 FeO 3− δ in air is presented. The various powders were synthesized under identical conditions. The DC electrical conductivity values of the compositions at 800 °C in air vary in a wide range from 15 to 1338 S cm −1 . The magnitude of electrical conductivity of the perovskites is mainly determined by the percentage of cobalt in the compositions. A similar behaviour was observed for the measured thermal expansion coefficients between room temperature and 1000 °C in air, increasing from 10.9 to 19.4 × 10 −6 K −1 as a function of cobalt content. Changes in the oxygen stoichiometry of the materials were characterized by temperature-programmed oxidation measurements.

Preparation and structural characterization of Co/Al2O3 catalysts for the ozonation of pyruvic acid

A series of Co/Al2O3 catalysts were prepared by the incipient wetness impregnation method using γ-Al2O3 support and (CH3COO)2Co·4H2O solutions, followed by calcination at 500–800°C. Characterization of catalysts was accomplished by several techniques such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), physisorption of nitrogen, mercury and helium-based pycnometries, Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and pH of zero charge (PZC). Impregnation of support produced a moderate decrease of its surface area and pore volume and also led to minor changes of its PZC. Depending on preparation conditions (i.e., calcination atmosphere and temperature and metal loading), one or more of the following Co-containing compounds were identified: CoO, Co3O4 and CoAl2O4. The support and prepared Co/Al2O3 catalysts were tested to catalyze the ozonation of aqueous pyruvic acid at pH 2.5. Pyruvic acid was shown refractory towards single ozonation but the use of γ-Al2O3 and Co/Al2O3 catalysts resulted in 56–96% pyruvic acid conversion and 41–78% decrease in DOC after 2h of ozonation of phosphate-buffered solutions. In the absence of the buffer, conversion rate was enhanced likely as a result of pH increase during the course of the process thus giving rise to the indirect way of ozonation through hydroxyl radicals. Acetic acid was found as the main by-product of pyruvic acid ozonation. Depending on the catalyst used, yield of acetic acid varied from 32 to 49%, values noticeably lower that that obtained from the control non-catalytic ozonation experiment (73%). Differences in catalytic activity amongst the various Co/Al2O3 catalysts investigated were attributed to the different Co active phases deposited on the γ-Al2O3 surface. The following sequence of increasing activity can be inferred from experimental results: CoO, CoAl2O4 and Co3O4. All the Co/Al2O3 catalysts prepared showed good stability as the percentage of cobalt leached out was rather low.

Process for cobalt separation and recovery in the presence of nickel from sulphate solutions by Cyanex 272

The present paper deals with the extraction of cobalt from a solution containing cobalt and nickel in a sulphate medium similar to the leach liquor obtained by the dilute sulphuric acid pressure leaching of the Pacific Ocean nodules matte followed by copper extraction. The commercial extractant Cyanex 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid) is used for this purpose. The leach liquor used for the present study contains Co =1.78 g/L and Ni=16.78 g/L. Before cobalt extraction, impurities, such as copper and iron, are removed from the leach liquor by the precipitation method. Increasing the concentration of Cyanex 272 increased the extraction percentage of cobalt due to the increase of equilibrium pH. Cobalt extraction efficiency of >99.9 % is achieved with 0.20 M Cyanex 272 in two counter-current stages at an aqueous: organic (A:O) phase ratio of 1.5∶1. Complete stripping of cobalt from the loaded organic containing 2.73 g/L Co was carried out at pH 1.4 by a synthetic cobalt spent electrolyte in two stages at an A:O ratio of 1∶2. The enrichment of cobalt during extraction and stripping operations was about 3.5 times. A complete process flowsheet for the separation and recovery of cobalt is presented.

Electrodeposition of nano-grain sized Bi–Co thin films in organic bath and their magnetism

In this paper we report the preparation of nano-grain sized Bi 1− x Co x thin films containing different percentages of bismuth and cobalt by galvanostatic electrodeposition on Cu substrates in organic baths, and provided a good procedure to prepare nano-grain sized Bi-based alloy thin films. The prepared Bi 1− x Co x thin films consisted almost entirely of nanograins with sizes of 20–80 nm, and they were very compact. The results of X-ray diffraction (XRD) indicated that the nano-grain sized Bi 1− x Co x thin films were amorphous. After heat treatment of crystallization at 280 °C for 1 h in a protecting atmosphere, Bi(110), Cu(111), Bi 10Co 16O 36(532), Co(102) and Co(110) phases could be found in XRD patterns, respectively. The magnetic measurements showed that the nano-grain sized Bi 1− x Co x thin films had a superparamagnetism-like behavior with the magnetization increasing rapidly and then reaching saturation, and a clear enlargement of deposit coercivity was obtained by increasing Co content.

Influence of a cationic surfactant in the properties of cobalt–nickel electrodeposits

The effect of a cationic surfactant, dodecyltrimethylammonium chloride (DTAC) on CoNi electrodeposition process has been analysed. CoNi electrodeposition is greatly modified by the presence of the cationic surfactant in the bath. The DTAC modifies the initial stages of the deposition process and enhances the cobalt percentage in the deposits. Structure and morphology of the deposits are also modified, as the manner that magnetic properties of the electrodeposited films were affected as a consequence of the structural change. The presence of the surfactant in the bath causes changes on the CoNi structure from face-centred cubic (fcc) to close-packed hexagonal (hcp). DTAC incorporation into the deposits is a function of its concentration in the bath. Thus, it is important to be careful with the effects caused by the surfactant on deposits when it assists the particles insertion.

Magnetic composites CoNi–barium ferrite prepared by electrodeposition

CoNi–barium ferrite magnetic composites have been prepared by using a chloride electroplating bath. The use of a cationic surfactant and a vigorous stirring of solution by means of a rod stirrer have been the key to assure a significant insertion of particles in the deposits. This incorporation was confirmed by chemical analysis, cross-section images and X-ray diffraction results. A maximum value of 12 wt.% of barium ferrite was obtained. Anomalous codeposition of CoNi was maintained, although the cobalt percentage was enhanced by the presence of the cationic surfactant. A clear enlargement of composite coercivity was obtained as a consequence of micrometric hard magnetic particles insertion in the deposits.

Structure and catalytic activity correlation of CoAlPO 4 in the synthesis of N,N-biphenyl urea via alkylation of aniline using dimethyl carbonate

Two sets of cobalt aluminophosphate materials, one at different pH (4.5, 7, 10, and 11.5) and the other containing different percentage of cobalt (0.5–20) were prepared by co-precipitation method. All the materials were characterized by XRD, SEM, 27Al MASS NMR, TGA and DSC, FTIR, for their textural and structural properties. The surface area of the samples was determined by BET method and total surface acidity by n-butylamine titration method. The CoAlPO 4 obtained under acidic pH were found to be crystalline AlPO 4 with nonmicroporous tridymit structure associated with cobalt phosphate, whereas the one obtained under alkaline pH were amorphous aluminophosphate and also associated with cobalt phosphate. Tridymit-AlPO 4 crystals exhibited Al atom in a tetrahedral environment of phosphate groups. In the amorphous material the Al atoms were in a mixed tetrahedral and octahedral environment. The concentration of acid sites were found to be higher in the sample obtained under alkaline pH. This has been attributed due to the partial coordination of hydroxyl groups in the octahedral aluminum sites. The amorphous materials obtained under alkaline pH were found to be thermally stable up to 900 °C. The catalytic activity of all the materials was investigated in aniline alkylation using dimethyl/ethyl carbonates (DMC/DEC) under refluxing conditions. N-methyl/ethyl aniline (NMA/NEA) and biphenyl urea (BPU) were formed as the major products with the catalysts prepared at acidic and alkaline pH, respectively. A good correlation has been observed between the catalytic activity of CoAlPO 4 materials towards their selectivity for NMA/NEA and/or BPU and their textural and structural properties. Reaction conditions such as the amount of the catalyst, duration of the reaction, reusability and efficiency of the catalyst have also been evaluated. CoAlPO 4 prepared under alkaline pH with 5% of cobalt has been found to be the best catalyst for BPU synthesis from aniline and DMC/DEC under refluxing conditions.

Solvent extraction with DP-8R/LIX 860 mixtures for the selective separation of cobalt and nickel

DP-8R and LIX 860 extractans diluted with Exxsol D100 was used to co-extract cobalt and nickel from sulphate aqueous media. The influence of equilibration time, temperature, equilibrium pH and extractants mixture concentration on the extraction of both metals has been studied. It was observed that neither cobalt nor nickel extraction is sensitive to temperature, reaching in both cases the extraction equilibrium within 5 min of contact; however nickel is extracted preferably to cobalt at slightly acidic pH values and also using various extractants mixture concentrations. For a solution containing 1 g/1 each of cobalt and nickel and initial pH value of 5.5, conditions were established for the co-extraction of both metals and selective stripping (with H2SO4) of cobalt and nickel. Using the appropriate extractants concentrations the yield (extraction stage) for both metals is near 90 %, whereas the percentage of cobalt and nickel stripping is almost also quantitative.

Influence of the electrical conductivity of dielectric on WEDM of sintered carbide

This work deals with the electrical conductivity of dielectric and cobalt percentage on output parameters such as metal removal rate and surface roughness value of sintered carbides cut by wire-electrical discharge machining (WEDM). To obtain a precise workpiece with good quality, some extra repetitive finish cuts along the rough cutting contour are necessary. Experimental results show that increases of cobalt amount in carbides affects the metal removal rate and worsens the surface quality as a greater quantity of solidified metal deposits on the eroded surface. Lower electrical conductivity of the dielectric results in a higher metal removal rate as the gap between wire electrode and workpiece reduced. Especially, the surface characteristics of rough-cut workpiece and wire electrode were analyzed too. To obtain a good surface equality without crack, 4 finish-cuts were necessary by reducing the electrical energy and the offset value.

Electrodeposited cobalt+copper thin films on ITO substrata

Cobalt+copper thin films with variable composition were obtained over indium–tin oxide covered glass plates (ITO) by means of electrodeposition, from a citrate bath upon varying both the [Co(II)]/[Cu(II)] ratio in solution and the deposition conditions. The ITO/glass substrate is sufficiently conductive to allow electrodeposition directly onto it, and also allows the measurement of the magnetoresistance without separating the films. The electrochemical and structural analyses indicated that a solid solution is formed in the electrodeposition conditions studied, although TEM analysis showed the random distribution of nanometric dense particles of cobalt distributed within the deposits. These particles were responsible for the magnetoresistance (MR) signal which was observed for all the Co+Cu films. The MR value increased when the cobalt percentage increased in the deposit.

Characterisation of zinc+cobalt alloy phases obtained by electrodeposition

The anomalous codeposition of Zn+Co alloys on vitreous carbon, copper and nickel substrates in a chloride bath was studied. The results indicate that the substrate influences both the initial electrodeposition stages and the alloy formation. For the same electrodeposition conditions, vitreous carbon and copper substrates favour the formation of deposits richer in zinc than those obtained over a nickel substrate. In the stripping analysis of deposits obtained during anomalous codeposition, up to three major oxidation peaks were observed, the two corresponding to the more negative potentials are attributable to the zinc oxidation in the alloy and the more positive one to the oxidation of the remaining porous cobalt matrix of the alloy. Under our experimental conditions, two kinds of deposits have been analysed using X-ray diffraction (XRD). XRD analysis showed that deposits with very low cobalt percentage (less than 3%) and a hexagonal platelet structure had a distorted hcp zinc η-phase. Polyhedral-grained deposits with between 4 and 10% cobalt were made up of quasi-pure zinc and a Zn+Co γ-phase of bcc structure. A correlation between the stripping curve and the type of deposit has been found.

Active‐center equilibrium in Ziegler–Natta butadiene polymerization

AbstractThe Ziegler–Natta‐catalyzed polymerization of 1,3‐butadiene was investigated at a low aluminum alkyl/cobalt (Al/Co) ratio using two different soluble catalyst systems: cobalt(II) octanoate/diethylaluminum chloride/water and cobalt(II) octanoate/methylaluminoxane/tert‐butyl chloride. When the active‐center concentration was determined by the number‐average molecular weight technique, it was found that the percentage of active cobalt depended on the Al/Co ratio. Subsequently, an equilibrium reaction was proposed to be Co + 2Al ⇌ CoAl2, where Co is cobalt(II) octanoate, Al is either of the aluminum alkyl‐activator species, and CoAl2 is the active catalyst. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2256–2261, 2001

Obtention and characterisation of cobalt+copper electrodeposits from a citrate bath

The electrodeposition of cobalt+copper alloy on vitreous carbon, copper and nickel electrodes in a citrate bath at pH ca. 5 has been studied for two [Co(II)]/[Cu(II)] ratios in solution. Voltammetric and stripping results on vitreous carbon show that co-deposition of the two metals takes place under these conditions. Electrodeposition leads to the formation of a solid solution of cobalt in copper, detected by only one oxidation peak that shifts from the copper to the cobalt position as the applied current density–applied potential is made more negative. Structural XRD analysis and compositional analyses, confirm the formation of a cobalt–copper solid solution of face-centred-cubic (fcc) structure. Diffractograms show peaks that appear at diffraction angles between the lines corresponding to copper and fcc cobalt. The value of the fcc lattice constant a of the alloy decreases linearly with the increase in the cobalt percentage in the deposits, following Vegard's law. Deposits obtained at the same charge and current density from the same bath on different substrates have similar morphology: nodular-grained deposits at low deposition current densities–applied potentials, which evolve gradually to more fine-grained and structured deposits as the cobalt percentage in the deposits is increased.

Analysis of tungsten carbide coatings by infrared laser-induced argon spark with inductively coupled plasma atomic emission spectrometry

Infrared laser ablation was studied for application to the analysis of plasma-sprayed tungsten carbide/cobalt coatings. The potential of the laser induced argon-spark (LINA-Spark™), as a sample introduction device in inductively coupled plasma atomic emission spectrometry was studied. The use of an IR laser along with defocusing led to laser-induced microplasma-based ablation. The mass ablation rate, represented by the ICP emission intensity per laser beam unit area, exhibited a flat increase in the irradiance range 2–250 GW/cm 2. A low slope (0.5) of this dependence in log–log scale gave evidence of plasma shielding. The steep increase in the measured acoustic signal when focused in front of the sample, i.e. in argon, indicated a breakdown of argon. Consequently, considerably lower ICP emissions were observed within the same range of irradiance. The cobalt/tungsten line intensity ratio in the ICP was practically constant from 1.5 up to at least 250 GW/cm 2. Acceptable precision (R.S.D.<5%) was obtained without internal standardization for irradiance between 2 and 8 GW/cm 2. Optimization of the laser pulse energy, repetition rate, beam focusing and sample displacement during interaction led to the linearization of dependences of signal vs. cobalt percentage, at least up to the highest studied value of 23% Co.

Separation of nickel from cobalt using electrodialysis in the presence of EDTA

Optimum conditions are determined for the removal of nickel from cobalt solutions by electrodialysis exploiting the greater stability of the EDTA complex with nickel. The Ni–(EDTA)2− complex and hydrated Co2+ ions are transferred from the feed solution to the electrodialysis anolyte and catholyte chambers, respectively. A three compartment cell is required to prevent the transfer of hydrated Ni2+ from the anolyte chamber as the EDTA present is destroyed at the anode. Complete removal of nickel from cobalt can be achieved but there is a compromise between cobalt purity and the percentage of cobalt transferred to the catholyte chamber for recovery.

Determination of potency factor of cobalt for estimation of nickel equivalent in 16Cr–2Ni martensitic stainless steel

Cobalt is considered to be a potential substitute for nickel in 16Cr–2Ni martensitic stainless steel. However, the percentage of cobalt that can substitute 1% of nickel remains to be determined. A computer program was developed for accurate prediction of δ ferrite content in Schaeffler type diagrams. The δ ferrite content in the steels was measured by metallography and estimated using the computation technique for various Schaeffler type diagrams. The percentage error in the experimentally measured and computed δ ferrite contents was ±1·0%. From the present study, the potency factor of cobalt was computed to be 0·64 that of nickel in the estimation of nickel equivalent.