Pulse plating of cobalt–iron–copper alloys

Pulse plating of cobalt–iron–copper (CoFeCu) alloys was studied. A simple theoretical model with an analytical solution developed for binary alloys is applied to predict the copper content of the pulse plated ternary alloys. Studied compositions are in the range of Co_90-x Fe₁₀Cu _x with x varying between 5 to 20 wt%. These compositions are of interest as soft magnetic materials with high saturation magnetization. The deposits were produced from a boric acid and sodium acetate electrolyte with low concentrations of copper and iron. All experiments were carried out under well-controlled mass transport conditions and current distribution using a recessed rotating cylinder electrode (rRCE) or an inverted rotating disc electrode (IrRDE). With the latter design alloys can be plated on flat substrates with or without application of a magnetic field to induce uniaxial magnetic anisotropy. Results show that by changing pulse parameters one can increase and decrease in opposite ways the copper and the iron content in the deposits. To test the influence of pulse parameters on the coercive field strength, a microstructure dependent property, theoretical predictions were used to produce films of identical composition with different pulse parameters. Within the range of pulse parameters studied the coercive field strength of this alloy does not vary. Transmission electron microscopy confirms that the deposits have the same nano-size grain structure.     

Tin–cobalt electrodeposition from sulfate–gluconate baths

The electrodeposition of tin + cobalt alloys from a slightly acidic sulfate–gluconate bath on both vitreous carbon and copper substrates has been studied for different [Sn(II)]/[Co(II)] ratios in the bath, varying between 1/10 and 1/2. A relationship between the electrochemical stripping analysis and the morphology of the deposits has been found. Two different types of deposit were obtained. At low [Sn(II)]/[Co(II)] ratios and relatively high deposition rates a nodular, cobalt-rich, nanocrystalline coating was obtained, while at high [Sn(II)]/[Co(II)] ratios and low deposition rates a new, well-defined tetragonal SnCo phase was obtained, with cell parameters of a = 3.087 Å and c = 5.849 Å. This structure favours hydrogen evolution.     

Comparison between cobalt and cobalt–platinum supported on zeolite NaY: Cobalt reducibility and their catalytic performance for butane hydrogenolysis

This work investigated reducibility of cobalt species in monometallic Co/NaY and bimetallic CoPt/NaY catalysts with various Co loading (1, 6 and 10 wt.%) and fixed Pt loading (1 wt.%). The form and environment of Co species after reduction was determined by X-ray absorption spectroscopy including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The cobalt species in the mono- and bimetallic catalyst with Co loading of 1 wt.% was not reducible whereas those with Co loading of 6 and 10 wt.% were partially reduced. The extent of reduction increased with Co loading and enhanced by the presence of Pt. Catalytic performance for n-butane hydrogenolysis mono- and bimetallic catalysts were compared. The higher extent of Co reduction in 6CoPt/NaY and 10CoPt/NaY resulted in higher conversions than the monometallic counterpart. Sequential hydrogenolysis was favored on the monometallic catalysts because methane was the only product. The presence of Pt suppressed such reaction resulting in ethane and propane. The effect of Pt on such effect was most prominent in 6CoPt/NaY.     

Influence of cobalt on manganese incorporation in Ni–Co coatings

The effect of alloying <1 wt% Mn with plain Ni, Ni–Co alloys and plain Co coatings in terms of the structure and properties has been studied. The alloys were electrodeposited from an additive free sulphamate electrolyte. The Mn concentration in the electrolyte was maintained at 5 g L⁻¹ so as to obtain <1 wt% Mn content in the alloy coatings. The Energy Dispersive X-ray analysis (EDX) showed that the Mn content reduced from 0.97 to 0.05 wt% with increase in Co content from 0 to 98 wt% in the alloy coating. An increase in microhardness was obtained on the addition of Mn to Ni/Ni–Co alloys. The X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) studies revealed a change in crystal structure and morphology. Pin-on-disc tribology test revealed better wear performance of Ni–18 wt%Co–Mn alloy coating compared to the other Ni–Mn/Ni–Co–Mn alloy coatings.     

Chemisorption of C3 hydrocarbons on cobalt silica supported Fischer–Tropsch catalysts

Chemisorption of propene and propane was studied in a pulse reactor over a series of cobalt silica-supported Fischer–Tropsch catalysts. It was shown that interaction of propene with cobalt metal particles resulted in its rapid autohydrogenation. The reaction consists in a part of the propene being dehydrogenated to surface carbon and CH_x chemisorbed species; hydrogen atoms released in the course of propene dehydrogenation are then involved in hydrogenation of remaining propene molecules to propane at 323–423 K or in propene hydrogenolysis to methane and ethane at temperatures higher than 423 K. The catalyst characterization suggests that propene chemisorption over cobalt catalysts is primarily a function of the density of cobalt surface metal sites. A correlation between propene chemisorption and Fischer–Tropsch reaction rate was observed over a series of cobalt silica-supported catalysts. No propane chemisorption was observed at 323–373 K over cobalt silica-supported catalysts. Propane autohydrogenolysis was found to proceed at higher temperatures, with methane being the major product of this reaction over cobalt catalysts. Hydrogen for propane autohydrogenolysis is probably provided by adsorbed CH_x species formed via propane dehydrogenation. Propene and propane chemisorption is dramatically reduced upon the catalyst exposure to synthesis gas (H₂/CO = 2) at 323–473 K. Our results suggest that cobalt metal particles are probably completely covered by carbon monoxide molecules under the conditions similar to Fischer–Tropsch synthesis and thus, most of cobalt surface sites are not available for propene and propane chemisorption.     

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.     

Effect of heat treatment on electroless ternary nickel–cobalt–phosphorus alloy

Ternary Ni–Co–P and binary Ni–P alloy coatings were deposited on mild steel panels from an alkaline bath in the presence and absence of cobalt sulfate using an electroless process. The effects of heat treatment on surface topography and crystal orientation of Ni–Co(11.17%)–P(3.49%) alloy coatings were studied in contrast to that of Ni–P ones. It was found that the as plated Ni–Co–P alloy is a supersaturated solid solution of P and Co dissolved in a microcrystalline Ni matrix with 111 preferred direction. Heat treatment induces structural changes. The formation of Ni₃P phase precipitates and recrystallization of nickel occur when the sample is treated at > 400 °C for one hour. It is observed that the Ni diffraction lines of treated Ni–Co–P alloy at > 400 °C are shifted to lower angles as compared to those of treated Ni–P or as plated Ni–Co–P alloys. The surface topography of Ni–Co–P alloy also changes with heat treatment temperature. The surface topography and crystal orientation were characterized by means of scanning electron microscopy and X-ray diffraction, respectively. The hardness and corrosion resistance, in 5 wt % NaCl solution, of heat treated Ni–Co–P samples were studied.     

4′-(Oxodiphenylphosphino)-2,2′:6′,2′′-terpyridine – crystal structure and complexes of cobalt(II) and cobalt(III)

The complex [Co(2)₂]²⁺ (2 = 4^′-(oxodiphenylphosphino)-2,2^′:6^′,2^′′-terpyridine) has been prepared either by the direct reaction of 2 with Co(II) or by careful oxidation of [Co(1)₂]²⁺(1 = 4^′-(diphenylphosphino)-2,2^′:6^′,2^′′-terpyridine). Further oxidation with H₂O₂ leads to [Co(2)₂]³⁺. The ¹H NMR spectra of the paramagnetic and diamagnetic [Co(2)₂]²⁺ and [Co(2)₂]³⁺ are reported. The crystal structure of ligand 1 has been determined; in the solid-state, 1 exhibits extensive intermolecular π–π stacking.     

Microstructure of single-phase cobalt and manganese oxide spinel Mn3−xCoxO4 ceramics

This paper reports microstructural studies of single-phase Mn_3−xCo_xO₄ (0.98 ≤ x ≤ 2.93) spinel ceramics using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). These ceramics were obtained by conventional sintering or by spark plasma sintering (SPS) of powders prepared by thermal decomposition of coprecipitated oxalate precursors. For x < 1.78 or x ≥ 1.78, the monophasic ceramics correspond respectively to quadratic (Q) or cubic (C) spinel structure. The ferroelastic character of the structural phase transition from C to Q is highlighted by specific microstructural features. The effect of chemical composition and heat treatment conditions on the microstructure and essentially on the presence and the characteristics of twins were investigated. The coherent twin interfaces are parallel to (1 1 2) planes in the Q cell. Twins can correspond to: tweeds, single lamellae (widths: 5–306 nm) arranged parallel to each other, large lamellae (widths: 69–928 nm) internally twinned and sometimes arranged in cyclic forms (triangular shapes).     

Novel magnetodielectric cobalt ferrite–titania–silica ceramic composites with tunable dielectric properties

The cobalt ferrite (CF)–titania (TiO₂)–silica (SiO₂) system has been studied to produce new ceramic composites by conventional solid state reaction. The microstructure of the sintered CF–TiO₂–SiO₂ mixture has been related to compositional modifications in terms of SiO₂/TiO₂ weight ratio keeping constant the CF weight percentage. Microstructural characterization of the sintered bodies was performed in order to understand microstructure evolution, and to quantify the phases volume fraction. The final compositions after sintering differ significantly from the starting ones as a consequence of the reaction of titania with the ferrite, and the formation of the ilmenite-type CoTiO₃. Four different distributed phases are present, depending on the starting SiO₂/TiO₂ weight ratio. The complex permittivity dispersion of ceramic composites was investigated and correlated to their microstructure. Lastly, CF-SiO₂ magneto-dielectric composites are suggested as possible candidates for high frequency applications as miniaturized antennas.     

Flame-retardant epoxy resin with good smoke-suppression endowed by chitosan–cobalt/phosphorus complex

Chitosan-based flame-retardant CS–Co–DOPA (CCD) was synthesized by the neutralization reaction of 10-hydroxy-9,10-dihydro-9-oxo-10-phosphaphenanthrene-10-oxide (DOPA) with chitosan-cobalt complex and fully characterized by scanning electron microscopy (SEM), energy-dispersive spectrometer, x-ray diffraction, X-ray photoelectron spectroscopy (XPS), optical emission spectrometer, and Fourier transform infrared (FTIR) characterizations. The epoxy resin (EP) modified with CCD exhibited good flame retardancy. With the addition of 5 wt% CCD, the EP/CCD achieved UL-94 V-1 rating and possessed limiting oxygen index (LOI) value of 30%. Cone calorimetry (CC) test demonstrated that EP/CCD resulted in a remarkable reduction of peak smoke production rate (pSPR) and total smoke production (TSP) by 63% and 40%, respectively, showing an outstanding smoke suppression. The char residue obtained from the CC test was further characterized using SEM, FTIR, Raman, and XPS techniques. The results revealed that CCD facilitated the formation of a dense and compact char layer on EP during combustion, thereby impeding gas and heat transfer. In addition, TG-IR was employed to investigate the gas-phase flame-retardant effect of EP/CCD composites, which revealed that CCD promotes the release of water, CO_2, and other incombustible gases, altering the decomposition path of EP.     

Sol–gel synthesis of novel cobalt doped zinc tin oxide composite for photocatalytic application

A novel photocatalyst based on cobalt doped zinc tin oxide is proposed. Cobalt doped zinc tin oxide thin films were deposited using a sol–gel deposition method and characterized by scanning electron microscopy (SEM), X-ray diffraction, Raman spectroscopy, photoluminescence emission measurement and UV–vis spectroscopy. It was found that the addition of Co into the zinc tin oxide does influence the structural and optical properties of the thin films and increases the overall photocatalytic degradation of methylene blue.     

NBS–rCDs(OH−) chemiluminescence analysis system for the determination of cobalt ions

A novel sensing system has been designed for cobalt ion detection based on a cobalt ion improved chemiluminescence (CL) in N-bromosuccinimide(NBS)-reduced carbon quantum dot (rCD) (OH⁻) system. The mechanism of this CL analysis system has been preliminarily studied. In this work, it was demonstrated that this facile methodology offers rapid, sensitive and reliable detection for cobalt ions with a detection limit as low as 3.252 × 10^− 6 mol/L and a linearity range from 1.004 × 10^− 5 to 1.004 × 10^− 3 mol/L (r = 0.9990), which has promising application prospects.     

Highly selective reductive cleavage of aromatic carbon–oxygen bonds catalyzed by a cobalt compound

A cobalt catalyst has been demonstrated, for the first time, to be effective for the reductive cleavage of inert aromatic CO bonds with high selectivity. Compared with previous Ni catalysts, the cobalt catalyst reported here is more commercially available and air-stable.     

On the formation of cobalt–molybdenum sulfides in silica‐supported hydrotreating model catalysts

Model catalysts, consisting of a conducting substrate with a thin SiO₂ layer on top of which the active catalytic phase is deposited by spincoating impregnation, were applied to study the formation of the active CoMoS phase in HDS catalysts. The catalysts thus prepared showed representative activity in the hydrodesulfurization of thiophene, confirming that these models of HDS catalysts are realistic. Combination of the sulfidation behaviour of Co and Mo studied by XPS and activity measurements shows that the key in the formation of the CoMoS phase is the retardation of the sulfidation of Co. Complexing Co to nitrilotriacetic acid complexes retarded the Co sulfidation, resulting in the most active catalyst. Due to the retardation of Co in these catalysts, the sulfidation of Mo precedes that of Co, thereby creating the ideal conditions for CoMoS formation. In the CoMo catalyst without NTA the sulfidation of Co is also retarded due to a Co–Mo interaction. However, the sulfidation of Mo still lags behind that of Co, resulting in less active phase and a lower activity in thiophene HDS. This revised version was published online in June 2006 with corrections to the Cover Date.     

Simultaneous spectrophotometric determination of manganese,zinc and cobalt by kernel partial least–squares method

Simultaneous spectrophotometric determination of Mn, Zn and Co was studied by two methods, classical partial least-squares (PLS) and kernel partial least-squares (KPLS), with 2-(5-bromo-2- pyridylazo)-5-diethylaminephenol (5-Br-PADAP) and cetyl pyridinium bromide (CPB). Two programs, SPGRPLS and SPGRKPLS, were designed to perform the calculations. Eight error functions were calculated for deducing the number of factors. Data reductions were performed using principle component analysis. The KPLS method was applied for the rapid determination from a data matrix with many wavelengths and fewer numbers of samples. The relative standard errors of prediction (RSEP) for all components with KPLS and PLS methods were the same (0.0247). Experimental results showed both methods to be successful even where there was severe overlap of spectra.     

Electrocatalytic oxidation of methanol on the nickel–cobalt modified glassy carbon electrode in alkaline medium

In this work, Ni–Co alloy coating on the surface of glassy carbon (GC) electrode was performed by cyclic voltammetry. The results showed that the deposition of Ni–Co is an anomalous process. The deposition bath was prepared according to the metal ion Ni/Co ratio of 4:1 using NiSO₄·7H₂O and CoSO₄·8H₂O, and the total concentration of all solutions was 40.0 mM. The pH of the bath solution was adjusted at 2.0 using boric acid at room temperature. The modified electrode was conditioned by potential recycling in a potential range of 100–700 mV (vs. Ag/AgCl) by cyclic voltammetric method in an alkaline solution. The Ni–Co modified electrode showed a higher activity towards methanol oxidation in the Ni (III) and Co (IV) oxidation states. Cyclic voltammetry was used for the electrochemical characterization of the Ni–Co modified electrode and the mechanism of methanol oxidation is proposed. The result of double steps chronoamperometry shows that the methanol electrooxidation is an irreversible reaction. Moreover, the effects of various parameters such as mole ratio of Ni–Co in the alloy in modification step, potential scan rate, methanol concentration and solution temperature on the electro-oxidation of methanol have also been investigated.     

Ferromagnetic interactions in a bis(μ-end-on azido)cobalt(II) linear trimer

A linear trinuclear Co(II) compound, [Co₃(μ_1,1-N₃)₄(N₃)₂(H₂O)₂(bpbp)₂] · 2H₂O (1, bpbp = 3,3′-bis-Dimethylamino-1,1′-pyridine-2,6-diyl-bispropenone), is reported. The central Co(II) ion is bridged to Co(II) ions on both sides by four end-on azide (${\mathrm{\mu }}_{1\text{,}1}\text{-}{\text{N}}_3^{-}$) ligands resulting in a centrosymmetric trimer with adjacent Co?Co distance of 3.233 Å. Each Co(II) ion possesses distorted octahedral geometry, the central one is coordinated by two aqua ligands and four ${\mathrm{\mu }}_{1\text{,}1}\text{-}{\text{N}}_3^{-}$ nitrogen atoms and each terminal Co(II) is coordinated by two ${\mathrm{\mu }}_{1\text{,}1}\text{-}{\text{N}}_3^{-}$ nitrogen atoms, one terminal ${\text{N}}_3^{-}$ nitrogen atom and capped by terminal tridentate bpbp ligand. Variable temperature magnetic studies indicate ferromagnetic coupling between adjacent Co(II) ions within the trimer.     

Detection and characterization of molybdenum oxides formed during the initial stages of cobalt–molybdenum electrodeposition

The initial stages of cobalt–molybdenum electrodeposition on a vitreous carbon electrode were studied to obtain information about the mechanism of cobalt–molybdenum induced codeposition. Solutions containing cobalt sulphate, sodium molybdate and sodium citrate at pH 6.6 were used. A first step in the mechanism of alloy deposition is proposed. This step takes into account the formation of molybdenum(IV) oxides over which Co–Mo alloy may be only deposited if sufficient potential is applied. Co–Mo electrodeposition occurs through an early stage involving low reduction current, related to the formation of molybdenum oxides, followed by a later stage in which the reduction current suddenly increases, corresponding to alloy codeposition. When a low potential is applied, a continuous coloured molybdenum oxide film is formed on the electrode and Co–Mo is not deposited. To induce the alloy deposition on the oxide film it is necessary to apply more negative potentials than a threshold value, which depends on the composition of the electrolytic bath. By increasing molybdate concentration in solution, the threshold potential shifts to more negative values. Intermediate molybdenum oxides were characterized using scanning electron microscopy (SEM), compositional analysis, Raman measurements and Auger and X-ray photoelectron spectroscopies.