Cobalt Deposition Research Articles

Comprehensive impedance model of cobalt deposition in sulfate solutions accounting for homogeneous reactions and adsorptive effects

A comprehensive physicochemical model for cobalt deposition onto a cobalt rotating disk electrode in sulfate-borate (pH 3) solutions is derived and statistically fit to experimental EIS spectra obtained over a range of CoSO 4 concentrations, overpotentials and rotation speeds. The model accounts for H + and water reduction, homogeneous reactions and mass transport within the boundary layer. Based on a thermodynamic analysis, the species CoSO 4(aq), B(OH) 3(aq), B 3O 3(OH) 4 −, H + and OH − and two homogeneous reactions (B(OH) 3(aq) hydrolysis and water dissociation) are included in the model. Kinetic and transport parameters are estimated by minimizing the sum-of-squares error between the model and experimental measurements using a simplex method. The electrode response is affected most strongly by parameters associated with the first step of Co(II) reduction, reflecting its control of the rate of Co deposition, and is moderately sensitive to the parameters for H + reduction and the Co(II) diffusion coefficient. Water reduction is found not to occur to any significant extent under the conditions studied. These trends are consistent with that obtained by fitting equivalent electrical circuits to the experimental spectra. The simplest circuit that best fits the data consists of two RQ elements (resistor-constant phase element) in parallel or series with the solution resistance.

Quasi unidimensional growth of Co nanostructures on a strained Au(111) surface

We investigated to which extent a uniaxially-strained Au(111) surface, thereby displaying linear reconstructions, may be used as a template for the growth of elongated nanostructures. Cobalt has been used as a deposition material and two routes have been followed satisfactorily. The first one consists of the control of diffusion through the temperature of deposition. The second one consists of a first step of platinum seeding in the reconstruction, followed by cobalt deposition with nucleation on the platinum seeds.

Study of the effect of cobalt content in obtaining olefins and paraffins using the Fischer-Tropsch reaction

This work presents the synthesis, characterization and testing of catalysts for the Fischer-Tropsch reaction. Molecular sieve MCM-41 was prepared under hydrothermal treatment at 150°C for 2 days, using the following molar composition of reagents: 1 SiO2:0.27 CTABr:0.19 TMAOH:40 H2O. Obtaining the mesoporous molecular sieve, Si-MCM-41, was confirmed by X-ray diffraction. The deposition of cobalt on MCM-41 support was carried out by wet impregnation, using an aqueous solution of cobalt nitrate. The images obtained from TEM clearly showed a good dispersion of the cobalt on the support (MCM-41). The textural characteristics of the samples were investigated by isothermal gas adsorption/desorption. Using the BJH method, it was possible to obtain the values of the average pore diameter on adsorption and desorption. The obtained catalysts containing different cobalt concentrations were evaluated for the Fischer-Tropsch reaction. Increasing the temperature increases the selectivity to olefins with the 15wt.% Co/MCM-41 catalyst, as well as increases the selectivity to methane with the 5wt.% Co/MCM-41 catalyst.

Electrodeposition of cobalt–yttrium hydroxide/oxide nanocomposite films from particle-free aqueous baths containing chloride salts

The feasibility of growing nanostructured films composed of cobalt and yttrium hydroxide/oxide phases by electrodeposition is demonstrated. Particle-free aqueous solutions containing YCl3 and CoCl2 salts and glycine were used. The incorporation of yttrium compounds into the cobalt deposit was achieved using pulse deposition (ton=0.1ms, toff=0.9ms) and for cathodic pulses higher than −500mAcm−2. Deposits obtained were crack-free, typically with 1–5wt% yttrium, and exhibited morphologies markedly different from the ones shown by pure cobalt deposits. Moreover, yttrium-rich films (up to 30wt% Y) could be deposited under certain conditions, though incipient cracking developed in this case. X-ray photoelectron spectroscopy analyses revealed that Y(OH)3/Y2O3 compounds were present in the films. From the structural viewpoint, the composites exhibited a partially amorphous/nanocrystalline character, with the crystalline fractions originating from the hexagonal-close packed structure of α-Co. A refinement of the α-Co crystallite size was observed in deposits containing higher weight percentage of yttrium compounds. Nanoindentation tests revealed that hardness increased with the yttrium content. This result can be explained by taking into account both the presence of intrinsically hard oxide phases and the effects promoted by incorporation of yttrium hydroxides/oxides on the α-Co matrix (namely, grain-refining and higher concentration of stacking faults).

Proton Transport during Electrodeposition of Cobalt in Chloride Electrolytes

In acid cobalt chloride electrolytes the electrodeposition of cobalt and evolution of hydrogen take place simultaneously. On a rotating platinum disc electrode the current efficiency for cobalt deposition was calculated based on the anodic charge needed for stripping of the cobalt deposits divided by the total cathodic charge. The results showed a decrease in current efficiency with increasing rotation rate. From the partial current density for hydrogen evolution the diffusion coefficient for protons was calculated. The derived diffusion coefficients varied with overpotential and pH, but were always one order of magnitude lower compared to what was expected from literature values. This was attributed to water drag when transporting cobalt ions towards the electrode. The variations in the calculated diffusion coefficients were explained by change in the transfer number when the proton concentration was changed.

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Abstract Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g−1, remanent magnetization of 6.0 emu g−1 and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.

Fabrication of an a-IGZO Thin Film Transistor Using Selective Deposition of Cobalt by the Self-Assembly Monolayer (SAM) Process

Interest in transparent oxide thin film transistors utilizing ZnO material has been on the rise for many years. Recently, however, IGZO has begun to draw more attention due to its higher stability and superior electric field mobility when compared to ZnO. In this work, we address an improved method for patterning an a-IGZO film using the SAM process, which employs a cost-efficient micro-contact printing method instead of the conventional lithography process. After a-IGZO film deposition on the surface of a SiO2-layered Si wafer, the wafer was illuminated with UV light; sources and drains were then patterned using n-octadecyltrichlorosilane (OTS) molecules by a printing method. Due to the low surface energy of OTS, cobalt was selectively deposited on the OTS-free a-IGZO surface. The selective deposition of cobalt electrodes was successful, as confirmed by an optical microscope. The a-IZGO TFT fabricated using the SAM process exhibited good transistor performance: electric field mobility (micro(FE)), threshold voltage (V(th)), subthreshold slope (SS) and on/off ratio were 2.1 cm2/Vs, 2.4 V, 0.35 V/dec and 2.9 x 10(6), respectively.

COBALT ELECTRODEPOSITION ONTO STAINLESS STEEL 304 FROM AMMONIACAL SOLUTIONS

ABSTRACT In this work we studied the cobalt electrodeposition onto a stainless steel 304 electrode from an aqueous solution containing 10 -1 M of CoSO 4 + 1M (NH 4 ) 2 SO 4 at natural pH of 4.5. Black cobalt deposits were obtained under our experimental conditions. The average diffusion coefficient calculated was 9.8X10 -6 cm 2 s -1 while the ∆G for the formation of stable nucleus was 1.013X10 -20 J/nuclei. The critical cluster´s size calculated was 0 which suggested that each active site is a critical nucleus on the SSE-304 surface. The Scanning Electron Microscopy images showed the formation of non-uniform cobalt particles. Keywords: Black cobalt, SSE 304, electrodeposition, kinetic. e-mail: hhuizar@uaeh.edu.mx INTRODUCTION Often, a cobalt film is deposited onto a stainless steel electrode (SSE) to prevent its oxidation 1 . Several studies suggest that the cobalt films can be electrodeposited onto an SSE, if the deposition time and the cobalt concentration in solution can be controlled

Quantification and minimization of disorder caused by focused electron beam induced deposition of cobalt on graphene

Graphene has attracted a lot of attention due to its unique transport properties, including applications in Spintronics. Therefore, one of the key issues is the investigation of the spin polarized transport phenomena, which requires the use of magnetic contacts for electrical measurements. Here we present results of the micro-Raman spectroscopy and in situ transport measurements during the electron beam irradiation and electron beam induced deposition of metallic Co on graphene. We aim to understand the effects caused by the Co deposition on the graphene in order to minimize undesired deterioration and induced disorder. Annealing procedures have been also carried out to recover the initial graphene properties.

Speciation and thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35–440 °C and 600 bar: An in-situ XAS study

Aqueous Co(II) chloride complexes play a crucial role in cobalt transport and deposition in ore-forming hydrothermal systems, ore processing plants, and in the corrosion of special Co-bearing alloys. Reactive transport modelling of cobalt in hydrothermal fluids relies on the availability of thermodynamic properties for Co complexes over a wide range of temperature, pressure and salinity. Synchrotron X-ray absorption spectroscopy was used to determine the speciation of cobalt(II) in 0–6 m chloride solutions at temperatures between 35 and 440 °C at a constant pressure of 600 bar. Qualitative analysis of XANES spectra shows that octahedral species predominate in solution at 35 °C, while tetrahedral species become increasingly important with increasing temperature. Ab initio XANES calculations and EXAFS analyses suggest that in high temperature solutions the main species at high salinity (Cl:Co >> 2) is CoCl 4 2−, while a lower order tetrahedral complex, most likely CoCl 2(H 2O) 2(aq), predominates at low salinity (Cl:Co ratios ∼2). EXAFS analyses further revealed the bonding distances for the octahedral Co(H 2O) 6 2+ ( octCo–O = 2.075(19) Å), tetrahedral CoCl 4 2− ( tetCo–Cl = 2.252(19) Å) and tetrahedral CoCl 2(H 2O) 2(aq) ( tetCo–O = 2.038(54) Å and tetCo–Cl = 2.210(56) Å). An analysis of the Co(II) speciation in sodium bromide solutions shows a similar trend, with tetrahedral bromide complexes becoming predominant at higher temperature/salinity than in the chloride system. EXAFS analysis confirms that the limiting complex at high bromide concentration at high temperature is CoBr 4 2−. Finally, XANES spectra were used to derive the thermodynamic properties for the CoCl 4 2− and CoCl 2(H 2O) 2(aq) complexes, enabling thermodynamic modelling of cobalt transport in hydrothermal fluids. Solubility calculations show that tetrahedral CoCl 4 2− is responsible for transport of cobalt in hydrothermal solutions with moderate chloride concentration (∼2 m NaCl) at temperatures of 250 °C and higher, and both cooling and dilution processes can cause deposition of cobalt from hydrothermal fluids.

Scattering effects of primary electrons in Co/Cu(1 1 1) measured by Auger; elastic and loss electrons

Electron energy losses were measured as a function of the incidence angle of the primary electron beam for the Co/Cu(111) adsorption system. The measurements performed for the clean and covered substrate reveal characteristic intensity maxima associated with the close packed rows of atoms, as it was observed in the so called directional Auger and directional elastic peak electron spectroscopy profiles. The incidence angle dependent signal of electron energy losses measured for the clean (Cu 3p3/2) and covered (Co 3p3/2) substrate gives the so called directional electron energy loss spectroscopy (DEELS) profiles which contain structural as well as chemical information. The scattering of primaries and different emission processes associated with electron energy losses, Auger, and elastically backscattered electrons are discussed. A change in the hCu (Cu M2,3VV transition) Auger signal recorded during the continuous cobalt deposition shows that the growth mode is not a pure layer by layer type. The complete covering of the substrate by Co at higher coverages is confirmed by the comparison between experimental and theoretical ratios of the Auger peak heights.

Magnetoimpedance of cobalt-coated silicon steels

Magnetoimpedance (MI) effect of cobalt-coated silicon steels is measured as a function of cobalt thickness (0−45 μm), DC magnetic field (0–2 kOe), frequency (1 kHz–1 MHz) and magnitude (1–20 mA) of AC current. With increase in deposition thickness, the MI ratio and the characteristic frequency are decreased because the samples are magnetically hardened by the coating. Nevertheless, cobalt deposition broadens the frequency-dependent MI curves, and the frequency range with a large MI ratio is extended. The variations of this peak width as well as the characteristic frequency and the MI ratio are explained by the skin effect and crossing effect.

Investigation of Co(OH)2 formation during cobalt electrodeposition using a chemometric procedure

The mechanism of Co electrodeposition in sulphate solutions containing boric acid was investigated using the EQCM technique and potentiostatic measurements. The effects of solution composition, temperature and deposition potential were studied using factorial design as a chemometric procedure. The boric acid was used as a buffer to prevent pH changes due to the hydrogen evolution reaction (HER) during electrodeposition. The results showed that Co(OH)2 was formed as a parallel reaction to metallic Co formation under some experimental conditions. The analysis of the factorial design revealed that temperature and [Co2+:H3BO3] molar ratio were the critical variables that affect the mechanism of cobalt electrodeposition. At high temperatures (48°C) and using a 5:1 molar ratio of [Co2+:H3BO3], the formation of cobalt hydroxide was detected simultaneously with cobalt deposition.

Geochronological and isotope geochemical characteristics of mafic intrusions of the Norilsk region

Layered intrusions of the Norilsk group contain unique deposits of copper-nickel, cobalt and plati� noid ores, and platinoids. The origin of silicate matrix was traditionally considered to be mantle. However, the first study of the isotopic composition of fluid components (He and Ar (1) and sulfur (2)) revealed largescale mantle-crust interaction. The complex isotopic investigations of rocks and ores of mafic intrusions of the Norilsk region performed at the Karpinskii Geological Research Institute in 2003- 2008 demonstrated the quantitative genetic indicators allowing us to refine the models of the formation of unique Cu-Ni-PGE deposits. We performed several hundred isotopic analyses: isotopic composition of helium and argon from fluid microinclusions in rocks and ores; sulfur, copper, and nickel from sulfides. The absolute (isotopic) age of sul� fide ores and zircons from rocks in intrusions with var� ious ore potential was determined. To obtain an inte� grated pattern, we also used the latest data of Russian and foreign researchers in this region (3-5 and refer� ences therein). The helium isotopic composition ( 3 Не/ 4 Не ratio) is considered to be the only reliable and strong criterion of the link between mineralforming fluids and the mantle. It is revealed that the ratio of helium isotopes in the Earth's upper mantle (1.2 × 10 -5 ) is ~1000 times higher than in helium formed in rocks of the Earth's crust (~ 2 × 10 -8 ). This allows us to reveal and calculate the portion of mantle helium, if it exceeds 1% of the total helium in the sample. Measurements demon� strated that crustal helium dominated in paleofluids from the Norilsk intrusions and the contribution of mantle helium ranged from 1 to 22%. The contribu� tion of helium of such origin is especially low (1-4%) in rich and intermediate intrusions. Poor intrusions significantly differ by this parameter (4-22%). The argon isotopic composition ( 40 Ar/ 36 Ar) pro�

An Investigation on the Electrochemical Behavior of the Co/Cu Multilayer System

Co/Cu multilayers were deposited in a sulfate solution by controlling the current and potential for the deposition of cobalt and copper layer respectively. The electrochemical behavior of these multilayers was studied by cyclic voltammetry and current transients. In addition, a mathematical analysis was used to characterize the electrodeposition system. Simultaneously, the nucleation and growth mechanisms were monitored by these techniques. In this case, the results clearly showed that electrodeposition of cobalt layers was a kinetically controlled process while the reduction of copper ions was a diffusion-control process. Although nucleation mechanism of the single Co deposit was found as a progressive system, it was found as an instantaneous system with three-dimensional growth mechanism in the Co/Cu bilayer deposition. Atomic Forced Microscopy images of the Co/Cu multilayer also confirmed the aforementioned nucleation mechanism, where it was expected that the growth of multilayer films would form a laminar-type structure containing a large number of equally-sized rounded grains in each layer.

Development of a Suppression Method for Deposition of Radioactive Cobalt after Chemical Decontamination: (II) Consideration of Fe3O4 Plating Mechanism on Stainless Steel in Aqueous Solution at 363K

Recently, chemical decontamination at the beginning of periodical inspection has been applied to many Japanese boiling water reactors in order to reduce radiation exposure. However, following the chemical decontamination, a dose rate increase can be seen in some plants after just a few operation cycles. The Hitachi ferrite coating (Hi-F Coat) process has been developed to reduce the recontamination by radioactive cobalt after the chemical decontamination. In this process, a fine Fe3O4 coating film is formed on the stainless steel base metal of the piping following the chemical decontamination in aqueous solution at 363 K. In this study, we investigated a Fe3O4 plating mechanism on the base metal in aqueous solution at 363K by measurements using a quartz crystal microbalance. We found that the Fe3O4 film grew in three steps. First, the Fe3O4 particles were produced on a stainless steel surface. Second, the Fe3O4 particles grew as dome shapes and the converged domes became filmlike. Third, the film grew and became a closely packed Fe3O4 film. Furthermore, we determined the equation of the time dependence of the Fe3O4 film amount using crystal growth theory. The equation predicted the film amount at 10,000 s within a margin of error of 5%.

Geodynamic and climate controls in the formation of Mio–Pliocene world-class oxidized cobalt and manganese ores in the Katanga province, DR Congo

The Katanga province, Democratic Republic of Congo, hosts world-class cobalt deposits accounting for ~50% of the world reserves. They originated from sediment-hosted stratiform copper and cobalt sulfide deposits within Neoproterozoic metasedimentary rocks. Heterogenite, the main oxidized cobalt mineral, is concentrated as "cobalt caps" along the top of silicified dolomite inselbergs. The supergene cobalt enrichment process is part of a regional process of residual ore formation that also forms world-class "manganese cap" deposits in western Katanga, i.e., the "black earths" that are exploited by both industrial and artisanal mining. Here, we provide constraints on the genesis and the timing of these deposits. Ar­Ar analyses of oxidized Mn ore and in situ U­Pb SIMS measurements of heterogenite yield Mio­Pliocene ages. The Ar­Ar ages suggest a multi-phase process, starting in the Late Miocene (10­5 Ma), when the metal-rich substratum was exposed to the action of meteoric fluids, due to major regional uplift. Further oxidation took place in the Pliocene (3.7­2.3 Ma) and formed most of the observed deposits under humid conditions: Co- and Mn-caps on metal-rich substrata, and coeval Fe laterites on barren areas. These deposits formed prior to the regional shift toward more arid conditions in Central Africa. Arid conditions still prevailed during the Quaternary and resulted in erosion and valley incision, which dismantled the metal-bearing caps and led to ore accumulation in valleys and along foot slopes.

Transient and steady-state model of cobalt deposition in borate-sulfate solutions

A model for cobalt deposition on a cobalt rotating disk in borate-sulfate solutions is fit to experimental impedance spectroscopy (EIS) data obtained at different CoSO 4 concentrations and electrode potentials and steady state polarization curves obtained in the same solutions. The model also accounts for the evolution of hydrogen (HER), adsorption–desorption of boric acid and the transport of dissolved species to and from the electrode. The kinetic parameters are estimated by minimization of the sum-of-squares error between the measurements and model predictions using a genetic algorithm. The model could not be satisfactorily fit to all of the EIS spectra in this study with a unique set of kinetic parameters. A single set of parameters could fit the spectra well over the range of potentials at a given CoSO 4 concentration, but the parameters obtained vary with the CoSO 4 concentration. Conversely, the steady-state current–potential curves obtained at the same CoSO 4 concentrations are very well fit with a single set of parameters. Model analysis indicates that the Co(II) reduction rate is controlled by the first step involving the formation of the adsorbed intermediate Co(I) ads. The situation is less clear for the HER where both the first and second steps appear to influence its rate.

The Geological Setting, Mineralogy, and Paragenesis of Gold-Bearing Polymetallic (Cu+Co+Ag+Au+Bi Pb Ni U) Veins of the Merico-Ethel Property, Elk Lake, Northeastern Ontario, Canada

The Cobalt embayment is a large domain of Paleoproterozoic clastic sedimentary rocks that unconformably overlies the Archean Abitibi greenstone belt. Regionally extensive sills and dikes of Nipissing diabase, emplaced circa 2219 Ma, occur throughout the embayment and are the preferential host to gold-bearing polymetallic vein systems on the Merico-Ethel property, near the northeastern margin of the Cobalt embayment. These gold-bearing, polymetallic veins are predominantly east–west-trending, steeply dipping, discordant calcite-quartz vein systems that formed close to the time of crystallization (within ~15 m.y., based on Pb-Pb ages) of the Nipissing diabase. The ore mineralogy is complex in character, typically comprising sulfides, arsenides, native metals (gold and silver), and specular hematite, preferentially concentrated along the interface between silicate and calcite gangue. A simplified sequence of mineral deposition in the veins is: (1) “Early-stage” pyrite ± chalcopyrite hosted in quartz ± chlorite gangue; (2) “Main-stage” polymetallic (Cu + Co + As + Ag + Au + Bi ± Pb ± Ni ± U) sulfides, arsenides, and native metals hosted in calcite gangue; and (3) “Late-stage” calcite flooding ± galena. Wall-rock alteration in Nipissing diabase is restricted to narrow (<5 cm) haloes of calcite-chlorite-epidote-bearing assemblages, whereas a weak alteration halo of specular hematite, calcite, and allanite-epidote has been observed in the surrounding sedimentary rocks. In terms of their age, geology, mineralogy, paragenesis, and morphology, the gold-bearing vein systems at Merico-Ethel closely resemble the silver-sulfarsenide vein deposits of the historic Cobalt and Gowganda mining camps. These observations indicate that the Au-bearing veins are variants of the Ag-vein systems and as such, have a common genesis belt.

EFFECT OF DIFFERENT PRETREATMENTS TO ELECTROLESS NICKEL OR COBALT PLATING ON HOLLOW MICROSPHERES

Different pretreatment methods for electroless nickel and cobalt plating are demonstrated and compared in the present investigation. The surface morphologies of the nickel or cobalt deposits are investigated by scanning electron microscopy (SEM), and the chemical compositions of the coatings are analyzed by energy-dispersive X-ray spectroscopy (EDX). Method of single-step pretreatment is selected as the optimized method for electroless nickel plating process, while improved two-step sensitization-activation and single-step pretreatment methods can be selected for electroless cobalt plating. It can be found that the content of free Co is much lower compared to electroless Ni plating.