Mössbauer and XRD investigation of electrodeposited Fe,Co and Fe-Co alloys using a gluconate plating process

Summary A fundamental requirement for electrodeposition systems of the 21st century is that the processes involved should be environmentally safe, as well as they should be suited to replace hazardous conventional processes thereby supporting global sustainability. Conventional plating baths contain hazardous components and facilitate the generation of non-desirable compounds. The subject of the present article is the electrodeposition of Fe, Co, and Fe-Co alloys from an electrolyte based on gluconate. Preliminary studies showed that good quality iron-cobalt alloy coatings could be obtained on copper substrates from an environmentally acceptable gluconate plating system. The gluconate bath is inexpensive, non-toxic and easily disposed of. We report the successful deposition of Fe, Co and Fe-Co alloys from a modified gluconate based electrolyte which has not been used previously to deposit these materials. The effect of process parameters, such as current density, pH and deposition time were investigated using the gluconate electrolyte at a temperature of 60 °C and a pH of 7. The phase composition, crystal structure and magnetic anisotropy of the obtained alloy deposits are correlated with the applied process parameters. The structural analysis of the deposits is mainly based on ⁵⁷Fe CEMS and XRD measurements. α-Fe and Co-Fe were identified as dominant phases in Fe and Co/Fe deposits, respectively. The magnetic anisotropy of the Fe-containing deposits was found to correlate with the current density applied during deposition. The time of electrodeposition, at the same time, had little if any effect on the magnetic anisotropy of the obtained deposits. The mechanism and formation of the electrodeposits are discussed on the basis of the obtained results.     

Role of Complex Formation in Mass Transport during Nickel Electrodeposition from Low-Concentration Formate–Chloride Electrolytes

Nickel electrodeposition from 0.2 M formate–chloride solutions is studied. Depending on electrolyte pH₀, the highest current density of the electrodeposition of compact nickel deposits varies from 3 (pH₀3.5) to 40 A dm^–2(pH₀2.0). With the current efficiency for nickel taken into account, this corresponds to nickel deposition rates of 3 to 25 A dm^–2. One of the reasons for the high permissible current densities is good buffer properties of the electrolyte. Computer calculations show that the considerable acceleration of the nickel electrodeposition is due to mass transport accelerated by the formation of complex [NiL]⁺cations. The complex formation also affects the intensity of interaction between nickel and hydrogen ions transported to the cathode. The current by nickel increases due to the participation of formic acid molecules in the hydrogen evolution.     

Microdistribution of Electrolytic Nickel Deposits and Their Surface Topography: Effect of Hydrogen

The role of hydrogen and the near-electrode gas–liquid flows in the formation of the nickel surface microrelief on a smooth copper electrode in a sulfate electrolyte is studied at different values of solution pH, current density, and deposit thickness. Depending on the discharge kinetics of ions being reduced and the mechanism of removal of bubbles from the electrode surface, a nickel-plating electrolyte displays either ideal or poor microthrowing and leveling powers. The development of three- and two-dimensional microwaves discovered on the deposits is closely related to the nature of natural-convective motion of electrolyte and the influence exerted by mass transfer on the electrocrystallization process.     

Numerical Solution of the Problem of the Limiting Current for the Copper Electrodeposition from a Solution of Cupric Sulfate and Sulfuric Acid in Conditions of Natural Convection

Equations for a boundary layer, written in self-similar variables, are integrated numerically to obtain distributions of concentration of ions Cu²⁺, H⁺, and SO₄ ^2–; a hydrodynamic velocity; partial currents of electrolyte components; and the limiting current of copper deposition and determine the Rayleigh number for the system under consideration. The results are compared with an approximate analytical solution obtained earlier.     

Distribution of components of binary nickel—chromium alloys electrodeposited from sulfate—oxalate solutions

The composition and distribution of elements over the thickness of electrodeposited nickel—chromium layers are studied by x-ray photoelectron and Auger electron spectroscopy techniques. During a layer-by-layer etching, the Cr : Ni ratio varies with a period of 2–5 nm. This period and the amplitude of the ratio of concentrations of components increases with the current density. During alloy deposition on a copper cathode, the first to deposit is nickel, which exerts a catalytic effect on the chromium deposition, which in turn exerts a catalytic effect on the oxalate reduction to carbon. Once a deposit thicknesses of ~100 nm is reached, the alloy composition becomes constant. The deposits contain considerable amounts of carbon (in the form of graphitized structures and carbides), which increases from 0.6 to 2 wt % with the current density. The surface of the growing alloy 50–70 nm thick is rich in nickel and chromium hydroxides and organic compounds containing carboxyl groups.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1481–1486.Original Russian Text Copyright © 2004 by Edigaryan, 4, Lubnin, Polukarov.     

Composition of magnetic layer and magnetotransport properties of electrodeposited layered nanostructures (Co-Cu)/Cu and (Ni-Co-Cu)/Cu

The magnetotransport characteristics of Co-Ni-Cu layered coatings containings 100 nanobilayers were measured at room temperature in a magnetic field of ±5 kOe. The coatings were deposited onto nickel sputtered on glass. It is shown that a decrease in the content of copper in the magnetic layer due to the conversion of copper ions in the solution into the multi-charge anionic complexes (by the example of sulfosalicylate electrolyte) leads to an increase in the giant magnetoresistance (GMR) effect. The stabilization of composition of Co-based magnetic layer by shifting the copper deposition potential to the equilibrium potential of Co or by introducing Ni, which assists the deposit passivation, leads to a decrease of the GMR effect. A benefit effect of partial dissolution of Co at the deposition potentials of nonmagnetic layer on the magnetotransport characteristics of multilayered coatings is first revealed. It is supposed that the effect is caused by the morphological factor of surface smoothing due to preferential dissolution of projecting areas of magnetic layer.     

Electrodeposition of Ni–Fe Alloys in the Presence of Complexing Agents

The electrodeposition of binary Ni–Fe alloys is studied in chloride-based solutions with organic additives. Specific codeposition composition of the electrolyte and operating variables are taken for deposition a wide range of Ni–Fe deposits. Results reveal that in solutions containing sodium citrate and glycolic acid, the nickel content always increases with the current density and nickel concentration. Therefore, nickel reduction rate and the Ni/Fe ratio in the deposits increase. The anomalous codeposition of iron is minimized and the quality of the alloy deposits is improved with the combination of sodium citrate and glycolic acid. Scanning electron micrographs show that, with addition of glycolic acid, the spherical particles become finer and the surface roughness relatively decreases. The XRD patterns of the Ni–Fe deposits exhibit the fcc structure and (111) preferred orientation for alloys with nickel content exceeding 60 wt %. After a heat treatment, additional peaks appear for an Ni–Fe solid solution.     

Voltammetric Detection of Copper Ions on a Gold Electrode Modified with a N-methyl-2-naphthyl-cyclam film

A voltammetric sensor based on a methyl-naphthyl cyclam (1,4,8,11-tetraazacyclotetradecane) film deposited through dip coating on gold electrodes allowed the sensitive detection of copper (II). The obtained film was characterized in terms of the composition and morphology using Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy. In the presence of divalent metallic ions (copper and nickel) and trivalent metallic ions (iron), at pH 7 and 7.7, the current density of the ionic oxidation peak maximum was determined using square wave voltammetry. The relative variation of this current density varies linearly with the base-ten logarithm of the ion concentration. From this calibration curve, a detection limit of 7?×?10^?12?M was obtained for copper (II) at pH 7. At this pH value, the sensitivity of detection of copper (II) was 2.5 times higher than for nickel (II) and 5.8 times higher than for iron (III). The methyl-naphthyl cyclam film-modified gold sensor was validated for the detection of copper in spiked urine samples.     

Initial stages of copper electrocrystallization from sulfate electrolytes: Cyclic voltammetry on a platinum ring-disk electrode

Initial stages of copper electrocrystallization on platinum rotating and stationary ring-disk electrodes are studied in sulfate electrolytes of different acidities by cyclic voltammetry with a variable cathodic limit. In a weakly acid sodium sulfate solution of pH 3.7, copper deposition occurs at a higher rate than in a sulfuric acid electrolyte, which is due to an acceleration of the discharge of copper ions caused by local electrostatic effects that occur during the specific adsorption of sulfate anions and hydroxyl ions and to alterating nature of electroactive species. The mechanism of the formation of intermediate species (ions Cu⁺) during the deposition and dissolution of copper in solutions of different acidities is established.     

Kinetics of Cathodic Processes of Deposition of Nickel–Molybdenum Alloys from an Ammonia–Citrate Electrolyte

Kinetics of cathodic processes in an ammonia–citrate electrolyte for depositing Ni–Mo alloys is studied. During electrolysis at potentials of up to –0.92 V (NHE) the cathode surface becomes covered by a film consisting of compounds of molybdenum of lower valencies. The beginning of the alloy deposition, which occurs at potentials more negative than –0.92 V, barely affects the partial density of the current of reduction of molybdate ions.     

Copper Complexes Stabilized by Chitosans: Peculiarities of the Structure,Redox, and Catalytic Properties

Peculiarities of the structure and physicochemical properties of copper–chitosan complexes prepared by different methods were studied by IR, UV-visible, ESR spectroscopy, and electron microscopy. The catalytic activity of redox copper centers stabilized by the chitosan matrix in the reactions of oxidation of o- and p-dihydroxybenzenes in an aqueous medium was determined. Quantitative ESR measurements provide evidence for the localization of virtually all copper ions introduced in the initial heterogeneous chitosan samples with copper contents below 1.5 wt % in the form of isolated Cu²⁺ ions in square planar coordination. The chitosan matrix was shown to strongly bind copper ions under conditions of redox transformations in the catalytic tests or upon prolonged heating in boiling water. Reoxidation of the samples with H₂O₂ results in quantitative restoration of the initial ESR signal of Cu(II). Heterogenized copper–chitosan samples exhibited high activity and stability in the catalytic oxidation of dihydroxybenzenes into quinones, whereas the homogeneous system was characterized by irreversible poisoning due to formation of copper–hydroquinone complexes. Preparation of the binary composite system with a thin heterogeneous copper–chitosan film supported on a macroporous silica allows one to dramatically enhance the specific catalytic activity and the efficiency of the active component. Such an approach may turn out to be useful in the synthesis of supported chitosan catalyst with a low noble metal content.     

Determination of heavy metals by electrothermal atomic absorption spectrometry after electrodeposition on a graphite probe

Traces of heavy metals were separated and preconcentrated electrochemically at a controlled potential on the graphite ridge probe. After the electrolysis, the electrode-probe was inserted in the graphite furnace for atomization of metal deposit by an automatic system. Conditions for the electrodeposition, such as pH of solutions, the deposition potential and concentration of electrolyte, were optimized. Detection limits improved with increased time of electrodeposition and were 16 ng l⁻¹ Cu, 1.0 ng l⁻¹ Cd, 6.0 ng l⁻¹ Pb, 64 ng l⁻¹ Ni, 14 ng l⁻¹ Cr (III) and 17 ng l⁻¹ Cr (VI) for a 10-min deposition. This method was applied for the determination of copper, cadmium, lead, nickel and of chromium species in seawater.     

Throwing power of a dilute sulfuric acid copper plating electrolyte during intensive electrodeposition

A method of determination of the throwing power (TP) of electrolytes in conditions of forced convection in a Hull cell with a rotating cylindrical electrode is presented. The method is used to determine TP of a copper plating electrolyte containing 0.15–0.5 M CuSO₄ and 1 M H₂SO₄ at current densities of up to 75 mA cm^-2. The TP decreases with increasing current density at a constant i _av/i _d ratio, where i _av is the average working current density and i _d the limiting diffusion current density. With increasing the i _av/i _d ratio due to an increase in the cathodic polarizability conditions for an increase in TP may be achieved. In optimum (for uniform deposition) modes, i _av/i _d 0.4–0.5. The TP may increase upon diluting electrolyte with respect to its main component.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 91–96.Original Russian Text Copyright © 2005 by Dikusar, Bobanova, Yushchenko, Yakovets.To the Centennial of B.N. Kabanov.     

Properties of Co-Mo coatings obtained by electrodeposition at pH 6.6

Cobalt-molybdenum coatings were prepared by electrodeposition in a sulfate-citrate bath and their morphology, structure and magnetic properties were analysed. Concentrations of 0.1 mol dm^–3 CoSO₄ and 0.005 mol dm^–3 Na₂MoO₄ at pH 6.6 led to Co-Mo deposits of 20–23% Mo that can be grown to several microns over graphite or copper substrates. At low deposition potentials or current densities, the deposits presented a close-packed hexagonal structure (hcp) that evolved to a (100)+(110) preferred orientation and acicular morphology as the deposit thickness increased. When the deposition potential or the current density was made more negative, a mixed crystalline+amorphous structure was obtained. The degree of crystallinity depended on the thickness: thin films were more amorphous than the thicker ones. Co-Mo deposits showed lower saturation magnetization (M_s) and coercivity (H_c) than the pure cobalt deposits. The crystalline+amorphous films showed the lowest H_c values (around 40 Oe).     

CuInSe2 thin-film deposition on flexible plastic substrate: electrolyte recirculation rate and deposition potential effects

Copper indium diselenide (CuInSe₂; CIS) layer was electrolytically plated from an aqueous medium at room temperature onto electroless nickel deposited on flexible plastic (Kapton). The CIS depositions were carried out under constant deposition potentials (−0.5 to −1.1 V vs. Ag/AgCl) and at various electrolyte flow rates (0.3 to 1.5 ml/s) under constant applied current. The resulting thin films were characterized using atomic force microscopy, energy-dispersive X-ray spectroscopy, environmental scanning electron microscopy, and X-ray diffraction. The surface morphology and the atomic composition of the deposited CIS film were found to be influenced by the deposition potential under potential control and the electrolyte recirculation rate under current control. Low electrolyte flow rates under constant current control and high cathodic deposition potential under voltage control favor the deposition of indium. CIS films of uniform deposit, smoother surfaces, and with better adhesion properties are favored by moderate electrolyte recirculation rate. At a current density of 0.6 mA/cm², the electrolyte recirculation rate required to achieve ideal CIS atomic composition was found to be 1.0 ml/s in such a setting. The crystallinity of the film improved after annealing for 2 h at 390 °C under argon atmosphere.     

Use of Silica Gel Chemically Modified with Mercapto Groups for the Extraction, Preconcentration, and Spectroscopic Determination of Palladium

Silica gel chemically modified with mercaptopropyl groups is proposed for the extraction and preconcentration of palladium. This silica gel extracts palladium(II) at an acidity from 6M HCl to pH 4 with distribution ratios at a level of n× 10⁴ g/cm³. Hyphenated procedures for the adsorption–photometric determination of palladium with detection limits of 0.1 g/0.1 g of the adsorbent have been developed. The procedure includes the adsorption preconcentration of palladium, elution by hot (50 ± 5°C) 8% thiourea in 1M HCl, and atomic absorption determination of palladium in the eluate (detection limit is 0.05 g/mL). The procedures were applied to the determination of palladium in standard reference samples of copper–nickel ore and copper concentrate.     

Electrodeposition of a cobalt-molybdenum alloy from an ammonia-citrate electrolyte

Kinetics of processes of electrochemical production of a cobalt-molybdenum alloy out of an ammonia-citrate electrolyte is studied. The electrolyte’s composition is similar to that used for depositing a nickel-molybdenum alloy. It is established that the cobalt-molybdenum alloy undergoes deposition at smaller values of pH (5.0–6.0) than the nickel-molybdenum alloy (7.0–9.0). The current efficiency for the cobalt-molybdenum alloy is substantially dependent on the electrolyte pH, whereas the chemical composition of the obtained deposits is practically independent of the electrolyte pH in the pH interval 5.0–8.0 at current densities of 0.025 to 0.100 A cm^?2. On the other hand, a change in the electrolyte pH produces a considerable effect on the morphology of the obtained deposits. At large values of pH (pH 8.0), one can obtain a powder-like deposit of the cobalt-molybdenum alloy with a small value of the current efficiency. The deposits that are obtained in the pH region 5.0–6.0 have some cracks, with the number of cracks increasing with the electrolyte pH.     

Mutual Influence of Electrode Processes during Electrodeposition of Layered Structures by the Single-Bath Method: The Effect of Nickel Deposition and Hydrogen Evolution on the Transport of Copper Ions in Acetate and Sulfamate Electrolytes

The effect of nickel deposition and hydrogen evolution on the transport of copper-containing ions is studied by numerically solving an electrodiffusion problem with use made of variational values of the formation constants of nickel and copper complexes in acetate and sulfamate electrolytes and thicknesses of the diffusion layer. It is concluded that the major contribution to the mass transfer is made by the effects of exaltation of the migration current and by the agitation of the near-electrode layer of electrolyte by evolving hydrogen. The possibility of employing migration effects in order to reduce the limiting current of copper in the region of nickel deposition and hydrogen evolution is substantiated. This will decrease the copper content in a layer of alloy during electrodeposition of layered structures.     

Electrocatalytic oxidation of thiosulfate on a modified nickel hexacyanoferrate film electrode

Summary A modified nickel hexacyanoferrate film glassy carbon electrode is prepared by the electrochemical deposition technique. The film is very stable upon voltammetric scanning in the potential range of 1.0 to –0.5 V (vs. SCE) and an oxidation peak occurs at 0.35 V (vs. SCE) (1 mol/l NaNO₃). The effects of electrolyte, solvent, coexisting ions and other variables on the voltammetric behaviour of the modified film have been studied. The thickness of the resulting film can be controlled by changing the number of voltammetric cycles and the concentrations of nickel(II) and hexacyanoferrate(III) ions. The film shows catalytic activity towards electrooxidation of thiosulfate with a peak potential +0.5 V (K^–-containing media). This oxidation potential of thiosulfate on the modified electrode is shifted negatively by about 550 mV as compared to the naked glassy carbon electrode. For practical application, the modified electrode can be used for the determination of thiosulfate in concentrations from 5.0×10^–5 to 1.0×10^–1 mol/l. This method has been successfully applied to the determination of thiosulfate in photographic waste effluents.     

The electrodeposition and properties of Zn-Ni + Ni composite coatings

The Zn-Ni+Ni coatings were deposited under galvanostatic conditions at the current density range from 20 to 60 mA cm^?2. The influence of deposition current density on surface morphology, chemical and phase composition and corrosion resistance of obtained coatings, was investigated. Structural investigations were conducted by X-ray diffraction method. Surface morphology and surface chemical composition of the obtained coatings were determined by a scanning electron microscope. Studies of electrochemical corrosion resistance were carried out in the 5% NaCl solution, using potentiodynamic and Scanning Kelvin Probe (SKP) methods. A possibility of incorporation of nickel powder from a suspension bath to the Zn-Ni matrix, during galvanostatic deposition was demonstrated. The results of chemical composition analysis show that the Zn-Ni + Ni coatings contain approximately 15?C18% at Ni. It was found that surface morphology, surface chemical and phase composition of Zn-Ni + Ni coatings depend in small degree on deposition current density. However, the current density influences distribution of nickel powder on the surface of these coatings. The optimal values of current density on account of corrosion resistance, are found to be j = 40?C50 mA cm^?2.