Electrodeposition of Ni–Co alloys from sulfamate baths

The paper describes the results of electrochemical investigations of Ni–Co deposition from a sulfamate bath in the presence of boric acid and two additives. The individual deposition of nickel was shown to be partly inhibited by the adsorption of sulfamate ions at low polarization; such inhibition was not observed for cobalt. The introduction of saccharin at 100 ppm, with a wetting agent seems to hinder sulfamate adsorption and Ni deposition departs at less cathodic potentials. The presence of cobalt has no effect on nickel deposition, whereas cobalt deposition is hindered by the presence of nickel in the bath. Galvanostatic deposition was carried out at the surface of a RDE and with a rotating cylinder Hull cell. At low current densities deposits with a Co content of approx. 40% were produced, but this content was shown to decrease with the applied current density. Examination of experimental data showed that cobalt deposition is diffusion-controlled and that Co content decreases with the applied current density relative to the limiting current density.     

Electrodeposition of zinc–nickel alloys from ammonia-containing baths

This paper describes the use of ammonia-containing baths for Zn–Ni alloy electrodeposition. Buffering properties of the ammonia/ammonium couple limit the local change in pH in the vicinity of the electrode surface caused by simultaneous hydrogen evolution. In addition, it is shown that the divalent zinc and nickel species exist in the form of Zn(NH₃) ₄ ²⁺ and Ni(NH₃) ₆ ²⁺ complexes over a large pH range. The electrochemistry of the deposition at pH 10 was investigated by galvanostatic experiments and cyclic voltammetry, and compared with deposition from ammonium chloride baths at pH 5. The Ni content in the alloys were found to be 40–60% higher from the ammonia-containing bath than from the acidic baths. Reduction of divalent ions and hydrogen evolution were shown to occur at potentials 250mV more cathodic than with baths at pH 5; the deposition mechanism may be affected by complexation of the metal cations by ammonia.     

Electrodeposition of Au–Sn alloys from alkaline baths

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed. The investigated system is an alkaline KAu(CN)₂ bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations are based on cyclic voltammetry and electrodeposition experiments. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Co-deposition of Au and Sn gives rise to the formation of a series of intermetallic phases, which can be detected by X-ray diffraction and anodic stripping. Deposits are typically polyphasic; the phase composition generally does not correspond to the equilibrium one. Chemical compositions ranging from high-Au to high-Sn can be obtained by galvanostatic deposition at suitable current densities.     

Electrodeposition of silver–tin alloys from pyrophosphate-cyanide electrolytes

Using cyclic-voltammetric techniques, a pyrophosphate-cyanide electrolyte for the electrodeposition of compact Ag–Sn alloy coatings is investigated. This electrolyte is suited to further investigations on the alloy composition, structure and properties. The electrodeposition of coatings with up to 40 wt% Sn is possible from the investigated complex electrolytes. The alloy surpasses the saturation limit of the silver lattice with Sn and allows the formation of coatings with phase heterogeneity. At high tin content an ordered spatial distribution of different alloy phases on the cathodic surface can be observed. The pattern formation in this system looks very similar to the phenomena and structures observed during electrodeposition of other silver alloys, such as Ag–Sb, Ag–Bi and Ag–In.     

Electrodeposition of Au–Sn alloys from acid Au(III) baths

A bath for the electrodeposition of white gold alloys of interest for the electroforming of hollow jewellery is proposed and investigated. The system was an acidic Au(III)–Sn(IV) bath for the electrodeposition of Au–Sn alloys. The electrochemical investigations were based on cyclic voltammetry, linear-sweep voltammetry, galvanostatic electrodeposition experiments and in situ Raman spectroscopy. The electrode kinetics of alloy formation were elucidated by stripping voltammetry. The effects of cathodically adsorbed CN^– were studied by in situ Raman spectroscopy. Electrodeposited foils were studied from the crystallographic, compositional and morphological points of view. Codeposition of Au and Sn gives rise to a single phase of approximately equiatomic composition over a current density interval of 10 to 40 mA cm^–2. This orthorhombic phase is structurally the same as the phase of the equilibrium Au–Sn system, but its stoichiometry and lattice parameters are different. The equilibrium two-phase , structure can be obtained by heat-treatment.     

Electrodeposition of zinc–iron alloy from an alkaline bath in the presence of sorbitol

The chronopotentiometric technique was used to analyze the electrodeposition of Fe–Zn film on a Pt electrode. Three different Fe³⁺/Zn²⁺ molar ratios, Fe26.8 wt.%–Zn73.2 wt.%, Fe46 wt.%–Zn54 wt.% and Fe66.6 wt.%–Zn33.4 wt.%, were used in a solution containing sorbitol as the Fe³⁺-complexing agent, with a total concentration of the two cations of 0.20 M. Coloration of Fe–Zn films were light gray, dull dark gray and bright graphite, depending on the Fe³⁺/Zn²⁺ ratios in the deposition bath. The highest stripping to deposition charge density ratio was 47.5%, at 15 mA cm⁻² in the Fe26.8 wt.%–Zn73.2 wt.% bath. Energy dispersive spectroscopy indicated that the codeposition type of Fe and Zn in the Fe26.8 wt.%–Zn73.2 wt.% and Fe46 wt.%–Zn54 wt.% baths was normal at all j_d tested, while in the Fe66.6 wt.%–Zn33.4 wt.% bath there was a transitional current density from normal to equilibrium codeposition at 50 mA cm⁻². Scanning electron microscopy showed that Fe–Zn films of high quality were obtained from the Fe66.6 wt.%–Zn33.4 wt.% and Fe26.8 wt.%–Zn73.2 wt.% baths, since the films were smooth. X-ray analysis of the Zn–Fe films obtained at 15, 25 and 50 mA cm⁻², in the Fe26.8 wt.%–Zn73.2 wt.%, Fe46 wt.%–Zn54 wt.% and Fe66.6 wt.%–Zn33.4 wt.% plating baths, suggested the occurrence, in general, of a mixture of Fe₁₁Zn₄₀, Fe₄Zn₉, βFe, αFe, Fe₂O₃, Zn and PtZn alloys in the deposit.     

Electrodeposition of Cu–Zn alloy coatings from citrate baths containing benzotriazole and cysteine as additives

Alternative electrolytes, such as citrate baths, are now studied, aiming to reduce the toxicity and the cost of the electroplating process while maintaining the decorative qualities and anticorrosive properties of the coatings. For this purpose, brightening and/or leveling compounds are usually added to the base citrate bath. In this work, Cu–Zn alloys were electroplated on mild steel substrates from electrolytes containing sodium citrate and additives (benzotriazole and cysteine) at constant stirring speed. The results showed that coatings produced from baths containing additives were brighter than those obtained from the base citrate bath. Additionally, the presence of benzotriazole directly influenced the coating composition and the properties of the deposited alloy: the amount of zinc in this coating increased excessively, and the coating/substrate corrosion presented a poor anticorrosive performance.     

Electrolyte solutions in liquid ammonia—IX. Electrodeposition and electrodissolution of metals from their salts

Anodic dissolution and cathodic deposition of 20 transition metals in acidic solutions in liquid ammonia has been surveyed. The early transition metal elements Ti, Zr, V Nb, Mo and W form high oxidation-state insoluble amido complexes during anodic oxidation. Soluble ammines of normal metal oxidation states are produced with Cr(III), Mn(II), Fe(II), Co(III), Ni(II), Cu(II), Ag(I), Zn(II), Cd(II) and Hg(II) (Mn dissolves spontaneously). The metals Ru, Pd, Pt and Au only dissolve slightly after prolonged electrolysis. Anodic enrichment of Au in its alloys is unlike that in aqueous solution; in ammonia both Cu and Ag can be simultaneously depleted from a 9 carat gold alloy. Cathodic reduction of metal-bearing solutions follows wide variations of behaviour. Fe and Ru ammines reduce to amido-complexes with concomittant hydrogen evolution, but Cr is not reduced. Solutions of Mn, Co, Ni, Pd, Pt, Ag, Au, Zn, Cd and Hg give metallic cathode deposits under differing conditions. Electrodeposition is potential dependent for Ni, Cu and Ag; metal plate at low potentials, and powders at high potentials. The two different products are the result of reduction of species with different degrees of solvation.     

Electrodeposition of Zn–SiC nanocomposite coatings

Zn–SiC composite coatings were obtained on mild steel substrate by electrodeposition technique with high-current efficiency. A slightly acidic chloride bath, containing SiC nanoparticles and gelatine as additive, was used. The electrodeposition was carried out under galvanostatic control with pulsed direct current; the effect of experimental parameters (temperature, average current density and particles concentration) on composition, morphology and structure of the deposit was studied. Coatings were characterized by means of scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry and Vickers microhardness measurements. Zn–SiC electrodeposits with the best characteristics were obtained by performing electrodepositions at 45 °C, with 20 g L^?1 SiC in the bath and with average current density in the range 100–150 mA cm^?2. Under these experimental conditions, homogeneous and compact coatings, with low-grain size and SiC content ranging from 1.7 to 2.1 wt%, were found to be electrodeposited. Microhardness measurements showed for these deposits an increase of about 50 % with respect to those without nanoparticles obtained in the same experimental conditions.     

Electrodeposition, composition and structure of Zn—Cr alloys

The effect of polyethylene glycol (PEG 1500) as additive and of deposition conditions on Zn—Cr alloy electrodeposition from an acidic sulfate electrolyte at room temperature, without agitation was investigated. PEG polarizes the overall cathodic reaction and inhibits Zn deposition. Cr codeposition with Zn starts at a cathodic potential of about –1,95 V vs Hg/Hg₂SO₄, which is reached at current density of about 20 A dm^–2 in galvanostatic conditions. Zn—Cr alloy coatings containing up to 28 at % Cr were obtained depending on the plating conditions. SEM observations showed an island-like structure, formed by the local growth of crystals, which covered the surface during further deposition. In the first stages of electrodeposition the powder diffraction spectra contain lines of b.c.c. -(Zn,Cr) phase (a 3.02 Å). After 30 s deposition time weak lines of Zn-based phase (a 2.67 Å, c 4.90 Å) appear, and become clearly visible in coatings deposited for 90 s. The average Cr content in the alloy coatings decreases with advancing deposition. The as-plated surface contains C in organic compounds and Zn(OH)₂. After 50 min sputtering, Zn and a mixture of Cr, Cr₂O₃ and Cr₇C₃ were found. The presence of organic C and O, probably from inclusions of PEG, were also detected.     

Electrodeposition and properties of cyclically modulated silver–antimony alloys

An investigation was carried out on the influence of electrodeposition conditions on the properties of cyclically modulated Ag–Sb alloys, such as internal stress, microhardness, roughness, electrical contact resistance, wear resistance and plug-in forces. Pulses of different amplitude and duration were used, leading to different composition and thickness of the deposited sublayers, and the resulting changes in the coating properties were demonstrated. The possibility of depositing coatings free of internal stress is shown. The electrical contact resistance does not depend on the multilayer structure of the coating, but on the type and properties of the upper sublayer. The microhardness of the multilayer coatings increases with the increase in their antimony content. It decreases for very short pulses whereby the effect of the higher current density cannot be realized. The wear resistance of the multilayer coatings displays values between those of the respective monolayer coatings deposited under the conditions of separate sublayer deposition. It increases at a very small sublayer thickness, at decreasing contribution of the higher current density and at lower stress values of the multilayer coatings. The roughness of the coatings is not influenced by their multilayer structure, and the plug-in forces increase with the reduction of the sublayer thickness to about 0.03 m.     

Electrodeposition of PbO2 and Bi–PbO2 on Ebonex

Electrodeposition of PbO2 and Bi–PbO2 on Ebonex was carried out under various conditions, and the surfaces and coating/substrate interfaces examined by SEM, XPS and SIMS. Excellent adhesion to Ebonex was obtained with both crystalline and amorphous surfaces. Low plating temperatures resulted in dark grey, bright PbO2 and black, mirror-like Bi–PbO2 surfaces. Extrapolation of electrode lifetime test data indicated corrosion rates of 716 m yr–1 for PbO2 and 158 m yr–1 for Bi–PbO2.     

Electrodeposition of La–Ni alloy films in a nonaqueous system

The codeposition of La–Ni alloy films in a nonaqueous system was investigated. The effects of several factors including the concentrations of main salts, pH, temperature, current density and substrates on the lanthanum content in the deposit were studied. The results show that the lanthanum content in the deposit can reach 18 wt% by controlling the system composition and deposition conditions. X-ray photoelectron spectrometry, X-ray diffraction and scanning electron microscope were used to characterize the morphology and structure of the deposit. The results show that the majority of lanthanum exists in the form of LaH₂, while the rest exists as metal and its oxide in the deposit, and the structure of the alloy deposited is amorphous.     

Electrodeposition and optical properties of highly oriented γ-CuI thin films

A simple electrochemical process has been demonstrated to grow highly oriented γ-CuI thin films on indium doped tin oxide (ITO) glass through reducing Cu(II)-ethylene diamine tetraacetic acid disodium (EDTA) complex in aqueous solutions at or near room temperature. The CuI thin films grow preferential orientation along the 〈1 1 1〉 crystal axis from the X-ray diffraction patterns. The oriented growth of the CuI thin films is not affected by the solution pH and the applied potentials. The possible mechanism of the oriented growth is discussed, and the surface energy of different crystal planes of CuI crystal is believed to play an important role to control the oriented growth of the CuI thin films. The bandgap of the electrodeposited CuI films is 2.98 eV and the photoluminescence spectra of the CuI thin films exhibit relative intense exciton band luminescence at room temperature.     

Electrodeposition of Fe−Ni−Co alloys part I: Direct current deposition

Effects of hydrodynamic conditions, current density and solution temperature on the d.c. electrodeposition of Fe–Ni–Co alloys have been investigated with stationary planar and rotating cylindrical electrodes. The deposition rate of Fe showed mass transfer effects at cathodic potentials –1.35 V/sce. Deposition of Ni appeared to be kinetically controlled; deposition of Co appeared to be under kinetic control at potentials –1.35 V/sce but under mixed control at –1.65 V. Current efficiency of the codeposition process increased with increasing current density and decreased with increasing rotation rate. Higher solution temperatures and rotation rates extended the applied current density range where smooth, adherent, and metallic-looking deposits could be obtained. An increase in solution temperatures also decreased anomalous codeposition of Fe–Ni–Co. Calculations based on the Hessami-Tobias model provide qualitative agreement with dependence of experimental electrodeposition on applied current density, hydrodynamics and temperature.     

Electrodeposition and characterization of Zn–Ni alloys as sublayers for epoxy coating deposition

The chemical composition and phase structure of Zn–Ni alloys obtained by electrodeposition under various conditions were investigated. The influence of the deposition solution and deposition current density on the composition, phase structure, current efficiency and corrosion properties of Zn–Ni alloys were examined. It was shown that the chemical composition and phase structure affect the anticorrosive properties of Zn–Ni alloys. A Zn–Ni alloy electrodeposited from a chloride solution at 20 mA cm^–2 exhibited the best corrosion properties, so this alloy was chosen for further examination. Epoxy coatings were formed by cathodic electrodeposition of an epoxy resin on steel and steel modified with a Zn–Ni alloy. From the time dependence of the pore resistance, coating capacitance and relative permittivity of the epoxy coating, the diffusion coefficient of water through the epoxy coating, D(H₂O), and its thermal stability, it was shown that the Zn–Ni sublayer significantly affects the electrochemical and transport properties, as well as the thermal stability of epoxy coatings. On the basis of the experimental results it can be concluded that modification of a steel surface by a Zn–Ni alloy improves the corrosion protection of epoxy coatings.     

Electrodeposition and characterization of nickel–copper metallic foams for application as electrodes for supercapacitors

Nickel–copper metallic foams were electrodeposited from an acidic electrolyte, using hydrogen bubble evolution as a dynamic template. Their morphology and chemical composition was studied by scanning electron microscopy and related to the deposition parameters (applied current density and deposition time). For high currents densities (above 1 A cm^?2) the nickel–copper deposits have a three-dimensional foam-like morphology with randomly distributed nearly-circular pores whose walls present an open dendritic structure. The nickel–copper foams are crystalline and composed of pure nickel and a copper-rich phase containing nickel in solid solution. The electrochemical behaviour of the material was studied by cyclic voltammetry and chronopotentiometry (charge–discharge curves) aiming at its application as a positive electrode for supercapacitors. Cyclic voltammograms showed that the Ni–Cu foams have a pseudocapacitive behaviour. The specific capacitance was calculated from charge–discharge data and the best value (105 F g^?1 at 1 mA cm^?2) was obtained for nickel–copper foams deposited at 1.8 A cm^?2 for 180 s. Cycling stability of these foams was also assessed and they present a 90 % capacitance retention after 10,000 cycles at 10 mA cm^?2.     

Electrodeposition of Al,Mn, and Al–Mn Alloy on aluminum electrodes from molten salt (AlCl<Subscript>3</Subscript>–NaCl–KCl)

Electrochemical deposition of aluminum and manganese from basic and acidic molten AlCl₃–NaCl–KCl mixture on an aluminum electrode at 180 °C was studied by the methods of voltammetry, and potential and current transient. The deposition of aluminum was found to proceed via a nucleation/growth mechanism in basic melt, while the deposition of manganese was found to be diffusion controlled in basic melt. The diffusion coefficient of Mn²⁺ ions in basic melt, as derived by voltammetry was in agreement with the deductions of transient methods. Analysis of the chronoamperograms indicates that the deposition of manganese on Al was controlled by 3D diffusion controlled nucleation and growth. The processes are manifested as peaks on a decaying chronoamperogram. Non-linear fitting methods were applied to obtain the kinetic parameters from theoretical formulae proposed to describe this system. It is also found that under more cathodic potentials, the saturation number density of the manganese nuclei and also the efficiency of use of the available surface nucleation sites increased.     

Electrodeposition and tribocorrosion behaviour of ZrO<Subscript>2</Subscript>–Ni composite coatings

With the objective of producing new functional surfaces with enhanced tribo-corrosion properties we have investigated the electrochemical codeposition of composites in which an electrodeposited metal (nickel) is the matrix and a transition metal oxide (ZrO₂) is the dispersed phase. This paper describes the effect of ZrO₂ dispersed particle codeposition on nickel electrocrystallisation steps as well as the tribocorrosion behaviour of the composite coatings obtained. This system was selected because nickel is an industrially important coating material on steel and other support materials. The cathodic polarization curves have been plotted both in the presence and absence of the insoluble dispersed phase. Electrochemical impedance spectroscopy was used to obtain additional information on the early steps of nickel and nickel matrix composite electrodeposition. Impedance data were acquired with a Solartron type electrochemical interface and frequency response analyzer. A schematic codeposition mechanism is proposed. The influence of zirconium oxide on the nickel electrodeposition steps is discussed. The tribocorrosion properties of ZrO₂–Ni composite coatings (100 μm thickness) have been studied in 0.5 M K₂SO₄ solution on a pin on disc tribo-corrosimeter connected to an electrochemical cell. The normal force applied was 10 N at a rotation speed of 120 rpm. The counterbody (pin) was a corrundum cylinder (7 mm in diameter), mounted vertically on a rotating head, above the specimen. The lower spherical end (radius = 100 mm) of the pin was then applied against the composite surface (disc).     

Composite Electrodeposition of Ultrafine γ-Alumina Particles in Nickel Matrices; Part I: Citrate and chloride electrolytes

Electrodeposition of nanocomposite -alumina–nickel was examined using citrate and chloride electrolytes with rotating cylinder electrodes. Ultrafine alumina was detected in the nickel matrices and was found to depend on the applied current density. The particle incorporation rate dependence on the applied d.c. current density varied for the different electrolytes. In the chloride baths, higher particle concentrations were found in the deposits plated at low current densities compared to higher values. However, the opposite trend was noted for the citrate electrolyte where an increase in particle deposit content was observed with an increase in applied current density. Additionally, the nickel anodic behaviour was examined in order to devise a pulse-reverse (PR) plating method. PR deposition lead to an enhancement in the -alumina deposit concentration compared to DC plating in chloride electrolytes.