Zinc–cobalt alloy electrodeposition from chloride baths

Electrodeposition of Zn–Co alloys on iron substrate from chloride baths under galvanostatic and potentiostatic conditions were carried out. Current density, temperature and cobalt percentage in the bath were found to strongly influence the composition of the deposits and their morphology. Changes in potentials, current efficiency and partial current densities were studied. The results show that the shift in potential and in the cobalt percentage of the deposits, for a particular current density during galvanostatic electrodeposition, does not always correspond to the transition from normal to anomalous codeposition. This shift is attributed to zinc ion discharge, which passes from underpotential to thermodynamic conditions. In the range of potentials for the underpotential deposition of zinc, the electrodeposition of zinc–cobalt alloys is discussed, emphasizing the influence of the electrode potential on the composition and microstructure of the deposits.     

Role of polyethylene glycol in electrodeposition of zinc–chromium alloys

The role of polyethylene glycol (PEG) as an additive in the electrodeposition of zinc–chromium alloys was investigated in sulfate baths containing trivalent chromium. PEG with high molecular weight enabled the codeposition of metallic chromium with zinc, while chromium(III) was present in the deposits obtained from the baths containing PEG with lower molecular weight as well as the PEG-free bath. The polarization curves for the alloy deposition revealed that PEG with high molecular weight polarized the deposition potential of zinc to the reduction potential of chromium to permit the codeposition of chromium with zinc.     

Electrodeposition of Co–Cu alloy coatings from glycinate baths

The cathodic polarization, cathodic current efficiency of codeposition, composition and structure of Co–Cu alloy as a function of bath composition, current density and temperature were studied. Electrodeposition was carried out from solutions containing CuSO₄ · 5H₂O, CoSO₄ · 7H₂O, Na₂SO₄ and NH₂CH₂COOH. The cathodic current efficiency of codeposition (CCE) was high and it increased with increasing temperature and Cu²⁺ content in the bath, but it decreased with current density. The codeposition of Co–Cu alloys from these baths can be classified as regular. The Co content of the deposit increased with Co²⁺ content and current density and decreased with glycine concentration and temperature. The structure of the deposited alloys was characterized by anodic stripping and X-ray diffraction techniques. The data showed that the deposited alloys consisted of a single solid solution phase with a face-centred cubic (f.c.c.) structure.     

Electrodeposition and characterization of thin layers of Zn–Co alloys obtained from glycinate baths

An alkaline bath containing CoSO₄ · 7H₂O, ZnSO₄ · 7H₂O, Na₂SO₄ and NH₂CH₂COOH is proposed for the deposition of thin layers of Zn–Co alloys onto steel substrates. Electrodeposition was carried out at 0.216–1.080 A dm^–2, pH 10 and 10–55 °C. The influence of bath composition, current density and temperature on galvanostatic cathodic polarization, cathodic current efficiency and alloy composition was studied. Different proportions of the two metals were obtained by using different deposition parameters, but at all Zn(II)/Co(II) ratios studied, preferential deposition of zinc occurred and anomalous codeposition took place. Increasing the bath temperature enhanced the cobalt content in the deposit. X-ray diffraction measurements indicated that the phase structure of the deposits was controlled by the applied current density. The Co₅Zn₂₁ phase was formed at low current density, while the CoZn₁₃ phase was formed at high current density. The potentiodynamic dissolution of the coatings showed that they contained Zn–Co alloy of different content and structure.     

Microstructural characterization and corrosion resistance of Ni–Zn–P alloys electrolessly deposited from a sulphate bath

Electroless Ni–Zn–P alloy coatings were obtained on an iron substrate from a sulfate bath at various pH values. The effects of changes in bath pH on alloy composition, morphology, microstructure and corrosion resistance were studied. Scanning electron microscopy was performed to observe the morphological change of the deposits with bath pH. Coating crystallinity was investigated by grazing incidence asymmetric Bragg X-ray diffraction and transmission electron microscopy. A transition from an amorphous to polycrystalline structure was observed on increasing the bath alkalinity, and thus decreasing the phosphorus content of the alloys. A single crystalline phase corresponding to face-centred-cubic nickel was identified in the alloys obtained from a strong alkaline solution. An increase in zinc percentage up to 23% in the deposits does not change the f.c.c. nickel crystalline structure. Corrosion potential and polarization resistance measurements indicated that the corrosion resistance of electroless Ni–Zn–P alloys depends strongly on the microstructure and chemical composition. The deposits obtained at pH 9.0–9.5 and with 11.4–12.5% zinc and 11.8–11.2% phosphorous exhibited the best corrosion resistance.     

Ni–Zn–P alloy deposition from sulfate bath: inhibitory effect of zinc

Electroless Ni–Zn–P alloy deposition from a sulphate bath, containing sodium hypophosphite as reducer, was investigated. To increase the plating rate, the deposition parameters were optimized. The effect of process parameters (T, pH and [Zn²⁺]) on the plating rate and deposit composition was examined and it was found that the presence of zinc in the bath has an inhibitory effect on the alloy deposition. As a consequence, the percentage of zinc in the electroless Ni–Zn–P alloys never reaches high values. Using cyclic voltammetry the electrodeposition mechanism of Ni–Zn–P alloys was investigated. It was observed that the zinc deposition inhibits the nickel discharge and, as a consequence, its catalytic activity on hypophosphite oxidation. It was also found that increase in temperature or pH leads to the deposition of nickel rich alloys.     

Effect of some operating variables on the characteristics of electrodeposited Cu?Ni alloys with and without α-Al2O3 and TiO2 inert particles

A study was carried out on the electrodeposition of Cu Ni alloys containing inert (α-Al₂O₃ and TiO₂) particles from a selected citrate bath. The cathodic polarization curves show that alloy deposition occurs at more noble potentials relative to either of the two parent metals and this indicated the formation of a solid solution. The addition of the inert particles into the selected bath led to a polarization-increasing effect and this increased with increases in the size and concentration of the particles in the bath. An explanation of the mechanism of codeposition of the inert particles with the alloy has been presented. On controlling the bath composition, Cu Ni alloys containing 11–40% of nickel could be deposited. The effect of the operating variables such as the concentration of the metal ions in the bath, pH and current density on the alloy composition indicated that the formation of the Cu Ni alloy belongs to the regular alloy deposition system. The current efficiency of the alloy deposition is relatively lower than for either of the two parent metals, from similar baths, and ranges between 76 and 84%. The microhardness of the deposited Cu Ni alloy improved from 170 to 248 kfg mm⁻² as a result of codeposition of 1–2% of the inert particles. A direct correlation between the surface morphology of the deposited Cu Ni alloy, as revealed by SEM, and its microhardness could be detected. X-ray diffraction studies confirmed the dispersion of the α-Al₂O₃ and TiO₂ phases in the Cu Ni alloy phase.     

Electroplating of a Co–Cu alloy from a citrate bath containing boric acid

The effects of bath composition, current density and temperature on cathodic polarization, cathodic current efficiency of codeposition, composition and structure of Co–Cu alloys electroplated on a steel substrate from citrate baths have been studied. Addition of boric acid to citrate electrolyte increases the percentage of Co in the deposits and improves the quality of these deposits. The cathodic current efficiency of the baths is relatively high and increases with increases in the metal content in the bath and the current density but decreases with temperature. The composition of the deposit is controlled by the applied current density. At low current densities, Cu‐rich alloys were obtained. At higher current densities, the composition of the alloys was controlled by the limiting current density of Cu codeposition. The Co content of the deposits increases with increases in the metal content in the bath and the temperature. The structure of the deposited alloys was characterized by anodic stripping and X‐ray diffraction techniques. The deposited alloys consisted of a single solid solution phase with a face‐centred cubic structure. © 2000 Society of Chemical Industry     

Electroplating of Fe-Ni alloys: Effects of sulphamic acid and sulphosalicylic acid

The electroplating of thin films of Fe–Ni alloys from acidic sulphate baths containing sulphamic acid and sulphosalicyclic acid has been studied under different plating conditions. The alloy composition varied with bath composition, current density and the concentrations of sulphosalicylic acid and sulphamic acid. Stirring of the bath solution enhanced the percentage of Fe in the alloy. The deposition potential became less noble with increase in the current density. Under some plating conditions, the plating system had a cathodic current efficiency greater than 90%. The coercivity values of the alloys were in the range 5–18 oersteds. From the X-ray analysis data f c c structure is assigned to the alloy films. Electroplating conditions have been optimized in order to obtain thin films of 20–80 Fe–Ni permalloy.     

Anomalous codeposition of Co–Ni: alloys from gluconate baths

Thin films of cobalt–nickel alloys were galvanostatically deposited onto steel substrates from gluconate baths. Cathodic polarization curves were determined for the parent metals and Co–Ni alloy. The effects of bath composition, current density and temperature on cathodic current efficiency (CCE) and alloy composition were studied. The deposition of Co–Ni alloy is of anomalous type, in which the less noble metal (Co) is preferentially deposited. The CCE of codeposition is high and increases with increase in temperature and current density, but it decreases as the [Co²⁺]/[Ni²⁺] ratio in the bath increases. The percentage of Co in the deposit increases with increasing cathodic current density, temperature and increasing Co²⁺ ion concentration. The structure and surface morphology of the deposit were studied by XRD, ALSV and SEM. The results showed that the alloys consisted of a single solid solution phase with a hexagonal close packed structure.     

Electrodeposition and characterization of Au–Cu–Cd alloys

The electrodeposition of Au–Cu–Cd alloys from cyanide baths was investigated under different hydrodynamic conditions. Alloys obtained at different current densities were characterized from the compositional, structural and morphological points of view. Depending on the electrodeposition current density, the deposit structure displays either one or two-phase disordered solid solutions; corresponding changes in mechanical properties were observed. Morphology and roughness show a marked smoothing transition when the current density is increased over the limit for the inception of Cu codeposition. The Cd²⁺ concentration in the bath is a critical factor for control of the electrodeposition process, especially in respect to compositional stability and absence of hydrogen incorporation. Alloy composition was shown to be critically affected by hydrodynamic conditions; strict control of flow conditions is needed in order to obtain alloys of desired and reproducible composition.     

Electrodeposition of Sn-Co alloys from gluconate baths

Electrodeposition of Sn-Co alloys was carried out from baths containing 2–20 g dm^–3 SnSO₄, 4–18 g dm^–3 CoSO₄.7H₂O, C₆H₁₁O₇Na and K₂SO₄ under different conditions of bath composition, pH, current density and temperature on to copper substrates. The influence of these variables on the cathodic potential, cathodic current efficiency and composition of the deposit were studied. The results show that the deposition of Sn-Co alloys from gluconate baths depends greatly on the concentration of tin. At high tin concentrations, tin is the more noble component. At low tin concentrations, tin reduction is strongly suppressed due to the formation of a more stable Sn-gluconate complex species and tin becomes the less noble component. The codeposition of Sn-Co alloy from these baths can be classified as an irregular plating system. The surface morphology of deposits was examined by scanning electron microscopy and crystal structure by X-ray. The results show that the structure of the deposits was controlled by the alloy composition.     

Effect of some plating variables on the electrodeposition of Cu-Zn alloys from alkaline tartrate baths

The electrodeposition of copper, zinc and copper-zinc alloys from alkaline tartrate solutions has been investigated under different conditions of bath composition, added ammonium chloride, current density and temperature. A detailed study has been made of the effect of the variables on the cathode potentials and cathode efficiencies of copper, zinc and Cu-Zn alloys; the compositions of the alloys were determined. The results were consistent with the behaviour of a regular alloy plating system with zinc being the less noble metal.     

Electrochemical deposition of superconductor alloy precursor in a low melting molten salt medium

The applicability of the room temperature molten salt medium based on the 1-methyl-3-ethylimidazolium chloride/AlCl3 (MeEtImCl/AlCl3) system for the deposition of superconductor alloy precursors (Bi–Sr–Ca–Cu) was investigated. Problems of poor solubility of the constituent metal salts in the neutral melt and aluminium codeposition in the acidic melt were identified for the use of the chloroaluminate room temperature molten salt. Thus, a novel all-chloride molten system (MeEtImCl) was developed in the present work and used at 120°C. Cyclic voltammetry was used to investigate the suitability of Pt, Al, Ti, Cu and Ag as substrate for alloy deposition and aluminium was found to be the best for depositing alkaline earth metal alloys. The working deposition conditions were a constant potential of –1.72V for 75s in an electrolytic bath containing BiCl3 (0.068mol), SrCl2 (0.50mol), CaCl2 (0.18mol) and CuCl2 (0.050mol) in 1kg MeEtImCl (6.83mol). The compositions of the electrodeposits obtained were in close agreement with the mole ratios of the Bi–Sr–Ca–Cu superconductor alloy precursor.     

Normal and anomalous codeposition of Zn–Ni alloys from chloride bath

The codeposition of Zn–Ni alloys from chloride bath has been studied by means of potentiostatic electrodeposition in the potential range –700 to –1100mV vs Ag/AgCl, where both normal and anomalous codeposition occurs. Deposition of alloys of different composition, morphology and structure, depending on the cathodic potential, was found. Analysis of the partial current densities showed that the production of nickel rich alloys in the potential range –700 to –900mV is due to the underpotential reduction of zinc, driven by nickel ion discharge. Morphological and microstructural analyses showed that these alloys have the face-centred-cubic structure of nickel ( phase) and that the addition of zinc in the nickel lattice causes internal stresses in the deposits, which are prevalently amorphous. At potentials more negative than –910mV, corresponding to the equilibrium potential of the zinc rich phase deposition, the rate of deposition of the phase decreases and the further increase in deposit zinc content leads to the formation of the phase, with a decrease in internal stress. In this range of potential, zinc and nickel reduction can occur separately, according to their respective exchange current densities.     

Effect of benzylideneacetone on the electrodeposition mechanism of Zn–Co alloy

The influence of benzylideneacetone (BA) on the mechanism of Zn–Co alloy electrodeposition onto AISI 1018 steel was studied in chloride acidic solutions. Results indicate that BA modifies the exchange current densities of zinc and cobalt such that the alloy is electrodeposited via a normal codeposition mechanism. Analysis of the deposits by Auger spectroscopy and X-ray diffraction shows that BA increases the cobalt concentration in the electrodeposited alloys and gives deposits with a constant concentration profile of both Zn and Co. BA also inhibits the formation of zinc hydroxide in the initial deposition stages, which supports the proposed mechanism of normal codeposition. Finally, it is shown that BA modifies the morphology of the deposits by inducing a reduction in the cluster size, leading to compact, smooth and shiny coatings.     

Hydrogen permeation inhibition by thin layer Zn–Ni alloy electrodeposition

The inhibition of hydrogen permeation by zinc-nickel electrodeposited alloy was investigated using the Devanathan–Stachurski permeation technique. The hydrogen evolution and hydrogen permeation rates for the zinc–nickel alloy electrodeposits on iron are compared with the rates for bare iron, zinc electroplated on iron, and nickel electroplated on iron. Hydrogen evolution rates and hydrogen permeation rates were followed as functions of time at different applied potentials. The hydrogen permeation inhibition for thin zinc–nickel electroplates (20s at 10mAcm–2 and 10s at 20mAcm–2) averaged 80% and intermediate to that of nickel and zinc. This inhibition was considered to be mostly due to kinetic effects. Zinc–nickel electroplated for 20 and 40min. at 10mAcm–2 inhibited the hydrogen permeation greater than 95% as compared to bare iron. This inhibition was due to both kinetics and the barrier effect caused by the diffusion resistance of the membrane.     

Electrodeposition of Ni, Fe and Ni–Fe alloys on a 316 stainless steel surface in a fluorborate bath

Electrodeposition processes of Ni, Fe and Ni–Fe alloys on 316 stainless steel surfaces in fluorborate baths were studied using conventional electrochemical techniques and atomic force microscopy. The results showed that these processes occurred under mass transfer control, associated with nucleation and growth process. Cathodic current–time transients indicated that the nucleation and growth of Ni–Fe alloy was different from that of the single metal (Ni or Fe). For one, two nucleation and growth processes occurred during Ni–Fe alloy codeposition. Also, there was a nucleation and growth process of Ni–Fe alloy on Ni–Fe clusters, due to a change of the Ni–Fe alloy composition and phase. Homogeneous Ni–Fe alloy deposits could be obtained by pulse potential plating. AFM images of Ni, Fe and Ni–Fe deposits prepared by pulse potential plating revealed the following results: (1) the growth rate of Ni nuclei was faster in parallel than in perpendicular to the 316 electrode surface; (2) for Fe nuclei, the preferential growth direction was perpendicular to the 316 electrode surface; and (3) for Ni–Fe nuclei, there was no preferential growth direction and uniformly hemispherical Ni–Fe clusters were obtained.     

Electrolytic nickel—molybdenum—vanadium alloy coatings as a material with a decreased hydrogen overvoltage

The process of electrodeposition of Ni-Mo-V alloys from an alkaline tartrate bath was studied. The effect of the cathodic current density on the chemical composition, phase composition and surface morphology of Ni-Mo-V alloy deposits, as well as on the current efficiency of the deposition process, was determined. Codeposition of molybdenum and vanadium with nickel and formation of the Ni-Mo-V alloy is possible due to the effects of depolarization and overpolarization occurring in the process of codischarge of the complex ions of these metals. It was observed that the use of cathodes electrodeposited with Ni-Mo-V alloy containing 9–12% Mo and 0.1–0.2% V for water electrolysis resulted in a decreased overpotential for hydrogen evolution.     

Electrodeposition of zinc-nickel alloy coatings: influence of a phenolic derivative

The electroplating of Zn–Ni alloy films from a chloride bath has been studied under different plating conditions, both in the absence and presence of a phenolic derivative. Under the conditions examined, the electrodeposition of the alloys belonged to the anomalous type. The morphology and composition of the deposits varied with current density, temperature, bath composition and additive concentration. The results show that the additive modifies the structure and surface topography of the deposits to a large extent and produces smoother deposits. The corrosion resistance of the alloys has been analyzed by means of salt-spray tests.