Electrodeposition of cobalt-nickel alloys from ammoniacal single-complex baths

The electrodeposition of cobalt-nickel alloys has been studied from ammoniacal single-complex baths containing 5–50 CoSo₄·7H₂O, 5–50 NiCl₂·46H₂O, 20–50 g dm^?3 (NH₄)₂SO₄ and 250–350 cm³ dm^?3 NH₄OH (20.5% solution). The effects of the plating current density and the concentrations of the bath constituents on the cathodic polarisation, current efficiency and composition of the alloy were investigated. A wide range of alloy compositions with a current efficiency of 60–80% could be obtained from the main baths examined. The alloy plating system interchanged between the normal and the anomalous types depending upon the plating current density and the concentration of NH⁺₄ ion in the bath. Electron microscopic and X-ray diffraction studies proved that the structure of the electrodeposited alloy was controlled by the alloy composition.     

Electrodeposition of lead alloys from fluoborate baths

The codeposition of some elements with lead from fluoborate baths has been studied in order to obtain lead alloys with a low concentration of a second metal. The metals considered were As, Bi, Cu, Sb, Se, Sn and Te. The chemical analysis of alloys obtained in various electrolysis conditions permitted an investigation of the kinetic behaviour of the metals codeposited with lead. The results showed that only Bi, Sb, Se and Te attain a limiting value of discharge current density and that the codeposition is regular for all metals. SEM observation of the deposits revealed that Sb and Se have a marked influence on the crystal morphology while the remaining metals induce only minor modifications.     

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.     

Electrodeposition of Cd-Ni alloys from acetate baths using a superimposed alternating current

The electrodeposition of Cd–Ni alloys from some selected acetate baths has been investigated. The influences of the proportions of Ni²⁺ and Cd²⁺ ions in the bath, the operating current density and superimposed alternating current on the electrodeposited alloys have been examined. The study includes the effect of these variables on the cathodic polarization curves, current efficiency, chemical composition and surface morphology of the alloys. Under all conditions the electrodeposition process is of the anomalous type. An explanation of this phenomenon with the help of a comparison between the experimental and the calculated polarization curves is given. X-ray diffraction studies show that the nickel-rich alloys consist of Ni and (Cd–Ni) phases, while the cadmium-rich alloys contain Cd, (Cd–Ni) and Ni phases. The optimum bath composition and operating conditions for the electrodeposition of sound, smooth and bright Cd–Ni alloys have been identified.     

Electrodeposition of amorphous/nanocrystalline and polycrystalline Ni-Mo alloys from pyrophosphate baths

Pyrophosphate plating bath was found to be a good alternative to citrate bath for deposition of Ni-Mo amorphous alloys. The addition of wetting agents such as 2-butyne-1,4-diol and rokafenol N-10 to the pyrophosphate bath resulted in the removal of bumps, spheres and cracks from the Ni-Mo alloy surface. The plated alloy layers adhered well to Cu-Zn brass and steel, were of thickness from a fraction to tens of micrometers and the molybdenum content was independent of the distance from the support. An increase in the concentration of the molybdate ion in the bath leads to an increase in the amount of Mo in the alloys up to 33-35 at.% and to a decrease in the deposition rate. These changes and the influence of pH are discussed in the paper. The atom arrangement in the alloys changes from (2 2 0) preferred for pure-nickel deposition to (1 1 1) for content of Mo higher than 15 at.%. For 20 and more at.% of Mo the structure of the alloy is amorphous like. An analysis of SEM and STM micrographs obtained indicates that contrary to the Ni-W alloy the “amorphous” phase is made of circa 10-50 nm in diameter objects and not by long needles perpendicular to the substrate.     

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.     

Electrodeposition of PbTe thin films from acidic nitrate baths

Electrodeposition of PbTe thin films from an acidic nitric bath was systematically investigated to understand the kinetics and the effect of electrodeposition conditions on film composition, crystallographic structure, texture and grain size. The electroanalytical studies employed initially with a rotating disk electrode to investigate the kinetics associated with Te, Pb and PbTe electrodeposition. The results indicated that the PbTe thin films were obtained by the underpotential deposition (UPD) of Pb atoms onto the overpotentially deposited Te atoms on a substrate.Based on these studies, PbTe thin films were potentiostatically electrodeposited using e-beam evaporated gold thin films on silicon substrate to investigate the effect of various deposition conditions on film composition and microstructure. The data indicated that the microstructure, composition and preferred film growth orientation of PbTe thin films strongly depended on the applied potential and electrolyte concentration. At −0.12 V, the film was granular, dense, and preferentially oriented in the [1 0 0] direction. At potentials more negative than −0.15 V, the film was dendritic and preferentially oriented in the [2 1 1] direction. A smooth, dense and crystalline film with nearly stoichiometric composition was obtained at −0.12 V from a solution containing 0.01 M HTeO₂⁺, 0.05 Pb²⁺ and 1 M HNO₃.     

Electrodeposition of silver telluride thin films from non-aqueous baths

We describe a method for preparation of crystalline silver telluride films by cathodic deposition from dimethyl sulfoxide (DMSO) solutions containing 0.1 M NaNO₃, 5.0 mM AgNO₃ and 3.5-7.0 mM TeCl₄. X-ray diffraction data indicated that the deposited silver telluride films could be adjusted from Ag excess and stoichiometric monoclinic Ag₂Te to hexagonal Ag₇Te₄ by increasing the concentration of TeCl₄ in the electrolyte or lowering the deposition potential. The Ag₂Te film is gray and the Ag₇Te₄ film is dark blue-gray and mirror like adhered strongly to the substrates. Scanning electron microscopy images show that Ag₂Te films were formed with globular grains with average diameters of more than 1 μm. In contrast, Ag₇Te₄ film consists of triangles characteristic of a (1 1 1) single-crystal with a hexagonal structure in average sizes of about 0.4 μm. The X-ray photoelectron spectra (XPS) indicated that the binding energies deviation of Te3d in Ag₇Te₄ is less than that in Ag₂Te, which is consistent with the apparent valences of Te in Ag₂Te and Ag₇Te₄. Finally, the cathodic deposition reactions were studied by cyclic voltammetry.     

Electrodeposition of catalytically active nickel-thallium alloy powders from sulphate baths

The electrodeposition of nickel-thallium alloy powder was investigated from acidic sulphate baths containing 0.0125 NiSO₄·6H₂O, 0.005–0.020 Tl Cl, 0.05–0.23 (NH₄)₂SO₄, 0.1 H₃BO₃ and 0.07 mol l^–1 Na₂SO₄ · 10H₂O. The polarization curves, the percentage composition and the current efficiency of the electrodeposited alloy powders were determined as a function of the bath composition. In addition, some properties of the deposits were examined such as the surface morphology, the structure as revealed by X-ray diffraction analysis and the catalytic activity towards the decomposition of 0.4% H₂O₂ solution. The results indicate that the characteristics of the alloy deposition and the properties of the alloy powder are affected to different extents by the bath composition.     

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 of antimony telluride thin films from acidic nitrate-tartrate baths

Electrochemical quartz crystal microbalance (EQCM) and rotating disk electrode (RDE) techniques were utilized to systematically investigate the electrodeposition of Sb_xTe_1−x (0.1 < x < 0.8). In addition, the effect of applied potential and agitation were correlated to the film composition, crystal structure, and morphology. Although the film composition was independent of the agitation rate, the deposition rate, current efficiency, crystallinity and phase of Sb_xTe_1−x were all strongly influenced by it. The deposition rate monotonically increased with increases in the rotation rate because of the faster diffusion rate of HTeO₂⁺ ions to the cathode. Amorphous thin films were electrodeposited in the absence of agitation, whereas polycrystalline Sb₂Te₃ with elemental Sb and Te were co-deposited at a higher agitation independent of the applied deposition potential.     

Electrodeposition of Pb–Cu alloy coatings from gluconate baths

Pb–Cu alloy coatings were electrodeposited on steel sheet cathodes from baths containing mixtures of lead nitrate, copper nitrate and sodium gluconate. Cathodic polarization, cathodic current efficiency and deposit composition were determined under different plating conditions. The results were consistent with the behaviour of a regular plating system with copper being the preferentially depositable metal. The lead (the less noble metal) content in the deposits increased with increase in current density and concentration of lead in the bath but decreased with increase in bath copper concentration. The structure and morphology of the as-deposited coatings were examined by X-ray, AES and SEM. The results showed that the deposits consist of a mixture of fine crystals of the two metals and the morphology of the deposits is mainly controlled by the composition of the deposit.     

Electrodeposition of catalytically active Co-Ni-Tl alloy powders from dilute sulphate baths

Cobalt-nickel-thallium alloy powders were electrodeposited from dilute metal sulphate baths of composition: 0.007–0.0245 mol l^–1 CoSO₄·7H₂O, 0.0245–0.007 mol l^–1 NiSO₄·6H₂O, 0.001 mol l^–1 TlCl, 0.5 mol l^–1 (NH₄)₂SO₄, 0.07 mol l^–1 Na₂SO₄·10H₂O and 0.4 mol l^–1 H₃BO₃. The cathodic polarization curves were traced during electrodeposition and utilized in the discussion of a reaction mechanism for the electrolytic powder deposition. The alloy composition and the cathodic current efficiency were influenced to a great extent by the bath composition (I) and slightly by the deposition current density (II). Irrespective of variables (I) and (II), the electrodeposition of the alloy belonged to the anomalous type. The surface morphology and the catalytic activity, towards the decomposition of 0.4% H₂O₂ solution, of the as-deposited alloy powders were affected predominantly by the percentage of cobalt in the alloy. X-ray diffraction studies showed that the alloys consisted mainly of the face-centred cubic nickel phase either alone or with minor proportions of face-centred cubic cobalt phase and hexagonal close-packed -cobalt phase. The occurrence of the latter phases was observed only in the alloys with a higher cobalt percentage than nickel.     

Electrodeposition of zinc-nickel alloys from chloride solution

Operating conditions for zinc and nickel codeposition from chloride baths were studied in order to obtain alloys containing up to 20% nickel. Satisfactory deposits were produced at 50°C using current densities ranging from 5 to 20 mA cm^–2 and nickel to zinc ratios ranging from 6.8 to 37.5%.Under the conditions studied, an empirical relationship was deduced in order to calculate the nickel percentage in the deposit from baths of prefixed composition using a given current density. Deposits having a nickel concentration lower than 11% were found to comprise the and phases, while at higher nickel concentration (up to 20%), the alloys showed only the phase structure, with preferred orientation (442) and (600) and excellent microhardness and corrosion resistance properties.     

Electrodeposition of rhenium-nickel alloys from aqueous solutions

Rhenium-nickel alloys were deposited on copper substrates in a small three-electrode cell, under galvanostatic conditions. The bath solution consisted of ammonium perrhenate, citric acid and nickel sulfamate. The effects of bath composition and deposition time were studied. The Faradaic efficiency (FE) and partial deposition current densities were calculated based on mass gain and elemental analysis using energy dispersive spectroscopy. The surface morphology was characterized by scanning electron microscopy. The thickness of the coating was measured on metallographic cross-sections. The results are discussed with emphasis on routes to increase the Faradaic efficiency and rhenium content in the coating. A plausible mechanism for the electrodeposition of rhenium-nickel alloys is presented.     

Electrodeposition of nickel-cobalt-zinc alloys from a borate bath

The electrodeposition has been studied of nickel-cobalt-zinc alloys from a borate bath containing nickel sulphate (120–140 g dm^–3), cobalt sulphate (30–46 g dm^–3), zinc sulphate (144–168 g dm^–3), boric acid (30 g dm^–3) and ammonium chloride (2 g dm^–3). The operating conditions were: current density, 2.0–5.0 A dm^–2; temperature, 30–40°C and pH, 2.4 to 5.4. Light grey, semibright, stressed films have been obtained. However, the deposits consist partially of black powder when the concentration of the various components is increased. The brightness is found to increase with decreasing temperature and pH of the solution. The total cathode efficiency increases when the pH and temperature of the solution decrease, whereas at any particular pH and temperature it first decreases, reaches a minimum and then increases with increasing current density.     

Electrodeposition of Ni-Cu-Mo ternary alloys from citrate electrolytes

Conditions for the electrodeposition of Ni–Cu–Mo alloys from citrate electrolytes have been developed. The composition variations of the deposits with electrolyte pH and concentration have been investigated. A maximum molybdenum and nickel content is obtained for a pH of 7 and for low copper and large citrate concentrations. Molybdenum and copper are preferentially discharged at low current density whereas at high current density nickel becomes predominant. The deposits have a nodular morphology similar to that of the binary Ni–Mo layers     

Electrodeposition of aluminium-copper alloys from alkyl benzene electrolytes

An experimental programme in which aluminium-copper alloys were electroplated from alkyl benzene/ AlBr₃ electrolytes is described. The investigation showed that Al-Cu alloys (0–3.5 wt% Cu) can be plated onto steel and that the resulting coatings are bright, adherent and less porous than equivalent coatings of pure aluminium. The composition of the cathode deposits can be readily controlled by using Al-Cu anodes of specified copper content. About half the copper dissolved from the anodes is transferred to the cathode, the remainder being precipitated from the electrolyte as CuBr. Coating composition varies with current density and this parameter can also be used to control the process. In a parallel investigation, potential differences between aluminium and a number of other metals (Zn, Pb, Cd, Sn, Cu, Ag) were measured. Potential differences in the alkyl benzene electrolytes were found to be 10–30 times less than in aqueous electrolytes which indicates that the alkyl benzenes should be useful for plating other alloys in addition to those of aluminium and copper.     

Electrodeposition of ternary nickel-iron-molybdenum alloys from an acetate bath

Ternary nickel-iron-molybdenum alloys containing 0.5–8.5% molybdenum, 18–48% iron and balance nickel were electrodeposited from an acetate bath under a variety of conditions. Satisfactory deposits were obtained from the bath containing 0.3394 M nickel acetate, 0.02878 M ferrous sulphate, 0.0015 M sodium molybdate at current density 2.0 A dm^–2, pH 5.0 and temperature 20°C without agitation for plating times up to 30min. The alloy deposits were examined for their crystal structure by X-ray diffraction and microstructure by metallography.Dedicated in honour of the late Dr D. Singh, Reader in Chemistry, Banaras Hindu University.