Electroplating of Fe-Ni alloys: a sulphate-amine bath

Thin films of Fe-Ni alloys have been electroplated from acidic sulphate bath (0.06 mol dm^–3 NiSO₄, O.O15 mol dm^–3 FeSO₄, 0.005 mol dm^–3 ascorbic acid, 20 g dm^–3 boric acid and 1 g dm^–3 saccharin) containing aliphatic amines. The percentage Ni in the alloy varied with bath composition (Fe/Ni), current density, stirring of the medium, nature and concentration of the amine. Increase of temperature and pH of the medium increased the percentage Ni in the deposit. The composition of the alloy remained constant with thickness of the film. The cathodic current efficiency depends on the plating variables. The plating potential in acidic sulphate bath was shifted in the less noble direction by the presence of amines. Smooth and bright films are obtained with small grain size when the Ni in the film is 75% or above. Electroplating conditions are optimized to get thin, magnetic 2080 Fe-Ni films.Presented at the International Symposium on Recent Aspects of Electroanalytical Chemistry and Electrochemical Technology at Chanigarh, India.     

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.     

Preparation and characterization of nanocrystalline Fe–Ni–Cr alloy electrodeposits on Fe substrate

Fe–Ni–Cr alloy layers were prepared by electrodeposition from trivalent chromium plating bath in chloride-sulfate based solution. The influences of bath composition and plating parameters on the alloy electrodeposition process and the properties of deposited alloy were studied. The effects of plating parameters and bath composition such as current density, bath pH, bath temperature, the concentrations of FeSO₄ · 7H₂O and CrCl₃ · 6H₂O on the contents of Fe and Cr in Fe–Ni–Cr alloy layer were investigated. Electrodeposited Fe–Ni–Cr alloy layers on Fe substrate were characterized by X-ray diffraction (XRD), Electronic Differential System (EDS) and a CHI600B electrochemistry workstation. The composition of the Fe–Ni–Cr coatings depends on bath composition and plating conditions including pH, current density, and temperature. The internal structure of the alloy is nanocrystalline, the average grain size is 87 nm, and the corrosion resistance of the alloy layers is better than that of pure nickel layers.     

Electrodeposition of Ni-W-B amorphous alloys

Partial polarization curves at the glassy carbon rotating disc electrode have been used to study the electrodeposition of Ni and Ni-W alloy from citrate-containing solution. For deposition of Ni-W alloys, the partial polarization curves indicate diffusion control for nickel reduction and stoichiometric limitation for tungsten deposition by the composition of the alloy. Plating experiments show that current efficiency of the electrodeposition and composition of the resulting alloy depend on the parameters of the electrolysis. The best conditions for electrodeposition of the alloy Ni-W-B are current density of 45–50 mA cm^–2, temperature of 60–70 °C, Ni(II) concentration of 20–25 mm, and pH 8.5. Pulsed galvanostatic plating at 1 Hz increased slightly the current efficiency. The concentration of Ni(II) in the solution can be self-regulated by using a nickel bipolar electrode in the cathode compartment.     

Effects of boric acid on hydrogen evolution and internal stress in films deposited from a nickel sulfamate bath

The effects of boric acid additions on the pH close to the electrode surface, on the hydrogen evolution reaction and on the internal stress in the plated films were studied for the high speed electroplating of nickel from a nickel sulfamate bath at a current density close to the nickel ion limiting current density. The study was carried out at 50 °C and pH 4.0 using a 1.55 M nickel sulfamate plating bath containing boric acid at concentrations ranging from 0 to 0.81 mol L^–1. The variation of the internal strain in the plated nickel films was determined in situ using a resistance wire-type strain gauge fitted to the reverse side of the copper electrode substrate. The solution pH at a distance of 0.1 mm from the depositing nickel film was measured in situ using a miniature pH sensor assembly consisting of a thin wire-type antimony electrode and a Ag/AgCl/sat. KCl electrode housed in a thin Luggin capillary. The addition of boric acid was shown to effectively suppress the hydrogen evolution reaction at nickel electrodeposition rates (18.0 A dm^–2) close to the limiting current density (~20 A dm^–2). Consequently, the solution pH adjacent to the plating metal surface was maintained at a value close to that in the bulk solution and the development of high internal stresses in the deposited nickel films was avoided.     

Electrodeposition of noncrystalline cobalt–tungsten alloys from citrate electrolytes

Induced electrodeposition of Co–W alloys onto steel substrates from acid citrate baths has been investigated. The effects of some plating parameters, such as current density, pH and temperature on the potentiodynamic cathodic polarization curves, cathodic current efficiency of the alloy and the percentage tungsten in the alloy were studied. Highly adherent and compact Co–W alloys codeposited from citrate baths containing up to 28 mass % tungsten were obtained. The percentage W (w/w) in the alloy increases with increasing pH, bath temperature and Co²⁺ ion concentration. On the other hand, the percentage W in the alloy decreases with increasing current density. Anodic linear stripping voltammetry (ALSV) indicated that the alloy might consist of one phase solid solution. These alloys were determined to be noncrystalline by X-ray diffraction analysis.     

Electrodeposition of ternary nickel-iron-cadmium alloys

Ternary nickel-iron-cadmium alloys have been electrodeposited from an acetate bath. The effect of bath composition current density, pH, temperature and duration of electrolysis on the deposit composition, quality and cathode current efficiency has been studied. The influence of some addition agents and cathodic polarization has also been studied. The iron and cadmium content decreased with an increase in current density or pH but did not alter significantly with respect to temperature, time or addition agents. X-ray studies confirmed the formation of a single-phase alloy within the composition range studied (84–88 wt% Ni).Dedicated to the memory of the late Dr D. Singh DSc, Reader in Chemistry, Banaras Hindu University.     

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 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.     

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.     

Electrochemical activation of the electroless deposition of Ni–P alloy and phase structure characterization of the deposit Part II: Single bath system

The process of electroless Ni plating (EP) was activated by the cathodic deposition of precursors of Ni in the same bath in which EP takes place. The current density (c.d.), duration of cathodic activation, as well as the duration of subsequent EP were varied and the effect of these parameters on the phase composition of the resulting Ni–P deposits was determined by anodic linear sweep voltammetry (ALSV). It was found that electrochemical activation can be achieved with relatively low c.d. and short current pulses, to run at rates comparable to EP activated in other ways. The rate of EP alone was found to be in the range between 1 and 5 mC cm^–2 s^–1, regardless of the activation c.d. or the amount of electrochemically deposited Ni precursors. A synergistic effect was obtained in cases when a little low c.d. cathodic current was passed simultaneously with the EP. The alloys were found to consist of a solid solution of P in Ni, as well as of some phosphide compounds and pure Ni (at increasing activation c.d.). During EP, however, only the solid solution was deposited. The phase structure of the deposit can be varied to a certain extent by the activation c.d.     

Electrodeposition behaviour of zinc-iron group metal alloys from a methanol bath

Electrodeposition of zinc–iron-group metal alloys is carried out in a methanol bath. The effects of different parameters, such as bath composition and current density on current efficiency and alloy composition are investigated. Partial polarization curves of zinc and nickel are measured for both alloy and single metal deposition to evaluate the codeposition behaviour of zinc–iron-group metal alloys. Attempts are also made to confirm the proposed hydroxide suppression mechanism explaining the anomalous type of codeposition of zinc–iron-group metal alloys by investigating the role of water in the electroreduction process of zinc and iron-group metal ions.     

Electroless deposition of Ni–B, Co–B and Ni–Co–B alloys using dimethylamineborane as a reducing agent

Fundamental aspects of electroless Ni–B, Co–B and Ni–Co–B alloys have been systematically examined. The composition, crystal structure and deposition rate of the alloys were determined as a function of the concentration of reducing agent (dimethylamineborane) and complexing agents (tartrate, citrate, malonate and succinic acid), bath pH and Ni2+/Co2+ ratio. Changes in the deposition rate and metallurgical features of the alloys induced by the change in plating parameters are discussed, based on electrochemical polarization data and the formation enthalpy of the nickel and cobalt borides.     

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 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.     

A tartrate-based alloy bath for brass-plated steel wire production

The plating of brass on steel from a tartrate based alloy bath has been studied using electrochemical methods and surface analysis techniques. The coating composition obtained using both direct current (d.c.) and pulsed current (p.c.) electrolysis was examined for a variety of temperatures, current densities and bath compositions. The dissolution process of a suitable composition of brass anodes was studied using small amounts of nitrate as depolarizing agent. Tests in a pilot plant showed that when electrolysis is carried outin continuo the coating composition remains constant with time (±1%). Tests were performed at cathode current densities of industrial interest (20–30 A dm^–2). The Auger and XPS analyses combined with Ar⁺ etching indicated a homogeneous composition throughout the coating.     

Effect of tartrate on the morphological characteristics of the copper–tin electrodeposits from a noncyanide acid bath

Copper and tin were electrodeposited on platinum substrates from a 1.0 M sulphuric acid plating bath in the presence and absence of tartrate. Voltammetric curves indicated two deposition processes, at –0.310 and –0.640 V, which do not shift upon addition of tartrate to the plating bath. The presence of tartrate decreased the current density in the region of the more cathodic process. The metals were electrodeposited at both deposition potentials and the deposits have the same proportions of copper and tin either with or without tartrate in the plating bath, as observed by AAS. X-ray spectra suggested that a mixture of Cu and -Cu₆Sn₅ alloy was deposited at the less cathodic potential. SEM analysis showed that tartrate affects the morphology of the films.     

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.     

Effects of anode materials in the electroforming of iron-nickel alloy foil

The effects of soluble and insoluble anodes upon the composition and mechanical properties of iron-nickel alloy foil of thickness about 0.1 mm have been studied. The soluble materials include stainless steels, main constituents 17.5–19% Cr, 9–11% Ni or 16–18% Cr, 0.5% Ni, and iron-nickel alloys of composition 60% Fe, 40% Ni or 30% Fe, 70% Ni. The performance of these materials is compared with graphite, an insoluble anode. The presence of chromium as a constituent in soluble anodes has an adverse effect on the electroforming process: the current efficiency of metal deposition is reduced, as is the working current density for the production of foil of acceptable quality and with satisfactory mechanical properties. The nickel content of the alloy foil can be increased, and the quality of the foil improved, by using iron-nickel anodes which are free of chromium.     

Electrodeposition and corrosion behaviour of a Ni–W–B amorphous alloy

Electrodeposition of Ni–W–B alloys from plating baths containing ammonia and citrate is reported. Optimum conditions for plating including current density, temperature, mechanical agitation and pH were studied. The corrosion resistance and amorphous character were also evaluated. The operational conditions for depositing the alloy with good corrosion resistance were: current density 35 mA cm⁻², bath temperature 40 °C, pH 9.0 and cathode rotation at 90 rpm. The alloy was deposited at 38% current efficiency, with an average composition of 73 wt% Ni, 27 wt% W and traces of boron and with E _corr −0.300 V and R _p 3.369×10⁴ Ω. The deposit obtained under these conditions had an amorphous character with the presence of some microcracks on its surface reaching down to the copper substrate. Electrochemical corrosion tests verified that the Ni–W–B alloy had better corrosion resistance than Co–W–B.