Model of nickel electrodeposition from acidic medium

A step-wise computer model is presented for simultaneous deposition of nickel and nickel hydroxide in aqueous solutions. In acidic solutions ({pH} 1), the potentiostatic current-time transient response on glassy carbon or titanium was analysed with respect to nucleation and radial growth mechanism. pH changes influence the current-time response greatly. A marked maximum in the current transient appears for slightly acidic solutions ({pH} 4.5) and a consecutive decrease in the deposition current density at long times is obtained. This behaviour is attributed to early precipitation of nickel hydroxide due to a local pH increase at the cathode surface.     

Black nickel electrodeposition from a modified Watts bath

Black nickel coatings were electrodeposited on to steel substrates from a Watts bath containing potassium nitrate. The best operating conditions necessary to produce smooth and highly adherent black nickel were found to be NiSO₄ · 6H₂O 0.63 M, NiCl₂ · 6H₂O 0.09 M, H₃BO₃ 0.3 M and KNO₃ 0.2 M at pH of 4.6, i=0.5 A dm⁻², T=25 °C and t=10 min. The modified Watts bath has a throwing power (TP) of 61%, which is higher than that reported, not only for nickel, but also for many other metals electrodeposited from different baths. The potentiostatic current–time transients indicate instantaneous nucleation. X-ray diffraction (XRD) analysis shows that the black nickel deposit is pure metallic nickel with Ni(111) preferred orientation.     

Cathodic inhibition and anomalous electrodeposition of Zn-Co alloys

The electrodeposition of Zn-Co alloys from chloride electrolytes was studied on steel substrate. Electrodeposition of Zn-Co alloys is usually divided into two potential regions, i.e. normal (positive to Zn deposition potential versus SCE) and anomalous (negative to ). In order to elucidate the deposition mechanism a complementary approach was used based on the combination of various electrochemical techniques. The morphology of the deposits and elemental composition analysis were determined by using SEM/EDX. It was found that the presence of Zn²⁺ in electrolyte inhibited Co²⁺ and H⁺ reductions in normal region. A critical potential was also noticed in the so-called normal deposition range above which a Co-enriched phase of Co-Zn alloy was favored and below that a severe mitigation to deposition occurred that was considered due to underpotential deposition (UPD) of Zn on the substrate and on active Co sites at either nucleation or growth stage. Beyond the deposition is considered anomalous due to the fact that Zn deposits preferentially compared to the more noble Co. This anomalism was explained by the faster deposition kinetics of Zn as compared to Co on steel and could be overcome by either increasing the Co²⁺/Zn²⁺ ratios in the electrolyte or by carrying out the deposition at higher temperature.     

Influence of polyethoxylated additives on zinc electrodeposition from acidic solutions

The influence of several ethoxylated additives (ethyleneglycol and polyethyleneglycol polymers of different molecular weights) on the nucleation, growth mechanism and morphology of zinc electrodeposited from an acidic chloride bath is reported. The electrochemical study was carried out using cyclic voltammetry, inversion potential and chronoamperometric techniques. The dimensionless graphs model was applied to analyse the nucleation process and the results showed that the studied additives have a blocking effect on the electrodeposition of zinc. This effect occurs in the first stages of the nucleation process and is dependent on the molecular weight of the additive. Changes induced by the presence of additives in the morphology and grain size of the deposits were observed using SEM analysis. Results show that the presence of additives modifies the nucleation process and determines the final properties of the deposits.     

Synthesis and characterization of nickel tungsten alloys by electrodeposition

The objective of the current work was to study in detail the effect of bath chemistry, additives and operating conditions on the chemical composition, microstructure and properties of Ni-W alloys deposited from citrate-containing baths, in the absence of ammonia or ammonium salts, on stationary working electrodes. The morphology of the deposits was studied by scanning electron microscopy (SEM) as well as atomic force microscopy (AFM), and the approximate composition by energy dispersive spectroscopy (EDS). Metallographic cross-sections were also analyzed, and micro-hardness tests conducted. The results are discussed in detail with emphasis on routes to increase the tungsten content and deposit thickness, while reducing the extent of cracking.     

Effect of the electrolyte composition on In and Ag–In alloy electrodeposition from cyanide electrolytes

A procedure for preparation of clear and stable indium cyanide electrolytes, containing indium salt, d(+)-Glucose and KCN is proposed. NMR investigations revealed that the formation of a complicated indium complex in which the products of the disintegration of d(+)-Glucose in the KCN-solution are closely situated to the indium ion ensures the clearness of the electrolyte. The effect of nitrate, chloride and sulphate ions on the electrochemical processes of indium and silver–indium alloy electrodeposition is studied by cyclic voltammetry. During alloy electrodeposition under galvanostatic conditions unique spatio–temporal structures are observed on the cathodic surface.     

Response surface modeling and optimization to study the influence of deposition parameters on the electrodeposition of Cu–Zn alloys in citrate medium

Copper–zinc alloy coatings were deposited on mild steel substrates using sodium citrate electrolytes at room temperature and under direct current. For the bath composition studied, factorial design was used to verify the influence of deposition parameters, such as current density and mechanical stirring, on the cathodic efficiency, the contents of copper and zinc, and the amount of hydrogen evolution. Moreover, the four responses were simultaneously studied by using an optimization methodology. The results suggest that the optimum point for reaching good quality copper–zinc alloy deposits from the proposed citrate electrolytes are 29 A m⁻² and 247 rpm for bath 3 and 13 A m⁻² and 67 rpm for bath 4. Applying these conditions, a yellow-reddish coating was obtained from bath 3, while a bright red deposit was produced from bath 4.     

Recent developments in the electrodeposition of nickel and some nickel-based alloys

The numerous theoretical and practical studies of the electrodeposition of nickel and its binary and selected ternary alloys with copper and cobalt over the last 10–15 years are reviewed. The reported mechanisms of the electrodeposition processes and accompanying evolution of hydrogen are considered. The complex influence of different bath compositions, pHs, current densities or potential ranges and temperature on the formation of single or multiple deposition layers are compared. The determination of the structure and morphology of the deposits on different substrates, including solid surfaces and particulate materials, using a range of analytical techniques are reported.     

The anomalous codeposition of tungsten in the presence of nickel

Deposition of tungsten-rich alloys from plating baths that do not contain ammonia is reported. Alloys with nominal composition of NiW and even NiW₂ have been formed for the first time by electroplating. It was shown in this paper, and in our previous work [Electrochem. Solid-State Lett. 3 (2000) 543; Proc. Advanced Metalization Conf. (AMC 2000) p. 337; Langmuir 17 (2001) 8270; J. Electrochem. Soc. 149 (2002) C100; J. Appl. Surf. Sci. 200 (2002) 1], that alloys of tungsten and nickel having any composition between a few a/o and 67 a/o of tungsten can be electroplated, by suitable choice of the experimental conditions. The most important factors among these are the concentrations of citrate, which acts as the complexing agent, the ratio of concentrations of nickel and tungstate ions and the pH of the solution. New indirect evidence for the existence of a mixed metal complex of the type [(Ni)(WO₄)(Cit)(H)]²⁻ was obtained by: (a) the pH dependence of the composition of the alloy and (b) by the linear dependence of the partial current density for deposition of tungsten on the calculated concentration of this complex, over a wide range of solution compositions. Removing ammonia from the plating bath allows the deposition of tungsten-rich alloys, but this is achieved at the cost of a substantial reduction in Faradaic efficiency.     

电沉积制备镍-铁-钨合金析氢电极的工艺研究

以紫铜片为基体电沉积制备了Ni–Fe–W合金电极。研究了镀液中不同组分的浓度和工艺条件对Ni–Fe–W合金析氢性能的影响,得到最佳镀液配方和工艺条件为:NiSO4·6H2O80g/L,FeSO4·7H2O20g/L,Na2WO4·2H2O0.020mol/L,Na3C6H5O7·2H2O 0.5 mol/L,H3BO3 0.65 mol/L,Na2SO4 0.1 mol/L,十二烷基硫酸钠0.1 g/L,pH 5~6,温度30°C,电流密度4 A/dm2,磁力搅拌800 r/min,时间30 min。在该条件下所得Ni–Fe–W合金电极表面Ni、Fe和W的原子分数为63.79%、34.35%和1.86%,具有较大的比表面积,在30%KOH溶液中的析氢催化活性较好。     

Effect of temperature on nickel electrodeposition from a nickel sulfamate electrolyte

The effect of temperature on nickel electrodeposition from a nickel sulfamate electrolyte has been investigated. All the experimental points in a plot of nickel film thickness vs. current density collapse onto a single straight line irrespective of deposition temperature. A relation derived from the Butler–Volmer equation is successful in predicting cathode potential shifts caused by change of deposition temperature. Moreover, an interface width, which characterizes the roughness of the surface and is defined by the root mean square of fluctuation in the height, is shown to have a saturated value that is related to the deposition temperature. Thus, two kinds of activation energies for the charge transfer reaction and for grain growth are estimated from the temperature dependence of the cathode potential shift and the grain size.     

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.     

配位剂对弱酸性体系电沉积Sn-Ag-Cu镀层的影响

在含有甲磺酸盐和碘化物的弱酸性镀液中电沉积得到了Sn-Ag-Cu三元合金镀层.研究了该镀液体系中配位剂的用量对Sn-Ag-Cu合金镀层外观和镀液电流效率的影响,探讨了配位剂对镀液阴极极化的影响.结果表明,配位剂K4P2O7、KI、TEA的加入使Sn、Ag、Cu三种金属的沉积电势趋于一致,能够实现共沉积.优化的镀液组成及工艺条件为:0.2 mol/L Sn(CH3SO3)2,4.5 mmol/L AgI,1.5 mmol/L Cu(CH3SO3)2,0.6 mol/L K4P2O7,1.35mol/L,0.225mol/L TEA,1 g/L光亮剂,1 g/L抗氧化剂,温度20℃,pH 5.5.     

Characteristics of zinc electrodeposits from acetate solutions

This paper deals with zinc plating from an acetate electrolyte and the resultant deposit properties. The addition of thiamine hydrochloride and gelatin to the plating bath improves the corrosion resistance and surface morphology of the zinc deposits. The XRD pattern obtained for electrodeposited zinc show a polycrystalline nature with a hexagonal structure. A uniform and pore free surface was observed under SEM analysis.     

Surface characterization of zincated aluminium and selected alloys at the early stage of the autocatalytic electroless nickel immersion process

In this work the changing structure of nickel–phosphorus deposits on aluminium and its alloys at the early stage of electroless nickel phosphorus deposition using hypophosphite ion as reducing agent has been studied. Prior to electroless nickel deposition, zincating is used for pre-treatment of aluminium substrates. The surface morphology and structure of the electroless Ni–P layers were characterized by scanning electron microscopy and X-ray diffraction analysis. Results show that Ni–P deposition is closely related to the dissolution of the zincating layer, followed by progressive nickel nucleation. The nuclei serve as a catalytic surface for further Ni–P deposition which increases with deposition time. The growth and coalescence of the nuclei on the aluminium substrate results in crystalline layers of Ni–P.     

Effect of ferrous ion concentration on the electrodeposition of iron–nickel alloys

Ni–Fe alloys were deposited galvanostatically on the disk part of the platinum rotating ring-disk electrodes (RRDEs). Contents of nickel and iron were determined using the electrochemical stripping method. It was shown experimentally and explained theoretically that nickel deposition rate is inhibited as the ferrous ion concentration in the bath is increased. A mathematical model that includes the phenomenon of surface competition between FeOH⁺ and NiOH⁺ ions can quantify the inhibition of nickel deposition rate in the presence of ferrous ion species. ©1997 SCI     

Electroless deposition of copper in acidic solutions using hypophosphite reducing agent

A new bath formulation was developed, which allowed deposition of copper-rich Cu–Ni–P alloys in electroless acidic solutions in the absence of formaldehyde. The reducing agent was sodium hypophosphite. Though cupric ions do not catalyse the oxidation of hypophosphite, we show that, in the presence of a low concentration of Ni(II) species, it is possible, even at low pHs, to induce the reduction of the cupric species. A very strong preferential deposition of copper was observed, which gives Cu–Ni–P layers with copper content up to 97 wt%. The phosphorus content decreased from 13% to 1% with increasing copper content. The plating rate decreased when the copper sulfate concentration in the solution increased. It increased with increasing pH or temperature, but the influence was less pronounced than in alkaline solutions. Compact layers were obtained with a nodular morphology which did not markedly changed with composition.     

Thermal effects of a laser beam on the electrodeposition of Ni–P alloys

The paper deals with the effects of an incident laser beam on electrodeposition of Ni–P alloys from dilute acetate solutions. The kinetics of separate reductions of Ni2+ and H2PO–2 species were first investigated by linear sweep voltammetry, varying the hypophosphite concentration and the solution temperature: comparison of the kinetically limited current densities of the two reductions suggested that increasing temperature might reduce the significance of P codeposition. This tendency was confirmed by deposition runs carried out at controlled current. Deposition performance was discussed in terms of faradaic yield and deposit properties, namely P content together with the aspect and the structure of the alloys. Use of a continuous or pulsed laser beam was shown to reduce the P content in the deposit at high current densities; in some cases, amorphous structures were replaced by more crystalline forms with assistance of a laser beam.     

Impedance investigation of the mechanism of copper electrodeposition from acidic perchlorate electrolyte

The mechanism of the copper electrodeposition from acidic perchlorate electrolyte has been investigated with polarization and impedance methods. The impedance of the copper electrode in copper perchlorate electrolytes has been measured as a function of frequency for different Edc overpotential values and different copper(II) ion concentrations. The relations between the shape of a complex plane impedance display and the copper electrode potential values as well as the concentration of CuII ion were analysed in terms of the electrode reaction mechanism. It is shown, that the presence of the intermediate cuprous ion and its sinusoidal change of transport rate is one of the main factors determining the depressed shape of the impedance arc. The quantitative relation between the faradaic impedance and the rates of electrode reaction rates was established. The impedance arc was simulated with a set of parameters involving: rate constants, Tafel slopes, diffusion coefficient of cuprous ion and double layer capacitance. The rate constants were calculated with respect to ECu2 + Cu00 as: k10 = 6.50 × 10−5 cm s−1, k20 = 0.139 cm s−1, k−20 = 1.88 × 10−7 mol cm−2 s−1.     

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.