Electrochemical behaviour of zinc acetate complexes: a cyclic voltammetry study

Abstract

The search for eco-friendly non-cyanide zinc plating solutions has resulted in the development of zinc acetate baths. Cyclic voltammetric studies of the dissolution and deposition of zinc in the presence of acetate complexes were carried out. In the pH range of 4·5–5·5, zinc acetate complexes underwent successive reduction to zinc. Acetate ions and OH^? ions were shown to affect both the dissolution and deposition of zinc. The dissolution of zinc required the participation of OH^? ions.     

Electroless deposition of copper from methane sulphonate complexed bath

Abstract

Electroless copper deposition is widely used for printed circuit applications. A new bath based on copper methane sulphonate replacing copper sulphate, EDTA and paraformaldehyde has been developed, which is very useful for plating on non-conductors and through hole plating in printed circuit manufacturing processes. The new bath has a higher rate of deposition of 3·3 μm h^?1 than the conventional sulphate bath (with a rate of 1·5 μm h^?1) and the bath stability and the quality of the deposits are very good. Scanning electron microscopy, X-ray diffraction and atomic force microscopy studies have been carried out and the crystallite size of the copper is measured to be 134 nm with a preferred orientation of 200 planes. The deposit obtained is pure copper and the surface roughness is of the order of 10 nm.     

Electrodeposition,characterisation and mathematical model of nickel–iron film in a parallel plate flow system

Abstract

Nickel–Iron alloy films were electrodeposited in a parallel plate flow system. The volumetric flow rate of electrolyte was fixed at 12 dm³ min^?1 through the 1 cm thick and 9 cm wide slit parallel plate. Fluid velocity was ca 0.22 m s^?1 under fully turbulent convective flow. Alloy films with iron content varying from 7·5 to 40 wt-% were deposited as a function of solution pH, temperature, bath ingredient concentration and applied current density. It is shown that the magnetic property is strongly correlated to the alloy content: the saturation moment, B _s, increases with the iron composition, while the coercivity, H _c, increases with nickel content. Current efficiency increases with pH and applied current density. The nickel deposition rate is inhibited in the presence of ferrous ion in the plating bath. The microhardness of the deposit is increased as the iron content is increased over the range studied. A mathematical model that considers the convective mass transfer of Fe(II) and Ni(II) species in the diffusion layer, the competition of adsorbed metal species on surface active sites, and Tafel electrochemical kinetics describe the alloy plating system well.     

The effect of additives on the pulsed electrodeposition of copper

Abstract

The pulsed electrodepostion of copper has been systematically investigated from a copper sulphate bath. Pulse duty cycles of 5–80%, at frequencies from 10 to 100 Hz with current densities ranging from 2·5 to 7·5 A dm^?2 were employed. The influences of pulsed current duty cycle, peak current density and frequency on the thickness and hardness of the copper deposit, current efficiency and throwing power of the plating process were studied. The effect of additives, polyethylene glycol and di-sodium EDTA on the properties of deposit were investigated.     

An electrochemical study on the influence of sodium molybdate on electrodeposition process and phase composition of ternary Zn–Ni–Mo alloy coatings

Ternary Zn–Ni–Mo alloy coatings were deposited from a citrate-sulphate bath at pH 5.7 containing different amounts of sodium molybdate. The content of molybdenum in the coatings (from 0.3 to 5.2?at.-%) can be easily controlled by increasing sodium molybdate concentration in the plating bath from 0.0025 to 0.05?mol?dm^??3, which results also in deposition of smoother deposits. An increase in molybdate concentration leads to the shift of reduction potentials towards more negative values and to the decrease in current efficiency of deposition process. XRD analyses and anodic linear sweep voltammetry (ALSV) measurements demonstrated that at least two phases are formed in the Zn–Ni–Mo alloy: a hexagonal zinc phase or solid solution of nickel in zinc and Ni₅Zn₂₁ intermetallic compound. Furthermore, the XRD analyses revealed a third phase, which could be assigned to the oxidised species of molybdenum or other alloying metals.     

The electrochemical behaviour of the bright chromium deposits plated with direct- and pulse-current in 1 M H2SO4

The electrochemical behaviour of bright Cr-deposits was studied in 1 M H₂SO₄ at 27 °C. The bright Cr-deposits were electroplated by using direct- or pulse-current (DC or PC) at 50 °C in a sulfate-catalyzed chromic acid bath with plating current densities of 30, 40, 50 and 60 A/dm² respectively. The results show that the surface-crack density of bright Cr-deposits plated with either DC or PC decreased with increasing the plating current density, whereas the passive current densities in their anodic polarization curves increased when plating current densities increased. From the results of electrochemical tests, it was found that passive and active dissolution rates of the Cr-deposits were not affected by the amount of the surface cracks developed on the Cr-deposit. Corrosion resistance of the Cr-deposit plated with PC was better than that with DC. The critical current density in the anodic polarization curve of the former is approximately one order less than that of the latter. The Cr-deposit plated with PC can be passivated more easily than that with DC. The rate of active dissolution of Cr deposits is much higher than that of passive dissolution. The aforementioned results can be recognized with AC impedance test polarized in passive and open-circuit potentials.     

Microstructure study of the hardening mechanism of Cr–Ni alloy deposits after flame heating for a few seconds

Cr–Ni alloy deposits with different chemical compositions could be obtained from a bath with trivalent Cr and divalent Ni ions. With a plating current density above 20 A dm^? 2, amorphous Cr-rich alloy deposits were obtained, and crystalline Ni-rich deposits were achieved with an electroplating current density lower than 15 A dm^? 2. The hardness of the Ni-rich deposit decreased gradually with increasing flame-heating time. On the contrary, the hardness of Cr-rich alloy deposit could be significantly increased from 550 Hv to 1450 Hv after flame heating for 3 s. The results of a microstructure study show that the precipitation of nano-sized carbon-related particles, possibly diamond-like particles, could be the main hardening mechanism of flame-heated Cr-rich alloy deposit. These particles have particularly high hardness values, and they distort the nearby Cr-rich lattice, which leads to obvious strain fields in the flame-hardened Cr-rich alloy deposits.     

Electrodeposition of Lead from Acetate Electrolyte Containing Additives

The electrodeposition of lead on to steel substrates from acidic acetate electrolyte containing hexadecyl pyridinium bromide (HDPB) and sodium dodecyl sulphate (SDS) has been investigated. In the acetate electrolyte containing a combination of HDPB and SDS, lead of good quality can be deposited. The optimum operating conditions necessary to produce a highly adherent lead deposit have been found to be: pH=5.0, j = 0.33 A dm^?2, T=25°C and time= 10 min. The optimum bath has a throwing power of 19.5% which is relatively high compared with that reported for Pb electrodeposited from sulphamate and fluoroborate baths. X-ray diffraction analysis shows that the Pb deposited from the acetate bath is pure and the surface morphology of the deposit shows that the lead deposited from the optimum bath is compact, non-porous and composed of fine-grains covering the entire surface.     

Effect of Some Operating Variables on the Characteristics of Electrodeposited Cu-α-Al2O3 and Cu-TiO2 Composites

Copper- χ-Al₂O₃, and Copper-TiO₂ composites were electrodeposited from acidic baths containing 150 CuSO₄.5H₂O₂ 50 Na₂SO_4.10H₂O, 25 H₃BO₃ and either 1–20 gl^?1 α-Al₂O₃ or TiO₂ particles suspended in the bath. The effects were studied of particle size, particle concentration and plating conditions on the cathodic polarization, current efficiency, inert particle content in the composite deposit and on the surface morphology and microhardness of the as-received plate. A mechanism of coelectrodeposition of the inert particles with copper could be suggested from measurements of the cathodic polarization. The efficiency of copper electrodepostion from the selected bath was relatively high (98.5%) and was increased further by increasing the current density and by raising the pH of the bath. The inert particle content reached 1.7% for α-Al₂O₃ and 2.3% for TiO₂. At a current density of 0.66A dm^?2, the microhardness of the copper plate approached 100 kgf mm and the inclusion of the inert particles in copper composites led to an increase of about 25% in the microhardness. A further increase in the microhardness of copper-α-Al₂O₃, was achieved by raising of the deposition current density, where it reached 165 kgf mm^?2 at 1.66 A dm^?2. Scanning electron microscopy examination showed a direct correlation between both the inert particles content, their morphological shape and the microhardness of the copper composites.     

Influence of surfactants on electrodeposition of a Ni-nanoparticulate SiC composite coating

Abstract

Nickel coatings containing well-dispersed, submicron (150–500?nm) silicon carbide particles were electrodeposited on copper from an agitated, modified Watts nickel electrolyte at 60°C using current densities of 10–100?mA?cm^??2. Coumarin additions (0–5?g?dm^??3) to a bath containing 10?g?dm^??3 SiC at 6?A?dm^??2 resulted in lower microhardness but considerably reduced abrasive wear in the composite coatings. Over 20 other surfactants including anionic, cationic, and non-ionic types were evaluated for their influence on the surface and tribological properties of the nanocomposite coatings. The surfactant levels (typically 0–3?g?dm^??3) were chosen to give good particle dispersions in the bath while avoiding any obvious deposit quality problems. Coating microhardness (via nanoindentation measurement), surface coefficient of friction (COF) and abrasive wear performance of the coatings under three-body, water-based conditions were investigated. The surfactants affected the degree of silicon carbide nanosized particles incorporated into the coating, from 5 to 54?vol.-%, and altered the surface microstructure from a matte to a bright surface finish and from porous to nodular, compact coatings. The nickel-nanosized silicon carbide composite coatings showed improved resistance to abrasive wear compared to a plain nickel (PN) deposit by a factor of 2–20.     

Properties of ‘Sulpho-Chromispel-I’ electrolyte of standard concentration for the electrodeposition of chromium

The most important properties of non-standard highly efficient “Sulpho-Chromispel- I” type electrolytes for chromium plating have been investigated. They contain as side anions catalysing the cathodic process, both SO^2-₄ and I^?. The effects of cathodic current density and concentration of hydroiodic acid on the total current distribution are evaluated. The deposition rate is determined. The effect of operating parameters on the throwing power is established. The properties of the electrolytes studied are compared with those of standard sulphate electrolytes and “Chromispel-I” compositions. The most efficient electrolyte comprises CrO₃:I- = 20:1 and 20 cm³ dm^?3 sulphuric acid. The deposition rate can reach a value of 250 μm h^?1 at a current density of 200 A dm^?2. The throwing power of this electrolyte is close to that of standard sulphate electrolytes. As a whole “Sulpho-Chromispel-I” electrolytes exhibit lower throwing power compared to standard sulphate electrolytes or pure “Chromispel-I” electrolytes. They are recommended for chromium plating details of simple profile.     

Corrosion stability of electrodeposited cyclic multilayer Zn–Ni alloy coatings

Abstract

This paper reports on a study of electrodeposition and characterisation of cyclic multilayer coatings of Zn–Ni alloy from a sulphate bath. Cyclic multilayer alloy coatings were deposited on mild steel through the single bath technique by appropriate manipulation of cathode current densities. The thickness and composition of the individual layers of the CMA deposits were altered precisely and conveniently by cyclic modulation of the cathode current during electrodeposition. Multilayer deposits with sharp change in composition were developed using square current pulses, using thiamine hydrochloride and citric acid as additives. Laminar deposits with different configurations were produced and their corrosion behaviours were studied by AC and DC methods in 5%NaCl solution. It was observed that the corrosion resistance of the CMA coating increased progressively with the number of layers (up to certain optimal numbers) and then decreased. The decrease in corrosion resistance at high degree of layering was attributed to interlayer diffusion due to less relaxation time for redistribution of metal ions at cathode during deposition. The coating configurations have been optimised for peak performance of the coatings against corrosion. It was found that CMA coating developed at cyclic cathode current densities of 3·0/5·0 A dm^?2 with 300 layers showed the lowest corrosion rate (0·112×10^?2 mm/year) which is ～54 times better than that of monolithic Zn–Ni alloy, deposited from the same bath. The protection efficacy of CMA coatings is attributed to the difference in phase structure of the alloys in successive layers, deposited at different current densities, evidenced by X-ray diffraction analysis. The formation of multilayers and corrosion mechanism were examined by scanning electron microscopy.     

Electrochemical deposition of nanocrystalline zinc on steel substrate from acid zincate bath

Nanocrystalline zinc coatings were deposited from acid zincate bath containing newly synthesized condensation product. The effect of bath constituents, pH, temperature and current density on the deposit nature were investigated through Hull cell experiments. Current efficiency, throwing power, cathodic polarization and corrosion behavior in 3.5 wt.% NaCl were studied under optimum concentration of additives. Salt spray test and electrochemical measurements showed that nanocrystalline zinc coatings have better corrosion resistance than the zinc coatings deposited from a simple acid zincate bath without additive. The surface morphology and thickness (cross section) of the zinc deposits were studied by scanning electron microscopy (SEM). The preferred orientation and average grain size of the zinc electrodeposit were obtained by X-ray diffraction analysis. The particle size was also characterized by TEM analysis. Energy X-ray diffraction (EDX) and FT-IR spectral analysis were carried out to determine the inclusion of addition agent in the deposit. The experimental results indicated that the addition of condensation product of thiamine hydrochloride (THC) and furfural (FFL) leads to a more uniform nanocrystalline deposition with the grain sizes varying from 20-22 nm.     

Electrochemical codeposition of PMMA particles with zinc

Zinc matrix composite coatings containing polymethyl methacrylate (PMMA) particles were electrodeposited from an aqueous acidic (pH 2.0 and 4.0), lignosulfonate solution of zinc sulfate on low-carbon steel substrates, under galvanostatic, either constant or pulse current, plating conditions at current densities of 2 and 20 A dm⁻². The effect of particle inclusion on the deposit electrocrystallization was investigated by X-ray diffraction and scanning electron microscopy. The observed dependence of the PMMA content of the deposits on bath pH and applied current density was illustrated in terms of the particle surface charge variation and their interaction with the growing metal phase. The corrosion resistance of the composite coatings was evaluated by Tafel analysis.     

Electrodeposition of alloys XIX: Electrodeposition of lead-tin alloys

Pb-Sn alloys containing from 1.2 to 94.3 wt.% Sn were electrodeposited from aqueous solutions prepared from diethylenetriaminepentaacetates of the two metals. The effects of current density and the solution composition on the composition of deposits and cathodic current efficiencies were investigated. Pb-Sn alloy deposition was of irregular type. At current densities equal to or less than 2.0 A dm^-2, lead deposited preferentially. At current densities of more than 2.0 A dm^-2 and in solutions containing more than 50.0 met.% Sn (the percentage weight of the total metal content), preferential deposition of tin occured. An increased in the tin content of the bath increased the percentage of tin in the deposit. The presence of chloride ions in the bath did not seem to affect the composition of the deposit.     

Dissolution Current and Pitting Potential of Zinc in KOH Solutions in Relation to the Concentration of Aggressive Ions

Abstract

Potentiodynamic anodic polarisation curves for zinc were obtained in dilute (10^?3 M) solutions of KOH that favoured metal dissolution with only a slight tendency to passivate the zinc, and in more concentrated (10^?2 M) solutions that favoured passivation of the zinc. Addition of aggressive halide ions (Cl^?, Br^?, I^?) to the 10^?3 M solution caused a shift of the dissolution potential to more negative values and a marked increase in corrosion rate, suggesting adsorption of the anions on to the bare metal surface. The difference between the dissolution current density, i_o, in 10^?3 M KOH alone, and in the presence of halide ions, i_agg, was given by: log (i_agg?i_o) = a + b log C_agg, where a and b are constants.

In 10^?2 M KOH, small additions (2 × 10^?4 M) of aggressive ions did not affect the dissolution kinetics. At higher concentrations the c.d. increased sharply at a well defined potential, or pitting potential, E_p, given by the relation: E_p = α ? β log C_agg, α and β being constants. It is assumed that in 10^?2 M KOH the aggressive anion acts by penetrating the oxide, or by becoming incorporated in it as an impurity, altering its physical and electrical properties.     

Influence of Bath Compositions and Some Operating Conditions on the Electroplating of Cobalt from Aqueous Sulphate Baths

A systematic study has been made of the influence of aqueous sulphate bath constituents on the cathodic polarization curves during cobalt electrodeposition. The optimum bath composition has been established and it contains: 0.30 mol l^?1 CoSO₄.7 H₃0, 0.30 mol^?1 H₃BO₃. 0.05 mol l^?1 (NH₄)₂SO₄ and 0.10 mole l^?1 Na₂SO₄.10 H₂o. Cobalt electroplating from the optimized bath has been performed under a variety of conditions viz: pH, 1.5 to 5.3; current density, 0.2 to 2.0 A dm^?2 and temperature 25 to 53°C. Under the most suitable conditions, the optimum bath is characterized by a high cathodic efficiency (~ 99%), moderate throwing power (21.6%) and throwing index (1.47). The bath produced smooth, adherent and semibright plates characterized by a high microhardness (411.4 kgf mm^?2) and their morphologies, as revealed by scanning electron microscopy, showed a dependence on the plating variables.     

Optimization of deposition conditions for bright Zn-Fe coatings and its characterization

Sulfate bath having ZnSO₄ · 7H₂O, Fe₂(SO₄)₃ · H₂O and thiamine hydrochloride (THC) and citric acid (CA) in combination, represented as (THC + CA) was optimized for deposition of bright Zn-Fe alloy coating on mild steel. Bath constituents and operating parameters were optimized by standard Hull cell method, for peak performance of the coating against corrosion. The effect of current density (c.d.), pH and temperature on deposit characters, such as corrosion resistance, hardness and glossiness were studied and discussed. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods were used to assess the corrosion behaviors. Surface morphology, and composition of the coatings were examined using Scanning Electron Microscopy (SEM), interfaced with EDXA facility, respectively. The Zn-Fe alloy, with intense peaks corresponding to Zn(100) and Zn(101) phases, showed highest corrosion resistance, evidenced by X-ray diffraction (XRD) study. A new and cheap sulfate bath, for bright Zn-Fe alloy coating on mild steel has been proposed, and results are discussed.     

The Electrodeposition of Iron-Zinc Alloys

Methods are given for depositing iron-zinc alloys of 3 to 90% zinc content from sulphate baths and attention is drawn to the useful properties of these deposits. Under a given set of plating conditions the iron-zinc ratio in the deposit is directly proportional to that in the bath. Lowering either the current density or the pH raises the zinc content of the deposit. Some baths have a levelling action, since bright deposits can be prepared from them on an etched surface. Examples of such baths are: (i) FeSO₄-7H₂O 248, ZnSO₄-7H₂O 8·8, (NHJ₄)₂SO₄ 118, KCl 10, citric acid 0·5 g./l., operated at pH 1·7, 50°G, 200 amps./ft.² and giving a 6% zinc alloy of 560 D.P.N, hardness;

(ii) FeSO₄-7H₂O 174, ZnSO₄-7H₂O 88, (NH₄)₂ SO₄ 118, KCl 10, citric acid 0·5 g., Teepol 0·4 ml./l., operated at pH 1·7, 50°C, 180 amps./ft.² and giving a 60% zinc alloy of 350 D.P.N, hardness.

The throwing power of the baths is comparable with that of a bright nickel bath. Pitting can be overcome by using a wetting agent (Teepol or Lubrol W) and operating at high temperature (80° C.) and low pH (<1·8). Under these conditions the deposits are usually matt and light grey in colour.

Alloys with zinc contents >ca. 30% have electrode potentials in N/10 KCl nearly equal to that of pure zinc. In the C.R.L. beaker test, the alloys with zinc contents between 30 and 90% are, in general, more corrosion resistant than pure zinc. Various applications of these alloys are proposed, including their use as an undercoat for paints and chromium plating and for decorative finishes indoors.

Deposition of iron-zinc alloys from chloride baths is dealt with briefly. A matt, corrosion-resistant alloy of 60% zinc content can be obtained, at pH 1·8, 50° C., and 50 amps./ft.², from a vigorously stirred bath of the following composition:—FeCl₂·4H₂O 177, ZnCl₂ 42, NH₄Cl 100, KCl 15, citric acid 0·5 g./l.

A colorimetrie method for the analysis of zinc in the presence of iron is described.     

Properties of Chromium Coatings Deposited from “Sulpho-Chromispel-I” Electrolyte of Standard Concentration

The most important properties of reflectivity, internal stress, hardness and surface morphology of chromium coatings deposited from “Sulfo-Chromispel-I” electrolytes (250 g dm^?3 CrO³) are studied The effects of operating parameters and electrolyte composition are evaluated. It is established that chromium coatings depositedfrom “Sulpho-Chromispel-I” electrolytes exhibit low internal stress. The current density and thickness of the coating affect the latter. Internal tension is reduced with the increase in coating thickness at current density of 50 A dm^?2, which is very favourable for depositing thick functional chromium layers. The reflectivity is affected by the concentration of iodide and cathodic current density. At current densities up to 35 A dm^?2 the higher the iodide concentration, the brighter the coating. With increased current densities the coatings produced are coarser and their brightness is reduced. Small amounts of sulphuric acid (4–20 cm³ dm^?3) improve the brightness. The hardness of the coatings deposited from the electrolytes studied is less than that of coatings deposited from a standard sulphate bath—300–400 kg mm^?2. The roughness grade is 0.5-0.6 mm. The coatings deposited from “Sulpho-Chromispel-I” electrolytes are bright with low tensile stress and moderate hardness. They are deposited at ambient temperature over a wide interval of current density, which is rather advantageous from a technological point of view.