Organic additive-copper(II) complexes as plating precursors

Cu(II) ions previously coordinated with typical electroplating organic additives were investigated as an alternative source of metal for plating bath. The coordination complexes were isolated from reaction between CuSO₄ and organic additives as ligands (oxalate ion, ethylenediamine or imidazole). Deposits over 1010 steel were successfully obtained from electroplated baths using the complexes without any addition of free additives, at pH = 4.5 (H₂SO₄/Na₂SO₄). These deposits showed better morphologies than deposits obtained from CuSO₄ solution either in the absence or presence of oxalate ion as additive (40 mmol L^− 1), at pH = 4.5 (H₂SO₄/Na₂SO₄). It is suggestive that the starting metal plating coordinated with additives influences the electrodeposition processes, providing deposits with corrosion potentials shifted over + 200 mV in 0.5 mol L^− 1 NaCl (1 mV s^− 1). The resistance against corrosion is sensitive to the type of additive-complex used as precursor. The complex with ethylenediamine presented the best deposit results with the lowest pitting potential (− 0.27 V vs 3.0 mol L^− 1 CE). It was concluded that the addition of free additives to the electrodeposition baths is not necessary when working with previously coordinated additives. Thus, the complexes generated in ex-situ are good alternatives as plating precursors for electrodeposition bath.     

Combinatorial performance characteristics of agitated nickel hypophosphite electroless plating baths

In this article, we present the combinatorial performance characteristics of agitated sodium hypophosphite electroless plating baths. Various performance characteristics assessed include bath conversion, plating efficiency, selective conversion, metal film thickness, average pore size, effective porosity and percent pore densification (PPD). Bath agitation was brought forward by rotating a symmetric disk shaped porous ceramic substrate with a nominal pore size of 275 nm. The plating characteristics were investigated for wide range of nickel solution concentrations (0.04-0.16 mol/L), stirrer speed (0-200 rpm) and for two different loading ratios (defined as substrate surface area per unit volume of plating solution) values (196 and 393 cm²/L). It was evaluated that stirring had a profound effect on sodium hypophosphite based electroless nickel baths, which are characterized with lower conversions (10-39%) and higher plating efficiencies (62-99%) without stirring phenomena. The stirred plating baths provided about 20-56% excess nickel plating rate when compared to the baths without stirring. This lead to a reduction in average membrane pore size by 20-42 nm and an enhancement in percent pore densification values by about 2-7%. Further, higher concentrations as high as 0.16 mol/L have been found to be detrimental to reduce the metal plating efficiency to lower values (42%). Observed data trends confirm upon the urgent need to identify suitable mass transfer enhancement techniques that target enhancement in selective conversion while providing good values of plating efficiency and PPD.     

Electrodeposition of copper-zinc from an alkaline bath based on EDTA

The electrodeposition of copper-zinc on 1010 steel from a non-cyanide alkaline electrolyte based on EDTA (ethylenediaminetetraacetic acid, disodium salt) — alkaline with various proportions of copper and zinc ions, was investigated. The complexation of copper and zinc by EDTA stabilized the solution. The deposition potential and the composition of the Cu-Zn bath were shown to influence the composition, morphology and phase composition of the Cu-Zn deposits. Scanning electron microscopy analysis showed that the best conditions to obtain smooth Cu-Zn deposits were at − 1.45 V, with Cu70-Zn30 and Cu50-Zn50 baths, and at − 1.60 V, with Cu30-Zn70. Besides being smoother than others, these deposits were golden in colour. Energy-dispersive X-ray spectroscopy analysis showed that a Zn content above 60 wt.% in the Cu-Zn deposits was achieved from the last bath, at − 1.45 V. X-ray diffractograms of the Cu-Zn deposits produced at -1.45 V, from Cu70-Zn30, Cu50-Zn50 and Cu30-Zn70 baths, indicated the occurrence of phases Cu_0.61Zn_0.39 and Cu, CuZn, Cu₅Zn₈ and Cu, CuZn, Cu₅Zn₈, CuO, Cu_0.61Zn_0.39, respectively. For the Cu30-Zn70 bath at − 1.60 V, Cu, CuZn, Cu₅Zn₈, and CuO phases were observed.     

Electroplating of catalytically active nickel coatings from baths of various anionic compositions

The effect of the nature of bath anions (Cl⁻, SO₄²⁻ and CH₃COO⁻) on the characteristics of the electrochemical plating of nickel coatings, namely, parameters of the cathodic polarization curves, bath stability, and current efficiency, as well as the composition and morphology of deposits and their catalytic activity in the anodic oxidation of hypophosphite ions and cathodic evolution of hydrogen, is studied. The anionic composition of the baths is found to substantially affect not only the kinetics of the deposit growth, but also the properties of the deposit. The differences observed are determined by the complex-forming and buffering properties of the anions.     

Effects of pre-treatments on the corrosion properties of electroless Ni-P layers deposited on AlMg2 alloy

Amorphous Ni-P layers with 8-10 wt.% phosphorus were deposited by sodium hypophosphite onto AlMg2 type aluminium alloy substrates after different pre-treatments. Prior to the electroless nickel-phosphorus (ENP) deposition in an acetate and lactic acid based nickel bath, the widely applied Zn (zincate) or Ni displacement (Ni strike) pre-treatments for aluminium substrates as well as a non-conventional surface conditioning one (soaking in a warm solution containing only hypophosphite and lactic acid) were all tested and their effects evaluated on the corrosion and other properties of the Ni-P layers developed right afterwards. The surface morphology and structure of the ENP layers were characterized by scanning electron microscopy and X-ray diffraction analysis. Polarization resistances were measured in 0.5 mol dm^− 3 Na₂SO₄ solution at pH 3. Compared to the direct electroless plating on the bare aluminium alloy AlMg2, it was found, that the hypophosphite adlayer (hypophosphite immersion pre-treatment) have also increased the corrosion resistance as the displacement pre-coatings, but without decreasing the deposition rate unlike conventional displacement methods. In the studied ENP deposition systems the decrease of corrosion rate could mainly be attributed to the lower microporosity and smoother morphology of the nickel-phosphorus coatings.     

A study of chromium-free pickling process before electroless Ni-P plating on magnesium alloys

A chromium-free pickling process of magnesium alloys in H₃PO₄ + Na₂MoO₄ solution for electroless Ni-P plating was described. The dosage of Na₂MoO₄ was established by detecting adhesion and corrosion resistance of chemical nickel coatings. Electrochemical behaviors of pickling solution of H₃PO₄ + Na₂MoO₄ and NH₄HF₂ activation solution were investigated with the open circuit potential curves and the polarization curves. The results show that the Na₂MoO₄ has strong inhibition ability. Na₂MoO₄ in H₃PO₄ solution can reduce active sites of microcathodic and microanodic zones in the corrosion cells of the substrate surface of magnesium alloys and plays an inhibition role. The activation film with some oxides and fluorides can prevent the substrate magnesium from the fierce displacement and corrosion reaction of electroless plating bath. The chemical Ni-P coating with good adhesion and corrosion resistance was obtained by the pretreatment of 200 cm³ dm⁻³ 85% H₃PO₄ + 5 g dm⁻³ Na₂MoO₄ pickling bath and activation in 200 g dm⁻³ NH₄HF₂ solution. This procedure of surface pretreatment before electroless nickel plating can replace the existing acid pickling containing chromium and HF activation.     

TiO2 nanotube-supported amorphous Ni-B electrode for electrocatalytic oxidation of methanol

Amorphous Ni-B/TiO₂ electrodes were successfully prepared by electroless plating. Highly ordered TiO₂ nanotube arrays fabricated by anodic oxidation were employed as substrate and loaded with Ni-B alloy by electroless plating. The phase formation, microstructures and catalytic activity of electrodes were investigated by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and electrochemistry analyzer, respectively. The results show that Ni-B/TiO₂ electrodes with an average particle size of 200 nm present a typical amorphous structure of Ni and B, and have high catalytic activity for methanol electrooxidation in alkaline medium. The peak current density in cyclic voltammetry (CV) curves reaches 360 mA cm⁻² in the solution with 0.5 mol L⁻¹ methanol, much higher than that of Ni-B/Ti electrode. With the methanol concentration increasing to 1.5 mol L⁻¹, the peak current density increases to 488 mA cm⁻², after which it remains almost constant. The Ni-B/TiO₂ electrodes are relatively stable according to catalytic lifetime test; the peak current density remains 72.1% of the original value after 1300 times cycles. The amorphous Ni-B/TiO₂ electrode should be a promising candidate for direct methanol fuel cell.     

A method for polyaniline coatings on solid polystyrene surfaces and electroless copper deposition

A new efficient method is presented for electroless copper deposition on solid polystyrene surfaces via polyaniline (PANI) coatings. It was demonstrated that, partial polymerization of aniline by catalytic air oxidation in the presence of dissolved polystyrene (PS) (M_n: 87.000 K) gives viscous solution of PANI-PS mixture in aniline. Direct application of the polymerization mixture with copper catalyst onto polystyrene sheets (5 × 15 cm) resulted in extension of the polymerization by air oxygen to give a smooth PANI-PS composite layer on the host surface. Treatment of the surface with a similar PANI solution without PS gave Emeraldine base film with homogenously dispersed copper. Reduction of the surface copper by diluted hydrazine (5%) yielded zero-valent copper serving as seed points for accumulation of more copper from an electroless plating solution in the following process. Experiments showed that, the method presented offers a simple pathway to produce excellent copper deposits on PS substrate. This method is superior to traditional electroless plating process, since tedious surface etching and expensive palladium activation steps are being avoided. The surface characteristics were examined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), adhesion tests and contact angle measurements. The results showed that, the electroless plating process gives a homogeneous and highly robust copper layer with 34.2 μm of thickness within 48 h. Adhesion of the copper layer to the underlining surface was satisfactory as inferred from pull-off measurements (1.6 N/mm²).     

Kinetics of Electroless Plating of Ni–P Alloys with Organic Additives Containing –S–S-Fragments

Being added to electroless plating baths, organic compounds with –S–S– fragments are shown to inhibit the bulk reaction and exert the catalytic effect on the surface reaction in a certain concentration range. An introduction of an NH₂ group promotes the inhibition effect and reduces the catalytic action due to the formation of complexes which results in a decrease in the polarizing ability of sulfur atoms and the formation of the less active surface. A correlation between the electroless plating parameters and the anodic oxidation rate of hypophosphite is revealed.     

Transparent p-type CuxS thin films

The effect of different mild post-annealing treatments in air, at 270 °C, for 4-6 min, on the optical, electrical, structural and chemical properties of copper sulphide (Cu_xS) thin films deposited at room temperature are investigated. Cu_xS films, 70 nm thick, are deposited on glass substrates by vacuum thermal evaporation from a Cu₂S:S (50:50 wt.%) sulphur rich powder mixture. The as-deposited highly conductive crystalline CuS (covellite) films show high carrier concentration (∼10²² cm⁻³), low electrical resistivity (∼10⁻⁴ Ω cm) and inconclusive p-type conduction. After the mild post-annealing, these films display increasing values of resistivity (∼10⁻³ to ∼10⁻² Ω cm) with annealing time and exhibit conclusive p-type conduction. An increase of copper content in Cu_xS phases towards the semiconductive Cu₂S (chalcocite) compound with annealing time is reported, due to re-evaporation of sulphur from the films. However, the latter stoichiometry was not obtained, which indicates the presence of vacancies in the Cu lattice. In the most resistive films a Cu₂O phase is also observed, diminishing the amount of available copper to combine with sulphur, and therefore the highest values of optical transmittance are reached (65%). The appearance on the surface of amorphous sulphates with annealing time increase is also detected as a consequence of sulphur oxidation and replacement of sulphur with oxygen. All annealed films are copper deficient in regards to the stoichiometric Cu₂S and exhibit stable p-type conductivity.     

High rate of copper electrodeposition from the hexafluorosilicate bath

A high-rate copper electrodeposition performed from a hexafluorosilicate bath is presented in this article. It is shown that the current density for electrodeposition ranges from 1 to 30 A dm^− 2 and the optimal suggested current density is 15 A dm^− 2 or a rate of 200 μm h^- 1. High plating rate is due to a higher mass transport through the hexafluorosilicate media when compared to a conventional sulphate-based bath. The microstructure, texture and mean grain size of the 30 μm-thick films plated from the additive free bath and the bath containing 10^− 3 mol dm^− 3 thiourea and 500 ppm Cl⁻ is studied with respect to the applied current density. Copper plated from the bath without additives has a macrocrystalline structure with preferable 110 texture and mean grain size of 65-85 nm, while thiourea produces a microsmooth surface and 111 texture with grain size of 40-70 nm.     

Phase transformation behavior of nanocrystalline Ni-W-P alloys containing various W and P contents

In the present investigation, electroless (EL) ternary Ni-W-P coatings were prepared using hypophosphite based alkaline bath by varying sodium tungstate as tungsten source (5-80 g/L). Maximum amount of W incorporation (8.2 ± 1 wt.%) was obtained when the bath contained about 20 g/L of tungsten source. At very high concentrations of W source in the bath the deposit contained about 4 wt.% W and 2 wt.% P. All the as-deposited ternary coatings exhibited nodular surface morphology. X-ray diffractograms (XRD) obtained for as-deposited EL NiWP alloys indicated that crystallinity of the coatings increased with decrease in phosphorus content. Calculated grain size for the deposits varied from 1.2 to 12.7 nm when the tungsten source varied from 5 to 80 g/L in the bath. Higher crystallization temperatures were obtained due to W codeposition in NiP matrix. Presence of metastable phases such as Ni₅P₂ and NiP apart from stable Ni and Ni₃P was identified for the heat treated deposits (400 °C/1 h) containing lower amount of W and higher amount of P. Whereas other ternary deposits after the heat treatment predominantly revealed face centered cubic (f.c.c.) Ni (111) peak. Activation energy for the crystallization of all the alloys has been carried out by modified Kissinger method. Microhardness measurements were carried out on all the deposits isothermally heat treated at 600 °C for 1 h.     

Copper patterned polystyrene panels by reducing of surface bound Cu (II)-sulfonyl hydrazide complex

A modified electroless metal deposition method has been developed for copper plating of polystyrene (PS) surfaces. The modified procedure avoids the plasma conditioning and surface activation steps in the classical electroless metal plating process.First step of the present procedure is chlorosulfonation of PS surface by soaking into chlorosulfonic acid, yielding chlorosulfonated surface with density of 0.046-0.110 mmolcm^− 2 depending on contact time (10-60 min).In the second step chlorosulfone groups on the surface are converted to sulfonyl hydrazides almost quantitatively by reaction with hydrazine solution (80%). Green Cu (II)-sulfonylhydrazide complex is formed at the surface, in the third step, by interaction with ammoniacle Cu (II) solution at room temperature. The copper in the complex is reduced rapidly in the fourth step, by immersing the specimen into 5% of hydrazine solution. The elemental copper deposited onto the surface serves activating sites to accumulate more (5-7 mg per cm²) elemental copper from electroless copper solutions in the final step. The present method avoids the surface activation with palladium and allows preparing copper patterns with reasonably high pull-off strengths (3.77 Nmm^− 2) on PS panels.In the study the copper deposition has been investigated using standard analytical procedures, X-ray photoelectron spectrometry (XPS) and Scanning Electron Microscopy.     

Microwave absorbing properties of Ag-coated Ni-Zn ferrite microspheres prepared by electroless plating

This investigation presents an electromagnetic radiation absorptive composition comprising Ag-coated ferrite microspheres dispersed in a silicone rubber matrix for use as a thin microwave absorber in GHz frequencies. Ni-Zn ferrite microspheres with an average diameter of 50 μm were prepared by spray-drying and sintering at 1130 °C. A conductive Ag layer was coated on the ferrite spheres by electroless plating. Uniform Ag coating can be obtained using the plating solution with a high AgNO₃ concentration. For particle compacts of the conductive Ni-Zn ferrite spheres, electrical resistance is reduced to as low as 10⁻² Ω. Rubber composites containing the Ag-plated ferrite spheres exhibit a high value of both real and imaginary parts of complex permittivity, while the complex permeability spectrum is not significantly changed with Ag plating. Due to the conductive and magnetic property of the microspheres, matching thickness can be reduced to as low as 2 mm at the frequency of 7.6 GHz, which is much thinner than non-coated ferrite absorbers.     

Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds

We have prepared polycrystalline single-phase ACo_2+xRu_4−xO₁₁ (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10⁻⁵ Ωm and their Seebeck coefficients are positive and range from 1 μV K⁻¹ (T = 100 K) to 20 μV K⁻¹ (T = 450 K). The maximum power factor at room temperature is displayed by BaCo₂Ru₄O₁₁ (P.F.: 0.20 μW K⁻² cm⁻¹), value that is comparable to that shown by compounds such as SrRuO₃ and Sr₆Co₅O₁₅.     

Corrosion behaviour of zinc deposits obtained under pulse current electrodeposition: Effects of coumarin as additive

The corrosion behaviour of zinc deposits obtained under pulsed current electrodeposition from an acidic chloride bath in the presence and absence of coumarin has been investigated. The effects of pulse peak current density (J_p) on the morphology of zinc deposits were studied by scanning electron microscopy. An increase in J_p from 40 to 280 A dm⁻² yields deposits with a finer grain size. The refinement of the grain size was more considerable in the presence of coumarin (J_p = 280 A dm⁻²). The preferred orientation of zinc deposits was studied by X-ray diffraction. At J_p = 40 A dm⁻², the preferred orientation of zinc deposits was (1 0 3) and changed to (0 0 2) at J_p = 80 A dm⁻². An increase in J_p to 280 A dm⁻² did not change the preferred crystallographic orientations except for an increase in the peak intensity of the (0 0 2) plane. In the presence of coumarin, the preferred crystallographic orientations changed at J_p = 280 A dm⁻² from the (0 0 2) plane to the (1 0 3) plane. The corrosion behaviour was investigated in an aerated 3.5% NaCl solution; the anodic polarization and electrochemical impedance spectroscopy curves were performed. The corrosion resistance of zinc deposits was improved by increasing the pulse peak current density (J_p); whereas, the presence of coumarin did not improve the corrosion resistance.     

Comparison of corrosion-resistance and hydrogen permeation properties of Zn-Ni, Zn-Ni-Cd and Cd coatings on low-carbon steel

Zn-Ni-Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion and hydrogen permeation characteristics of Zn-Ni-Cd alloy coatings electrodeposited from alkaline bath were studied and compared with those of Cd and Zn-Ni coatings obtained using commercial baths. Zn-Ni-Cd alloy was electroplated from an alkaline sulfate bath under potentiostatic conditions. The corrosion potential of this Zn-Ni-Cd coating was −0.62 V vs. SCE, which is still negative potential compared to iron. The corrosion rate of Zn-Ni-Cd coated steel was 0.073 mm y⁻¹, which is estimated in a solution at a pH of 7. This value is much lower than the corrosion rate of Zn-Ni alloy (0.502 mm y⁻¹) and Cd (0.306 mm y⁻¹) coatings deposited from commercial baths. Zn-Ni-Cd alloys are also demonstrated to have superior hydrogen permeation inhibition properties compared to Cd and Zn-Ni coatings. Kinetic parameters of hydrogen permeation such as the transfer coefficient, α, the modified exchange current density, i₀^′, thickness dependent adsorption-absorption rate constant, k^″, recombination rate constant, k₃, surface hydrogen coverage, θ_s, were evaluated by applying a mathematical model to analyze experimental results.     

Fabrication of various electroless Ni-P alloy/multiwalled carbon nanotube composite films on an acrylonitrile butadiene styrene resin

Ni-P alloy/multiwalled carbon nanotube (MWCNT) composite films were fabricated on acrylonitrile butadiene styrene (ABS) resin by electroless plating and their microstructures, adhesion strengths, and friction properties were investigated. Various types of MWCNTs were used. In addition, various electroless plating baths were prepared to form Ni-P alloy matrices with various phosphorus contents. To enhance the adhesion strength, the ABS resin substrate was subjected to roughening treatment. The microstructures of the composite films were examined by scanning electron microscopy and X-ray diffraction. Their adhesion strengths were measured by tensile tests. The friction properties of the composite films were investigated using the ball-on-plate method. Ni-P alloy/MWCNT composite films containing various types of MWCNTs and with Ni-P alloy matrices having various phosphorus contents were fabricated on the ABS resin substrates by electroless deposition. The adhesion strength between the Ni-P alloy/MWCNT composite films and the ABS resin substrate was more than 1300 N cm^− 2. The Ni-P alloy/MWCNT composite films had considerably lower friction coefficients than the Ni-P alloy films. The friction coefficients of the composite films were significantly affected by the type of MWCNTs used.     

Synthesis and characterization of electroless deposited Co-W-P thin films as diffusion barrier layer

Selective barriers against copper diffusion deposited by electroless reaction are interesting in term of electromigration. In this article, the barrier layer of cobalt-tungsten-phosphorus (Co-W-P) alloy was electroless deposited onto copper substrates for ultra large scale integration (ULSI) applications. The Co-W-P thin film was formed directly on copper, without a palladium catalyst, from citrate plating baths with sodium hypophosphite as reducing agents. The influence of tungsten addition on the barrier properties has been studied and the optimum conditions to obtain films with the highest oxidation protection have been determined. Co-W-P layer properties such as chemical composition, surface morphology, and phase structure and corrosion behavior have been investigated. The deposited CoWP layer showed higher oxidation and corrosion resistance and soft magnetic behavior.     

Effect of synthesis conditions and post-deposition treatments on composition and structural morphology of medium-phosphorus electroless Ni-P films

The optimized plating bath composition (mol%) of 0.47NiCl₂:0.23NaH₂PO₂:0.13C₄H₄Na₂O₄:3.47NaCl:95.70H₂O produced Ni-P films with ~ 10 wt.% P at 85 °C over copper and steel substrates. The presence of chloride ions (Cl⁻) in the plating solution was found to facilitate initial deposition without any need of surface activation. Film growth rates as high as 7-8 μm/h were achieved with minimal or no deposition on surfaces other than the substrates. Scanning electron microscope (SEM) and atomic force microscope (AFM) studies revealed cauliflower-like morphology with submicron size grains. Increasing the amount of reducing agent increased film smoothness and refined grain size with corresponding increase in P content. X-ray diffraction studies of the deposit revealed semi-crystalline nature of the film which underwent transition to fully crystalline form upon heat treatment with an associated increase in average HK value from ~ 390 to 807 HK. High temperature provided driving force for surface and volume diffusion that subsequently led to reduced porosity and more homogeneous composition through rearrangement of atoms to form certain Ni_xP_y phases. Acid etching of the deposits transformed shiny films into matte black surfaces due to preferential removal of nickel leading to formation of porous structure with stalagmite-like morphology.