Showing papers in "Transactions of The Institute of Metal Finishing in 2002"

Electrodeposition of Ni/SiC composites by pulse electrolysis : Electrodeposition in Electronics

Abstract: Nickel matrix composite coatings containing micron- and nano-sized SiC particles were prepared in order to study the interdependence of the SiC particles embedding and the deposits 'mechanical behaviour SiC particles of two different sizes, namely 1 μm and 20 nm, were codeposited with nickel from Watts solutions under pulse current conditions. It has been observed that the embedding of SiC particles in the nickel matrix and the pulse current application result in deposits with more uniform particle distribution and better surface morphology than those obtained under direct current conditions. The study of the composite deposits revealed that the microhardness is not only increased by the presence and the reduced size of the particles, but also influenced by the current conditions, i.e. duty cycle and pulse frequency. Moreover, microhardness of the deposits can be further ameliorated by specific thermal treatment.

Electrochemical deposition of Ag, Au and Ag-Au alloys on n-Si(111) : Electrodeposition in Electronics

Abstract: The mechanisms of silver and gold-silver alloy electrodeposition on n-Si(111) in a cyanide medium have been studied combining electrochemical and surface analytical techniques. The kinetics during the initial stages of deposition were investigated by cyclic voltammetry and chronoamperometry combined with AFM and SEM. The conditions for progressive and instantaneous primary nucleation were elucidated from the analysis of current transients. Based on experimental results a double pulse routine (including a short nucleation pulse to a relatively high cathodic potential E 1 followed by a low growth potential E 2 ) was introduced for obtaining continuous and adherent thin metal films. The morphology of deposited films was found to be strongly dependent on the growth potential. The influence of deposition conditions on composition of Ag-Au alloy films was investigated by EDX and XPS. Current-voltage and capacity-voltage measurements showed an ideal Schottky behaviour of the n-Si/Ag, n-Si/Au and n-Si/alloy solid-state contacts, and the formation of high quality junctions in all cases. Specific aspects of metallisation of n-Si/SiO 2 microstructure arrays, applying the double pulse polarisation technique, are discussed. The use of the so-called capillary based electrochemical microcell for localised metallisation on microstructure arrays is demonstrated.

Adsorption Behaviour of Laprol 2402 C on a Tin Electrode

Abstract: Voltammetry and EIS were used to study the adsorption behaviour of laprol 2402 C (the copolymer of ethene and propene oxides) on a Sn electrode in strongly acid Sn(11) sulphate solutions. At least two states of adsorption layers were found to exist depending on cathodic polarisation. Adsorption of laprol, observed at low or sufficiently high cathodic polarisations, results in a moderate decrease in the double layer capacitance (from 100 to 18 μF cm 2 ) and is accompanied by 100-fold reduction in the exchange current density A pronounced inhibition of Sn(II) reduction takes place in the vicinity of -0.3 V where voltammograms acquire a negative slope. High negative charge transfer resistance ranging from -2.3 to -4.5 kΩ cm 2 and low (7-9 μF cm 2) double layer capacitances are indicative of the formation of a more compact surface layer.

Electrodeposition of Amorphous Cobalt-Manganese Alloys on to Steel from Gluconate Baths

Abstract: Electrodeposition of codeposited Co-Mn alloys on to steel substrates was obtained from an acidic gluconate bath. The effects of several plating variables such as current density, bath composition, pH and temperature, on the potentiodynamic cathodic polarisation curves, cathodic current efficiency of the deposited alloy as well as on the alloy composition were investigated. The codeposition of Mn and Co from these electrolytes follows the normal type of deposition. The cathode current efficiency, f Co-Mn %, of the alloy is relatively high (» 95%). The Mn percentage in the deposits increases with either decreasing current density or increasing [Mn 2+ ]/[Co 2+ ] concentration ratio in the bath. Anodic linear stripping voltammetry (ALSV) indicated that the alloy might consist of a solid solution in which manganese is dissolved in cobalt. The Vickers microhardness of Co-Mn alloy electrodeposited from the present bath is higher than those of the parent metals. It is found that the Vickers microhardness values of the alloys are raised by decreasing pH or increasing current density. Increasing the electrolyte temperature greatly decreases the microhardness. These alloys were determined to be amorphous by X-ray diffraction analysis (XRD). Scanning electron microscopy (SEM) photomicrographs were obtained from the surfaces of selected deposits.

Raman spectroscopy of organic species incorporated into electrodeposited gold layers

Abstract: Surface micro-Raman spectroscopy is employed for the detection of organic species incorporated in gold layers obtained by electrodeposition from baths containing organic additives. The bulk of thick electrodeposited layers is exposed by metallographic polishing and subsequently analysed spectroelectrochemically. In-situ work in 0.1 M KCl aqueous solution proves the possibility of observing spectral features which can be assigned to additives: specifically, bands related to CN (from KAu(CN) 2 ) and benzyldimethylphenylammonium chloride (this quaternary ammonium salt is used as a hydrogen scavenger) are recorded. The intensity of the spectra from incorporated organics is a function of SERS-inducing oxidation-reduction cycles (ORC) and electrode polarisation. Surface restructuring brought about by electrochemical polarisation and release of incorporated material to the surface where spectroscopy is being carried out can explain the observed steady state and time dependent phenomena.

Synthesis of Nanocrystalline Nickel in Pulse Deposition

Abstract: SUMMARYThis paper describes a new method developed to synthesise bulk nanocrystalline nickel. A high frequency pulse current and high deposit current density were employed to increase the deposit cathodic overpotential and the nucleation rate. With increasing peak current density, the deposit grain sizes was found to decreased markedly, e.g. average grain sizes ranging from 200 to 50 nm were determined when the peak current density varied from 60 to 300 A dm2 at the on-time of 10 μs and the off-time of 90 μs. In the saccharin-containing electrolyte, the deposit grain size ranges from 80 to 15 nm under the same conditions. The hardness of the nickel deposits was examined when the average current density ranged from 2 to 40 A dm 2.

An electrochemical and in situ Raman investigation of the electrodeposition of Gold from a sulphite electrolyte

Abstract: Gold electrodeposition from Au(1) sulphite 0.05M and 0.5M baths at pH 6 was investigated by cyclic voltammetry and in situ Raman spectroscopy. Two electroplating regimes were recognised: at low cathodic potentials a form of cathodic passivation occurs, while charge-transfer controlled reduction occurs at high cathodic potentials. The combination of electrochemical and spectroscopic methods reveals that the cathodic passivation is related to the formation of a sulphur film at the electrode, due to the simultaneous reduction of Au(1) and sulphite. This film can be either oxidised electrochemically or reduced by polarising the cathode at potentials at which HS forms. Gold electroplating from slightly acidic sulphite baths is of commercial interest. but the efficiency of the process and the quality of the deposits can be impaired by the concurrent cathodic formation of sulphur This phenomenon can nevertheless be avoided even in the absence of the additives proposed in the patent literature, provided that the plating conditions are suitably selected.

A sulphate bath for the preparation of Zn-Fe alloy coatings

Abstract: A new acidic sulphate bath was developed for the preparation of Zn-Fe alloy coatings. The percentage of iron in the deposits produced was measured by atomic absorption spectrophotometry and was fou...

Thin Films of Chromium Electrodeposition from a Trivalent Chromium Electrolyte

Abstract: SUMMARYThe electrodeposition of thin films of chromium has been investigated under different operating conditions of bath composition, current density, pH and temperature. A detailed study has been made of the influence of these variables on the potentiodynamic polarization curves as well as on the film thickness. The optimum bath composition has been established, it contains: CrCl3.6H2O 150, NH4Cl 50, NaCl 24 and H3BO3 30 g l−1. The optimum operating conditions necessary to produce a firmly adherent chromium thin film have been found to be: pH = 3.5, J = 3 A dm−2, temp. = 25°C and time = 30 min. The film thickness is greatly sensitive to the operating conditions as well as to the bath composition. X-ray diffraction analysis proved that the Cr deposit under the optimum conditions consists, mainly, of u-chromium and a small amount of γ-chromium.

Electroplating and Properties of SnBi and SnCu for Lead-Free Finishes

Abstract: SUMMARYTin alloys such as Sn-0.7% Cu and Sn-2%Bi were identified as viable alternatives to tin-lead finishes. Electroplating of these alloys is challenging because of the great difference in reduction potentials of the individual elements and the usual problems associated with strong immersion deposition and poor alloy control. To overcome these problems we utilised metal-specific non-complexing organic additives, which can significantly slow down or completely inhibit deposition of the alloying element in a certain range of potentials. In this paper, we present the recent developments for SnBi and SnCu plating chemistries. The plating electrochemistry and materials properties of deposited alloys are discussed.

Influence of chloride and PEG on electrochemical nucleation of copper

Abstract: The influence of chloride ions and polyethylene glycol (PEG) on the nucleation of copper on glassy carbon from acid sulphate solutions was studied by measuring potentiostatic current transients (the chronoamperometry method). It was found that instantaneous nucleation occurred at the surface for solutions without additives. The initial stage of copper nucleation did not change on addition of chloride ions, but gradually changed from progressive nucleation to instantaneous nucleation at increasing potentials in the presence of PEG Chloride ions and PEG increase the nucleation rate and the nuclear number density of nuclei at the surface.

Electrodeposition of compositionally modulated alloys: An overview

Abstract: A new class of materials known as compositionally modulated alloys (CMA) or artificially modulated multilayers has generated an ever-increasing enthusiasm due to their unique properties. This paper reviews the recent developments in the field of electrodeposition techniques for the production of CMA, which offers many advantages over other methods. It also discusses the structure of CMA and their salient properties such as corrosion resistance, magnetic and mechanical properties, which differ to those obtainable in normal metallurgical alloys. Some of their interesting applications are also discussed.

Fabrication of graded nickel-quasicrystal composite by electrodeposition

Abstract: Functionally graded coatings with a gradual change in composition and microstructure can perform specific functions and meet stringent performance requirements. A new graded composite coating, nickel-quasicrystal, was examined in this paper It was found that the volume percentage of embedded quasicrystal particles in the composite increased with an increase in current density up to 10 A dm 2 . A maximum volume percentage quasicrystal particles of 48.2% was obtained at the current density of 10 A dm 2 , an electrolyte particle content of 50 g dm 3, agitation speed of 400 rpm, and particle size of 5 μm. Graded Ni-quasicrystal composite coatings were produced by manipulating the current density and the deposition time, and their hardness and composition were evaluated.

Electrodeposition of Silverbismuth Alloys from Thiocyanate-tartrate Electrolytes investigated by Cyclic Voltammetry

Abstract: The electrochemical processes during the deposition and dissolution of Ag-Bi alloys from alkaline thiocyanate-tartrate electrolytes have been investigated by cyclic voltammetry.Two cathodic reactio...

Zinc plating from acetate based electrolytes: Effect of brighteners

Abstract: SUMMARYZinc electrodeposits are widely used to protect iron and steel from corrosion. Zinc coatings are presently obtained from chloride and non-cyanide alkaline baths. Environmental corrosion along with the electrolyte's sensitivity towards metallic impurities limit the use of the chloride electrolyte. The use of brighteners, less cathode efficiency and the effluent treatment restrict the use of non-cyanide zinc plating baths. Hence, there is a need for a better zinc plating electrolyte. In this paper details of zinc plating from acetate electrolytes, and the effects of brighteners I. vanillin. 2. polyvinyl alcohol. 3. triethanolamine, 4. lactic acid, 5. thiamine hydrochloride in acetate based zinc plating electrolyte are presented.

Co-deposition of luminescent particles with Electroless nickel

Abstract: Electroless nickel composite coatings containing luminescent particles have potential application as indicator coatings and for product authentication. In this paper composite coatings containing europium doped yttrium vanadate has been prepared. The effects of various parameters, such as concentration of suspension of luminescent particles in bath solution, temperature and pH on the incorporation of YVO 4 :Eu 3+ into the nickel matrix have been studied. The conditions for optimum incorporation were bath loading of 15 g dm -3 at 90 °C and pH 5.4. When viewed under UV light of wavelength 254 nm. bright red luminescence was observed for coating prepared under different operating conditions and the intensity increased with increased volume percent incorporation. The corrosion protection characteristic of Ni-P coating was lost due to the presence of luminescent particles. Microhardness remained almost unchanged while the surface roughness increased with the extent of particle incorporation. Optical microscopy of the surface and cross-section of coating revealed an increased density of particle distribution with bath loading. Composite Ni-P coating containing as little as 5.16% (v/v) of YVO 4 :Eu 3+ can be successfully used as an indicator undercoat between the substrate and the functional coating.

Multilayer Compound Co-P Films with Controlled Magnetic Properties

Abstract: The influence of the quantity and thickness of successive crystalline and amorphous layers on magnetic properties of multilayer Co 100 N P N (8

Electrodeposition of Silver from Thiocyanate-cyanide Electrolytes investigated by Cyclic Voltammetry

Abstract: SUMMARYThe electrochemical processes during the electrodeposition of silver from alkaline thiocyanate-cyanide electrolytes are investigated by cyclic voltammetry as a function of silver concentration and potential sweep rate.Two cathodic reactions during the electrodeposition of silver and two anodic ones during its dissolution have been established. The ranges of sweep rates and silver concentrations in the electrolyte within which the processes proceed with diffusion control are determined. The investigations show the presence of chemical reactions along with the electrochemical silver deposition process.A potential region of formation of a layer of insoluble compounds, as well as a region of dissolution and passivation of the silver surface are determined. The passive oxide layers formed are reduced during the next cathodic scan.

Internal Stress in Electrodeposited Nanocrystalline Ni-Cu Alloys

Abstract: Brenner and Senderoffs spiral contractometer has been used to measure the residual stress (macrostress) in the electrodeposited nanocrystalline Ni-Cu alloys plated by pulse electrolysis. The stress in the deposit was observed as tensile in nature. The effects of the various pulse parameters, pulse frequency (f), average current density (J a ), pulse on-time (T on ), pulse off-time (T off ), temperature and pH on the stress of the deposit were studied and compared to those obtained under direct current deposition, Bath temperature and pH effects on the variation of tensile stress (a) with thickness have also been studied. Microstress in the nanocrystalline deposit has been studied from the peak broadening of the X-ray diffraction peaks.

Conducting Polymers as Coatings: Electrochemical and density functional theory investigations of the polymerisation of (Z)-α,β-2-diarylacrylonitriles

Abstract: Electroactive materials such as polypyrrole and polythiophene have many applications including their use as coatings in the metal finishing industry. Electrochemical and density functional theory (...

Influence of microstructure of 1050 alloys on electrograining in nitric acid

Abstract: Electrograining of structurally characterised 1050 aluminium alloys in nitric acid has been examined by scanning electron microscopy With control of alloy microstructure, particularly the size and distribution of second phase material, acceptable electrograined structures are generated with reduced power consumption. This is related directly to second phase particles providing sites in their zone of influence where pits initiate and subsequently propagate to develop the required uniformly convoluted surface.

Conducting polymers as coatings: Electrochemical and density functional theory investigations of the polymerisation

Abstract: Electroactive materials such as polypyrrole and polythiophene have many applications including their use as coatings in the metal finishing industry Electrochemical and density functional theory (DFT) studies of a series of derivatised thiophene molecules have revealed that the production of electroactive polymeric films can be related to the coupling pathways of the radical cations generated during anodic oxidation of the monomer Electro-oxidation of (E)-styrylheterocycles shows complex electrochemical behaviour with alkene oxidation preceeding that of the aromatic/heterocyclic rings to produce redox inactive insulating films A nitrile substitutent was introduced at the alkene spacer linkage in an attempt to alter the electron density distribution in the radical cation and thus minimise the likelihood of adverse couplings via this site This strategy proved successful with redox-active polymers formed on oxidation of (Z)-α,β-diarylacrylonitriles These results were supported by the use of DFT which confirmed that the π-spin density at the alkene spacer linkage was significantly reduced in the presence of the nitrile substituent allowing α,α'-coupling reactions to predominate

The development of structure in electrodeposited Co

Abstract: Co layers 25, 50 and 100 nm thick have been electrodeposited onto polycrystalline Cu. The development of the crystal structure of the layers has been examined using crystal orientation mapping (COM) and related to that of the underlying Cu. The magnetic properties of the electrodeposited Co film 100 nm thick have been examined using the MOKE and the magnetic properties have been related to the crystallographic structure.

Electrodeposition of Bismuth from Alkaline Thiocyanate-tartrate Electrolytes investigated by Cyclic Voltammetry

Abstract: The electrochemical processes during the deposition and dissolution of bismuth in alkaline thiocyanate-tartrate electrolytes as a function of bismuth concentration in the electrolyte and potential ...

The colour of chromium electroplate

Abstract: The reflectance of average daylight (D65) from chromium electroplated from a commercial chromium III electrolyte has been compared with that from a commercial chromium VI bath. The perceived colour...

Development of a non-cyanide alkaline bath for industrial copper plating

Abstract: A cyanide-free alkaline bath containing sodium potassium tartarate (SPT), and triethanolamine (TEA) has been developed by Hull cell studies to electroplate copper A trace amount of potassium thiocyanate (KCNS) in the bath solution improved the quality of the copper deposit and also improved the efficiency of the plating process. The developed solution is Eco-friendly with good throwing power and a workable effective current density range. Chromate, zinc and iron (Fe 2+ ) in trace amounts did not affect the copper deposit. Copper in the bath is in the complex state with TEA and SPT A simple conductometric procedure was developed to analyse the solution components of the bath solution. Working conditions and electrolyte composition were optimised for a good quality copper deposit.

Study of the cryolite formation during the zinc phosphating of aluminium

Abstract: To improve the corrosion resistance and the adhesion properties of aluminium, chemical conversion processes, such as zinc phosphating, are applied. During zinc phosphating of aluminium the co-precipitation of cryolite often occurs. Cryolite needs to be formed in solution to remove Al 3- ions, which have a poisoning effect on the phosphating process, away from the surface. Cryolite formation on the surface must be avoided, since it leads to a decrease of the corrosion resistance and of the adhesion properties In this paper the influence of mass transport on this co-precipitation competition is reported The resulting conversion layers are investigated by SEM/EDX. It can be concluded that the amount of mass transfer has a large influence on the formation of both the phosphate and cryolite crystals. Hence, this competition in precipitation is explained in terms oJ mass transport of the different species involved in the chemical reactions at the surface.

Composition and morphologies of electrodeposited zinc-nickel-manganese coatings

Abstract: A ternary alloy of Zn-Ni-Mn was electrodeposited onto mild steel from a sulphate-citrate bath containing boric and ascorbic acid using both pulse and direct current (DC). The relationships between current density current efficiency and composition were investigated. Thickness measurements, current efficiency calculations, and compositional analysis using energy dispersive X-ray analysis (EDAX) and SEM characterisation, were undertaken. It was possible to produce an alloy containing up to 10% Ni and 6% Mn. The nickel underwent anomalous co-deposition and the manganese regular co-deposition. Both DC and pulse electrodeposition showed an increase in the Mn and Ni percentage as the applied current density was increased. DC electrodeposition tended to produce higher nickel and manganese contents.

75 Years of Sulphuric Acid Anodizing

Abstract: It is 75 years since the process of sulphuric acid anodizing was patented in the United Kingdom. It is the most widely used anodizing process internationally and finds applications as diverse as cosmetic containers to components in space vehicles. The main areas of specialist technology -architectural, aerospace, decorative and hard anodizing are considered in detail. Developments in ancillary processes, such as cleaning etching dyeing and colouring as well as sealing are considered. Developments in plant and power supplies, as well as jigs and racks are also reviewed. A comprehensive list of literature references is also included.

EIS Study of the Codeposition of SiC Powder with Nickel in a Watts Bath

Abstract: The results of impedance investigations of the nickel electrocrystallisation from the Watts baths (with additions of a wetting substance—sodium dodecyl sulphate and of brightening components—2-buty...