Microstructural investigation of nickel deposits obtained by pulsed current

Electrodeposited nickel coatings are applied in functional applications to modify or improve corrosion resistance, hardness, wear, magnetic, and other properties. In this work, Nickel deposits were produced by simple pulse electrodeposition using a free-additive Watts bath. It has been shown that pulse current deposition is able to produce coatings with excellent properties in morphology, particle distribution, structure, grain size, hardness and wear resistance. Pulsed techniques present a larger number of variables, so we propose to optimize the parameters which define the pulsed current to obtain deposits with improved properties. The optimization of the conditions of deposition was established and the influence of pulse parameters, namely, pulse on-time, off-time and average current density, on the grain size, surface morphology and crystal orientation was determined. The morphology of the coatings was characterized by observations in scanning electronic microscopy (SEM). X-ray diffraction in symmetric mode was also used to evaluate the structure and principal crystallographic orientations of the deposits. The study showed that pulse current results in better properties of deposits and significantly refined the crystal grain.     

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.     

Electrodeposition of composite Ni–B coatings in a stirred heterogeneous system

The formation of composite electrochemical coatings of a nickel matrix with boron microparticles was investigated. Electrolytical nickel–boron layers were deposited on a paraffin-impregnated graphite electrode in a stirred heterogeneous system formed by a Watts-type nickel plating bath and dispersed boron powder particles. The polarisation behaviour of the composite plating bath as a function of the boron particle loading was examined. The effect of deposition conditions, as well as of the amount of boron powder in the plating bath on the boron content in the composite Ni–B coatings, was examined. The composite coating structure was established using scanning electron microscopy and light optical microscopy. The distribution of boron particles in the composite deposits was investigated by dynamic secondary ion mass spectrometry. The boron particles content was determined gravimetrically. The obtained results suggest that the content of incorporated boron particles increases with an increasing amount of boron in the plating bath. The potentiodynamic deposition method is demonstrated to be more suitable for production of composite coatings with a high content of boron particles than the potentiostatic one. Homogeneous distribution of boron particles in the nickel matrix without coagulation or sedimentation was associated with the electrochemical fabrication method in stirred heterogeneous systems.     

Preparation and properties of uniform amorphous and crystalline colloidal nickel sulfide

 Amorphous spherical particles of nickel sulfide of 10 nm in diameter were synthesized by the controlled double-jet precipitation (CDJP) technique using nickel sulfate and sodium sulfide. Cubic crystalline particles of ∼200 nm were obtained by aging dispersions of amorphous particles at 80 °C for more than a week, as long as the pH was kept between 3 and 3.5. Electrokinetic mobilities of these particles are reported, as well as color properties of their dispersions in liquids and in poly(vinyl alcohol) films are described. Received: 20 January 1997 Accepted: 21 January 1997     

Effect of current density on the microstructure and morphology of the electrodeposited nickel coatings

The aim of this research work was to study the effect of deposition current density on microstructure and surface morphology of electrodeposited nickel coatings. For this purpose, nickel deposits have been synthesized by direct current from Watts bath without additive, to limit the incorporation of pollutants resulting from surface adsorption or electro-activity of these compounds. Nickel deposits have been investigated by scanning electron microscopy and X-ray diffraction. Cyclic voltammetry was also used to gain information on the general behavior of the deposition. The optimum conditions of deposition were established and the influence of current density on the grain size, surface morphology, and crystal orientation was determined.     

Influence of the Oxide Content in the Catalytic Power of Raney Nickel in Hydrogen Generation

The influence of oxides in the hydrogen evolution on Raney nickel electrocatalysts was characterized by electrochemical impedance measurements. In addition, these materials show competitive overpotentials for hydrogen evolution with a modified Watts bath as a binder for the Raney nickel. The optimum result was ?190?mV of overpotential at 100?mA?cm^?2. Oxygen in the Raney Ni catalyst affects its electroactivity toward hydrogen evolution. The source of oxygen is related to the presence of chloride ions in the modified Watts bath. A Watts bath binds Raney Ni particles to the surface of the catalysts and chloride regulates the oxygen content in the nickel binder during electrodeposition. High oxygen content increases the hydrogen evolution overpotential of the electrode. The electroactivity of the synthesized porous coatings was evaluated by polarization curves and impedance plots. In addition, surface characterization by X-ray diffraction, field emission–scanning electron microscopy equipped with energy-dispersive analysis, and X-ray photoelectron spectroscopy is reported.     

The study of morphology and wear behavior of nanocomposite Cr-WC coating produced via electrodeposition with direct and pulse current

Nanocomposite Cr-WC coatings are widely used in different industries due to the favorite characteristics such as high wear and corrosion resistance. In this article, at the first time the nanocomposite Cr-WC coatings are produced via square pulsed and direct current in Watts’ deposition bath containing tungsten carbide particles of 70 nm in diameter. And then the effects of applied current to deposition on the size of tungsten carbide particles, distribution in the coating, homogeneity, hardness and the coatings wear ratio are investigated. The morphology of coating is studied by scanning electron microscope (SEM). The weight percentage of the tungsten carbide particles and the coatings hardness are determined by EDX composite analysis and Vickers micrometer ingressive hardness system, respectively. The results reveal that the amounts of nanoparticles and homogeneous distribution in the pulse current coating are more than direct current. The coating wear behavior and homogeneity of thickness in pulse current are better than direct current.     

Electrodeposition of nanocrystalline zinc from acidic sulfate solutions containing thiourea and benzalacetone as additives

Nanocrystalline zinc coatings were produced by pulse electrodeposition in acid sulfate bath containing thiourea and benzalacetone additives and characterized by X-ray diffraction and scanning electron microscopy techniques. The influence of benzalacetone concentration and pulse peak current density on the grain size and crystallographic orientation of zinc deposits was investigated. Zinc electrodeposited from additive-free solutions or with one of the two additives is not composed of nanosized crystals. The mixture additives of thiourea and benzalacetone give rise to the formation of particle-like nanocrystalline zinc with a (10ī1) random orientation. A change in peak current density from 2 to 1 A/cm² only increases the grain size from 60 to 62 nm.     

Influence of bath composition and deposition parameters on nanostructure and thermal stability of gold

Nanocrystalline gold is electrodeposited from a stable nontoxic bath, in which Au⁺ is stabilized by complex formation with 3-mercapto-1-propanesulfonic acid sodium salt. Nanoscaling is achieved by pulse techniques. The crystallite size is strongly dependent on physical and chemical process parameters, such as pulse duration, current density, bath temperature, type, and amount of additives; especially, we observe a decrease of the crystallite size down to 16 nm by the proper choice of current density and temperature, and down to 7 nm by the use of additives. The thermal stability of nanocrystalline gold is investigated by in situ high-temperature X-ray diffraction; nanogold exhibits a thermal stability up to 673 K. An activation energy of 37 kJ mol⁻¹ is determined for the grain-growth kinetics.Paper presented at the “Jahrestagung der Fachgruppe Angewandte Electrochemie der Gesellschaft Deutscher Chemiker, Düsseldorf, 11.–14.06.2005”     

Electroless Ni–P coated on graphite as catalyst for the electro-oxidation of dextrose in alkali solution

Graphite particles were coated with Ni–P by electroless deposition using a conventional bath consisting of a nickel salt and hypophosphite. After 15 min of electroless deposition, the graphite particles were covered with 10 wt% nickel and 0.7–1.0 wt% phosphorus as analysed by wet chemical method. Surface morphology was studied by scanning electron microscopy (SEM). Electrochemical characterisation for the catalytic activity was done by cyclic voltammetry. Pure Ni powder and electroless Ni–P coated on graphite were used as catalysts for the electro-oxidation of dextrose (1.8 × 10⁻³ to 4.5 × 10⁻³ M) in 0.1 M KOH solution. Comparative studies revealed that electroless Ni–P coated on graphite particles acted as a better catalyst than pure Ni powder for catalytic reaction.     

Electron Microscopy Study of Nickel and Nickel Composite Electrocoatings

 It has been proved that the electrolysis parameters strongly influence the structural properties of nickel electrodeposits, mainly the crystalline growth, preferred orientation and surface morphology. To determine the structural characteristics of nickel and composite nickel matrix electrocoatings, prepared under either direct current or pulse current conditions, the electron microscopy techniques have proved very important tools. In particular, investigation of the distribution and percentage of microparticles incorporated in the metallic matrix during preparation of nickel composite electrocoatings demands the use of techniques such as energy dispersion spectroscopy (EDS) or image analysis.     

玻碳材料脉冲电沉积纳米晶体镍的制备及其性能研究

由于纳米晶体镍具有电催化甲醇的活性,本文采用双脉冲法在玻碳表面上电沉积制备了纳米晶体镍,并分析了脉冲条件对其晶粒尺寸的影响。电沉积的溶液组成为300 g·L^-1 NiSO₄·6H₂O,45 g·L^-1 NiCl₂·6H₂O,40 g·L^-1 H₃BO₃,5 g·L^-1 C₇H₅NO₃S,0.05 g·L^-1 C₁₂H₂₅NaO₄S,最优的脉冲工艺参数是脉冲平均电流密度为100 mA·cm^-2、脉冲占空比为30%,脉冲频率为100 Hz, pH为1.5、温度为55 ^oC。利用XRD、TEM、循环伏安以及电化学阻抗分析了纳米晶体镍的晶粒尺寸、结构及性能。制备的电沉积层致密均匀,为典型的面心立方结构,晶体镍的平均粒径在18 nm左右,玻碳材料表面上通过电沉积得到的纳米晶体镍在碱性环境下对甲醇具有良好的电催化活性。     

Effect of parameters of pulse electrolysis on concentration changes in the loose zinc deposit and deposit properties

The parameters of pulse current modes (durations of pulses and pauses between pulses) have a significant influence on the growth dynamics and properties of loose zinc deposits if the process takes place under unsteady-state diffusion conditions. The coefficient k defined as the ratio of the growth time of the loose deposit to the transition time in the pulse was proposed as a criterion for describing the concentration changes. By varying the parameters of pulse electrolysis, one can change the density in situ and the morphology of the electro-deposited metal from highly porous loose deposits with branched dendritic particles to compact deposits.     

Studies on electrodeposition of Zn–MoS<Subscript>2</Subscript> nanocomposite coatings on mild steel and its properties

Pure zinc and Zn–MoS₂ composite coatings were prepared by electrodeposition from zinc sulfate–chloride bath containing uniformly dispersed MoS₂ nanoparticles. The effect of MoS₂ on the deposition properties morphology, crystallographic orientation, and corrosion behavior were studied. The electrokinetic properties (zeta potential) and size distribution statistics in plating bath for the particles were evaluated using dynamic light scattering experiments. The Zn and Zn–MoS₂ deposition process was studied by linear polarization and cyclic voltammetry. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction analysis, and potentiodynamic polarization measurements were used to characterize the coatings. The addition of MoS₂ to the electrolyte significantly changed the microstructure and crystallographic orientation of the zinc deposits and enhanced the corrosion resistance of the coatings. The morphological and electrochemical properties of the zinc coatings were observed to be significantly affected by the incorporation of MoS₂ particles into the zinc matrix.     

Laser Emission from Dye-Doped Organic-Inorganic Particles of Microcavity Structure

Interaction between laser light and a micrometer-size spherical particle causes an optical resonance in its interior since a spherical wall acts as a cavity. The present work seeks to investigate the preparation of organicinorganic particles containing laser dyes and demonstrate their lasing behavior. Rhodamine 6G was incorporated into organic-inorganic spherical particles of micrometer-size using sol-gel technique. Phenyl triethoxy silane was used as a starting material for particles. Particle size was 1–10 μm and dye content was 1–7 × 10⁻⁵ mol/g. A particle was set on a glass plate in air and pumped by a second harmonic pulse ofQ-switched Nd-YAG laser (532 nm wavelength). From a particle of 6 μm in diameter, a strong laser emission peak was observed at 598 nm wavelength which corresponded to the whispering-gallery mode resonance.     

Ultrasound technique as a tool for high-rate incorporation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in NiCo layers

NiCo–Al₂O₃ composite coatings were prepared by electrodeposition in a sulfamate plating bath containing Al₂O₃ particles to be co-deposited under sonication. For reliable determination of the microstructure, detailed studies on composite cross-sections were carried out by energy-dispersive spectrometer (matrix composition, particle content) and FE-SEM/electron backscattered diffraction data (particle distribution, grain size), accompanied by XRD analyses concerning texture, lattice parameter, grain size, and residual stress. The NiCo matrix with a Co/Co + Ni ratio up to 0.4 is a face-centered cubic solid solution with <100> and <110> fiber textures. The distribution of the particles (size 250 nm) was well-dispersed and enhanced up to 15 wt.% by ultrasound application during plating. Vickers hardness increased up to 50% by dispersion hardening. First-order residual stress in the matrix increased with rising Co content, thus decreasing wear resistance and revealing the complex of composite properties with partially opposite effects.     

Elucidation of the chemical state of phosphorus and boron in crystallographically amorphous nickel electroplates

Using the valence-to-core version of X-ray emission spectroscopy (valence-to-core XES) together with X-ray diffraction analysis, the structure and the composition of nickel coatings deposited from solutions containing hypophosphite ions or dimethylaminoborane (DMAB) are studied. The diffraction patterns of prepared deposits are characterized by the presence of a wide “halo”. Annealing of crystallographically amorphous deposits at temperatures of 500°C and higher transforms these haloes into the spectra corresponding to metal nickel and its phosphides or borides present in the crystallized deposits. A result of fundamental importance obtained in the simultaneously conducted examination of the same deposits by the valence-to-core XES method is that both the binding energy and the intensities of Kβ satellite spectral lines of annealed samples remain unchanged as compared with original samples. Based on this comparison, it is concluded that phosphide and boride nickel compounds were already formed in the course of electrodeposition, whereas the thermal treatment of deposits (crystallization) leads only to aggregation of the metal and metal-metalloid nanoparticles.     

CZTS nanoparticles by one-pot sonochemical route – Effect of power density,pH and bath temperature

One-pot synthesis of nanosized CZTS particles using ultrasound employing citric acid as the complexing agent has been studied. The CZTS nanoparticles synthesis at different bath temperatures, pH and power densities was attempted. The power density used for the reaction did not alter the crystallinity and morphology of the synthesized particles. However, the chemical composition and the bandgap of the particles showed significant variation with the applied power density. Apart from affecting the composition, bandgap and electrical characteristics, the bath temperature considerably affected the crystallinity of the CZTS nanoparticles. Based on the conditions of synthesis, the particle size ranged between 25 ​nm and 40 ​nm. Depending on the process conditions, the bandgap of the particles varied between 1.4 ​eV and 2.9 ​eV. The samples synthesized under a power density of 46 ​W ​L⁻¹ and 40 ​°C bath temperature with reactant pH of 3.5 showed composition closer to the required stoichiometry.     

Electrochemical preparation and characterisation of CoPt magnetic particles

CoPt particles of different size and modulate magnetic properties have been prepared by electrodeposition. Particles of growing size from 50 nm until continuous deposits have been obtained and their composition, crystalline structure and magnetic properties have been analyzed. The prepared CoPt particles from 50 nm to 250 nm showed ferromagnetic behaviour so did the continuous deposits. However, drastic changes in magnetism have been detected related to the size of the particles: the smallest particles presented lower coercivity which increases with increasing size, with a maximum value for particles of 150–250 nm diameter. The coercivity decreased when continuous deposits were attained due to the disordered growing and the loss of the surface anisotropy.     

Electrochemical modification of Bi2S3 coatings in a nickel plating electrolyte

The electrochemical behavior of Bi₂S₃ coatings in Watts nickel plating electrolyte was investigated using the cyclic voltammetry, electrochemical quartz crystal microbalance, X-ray diffraction, and energy dispersive X-ray analysis methods. During the bismuth sulfide coating reduction in Watts background electrolyte in the potential region from −0.4 to −0.6 V, the Bi₂S₃ and Bi(III) oxygen compounds are reduced to metallic Bi, and the decrease in coating mass is related to the transfer of S²⁻ ions from the electrode surface. When the bismuth sulfide coating is reduced in Watts nickel plating electrolyte, the observed increase in coating mass in the potential region −0.1 to −0.4 V is conditioned by Ni²⁺ ions reduction before the bulk deposition of Ni, initiated by Bi₂S₃. In this potential region, the reduction of Bi(III) oxygen compounds can occur. After the treatment of as-deposited bismuth sulfide coating in nickel plating electrolyte at E = −0.3 V, the sheet resistance of the layer decreases from 10¹³ to 500–700 Ω cm. A metal-rich mixed sulfide Ni₃Bi₂S₂–parkerite is obtained when as-deposited bismuth sulfide coating is treated in Watts nickel plating electrolyte at a potential close to the equilibrium potential of the Ni/Ni²⁺ system and then annealed at temperatures higher than 120 °C.