Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO₃-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H₃BO₃. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H₂O₂ in the electrolytic bath is also proposed.

     

Enhancement of the electrochemical reduction of oxygen at platinum by nickel underpotential deposition

Polycrystalline Pt electrode was modified by underpotential deposition (upd) of nickel. The modification was performed by potential cycling in phosphate buffer pH 7. 0 containing NiSO₄, in which hydrogen and nickel upd processes were well separated. The maximum Ni upd coverage was found to be 0.3. Oxygen reduction was studied at bare and nickel upd-modified Pt. It was found that the reaction rate increased with increasing Ni upd coverage. At θ(Ni)=0.3, the current density was a factor of 2 higher compared to bare Pt (at the potential of 0.85 V). The capacitance of the electrode interface was determined in potential-relaxation experiments following interruption of the polarization current. It was found that the pseudocapacitance owing to a coverage by the adsorbed reaction intermediates was higher on the Ni-modified Pt surface than on bare Pt, which resulted in higher reaction rate. The influence of Ni adatoms on the surface coverage by the reaction intermediates was attributed to the inhibition of OH adsorption on Pt by OH ligands attached on neighboring Ni atoms.     

Correlation between acidic properties of nickel catalysts and catalytic activities for ethylene dimerization and butene isomerization

Catalytic activities of NiO–SiO₂ for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maxima in activities. The variations in catalytic activities are closely correlated to the acidity of NiO–SiO₂ catalysts. Catalytic activities of NiO–TiO₂ catalysts modified with H₂SO₄, H₃PO₄, H₃BO₃, and H₂SeO₄ for ethylene dimerization and butene isomerization were examined. The order of catalytic activities for both reactions was found to be NiO–TiO₂/SO₄^2- >> NiO–TiO₂/PO₄^3-NiO–TiO₂/BO₃^3- > NiO–TiO₂/SeO₄^2-> NiO–TiO₂, showing clear dependence of catalytic activity upon acid strength. The high catalytic activity of supported nickel sulfate for ethylene dimerization was related to the increase of acidity and acid strength due to the addition of NiSO₄. The asymmetric stretching frequency of the S=O bonds for supported NiSO₄ catalysts was related to the acidic properties and catalytic activity. That is, the higher the frequency, the larger both the acidity and catalytic activity. For NiSO₄/Al₂O₃–ZrO₂ catalyst, the addition of Al₂O₃ up to 5 mol% enhanced catalytic activity for ethylene dimerzation and strong acidity gradually due to the formation of Al–O–Zr bond. The active sites responsible for ethylene dimerization consist of a low-valent nickel, Ni⁺, and an acid, as evidenced by the IR spectra of CO adsorbed on NiSO₄/ -Al₂O₃ and Ni 2p XPS.     

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.     

Electronic absorption spectra of nickel dichloride and nickel oxide solutions in the 2CsCl-NaCl and KCl-NaCl metls

The electronic absorption spectra of nickel dichloride and nickel oxide dilute solutions in the 2CsCl-NaCl and KCl-NaCl melts have been measured by ultraviolet reflection absorption spectroscopy in the range 250–2500 nm. The spectroscopic data demonstrate the formation of stable Ni(II)-based tetrahedral groups (NiCl ₄ ^2? ) in solutions of nickel dichloride in the 2CsCl-NaCl melt, whereas in the KCl-NaCl melt, nickel dichloride undergoes thermal dissociation to give Ni(II)-and Ni(I)-based complex groups: NiCl ₄ ^2? , NiCl ₆ ^4? , and NiCl ₄ ^3? . The dissolution of nickel oxide in the 2CsCl-NaCl and KCl-NaCl melts gives mainly NiOCl ₃ ^3? complex groups.     

Corrosion properties of nickel coatings obtained from aqueous and nonaqueous electrolytes

Nickel was deposited on a copper substrate from aqueous and nonaqueous ethanol electrolytes. X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and chronovoltametry, scanning electron microscopy, and atomic force microscopy were used to study the effect of the solvent on the surface and corrosion properties of the Ni coatings formed. Unifom and relatively smooth Ni films were obtained as measured with microscopy techniques. The formation of a passive film in acidic, alkaline, and neutral chloride-containing media was confirmed with X-ray photoelectron spectroscopy. The water-based nickel-plating electrolyte makes it possible to deposit coatings with higher corrosion resistance as compared with coatings deposited from ethanol electrolyte in NaOH and NaCl media. The proposed mechanism of corrosion in a 0.5 M H₂SO₄ solution involves cycles of active-passive surface behavior due to its passivation by corrosion products.     

Synthesis and characterization of (pyrazolylethylphosphinite)nickel(II) complexes and catalytic activity towards ethylene oligomerization

Compounds (2‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)ethyldiphenylphosphinite ( L1 ), 2‐(3,5‐di‐tert‐butyl‐1H‐pyrazol‐1‐yl)ethyldiphenylphosphinite ( L2 ) , and 2‐(3,5‐diphenyl‐1H‐pyrazol‐1‐yl)ethyldiphenylphosphinite ( L3 ) were prepared using the synthetic routes reported in literature. These compounds were reacted with [NiCl₂(DME)₂] or [NiBr₂(DME)₂] under appropriate reaction conditions to afford six new nickel(II) compounds ([NiCl₂( L1)] ( 1 ), [NiCl₂( L2 )] ( 2 ), [NiCl₂( L3 )] ( 3 ), [NiBr₂( L1 )] ( 4 ), [NiBr₂( L2 )] ( 5 ) and [NiBr₂( L3 )] ( 6 )). The new nickel(II) pre‐catalysts catalyze the oligomerization of ethylene, in the presence of ethylaluminium dichloride as co‐catalyst, to produce butenes, hexenes, octenes and higher carbon chain ethylene oligomers with very little Friedel‐Crafts alkylation products when the reactions were run in toluene.     

The hexagonal close-packed nickel nanocrystals prepared by fast scan voltammetry

The nickel (Ni) nanocrystals (average diameter 9.7 ± 2.3 nm) were deposited onto composite graphite electrode from a plating solution of 5.0 mM NiCl₂6H₂O and 1.0 M NH₄Cl using scan rate of 6500 mV s⁻¹. The initial potential −1.5 V and final potential −0.5 V vs. Ag/AgCl with applied time 120 s were used for the whole deposition process. The variations of applied overpotentials and deposition times have affected the characteristics of Ni nanocrystals. It was found that the structural formation of Ni nanocrystals obtained were almost pure hexagonal close-packed (hcp). This study has demonstrated that the tuning of the final size, morphology and structural formation of the Ni nanocrystal were affected by control of nucleation, growth and hydrogen evolution processes in fast scan voltammetry technique used.     

Production of nickel sulfate single crystals in processing of nickel oxide electrodes of alkaline batteries

[NiSO₄(H₂O) _n ] single crystals were grown by slow cooling and evaporation of a solution for sulfuric acid leaching of the active paste of a nickel oxide electrode from a spent alkaline battery. The crystals were studied by X-ray phase analysis in two measurement configurations (transmission and Bragg-Brentano focusing).     

New nickel(II) chloride-morpholine complexes

The compounds [NiCl₂(Morph)₃(H₂O)₂] and [NiCl₂(Morph)₃] have been prepared by treating NiCl₂·6H₂O with morpholine (Mo     

Electrochemical studies on Zn deposition and dissolution in sulphate electrolyte

The electrochemical deposition and dissolution of Zn on Pt electrode in sulphate electrolyte was investigated by electrochemical methods in an attempt to contribute to the better understanding of the more complex Zn–Cr alloy electrodeposition process. A decrease of the Zn electrolyte pH (from 5.4 to 1.0) so as to minimise/avoid the formation of hydroxo-products of Cr in the electrolyte for deposition of alloy coatings decreases the current efficiency for the Zn reaction, but the rate of the cathode reaction increases significantly due to intense hydrogen evolution. The results of the investigations in Zn electrolytes with pH 1.0–1.6 indicate that Zn bulk deposition is preceded by hydrogen evolution, stepwise Zn underpotential deposition (UPD) and formation of a Zn–Pt alloy. Hydrogen evolution from H₂O starts in the potential range of Zn bulk deposition. Data obtained from the electrochemical quartz crystal microbalance (EQCM) measurements support the assumption that electrochemical deposition of Zn proceeds at potentials more positive than the reversible potential of Zn. Anodic potentiodynamic curves for galvanostatically and potentiostatically deposited Zn layers provide indirect evidence about the dissolution of Zn from an alloy with the Pt substrate. The presumed potential of co-deposition of Cr (−1.9 V vs. Hg/Hg₂SO₄) is reached at a current density of about 300 mA cm⁻².     

Study on corrosion resistance of electroplating zinc–nickel alloy coatings

Electrodeposited zinc–nickel alloy coatings have been widely adopted for surface treatment of automobile body steel sheet for high corrosion resistance. The corrosion behavior of the coatings has been related with the components of nickel, and the zinc–nickel alloy passive coatings have much higher corrosion resistance than that of zinc–nickel alloy coatings. In the present paper, the corrosion resistance behavior of the zinc–nickel alloy coatings obtained by new process and formulation has been studied by means of the electrochemistry test and neutral salt spray test. And it is discovered that the properties of corrosion resistance of zinc–nickel alloy passive coatings were better than that of zinc passive coatings, Cadmium passive coatings and alloys of electrodeposited cadmium–titanium. The components of corrosion productions, in terms of X‐ray diffraction (XRD), are mainly ZnO, ZnCl₂ · 4Zn(OH)₂ and small quantity of 2ZnCO₃· 3Zn(OH)₂. The component of zinc–nickel alloy coatings has been investigated with Glow Discharge Optical Emission Spectrometry (GDA‐750). And it is found that as the thickness of zinc–nickel alloy coatings increases, the component of zinc increases from beginning to end, but the peak value of nickel appears and an enrichment of nickel in the coatings comes into being. Because the electrodeposited zinc–nickel alloy coatings exhibit different alloy phases as a function of their alloy composition, in this paper, the crystal structure changing with the different component of nickel has been studied in terms of XRD. The result shows that electrodeposited zinc–nickel alloy has different phases: α‐phase, a solid solution of zinc in nickel with an equilibrium solubility of about more than 79% nickel; γ‐phase, an intermediate phase with a composition Ni₅Zn₂₁; η‐phase, a solid solution of nickel in zinc with less than 5% nickel; and δ‐phase (Ni₃Zn₂₂) appeared from η‐phase to α‐phase with increasing content of nickel. Copyright © 2009 John Wiley & Sons, Ltd.     

Biphasic oligomerization of ethylene with nickel complexes immobilized in organochloroaluminate ionic liquids

Ethylene was selectively oligomerized by nickel complexes such as (PPh₃)₂NiBr₂ and (PPh₃)₂NiCl₂ immobilized in chloroaluminate ionic liquid in biphasic catalytic reactions. The influence of reaction parameters such as reaction media, reaction temperature and Et₂AlCl:Ni molar ratio was also evaluated. Turnover frequency up to 24000 mol C₂H₄/(mol Ni h) was achieved under mild reaction conditions (0.5 atm and 40 °C). GC‐MS analyses showed that the obtained oligomers completely consist of C4 and C6. The olefinic products can be easily separated from the catalytic ionic liquid phase by simple decantation, and the nickel catalyst can be reused without a significant decrease in turnover frequency and change of the distribution of the olefinic products. Copyright © 2009 John Wiley & Sons, Ltd.     

Design of nickel chelates of tetradentate N-heterocyclic carbenes with subdued cytotoxicity

A series of nickel complexes, 1b-3b, exhibiting subdued cytotoxicity have been designed with the intent of their use as agents for developing resistance to nickel toxicity. Indeed, the nickel complexes, 1b-3b, display less cytotoxic activity towards two commonly occurring human cancer cell lines namely, HeLa cells (16-64%) and MCF-7 cells (70-90%) in culture as compared to the maximum inhibition by NiCl₂ · 6H₂O under analogous conditions at three different concentrations (1 μM, 5 μM and 20 μM). Similarly, the suppression of cytotoxicity through chelation of the metal ion can also be seen in normal cells as was evident from a significant reduction in cytotoxicity (9-41%) for a non-tumorigenic CHO cell line in case of a representative complex 3b. The reduction in carcinogenic activity in the complexes relative to nickel(II) ion from NiCl₂ · 6H₂O is brought about by successful chelation of the metal center by a class of specially designed new tetradentate N/O-functionalized N-heterocyclic carbene ligands. The two strongly σ-donating carbene moieties coupled with two negatively charged amido moieties present in the N-heterocyclic carbene ligands facilitate complete chelation of the metal center and thereby significantly reduce the cytotoxic effects of the metal.     

Electrodeposition of Zn–Ni alloys from sulfate bath

The electrodeposition of zinc–nickel (Zn–Ni) alloys from sulfate baths has been studied at different deposition times and H₂SO₄ and NiSO₄ concentrations; various characteristics have been observed during alloy deposition and dissolution. The deposit has been investigated by using scanning electron microscopy (SEM) and X-ray diffractometry. Cyclic voltammetry and galvanostatic measurements during electrodeposition have been conducted. Electrochemical and surface analysis indicate that deposition takes place with the formation of two different structures corresponding to γ-phase and δ-phase zinc–nickel alloys. During anodic part of the cyclic voltammetry of the alloys, a reduction process has been observed, which may be due to hydrogen evolution. With the increase of nickel concentration in the bath, the amount of γ-phase increases, as indicated by the relative increase in the height of the peaks in the X-ray patterns and anodic peaks in the cyclic voltammograms. Also, the corrosion resistance of the zinc–nickel alloy has been improved with an increased concentration of nickel. Under these experimental conditions the electrodeposition of the alloys is of anomalous type.     

Extraction systems of flame atomic absorption determination of trace impurities in high purity nickel salts

Summary Different extraction sytems including long chain quaternary alkylammonium salts and APDC were investigated in order to determine the optimal conditions for extraction separation and preconcentration of traces of Ag, Bi, Cd, Cu, Fe, Mo, Pb, Sb and Zn from high purity NiSO₄·6H₂O, NiCl₂·6H₂O, Ni(OOCCH₃)₂·4H₂O and Ni(NO)₃)₂·6 H₂O. Best results for multielement preconcentration were found with the extraction system HCl-trioctylmethylammonium chloride-0,002 mol/l APDC/MIBK. The proposed method permits the flame atomic absorption determination of 5·10^–6%, Ag, Cd, Cu and Zn, 1·10^–5% Bi, Fe, Pb and 5·10^–5% Mo and Sb with good accuracy and precision.     

Nickel(II) complexes bearing pyrazolylpyridines: synthesis,structures and ethylene oligomerization reactions

Reactions of 2‐bromo‐6‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine ( L1 ) and 2,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridine ( L2 ) with NiCl₂ and NiBr₂ led to the formation of their respective metal complexes [NiCl₂(L1)] ( 1 ), [NiBr₂(L1)] ( 2 ) and [NiBr₂(L2)] ( 3 ) in moderate to high yields. The complexes were characterized using elemental analyses, mass spectrometry and single‐crystal X‐ray diffraction for 2 . The solid‐state structure of 2 confirmed the bidentate coordination mode of L1 and formation of a monometallic compound. Activation of the nickel(II) pre‐catalysts with methylaluminoxane afforded active catalysts in the ethylene oligomerization reaction to produce mainly butenes (84–86%). In contrast, activation of nickel(II) pre‐catalyst 2 with ethylaluminium dichloride resulted in partial Friedel–Crafts alkylation of the toluene solvent by the preformed oligomers. Complex structure, nature of co‐catalyst employed, type of solvent and reaction conditions influenced the catalytic behaviour of these pre‐catalysts. Copyright © 2015 John Wiley & Sons, Ltd.     

The dehydration of nickel sulfate

Nickel sulfate was recrystallized to obtain the 7 H₂O, β6 H₂O and various habits of α6 H₂O. Dehydration and phase transitions were studied using X-ray analysis and DSC with effluent gas analysis. NiSO₄ · 7 H₂O dehydrates spontaneously via 7 → 6β → 6α at room temperature, while the dehydration pathway of NiSO₄ α6 H₂O is 6α → 6γ → 4 → 1. The effect of time and storage on the 6α—6β phase transition was investigated.     

Electrooxidation of dihydroxybenzenes at a mechanically renewed nickel electrode

The dependence of the potentials and peak currents of the electrooxidation of isomeric dihydroxybenzenes on the polarization mode of a mechanically renewed nickel electrode is studied by direct-current cyclic voltammetry. The results indicate that the oxidation peaks of hydroquinone, pyrocatechol, and resorcinol appear in alkaline (0.05–0.10 M KOH), neutral (0.02–0.10 M Na₂SO₄) and acidic (0.02–0.05 M H₂SO₄) supporting electrolytes. The peak shape and parameters depend on the composition of the supporting electrolyte, which creates the conditions for the formation of different nickel oxides on the electrode surface then involved in the electrooxidation of dihydroxybenzenes. The regeneration of the electrode surface also affects the peak parameters, especially for resorcinol, whose signals completely disappear without the electrode renewal. The analytical signals for three isomeric dihydroxybenzenes are peaks in an alkaline solution, and also hydroquinone and pyrocatechol peaks in neutral and acidic solutions.