Morphological and structural studies of nanoporous nickel oxide films fabricated by anodic electrochemical deposition techniques

Porous nickel oxide films are directly deposited onto conducting indium tin oxide coated glass substrates by cyclic voltammetric (CV), galvanostatic, and potentiostatic strategies in a plating bath of sodium acetate, nickel sulfate, and sodium sulfate. By tuning the deposition parameters, it is possible to prepare nickel oxide films with various morphologies and structures. Film formation relies on the oxidation of dissolved Ni²⁺ to Ni³⁺, which further reacts with the available hydroxide ions from a slightly alkaline electrolyte to form insoluble nickel oxide/hydroxide deposits on the substrate. A compact film with particularly small pores is obtained by CV deposition in a potential range of 0.7-1.1 V. A galvanostatically deposited film is structurally denser near the surface of the substrate, and becomes less dense further away from the surface. Interestingly, a potentiostatically deposited film has pores distributed uniformly throughout the entire film. Therefore, for obtaining a uniform film with suitable pore size for electrolyte penetration, potentiostatic deposition technique is suggested. In addition, except for CV deposition, the deposited films resemble closely to cubic NiO when the annealing temperature exceeds 200 °C.     

The catalytic dehydrogenation of cyclohexane and methylcyclohexane over nickel loaded Y zeolites

The dehydrogenation of cyclohexane to benzene and of methylcyclohexane to toluene was investigated over a range of nickel Y zeolites, varying the nickel content and the nature of the alkali metal co-cation (Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺). The overall reaction is viewed as occuring via a series of consecutive dehydrogenation steps. Catalytic activity is correlated with the reaction time, the reaction temperature, the level of Ni²⁺ exchange and the effects of pyridine adsorption. The level of dehydrogenation is strongly dependent on the mass of supported nickel metal and the surface Bronsted acidity. Catalyst deactivation results from the deposition of coke on the catalyst surface which is promoted with increasing zeolite acidity.     

Effects of K<Subscript>4</Subscript>Fe(CN)<Subscript>6</Subscript> on electroless copper plating using hypophosphite as reducing agent

K₄Fe(CN)₆ was used to improve the microstructure and properties of copper deposits obtained from hypophosphite baths. In electroless copper plating solutions using hypophosphite as the reducing agent, nickel ions (0.0038 M with Ni²⁺/Cu²⁺ mole ratio 0.12) was used to catalyze hypophosphite oxidation. However, the color of the copper deposits was dark or brown and its resistivity was much higher than that obtained in formaldehyde baths. The effects of K₄Fe(CN)₆ on the deposit composition, resistivity, structure, morphology and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The deposition rate and the resistivity of the copper deposits decreased significantly with the addition of K₄Fe(CN)₆ to the plating solution and the color of the deposits changed from dark-brown to copper-bright with improved uniformity. The nickel and phosphorus content in the deposits also decreased slightly with the use of K₄Fe(CN)₆. Smaller crystallite size and higher (111) plane orientation were obtained by addition of K₄Fe(CN)₆. The electrochemical current–voltage results show that K₄Fe(CN)₆ inhibited the catalytic oxidation of hypophosphite at active nickel sites and reduced the reduction reaction of cupric ions on the deposit surface by adsorption on the electrode. This results in lower deposition rate and a decrease in the mole ratio of NaH₂PO₂/CuSO₄ consumed during plating.     

Electroless plating of rhenium–nickel alloys

In this study, rhenium–nickel (Re–Ni) films were formed by electroless deposition on conductive (Cu) and non-conductive (SiO₂) substrates. Different bath compositions were evaluated, aiming to achieve high Re-content. Both sodium hypophosphite and dimethylamine-borane were used as reducing agents. Films containing up to 75 at% Re were obtained. The influence of nickel concentration in the solution on alloy composition, deposition rate and surface morphology were determined. It is shown that Ni²⁺ acts as a catalyst for the in situ reduction of the perrhenate ion, in a manner similar to what was proposed for electroplating of the same alloy. The rate of electroless plating is similar to that found in electroplating at an applied current density of 50 mA cm⁻². While pure Re cannot be deposited from our electroless plating baths, the addition of even a very small amount of Ni²⁺ ions (0.25 mM) is enough to start the induced codeposition of Re. Proper selection of the bath composition can lead to fine control of the alloy thickness and its Re-content, thus making it potentially attractive for thin barrier layers.     

The influence of 2,2′-dipyridyl on non-formaldehyde electroless copper plating

High electroless copper deposition rates can be achieved using hypophosphite as the reducing agent. However, the high deposition rate also results in dark deposits. In the hypophosphite baths, nickel ions (0.0057 M with Ni²⁺/Cu²⁺ mole ratio 0.14) were used to catalyze hypophosphite oxidation. In this study, additives (e.g. 2,2′-dipyridyl) were investigated to improve the microstructure and properties of the copper deposits in the hypophosphite (non-formaldehyde) baths. The influence of 2,2′-dipyridyl on the deposit composition, structure, properties, and the electrochemical reactions of hypophosphite (oxidation) and cupric ion (reduction) have been investigated. The electroless deposition rate decreased with the addition of 2,2′-dipyridyl to the plating solution and the color of the deposits changed from dark brown to a semi-bright with improved uniformity. The deposits also had smaller crystallite size and higher (1 1 1) plane orientation with the use of 2,2′-dipyridyl. The resistivity and nickel content of the deposit were not affected by 2,2′-dipyridyl additions to the bath. The electrochemical current-voltage results show that 2,2′-dipyridyl inhibits the catalytic oxidation of hypophosphite at the active nickel site. This results in a more negative electroless deposition potential and lower deposition rate.     

Preparation of nickel coating on ZTA particles by electroless plating

With the aim to effectively improve the interface between ZrO₂ toughened Al₂O₃ (ZTA) particles and metal matrix, nickel was deposited on the surface of ZTA particles by electroless plating method. Formation mechanism of nickel coating and effects of the solution pH, loading capacity of ZTA particles and temperature on the nickel deposition were investigated. Microstructures, thickness and element distributions of nickel coating were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that the nickel was successfully deposited on the surface of ZTA particles by electroless plating without noticeable defects. The process of electroless nickel plating could be explained by combination of atomic hydrogen and electrochemistry theories. The interfacial nucleation of nickel is easier to form than spontaneous nucleation in the solution. Deposited Nickel has priority on the surface of ZTA particles comparing to that in solution. The optimal conditions to coat nickel on the surface of ZTA particles are: solution pH 4.7–4.8, loading capacity 15–20?g/L, and electroless plating temperature 85?°C. The ZTA particle reinforced iron matrix composites prepared by powder metallurgy could have better interfacial bonding between ZTA particle and iron matrix because of the nickel coating on the surface of ZTA particle. Nickel diffuses into the iron matrix during the sintering preparation of composite materials. The interface between ZTA particle and iron matrix presents the evidence of non-chemical bonding.     

Mechanism of the reverse dissolution of zinc in the presence of nickel Part I: Influence of anodic products and substrate purity

From galvanostatic potential-time curves, voltammograms and impedance measurements, it is shown that the destabilization of the zinc deposition process by Ni²⁺ ions present in the acidic sulphate electrolyte is considerably favoured in the absence of a diaphragm separating the anode and cathode compartments. It is concluded that the deleterious influence of Ni²⁺ ions is enhanced by the anodically formed products which interfere with the slow interfacial processes taking place at the cathode surface. A stronger synergetic influence of nickel and oxidized species is demonstrated when using an aluminium cathode containing Fe impurities.     

Effect of halide ions on electroless nickel plating

The effect of halide ions (F^–, Cl^–, Br, I^–) on nickel deposition in acidic electroless nickel plating baths is investigated. Halide ions were found to have a significant effect on the nickel deposition and the results could not fully be explained using mixed-potential theory. A correlation between the stability constants of halide ions with palladium (ii) ions and the plating rate is proposed to explain the observations. Various parameters, such as the activation energy, deposit microstructure and phosphorus contents of the plating bath in the presence of various halide ions, were also studied.     

KINETICS AND MECHANISM OF THE INTERFACIAL MASS TRANSFER OF Zn2+, Co2+, Ni2+ IN THE SYSTEM: BIS(2-ETHYLHEXYL)PHOSPHORIC ACID,n-DODECANE - KNO3, WATER

ABSTRACT

The mass transfer rate of Zn(II), Co(II) and Ni(II) between aqueous nitrate solutions and n-dodecane solutions of the organic soluble ligand HDEHP has been investigated using a forced convection, constant interfacial area stirred cell. The distribution ratios necessary to evaluate the kinetic experiments have been determined and the equilibrium constants which describe the heterogeneous complex formation reaction between Zn²⁺, Co²⁺, Ni²⁺ and HDEHP have been evaluated. The results have been interpreted according to two limiting models: 1) the mass transfer rate is controlled by slow reversible interfacial reactions, 2) the mass transfer is controlled by interfacial film diffusion. Both models are adequate to Interpret the experimental data. The conclusion Is reached that, if interfacial chemical reactions are rate controlling, rate constants of interfacial complex formation reactions independent of the nature of the cation are obtained. This result supports a reaction mechanism which is rate controlled by the microscopic diffusion of the cation through a viscous and structured layer of interfacial water adjacent to the liquid interface     

Dynamic behavior of electroless nickel plating reaction on magnesium alloys

In order to obtain better control over the quality of electroless nickel–phosphorous (EN) coatings on magnesium AZ91D alloy, the effects of metal salt concentrations, reducing agent, pH, and temperature on deposition rate were studied. The reaction orders and activation energy of the deposition were determined. The results show that the apparent activation energy (E _a) in the EN plating reaction is approximately 38.03 kJ/mol. The deposition rate increased with increasing temperature, concentration of H₂PO₂ ⁻, and pH, and decreased with increasing concentration of complexing agents. For nickel ions, the deposition rate increased gradually with increasing concentration (x) when x < 4.69 g/L. However, it decreased when the concentration exceeded 4.69 g/L. Finally, various types of the deposition reaction were also discussed. The results indicate that nickel was first deposited by replacement deposition in the initial 0.5 min, then by both replacement deposition and autocatalytic deposition in plating, and finally by autocatalytic deposition after 5 min of plating.     

Vacuum evaporated thin films of mixed cobalt and nickel oxides as electrocatalyst for oxygen evolution and reduction

Mixed cobalt and nickel oxides, obtained by vacuum coevaporation of Co, Ni and TeO₂ are investigated as electrocatalysts for oxygen reduction and evolution reaction. Gas-diffusion bifunctional oxygen electrodes (GDE) are prepared by direct deposition of catalyst on gas-supplying membrane. Thus obtained GDE with different atomic ratio R_Co/Ni and R_(Co+Ni)/Te of the catalyst are electrochemically tested by means of steady-state voltammetry. It is shown that the films exhibit high catalytic activity toward both oxygen reduction and evolution reactions despite very small catalyst loading of about 0.07 mg cm⁻².     

Nickel ions removal from water by two different morphologies of induced CNTs in mullite pore channels as adsorptive membrane

In this study, chemical vapor deposition (CVD) method (with two proposed synthesis processes) was used for inducting two different morphologies of CNTs in mullite pore channels as a novel adsorptive membrane for nickel ions (Ni²⁺) removal from water. Cyclohexanol and ferrocene were used as carbon source and catalyst, respectively. The first proposed synthesis process involves coevaporation and pyrolysis of a mixed solution composed of cyclohexanol and ferrocene in a neutral atmosphere and the second involves sublimation and decomposition of ferrocene in a reactor individually and subsequently introduction of cyclohexanol as vapor to the reactor by a carrier gas during the reaction. Effects of synthesis parameters such as reaction time, catalyst content and reactor pressure on growth process, and structure and properties of the induced CNTs in pore channels of the mullite substrate were also investigated. Finally the optimized CNTs growth conditions for achieving a uniform distribution of the CNTs in the mullite pore channels were reported. The CNTs–mullite composite membranes prepared under the optimum conditions were oxidized with nitric acid and then successfully used as adsorptive membranes for nickel ions removal from water. Moreover, Langmuir and Freundlich isotherm models were used to describe adsorption behavior of nickel ions by the prepared adsorptive membrane.     

Electroless immobilization and electrochemical characteristics of nickel hexacyanoruthenate film at an aluminum substrate

The surface of an aluminum (Al) electrode was modified with a thin film of nickel hexacyanoruthenate (NiHCR) as a novel electrode material. The modification procedure of Al surface, includes two consecutive procedures: (i) the electroless deposition of metallic nickel on the Al electrode surface from NiCl₂ solution, and (ii) the chemical transformation of deposited nickel to nickel hexacyanoruthenate films in solution of 20 mM K₃[Ru(CN)₆] + 0.5 M KNO₃. Cyclic voltammogram of the modified Al electrode showed a well-defined redox reaction due to [Ni^IIRu^III/II(CN)₆]^1−/2− system. The effects of different supporting electrolytes and solution pH were studied on the electrochemical characteristics of the modified electrode. The diffusion coefficients of K⁺ and Na⁺ cations in the film (D), the transfer coefficient (α), and the charge transfer rate constant at the modifying film/electrode interface (k_s), were calculated in the presence of both K⁺ and Na⁺ cations. The stability of the modified electrode was investigated under various experimental conditions.     

Nickel phosphide catalyst for autothermal reforming of surrogate gasoline fuel

An investigation into the catalytic autothermal reforming (ATR) of a mixture of n‐octane and naphthalene (6 wt %), designed as a surrogate gasoline, is undertaken. Carbon deposition on the metallic Ni catalyst has been aware of the main hurdle for the catalytic reforming of hydrocarbons especially those with high carbon numbers. This work develops Ni_xP_y crystallites on a CeO₂ powder support by electroless nickel plating and calcination. The catalyst exhibits nil coking extent after reforming the surrogate fuel. The Ni_xP_y crystallites are determined by XRD and its Ni‐P bonding is confirmed by XPS, where the Ni carries slightly higher negative charge than the Ni⁰ as usually observed. The XPS investigation also divulges the presence of Ce³⁺ species in the CeO₂ support on which the Ni_xP_y crystallites are distributed, indicating that the support contains oxygen vacancies. These two subtle structural differences are proposed to provide the catalyst with resistance to coking. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

EXTRACTION OF NICKEL FROM AQUEOUS SULFATE SOLUTION INTO BIS(2,2,4-TRIMETHYLPENTYL)PHOSPHINIC ACID,CYANEX 272TM -EQUILIBRIUM AND KINETIC STUDIES

ABSTRACT

Equilibrium and kinetic studies have been carried out on the extraction of nickel from sulfate solutions using bis(2,2,4 trimethylpentyl) phosphinic acid HDTMPP, “Cyanex 272tm”- It was found that nickel extraction in HDTMPP was favored by the presence of sodium in the organic phase and that equilibrium nickel concentration could be written in terms of the pre-equilibrated extractant concentration

Kinetic studies were carried out using the rising drop method, reaction orders were determined with respect to the aqueous phase nickel concentration, Ni²⁺, the aqueous phase sodium concentration, Na ⁺ the pH, the organic phase dimer concentration ------ and the organic phase sodium salt concentration ---- In addition, it was found that the extraction kinetics could be explained in terms of an aqueous phase interfacial reaction accompanied by diffusion through the interface. Mass transfer coefficient values were determined indicating extraction rates for metal extraction into HDTMPP were the same order of magnitude as those found for HDEHP.     

Understanding CO-stripping mechanism from NiUPD/Pt(1 1 0) in view of the measured nickel formal partial charge number upon underpotential deposition on platinum surfaces in sulphate media

We recently showed nickel-underpotential deposition (Ni-UPD) occurs on polycrystalline or single crystal platinum electrodes in acidic media. Whereas the decoupling of the nickel and hydrogen adsorption/desorption peaks is difficult for low pH, these processes can be better separated for higher pH values, typically pH > 3. However, even for platinum single crystals, high pH solutions do not enable to sufficiently separate nickel from hydrogen phenomena. As a result, electrochemistry alone cannot yield important information about Ni-UPD, such as the formal partial charge number (valency of electrosorption) and the role of the sulphate or hydrogen sulphate anions.So, we decided to couple cyclic voltammetry to electrochemical quartz crystal microbalance (EQCM). EQCM measurements enable to decorrelate the simultaneous hydrogen and nickel adsorption/desorption peaks, which we could not attempt solely with electrochemistry. The coupling between gravimetric and electrochemical measurements allows us to detect the contribution of the anions and thus to isolate that of nickel: nickel coverage can then be determined. Nearly 4/5 Ni_UPD monolayer (θ_Ni ≈ 0.8) over platinum is reached at nickel equilibrium potential for high pH solutions (5.5). The QCM and electrochemistry coupling further allows the determination of nickel formal partial charge number: ι_Ni,EQCM = 1.3 ± 0.13. Direct electrochemistry measurements (Swathirajan and Bruckenstein method) yield: ι_Ni,Pt(poly) = 1.5 ± 0.17. These two values are close, which validates the electrochemical method for the nickel/platinum system. In consequence, we used Swathirajan and Bruckenstein method for Pt(1 1 0)-(1 × 2) crystal and found: ι_{Ni,Pt(1 1 0)} ≈ 1.4 ± 0.1. Whatever the system (Ni_UPD/Pt(poly) or Ni_UPD/Pt(1 1 0)-(1 × 2)) or the experimental technique, nickel formal partial charge number is lower than nickel cation charge: ι_Ni < z_Ni = 2. In consequence, upon underpotential deposition on platinum surfaces, nickel cations discharge and then undergo additional charge exchange processes, such as anion (or water) adsorption, resulting in apparent partial nickel cation discharge. Moreover, Ni_UPD/Pt(1 1 0) surface displays high activity towards CO_ad oxidation reaction. We explain such positive effect by the possible existence of a bifunctional mechanism in which oxygenated-species-covered Ni_UPD adatoms provide the oxygen atom to CO_ad?Pt species, enabling its facile oxidation.     

Effect of surface roughness and mass transfer enhancement on the performance characteristics of nickel-hypophosphite electroless plating baths for metal–ceramic composite membrane fabrication

Mass transfer enhanced electroless plating is a relatively new concept in the field of metal–ceramic composite membrane fabrication. In this article, we present the effect of substrate surface roughness along with various mass transfer enhancement techniques such as solution stirring, membrane stirring and sonication on metal conversion, plating efficiency, thickness, and percent pore densification using electroless plating of nickel on a porous disk shaped ceramic support with a nominal pore size of 700 nm. The plating characteristics were investigated for three different roughness values, stirrer speeds (0–300 rpm) and a loading ratio (defined as membrane area per unit volume of plating solution) value of 196 cm²/L. It was evaluated that stirring as well as sonication had a profound effect on sodium hypophosphite based electroless nickel baths. This led to a reduction in average membrane pore size by 100 nm for stirring and 130 nm for sonication when compared to the base case. Surface roughness was observed to influence the metal deposition characteristics for base case without mass transfer enhancement. Sonication, irrespective of surface roughness, provided the maximum values of selective conversion, densification and membrane thickness along with acceptable values of plating efficiency.     

Separation of Cobalt and Nickel with Phenylphosphonic Acid Mono-4-tert-octylphenyl Ester by Liquid Surfactant Membranes

Abstract

The separation of cobalt and nickel with liquid surfactant membranes (LSMs) was carried out in a stirred cell using a newly synthesized extractant. The effect of a surfactant on the kinetics of cobalt and nickel extraction was investigated to elucidate the role of a surfactant used in LSMs. The extraction equilibrium of these metals was also examined. Further, the interfacial tension between the organic and aqueous phases was measured to elucidate the adsorption equilibrium of a surfactant. It was found that the interfacial activity of the extractant is as high as that of a surfactant. In the extraction equilibrium study of these metals, extraction equilibrium constants were obtained for cobalt and nickel for the following equations:

Co²⁺ + 2(HR)₂=CoR₂(HR)₂ + 2H⁺ Ni²⁺ + 3(HR)₂=NiR₂2(HR)₂ + 2H⁺ The effects of the extractant and surfactant on the extraction rate of cobalt and nickel in LSMs were studied. The results were analyzed by a proposed model with an interfacial reaction, and rate constants were obtained for each metal. It was found that the new extractant has a very strong extractability for each metal compared with a conventional commercial extractant such as 2-ethylhexylphosphonic acid mono-2-elhylhexylester (commercial name, PC-88A) or di(2-ethylhexyl)phosphoric acid (D2EHPA). Further, a surfactant strongly affected the extraction rate and the separation of these metals, and a cationic surfactant was selected.     

Effect of donor W and acceptor Ni codoping at Ti site on the structure and electrical properties of Na0.5Bi0.5TiO3 thin film

Pure Na_0.5Bi_0.5TiO₃ (NBT), donor W⁶⁺ doped NBT (NBTW), acceptor Ni²⁺ doped NBT (NBTNi), as well as donor W⁶⁺ and acceptor Ni²⁺ codoped NBT (NBTWNi) polycrystalline films are fabricated on indium tin oxide (ITO)/glass substrates via a chemical solution deposition method. The roles of aliovalent-ion substitution on the crystallinity, ferroelectric and dielectric properties of NBT film are mainly investigated. With the introduction of aliovalent-ion, the surface of the doped film becomes more uniform and the leakage current is reduced. Well saturated polarization-electric field (P-E) loops can be observed in W⁶⁺ and Ni²⁺ codoped NBT film due to its lowest leakage currents compared to those of other films. Also, the effect of voltage and frequency on the capacitance-voltage (C-V) curve and the dielectric tunability for the NBTWNi film is discussed. The ferroelectric and dielectric properties are largely improved in NBTWNi film, which can be ascribed to the synergetic effect of high-valence W⁶⁺ and low-valence Ni²⁺ ions. The cooperation between the acceptor and donor cations can effectively eliminate the mobile oxygen vacancies in NBT films.     

Direct adhesion of natural rubber to nickel/sulfur plating during curing

- Direct adhesion between natural rubber and nickel/sulfur plating during curing was investigated. A nickel/sulfur plating was obtained by the addition of sodium thiosulfate Na₂S₂O₃ ·a 5H₂O to a nickel chloride plating bath. The sulfur content of the plating depends on the concentration of sodium thiosulfate, Na₂S₂O₃ · 5H₂O, the bath temperature and the plating current density. The nickel/sulfur plating is deposited in an amorphous form and the sulfur is distributed uniformly. When the nickel/sulfur plating and natural rubber are cured in a hot press, direct adhesion is formed. The sulfur content around 30% gives the best adhesion and a thinner plating is preferable. The amorphous nickel/sulfur plating is transformed to a crystalline phase [mixture of α-nickel and nickel sulfide (Ni₃S₂)] during curing. It is suspected that less heat stress is generated in the case of a thinner plating which causes better adhesion to rubber.