Molecular plating of actinides on thin backings

Actinide targets on thick and thin backings are needed for experiments at heavy-ion accelerators. One of the efficient ways to prepare such targets is by molecular plating. Although many laboratories have successfully prepared targets on thick backings by this technique, it is quite difficult to make targets on thin backings (100 μg/cm² up to 1 mg/cm²). In recent years, we have plated targets on thin Ni and carbon backings, for example ²³⁴U targets on a 200 μg/cm² Ni backing. The Ni foils, evaporated on a copper substrate, are available commercially. We used these foils to plate ²³⁴U and afterwards we removed the copper by dissolving it in a mixture of ammoniacal trichloroacetic acid. In this way 400 μg/cm^{2 234}U targets were prepared on a 200 μg/cm² Ni backing. A 100 μg/cm^{2 243}Am target was prepared by plating onto a 75 μg/cm² carbon film left on its glass substrate for later floating. We found that a plating cell made from Teflon was difficult to use because it scratched the C film producing a liquid leak at the joint of the column and the C film. This sealing surface needs to be extremely smooth to avoid leakage. A column made of Delrin™ was then tried and did not produce any scratch on the carbon film surface. This column was used to prepare 100 μg/cm^{2 243}Am targets. Details of the technique will be presented.     

X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel–copper spinel manganites

The surface of non-stoichiometric nickel and nickel–copper spinel manganites has been investigated by X-ray Photoelectron Spectroscopy (XPS). The oxidation states of the nickel, copper and manganese cations present on the surface of the samples were determined from the analysis of the M 2p_3/2 core levels (M=Ni, Cu, Mn). In particular, both Cu²⁺ and Cu⁺ were evidenced in the structure whereas only bivalent nickel was observed. The partial substitution of manganese by copper led to a chemical shift towards lower binding energy in the Ni 2p_3/2 region, which was explained by the displacement of some Ni²⁺ cations from tetrahedral to octahedral sites of the spinel structure. Finally, the surface atomic ratios Ni/Mn for nickel manganites, Ni/(Mn+Cu) and Cu/(Mn+Ni) for nickel–copper manganites, determined from XPS data, were compared to the ratios corresponding to the bulk composition. This study shows in all cases a nickel enrichment at the surface which is not affected by the copper content of the oxide. On the contrary, the ratio Cu/(Mn+Ni) was found to be lower than the corresponding bulk value.     

Fast and simultaneous growth of graphene,intermetallic compounds,and silicate on Cu–Ni alloy foils

A graphene bilayer was grown on copper–nickel alloy foils (30 at-% Ni: 70 at-% Cu designated as a 30Ni–70Cu) via an inductively coupled plasma–chemical vapor deposition chamber, and was characterized. The first layer fully covered the foil, while there was partial coverage of the second layer. At the same time, the alloy catalyst produced a compound of magnesium silicate in some regions and of copper sulfide in other regions on which a graphene monolayer simultaneously grew without any discontinuity or boundaries of the 1st graphene monolayer between simultaneous growth and graphene-only growth regions. Compared with Cu foils, the alloy foils led to faster growth of the graphene film in graphene-only growth regions, while maintaining the same quality, homogeneity, and thickness uniformity as a monolayer graphene grown on Cu. Raman spectroscopy and scattering demonstrated that the 2D and D bands of the Raman spectra were in the same position for the monolayer graphene on 30Ni–70Cu regardless of the grown regions and for the graphene on the Cu with a full width at half maximum of ∼38 cm⁻¹ ranging from 30 to 55 cm⁻¹ of 2D, and without a D band in the spectra of the graphene monolayer and bilayer. Thus the resulting graphene growth is affected primarily by the Cu catalyst, partly by the compounds grown simultaneously with the graphene monolayer on the foil surface via thermal reactions of the impurities dissolved in the alloy matrix, and partly by the Ni. The quality of the graphene is dependent on the major composition of Cu catalyst in the alloy foils. On the other hands, the alloying element of Ni governs the growth kinetics unless the alloy foils is covered with the intermetallic compounds and silicate.     

A study of very thin DLC foils as a gas barrier

Measurements of vacuum tightness and mechanical strength of diamond-like carbon (DLC) foils in the thickness range of 1–7 μg cm⁻² have been performed with a purpose to evaluate suitability of foils as a gas barrier. Hydrogen and argon at pressures from 10⁻² Pa to 20 kPa were used as test gases. The permeation rate specified as conductance density was found for the best sample of self-supporting foil to be around 1.5×10⁻³ l and 3.3×10⁻⁴ l s⁻¹ cm⁻² for H₂ and Ar, respectively. Conductance density of the same foils mounted on the frames with a mesh along the apertures as support was about twice higher than that for the self-supporting ones, likely due to the mechanical imperfections of the foil assemblies of the first ones. On the other hand, mesh-supported foils as thin as 3 μg cm⁻² and of 5 mm in diameter were withstanding the pressure of up to 18 kPa, while self-supporting foils of the same thickness ruptured at around 1.2 kPa. There was no observed relation between thickness of the foil and its mechanical properties and permeation rate. This suggests that rather tears and pinholes present in foils are the limiting factors of the foil–vacuum tightness and strength. Results obtained in the studies, presented in this work, demonstrate the ability of very thin DLC to isolate a high vacuum beam line from a gas cell in a variety of applications and ability to withstand the gas pressure relevant, in particular, to some gas-filled ionization chambers.     

Synergistic Coupling of Ni Nanoparticles with Ni3C Nanosheets for Highly Efficient Overall Water Splitting

Exploring earth‐abundant bifunctional electrocatalysts with high efficiency for water electrolysis is extremely demanding and challenging. Herein, density functional theory (DFT) predictions reveal that coupling Ni with Ni₃C can not only facilitate the oxygen evolution reaction (OER) kinetics, but also optimize the hydrogen adsorption and water adsorption energies. Experimentally, a facile strategy is designed to in situ fabricate Ni₃C nanosheets on carbon cloth (CC), and simultaneously couple with Ni nanoparticles, resulting in the formation of an integrated heterostructure catalyst (Ni–Ni₃C/CC). Benefiting from the superior intrinsic activity as well as the abundant active sites, the Ni–Ni₃C/CC electrode demonstrates excellent bifunctional electrocatalytic activities toward the OER and hydrogen evolution reaction (HER), which are superior to all the documented Ni₃C‐based electrocatalysts in alkaline electrolytes. Specifically, the Ni–Ni₃C/CC catalyst exhibits the low overpotentials of only 299 mV at the current density of 20 mA cm^?2 for the OER and 98 mV at 10 mA cm^?2 for the HER in 1 m KOH. Furthermore, the bifunctional Ni–Ni₃C/CC catalyst can propel water electrolysis with excellent activity and nearly 100% faradic efficiency. This work highlights an easy approach for designing and constructing advanced nickel carbide‐based catalysts with high activity based on the theoretical predictions.     

Formation and growth of Ni3Sn4 intermediate phase in the Ni - Sn system

Dipping experiments of Ni foils in molten tin were made in the temperature range, 280–310°C. In addition, experiments were conducted while passing a constant current through the system, the foils being used as electrodes. In SEM - EDS observations and analysis the Ni₃Sn₄ equilibrium intermediate phase was found to grow both as a layer at the solid/liquid interface and as platelets in the melt. Growth kinetics were found to be influenced by the dissolution of Ni in the melt. The voltage between the electrodes vs. time (V(t) curve), measured in-situ, was found to conform to SEM observations. The V(t) curves permit a qualitative evaluation of the layer growth process.     

Ni(OH)2 Nanoflakes Supported on 3D Ni3Se2 Nanowire Array as Highly Efficient Electrodes for Asymmetric Supercapacitor and Ni/MH Battery

Porous Ni(OH)₂ nanoflakes are directly grown on the surface of nickel foam supported Ni₃Se₂ nanowire arrays using an in situ growth procedure to form 3D Ni₃Se₂@Ni(OH)₂ hybrid material. Owing to good conductivity of Ni₃Se₂, high specific capacitance of Ni(OH)₂ and its unique architecture, the obtained Ni₃Se₂@Ni(OH)₂ exhibits a high specific capacitance of 1689 µAh cm^?2 (281.5 mAh g^?1) at a discharge current of 3 mA cm^?2 and a superior rate capability. Both the high energy density of 59.47 Wh kg^?1 at a power density of 100.54 W kg^?1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni₃Se₂@Ni(OH)₂ as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L^?1 at a power density of 83.62 W L^?1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm^?2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni₃Se₂@Ni(OH)₂ composite can become a promising electrode material for energy storage applications.     

A Unique Etching-Doping Route to Fe/Mo Co-Doped Ni Oxyhydroxide Catalyst for Enhanced Oxygen Evolution Reaction

Fe-doped Ni (oxy)hydroxide shows intriguing activity toward oxygen evolution reaction (OER) in alkaline solution, yet it remains challenging to further boost its performance. In this work, a ferric/molybdate (Fe³⁺/MoO₄²⁻) co-doping strategy is reported to promote the OER activity of Ni oxyhydroxide. The reinforced Fe/Mo-doped Ni oxyhydroxide catalyst supported by nickel foam (p-NiFeMo/NF) is synthesized via a unique oxygen plasma etching-electrochemical doping route, in which precursor Ni(OH)₂ nanosheets are first etched by oxygen plasma to form defect-rich amorphous nanosheets, followed by electrochemical cycling to trigger simultaneously Fe³⁺/MoO₄²⁻ co-doping and phase transition. This p-NiFeMo/NF catalyst requires an overpotential of only 274 mV to reach 100 mA cm⁻² in alkaline media, exhibiting significantly enhanced OER activity compared to NiFe layered double hydroxide (LDH) catalyst and other analogs. Its activity does not fade even after 72 h uninterrupted operation. In situ Raman analysis reveals that the intercalation of MoO₄²⁻ is able to prevent the over-oxidation of NiOOH matrix from β to γ phase, thus keeping the Fe-doped NiOOH at the most active state.     

Electrochromic properties of Ni(V)Ox films deposited via reactive magnetron sputtering with a 8V-92Ni alloy target

NiO_x has been extensively used as complementary counter electrochromic (EC) layer in smart windows. Reactive sputter deposition for obtaining NiO_x layer using metallic Ni targets has been very often considered, however, the ferromagnetic property of metallic Ni failed to be applied by conventional magnetron enhancement, particularly when considering large-area deposition. To overcome this, 8 at.% V is alloyed into Ni target for eliminating the ferromagnetism, and Ni(V)O_x films are deposited via the reactive magnetron sputter technique in this study. Microstructure and the related EC properties were investigated.Experimental results show that the sputtering erosion of the non-ferromagnetic Ni(V) target surface becomes controllable as opposed to the pure Ni target. The Ni(V)O_x film deposited at the working atmosphere of 1.33 Pa and oxygen flow ratio of 40% exhibits the highest optical transmission change (colored to bleached). The half device assembled with a 200 nm-thick film presents the shortest response time (3 s for coloring, 2 s for bleaching) and the greatest optical transmittance change in visible region (69.5% for bleached, 42.0% for colored). This study demonstrates that alloying 8 at.% V as a de-ferromagnetiser in Ni target does not observably affect the electrochromic properties of deposits.     

Density Determination of Liquid Copper, Nickel, and Their Alloys

A method for the determination of the density of electromagnetically levitated metallic liquids has been developed. This method employs an enlarged beam of parallel laser light to produce a shadow image of the sample. The shadow is recorded by a digital CCD-camera, and the images are analyzed using an edge detection algorithm. The circumference is fitted by Legendre polynomials that can be used for calculations of the volume of the sample. The method has been tested successfully on various alloys of copper-nickel (Ni _x Cu _y ), as well as on the pure elements, Cu and Ni. Densities were measured for each sample at different temperatures below and above the melting point, and a linear behavior was observed. At the melting point the densities for copper and nickel were 7.9 and 7.93gcm^–3, respectively. For T=1270°C liquid copper has a density of 7.75gcm^–3 which strongly increases up to roughly 8.1gcm^–3 if a small amount (10–40 at.%) of nickel is added to the system. For nickel concentrations larger than 50at.% the density remains nearly constant.     

Fabrication of Ni electrode films by sintering Ni nanoparticle pastes: Compositional dependence of specific resistance and optimal composition

Ultra-thin nickel films are essential for the internal electrodes of the high density multi-layered ceramic capacitors (MLCCs) used in a variety of electronic devices. In this study, Ni electrode films were fabricated by sintering Ni nanoparticle pastes prepared by mechanically stirring mixtures of Ni nanoparticles (d = 40–150 nm), dispersant, binder, and solvent. Paste compositions were varied by using three solvents, two binders, one dispersant, and different amounts of nickel nanoparticles. In total 36 pastes and electrode films were prepared. The electrode film defects such as voids in films and exfoliation (film loss due to lack of adhesion to substrate) were noted, and film thicknesses and specific resistances (ρ) were measured. Voids were observed in all samples whereas exfoliations were observed only for several samples. Ni electrode film thicknesses and ρ values ranged from 2 to 7 μm and from 10⁻⁵ to 10⁻⁴ Ω cm, respectively, depending on paste composition. Based on considerations of ρ values, an optimal composition was determined. Of the three solvents and two binders used, terpineol and EC produced better quality films with lower ρ values and without exfoliation, suggesting that they are probably the most suitable for fabricating internal electrodes for high density MLCCs.     

Polymer coating method developed for carbon stripper foils

The problem of handling the fragile carbon foils (mounting on the frame, placing in the stripper changer) that easily break when self-supporting has been solved by coating carbon foils with poly-monochloro-para-xylylene. It was found that the polymer-coating method could also be used to produce carbon foils thicker than 100 μg/cm² by alternated deposition of carbon and poly-monochloro-para-xylylene layers. Carbon foil of 500 μg/cm² thick and 10 cm in diameter was produced by this method and mounted to a foil holder. Results of lifetime measurement for singly coated foils are also presented.     

Absolute Isotopic Abundance Ratios and Atomic Weight of a Reference Sample of Nickel

Absolute values have been obtained for the isotopic abundance ratios of a reference sample of nickel (Standard Reference Material 986), using thermal ionization mass spectrometry. Samples of known isotopic composition, prepared from nearly isotopically pure separated nickel isotopes, were used to calibrate the mass spectrometers. The resulting absolute isotopic ratios are: ⁵⁸Ni/⁶⁰Ni=2.596061±0.000728, ⁶¹Ni/⁶⁰Ni=0.043469±0.000015,⁶²Ni/⁶⁰Ni=0.138600±0.000045, and ⁶⁴Ni/⁶⁰Ni=0.035295±0.000024, which yield atom percents of ⁵⁸Ni=68.076886 ±0.005919, ⁶⁰Ni = 26.223146±0.005144,⁶¹Ni=1.139894±0.000433, ⁶²Ni =3.634528±0.001142, and ⁶⁴Ni =0.925546±0.000599. The atomic weight calculated from this isotopic composition is 58.693353 ±0.000147. The indicated uncertainties are overall limits of error based on two standard deviations of the mean and allowances for the effects of known sources of possible systematic error.     

Comparison of microstructures and tensile properties of pulse electrodeposited Ni on polycrystalline and amorphous substrates

Abstract

Ultrafine grained nickel (UFG Ni) and microcrystalline nickel (MC Ni) were fabricated on two types of substrates, i.e. the amorphous (Ni–P) and polycrystalline (stainless steel) substrates by pulse electrodeposition without additives. This study demonstrates that when inhibiting the epitaxial growth by first depositing a thin amorphous layer on the polycrystalline substrates, the grain size of the subsequent Ni deposit decreases dramatically from microscale to the UFG regime, which depends on the deposition conditions. Compared with MC Ni, which has an ultimate tensile strength σ_UTS of 397 MPa and an elongation to failure ε_TEF of 11·98%, UFG Ni with an average grain size of 120·72 nm exhibits an enhanced σ_UTS of 807 MPa and a comparable ε_TEF of 10·44%. The electrodeposited method used in this study provides an effective and low cost way to produce UFG materials with both high strength and ductility, which can meet the demands for practical application as structural materials.     

Low temperature interdiffusion in Cu/Ni thin films

Interdiffusion in Cu/Ni thin films was studied by means of Auger electron spectroscopy in conjunction with Ar⁺ ion sputter profiling. The experimental conditions used aimed at simulating those of typical chip-packaging fabrication processes. The Cu/Ni couple (from 10 μm to 60 nm thick) was produced by sequential vapor deposition on fused-silica substrates at 360, 280 and 25 °C in 10^-6 Torr vacuum. Diffusion anneals were performed between 280 and 405 °C for times up to 20 min. Such conditions define grain boundary diffusion in the regimes of B- and C-type kinetics. The data were analyzed according to the Whipple-Suzuoka model. Some deviations from the assumptions of this model, as occurred in the present study, are discussed but cannot fully account for the typical data scatter. The grain boundary diffusion coefficients were determined (for nickel through copper, Q_b = 33.7 kcal mol^-1 (1.46 eV), D_b⁰ = 4.2 × 10^-2 cm²s^-1; for copper through nickel, Q_b = 30.2 kcal mol^-1 (1.3 eV), D_b⁰ = 7.6 × 10^-5 cm²s^-1) allowing calculation of respective permeation distances.     

Solubility of Ni in Anoxic Groundwater and Cement Water

The Ni solubility and Ni-colloid association were studied in natural groundwater, cement-conditioned groundwater, and synthetic saline groundwater. The experiments were performed under N₂ at 28°C. The duration of the experiments was up to 177 days. The Ni solubility was studied by adding ^{6 3}Ni-spiked NiCl₂ to the samples and by measuring the activities using liquid scintillation counting. The initial Ni concentrations were 1 × 10^{- 6} and 1 × 10^{- 3} M. The nickel solubilities in the water samples differed significantly. The association of Ni with colloids in the natural groundwater was detected.     

Fabrication of antiferroelectric PLZT films on metal foils

Fabrication of high-dielectric-strength antiferroelectric (AFE) films on metallic foils is technically important for advanced power electronics. To that end, we have deposited crack-free Pb_0.92La_0.08Zr_0.95Ti_0.05O₃ (PLZT 8/95/5) films on nickel foils by chemical solution deposition. To eliminate the parasitic effect caused by the formation of a low-permittivity interfacial oxide, a conductive buffer layer of lanthanum nickel oxide (LNO) was coated by chemical solution deposition on the nickel foil before the deposition of PLZT. Use of the LNO buffer allowed high-quality film-on-foil capacitors to be processed in air. With the PLZT 8/95/5 deposited on LNO-buffered Ni foils, we observed field- and thermal-induced phase transformations of AFE to ferroelectric (FE). The AFE-to-FE phase transition field, E_AF = 225 kV/cm, and the reverse phase transition field, E_FA = 190 kV/cm, were measured at room temperature on a ≈1.15 μm-thick PLZT 8/95/5 film grown on LNO-buffered Ni foils. The relative permittivities of the AFE and FE states were ≈600 and ≈730, respectively, with dielectric loss ≈0.04 at room temperature. The Curie temperature was ≈210 °C. The thermal-induced transition of AFE-to-FE phase occurred at ≈175 °C. Breakdown field strength of 1.2 MV/cm was measured at room temperature.     

Calculation and experimental determinations of the residual stress distribution in alumina/Ni/alumina and alumina/Ni/nickel alloy systems

Residual stress problems encountered in joining ceramics–ceramics or ceramics–metals systems for high-temperature applications >1000 °C have been studied. A solid-state bonding technique under hot-pressing via metallic foils sheet of Ni was used for joining alumina–alumina and alumina–nickel alloy (HAYNES^? 214™). The residual stresses expected in the specimen were predicted by finite-element method (FEM) calculations using an elastic–plastic-creep model (EPC). Stress distributions in the specimen were characterized experimentally using X-ray diffraction (XRD) and Vickers Indentation Fracture (VIF) techniques. The tensile and shear stress profiles have been determined along selected lines perpendicular to the bonding interface. The results of the FEM calculation of residual stresses have been compared experimentally with the results of classical XRD and indentation methods. It was found that the tensile stress concentration showed higher values at the edge of the boundary. The residual stresses caused by the thermal expansion mismatch between alumina (Al₂O₃) and Ni-based super-alloy (HAYNES^? 214™) severely deteriorated the joints compared to Al₂O₃–Al₂O₃ joint with the same solid-state bonding parameters. The correlations between the FEM calculations and experimental results obtained by XRD and VIF method were discussed.     

Exothermic reaction characteristics of continuously ball-milled Al/Ni powder compacts

Self-propagating reactions in compacted pellets of continuously low-energy ball-milled aluminium (Al) and nickel (Ni) powders at a composition corresponding to AlNi₃ were investigated. The formation of a bi-modal structure with nanoscale lamellae of Al and Ni surrounding thicker Ni layers was observed. The milled powder sizes decreased for milling durations longer than 4 h, but the pellet green densities remained mostly constant for longer than 2 h of milling. The ignited pellets observed using high-speed optical and infrared imaging revealed that the thermal wave velocity, maximum reaction temperature, ignition initiation duration and ignition temperature decreased with increasing milling times due to solid-state diffusion. X-Ray Diffraction (XRD) analysis after ignition tests showed that the AlNi₃ amount increased with milling time. Thermal analysis using interrupted Differential Scanning Calorimetry (DSC) in combination with XRD revealed that the ball-milled pellets have similarities to nanoscale magnetron sputtered multilayer foils in terms of phase formation sequence and exothermic peak shifts.     

Transparent conducting properties of Ni doped zinc oxide thin films prepared by a facile spray pyrolysis technique using perfume atomizer

Undoped and Ni doped zinc oxide (Ni–ZnO) thin films were prepared by a facile spray pyrolysis technique using perfume atomizer from aqueous solution of anhydrous zinc acetate (Zn(CH₃COOH)₂ and hexahydrated nickel chloride (NiCl₂·6H₂O) as sources of zinc and nickel, respectively. The films were deposited onto the amorphous glass substrates kept at (450 °C). The effect of the [Ni]/[Zn] ratio on the structural, morphological, optical and electrical properties of Ni doped ZnO thin film was studied. It was found from X-ray diffraction (XRD) analysis that both the undoped and Ni doped ZnO films were crystallized in the hexagonal structure with a preferred orientation of the crystallites along the [002] direction perpendicular to the substrate. The scanning electron microscopy (SEM) images showed a relatively dense surface structure composed of crystallites in the spherical form whose average size decreases when the [Ni]/[Zn] ratio increases. The optical study showed that all the films were highly transparent. The optical transmittance in the visible region varied between 75 and 85%, depending on the dopant concentrations. The variation of the band gap versus the [Ni]/[Zn] ratio showed that the energy gap decreases from 2.95 to 2.72 eV as the [Ni]/[Zn] ratio increases from 0 to 0.02 and then increases to reach 3.22 eV for [Ni]/[Zn] = 0.04. The films obtained with the [Ni]/[Zn] ratio = 0.02 showed minimum resistivity of 2 × 10⁻³ Ω cm at room temperature.