Ni System Research Articles

Mechanism and Origin of Enantioselectivity in Nickel-Catalyzed Alkyl-Alkyl Suzuki Coupling Reaction.

Enantioselective Suzuki coupling reactions are a widely used method in asymmetric synthesis of chiral compounds. In an important extension of this protocol, 1-bromo-1-fluoroalkanes were coupled with alkyl-9-BBN using chiral NiCl2L* as the catalyst (where L* = bis(pyrrolidine) ligand) under Suzuki conditions to obtain a product with a stereogenic center bearing a fluorine. In view of the current interest in chiral fluorine-containing compounds as well as lack of clarity on the mechanism of Ni-catalyzed asymmetric Suzuki coupling reactions, we decided to examine various mechanistic pathways of the title reaction. The (U)M06 density functional theory computations have been employed to identify the energetically preferred pathway first and then to probe the origin of high enantioselectivity. In particular, we have compared the likely involvement of different redox couples such as Ni(0)/Ni(II) and Ni(I)/Ni(III) in the catalytic cycle. For the Ni(0)/Ni(II) pathway, both singlet and triplet spin states have been considered whereas a doublet spin multiplicity has been examined in the case of the Ni(I)/Ni(III) system. The most preferred catalytic pathway is found to proceed through a Ni(I)/Ni(III) redox cycle with key mechanistic steps such as (a) a transmetalation involving the transfer of the alkyl group of 9-BBN to the Ni-catalyst, (b) an oxidative addition of bromo(fluoro) alkane to give a penta-coordinate Ni(III) intermediate, and (c) an enantio-controlling reductive elimination (RE) that facilitates the C-C bond formation between the Ni-bound fluoroalkyl and alkyl moieties to yield the final product. The transmetalation is found to be the turnover determining transition state (TS) according to the activation span model. The RE is found to be the enantio-controlling step, wherein the TS for the addition of the si prochiral face of the Ni-bound fluoro alkyl moiety to the alkyl group is 4.3 kcal/mol lower than the corresponding re face addition. Distortion-Interaction analysis suggested that the extent of distortion in the catalyst Ni(Br)L* fragment in the si face reductive elimination TS is much lower than in the re face addition, thus making a vital contribution to the energy difference between diastereomeric TS.

Combining experiments and modeling to explore the solid solution strengthening of high and medium entropy alloys

The mechanical properties due to solid solution strengthening are explored within the single phase face-centered cubic (fcc) domain of the Co–Cr–Fe–Mn–Ni high entropy alloy (HEA) system. This is achieved by combining an efficient and reproducible metallurgical processing of alloys to X-ray diffraction and nanoindentation characterization techniques, thus enabling to get access to 24 different bulk alloys. Large variations of nanohardness are seen with composition. Experimental results are rationalized in terms of lattice misfit and elastic constant variations with alloy-composition, through the use of an analytical mechanistic theory for the temperature-, composition- and strain-rate-dependence of the initial yield strength of fcc HEAs, with predictions made using only experimental inputs. The good agreement obtained by comparing model predictions to experiments provides the basic framework for mechanical properties optimization within the Co–Cr–Fe–Mn–Ni system; the approach could be systematically applied to all classes of fcc HEAs.

Elastic scattering and total reaction cross sections for the 12B+58Ni system

Angular distributions for elastic scattering of radioactive 12B projectile on 58Ni target have been measured for the first time. They were obtained at two energies, ELab = 30.0 and 33.0 MeV, close to the Coulomb barrier. These angular distributions were analyzed with the conventional optical model using Woods-Saxon shape and double-folding São Paulo potentials. The total reaction cross sections were extracted from this analysis and compared with other similar masses systems.

Spin-orbit effects in the 8Li+58Ni elastic scattering

In this work we present an elastic scattering angular distribution for the 8Li+58Ni system measured at Elab = 26.1 MeV. The 8Li beam was produced in the Radioactive Ion Beams in Brasil (RIBRAS) facility using the 7Li primary beam delivered by the 8-UD Pelletron accelerator. The angular distribution covers the angular range from 20 to 85 degrees in the center of mass frame. The data have been analysed by optical model and coupled channels calculations, including couplings to low-lying states in 8Li and the spin-orbit interaction. Our results indicate that the inclusion of the spin-orbit interaction in the calculations is important to describe the data at backward angles.

Specific Features of the Transition of Amorphous Al87REM5Ni8(Fe) Alloys Into the Crystalline State Under the Influence of Temperature

We determine the kinetic parameters of crystallization of amorphous metallic alloys based on aluminum doped with rare-earth metals (REM) by the method of differential scanning calorimetry. It is shown that the amorphous metallic alloys based on aluminum crystallize in three stages. By using the Kissinger, Avrami, and Ozawa models, we compute the energies of activation for the first stage of crystallization on the basis of the results of differential scanning calorimetry. It is shown that the Al–REM–Ni alloys are nanocrystallized by a kinetically controlled mechanism. The substitution of Gd for Y leads to a decrease in the temperature of nanocrystallization by 20–40°K. At the same time, the substitution of Dy for Y leads to an increase both in the temperature of nucleation and in the temperature of growth of nanocrystals. As a result of the addition of Fe to the composition of the alloy, the range of nanocrystallization shifts by about 100°K. According to the Matusite model, for constant temperatures of phase transitions, it is shown that the growth of nanocrystals in amorphous metallic alloys of the Al–REM–Ni system is realized in the 1D direction and linearly (interface control). In amorphous alloys, Dy substantially increases the temperatures of phase transitions and the number of atoms in clusters and decreases the microhardness.

Thermodynamic assessment and experimental investigation of the systems Al–Fe–Mn and Al–Fe–Mn–Ni

The ternary Al–Fe–Mn and the quaternary Al–Fe–Mn–Ni systems were re-assessed/assessed with special emphasis on compositions relevant for Fe-based shape memory alloys (SMAs), to further improve materials properties and to reliably predict phase transformation in these systems. The thermodynamic assessment was based on literature data, as well as experimental investigations regarding the phase equilibria formed between the phases A1, A2, B2 and β-Mn. Key isothermal sections were studied at 725 and 1000 °C in the Al–Fe–Mn system and at 1000 and 1175 °C in the Al–Fe–Mn–Ni system, respectively. For the quaternary Al–Fe–Mn–Ni system, additional diffusion-couple experiments were conducted to investigate target regions of the phase diagram. Calculations based on the present description are in excellent agreement with the data available in literature and the experimental investigations of the present work for both, the Al–Fe–Mn and the Al–Fe–Mn–Ni systems.

Non-dissociative adsorption of glycerol on the (111) surface of Ni and Pt-based metallic systems: Hints on reforming activity from d-band center

In the context of catalyst design, particularly for glycerol conversion, glycerol adsorption on Pt3Ni(111) and Pt3Ni/Pt(111) surfaces has been studied using spin-polarized density functional theory within a non-local van der Waals approach (optB86b-vdW). Pure Ni and Pt metals, and Ni/Pt/Pt and Pt/Ni/Pt bimetallic systems were also studied for comparison purposes. Compared to the glycerol adsorption energy (Eads) predicted by the generalized gradient approximation (PBE), optB86b-vdW predicts an adsorption up to 70% stronger, though both functionals predict the same lowest energy adsorption sites. Glycerol adsorption does not change the segregation state of the catalyst, and involves either charge polarization or a small charge transfer to the substrate. Eads was found to be dependent not only on the nature of the three metallic atoms closest to glycerol, but also on their nearest neighbors lying both on the surface (L1) and subsurface (L2) atomic layers. For all the surfaces, Eads was predominantly determined by the stability of the non-covalent interaction between one of the lone pairs of the oxygen atom closest to L1 and its closest metallic atom in L1. In addition to the surface energy (γ), the occupied d-band center relative to the Fermi level, εd-εF, was found to correlate remarkably well with Eads when modelling of van der Waals forces is improved. Since Eads energy has been found to correlate well with the reforming yield for non-supported Ni and Pt-based catalysts, we suggest a dual descriptor based on both εd-εFL1 and Eads to estimate the reforming yield of these systems within the scope of a fundamental surface science study.

Catalytic Behaviour of Ce-Doped Ni Systems Supported on Stabilized Zirconia under Dry Reforming Conditions

Ni supported on bare and modified ZrO2 samples were synthesized using the incipient wet impregnation method. The t-ZrO2 phase was stabilized by incorporation of La2O3 into ZrO2. Moreover, the influence of CeO2-doping on the physico-chemical and catalytic properties under CO2 reforming conditions was probed. The characterization data of the investigated catalysts were obtained by using XRD, CO2/H2-TPD, BET, TPR, TPO, TGA, XPS and TEM characterization techniques. In the pristine Ni/Zr catalyst, the t-ZrO2 phase transformed into the monoclinic phase. However, upon support modification by La2O3, significant effects on the physicochemical properties were observed due to the monoclinic-to-tetragonal ZrO2 phase transformation also affecting the catalytic activity. As a result, superior activity on the La2O3 modified Ni/Zr catalyst was achieved, while no relevant change in the surface properties and activity of the catalysts was detected after doping by CeO2. The peculiar behavior of the Ni/La-ZrO2 sample was related to higher dispersion of the active phase, with a more pronounced stabilization of the t-ZrO2 phase.

A first-principles study on the interaction of CO molecules with VIII transition metals-embedded graphitic carbon nitride as an excellent candidate for CO sensor

We studied the adsorption behavior of CO molecules over graphitic carbon nitride (gCN) and VIII transition metals (TM)-embedded gCN systems (TM=Ni, Pd, and Pt atoms) using density functional theory. The results indicated that the Pt-embedded gCN is excellent candidate for adsorption of CO molecules with adsorption energy of −2.77 eV, which is much better than those of the other adsorbents. Furthermore, it was observed that the band gap energies of TM-embedded systems were less than that of pristine gCN and decoration of transition metal atoms leads to the formation of mid gap impurity states, resulting in increase of electrical conductivity. Additionally, the Lowdin charges displayed that upon adsorption of CO molecules, this molecule acts as an electron acceptor and gCN systems behave as an electron donor with electron transfer from d-orbitals of transition metal atoms to the states of CO molecule. The results of spin polarized band structure indicated that the pristine gCN, Ni and Pd-embedded systems are non-magnetic, whereas Pt-embedded gCN induces non-zero magnetic moment equal to 1.35 μB. Therefore, our results revealed that among the TM-embedded systems, Pt-embedded gCN is more effective than those of the other adsorbents in sensing and removing of this gas from the atmosphere.

Prediction on elastic properties of Nb-doped Ni systems

ABSTRACTOn the basis of first-principles simulation, the structure, formation enthalpy and mechanical properties (elastic constant, bulk and shear modulus and hardness) of five Nb-doped Ni systems are systematically studied. The calculated equilibrium volume increases with the Nb concentration increasing. The computational elastic constants and formation enthalpy indicate that all Nb-doped Ni systems are mechanically and thermodynamically stable in our research. The hardness of these systems was predicted after the bulk modulus and shear modulus had been accurately calculated. The results show that the hardness increases with the Nb concentration increasing when the Nb concentration was below 4.9%, beyond which the hardness will decrease; this is within the scope of our study.

Thermodynamic constitution of the Al–Cu–Ni system modeled by CALPHAD and ab initio methodology for designing high entropy alloys

The Al–Cu–Ni system has been thermodynamically assessed over the whole composition and temperature range based on a critical literature review. The L12 and B2 phases, in conjunction with their disordered counterparts, are described using partitioning models. Ab initio calculations were performed to support the assessment of these phases. A set of self-consistent thermodynamic parameters for describing the Gibbs energy of individual phases was obtained. The assessment was validated by comparing various calculations such as invariant reaction equilibria, thermochemical properties, isothermal and isoplethal sections with all available experimental data. The Al–Cu–Ni ternary is a vital subsystem of many high entropy alloys (HEAs), which can probably be attributed to the existence of stable ordered and disordered FCC and BCC structures. In near-equiatomic compositions of this ternary system, the phase formation and equilibrium and non-equilibrium solidification curves were calculated using the present thermodynamic description. The phase competitions and their impacts on the design of HEAs are discussed, e.g. the relative stability of the disordered FCC and BCC for dual-phase HEAs, and the equilibria between disordered FCC_A1 and ordered B2 phases for ductile high strength HEAs.

A general model to calculate coherent solid/solid and immiscible liquid/liquid interfacial energies

Interfacial energy plays a significant role in the microstructure evolution of materials. A general model for predicting both coherent solid/solid and immiscible liquid/liquid interfacial energies is derived from a thermodynamic point of view. In this model, the interfacial energy can be calculated only using the data about molar area and Gibbs energies of two bulk phases and interface phase. The present model is applied to the coherent solid/solid interfacial energies in the Al–Ni, Ni–Ge, Ni–Ga, Ni–Si, Ni–Ti, Au–Ni and Ni–Cr–Al systems. The model-predicted interfacial energies show a reasonable agreement with the literature data. The presently developed model can calculate the interfacial energies between the disordered γ (fcc_A1) and ordered γ’ (fcc_L12) phases, where the Gibbs energies of both γ and γ’ phases are given by the same expression. The previous model in the literature cannot capture some disordered/ordered interfacial energies, like the Al–Ni system. The present model can also be used to calculate the immiscible liquid/liquid interfacial energies in the Al–Pb, Al–In and Al–Bi systems, showing a good agreement with the literature data. These applications validate the reliability of present model in the calculation of coherent solid/solid and immiscible liquid/liquid interfacial energies in the binary and multi-component systems.

Heterogeneous Nickel‐Catalyzed Cross‐Coupling between Aryl Chlorides and Alkyllithiums Using a Polystyrene‐Cross‐Linking Bisphosphine Ligand

AbstractA polystyrene‐cross‐linking bisphosphine ligand PS‐DPPBz was used for Ni‐catalyzed cross‐coupling with organolithiums. A bench‐stable precatalyst [NiCl2(PS‐DPPBz)] enabled efficient coupling reactions between aryl chlorides and alkyllithiums. The heterogeneous Ni system showed good reusability.magnified image

Voltage-induced strain clocking of nanomagnets with perpendicular magnetic anisotropies

Nanomagnetic logic (NML) has attracted attention during the last two decades due to its promise of high energy efficiency combined with non-volatility. Data transmission in NML relies on Bennett clocking through dipole interaction between neighboring nanomagnetic bits. This paper uses a fully coupled finite element model to simulate Bennett clocking based on strain-mediated multiferroic system for Ni, CoFeB and Terfenol-D with perpendicular magnetic anisotropies. Simulation results demonstrate that Terfenol-D system has the highest energy efficiency, which is 2 orders of magnitude more efficient than Ni and CoFeB. However, the high efficiency is associated with switching incoherency due to its large magnetostriction coefficient. It is also suggested that the CoFeB clocking system has lower bit-density than in Ni or Terfenol-D systems due to its large dipole coupling. Moreover, we demonstrate that the precessional perpendicular switching and the Bennett clocking can be achieved using the same strain-mediated multiferroic architecture with different voltage pulsing. This study opens new possibilities to an all-spin in-memory computing system.

U-based binary strong glass forming system

Fundamental issues of U-based binary metallic glasses (MGs) have been scarcely studied due to their low thermostability and glass forming ability (GFA). In this work, the glass formation in U–Ni system was reexamined. It is found that currently designed U–Ni glassy alloys in the range of 54–75% U show a pronounced thermal glass transition feature for the first time among binary U-based systems, and also have the glass transition temperature (Tg) above 600 K and much stronger thermostability than other similar U-based glasses. The Tg presence contributes to the evaluation of their glass transition activation energy, liquid fragility, viscosity as well as the Kauzmann temperature. Moreover, the fragility value of the typical alloy U69.2Ni30.8 is about 20, almost the same as those of the oxide glass formers SiO2 and GeO2, illustrating that U–Ni is a binary strong glass forming system. The reasons for the remarkable Tg presence and low fragility together with the GFA level of U-based MGs are discussed.

Problems in Solidification Model for Microsegregation Analysis of Fe–Cr–Ni–Mo–Cu Alloys

Microsegregation of a Fe–Cr–Ni–Mo–Cu alloy was studied with the calculation model on the basis of two-dimensional concept considering diffusion of solutes during and after solidification. The calculated results were compared with the previous experimental results of the microsegregation profiles obtained by random sampling method. At first, a calculation model was created by applying two database sets of diffusion coefficients reported on Fe(γ)-X binary and Fe–Cr–Ni systems. The results using the database of the Fe–Cr–Ni systems fitted the experimental data better than those using the Fe(γ)-X systems in the region of lower solid fraction (fs). Meanwhile, in the higher fs region, the calculated lines passed below the arranged experimental data plots particularly for Cr and Mo. This inconsistency could be attributed to the following problems:

Viscosity of Cu–Ni Melts

The kinematic viscosity of Cu–Ni melts with nickel contents of 10, 20, 30, 40, 50, 60, 70, 80, and 90 at % is measured. Kinematic viscosity is measured using the damped torsional vibrations of a crucible with a melt in the mode of sample cooling. The measuring results are discussed within the theory of absolute reaction rates. The temperatures at which the viscous flow characteristics (and thus the structural state of the melt) change are determined by analyzing the temperature dependences of kinematic viscosity. The patterns of the liquid–liquid transition in metal alloys of the Cu–Ni system that form a continuous series of solid solutions during crystallization are analyzed.

Microstructure and Mechanical Properties of Al\u2013Co\u2013Cr\u2013Fe\u2013Ni Base High Entropy Alloys Obtained Using Powder Metallurgy

Four different compositions of high entropy alloys based on Al–Co–Cr–Fe and Al–Co–Cr–Fe–Ni systems were prepared using mechanical alloying and consolidation by spark plasma sintering. The chemical compositions of the studied alloys were experimentally selected to obtain a BCC solid solution and mixtures of BCC with FCC. The microstructure of the Al25Co25Cr25Fe25 (all in at%) high entropy alloy consisted of a matrix with a high concentration of Al, Co and Fe, in which spherical grains (50–200 nm) enriched in Cr were embedded. Both the matrix and grains had body centered cubic structures. The addition of nickel to a four-element system led to the formation of a multiphase composition. The microstructure of the Al20Co20Cr20Fe20Ni20, Al10Co30Cr20Fe35Ni5 and Al15Co30Cr15Fe40Ni5 HEAs consisted of fine grains measuring 50–500 nm composed of: AlNi-B2, BCC phase, FCC or BCC solid solutions and σ-sigma phase, respectively. The complex structure of the studied samples resulted in changeable mechanical properties. The highest compression strength of 3920 MPa was accompanied by an increased yield strength of 3500 MPa, and a low strain of 0.7%, for the Al25Co25Cr25Fe25 alloy. The addition of Ni led to the formation of plastic FCC phases responsible for a decrease in strength with increases in ductility, which, in the new non-equiatomic Al10Co30Cr20Fe35Ni5 high entropy alloy reached 6.3% at a yield strength of 1890 MPa and compression strength of 2230 MPa. The conducted abrasion studies revealed that non-equilibrium high entropy alloys have the highest abrasion resistance.

A modified generalized Langevin oscillator model for activated gas-surface reactions.

Surface motion has proven to influence the gas-surface reactions in various ways. An adequate model to describe the complex lattice effects in a relatively simple way is therefore highly desirable. In this work, we have modified the widely used Generalized Langevin Oscillator (GLO) model to incorporate the molecule-surface coupling that plays an important role in activated dissociation of polyatomic molecules on metal surfaces. To this end, taking the well-studied CHD3+Ni(111) system as an example, we add a coupling potential linearly dependent on the surface oscillating coordinate, which becomes essential in predicting the dissociative sticking coefficients for reactive scattering. We further scale the mass of the surface oscillator on the basis of a mechanic coupling parameter, which has significantly improved the description of the molecule-surface energy transfer for nonreactive scattering. This so-called modified GLO (MGLO) model retains the simplicity and advantages of the original GLO, while yields much more accurate dynamics results that are in remarkably good agreement with the benchmark data calculated using ab initio molecular dynamics. We argue that the MGLO model is applicable to these highly activated gas-surface reactions with strong molecule-surface couplings.

Developing technology of fabrication of functional nanostructured coatings on wear- and corrosion-resistant alloy based on the Cu–Ni system

The paper presents complex studies of nanostructured powder of Cu-Hf-BN alloy system and functional wear and corrosion-resistant coatings based on It are presented. A technology for applying a composite nanostructured coating of the Cu-Ni-Zr-Cr-Hf-BN system onto a steel substrate (steel Kh18Yu5S) was developed using supersonic cold and microplasma deposition techniques. The coatings have elevated level of microhardness (up to 32 GPa), adhesive strength (more than13 MPa), resistance to stress-corrosion crackingand a wide range of operating temperatures from 850 to –196°C.