Ni Mixture Research Articles

Composite WC–35% Ni produced from ultrafine WC + NiO powders. II. mechanical properties

The mechanical characteristics of ultrafine-grained WC–35 wt.% Ni composite produced by shortterm solid-phase pressing at different temperatures and at a pressure of ~1200 MPa are studied. The initial powder mixture consists of tungsten carbide and nickel oxide. One part of the mixture was reduced by hydrogen, while the other part was mixed with saccharose to reduce the oxide to nickel during heating of green briquettes. In the latter case, the synthesis of the metal phase and the consolidation of the WC–Ni mixture proceed in one stage. It is established that the powder mixture samples treated by hydrogen have lower bending strength if the composite is consolidated at temperatures below 1250°C. At this temperature, the samples acquire a bending strength of 2700–2800 MPa, irrespective of how the mixture was prepared. The liquid-phase consolidation of the composite leads to a decrease in the strength to 1800 MPa. It is shown that the fracture of the composite consolidated in the temperature range 950–1150°C occurs generally in the nickel matrix, which deforms severely before fracture in the composite pressed at 1150°C. The fracture toughness of the solid-phase compacted composite is ≥25 MPa ⋅ m1/2 and its hardness is higher than 6000 MPa.

Composite WC–35% Ni produced from ultrafine WC + NiO powders. I. Density and structure

The density and structure of an ultrafine-grained WC–35 wt.% Ni composite produced by short-term solid-phase compaction at different temperatures and about 1200 MPa are examined. The starting powder mixture consists of tungsten carbide and nickel oxide, but one part of the mixture is reduced in hydrogen and the other is mixed with saccharose to reduce nickel from its oxide during heating of green briquettes. In the latter case, it takes one stage to synthesize the metal phase and consolidate the WC–Ni mixture. It is established that the composite samples produced from the powder mixture containing saccharose show more intensive shrinkage during heating than the samples produced from the mixture preliminary treated with hydrogen. High pressure promotes practically porousless samples above 1150°C. It is shown that the composite produced from the carbide–oxide mixture by the reduction of saccharose carbon has finer grains and differs in more uniform distribution of tungsten carbide in the nickel matrix.

Thermal stability and magnetic saturation of annealed nickel–tungsten and tungsten milled powders

Crystal structures, microstructures and magnetic saturation of annealed pure W powder along with W–40 wt.% Ni powder mixtures processed by high-energy ball milling were investigated using XRD, DTA, SEM and saturation magnetization techniques. Thermally induced transformations occurred at low temperature annealing. Supersaturated metastable Ni(W) solid solution formed during mechanical milling decomposed during annealing treatment into FCC Ni-rich, FCC W-rich phases and an eta-type phase which was constituted of BCC lattice of W enveloped by two FCC lattices of Ni and W. The structures of the major annealing products were close to Ni 10W and W 3Ni 2. The magnetic saturation of the milled W powder and W–Ni mixtures decreased with the increase in annealing temperature. Milling time was more influential on the magnetic properties of the annealed pure W powders.

Effect of C (graphite) doping on the H 2 sorption performance of the Mg–Ni storage system

Binary Mg–Ni mixtures and ternary Mg–Ni–C (graphite) samples with fixed proportions of metals (Mg 85%–Ni 15% by weight) and amount of C increasing in increments of 5 wt % from 5 wt % to 15 wt % were prepared by high energy ball milling (BM) in Ar for t BM = 2 h. The purpose of the study was to evaluate the effect of C addition on the reactivity, the sorption activation and the storage performance of the Mg–Ni system. Increasing the amount of C had the effect of decreasing (from 10 to 3) the number of cycles needed for activation (performed at 623 K and 40 bar/0.9 bar charging/discharging H 2 pressure). After full activation, the 5 wt % C-containing sample exhibited the best absorption kinetics performance: the average rate to charge up to 5 wt % H 2 was about 3 times higher than that observed for the undoped sample. Unfortunately, increasing the amount of C had a negative impact on the desorption behaviour, causing an increase in the dehydrogenation activation energy and a decrease in the discharging rates. Within the present study, C reacted neither with H 2 nor with the H 2 active phases (the two discharged phases Mg and Mg 2Ni and the related hydrides) and consequently did not lead to variation in the sorption enthalpies of the Mg–Ni system. But, its presence did cause a small increase (4 K at 0.9 bar H 2) in the minimum desorption temperatures of the hydrides and a consequent minor decrease (0.2 bar) in the equilibrium pressures. The best sorption properties were obtained for the 5 wt % C-sample, that on the whole worked better than the binary mixture.

In situ study of the formation of silicide phases in amorphous Ni–Si mixed layers

In this paper, we investigated Ni silicide phase formation when Si is added within an as deposited 50 nm Ni film. A series of 22 samples with a Si content varying from 0 to 50 at. % was prepared and systematically investigated with in situ x-ray diffraction. The inert oxide substrate was used to identify the phases which first crystallize in an amorphous Ni–Si mixture of a given concentration. The noncongruent silicides Ni3Si and Ni3Si2 are never observed to crystallize readily out of the mixture. A remarkable observation is the initial crystallization at low temperature of a hexagonal Ni-silicide, observed over a broad mixed layer composition [35–49%Si]; this hexagonal phase nucleates readily as a single phase [39–47%Si] or together with Ni2Si [35–38%Si] or NiSi [49%Si]. This low-temperature phase is related to the high temperature θ-phase, but covers a wide composition range up to 47%Si. For the same Ni–Si films deposited on Si(100), the initial nucleation of the Ni(Si) mixture is similar as for the samples deposited on SiO2, such that the complex sequence of metal-rich Ni-silicide phases typically observed during Ni/Si reactions is modified. For samples containing more than 21%Si, a simpler sequential phase formation was observed upon annealing. From pole figures, the phase formation sequence was observed to have a significant influence on the texture of the technologically relevant NiSi phase. For mixture composition ranging from 38% to 43%Si, the initial transient θ-phase appears extremely textured on Si(100). The observed transient appearance of a hexagonal phase is of importance in understanding the phase formation mechanisms in the Ni–Si system.

Mg–Ti based materials for electrochemical hydrogen storage

Results of the mechanical alloying of binary Mg–Ti and ternary Mg–Ti–Ni mixtures using two different process control agents are reported. Both high- and low-energy milling resulted in the formation of cubic compounds. When all starting reactants had disappeared, a mixture of two face-centered cubic (fcc) phases was formed with lattice constants around 4.40 and 4.25 Å. The electrochemical hydrogen storage capacity, 450 mAh/g for (Mg0.65Ti0.35)0.95Ni0.05, was about one-third that reported for Mg–Ti thin films. This suggested that only one of the two fcc phases was active at ambient conditions. Prolonged mechanical alloying of (Mg0.60Ti0.40)0.95Ni0.05resulted in full conversion of the material into one fcc-phase with a very small crystallite size, an intermediate lattice constant (4.33 Å), and a sharply decreased storage capacity.

Structural characterization and hydrogen sorption properties of nanocrystalline Mg 2Ni

The structure, chemical distribution, microstructure and thermal stability of a 2Mg–Ni mixture milled at different times in a low energy ball mill were investigated. After short time processing, a mixture of amorphous Mg-rich phase, nanocrystalline Mg and crystalline Ni was obtained. The crystallite size reduction and strain increment along with the formation of an amorphous phase was associated to the refinement of Mg at this stage. After long time milling, nanocrystalline Mg 2Ni was produced and both amorphous Mg-rich phase and Ni remained in the mixture as residual phases. Stable nanocrystalline Mg 2Ni was successfully synthesized by a combination of low energy mechanical alloying and further non-isothermal heating up to 300 °C. The reactivity and equilibrium features of Mg 2Ni were characterized by both hydrogen absorption/desorption and pressure–composition isotherm measurements. The nanostructured intermetallic showed a 3.0 wt% hydrogen storage capacity without activation and excellent hydrogen absorption/desorption kinetics.

Difficulties with Ti-Ni Powder Metallurgy Process and Multi-Stage Sintering Technique for TiNi SMA

A study of the exothermic behavior of reactions that occur within Ni and Ti elemental powder mixtures during heating in medium vacuum (4 x 10 -3 Pa) has been conducted. In comparison with several other ordered intermetallic compound mixes, a much more violently released exothermic heat was observed in the Ti-50Ni mixture. It indicates that the difficulties associated with a common powder metallurgy process for TiNi shape memory alloy (SMA) include the possible oxygen interaction in a low vacuum condition and the large and rapidly generated exothermic heat in a medium or high vacuum condition. Therefore, a multi-stage sintering process is proposed to fabricate the TiNi SMA powder metallurgy (P/M) specimens and their composites. In order to prevent the violently released exothermic heat, the sintering process was divided into several repeated cycles with intermediate cold deformation, and a relatively low sintering temperature, 1030°C (or 1080°C), was employed. Further study of the SMA composites, Ti 50 Ni 50 + 5vol%TiC and Ti 50 Ni 50 + 10vol%TiC, with this technique was presented in this article. The obtained sintering density is above 85%. In the meantime, 94.5% (50%) recovery of Ti 50 Ni 50 + 5vol%TiC (Ti 50 Ni 50 + 10vol%TiC) after 1.0% tensile strain then heated to 80°C were observed. The results of phase transformation and microstructure examination will also be discussed.

A comparison of the evolution during the mechanical alloying of both a MmNi 5–Ni and a Mm–Ni mixtures: Stages of milling and microstructural characterization

The advantages attributed to hydride forming materials synthesized by either mechanical alloying (MA) or milling (MM) are related to an enhancement of the alloy conditioning previous to sorption of hydrogen, mainly due to the generation of defects and strain on the microstructure. This treatment can be done either after the synthesis by further MM of the alloy or simultaneously by MA of the constituents. To select the most suitable method, mixtures of Mm–Ni and MmNi 5–Ni were mechanically alloyed/milled in a low energy milling device. The changing of the microstructure during processing was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The evolution of particle morphology and size were analyzed and the stages of alloying/milling were identified. The MA process of the Mm–Ni mixture occurs in four stages: initial, intermediate, final and completion. The MM process of the MmNi 5–Ni mixture occurs in two main stages, governed successively by fracture and cold welding, respectively. The final alloy condition, structure and microstructure are correlated to the evolution of each process.

A new phase MgNi 3 synthesized by mechanical alloying

There are only two kinds of intermetallics Mg 2Ni and MgNi 2 formed in Mg–Ni binary alloy system as known now. However, X-ray diffraction results indicate a new phase MgNi 3 with the same crystal lattice as AuCu 3 phase was formed by mechanical alloying in Mg–50 at% Ni mixture powders milled for 40 h. MgNi 3 phase has the cubic crystal lattice and the crystal constant is 0.3717 nm.

Geometrical and electrical properties of NTC polycrystalline thermistors vs. Changes of sintering parameters

NTC thermistor powder was made of a Mn, Ni, Fe and Co oxide mixture calcinated at 1050?C / 60 min. The powder was milled in a ball mill down to an average particle diameter of 0.9 ?m. Small disc shaped pills of the powder obtained were made by pressing with a pressure of 2.5 MPa. The pills were sintered in the temperature range of 900-1400 ?C for 30-240 min. The volume and specific volume resistivity change were measured as a function of sintering conditions. Microstructure development was observed using a SEM microscope. Using the results obtained, optimization of sintering parameters was performed in order to determine optimal electrical properties of the selected thermistor composition.

Fabrication of Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub>~Ni Functionally Graded Pipes

The fabrication of Al2O3-ZrO2~Ni functionally graded pipes has been investigated by slurry coating and pressureless sintering process. Each slurry of Al2O3-ZrO2~Ni mixture and Ni was coated in order on the Al2O3-ZrO2 pipes formed by slip casting method with those slurries. The obtained laminar green pipes were 30 mm in diameter and approximately 90 mm in length. The laminar green pipes were sintered for 2 hours at 1430°C in a vacuum. The structure of pipes fabricated by this method was optically and microscopically examined and the graded distribution was examined by an EPMA analysis of Al and Ni. The pipes with 2 layers of Al2O3-ZrO2 and Ni had crevices in the bonding interface. Some functionally graded pipes with 3 layers were free from cracks and warps without porosity, and each interface had the complete bonding.

Modeling on the Counteractive Facilitated Transport of Co in Co–Ni Mixtures by Hollow-Fiber Supported Liquid Membrane

The separation of cobalt from mixed solutions of cobalt and nickel sulfate through the hollow-fiber supported liquid membrane using 2-ethylhexylphosphonic acid mono-2 ethylhexyl ester as a carrier has been studied. A mathematical model was developed to analyze the permeation of cobalt in the competitive permeation of cobalt and nickel. The model was based on the continuity equation and considered not only the cotransport of cobalt and nickel, but also the counter-transport of hydrogen ions. The concentrations in the stripping solution were taken into account in the model as well as the concentrations in feed solution and liquid membrane. The experimental results were in good agreement with the model.

Exothermic behavior of several elemental powder mixes

A study of the exothermic nature of the reactions that occur within elemental powder mixtures with compositions of Ni–24Al; Fe–29Al and Ti–50Ni during heating has been carried out. The experimental procedure consisted of heating and reacting powder compacts in vacuum (4×10 −3 Pa), and the temperature of the compacts was monitored in situ. Temperature variations of specimens sealed or unsealed in a stainless steel sheath were compared and analyzed. It was observed that the maximum temperature of Ni–Al compact was effectively depressed due to an absorption of the exothermic heat by the near equal-weight sealing sheath, and the reacted phase structures changed. Neither significant variation of the maximum temperature nor modification of the reacted phase was found in the Fe–Al compact when it came into contact with the sealing stainless steel sheath. It is suggested from the observed results that the reaction between Fe–Al particles is more violent and faster than that of Ni–Al particles, although the exothermic heat is less. In addition, a tremendous exothermic heat was released once the Ti–Ni mixture was heated up to 1100 °C. The sealing stainless steel sheath could not resist the maximum temperature of the mixture, so it melted down. The exothermic behavior of the three powder compacts is difficult to investigate with the common thermal analysis instruments and calorimetric measurement.

Hydrogen uptake characteristics of mechanically alloyed mixtures of Ti–Mg–Ni

It has been well established that hydrogen will react directly and reversibly with a large number of metals and alloys to form metallic hydrides. Extensive research has been done over the years to improve properties of these hydrogen storage media and in developing new compounds to use as hydrogen storage media. In the present study, the hydrogen uptake characteristics of mechanically alloyed titanium–magnesium–nickel have been studied. Thermal and composition data obtained for studies carried out using three different ball-to-powder ratios by mass are presented in a discussion of the hydriding properties of mechanically alloyed Ti–Mg–Ni. It was found that up to 11 wt% hydrogen was obtained for a Ti–Mg–Ni mixture that was ball milled at a ball-to-powder ratio by mass of 70:1.

Voltage-gated sodium channels shape subthreshold EPSPs in layer 5 pyramidal neurons from rat prefrontal cortex.

The role of voltage-dependent channels in shaping subthreshold excitatory postsynaptic potentials (EPSPs) in neocortical layer 5 pyramidal neurons from rat medial prefrontal cortex (PFC) was investigated using patch-clamp recordings from visually identified neurons in brain slices. Small-amplitude EPSPs evoked by stimulation of superficial layers were not affected by the N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonopentanoic acid but were abolished by the AMPA receptor antagonist 6-cyano-7-nitroquinoxalene-2,3-dione, suggesting that they were primarily mediated by AMPA receptors. AMPA receptor-mediated EPSPs (AMPA-EPSPs) evoked in the apical dendrites were markedly enhanced, or increased in peak and duration, at depolarized holding potentials. Enhancement of AMPA-EPSPs was reduced by loading the cells with lidocaine N-ethylbromide (QX-314) and by local application of the Na(+) channel blocker tetrodotoxin (TTX) to the soma but not to the middle/proximal apical dendrite. In contrast, blockade of Ca(2+) channels by co-application of Cd(2+) and Ni(2+) to the soma or apical dendrite did not affect the AMPA-EPSPs. Like single EPSPs, EPSP trains were shaped by Na(+) but not Ca(2+) channels. EPSPs simulated by injecting synaptic-like current into proximal/middle apical dendrite (simEPSPs) were enhanced at depolarized holding potentials similarly to AMPA-EPSPs. Extensive blockade of Ca(2+) channels by bath application of the Cd(2+) and Ni(2+) mixture had no effects on simEPSPs, whereas bath-applied TTX removed the depolarization-dependent EPSP amplification. Inhibition of K(+) currents by 4-aminopyridine (4-AP) and TEA increased the TTX-sensitive EPSP amplification. Moreover, strong inhibition of K(+) currents by high concentrations of 4-AP and TEA revealed a contribution of Ca(2+) channels to EPSPs that, however, seemed to be dependent on Na(+) channel activation. Our results indicate that in layer 5 pyramidal neurons from PFC, Na(+), and K(+) voltage-gated channels shape EPSPs within the voltage range that is subthreshold for somatic action potentials.

Conductivity transition of semiconducting boron carbide by doping

Boron carbide with Ni incorporation has been prepared by hot pressing of B 4.3C and 0.5 at.% Ni mixtures. Measurements of Seebeck coefficients vs. temperature indicate that n-type semiconductors have been obtained for the first time. Above 470 K, the sample changes to p-type material. X-ray diffraction (XRD) analyses show that the structure of B 4.3C crystals in the sample is similar to that of B 4.3C in the undoped sample. Scanning probe microscopy and X-ray photoelectron spectroscopy (XPS) studies reveal that Ni was incorporated in the boron carbide crystals in a combination state. Within the crystals, the Ni element is well distributed.

Effects of Reactive Mechanical Grinding on Both Chemical and Hydrogen Sorption Properties of Mg-M (M=Co, Ni and Fe) Mixtures

Effects of Reactive Mechanical Grinding on Both Chemical and Hydrogen Sorption Properties of Mg-M (M=Co, Ni and Fe) Mixtures

Effects of Reactive Mechanical Grinding on Both Chemical and Hydrogen Sorption Properties of Mg-M (M=Co, Ni and Fe) Mixtures

Effects of Reactive Mechanical Grinding on Both Chemical and Hydrogen Sorption Properties of Mg-M (M=Co, Ni and Fe) Mixtures

Microstructural evolution of Ni-NaCl mixtures during mechanochemical reaction and mechanical milling

The evolution of microstructure of Ni and NaCl mixtures formed by mechanochemical reaction and mechanical milling has been studied using X-ray diffraction, electron microscopy and magnetic measurements. Separate nano-sized Ni particles were formed by continuous solid-state reaction of NiCl2 + 2Na during mechanical milling. Further milling resulted in the growth of clustered particles due to inter-particle welding during collision events. On the other hand, milling of micron-sized Ni and NaCl powders resulted in a layered particle morphology and continuous decrease in particle size with increasing milling time.