Ni Composites Research Articles

Effect of milling temperature on structure and reactivity of Al–Ni composites

Reactive Al–Ni composites are of interest for combustion synthesis, for joining, and as components of energetic formulations. Mechanical milling is one of the most practical techniques used for their preparation. This study investigated the effect of ball milling at cryogenic temperatures on the reactivity and structure of Al–Ni composites. Stoichiometric mixtures of Al and Ni powders were milled both at room temperature and cooled by liquid nitrogen. Products were characterized using scanning electron microscopy, differential scanning calorimetry, and x-ray diffraction. Aluminum and nickel were mixed on a finer scale in cryogenically milled powders compared to those prepared at room temperature. DSC traces of the cryogenically milled powder showed three exothermic peaks, while only two clearly resolved peaks were observed for the powders milled at room temperature. A low-temperature reaction preceding the first peak was detected only for the cryomilled material. Apparent activation energies, obtained by model-free analysis, were consistent with previous work on nanofoils. Ignition temperatures of powders prepared at room temperature decreased with increasing structural refinement. This effect was even stronger for the cryogenically milled powder. Energetic characteristics of the prepared materials were correlated with their respective structural refinement. These correlations suggest that the cryomilled material has a narrower zone separating Al and Ni in which the elements are mixed together compared to the similar material prepared by room temperature milling.

Sol–gel Synthesis of LaBO3/Attapulgite (B=Mn, Fe, Co, Ni) Nanocomposite for NH3-SCR of NO at Low Temperature

LaBO3/attapulgite (ATP) (B=Mn, Fe, Co, Ni) composites were prepared by sol–gel method using citric acid as complex agent. The products were characterized by X-ray diffraction transmission electron microscopy, energy-dispersive spectroscopy, Battett–Emmett–Teller, fourier-transform infrared, H2 temperature-programmed reduction and temperature-programmed desorption of NH3 measurements. The catalytic activity of LaBO3/ATP nanocomposites was evaluated via selective catalytic reduction of NO with NH3 by fixed bed denitration equipment at low-temperature. The impact of the various B-site elements on the NO conversion was investigated. Results showed that the adsorption capacity of NH3 played significant role in the low temperature denitrification process, and Mn was the best B-site element where LaMnO3/ATP achieves 81% conversion of NO at 250 °C.

Fabrication and electrochemical properties of graphene/copper–nickel solid solution reinforced polyaniline composite

A new redox graphene/copper–nickel solid solution/polyaniline (RGO/Cu–Ni/PANI) composite as a supercapacitor electrode is designed and successfully prepared by a flexible two-step method: first nano copper–nickel is supported on the surface of the oxide graphene, forming the RGO/Cu–Ni composite, followed by PANI is coated on RGO/Cu–Ni via in-situ polymerization process. The structure of the ternary composite is characterized by X-ray power diffraction, X-ray photoelectron spectroscopy, fourier transform infrared and scanning electron microscope. The RGO/Cu–Ni/PANI composite material shows better electrochemical performances than the pure PANI. The results show that the RGO/Cu–Ni/PANI composite have a great specific capacitance 674.7 F g−1 at 1 A g−1 current density and good cyclic stability of 90.1% over 1000 charge–discharge cycles, which can be attributed to the synergistic effect between RGO, Cu–Ni and PANI. Thus, the RGO/Cu–Ni/PANI composite is excellent electrode material in supercapacitor with high specific capacitance and the long-term cycle stability, and that is helpful in developing new kinds of portable energy storage devices.

Preparation and mechanical properties of TiCx-Ni3(Al,Ti)/Ni composites synthesized from Ni alloy and Ti3AlC2 powders

In this work, a novel TiCx-Ni3(Al,Ti)/Ni alloy composite was successfully synthesized from Ti3AlC2 (20vol% and 40vol%) and Ni starting powders via in-situ hot-pressing route at 1200°C under 30MPa. As the interleaved Al atoms diffused out from Ti3AlC2 nanolayers, Ti3AlC2 decomposed into nonstoichiometric nano-TiCx particles while the additional Al and fractional Ti atoms reacted with Ni matrix to form Ni3(Al,Ti). Due to the homogeneous distribution of ultrafine TiCx and Ni3(Al,Ti) particles in Ni matrix, Hardness, flexural strength and fracture toughness of the composite reinforced with 20vol% of Ti3AlC2 increased 50%, 50% and 70%, in comparison with the pure Ni alloy prepared under the same condition. In addition, the positive temperature dependence of flexural strength was detected in 40vol%Ti3AlC2-Ni alloy sample in the temperature range of 20°C and 700°C, and the maximum of flexural strength could reach 989±28MPa at 700°C.

A computational and experimental study on the effective properties of Al2O3‐Ni composites

AbstractIt has been demonstrated that effective medium approximation and mean field homogenization technique is a useful computational tool to predict the effective thermal and structural properties of alumina‐nickel (Al2O3‐Ni) composites. Nickel particle size and volume fraction, thermal interface resistance and porosity are found significant factors that affect thermal conductivity, elastoplastic behavior, elastic modulus and thermal expansion coefficient of Al2O3‐Ni composite. To complement the computational design, Al2O3‐Ni composite samples with designed range of volume fractions and nickel particle size are developed using spark plasma sintering process and properties are measured for model verification.

Strengthened Synergistic Effect of Metallic Mx Py (M = Co, Ni, and Cu) and Carbon Layer via Peapod-Like Architecture for Both Hydrogen and Oxygen Evolution Reactions.

The smooth electric transmission is crucial for the high-efficient electrocatalysis. Herein, a series of peapod-like metallic Mx Py /C (M = Co, Ni, and Cu) composites is developed as bifunctional catalysts toward hydrogen and oxygen evolution reactions. For the first time, the metallic property of Cu3 P is confirmed through the theoretical calculation. The in-depth composition, structural and catalytic mechanism analysis of Mx Py /C discloses that the comparable activity and considerable durability of these catalysts mainly result from the strengthened synergistic effect between metallic Mx Py and carbon layer based on the unique peapod-like architecture. Especially, the atomic contact between Mx Py and carbon not only provides an open channel for electronic transmission but also ensures the integrity of peapod-like structure. Furthermore, the high electric conductivity of the inner metallic Mx Py and the outer carbon layer endows the Mx Py /C catalyst with rapid charge migration during the electrocatalytic pathway. These findings shed light on the origin of high catalytic activity of Mx Py /C and open a path for purposefully rationally synthesizing superior electrocatalysts.

Hydrogen storage thermodynamics and dynamics of La–Mg–Ni-based LaMg12-type alloys synthesized by mechanical milling

Nanocrystalline/amorphous LaMg12-type alloy–Ni composites with a nominal composition of LaMg11Ni + x wt% Ni (x = 100, 200) were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous hydrogen storage thermodynamics and dynamics of alloys were systematically investigated. The hydrogen desorption properties were studied by Sievert apparatus and a differential scanning calorimeter (DSC). Thermodynamic parameters (ΔH and ΔS) for the hydrogen absorption and desorption of alloys were calculated by Van’t Hoff equation. Hydrogen desorption activation energy of alloy hydride was estimated by Arrhenius and Kissinger methods. The increase in Ni content has a slight effect on the thermodynamic properties of alloys, but it significantly enhances the hydrogen absorption and desorption kinetics performance of alloys. Moreover, variation of milling time clearly affects the hydrogen storage properties of alloys. Hydrogen absorption capacity ($$C_{ 1 0 0}^{\text{a}}$$) and hydrogen absorption saturation ratio ($$R_{ 1 0}^{\text{a}}$$) (a ratio of the hydrogen absorption capacity at 10 min to the saturated hydrogen absorption capacity) have maximum values with milling time varying. But hydrogen desorption ratio ($$R_{ 2 0}^{\text{d}}$$) (a ratio of the hydrogen desorption capacity at 20 min to the saturated hydrogen absorption capacity) always increases with milling time prolonging. Particularly, prolonging milling time from 5 to 60 h makes $$R_{ 2 0}^{\text{d}}$$ increase from 10.89% to 16.36% for the x = 100 alloy and from 13.93% to 21.68% for the x = 200 alloy, respectively.

Thermodynamic behaviour and formation mechanism of novel titanium carbide dendritic crystals within a molten pool of selective laser melting TiC/Ti–Ni composites

Selective laser melting (SLM) was applied to prepare TiC/Ti–Ni composites by using a mixed powder composed of titanium powder, nickel powder and titanium carbide powder. The result indicated that fine TiC particles were transformed into in situ Ti6C3.75 dendrites based on the complete melting mechanism and coarse TiC particles just partly experienced melting to form epitaxial dendrites along the margin of the remaining TiC particles. Besides, laser scan speed was found to have a significant influence on Ti6C3.75 dendrite growth. To give a better insight into the thermodynamic behaviour of TiC within the mesoscopic molten pool which was difficult to be monitored by experimental methods, a numerical simulation method was used. Due to the existence of differences in thermal conductivity between TiC and the matrix, reverse thermal hysteresis within TiC particles was predicted, influencing the temperature and its gradient on the TiC particles. Furthermore, the melting mechanism of TiC particles and growth processes of Ti6C3.75 dendrites were discussed. Moreover, nanoindentation load–penetration depth curves were also measured, reaching a value of 6.84 GPa at the applied v of 350 mm s−1.

Metal–organic-frameworks derived porous carbon-wrapped Ni composites with optimized impedance matching as excellent lightweight electromagnetic wave absorber

In recent years, metal–organic-frameworks derived composites, especially magnetic nanoparticles embedded in porous carbon matrix have emerged as promising candidate for lightweight electromagnetic wave absorber. Nevertheless, investigation on the optimization of impedance matching in the microwave absorption properties is insufficient. In this work, impedance matching is optimized to achieve strongest absorption intensity and broaden the effective frequency bandwidth. In detail, electromagnetic parameters have been controlled through changing the carbonization temperature to fulfill optimized impedance matching. RL value of −51.8dB and an effective frequency bandwidth (fe) of 3.48GHz with a thickness of 2.6mm can be achieved by sample prepared at 500°C and RL value of −15.0dB and a fe of 4.72GHz with a thin thickness of 1.8mm can be reached by sample synthesized at 600°C. Comparative studies of each sample directly display the effect of impedance matching on the RL performance and possible attenuation mechanisms are also discussed. This work may deepen the understanding of the impedance matching and pave the way for the synthesis of high performance lightweight microwave absorber.

Hydrogen storage kinetics of nanocrystalline and amorphous NdMg12-type alloy–Ni composites synthesized by mechanical milling

Abstract Nanocrystalline and amorphous NdMg11Ni + x wt.% Ni (x = 100, 200) composites were synthesized by mechanical milling, and their gaseous and electrochemical hydrogen storage kinetic performances were systematically investigated. Hydrogen absorption and desorption properties were investigated by means of a Sievert apparatus and a differential scanning calorimeter connected with an H2 detector. Electrochemical hydrogen storage kinetics of the as-milled alloys were tested by an automatic galvanostatic system. Results show that increasing Ni content significantly improves gaseous and electrochemical hydrogen storage kinetics. The improved gaseous hydrogen storage kinetics of the alloys are ascribed to the decrease in hydrogen desorption activation energy caused by increasing Ni content and milling time.

Microstructural Evolution and Performance of In-situ Ag-Ni Composite after Solidification under Electromagnetic Stirring and Deformation

The effect of electromagnetic stirring (EMS) on microstructure and performance of Ag-8 mass% Ni composite was investigated under both solidified and deformed conditions. Without EMS, the Ag matrix formed short, thick dendrites in the ingot; whereas with EMS, dendrites were long and slim. Ni phase mainly formed particles or ribbons, distributed along boundaries between dendrite arms. Cold drawing of the solidified Ag-Ni ingots, both with and without EMS, produced high strength in-situ metal-matrix composite (MMC) consisting of Ag matrix reinforced by Ni ribbons. EMS improved the ductility of the composite, consequently enhancing its drawability and strength. EMS also increased the electrical conductivity in both solidified ingots and deformed in-situ composite wires. In both cases, hardness and tensile strength remained high. A model based on a combination of the modified linear rule of mixtures and the Hall-Petch relationship was used to rationalize the tensile strength and hardness with respect to its fabrication parameters and the microstructure of Ag-Ni in-situ composite.

Hydrogen storage in Mg2Fe(Ni)H6 nanowires synthesized from coarse-grained Mg and nano sized γ-Fe(Ni) precursors

In this work, Mg2Fe(Ni)H6 was synthesized under relatively mild conditions using precursors of coarse-grained Mg powder and Fe(Ni) composite containing γ-Fe(Ni) nano particles prepared through arc plasma method. The microstructure, composition, phase components and the hydrogen storage properties of the Mg–Fe(Ni) composite were carefully investigated. It is observed that the Mg2Fe(Ni)H6 formed from the Mg–Fe(Ni) composite has a “tangled nanowire” morphology with the wire diameter of 100–240 nm. In contrast, a typical columnar morphology was observed for the Mg2FeH6 produced from hydrogenation of coarse-grained Mg and pure α-Fe nano particles. A promotion effect on the synthesis of Mg2FeH6 is found for the utilization of γ-Fe(Ni) precursor instead of pure α-Fe. Indeed, γ-Fe(Ni) has the same fcc lattice as Mg2FeH6, which may remarkably shorten the diffusion distance of Fe during the formation of Mg2FeH6 from MgH2 and Fe. Meantime, the existence of Ni in Fe would catalyze the hydrogenation and influence the growing of Mg2Fe(Ni)H6/γ-Fe(Ni) interface, leading to the formation of Mg2Fe(Ni)H6 tangled nanowires. For hydrogen release, the peak desorption temperature of Mg2Fe(Ni)H6 is 593 K, which is 22 K lower than that of the Mg2FeH6. The absorption and desorption enthalpies of Mg2Fe(Ni)H6 were measured to be −68.8 ± 3.0 and 69.2 ± 3.2 kJ/mol H2, respectively. The improvements in both hydrogen sorption kinetics and thermodynamics can be attributed to destabilization effect of Ni substitution for Fe in the Mg2FeH6.

Effect of Ni content on microstructures and mechanical properties of hot-pressed TiC–TiB2–Ni composite

A TiC–TiB2–Ni composite with different Ni contents was synthesized using a hot pressing method. XRD analyses showed that the TiC–TiB2–Ni composite mainly consisted of TiC and TiB2 phases, and a small amount of metal Ni was also detected except the uncertain peaks. SEM observations showed that TiB2 phases were homogeneously distributed on the TiC matrix and the Ni enriched area in white contrast uniformly distributed on the phase interface, grain boundaries between the TiB2 and TiC grains or the triple junctions among the grains. The Ni enriched area contained metal Ni and NiTi2 compound according to TEM analyses. The experimental results showed that with increasing the Ni content, the volume density of the TiC–TiB2–Ni composite increased, and the hardness, flexural strength and fracture toughness all first increased and then decreased. When the Ni content was 8%, the optimum hardness, flexural strength and fracture toughness of the TiC–TiB2–Ni composite was 18.8GPa, 604MPa and 8.9MPa·m1/2, respectively.

Hydriding/dehydriding properties of NdMgNi alloy with catalyst CeO2

Hydrogen storage composites Nd2Mg17-50 wt.%Ni-x wt.%CeO2 (x=0, 0.5, 1.0, 1.5, 2.0) were obtained by induction-ball milling method. The catalytic effect of CeO2 on hydriding kinetics of Nd2Mg17-50 wt.%Ni composite was investigated. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) analyses showed that Nd2Mg17-50 wt.%Ni alloy had a multiphase structure, consisting of NdMg12, NdMg2Ni, Mg2Ni and Ni phases and the addition of catalyst CeO2 prompted the composites to be partly transformed into amorphous strucutre. The CeO2 improved the maximum hydrogen capacity of Nd2Mg17-50 wt.%Ni alloy from 3.192 wt.% to 3.376 wt.% (x=1.0). What's more, the increment of diffusion coefficient D led to the faster hydriding kinetics, which was calculated by Avrami-Erofeev equation. The dehydrogenation temperature reduced from 515.54 to 504.72 K was mainly caused by the decrease of activation energy from 93.28 to 69.36 kJ/mol, which was proved by the Kissinger equation.

Experimental and numerical study of anisotropic thermal conductivity of magnetically aligned PDMS/Ni particle composites

In this research, Polydimethylsiloxane (PDMS)/nickel (Ni) composites with embedded Ni spherical particle columns were studied for thermal conductivity enhancement. The volume fraction of Ni particles ranged from 2% to 20% while the strength of the applied magnetic field was fixed at 0.45 Tesla. The distribution and morphology of the column structures were quantitatively analyzed using optical microscope, Scanning Electron Microscope (SEM) and digital image processing. A reusable 3ω measurement technique was applied to measure the effective thermal conductivity of PDMS/Ni composites in the parallel direction to the magnetic field. The measured thermal conductivity was compared with the prediction from a finite element model built on the observed microscopic structures. Under a static magnetic field, Ni particles align parallel to the field forming columns. The results illustrated that the diameter of Ni columns increased with increasing particle volume fraction while the center to center spacing between columns did not change substantially under the fixed magnetic strength. The magnetically aligned particle columns significantly enhanced the thermal conductivity of PDMS compared to the randomly distributed particles by about two fold. However, the point contacts between magnetically aligned spherical fillers are the major limiting factor for the further improvement of thermal conductivity.

Influence of different reinforcing particles on the scratch resistance and microstructure of different WC–Ni composites

WC composites are largely used in many engineering and industrial fields such as mining, cutting tools, and underground works. This interest in WC materials is related to their high wear resistance due to their convenient mechanical properties and controllable microstructures. However, the abrasive behavior of WC materials is very complicated because they are formed from several phases and their damage mechanism involves numerous parameters and factors that may be related to the composites themselves and the external environment. Reinforcing particles play a critical role in the achievement of wear-resistant materials. In this study, the impact of the presence of different types of reinforcing particles in the chemical makeup of WC–Ni composites on their resistance to scratch formation is highlighted through experimental abrasion tests by a single diamond tip.

Hydrogen Storage Kinetics of Nanocrystalline and Amorphous LaMg12-Type Alloy–Ni Composites Synthesized by Mechanical Milling

The nanocrystalline and amorphous LaMg11Ni + x wt% Ni (x = 100, 200) composites were synthesized by the mechanical milling, and their gaseous and electrochemical hydrogen storage kinetics performance were systematically investigated. The results indicate that the as-milled composites exhibit excellent hydrogen storage kinetic performances, and increasing Ni content significantly facilitates the improvement of the hydrogen storage kinetics properties of the composites. The gaseous and electrochemical hydrogen storage kinetics of the composites reaches a maximum value with the variation of milling time. Increasing Ni content and milling time both make the hydrogen desorption activation energy lower, which are responsible for the enhancement in the hydrogen storage kinetics properties of the composites. The diffusion coefficient of hydrogen atom and activation enthalpy of charge transfer on the surface of the as-milled composites were also calculated, which are considered to be the dominated factors for the electrochemical high rate discharge ability.

Fabrication of thermosensitive hydrogel-supported Ni nanoparticles with tunable catalytic activity for 4-nitrophenol

Thermosensitive hydrogels displaying a high degree of swelling were successfully fabricated from cross-linked poly(N-isopropylacrylamide-co-2-acrylamido-2-methylpropanesulfonic acid) (P(NIPAM-co-AMPS)). The sulfonic acid groups in the copolymer networks strongly modulated the internal structure and swelling behavior of the P(NIPAM-co-AMPS), thereby lowering the critical solution temperature of the hydrogels. These groups acted as adsorption sites, enabling the in situ synthesis of Ni nanoparticles in P(NIPAM-co-AMPS) hydrogels. Significant changes in the average diameter and number of the Ni nanoparticles were observed when the concentration of AMPS was changed. The catalytic capability of P(NIPAM-co-AMPS)/Ni to act as a switched temperature reactor was demonstrated in a model reduction reaction. Kinetic data revealed that the adsorption of the reactants on the catalyst surface was the key factor in terms of the Langmuir–Hinshelwood model. The reaction rate of the P(NIPAM-co-AMPS)/Ni composite hydrogels did not increase monotonically; instead, the reaction rate decreased to some extent around the low critical solution temperature (LCST), demonstrating a thermally tunable catalytic activity. The P(NIPAM-co-AMPS)/Ni composites were also highly stable, and were usable after five cycles of use, retaining a high level of activity.

Fracture behavior of sandwich-structured metal/amorphous alloy/metal composites

The sandwich-structured ultrafine grained (UFG) Ni/Fe78B13Si9 amorphous alloy/UFG Ni composite were prepared through the electrodeposition technique. Tensile testing of the sandwich composites was conducted and fracture behavior of the composites was characterized. The results show that the yield and ultimate tensile strengths decrease gradually, while the ductility of the sandwich composite increases with increasing UFG-Ni layer thickness. The fracture mode of the sandwich-structured composite varies with changing the constraint UFG-Ni layer thickness. The local necking of the UFG-Ni layers plays an important role in fracture mode of the sandwich composites. The coupling effect of the UFG-Ni layer and amorphous layer on mechanical performance of the sandwich composites is discussed.

Ni coated Ti1.4V0.6Ni composite as the negative electrode in Ni–MH battery

Ti1.4V0.6Ni composite is synthesized by arc-melting and subsequent melt-spinning techniques. An improved electrochemical stability of Ti1.4V0.6Ni composite is obtained by chemical plating Ni. The phase structures of the composite contain icosahedral quasicrystal phase (i-phase) and TiNi-type phase. Different amount of Ni is coated on the surface of the composite particles. When Ti1.4V0.6Ni is plated with 1–9wt% Ni, the discharge capacity retention ratio is promoted. Ni coating layer inhibits the dissolution of V from the composite and also promotes the high rate discharge property.