Nano-sized Ni Particles Research Articles

Microstructural characterization of Al 2O 3–Ni composites prepared by electroless deposition

Al 2O 3–Ni composites were prepared by pressureless sintering using Ni-coated Al 2O 3 powders produced by electroless deposition. After deposition, most of Al 2O 3 powders were coated with Ni layer 20-nm thick but some of the nano-sized Ni particles also were attached to the Al 2O 3 powders. Microcracks and reaction compounds were not observed at the interfaces between the Al 2O 3 and Ni phases after pressureless sintering. The Al 2O 3–Ni composite was comprised of Al 2O 3, Ni and Ni 3P phases. A large number of dislocations were observed in the Ni phase due to the mismatch of thermal expansion coefficients (TEC) between Al 2O 3 and Ni phases. The main fracture mode showed a mixed type with intergranular and transgranular modes having some roughness. The fracture toughness was increased due to the plastic deformation mechanism of the Ni phase in the Al 2O 3 matrix.

Micromorphology and conductive property of the pellets prepared by HCl-doped polyaniline nanofibers

HCl-doped polyaniline nanofibers having a long nanosize fibril structure were prepared by an inverse microemulsion polymerization process using nanosize Ni particles as inorganic template. Powders of the polyaniline nanofibers were pressed to pellets in thickness of about 0.3 mm and in diameter of 13 mm. Micromorphology and conductive property of the pellets were studied by using scanning electron microscopy as well as by measuring the conductivity at room temperature and the variation of conductivity with temperature in 80–290 K. The pellets consist of granular particles and nanofibers. An array direction of the polyaniline nanofibers in the pellet is random. The conductivity of the pellets at room temperature is 0.55 ± 0.03 S/cm. The variation of conductivity with temperature reveals that the conductive mechanism can be considered to be three-dimensional variable-range-hopping (3D-VRH).

Preparation of Ni/Al 2O 3 nanocomposite powder by high-energy ball milling and subsequent heat treatment

The preparation of Ni/Al 2O 3 nanocomposite powder by high-energy ball milling and subsequent heat treatment was investigated. X-ray diffraction and transmission electron microscopy were employed to monitor the phase development. Elemental Al and NiO reacted at ambient temperature during milling process and resulted in the formation of nanosized Ni particles within 10 h of milling. After annealing at 1400 °C for 1 h, the powder mixture milled for 15 h consisted of Al 2O 3 and nanosized Ni particles.

Synthesis of carbon nanotube using Ni catalyst prepared by laser ablation in water

Nano-size Ni particles prepared by laser ablation in water were used as catalyst for synthesizing carbon nanotubes by a thermal CVD method. The width of synthesized CNT was almost the same as the size of the Ni particles. It was found that hydrogen-reduction treatment of the Ni particles was necessary to obtain nanotubes, suggesting that surface of the colloidal particles were oxidized in the laser ablation process.

Preparation and sintering behavior of Ni-Al2O3 nanocermets from coated powders

Since the concept of nanocomposite was proposed by Niihara, cermets have become one of the active fields in ceramic matrix composites in recent years [1–3]. With the combination of two constituents in nanoscale the microstructure and mechanical properties were greatly improved as compared to their convenient-prepared counterparts. Besides, the combination of functional ceramics with nanosized particles of transition metals leads to multifunctional composites with enhanced functions and better mechanical properties [4–6]. The toughening and strengthening mechanism of nanocermets was closely related to the microstructural refine ment and the transgranular fracture mode of nanocermets. These superior nanocermets were often prepared by in situ hydrogen reduction of powder mixture, and then hot pressing of powder compacts [7]. In this way the microstructure and mechanical properties of nanocermets would be influenced by several parameters, such as milling time [8]. In this letter we reported the preparation of Ni-Al2O3 nanocermets from coated powders, where nanosized Ni particles were coated with alumina layers. The main objective of this work is to explore the coating layer of nanosized metal particles on the microstructure and sintering behavior of Ni-Al2O3 nanocermets. Nanosized Ni powders were prepared by the arc plasma method [9]. The average particle size was about 34 nm. Ni fraction could be changed from 1–15 vol%. The aluminum hydroxide of coating phase came from the reaction of aluminum sulfate (Al2(SO4)3·18H2O, AR) with sodium aluminate (NaAlO2, CP). Solutions of sulfate and aluminate with equal volume were firstly prepared with distilled water. The molar ratio of aluminate to sulfate was kept at 6 to ensure complete neutralization of reactants. Then, the weighted Ni powder was dispersed into aluminate solution with the aid of a ultrasonic agitator to break down Ni agglomerates. After 15 min the sulfate solution was added dropwise into the suspension under vigorously stirring by a mechanical agitator to prevent from the sedimentation of Ni powder. When it finished, the precipitated powder was filtered, washed with distilled water and absolute alcohol, respectively. Finally, the powder collected was dried at 80 ◦C in air and passed through 200 meshes. The as-prepared powder was calcined in argon in the temperature range of 700–1000 ◦C. These powders were characterized by transmission electron

Effect of nickel content on the sintering behavior, mechanical and dielectric properties of Al 2O 3/Ni composites from coated powders

Al 2O 3/Ni composites were fabricated by hot pressing coated powders, in which nanosized Ni particles were coated with layers of alumina precursor by the heterogeneous precipitation method. The calcined powders could be sintered to above 96% of the theoretical density at as low temperature as 1350°C. The average alumina grain size in the composites decreased with increasing Ni content. Compared with that of monolithic alumina, the fracture toughness and the fracture strength of alumina could be increased by 28 and 43% by adding 2 and 5.5 vol.% Ni, respectively. The enhancement in mechanical properties can be explained from the unique microstructure of sintered bodies. The dielectric constant of Al 2O 3/Ni composites was found to increase with Ni content, which should be primarily attributed to the size effect of alumina grains.

Different susceptibilities of nanosized single-domain particles derived from magnetisation measurements

We briefly recall the magnetisation curves of an ideal super-paramagnet and the fact that the susceptibility exhibits a maximum when measured versus temperature in a constant magnetic field. This maximum is determined by the particles’ magnetic moment and the magnetic field applied. In real particle systems exhibiting an anisotropy energy this susceptibility maximum (and its dependence on the magnetic field) is determined while reaching the low-temperature magnetic state. For such systems we show that it is possible to `prepare’ them into a quasi-paramagnetic state if the low-temperature magnetic state is obtained during cooling in highly positive magnetic fields. Then, the theory of ideal super-paramagnetism is applicable in the limit of high magnetic fields. We demonstrate these simple experimental facts by measurements performed on samples consisting of nanosized Ni particles fixed in space by an aluminium oxide matrix. From the experiments we derive the susceptibility from two adjacent magnetisation curves measured between the magnetic fields B and B+Δ B.

Electrochemical properties of mechanically ground Mg2Ni alloy

The electrochemical properties of Mg 2 Ni type alloy powder prepared with a mechanical grinding (MG),of Mg 2 Ni and Ni or Pd powders were investigated. This alloy powder was found to be mainly changed to an amorphous-like matrix with dispersed nano-size Ni or Pd particles by the MG treatment. As a result, the negative electrode of the mechanically ground Mg 2 Ni alloy with Ni showed a large discharge capacity (830 mAh/g) which is 2.5 times larger than that of AB 5 type alloys. In the mechanically ground Mg 2 Ni alloy with Pd, the cycle life of the alloy electrode was considerably improved. The effect of partial substitution on the hydrogen storage properties of Mg 2 Ni was also investigated. It was found that the hydrogen reversibility of the mechanically ground Mg 1.9 M 0.1 Ni (M=Al, B, C, Ag) alloy electrode was remarkably improved by the substitution of Mg with more electronegative elements.

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.

Magnetic properties of nanosize nickel particles produced in silica glasses by ion-implantation and subsequent annealing

When Ni + ions are implanted into silica glasses at a dose of 6 × 10 16cm −2 at 160 keV and 3 μA cm −2, nanosize Ni particles (6.5 ± 1.5nm) of spherical shape are produced in the implanted layer, as confirmed by transmission electron microscopy (TEM), electron diffractometry and X-ray photoelectron spectroscopy. The relative intensity of ferromagnetic resonance (FMR) absorption at 298 K increases by a factor of ∼12 after annealing in 4% H 2 + 96% Ar for 4 h, although the Ni particle size observed by TEM does not change during this treatment. The mean Ni particle size, obtained from the temperature dependence of FMR intensity, increases from ∼4.5 nm to ∼5.5 nm by annealing. Magnetocrystalline anisotropy is observed in the FMR spectrum, measured at 133 K, of the annealed sample. The increase in FMR intensity by annealing is, therefore, attributed to an increase in the crystallinity of the Ni particles.

Magneto-Optical Properties of Ni-MgO and Co-MgO Nanocomposite Films Obtained by Partial Reduction Reactions

ABSTRACTA new processing technique was developed to synthesize metal-ceramic films containing nano-sized Ni or Co particles embedded in a MgO matrix. Sol-gel solutions were spun on different substrates with varying coefficients of thermal expansion, oxidized by heating in air and reduced to form a metal-ceramic two phase mixture. This method allows the generation of perpendicular magnetic anisotropy by use of residual stresses arising from a coefficient of thermal expansion difference between the film and substrate. Magneto-optical measurements show that the films can have relatively large Kerr and Faraday rotations, and that the metal particles have sufficient vertical magnetic anisotropy to support perpendicular magnetization. The magneto-optical properties of the films are related to the metal particle size, film thickness and substrate choice.