Synthesis and spark plasma sintering of the α-Si3N4 nanopowder

A two-step process (milling and then heat treatment) was used for the preparation of α-Si₃N₄ nanopowder. The influence of the milling time and heat treatment temperature as processing parameters were investigated on the formation of α-Si₃N₄. Silicon nitride ceramic was produced by spark plasma sintering at 1700 °C for 15 min, using MgSiN₂ additive. The optimum sample was produced in a 30 h milling time, heat treatment at 1300 °C, and a 22 °C/min heating rate conditions. X-ray fluorescence analysis showed that the purity of the final product is above 98%. Nanoindentation hardness and Young’s modulus of the SPS-ed sample were measured as 17±2.0 GPa and 290±11.0 GPa, respectively.     

Electrical and electrochemical studies of nanocrystalline mesoporous MgFe2O4 as anode material for lithium battery applications

Nanocrystalline mesoporous spinel magnesium ferrite (MgFe₂O₄) particles with high surface area were prepared by urea assisted modified citrate combustion process. The prepared sample was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field-emission scanning electron microscope (FE-SEM), BET surface area analyzer and impedance spectroscopy techniques. XRD results confirmed the formation of a single phase of nanocrystalline spinel magnesium ferrite sample. FTIR and Raman spectroscopy (FTIR) results confirmed the structural co-ordination of the magnesium ferrite sample. The spherical shape morphology of the prepared magnesium ferrite particles was confirmed from the FE-SEM images. Specific surface area and porosity of the MgFe₂O₄ sample were obtained from N₂ adsorption–desorption isotherms results. The D.C. and A.C. electrical conductivities of the MgFe₂O₄ sample as a function of temperature and frequency were investigated by analyzing the measured impedance data. The activation energy for the migration of the carriers in the MgFe₂O₄ sample was found to be 0.607 eV. The dielectric studies revealed that the dielectric constant of the mesoporous MgFe₂O₄ sample increases with increase in temperature. Further, lithium battery was fabricated using the developed nanocrystalline mesoporous spinel MgFe₂O₄ as anode material and investigated its electrochemical performance. The charge-discharge studies revealed that the fabricated lithium battery using the developed nanocrystalline mesoporous MgFe₂O₄ as anode exhibited high capacity and good cycleability in the voltage range 0.005–3 V. The results show that the developed nanocrystalline mesoporous spinel magnesium ferrite could be a better anode material for lithium battery applications.     

Effect of mechanical activation of coprecipitated precursor on synthesis of La2Zr2O7

A lanthanum zirconate (La₂Zr₂O₇, LZ) precursor has been prepared by coprecipitation of the relevant hydroxides from nitrate solution. The effect of the mechanical activation of the precursor on its thermal decomposition and LZ formation in the temperature range of 700–1100 °C has been investigated. After mechanical activation, the precursor releases volatile components (H₂O and CO₂) at lower temperatures. Mechanical activation accelerates the LZ crystallisation and results in the formation of phase-pure LZ without admixtures of unreacted zirconia and lanthana. The LZ powder prepared from the mechanically activated precursor is characterised by a larger BET surface area, in comparison to that synthesised from the as-prepared precursor under the same calcination conditions.     

Effect of average grain size and sintered relative density on the imaginary part – µ″ of the complex magnetic permeability of (Cu0.12Ni0.23Zn0.65)Fe2O4 system

The influence of the sintered microstructure on the electromagnetic properties of Cu-doped NiZn ferrites were investigated. Two of the main variables of the thermal cycle have been modified: the maximum sintering temperature and the dwell time at that temperature, or sintering time. The evolution of the imaginary part – µ″ of the complex magnetic permeability was studied as a function of relative density, grain size and amplitude of the grain size distribution of the sintered pieces. The results show that µ″ depends on the sintered microstructure and that there is a limiting value of the average grain size (~20–25 µm) from which the electromagnetic properties of these kinds of materials worsened significantly.     

Methoxypolyethylene glycol functionalized carbon nanotube composites with high permittivity and low dielectric loss

High relative permittivity and low dielectric loss were simultaneously achieved in the percolative nanocomposites with methoxypolyethylene glycol (mPEG) modified multi-walled carbon nanotubes (MWCNTs). The dense mPEG layer with a thickness of approximately 1.7 nm was continuously coated on the surface of MWCNTs. MWCNTs exhibited excellent dispersibility after being functionalized by mPEG (mPEG@MWCNTs), the mPEG@MWCNTs/ethanol suspension was still turbid even when the suspension was deposited for two months. A high permittivity of 69.7 and a low dielectric loss of 0.042 were simultaneously achieved in the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) nanocomposite with 4.02 vol% mPEG@MWCNTs at 1 kHz. The improved dielectric properties in the nanocomposite is mainly ascribed to the following reasons: (i) the increased microcapacitors formed by MWCNTs and insulated dielectric composite; (ii) the enhanced interfacial polarization due to the homogeneous dispersion of mPEG@MWCNTs in the nanocomposites and tight adhesion between mPEG@MWCNTs and P(VDF-HFP) matrix.     

A TEM study of morphological and structural degradation phenomena in LiFePO4‐CB cathodes

LiFePO₄‐based cathodes suffer from various degradation mechanisms, which influences the battery performance. In this paper, morphological and structural degradation phenomena in laboratory cathodes made of LiFePO₄ mixed with carbon black (CB) in a 1 mol/L LiPF₆ in EC : DMC (1:1 by weight) electrolyte are investigated by transmission electron microscopy at various preparation, assembling, storage, and cycling stages. High‐resolution transmission electron microscopy imaging shows that continuous SEI layers are formed on the LiFePO₄ particles and that both storage and cycling affect the formation. Additionally, loss of CB crystallinity, CB aggregation, and agglomeration is observed. Charge–discharge curves and impedance spectra measured during cycling confirm that these degradation mechanisms reduce the cathode conductivity and capacity. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and characterization studies of NiO nanorods for enhancing solar cell efficiency using photon upconversion materials

We report the effect of calcination on the structural and optical properties of nanocrystalline NiO nanoparticles were successfully synthesized by virtue of a single source precursor method at mild reaction conditions between nickel nitrate and sodium hydroxide. Composition, structure and morphology of the products were analyzed and characterized by X-ray powder diffraction (XRD). The ultra-violet visible (UV–vis) absorption peaks of NiO exhibited a large blue shift and the luminescent spectra had a strong and broad emission band centered at 328 nm. The intense band gap was also observed, with some spectral tuning, to give a range of absorption energies from 2.60 to 3.41 eV. The various functional groups present in the NiO nanorods were identified by FTIR analysis. High resolution transmission electron microscopy (HRTEM) and the chemical composition of the samples the valence states of elements were determined by X-ray photoelectron spectroscopy (XPS) in detail. The electrochemical response of NiO proved that the nano-nickel has a high level of functionality due to its small size and higher electrochemical activity without any modifications. The above studies demonstrate the potential for the utilization of NiO nanoparticles as a promising material for opto-electronics applications.     

Glowworm swarm optimization algorithm with topsis for solving multiple objective environmental economic dispatch problem

A new glowworm swarm optimization (GSO) algorithm is proposed to find the optimal solution for multiple objective environmental economic dispatch (MOEED) problem. In this proposed approach, technique for order preference similar to an ideal solution (TOPSIS) is employed as an overall fitness ranking tool to evaluate the multiple objectives simultaneously. In addition, a time varying step size is incorporated in the GSO algorithm to get better performance. Finally, to evaluate the feasibility and effectiveness of the proposed combination of GSO algorithm with TOPSIS (GSO–T) approach is examined in four different test cases. Simulation results have revealed the capabilities of the proposed GSO–T approach to find the optimal solution for MOEED problem. The comparison with own coded weighted sum method incorporated GSO (WGSO) and other methods reported in literatures exhibit the superiority of the proposed GSO–T approach and also the results confirm the potential of the proposed GSO–T approach to solve the MOEED problem.     

Cu-Containing Fe-Ni Corrosion-Resistant Alloys Designed by a Cluster-Based Stable Solid Solution Model

Copper is a good corrosion resisting element, but due to its immiscibility with Fe, it is only used as a minor-alloying element in stainless steels. In this work, we introduced a double-cluster structure model [CuNi₁₂][NiFe₁₂] _m for stable solid solutions in Cu-containing Fe-Ni corrosion-resistant invar alloys. Our model takes into account all of the enthalpies between the element pairs by assuming Fe-Ni and Ni-Cu nearest neighbors and by avoiding Fe-Cu ones, so that the ideally stabilized structures are described by mixing two cuboctahedral clusters in the fcc lattice, NiFe₁₂ and CuNi₁₂. Two alloy series were designed by varying the relative proportions of the two clusters and the Cu contents. It was proved that the alloys with Cu contents below those prescribed by this model could easily be solutionized and water-quenched to a monolithic fcc solid solution, and resultant alloys possessed good corrosion-resisting properties in 3.5 wt pct NaCl solution.     

Hydrophobic precipitation of carbonaceous spheres from fructose by a hydrothermal process

We report a new mechanism of hydrophobic ripening for the formation of carbonaceous spheres by the dehydration of saccharides in a hydrothermal aqueous environment using fructose as a model precursor material. We investigated the formation of carbonaceous spheres from fructose in aqueous solutions under hydrothermal conditions. The spheres were found to contain 65.7 wt.% C, 4.3 wt.% H and 30.0 wt.% O, implying incomplete dehydration of the fructose. The spheres, typically ranging between 400 nm and 10 μm in diameter, are found to be constructed entirely of primary particles of ～5 nm. The chemical structure of the carbonaceous spheres and the chemical compositions of residual solutions were analysed using solid state and solution ¹³C nuclear magnetic resonance and Fourier transform infrared spectroscopy. Based on these results, a four-step mechanism for the formation and growth of carbonaceous spheres has been proposed.