Synthesis and electrochemical properties of nanostructured Li2FeSiO4/C cathode material for Li-ion batteries

Nanostructured Li₂FeSiO₄/C was synthesized by high-energy ball-milling and the amorphous citrate-assisted techniques. Similar redox behaviour is observed for samples prepared by the amorphous citrate-assisted route followed by a 4 h heat treatment: 0.3 V polarization and more sloping behaviour was observed when cycling between 2.0 V and 3.7 V at 60 °C; lower capacity fade is also observed compared to Li₂FeSiO₄/C prepared by the solid-state reaction technique. A discharge capacity of 102 mA h g^− 1 is obtained for samples prepared by the high-energy ball-milling method, while capacities decrease from 95 to 77 mA h g^− 1 using the amorphous citrate method for heat-treatment times increasing successively from 4 h to 18 h.     

Magnetic properties and microwave absorption in Ni-Zn and Mn-Zn ferrite nanoparticles synthesized by low-temperature solid-state reaction

In this work, Mn_0.7Zn_0.3Fe₂O₄ and Ni_0.7Zn_0.3Fe₂O₄ nanoparticles with super-paramagnetic properties and size distribution from 10 to 52 nm were investigated. These particles were produced by a low-temperature solid-state reaction method without the ball-milling process. The size and morphology of the nanocrystallites were determined by X-ray diffraction, transmission electron microscopy and scanning tunneling microscopy methods. Magnetic measurements such as alternating gradient field magnetometers were used to justify the super-paramagnetic properties of these nanoparticles. Their microwave absorption in the range of 8-18 GHz was studied by a vector network analyzer. Responses of the device under tests were studied. Also, the percentage of the resin, the size and thickness of the mount were determined. The band width of 2.3 GHz was obtained with reflection-loss/written-loss of −16 dB around 10.4 GHz.     

Simultaneous variations of microstructure and magnetic properties of Ni58Fe12Zr20B10 nanostructure/amorphous alloy prepared by mechanical alloying

This study aims to evaluate magnetic and micro-structural properties of amorphous/nanocrystalline mechanically alloyed Ni₅₈Fe₁₂Zr₂₀B₁₀ powders with ball-milling time up to 190 h. Structural, micro-structural and thermal evaluations of the milled powders were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimetry (DSC) methods. Magnetic properties were also measured by a vibrating sample magnetometer (VSM) instrument. Results showed that the amorphous phase reached maximum value of 95% and the crystallite size was about 3 nm at the end of the milling. Magnetization saturation (M_s) decreased slightly and coercivity (H_c) reached to the highest value at 72 h of the milling time. At the 190 h of milling, the coercivity and saturation magnetization reached 18 Oe and 20 emu/g, respectively. While, after an appropriate amount of heat treatment, these two variables became approximately 2 Oe and 32 emu/g.     

Synthesis of (Mg0.476Mn0.448Zn0.007)(Fe1.997Ti0.002)O4 powder and sintered ferrites by high energy ball-milling process

(Mg_0.476Mn_0.448Zn_0.007)(Fe_1.997Ti_0.002)O₄ nanocrystalline powder prepared by high energy ball-milling process were consolidated by microwave and conventional sintering processes. Phases, microstructure and magnetic properties of the ferrites prepared by different processes were investigated. The (Mg_0.476Mn_0.448Zn_0.007)(Fe_1.997Ti_0.002)O₄ nanocrystalline powder could be prepared by high energy ball-milling process of raw Fe₃O₄, MnO₂, ZnO, TiO₂ and MgO powders. Prefired and microwave sintered ferrites could achieve the maximum density (4.86 g/cm⁻³), the average grain size (15 μm) was larger than that (10 μm) prepared by prefired and conventionally sintered ferrites with pure ferrite phase, and the saturation magnetization (66.77 emu/g) was lower than that of prefired and conventionally sintered ferrites (88.25 emu/g), the remanent magnetization (0.7367 emu/g) was higher than that of prefired and conventionally sintered ferrites (0.0731 emu/g). Although the microwave sintering process could increase the density of ferrites, the saturation magnetization of ferrites was decreased and the remanent magnetization of ferrites was also increased.     

Synthesis of fine-crystalline Ba0.6Sr0.4TiO3-MgO ceramics by novel hybrid processing route

We report the use of a novel powder-in-sol precursor hybrid processing route to synthesize dense, homogeneous, and fine-crystalline Ba_0.6Sr_0.4TiO₃-MgO (BST-MgO) ceramics as well as the study of the sintering behavior, microstructures, and dielectric properties of the ceramics. Nanosized BST powders are dispersed into BST sol-gel precursor and uniformly distributed BST slurry is obtained after ball-milling mixing. Mg(NO₃)·6H₂O solution is added to the BST slurry to give homogeneous BST-MgO slurry upon ball-milling mixing. The BST-MgO slurry is dried and calcined prior to pressing and sintering at low temperatures of 1200-1300 °C to form the ceramics. The ceramics possess very low dielectric loss tangent below 0.005 for frequency above 1 kHz and for temperature in the range −190-80 °C. The dielectric constant and dielectric tunability increase, while the ferroelectric transition broadening decreases, with increasing average grain size.     

Attractive microwave absorption and the impedance match effect in zinc oxide and carbonyl iron composite

The flower-like ZnO and ZnO/carbonyl-iron composite have been prepared by a sonochemical route and ball-milling process, respectively. For ZnO/carbonyl-iron composite, a reflection loss (RL) exceeding −20 dB was obtained in a broad frequency range of 8.4-17.9 GHz with a thin thickness of 1.2-2.3 mm. An optimal RL of −61 dB was found at 11.7 GHz for an absorber thickness of 1.91 mm. It is demonstrated that the attractive microwave-absorption properties are a consequence of a proper electro-magnetic impedance match and geometrical cancellation at the air-material interface. In addition, an impedance mismatch function was proposed, which provides an effective method to determine the microwave absorbing properties from the intrinsic materials constants. The calculated value of matching frequency and thickness is well consistent with the experimental data. The method also provides a simple theoretical graphic aid for determining the absorption characteristics and the location of the matching conditions in the frequency domain.     

Morphology and magnetic properties of FeCo nanocrystalline powder produced by modified mechanochemical procedure

Properties of FeCo nanocrystalline intermetallic powders prepared by salt-matrix hydrogen reduction of a milled Fe₂O₃-Co₃O₄ mixture were investigated. The product of 72 ks ball-milling at 350 rpm was CoFe₂O₄ nanopowder. Reduction of this powder for 3.6 ks by hydrogen at 750 °C resulted in the formation of Fe_0.67Co_0.33 stoichiometric compound. Scanning electron microscopy, electron dispersive spectrometry, X-ray diffraction and vibrating sample magnetometry were used to characterize the nanopowder. Using a salt-matrix (NaCl as a dispersion medium) resulted in the decrease of the reduction temperature and improvement of the morphology and magnetic properties of the nanopowder. Dispersion of the ball-milled product in Hexan resulted in further improvements of the magnetic properties.     

Mixing Si and carbon nanotubes by a method of ball-milling and its application to pyrotechnic delay composition

The original delay composition cannot ensure the reliability and safety of the ammunition under complicated environment, for example low precision of burning rate at high density charge. Carbon nanotubes are added into the delay composition for the first time. Si and CNTs were mixed by the ball-milling method. Particle size analysis showed that particle size exponential declined with increase in milling time. TEM showed that individual nanotubes were dispersed in silicon powder after 48 h of milling, and then they did not appear damaged. Optimum conditions of preparing Si/CNTs were found to be: milling time 48 h, milling intensity 300 rpm, CNTs-to-Si weight ratio=1:10 and ball-to-powder weight ratio=150:1. Then Si/CNTs were applied to fuel agent of delay composition. We studied the burning rate of Pb₃O₄/Si and Pb₃O₄/CNTs/Si delay composition with flaming velocity measurement. Results show that burning rate and delay precision of Pb₃O₄/CNTs/Si delay composition (5.85 mm/s and 1.03%) were higher than the ones of Pb₃O₄/Si delay composition (3.80 mm/s and 3.00%). Especially reliability of ignition is improved when charge density exceeds 6000 Kg/m³. It is proved that certain amount of CNTs added to delay composition can increase delay precision and further doing so achieved less temperature dependence.     

Energy distribution of plasma-assisted electron and ion emission from TGS single crystals

Electron and ion emission accompanying non-thermal plasma processes, produced at the surface of TGS single crystals under driving ac electric field exceeding 10³ V/cm, have been carried out. These plasma-assisted emission of electrons and ions were examined by means of time and energy distribution measurements. The intensity of registered charges (electrons and ions) displayed on the 2 ms time scale are represented by two distinct peaks. Time dependent energy spectrum of charges, detected under our experimental conditions, involves electrons and ions with maximum energy up to 30-40 eV for first peaks and up to 70-80 eV for second one. Additionally, the energy of electrons is focused at about 10-15 eV for first and second peaks and about 60-70 eV for second ones; the ion energy spectrum for both peaks exhibits only distinct low energy maximum focused at about 5-15 eV.     

Surface and redox chemistry of Sm0.95Ce0.05Fe1 − xNixO3 − δ perovskites

A new series of perovskite materials with formula Sm_0.95Ce_0.05Fe_1 − xNi_xO_3 − δ (0 ≤ x ≤ 0.10) has been prepared by sol-gel combustion via a citrate precursor route. X-ray diffraction data showed that materials prepared by this method had a single orthorhombic phase belonging to the Pnma (62) space group. The study of powders sintered in air and in reducing atmospheres reveals that these materials do not show phase separation in air (up to 1350 °C) nor under 5% v/v H₂/N₂ (up to 700 °C), but a phase separation of Sm₂O₃ does occur at and above 800 °C under 5% v/v H₂/N₂ without deterioration of the perovskite phase. The surfaces of all the powders (fresh, in-situ reduced and ex-situ reduced) were Sm rich, and multiple oxidation states for Fe were observed. XP analysis of in-situ reduced samples (800 °C and above) shows that metallic Fe forms in all nickel doped materials except x = 0.07. The surface oxygen vacancies and percentages of lattice and adsorbed oxygen for this series of Ni doped materials were determined and the oxygen recapturing ability is explained in terms of the multiple oxidation states of Fe.     

Synthesis, structural, magnetic and optical properties of nanocrystalline ZnFe2O4

Nanocrystalline zinc ferrite (ZnFe₂O₄) is synthesized by high-energy ball-milling after 12 h from a powders mixture of zinc oxide (ZnO) and hematite (α-Fe₂O₃) with balls to powders mass ratio of 20:1. X-ray diffraction, vibrating sample magnetometer (VSM), the Mössbauer spectrometry and photoluminescence (PL) are used to characterize the samples. Rietveld analysis and VSM measurements show that the powder has an average crystallites size of 10 nm and a ferrimagnetic behavior with a saturation magnetization of 30 emu/g. After annealing at 700 °C, the lattice parameter reduces from 8.448 to 8.427 Å and the sample transforms into a superparamagnetic behavior, which was confirmed as well by the room temperature Mössbauer spectrometry. Different mechanisms to explain the obtained results and the correlation between magnetism and structure are discussed. Finally, the broadband visible emission band is observed in the entire PL spectrum and the estimated energy band gap is about 2.13 eV.     

Structural and magnetic properties of Co2CrAl Heusler alloys prepared by mechanical alloying

Mechanical alloying has been used to produce nanocrystalline samples of Co₂CrAl Heusler alloys. The samples were characterized by using different methods. The results indicate that, it is possible to produce L2₁-Co₂CrAl powders after 15 h of ball-milling. The grain size of 15 h ball milled L2₁-Co₂CrAl Heusler phase, calculated by analyzing the XRD peak broadening using Williamson and Hall approach was 14 nm. The estimated magnetic moment per formula unit is ∼2 μ_B. The obtained magnetic moment is significantly smaller than the theoretical value of 2.96 μ_B for L2₁ structure. It seems that an atomic disorder from the crystalline L2₁-type ordered state and two-phase separation depresses the ferromagnetic ordering in alloy. Also, the effect of annealing on the structural and magnetic properties of ball milled powders was investigated. Two structures were identified for annealed sample, namely L2₁ and B2. The obtained value for magnetic moment of annealed sample is smaller than the as-milled sample due to the presence of disordered B2 phase and improvement of phase separation.     

Influence of Co amount on the efficiency of energy absorption of Fe-Co ferrite nanoparticles

We present the chemical synthesis, structural characterization and efficiency of AC field energy absorption of Fe-Co ferrite particles sized between 35 and 100 nm and containing different cobalt amounts up to 3 wt%. Dynamic magnetic measurements in an AC field with frequency of 430 Hz and amplitude of up to 1200 Oe were performed for both solid and liquid dispersions of obtained particles. The energy absorption per one field cycle in function of the field amplitude and Co content was always bigger in liquid systems, under the same conditions, than in solid systems. The obtained results are of significance for the technology of low-frequency ferromagnetic hyperthermia of tumors.     

High-intensity Si cluster ion emission from a silicon target bombarded with large Ar cluster ions

Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25 keV were used and the mean size of the Ar cluster ion was about 1000 atoms/cluster. Si_n⁺ ions with n values up to n = 8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size.     

Resistance anomaly and structural disorder in NiSi2 under high pressure

Results of X-ray diffraction, electrical resistance, thermoelectric power measurements and electronic band structure calculations on NiSi₂ under high pressure are reported. The thermoelectric power (TEP) changes sign near 0.5 GPa (from +30 to −20 μV/K). As the pressure is increased, the value of TEP increases further in magnitude and near 7 GPa it becomes −50 μV/K. The pressure vs. resistance curve measured up to 30 GPa using diamond anvil (DAC)-based technique exhibits a broad hump near 12 GPa and exhibits hysteresis on pressure release. The ADXRD patterns up to 42 GPa show a gradual irreversible loss of long-range order in NiSi₂ with the diffraction lines progressively broadening under pressure. The FWHM of the diffraction lines show a rapid increase in the half-widths close to 0.5 GPa and also near 12 GPa. The computed band structure at a compression (without any disorder) corresponding to 12 GPa, exhibits an electronic topological transition (ETT). The rapid increase in disorder above 12 GPa implies that the ETT may be facilitating the structural disorder. It is suggested that the pressure drives the material through a region of entropic and energetic barriers and induces disorder in the material.     

Heat capacity of CeIrSi3 under pressure

We measured the heat capacity of CeIrSi₃ (100 mK<T<6 K) under high pressure up to P=1.38 GPa. The measurements have been used a quasiadiabatic method utilizing a CuBe piston-cylinder pressure cell in a dilution refrigerator. At 0 GPa, a sharp anomaly which indicates the antiferromagnetically transition is observed at T_N=5 K. T_N decreases monotonically with increasing pressure up to P=1.38 GPa. The magnetic entropy is released below T_N only 19% of R ln 2 at 0 GPa. And the magnetic entropy decreases with increasing pressure up to 1.38 GPa, 64% compared to that at 0 GPa.     

Nanolayered multilayer coatings of CrN/CrAlN prepared by reactive DC magnetron sputtering

Single-phase CrN and CrAlN coatings were deposited on silicon and mild steel substrates using a reactive DC magnetron sputtering system. The structural characterization of the coatings was done using X-ray diffraction (XRD). The XRD data showed that both the CrN and CrAlN coatings exhibited B1 NaCl structure with a prominent reflection along (2 0 0) plane. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy and the surface morphology of the coatings was studied using atomic force microscopy. Subsequently, nanolayered CrN/CrAlN multilayer coatings with a total thickness of approximately 1 μm were deposited on silicon substrates at different modulation wavelengths (Λ). The XRD data showed that all the multilayer coatings were textured along {2 0 0}. The CrN/CrAlN multilayer coatings exhibited a maximum nanoindentation hardness of 3125 kg/mm² at a modulation wavelength of 72 Å, whereas single layer CrN and CrAlN deposited under similar conditions exhibited hardness values of 2375 and 2800 kg/mm², respectively. Structural changes as a result of heating of the multilayer coatings in air (400-800 °C) were characterized using XRD and micro-Raman spectroscopy. The XRD data showed that the multilayer coatings were stable up to a temperature of 650 °C and peaks pertaining to Cr₂O₃ started appearing at 700 °C. These results were confirmed by micro-Raman spectroscopy. Nanoindentation measurements performed on the heat-treated coatings revealed that the multilayer coatings retained hardness as high as 2250 kg/mm² after annealing up to a temperature of 600 °C.     

Large atomic disorder in nanostructured LaNi5 alloys: A La L3-edge extended X-ray absorption fine structure study

Local structure of the nanostructured LaNi₅ alloys, prepared by ball-milling, has been studied using La L₃-edge extended X-ray absorption fine structure spectroscopy. The near-neighbor distances tend to decrease with the ball-milling, and the mean square relative displacements (MSRD) show substantial increase suggesting an increased atomic disorder. High temperature annealing helps in partial recovery of atomic order in the ball-milled samples for milling times upto 20 h, however, the long-time ball-milled samples seems to gain only a local random order. The results suggest that reduced unit-cell volume together with large atomic-disorder might be causing a higher energy-barrier for the hydride-phase formation in the long time ball-milled LaNi₅ powders.     

Facile synthesis and capacitive performance of the Co(OH)2 nanostructure via a ball-milling method

Co(OH)₂ nanoparticles were synthesized using only CoSO₄·7H₂O and NaOH as reactants without other auxiliary reagents via a simple, low-cost and practical ball-milling technique and investigated as the active electrode materials for supercapacitors. The structure and morphology of the resulting Co(OH)₂ samples were examined by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and transmission electron microscopy (TEM). The observations revealed the formation of brucite-like phase of β-Co(OH)₂, which had an irregular sphere-like shape with an average size of 50-100 nm. When investigated as electrode materials for supercapacitors, the β-Co(OH)₂ exhibited good energy-storage performances in terms of high specific capacitance of 599 F g⁻¹ and excellent capacity retention, suggesting its potential application in the electrode material for supercapacitors.     

Research on preparing compact bulk nanocomposite Nd2Fe14B/α-Fe magnetic materials by hot extrusion

In this paper, compact bulk nanocomposite Nd₂Fe₁₄B/α-Fe magnetic materials were prepared by hot extrusion of amorphous and nanocrystalline powders, which were prepared by high-energy ball-milling (HEBM) of the Nd₂Fe₁₄ B-type hard magnetic phase with 20 vol% of α-Fe as soft magnetic phase. The extrusion temperature has important influence on magnetic properties and microstructure of magnetic materials. The results show that the grain size of Nd₂Fe₁₄B and α-Fe phase increases steadily with increasing extrusion temperature. Furthermore, optimal extrusion temperature of 1223 K occurs, at which the highest magnetic properties and relative density can be obtained.