Synthesis and characterization of barium hexaferrite nanoparticles

This investigation dealt with the synthesis of nanocrystalline barium hexaferrite (BaFe₁₂O₁₉) powders through the co-precipitation–calcination route. The ferrite precursors were obtained from aqueous mixtures of barium and ferric chlorides by co-precipitation of barium and iron ions using 5 M sodium hydroxide solution at pH 10 in room temperature. These precursors were calcined at temperatures of 800–1200 °C for constant 2 h in a static air atmosphere. The effect of Fe³⁺/Ba²⁺ mole ratio and addition of surface active agents during co-precipitation step on the structural and magnetic properties of produced ferrite powders were studied. It is found that the formation of single phase BaFe₁₂O₁₉ powders was achieved by decreasing the Fe³⁺/Ba²⁺ molar ratio from the stoichiometric value 12–8 and increasing the calcination temperature ≥1000 °C. In addition, the Fe³⁺/Ba²⁺ mole ratio of 8 the surface active agents promoted the formation of homogeneous nanopowders (ca. 113 nm) of BaFe₁₂O₁₉ at a low-temperature of 800 °C with resultant good magnetic saturations (50.02 emu/g) and wide intrinsic coercivities (642.4–4580 Oe).     

Synthesis and characterization of neodymium oxide nanoparticles

The nanometric precursors of neodymium oxide of various morphology from fibrous to well-dispersed spheroidal were prepared via a solvothermal reaction routes. The precursors and their thermal evolution to neodymium oxide phase were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was found that the reaction parameters, kind of solvent as well as neodymium salt used played a key role for the product formation of desired morphology and structure. Similarly, kind of neodymium oxide precursor determined the morphology and the crystal structure (haxagonal or cubic) of the final oxide. The potential application of Nd₂O₃ precursors prepared by solvothermal method as convenient material for preparation of homogeneous thin coatings on planar substrates is shown.     

Synthesis and characterization of silver nanoparticles by sonoelectrodeposition

Shaped silver nanoparticles with sphere, wire and dendrite were prepared by sonoelectrochemical deposition from an aqueous solution of AgNO3 in the presence of ethylenediaminetetraacetic acid disodium salt （EDTA） and polyvinylpyrrolidone （PVP）. The diameter of spherical silver particles was about 30 nm. The diameter of the silver nanowires was also about 30 nm and the length was 200-900 nm. The dendrites were synthesized with the concentration of silver solution increasing. Silver nanoparticles were characterized by transmission electron microscope （TEM）, X-ray powder diffraction （XRD）, scanning probe microscope （SPM） and UV-vis absorption spectrum. XRD patterns revealed that silver particles were of face-centered cubic structure. UV-vis absorption spectra indicated that different morphology and size of silver particles could influence the optical properties.     

Synthesis and characterization of Ag doped Cu nanoparticles

The synthesis of Cu_100−xAg_x (0.05 at.% < x < 0.30 at.%) nanoparticles using an evaporation–condensation process has been studied. Particular attention has been paid to the composition of the as-prepared powders. Compared to the master alloy, systematic enrichment in Ag of the particles is observed at the beginning of the synthesis but a continuous decrease in the Ag content of the powders is observed during the process. Even though, after de-agglomeration, the chemical composition of the powders is, in average, homogeneous. We have shown that optimized synthesis conditions give spherical particles with a mean diameter of 50 nm and a reasonable yield rate.     

Synthesis and characterization of CoFe2O4 nanoparticles

The reverse microemulsion composition consisting of 37.0% cyclohexane, 26.0% surfactant （TX-10 and AEO9）, 13.0% n-pentanol and 24.0% aqueous phase was investigated and chosen for the preparation of cobalt ferrite nanoparticles. Then silicon dioxide was coated onto the surface of the magnetite nanoparticles. The two kinds of nanoparticles were characterized by means of X-ray diffractometry（XRD）, scanning electron microscopy （SEM）, infrared spectroscopy （IR）, and energy dispersion spectrometry （SEM-EDS）. The SEM results indicate that both nanoparticles have narrow size distribution, less agglomeration and are in the size range of 10 -60 nm. XRD patterns show that there is not any peak detected except for the peaks of CoFe2O4, and imply that the coated silicon dioxide is amorphous. IR absorption spectra of the samples show the characteristic bands of Si—O—Si group and Fe—O group. SEM-EDS indicates that the molar ratio of Fe to Si is 96.11 ： 3.89. These results prove that a thin film of SiO2 is coated on the surface of the magnetite nanoparticles. And the characterization of cobalt ferrite nanoparticles prepared by conventional precipitation method are compared.     

Ferromagnetic nanoparticles: Synthesis,processing, and characterization

Ferromagnetic nanoparticles can be used as building blocks for advanced bulk and thin film magnets, and can also be applied in data storage and biomedical technologies. However, most ferromagnetic particles lose their hysteresis at room temperature when their size is reduced to nanoscale. The exceptions are a few materials such as FePt and SmCo compounds with extremely high magnetocrystalline anisotropy that can hold a permanent magnetic moment at room temperature in particles of several nanometers. By applying newly developed “salt-matrix annealing” and “surfactant-assisted milling” techniques, monodisperse ferromagnetic FePt, SmCo, and NdFeB based nanoparticles have been successfully synthesized. These first-ever-available nanoparticles display various ferromagnetic properties at room temperature, which are found to be strongly size dependent.     

Synthesis and characterization of polyaniline nanoparticles in SDS micellar solutions

Polyaniline (PANI) dispersions consisting of 10–20 nm sized nanoparticles were prepared by oxidation with ammonium peroxydisulfate (APS) in sodium dodecylsulfate (SDS) micellar solutions. Coalescence and coagulation were prevented by electrostatic repulsive interaction between anionic SDS micelles. Particle morphology was dependent on the initial shape of surfactant aggregates (micelles) and the molar ratio of SDS to aniline monomer. Spherical particles were obtained at very low monomer concentration and the shape of particles began to be distorted from the spherical shape as monomer concentration increased at constant 0.2 M SDS concentration. The size of spherical particles was the same order of the micellar size or slightly larger. UV–VIS spectroscopy, compositions of PANI powder, morphology, crystalline structure, thermal stability, molecular weight and conductivity of PANI particles synthesized at various monomer and surfactant concentrations were investigated.     

Synthesis and characterization of iron oxide nanoparticles by solvothermal method

In the present work iron oxide nanoparticles have been synthesized by alkaline solvo thermal method using anhydrous ferric chloride, sodium hydroxide, polyethylene glycol and cetyl trimethyl ammonium bromide and characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray Spectroscopy (EDX) and Thermal Gravimetric Analysis (TGA). XRD indicated that the product is a mixture of different phases of iron oxide viz. gamma-Fe₂O₃ (maghemite, tetragonal), Fe₂O₃ (maghemite, cubic), Fe₃O₄ (magnetite, cubic) and ?-Fe₂O₃(epsilon iron oxide). FESEM studies indicated that size of the particles is observed in the range of about 19.8 nm to 48 nm. EDX spectral analysis reveals the presence of carbon, oxygen, iron in the synthesized nanoparticles. The FTIR spectra indicated absorption bands due to O-H stretching, C-O bending, N-H stretching and bending, C-H stretching and Fe-O stretching vibrations. TGA curve represented weight loss of around 3.0446 % in the sample at temperature of about 180°C due to the elimination of the water molecules absorbed by the nanoparticles from the atmosphere.     

Synthesis and characterization of amorphous Zr-based alloys with Ta and W additions

A reference Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ bulk metallic glass as well as a number of alloys obtained by addition of refractory elements Ta or W (combined with Sn) to the main Zr–Cu–Al–Ni system were elaborated by mould casting, twin roll casting and planar flow casting. The chemical compositions were chosen according to empirical rules, and as combinations of the binary eutectics for strongly interacting elements, taking into account the corresponding enthalpies of mixing. Optical microscopy, X-ray diffractometry, differential thermal analysis, differential scanning calorimetry, scanning electron microscopy and tensile mechanical testing were used to characterize the fully and partially obtained amorphous materials. Correlation of glass forming ability, thermodynamic parameters, crystallization behaviour and mechanical properties with chemical composition and production technology is discussed.     

Synthesis and characterization of silver nanoparticles by a reverse micelle process

The preparation of silver nanoparticles by the reduction of AgNO₃ with hydrazine in lgepal CO-520/cyclohexane reverse micelle solutions has been studied. Transmission electron microscope, electron diffraction, and X-ray diffraction pattern analyses revealed the resultant particles to be silver. The average size of the synthesized nanoparticles first increased and thereafter approached a constant value with increased molar ratio of water to Igepal CO 520 and with increasing concentration of AgNO₃.     

Synthesis and characterization of electrospun polymer nanofibers incorporated with CdTe nanoparticles

CdTe nanoparticles were incorporated in polyvinyl alcohol (PVA) nanofibers by electrospinning. The hybrid nanofibers were characterized morphologically and optically by scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) measurements. The average diameter of the hybrid nanofibers was about 150 nm and the CdTe nanoparticles were present both inside them and on their surfaces. Compared with the PL of the CdTe nanoparticles dispersed in solution, the PL peak of the CdTe nanoparticles in the CdTe/PVA hybrid nanofibers was shifted from 525 to 426 nm. This blue shift of the PL peak results from the different quantum confinement effects, due to the different environment surrounding the CdTe nanoparticles, in the case of those dispersed in solution and those embedded in the PVA nanofibers.     

Synthesis and characterization of Ag nanoparticles–polyaniline composite powder material

The chemical deposition of silver particles in polyaniline (PANI) powder has been carried out via the reduction of Ag⁺ ions by PANI in various concentrations of AgNO₃ aqueous solutions. It is found that the rate of Ag(I) reduction and the size of the metal particles incorporated were strongly dependent on the reaction medium, the PANI redox form and the stirring method used. Homogeneous distribution of silver nanoparticles into PANI matrix was obtained at low Ag(I) concentration, PANI in emeraldine base form and short reaction time under ultrasonic stirring. The presence of silver particles dispersed into porous polyaniline structures was confirmed using X-ray diffraction, scanning electron microscopy and cavity microelectrode (CME) technique in acidic aqueous electrolyte. The electrochemical study of Ag-PANI composite by CME showed that the redox system of silver depends on the size and the distribution of metal particles incorporated into PANI.     

Synthesis and characterization of carbon nanotubes decorated with strontium ferrite nanoparticles

A uniform coated compound material was obtained by the in situ sol–gel reaction among modified carbon nanotubes, nitric acid strontium, and nitric acid iron. The results indicated that the carbon nanotubes were coated with M-type magnetoplumbite ferrite, and its size was at the nanometer level. Along with the increase in the content of carbon nanotubes, the tubular structures of the carbon nanotubes were clearer and the coating effect was better. The coercive force of the samples increased simultaneously with the increase in the content of carbon nanotubes.     

Synthesis and characterization of molybdenum aluminide nanoparticles reinforced aluminium matrix composites

Aluminium matrix composites reinforced with molybdenum aluminide nanoparticles were synthesized by ball milling and reactive sintering of the mixture of aluminium and 10 wt% hydrated molybdenum oxide powders. Sintering the as milled powder in air below 750 °C produced MoAl₁₂ intermetallic compound nanoparticles, at 750 °C produced a mixture of MoAl₅ and MoAl₄ nanoparticles and at 800 °C under Argon atmosphere produced predominantly MoAl₄ intermetallic nano-particles in the Al matrix. The powder compacts sintered in air below 750 °C produced MoAl₁₂ whereas at 750 °C or above formed the Al matrix composite reinforced with the MoAl₅ nanoparticles. These nanoparticles become agglomerated to take up some irregular shaped flakes in the metal matrix. The reaction between Al and hydrated Mo oxide powders was found to be a favorable way to produce predominantly a particular Mo–Al intermetallic compound at a particular temperature. The Al₂O₃ particles formed as another reaction product, in all the above reactions, remain distributed in these composites. The composites thus formed were characterized by SEM-EDS, DTA, XRD and TEM analysis.     

Synthesis and characterization of mechanical-alloyed Ti–xMg alloys

The synthesis and characterization of Ti–xMg (x=4, 9, 12, 15, 21, 24 at%) alloys using mechanical alloying was investigated. A nanometer-sized Ti–24Mg alloy was produced. During mechanical alloying, the height of the XRD peaks of the Mg in the Ti–9Mg alloy decreased, and then disappeared, whereas the Ti XRD peaks broadened, and the grain size decreased with increasing milling time. The Mg firstly dissolved in the grain boundaries of the Ti, and then diffused into the Ti grain interiors. The grain boundaries played an important role in enhancing the solid solubility of Mg in Ti. With increasing Mg content the volume fraction of grain boundaries increased, and a decrease in grain size occurred after mechanical alloying for 48 h.     

Synthesis and characterization of sol-gel hydroxyapatite coatings deposited on porous NiTi alloys

A hydroxyapatite (HA) coating was deposited onto a porous NiTi alloy via dip-coating using a sol-gel procedure with triethyl phosphite and calcium nitrate as phosphorus and calcium precursors, respectively. Adjusting the concentration and viscosity of the sol as well as changing the spin-coating rotational velocity or dip-coating times, enabled uniform coatings with controllable thickness at the sub-micron scale to be successfully deposited on the external surface and within the pores of the porous NiTi alloy. Cross-sectional SEM analysis and EDS characterization of the HA films show that the coating on the inner surface of the pores is thicker than that on the outer surface. The results of an immersion test in a Tris solution show that the HA coating possesses excellent stability, and the rates of Ni ion release through the HA coatings on the porous NiTi alloys of different porosity ratios in a simulated body fluid decrease markedly compared with the uncoated alloys. There is also a remarkable increase in the apatite forming ability of the HA coated porous NiTi alloy in a calcium containing solution.     

Synthesis and characterization of Er doped CaF2 nanoparticles

Er³⁺ doped CaF₂ nanoparticles were synthesized by a chemical co-precipitation method. Effect of the dopant concentrations on the structure and optical properties of the CaF₂ nanoparticles was investigated. The X-ray powder diffraction and transmission electron microscopy analysis was used to characterize the structure and morphology of the nanoparticles. The nanoparticles with different dopant concentration exhibited a sphere-like morphology with diameters of about 8-36 nm. The incorporation of Er³⁺ ions into CaF₂ resulted in the decrease in grain size and deterioration of crystallinity, but enlarged the lattice constants of CaF₂. Additional annealing treatment at 400 °C to the prepared CaF₂ removed the NO₃⁻ and OH⁻ groups adsorbed on the particles’ surfaces, and improved the optical properties of the nanoparticles. The fluorescence intensity, with a maximum at approximately 0.4 mol%, decreased with the increase in doping concentration because of concentration quenching.     

Synthesis and characterization of uniform nanoparticles of γ-Mo2N for supercapacitors

Uniform nanoparticles of molybdenum nitride were synthesized by temperature-programmed reaction(TPR) using MoO3 and ammonia as reactants. This material was characterized by X-ray diffractometry(XRD), transmission electron microscopy(TEM), scanning electron microcopy(SEM) and cyclic voltammetry(CV). Results show that the material consists of a pure phase of γ-Mo2N nanoparticles with average diameter of about 16 nm. The material presents a specific capacitance of 172 F/g in 1 mol/L H2SO4 electrolyte at a scan rate of 1 mV/s and the potential window is broadened to 1.1 V (-0.6 to 0.5 V). At the 6 000th cycle, the material remains 94.9% and 94.7% of the initial capacitance in 1 mol/L H2SO4 and KCl solution, respectively. A possible mechanism comprising surface control and diffusion control is proposed to explain the effect of scan rates on specific capacitance.     

溶剂热法Fe3O4纳米颗粒的制备及表征

以乙醇及水的混和溶剂、单质Fe为原料在高温高压反应釜中制备了Fe3O4纳米颗粒。XRD及红外分析表明所获得产物为Fe3O4。高分辨透射电镜观察表明,Fe3O4具有长棒状形貌,长度为200～500nm,直径为20～30nm。所获得Fe3O4纳米颗粒具有良好的铁磁性能,其饱和磁化强度达到64.75emu/g。讨论了Fe3O4纳米颗粒的形成机制。