Fabrication by Electrophoretic Deposition of Nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> 3D Structure on Carbon Fibers as Supercapacitor Materials

Core–shell nanostructured magnetic Fe₃O₄@SiO₂ with particle size ranging from 3 nm to 40 nm has been synthesized via a facile precipitation method. Tetraethyl orthosilicate was employed as surfactant to prepare core–shell structures from Fe₃O₄ nanoparticles synthesized from pomegranate peel extract using a green method. X-ray diffraction analysis, Fourier-transform infrared and ultraviolet–visible (UV–Vis) spectroscopies, transmission electron microscopy, and scanning electron microscopy with energy-dispersive spectroscopy were employed to characterize the samples. The prepared Fe₃O₄ nanoparticles were approximately 12 nm in size, and the thickness of the SiO₂ shell was?~?4 nm. Evaluation of the magnetic properties indicated lower saturation magnetization for Fe₃O₄@SiO₂ powder (~?11.26 emu/g) compared with Fe₃O₄ powder (~?13.30 emu/g), supporting successful wrapping of the Fe₃O₄ nanoparticles by SiO₂. As-prepared powders were deposited on carbon fibers (CFs) using electrophoretic deposition and their electrochemical behavior investigated. The rectangular-shaped cyclic voltagrams of Fe₃O₄@CF and Fe₃O₄@C@CF samples indicated electrochemical double-layer capacitor (EDLC) behavior. The higher specific capacitance of 477 F/g for Fe₃O₄@C@CF (at scan rate of 0.05 V/s in the potential range of ??1.13 to 0.45 V) compared with 205 F/g for Fe₃O₄@CF (at the same scan rate in the potential range of?~???1.04 to 0.24 V) makes the former a superior candidate for use in energy storage applications.     

A novel poly(o-anisidine)/CoFe2O4 multifunctional nanocomposite: Preparation,characterization and properties

A novel poly(o-anisidine) (POA)/CoFe₂O₄ nanocomposite was synthesized by a facile in situ polymerization of o-anisidine in the presence of CoFe₂O₄ nanoparticles which were obtained by a simple refluxing process in ethylene glycol. The structures of the resulting nanocomposite were investigated by means of X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra. The optical, thermal and magnetic properties of the POA/CoFe₂O₄ nanocomposite were characterized by UV–visible spectrometer, thermogravimetry analyzer (TGA) and vibrating sample magnetometer (VSM). It was indicated the existence of CoFe₂O₄ in the POA/CoFe₂O₄ nanocomposite. The scanning electron microscopy (SEM) observation illustrated that POA layers were wrapped on the surface of CoFe₂O₄ nanoparticles appearing as small aggregated globules. The POA/CoFe₂O₄ nanocomposite exhibited a ferromagnetic behavior under applied magnetic field at room temperature. The saturation magnetization of POA/CoFe₂O₄ nanocomposite was lower than that of pure CoFe₂O₄ nanoparticles due to the contribution of non-magnetic POA layers.     

Synthesis of SnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanomaterials Via High Energy Ball Milling of SnO (Stannous) and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> (Hematite) Solid Precursors

The synthesis of single phase tin-ferrite, SnFe₂O₄, from tin (II) oxide or stannous oxide (SnO), and hematite (α-Fe₂O₃) solid precursors was carried out via high energy ball milling (HEBM) under wet condition involving the addition of controlled amounts of acetone. The stoichiometric amounts of the precursor materials were ball milled continuously for up to 22 h in a Spex-8000D mill using a ball-to-powder ratio of 40:1, with hardened stainless steel balls in WC-lined jars. The time-dependent formation of the SnFe₂O₄ based on combined X-ray diffraction and room temperature Mössbauer spectroscopy (MS) measurements revealed reaction enhancements associated with particles size reduction. The 22 h milled material indicated that synthesized SnFe₂O₄ had a particle size of 10.91 nm, coercivity of 4.44 mT, magnetic saturation/remanent ratio (M _r/M _s) of 0.085, while its superparamagnetic behavior was confirmed based on the combined MS and vibrating sample magnetometer measurements.     

Strontium Ferrite Coupled Solid Acid (SO4 2−/ZrO2-SrFe12O19): Synthesis and Characterization

Magnetic solid acid catalysts (SO₄ ^2?/ZrO₂-SrFe₁₂O₁₉) were synthesized by loading SO₄ ^2?/ZrO₂ onto strontium ferrite (SrFe₁₂O₁₉). The properties of the magnetic solid acid catalysts were investigated with x-ray powder diffraction (XRD), Fourier transformation infrared (FTIR) spectra, vibrating sample magnetometer (VSM), and Brunauer-Emmett-Teller (BET). The catalytic activity of the as-prepared catalyst was probed through synthesis of n-butyl acetate. The results showed that the SrFe₁₂O₁₉ could improve the crystalline phase transition temperature of ZrO₂ and stabilize the metastable tetragonal phase (t-ZrO₂) at 600 °C. The saturation magnetization (M _s) and coercivity (H _c) of catalyst sintered at 600 °C were 16.8 emu/g and 4412 G, respectively, which conduced towards the recovery and reuse of the catalyst. After the catalyst was reused four times, the yield was still more than 70%, which revealed the catalyst had a high activity and better stability.     

The detection of genomic DNA from bacterial cells using iron oxide nanoparticles synthesized by a hydrothermal process

We used iron oxide nanoparticles in order to extract purified DNA from bacterial cells. Magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) are synthesized with FeSO₄·7H₂O via a hydrothermal process and used as a medium to detect DNA. Various characterizations were performed including X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy, vibrating sample magnetometry, and Mössbauer spectroscopy. According to the XRD results, the XRD peaks of the synthesized magnetite and maghemite nanoparticles corresponded well with JCPDS standard data, respectively. The particle size of the iron oxide nanoparticles was about 20 nm, and the particle shape was almost spherical, which was confirmed by observation of the HRTEM image. The magnetite nanoparticles have a face-centeredcubic inverse spinel structure with a space group Fd \(\bar 3\) m, as confirmed by HRTEM and Mössbauer spectroscopy analyses. An agarose gel eletrophoresis analysis was performed to confirm the extraction ability of DNA using these iron oxide nanoparticles, revealing stronger reaction of the maghemite nanoparticles than the magnetite nanoparticles.     

Low Temperature Synthesis of Negative Thermal Expansion Y2W3O12

The effect of variation of transmission ratio (r) in the pulverisette-4 (P4) ball-milling machine on the synthesis of Y₂W₃O₁₂ is reported. Y₂O₃ and WO₃ powders have been milled in a P4 planetary ball mill with different r values, i.e., ?1.5, ?1.75, ?2, ?2.25, ?2.75, and ?3, at a disk revolution speed of 300 rpm for 10 h with toluene as the process control agent. Differential thermal analysis results suggest that the reaction temperature of as-mixed powder is 1000 °C. It decreases down to 845 °C with an increase in the r value up to ?2.25. However, a further increase in the r value results in an increase in the reaction temperature. The average particle size for different r values varies in similar manner and it is found to be around 65 nm for r = ?2.25. XRD analysis of 10 h milled powders with the r value of ?2.25, heat treated at different temperatures confirms the formation of Y₂W₃O₁₂ at 800 °C. The low temperature synthesis leads to retention of finer grain size and hence, helps in good densification and sinterability. The above material shows a negative thermal expansion coefficient of the order of ?7.1 × 10^?6/°C in the temperature range 150-650 °C.     

Preparation and magnetic property of multi-walled carbon nanotube/a-Fe2O3 composites

In order to attain new functional nanomaterials with good magnetic property, multi-walled carbon nanotubes/hematite (MWNTs/α-Fe₂O₃) composites were synthesized using the co-deposition method. MWNTs/α-Fe₂O₃ composites were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), Raman spectroscopy and vibrating sample magnetometry (VSM). The experimental results show that the structure and magnetic properties of the MWNTs/α-Fe₂O₃ composites are related to the heat treatment temperature. MWNTs are modified by α-Fe₂O₃ nano-particles and α-Fe₂O₃ nanorods with a diameter of 10?50 nm after being treated at 450 °C. When the heat treatment temperature exceeds 600 °C, MWNTs are only modified by Fe₃O₄ particles. Furthermore, the MWNTs composites treated at 450 °C and 600 °C have good magnetic behaviour.     

Physicochemical Properties of Li4Ti4.95Zn0.05O12 Anode Material by a Two-Step Solid-State Method

Li₄Ti_5?x Zn _x O₁₂ (x = 0, 0.05) anode materials were prepared by a two-step solid-state method. The structure and over-discharge property of the as-prepared materials were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM), differential capacitance, and galvanostatic charge-discharge measurements. XRD patterns demonstrate that both samples have the phase of Li₄Ti₅O₁₂ with an ordered spinel structure indexed to the cubic Fd3m space group. The lattice parameter of the Li₄Ti_4.95Zn_0.05O₁₂ sample is slightly smaller than that for the pure Li₄Ti₅O₁₂ samples. SEM exhibits that the size of the Zn-doped Li₄Ti₅O₁₂ and pure Li₄Ti₅O₁₂ is about 1-1.5 μm. Charge-discharge tests show that Li₄Ti_4.95Zn_0.05O₁₂ exhibits excellent cycling performance and higher discharge capacity than those of Li₄Ti₅O₁₂ even at different charge-discharge rates. The differential capacitance curves confirm that the zinc doping is beneficial to the reversible intercalation and de-intercalation of Li⁺.     

Investigation of Co-Substituted Nanosized Mn2Y-Hexaferrites Synthesized by Sol-Gel Autocombustion Method

The structural and electrical properties of Co-substituted and nano-sized Y-type hexagonal ferrites have been investigated in the present work. The samples with chemical composition Ba₂Co _x Mn_2?x Fe₁₂O₂₂ (x = 0.0, 0.5, 1.0, 1.5, 2.0) were prepared by sol-gel autocombustion method. The powdered samples and pellets were sintered simultaneously at 1000 °C for 5 h and characterized by means of DTA/TGA, FTIR spectroscopy, x-ray diffraction (XRD), field emission gun scanning electron microscopy, and energy dispersive x-ray spectroscopy. The XRD analysis confirms that the investigated ferrites have single phased Y-type hexagonal structure without showing any impurity phase. Lattice constants (a and c), cell volume (V), crystallite size (D), and x-ray density (ρ _x ) have also been calculated from the XRD data. DC electrical resistivity is measured within the temperature range of 30-100 °C for each sample and is observed to increase with increasing Co-substitution. The dielectric constant (∈) has also been measured which is observed to decrease with Co-substitution. Thus, high electrical resistivity and low dielectric constant make these materials suitable for multi-layer chip inductors and also for RF components and circuits.     

Influence of High Pulsed Magnetic Field on the Dislocations and Mechanical Properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al Composites

At T6 state, Al–Zn–Mg–Cu aluminum matrix composites reinforced with Al₂O₃ particles generated in situ were subjected to high pulsed magnetic fields at different magnetic induction intensities (B = 2, 3 and 4 T). The results show that the dislocation densities in the treated samples increased with increasing B, and the magnetoplastic effect was determined to be the primary cause. The effect of the magnetic field is believed to alter the spin state of free electrons between dislocations and obstacles from the singlet state (associated with high bonding energy) to the triplet state (low bonding energy). The maximum ultimate tensile strength of 532 MPa was obtained at B = 4 T with 30 pulses, which was 20.7% higher than that of the initial sample, primarily because of dislocation strengthening. At B = 2 T, the elongation was at its maximum of 9.3%, representing an increase of 12% compared with the initial sample, while the associated ultimate tensile strength (447 MPa) was still higher than that of the untreated sample (440 MPa). The relationship between mechanical properties and microstructure was analyzed, and the improved properties observed in this work are explained by the transition of the electron spin state and the piling up of dislocations.     

Folate-conjugated Fe3O4 nanoparticles for in vivo tumor labeling

Highly biocompatible superparamagnetic Fe₃O₄ nanoparticles were synthesized by amide of folic acid (FA) ligands and the NH₂-group onto the surface of Fe₃O₄ nanoparticles. The as-synthesized folate-conjugated Fe₃O₄ nanoparticles were characterized by X-ray diffraction diffractometer, transmission electron microscope, FT-IR spectrometer, vibrating sample magnetometer, and dynamic light scattering instrument. The in vivo labeling effect of folate-conjugated Fe₃O₄ nanoparticles on the hepatoma cells was investigated in tumor-bearing rat. The results demonstrate that the as-prepared nanoparticles have cubic structure of Fe₃O₄ with a particle size of about 8 nm and hydrated diameter of 25.7 nm at a saturation magnetization of 51 A·m²/kg. These nanoparticles possess good physiological stability, low cytotoxicity on human skin fibroblasts and negligible effect on Wistar rats at the concentration as high as 3 mg/kg body mass. The folate-conjugated Fe₃O₄ nanoparticles could be effectively mediated into the human hepatoma Bel 7402 cells through the binding of folate and folic acid receptor, enhancing the signal contrast of tumor tissue and surrounding normal tissue in MRI imaging. It is in favor of the tumor cells labeling, tracing, magnetic resonance imaging (MRI) target detection and magnetic hyperthermia.     

Structure and magnetic properties of Cd doped copper ferrite

This report presents the synthesis of copper cadmium ferrite (Cu_1−xCd_xFe₂O_4,x = 0.3, 0.4, 0.5, 0.6 and 0.7) by citrate precursor method and its subsequent characterization by using X-ray diffraction (XRD), electron diffraction spectroscopy (EDS) and vibrating sample magnetometer (VSM) techniques. XRD results confirm the single cubic spinel phase formation with the particle size of 40 nm, which decreased up to 20 nm with increases in Cd content, while the lattice parameter increased with increase in Cd content. By using VSM technique, a significant change in the magnetic properties was observed in CuFe₂O₄ system with Cd doping. It is seen that magnetic field H_C and remnant magnetization M_R increases with increasing concentration up to x = 0.6 except for x = 0.4 and 0.7.     

Preparation of Self-Healing α-Al2O3 Films by Low Temperature Thermal Oxidation

This paper reports a new approach to lowering the temperature necessary for the preparation of α-Al₂O₃. Oxidation of Al–Cr alloys, with Cr contents of 18, 23 and 27 %, was performed at temperatures ranging from 620 to 720 °C in air for 100 h. The resulting oxide films were analyzed by SEM, EDS, XRD and XPS. The results showed that α-Al₂O₃ films were obtained following oxidation of the 18 and 23 wt% Cr alloy samples at 720 °C and that rough surfaces were conducive to the formation of α-Al₂O₃ such that peened surface samples showed significant α-Al₂O₃ growth while polished samples showed no oxide by XRD. A 23 wt% Cr sample with a roughened surface exhibited the formation of α-Al₂O₃ at a temperature of 670 °C. Conversely, only a very thin oxide film was observed on a 27 wt% Cr sample after oxidation at 720 °C.     

Structural,IR, and Magnetic Studies of Annealed Li-Ferrite Nanoparticles

Nanoparticles of spinel Li-ferrite, Li_0.5Fe_2.5O₄, were prepared by sol-gel autocombustion technique and annealed at different temperatures (T _a = 673, 873, and 1073 K), i.e., at relatively low annealing temperatures to control the crystallite size. The saturation magnetization (M _s) increased, and the surface area decreased by increasing the crystallite size, while Curie temperature (T _C) remained almost constant. The critical crystallite size (D _s), 74 nm, which corresponds to a maximum value of coercivity was determined. Samples with crystallite sizes ≤ D _s had low initial permeability μ_i, while the other samples lying in the multidomain region showed very high μ_i values indicating a reversible domain wall displacement mechanism. Hence, the crystallite size plays an important role in changing the physical and magnetic properties of Li-ferrite.     

Combustion synthesis and characterization of highly crystalline single phase nickel ferrite nanoparticles

A combustion route of synthesizing highly crystalline single phase nickel ferrite (NiFe₂O₄) spinel nanoparticles using various amounts of dl-alanine as fuel has been reported in this paper. The role of the amount of fuel is found to be significant in the size control and phase purity of nano crystalline samples. The structural, thermal, morphological and magnetic studies have been carried out. XRD patterns reveal the formation of highly crystalline nano NiFe₂O₄ with high degree of phase purity when fuel concentration is maintained at 1 M and 2 M. FTIR spectra also prove the formation of pure nano NiFe₂O₄. The temperature and fuel effects are found to have strong influence on size, structural, and magnetic properties of materials. The magnetic measurements show that the nano NiFe₂O₄ samples exhibit soft ferromagnetism with the highest saturation magnetization Ms at room temperature as 42.53 emu/g.     

Structural, magnetic and electrical properties of nanocrystalline zinc ferrite

Nanoparticles of ZnFe₂O₄ with grain size of 30 nm have been synthesized via sol-gel auto combustion method and characterized using DSC (differential scanning calorimetry), XRD (X-ray diffraction), SEM (scanning electron microscopy), EDAX (energy dispersive X-ray analysis), FTIR (Fourier transform infrared spectroscopy), VSM (vibrating sample magnetometer) and Ac-electrical conductivity measurement setup. Structural analysis using XRD and FTIR show the formation of spinel structure in nano ZnFe₂O₄ particles. The cation distribution in the sample has been estimated theoretically and the results show that as-prepared nanoparticles of ZnFe₂O₄ have partially inverted ionic distribution in comparison with that of bulk zinc ferrite. Results from EDAX indicate the ratio of Fe:Zn as close to 2:1. The presence of a weak ferrimagnetic phase for nano ZnFe₂O₄ at room temperature has been established from its hysteresis behavior. Redistribution of cations occurring at nano-regime and surface spin canting of nanoparticles of ZnFe₂O₄ are expected to be responsible for the presence of magnetic ordering in nano ZnFe₂O₄. The Curie temperature of nano ZnFe₂O₄ determined from magnetization versus temperature measurement is equal to 375 °C. The electrical conductivity of the present ZnFe₂O₄ at a frequency of 100 kHz at room temperature is observed to be 2.11 × 10⁻⁸ Ω⁻¹ cm⁻¹ which is four orders lesser in magnitude than the value of bulk ZnFe₂O₄. Overall conductivity response with respect to temperature and frequency confirm that ZnFe₂O₄ tends to become more dielectric in the nano-regime.     

Ultrasonic-assisted in situ synthesis and characterization of superparamagnetic Fe3O4 nanoparticles

Superparamagnetic Fe₃O₄ nanoparticles were synthesized via a modified coprecipitation method, and were characterized with X-ray diffraction (XRD), vibrating sample magnetometer (VSM), Zeta potential and FT-IR, respectively. The influences of different kinds of surfactants (sodium dodecyl benzene sulfonate, polyethyleneglycol, oleic acid and dextran), temperatures and pH values on the grain size and properties were also investigated. In this method, Fe³⁺ was used as the only Fe source and partially reduced to Fe²⁺ by the reducing agent with precise content. The following reaction between Fe³⁺, Fe²⁺ and hydroxide radical brought pure Fe₃O₄ nanoparticles. The tiny fresh nanoparticles were coated in situ with surfactant under the action of sonication. Comparing with uncoated sample, the mean grain size and saturation magnetization of coated Fe₃O₄ nanoparticles decrease from 18.4 nm to 5.9-9.0 nm, and from 63.89 emu g⁻¹ to 52-58 emu g⁻¹ respectively. When oleic was used as the surfactant, the mean grain size of Fe₃O₄ nanoparticles firstly decreases with the increase of reaction temperature, but when the temperature is exceed to 80 °C, the continuous increase of temperature resulted in larger nanoparticles. the grain size decreases gradually with the increasing of pH values, and it remains unchanged when the PH value is up to 11. The saturation magnetization of as-prepared Fe₃O₄ nanoparticles always decreases with the fall of grain size.     

Fabrication and magnetic properties of NiFe-ZnO nano-granular films

Excellent soft magnetic and high frequency properties were obtained successfully in the (Ni75Fe25 )x(ZnO)1-x granular films fabricated on the glass substrate by RF magnetron oblique sputtering. The microstructure, mag- netic and high frequency properties were investigated systematically. High resolution transmission electron micrographs show that the film consists of fcc Ni75Fe25 particles uniformly embedded in an amorphous insulating matrix ZnO with particle size a few nanometers. The (Ni75Fe25 ) x(ZnO)1-x films exhibit excellent soft magnetic properties in a wide x range from 0.50 to 0.80 with coercivity not exceeding 5×10-4T, which is ascribed to the exchange coupling between magnetic particles. Especially for the sample with x = 0.64, coercivities in hard and easy axes are 5.0×10-5 and 3.6×10-4 T, respectively, and the electric resistivity ρ reaches 1,790 μΩ·cm. The dependence of complex permeability u = u’ - ju" on frequency f shows that the real part u’ is more than 130 below 500 MHz, and the ferromagnetic resonance frequency fr reaches 1.32 GHz, implying the promising for high frequency application.     

Phase Relations in SiC-AlN-R2O3 (R = Nd, Gd, Yb, Y) Systems

The phase relations in SiC-AlN-R₂O₃ (R = Nd, Gd, Yb, Y) systems were determined by XRD and EPMA analyses of the solid-state reacted samples from powder mixtures of SiC, AlN and various R₂O₃. Subsolidus phase diagrams of these systems were established. In the Nd-system by Si-C partially substituted for Al-N in Nd₂AlO₃N, the formation of solid solution with formula Nd₂Al_1?x Si _x O₃N_1?x C _x (x = 0-0.5) was first found. Impurities of Al₂O₃ and SiO₂ from AlN and SiC starting powders respectively often caused the formation of some salt compounds, RAP type (R = Nd) and RAM type (R = Gd, Yb, Y), in corresponding systems. Mechanism of the reactions of forming salt compounds and their relations with rare earth oxides series are discussed.     

Air Plasma-Sprayed Yttria and Yttria-Stabilized Zirconia Thermal Barrier Coatings Subjected to Calcium-Magnesium-Alumino-Silicate (CMAS)

Yttria (Y₂O₃) and zirconia (ZrO₂) stabilized by 8 and 20 wt.%Y₂O₃ thermal barrier coatings (TBCs) subjected to calcium-magnesium-alumino-silicate (CMAS) have been investigated. Free-standing Y₂O₃, 8 and 20 wt.%YSZ coatings covered with synthetic CMAS slurry were heated at 1300 °C in air for 24 h in order to assess the effect of Y₂O₃ on the corrosion resistance of the coatings subjected to CMAS. The microstructures and phase compositions of the coatings were characterized by SEM, EDS, XRD, RS, and TEM. TBCs with higher Y₂O₃ content exhibited better CMAS corrosion resistance. Phase transformation of ZrO₂ from tetragonal (t) to monoclinic (m) occurred during the interaction of 8YSZ TBCs and CMAS, due to the depletion of Y₂O₃ in the coating. Some amounts of original c-ZrO₂ still survived in 20YSZ TBCs along with a small amount of m-ZrO₂ that appeared after reaction with CMAS. Furthermore, Y₂O₃ coating was found to be particularly highly effective in resisting the penetration of molten CMAS glass at high temperature (1300 °C). This may be ascribed to the formation of sealing layers composed of Y-apatite phase [based on Ca₄Y₆ (SiO₄)₆O and Y_4.67(SiO₄)₃O] by the high-temperature chemical interactions of Y₂O₃ coating and CMAS glass.