Fe2O4 Nanopowders Research Articles

Effect of particle size distribution on the structure, hyperfine, and magnetic properties of Ni0.5Zn0.5Fe2O4 nanopowders

Ni0.5Zn0.5Fe2O4 nano powders were synthesized by an auto combustion method and then heat treated at different temperatures in air for a fixed time. As a consequence, a distribution in particle size and strain was incorporated within the specimens, as estimated from the Rietveld refinement analysis of the powder x-ray diffraction data. The changes in the microstructure and crystal structure parameters were carefully extracted through the refinement analysis. Thermal annealing causes increment in the dispersion and mean of the size distribution. Reallocation of cations in the lattice sites occur as a consequence of the heat treatment which was manifested in their altered unit cell length (a), r.m.s. strain (⟨ε2⟩1/2), oxygen positional parameter (u), metal-oxygen bond lengths (ROA and ROB), and the band positions (ν1and ν2) in the vibrational spectroscopy. We also investigate the hyperfine and magnetic properties of the samples using different instrumental techniques (with different operating time scales) like Mössbauer spectroscopy, electron paramagnetic resonance spectroscopy, and superconducting quantum interference device magnetometry. Results show that the effect of particle size distribution was manifested in their hyperfine field distribution profile, paramagnetic resonance spectra, and magnetic anisotropy energy distribution profile. Co-existence of superparamagnetic and ferrimagnetic phase was recorded at room temperature in the samples when annealed at lower temperature. However, with increase in annealing temperature, the nature of the size distribution changes and ferrimagnetic ordering predominates for the larger size nanoparticles. Thus, the effect of particle size distribution on the structural, hyperfine, and magnetic properties of various Ni0.5Zn0.5Fe2O4 nanoparticles was investigated herein which hitherto has not been discussed in the literature.

Synthesis, characterization and catalytic activity of Al/Fe2O3 nanothermite

Nanothermites have attracted much attention owing to their excellent sensitivity and catalytic activity. In this paper, Fe2O3 is used to achieve Al/Fe2O3 nanothermite by mixing nano-Al with Fe2O3 nanopowder. X-ray diffraction, field emission gun scanning electron microscopy, energy dispersive X-ray spectra, and transmission electron microscopy were employed to study the structural features of the nanothermite. Its catalytic activity was investigated on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellants (CSPs) using thermogravimetric analysis (TG), TG coupled with differential scanning calorimetry, and ignition delay measurements. Kinetics of thermal decomposition of AP with and without Al/Fe2O3 has also been investigated using model fitting and isoconversional methods which have been applied to data for isothermal TG decomposition. Activation energy values have been found to be lowered in case of AP + Al/Fe2O3. The results revealed enhancement in the rate of decomposition of AP and CSPs.

Enhanced hydrogen storage properties of 4MgH2 + LiAlH4 composite system by doping with Fe2O3 nanopowder

In this paper, the hydrogen storage properties and reaction mechanism of the 4MgH2 + LiAlH4 composite system with the addition of Fe2O3 nanopowder were investigated. Temperature-programmed-desorption results show that the addition of 5 wt.% Fe2O3 to the 4MgH2 + LiAlH4 composite system improves the onset desorption temperature to 95 °C and 270 °C for the first two dehydrogenation stage, which is lower 40 °C and 10 °C than the undoped composite. The dehydrogenation and rehydrogenation kinetics of 5 wt.% Fe2O3-doped 4MgH2 + LiAlH4 composite were also improved significantly as compared to the undoped composite. Differential scanning calorimetry measurements indicate that the enthalpy change in the 4MgH2–LiAlH4 composite system was unaffected by the addition of Fe2O3 nanopowder. The Kissinger analysis demonstrated that the apparent activation energy of the 4MgH2 + LiAlH4 composite (125.6 kJ/mol) was reduced to 117.1 kJ/mol after doping with 5 wt.% Fe2O3. Meanwhile, the X-ray diffraction analysis shows the formation of a new phase of Li2Fe3O4 in the doped composite after the dehydrogenation and rehydrogenation process. It is believed that Li2Fe3O4 acts as an actual catalyst in the 4MgH2 + LiAlH4 + 5 wt.% Fe2O3 composite which may promote the interaction of MgH2 and LiAlH4 and thus accelerate the hydrogen sorption performance of the MgH2 + LiAlH4 composite system.

Combustion synthesis of Co2 + substituted Li0.5Cr0.5Fe2O4 nano-powder: Physical and magnetic interactions

Nanocrystalline ferrite powders of Co2+ substituted Li0.5Cr0.5Fe2O4 were synthesized by sol-gel auto-combustion method. The samples were obtained by annealing at relatively low temperature at 600°C and investigated by XRD, TEM, IR, magnetization, and dielectric and resistivity measurements. Lattice parameter, X-ray density, crystallite size and bulk density are found to increase, whereas specific surface area and porosity size showed the decreasing trend with the Co2+ substitution. Splitting of major absorption bands related to Li+ substituted ferrites was observed in IR spectra. Site occupancy is obtained from XRD and the variation of the cation distribution has been discussed on the basis of site preference of the substituting cations. Substitution of the magnetic Co2+ ions considerably improved the magnetic properties; as reflected by the advancement in the values of saturation magnetization and coercivity. The variation of the magneton number with the Co2+ content is satisfactorily explained on the basis of Néel's collinear spin ordering model. Resistivity plots show the semiconducting nature of the synthesized samples. The observed variation in resistivity is explained by Verwey hopping mechanism. The dielectric constant and dielectric loss tangent were also studied as a function of temperature.

Preparation of pure iron/Ni–Zn ferrite high strength soft magnetic composite by spark plasma sintering

A dense microcellular structure is fabricated using micron-sized pure iron powder cladded with 10wt% Zn0.5Ni0.5Fe2O4 nanopowder by filling the pure iron with Ni–Zn-ferrites composite and subjecting the mixture to a temperature of 600°C. The SEM image shows that the thickness of cell wall is in the range of 1.0–2.0μm, and the inner dimension of the alloy is in the range of 15–40μm. By coating Ni–Zn-ferrites, the electrical resistivity is increased. The composite exhibits not only good soft magnetic properties but also good mechanical strength.

Facile hydrothermal synthesis of core/shell-like composite SrFe12O19/(Ni, Zn)Fe2O4 nanopowders and their magnetic properties

SrFe12O19/(Ni, Zn)Fe2O4 nanopowders with exchange coupling were synthesized via a facile hydrothermal method, and their structural and magnetic properties were studied. It is found that only when the mass ratio of SrFe12O19 to (Ni, Zn)Fe2O4 is 2 : 1, the specimen exhibits a two-phase composite structure. The synthesized composites are quite stable under high temperatures lower than 950 °C. It is also found that the nanocomposites exhibit a core/shell-like structure, and both the saturation magnetization and coercivity are greatly influenced by the content of soft phase and impurity.

Control of the Crystal Phase Composition of FexOyNanopowders Prepared by CO2Laser Vaporization

Crystalline magnetic iron oxide nanopowders are prepared by CO2 laser vaporization (LAVA) of a hematite (α-Fe2O3) raw powder. Condensation at normal pressure leads to maghemite (γ-Fe2O3) as the main phase in the nanopowders. With an increasing oxygen partial pressure in the zone of condensation, an increasing amount of Fe2O3 polymorph ε-Fe2O3 is found. The LAVA-prepared Fe2O3 nanopowders are characterized by X-ray diffraction, transmission electron microscopy, and chemical analysis and with respect to their magnetic properties. A mechanism for the initial nucleation is proposed to explain the formation of ε-Fe2O3 with an increasing oxygen content in the condensation atmosphere. The model is based on the evidence of ozone in oxygen-rich condensation atmospheres. Density functional theory calculations indicate that ozone facilitates the formation of 6-fold oxygen-coordinated Fe ions acting as building units for the emerging crystal structure during the solidification of the nanoparticles. This insight into early nucleation stages will be useful for the functional design and crystal engineering of either isostructural materials like alumina (Al2O3) or, more generally, vapor phase synthetic routes for ceramic materials.

Magnetoelectric Properties of BaTiO<sub>3 </sub>– Co<sub>0.5</sub>Ni<sub>0.5</sub>Fe<sub>2</sub>O<sub>4</sub> Composites Prepared by the Conventional Mixed Oxide Method

Multiferroics, which display simultaneous ferrimagnetic and ferroelectric properties, have been interesting recently because of their potentially significant applications in multifunctional devices such as magnetic resonance, drug delivery, high-density data storage, ferrofluid technology, etc. Composites combining BaTiO3 with Co0.5Ni0.5Fe2O4 have influenced the interest of many researchers, due to their outstanding and distinguished character called magnetoelectric (ME). In this work, ferrimagnetic-ferroelectric composites of BaTiO3 nanopowder and Co0.5Ni0.5Fe2O4 nanopowders were prepared by a conventional mixed oxide method. The multiferroic ceramics were compounded with the formula, (1-x)BaTiO3-(x)Co0.5Ni0.5Fe2O4, in which x = 0, 0.05, 0.10, 0.20 and 0.35. All of the compositions were analyzed by an X-ray diffractometer (XRD) in order to reveal the phase of perovskite and spinal structure. Scanning electron microscopy (SEM) was used to examine the variation of morphology and grain size of the composited ceramics. The magnetism of all the ceramics was measured using a vibrating sample magnetometer (VSM). The results showed that microstructure and the amount of ferrite are related strongly with magnetization.

Atomic layer deposited thin film metal oxides for fuel production in a solar cavity reactor

Alumina thin film structures were produced by coating high surface area polymer particles via atomic layer deposition (ALD), using the polymer as a sacrificial template. Burnout of the polymer material left high surface area, high pore volume structures, with 15 nm wall thickness. Further deposition of up to 27 mol% Co and Fe was performed via ALD to produce high surface area CoFe2O4 particles for thermochemical water splitting. The ALD particles were thermally cycled in electrically heated lab reactors and on-sun using a concentrated solar, reflective cavity reactor. Surface area measurements of cycled ALD particles showed improved surface area retention as compared to bulk Fe2O3 nanopowders. Reaction rates as high as 15.2 and 9.8 μmol/s/g were observed, on-sun, for H2O and CO2 splitting respectively. Thermochemical cycling in a concentrated solar cavity reactor showed an order of magnitude increase in solar utilization efficiency between ALD particles and bulk Fe2O3 nanopowders.

Synthesis and Magnetic Properties of Co0.5Zn0.5Fe2O4 Nanoparticles by Template-Assisted Combustion Method

In the present article, zinc cobalt ferrite (Co0.5Zn0.5Fe2O4) nanopowders were synthesized by a template-assisted citric combustion method. Polyethylene Glycol (PEG-4000) and carboxymethyl cellulose (CMC) were used as the templating agents for controlling the anisotropy and the microstructure of the Co0.5Zn0.5Fe2O4 nanopowder. The synthesized nanopowders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and a vibrating sample magnetometer (VSM). The results indicated that pure samples were obtained at calcining temperature of 700°C and the templates remarkably changed microstructure and magnetic behavior of the nanopowders. All of the powders synthesized were ferromagnetic. The powder synthesized with template PEG-4000 had a smallest coercivity (75 Oe) but largest magnetization (80.3 emu · g−1) close to that of bulk material. The powders synthesized without template exhibited moderate coercivity (1864 Oe) and smallest magnetization (53.2 emu · g−1). A largest coercivity (3986 Oe) and a moderate magnetization (60.9 emu · g−1) were observed when the template CMC was used. The variation in the magnetic nature of the powders can be related to their anisotropy growth and average particle size.

Nano-structured Mg-doped Fe2O3–ferrihydrite powder – a new adsorbent for cation removal from aqueous solutions

The present studies were undertaken with a view to developing a low-cost, efficient adsorbent for removal of heavy metal ions from aqueous solutions. A new cost-effective nano-structured Mg-doped Fe2O3–ferrihydrite adsorbent exhibiting high uptake capacities for various cations was synthesized. After preliminary testing of a series of Mg-doped (0.38 to 0.98%) samples for Pb(II), Cd(II), Cu(II) or Co(II) adsorption, a typical sample containing 55.7% Fe and 0.38% Mg was chosen for detailed characterization studies (XRD, TG-DTA, FTIR and TEM techniques). The adsorption behaviour of cations on the prepared nano powder was studied under various experimental conditions. The generated data were fitted to kinetic and isotherm models. The Langmuir monolayer capacities were 99.1, 83.3, 111.1 and 151.5 mg/g for Pb(II), Cd(II), Cu(II) and Co(II), respectively. It is the first time that such a high loading capacity for Co(II) has been reported. The effect of the presence of chloride or sulphate was dependent on the nature of the cation. Lead(II) adsorption was endothermic in nature with increased randomness at the solid–liquid interface, while for the rest of the three cations the adsorption process was exothermic. The XRD and FTIR studies on the loaded samples revealed structural changes during the adsorption process. The high cation loading capacities along with the stability of the loaded adsorbent make the synthesized ferrihydrite–Fe2O3 nano powder a potential candidate for contaminated water purification.

Comparison study on magnetic property of Co0.5Zn0.5Fe2O4 powders by template-assisted sol–gel and hydrothermal methods

The nickel cobalt ferrite (Co0.5Zn0.5Fe2O4) nanopowders were synthesized by a sol–gel method and a hydrothermal method. Polyethylene glycol (PEG-4000) and carboxymethyl cellulose (CMC) were used as the templating agents for controlling the anisotropy and the microstructure of the Co0.5Zn0.5Fe2O4 nanopowders. The microstructure and magnetic property of the synthesized powders were comparatively studied. The results indicated that the synthesis technique and the template had remarkable dependence on the microstructure and the magnetic property of the nanopowders. The powder synthesized by the sol–gel method without any template had a maximum saturation magnetization of 73.6 emu g−1 closing to the value of the bulk material (80 emu g−1), while the PEG-4000 and CMC decreased the magnetization to 54.0 and 60.9 emu g−1. The three powders showed almost same coercivity (314–343 Oe). However, the PEG-4000 and CMC in the hydrothermal process obviously decreased and increased the coercivity respectively from 1,464 Oe to 5 Oe and 4,304 Oe but had small effect of the magnetization (55.5–59.0 emu g−1).

Interaction of diamond with ultrafine Fe powders prepared by different procedures

We have studied the interaction of synthetic diamond crystals with ultrafine Fe powders during catalytic diamond gasification in a hydrogen atmosphere at 900°C. The Fe powders were prepared by three procedures: reduction of Fe2O3 nanopowder; evaporation using an ELV-6 electron accelerator, followed by condensation; and reduction of ferric chloride. The surface-processed diamond crystals were examined by electron microscopy. The results indicate that ultrafine powders produced by the first two procedures cause predominantly lateral etching of diamond. The Fe particles prepared by the third procedure penetrate into the bulk of diamond crystals and produce etch pits and “tunnels,” thereby markedly increasing the specific surface area of the crystals.

Fabrication of α-Fe2O3 Nanopowder Modified Glassy Carbon Electrode for Applications in Electrochemical Sensing

In the present study, Fe2O3 nanopowder has been grown by Ultrasonic mist chemical vapor deposition (UM-CVD), which is a promising method for large area deposition at low temperatures taking in to account of its simplicity, inexpensiveness and safety. Room temperature XRD results revealed prominent hematite phase with intense (104) reflection and was also in agreement with the HR-TEM results. In situ high temperature X-ray diffraction (XRD) studies clearly indicated the change of phase from hematite to magnetite as the temperature increases above 300 degrees C. The surface morphology and particle size distribution of Fe2O3 nanopowder were characterized using field emission scanning electron microscope (FE-SEM) and high resolution transmission electron microscope (HR-TEM), which revealed that the particles were spherical in nature and distributed in range of 50-100 nm. SQUID magnetometry results indicate the ferromagnetic nature of the nanopowder with crystallite size of 6 nm as calculated from M-H curve. Transmittance of approximately 55% and estimated direct band gap of 2.5 eV was observed. Further, the nanopowder was used to modify glassy carbon electrode (GCE) and the modified electrode was found to exhibit electrocatalytic activity for the oxidation of dopamine. It is expected that the nanopowder will exhibit promising applications in the development of sensors.

SYNTHESIS OF MONODISPERSED IRON OXIDE PARTICLES BY A LARGE-SCALE MICROWAVE REACTOR

Well-defined mondispersed iron oxide particles can be synthesized in conventional hydrolysis approaches, but the synthesis generally takes two to seven days. Microwave hydrothermal approaches offer the possibility of significantly reducing synthesis time. This work demonstrates the feasibility of microwave synthesis in large scale. The batch size was 5 L, and the holding time was two hours. The crystallinity of the powders and the morphology and the monodispersity of the synthesized particles were comparable to those produced from conventional approaches. The particle size was in the nanosize range. The results indicated that for synthesis of monodispersed Fe2O3 nanopowders, it is possible to achieve the production rate of a 2.1 m3 conventional reactor with a 5 L microwave accelerated reactor.

Surface Segregation in SnO2–Fe2O3 Nanopowders and Effects in Mössbauer Spectroscopy

AbstractSnO2–Fe2O3 nanopowders prepared by the polymeric precursor method were studied by combined conventional and high‐resolution techniques. The powders treated at 500 °C were analyzed by EDS local probe associated with HRTEM to directly detect surface segregation of Fe ions onto SnO2 nanoparticles over a broad range of concentrations. The segregation of these ions controls the system microstructure by changing the surface energies and acting as nucleation sites for the formation of a Fe oxide phase (magnetite) at high Fe concentrations. A technologically interesting core–shell‐type particle structure, with a magnetic shell and semiconductor core, was observed for the first time. The influence of the segregated Fe ions in Mössbauer spectra is also addressed as a new proposal for the interpretation of the effects of composition changes in both the bulk and at the interface of particles. In this proposal, the two observed sites in Mössbauer spectra would be independently related to bulk‐substituted and surface‐segregated Fe ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Mössbauer Spectroscopy in Study of Thermally Induced Crystallization of Amorphous Fe<sub>2</sub>O<sub>3</sub> Nanoparticles

Fe Mossbauer spectroscopy is demonstrated as an effective tool in the identification, magnetic and structural characterization of iron(III) oxides formed by thermally induced oxidative decomposition of FeC 2O4·2H 2O and by the secondary crystallization of amorphous Fe 2O3 nanopowder. AFM measurements revealed that the primary amorphous nanoparticles are between 1 and 3 nm, in accordance with the large surface area of 250 m 2 /g as determined by BET analysis. The temperature depended Mossbauer measurements of amorphous Fe 2O3 showed the magnetic transition temperature lower than 70 K with the sharp evolution of the spectral lines between 53 and 76 K as typical for ultrafine and strongly interacted particles. As the primary crystallization product at low temperatures, γ-Fe 2O3 (maghemite) was identified by XRD. The broad distribution of magnetic fields in Mossbauer spectra illustrates the broad size distribution of maghemite nanoparticles. The thermally stable α-Fe 2O3 (hematite) can be produced by the direct crystallization of amorphous phase at higher temperatures or by the structural transformation of the primarily formed maghemite at lower temperatures. Particles of hematite formed at 200 °C reveal the Morin transition temperature suppressed below 20 K corresponding to the size about 20 nm.

Properties of Cu-Ni ferrite nanopowders prepared by coprecipitation method with ultrasound irradiation

Cu–Ni ferrite(Cu1−xNixFe2O4) nanopowders were synthesized by coprecipitation method with ultrasound irradiation. They were composed of a spinel phase having a spherical shape with the grain size of 20 ∼ 40 nm. The specific surface area of the nanopowders showed a tendency of decreasing with increasing Ni content (x). The maximum value of saturation magnetization was 73.5 emu/g at x = 0.5. The reflection loss was higher than 10 dB in the frequency range from 2.5 GHz to 5.5 GHz. The maximum reflection loss of 25 dB was observed at x = 0.5. Thermogravimetric analysis of the Cu1−xNixFe2O4 nanopowders for both H2 reduction and CO2 decomposition reaction was carried out with Cahn vacuum electrobalance system. The maximum CO2 decomposition occurred in the Cu0.5Ni0.5Fe2O4 nanopowder. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of heating conditions during combustion synthesis on the characteristics of Ni0,5Zn0,5Fe2O4 nanopowders

Ni-Zn ferrite powders were synthesized by combustion reaction. The effect of external conditions of heating on the characteristics of the resulting powders was evaluated. Two synthesis routes were studied. The first involved preheating on a hot plate at 300°C and subsequently heating in a muffle furnace at 700°C (RCPM). In the second route the powders (RCP) were heated directly to 600°C on a hot plate until self-ignition occurred. The resulting RCP products were evaluated before and after attritor milling in order to reduce the size and increase the uniformity of particles and/or agglomerates. The resulting powders were characterized by X-ray diffraction (XRD), BET, scanning electron microscopy (SEM), helium pycnometry, sedimentation and transmission electron microscopy (TEM). The results showed that it was possible to obtain Ni-Zn ferrite powders using both routes and that the second route (RCP) was the most favorable in terms of obtaining powders with high surface area. The efficiency of the grinding was confirmed by the reduction of the size of the particles.