Magnetic study above the curie temperature of γ-Fe2O3 in determining the dispersion nature of Co2+ ions in Co-modified γ-Fe2O3 thin films

Gamma (γ) iron oxide thin films containing 6 at% of cobalt atoms selectively dispersed at interstitial and octahedral locations have been prepared by a reactive chemical vapour deposition process. Such dispersion gives microscopic Co-trapped and Co-doped regions inγ-Fe₂O₃ matrix and introduces magnetocrystalline anisotropy leading to high coercivity values of 64–112 kA/m. Temperature dependence of coercivity and saturation magnetization forγ-Fe₂O₃ films confirm the dispersion model. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Synthesis and characterization of γ-Fe2O3 — a magnetic tape material

Acicular FeC₂O₄ · 2H₂O was precipitated from glycerol and starch media. Thermal decomposition of this oxalate in dry and moist nitrogen yielded primarily FeO and Fe₃O₄ respectively. Characterization was attempted through DTA, TG, x-ray diffraction, TEM and magnetization studies. It was found that the oxalate can be completely decomposed to Fe₃O₄ in moist nitrogen (P_{H 2}O ∼ 35 torr) at 775 K and then oxidised by dry air to acicular γ-Fe₂O₃ at 575 K. The resulting material has saturation magnetization (∼ 70 emu/g), coercive field (∼ 300 Oe) and squareness ratio (∼ 0·60–0·65), which values art comparable with those of the commercial samples.     

Low temperature Mössbauer studies on magnetic nanocomposites

Nanocomposites with magnetic components possessing nanometric dimensions, lying in the range 1–10 nm, are found to be exhibiting superior physical properties with respect to their coarser sized counterparts. Magnetic nanocomposites based on gamma iron oxide embedded in a polymer matrix have been prepared and characterized. The behaviour of these samples at low temperatures have been studied using Mössbauer spectroscopy. Mössbauer studies indicate that the composites consist of very fine particles of γ-Fe₂O₃ of which some amount exists in the superparamagnetic phase. The cycling of the preparative conditions were found to increase the amount of γ-Fe₂O₃ in the matrix.     

Dielectric,electrical and infrared studies of γ-Fe2O3 prepared by combustion method

This paper reports the electrical and spectroscopic investigation of the gamma ferrite synthesized through combustion route. The electrical study and dielectric behaviour showed a typical ferrite nature for the samples. The γ → α transition is observed from the electrical conductivity data. Infrared spectral study showed the transition of a typical ferrite. The effect of the presence of α-impurities in γ-Fe₂O₃ is also explained here.     

Synthesis and photocatalytic activity of cobalt oxide doped ZnFe2O4-Fe2O3-ZnO mixed oxides

Novel cobalt oxide doped ZnFe₂O₄-Fe₂O₃-ZnO mixed oxides with the Zn/Fe molar ratio of 1/2 were synthesized with a citric acid complex method. The effects of cobalt oxide and calcination temperature on phase composition and photocatalytic activity of the mixed oxides were investigated. X-ray diffraction (XRD) analysis revealed that there were mainly ZnFe₂O₄, α-Fe₂O₃, amorphous ZnO and Fe₂O₃ in the 6 mol% cobalt oxide doped products calcined at 500 °C. 5-10 mol% cobalt oxide doping could significantly enhance the formation of ZnFe₂O₄ and altered the phase composition of the mixed oxides. Experimental results showed that cobalt oxide doping could remarkably improve the photocatalytic activity of the mixed oxides for phenol degradation. The 6 mol% cobalt oxide doped mixed oxides calcined at 500 °C exhibited better photocatalytic activity as compared with other samples.     

A new combustion route to γ-Fe2O3 synthesis

A new combustion route for the synthesis of γ-Fe ₂ O ₃ is reported by employing purified a-Fe ₂ O ₃ as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe ₂ O ₃ .The as synthesized γ-Fe ₂ O ₃ is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on magnetic properties is also presented.     

Optoelectronic properties of β-Fe2O3 hollow nanoparticles

The effect of hollow structure on the optoelectronic properties of β-Fe₂O₃ hollow nanoparticles (HNPs) was determined. Spectrophotometry showed that the optical transmittance of the β-Fe₂O₃ HNPs was less than 40% in the visible-light region. This opaqueness was suggested to be an optical characteristic, commonly found in the authors' previous studies of TiO₂ and δ-Al₂O₃ HNPs. In addition, β-Fe₂O₃ HNPs had a band gap (1.86 eV) between amorphous (1.73 eV) and polycrystalline (1.97 eV) β-Fe₂O₃ thin films, which was a 5–7 nm thick shell that embraced an intermediate volume of the crystal phase, in-between the two thin films.     

Optical and magnetic properties of elliptical hematite (α-Fe2O3) nanoparticles coated with uniform continuous layers of silica of different thickness

Elliptical-type α-Fe₂O₃ nanoparticles with/without silica shell have been prepared. The core particles were coated with uniform continuous layers of silica of two different thicknesses by hydrolysis of TEOS. The obtained HCP structure elliptical α-Fe₂O₃ nanoparticles with ∼ 240 nm length and 100 nm width is polycrystalline in nature. The thicknesses of SiO₂ shell coated on α-Fe₂O₃ are about 55 and 30 nm, respectively. The optical and magnetic properties of these nanoparticles have been investigated.     

Preparation and characterization of γ-Fe2O3/ZnO composite particles

γ-Fe₂O₃/ZnO composite particles were prepared via a simple solution method using surface-modified γ-Fe₂O₃ nanoparticles as seeds. The phases and purity of the as-prepared γ-Fe₂O₃/ZnO composite particles were characterized by XRD analysis, and the morphology was studied by SEM, which showed that the γ-Fe₂O₃/ZnO composites are of typical sphere-like morphology with diameters in the range of 300-400 nm. The γ-Fe₂O₃/ZnO composites exhibit magnetic response to an external magnet field and efficient characteristic emissions of ZnO under UV excitation, respectively, indicating that these nontoxic, emissive and magnetic nanoparticles may find use as chemical/biological sensors especially in areas that directly impact human health.     

Preparation and application of novel magnetically separable γ-Fe2O3/activated carbon sphere adsorbent

Magnetic γ-Fe₂O₃/activated carbon microspheres have been synthesized by an activation process of carbon microspheres containing iron oxides, which were prepared by hydrothermal method. The structure and morphology of the magnetic porous carbon microspheres were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), thermogravimetry and differential thermal analysis (TG-DTA) and N₂ adsorption-desorption technique. The results showed that the as-prepared activated carbon spheres were the composite of single-phase γ-Fe₂O₃ and activated carbon material, and the content of carbon was about 3.87%. Using methyl orange as model pollutant, the magnetic porous carbon microspheres showed good adsorption capacities of 44.65 mg/g. The isotherm evaluations revealed that the Langmuir model attained better fits to the experimental equilibrium data than the Freundlich model. These magnetic porous carbon microspheres could potentially be applied in separation processes.     

Synthesis and characterisation of γ-Fe2O3 nanowire arrays via a versatile,simple and low-cost method

γ-Fe₂O₃ nanowire arrays embedded in anodic alumina template were fabricated by an improved sol–gel method. The morphologies, structures and magnetic behaviour of the as-prepared products were investigated by X-ray powder diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy and magnetic hysteresis analysis. The results show that arrayed γ-Fe₂O₃ polycrystalline nanowires with an average diameter about 40?nm and an average length about 0.5?µm were prepared. A number of superparamagnetic nanoneedles grew along the nanowires. The ordered one-dimensional arrays weaken the superparamagnetic effect. In addition, a possible formation mechanism about nanowires is proposed. The charge factor, gravity effect and molecular heat movement impelled the Fe sols filling into the pores of the template. γ-Fe₂O₃ nanowire arrays look forward to the applications of magnetic recording in the future.     

Structural behavior of laser-irradiated γ-Fe2O3 nanocrystals dispersed in porous silica matrix : γ-Fe2O3 to α-Fe2O3 phase transition and formation of ε-Fe2O3

The effects of laser irradiation on γ-Fe₂O₃ 4 ± 1 nm diameter maghemite nanocrystals synthesized by co-precipitation and dispersed into an amorphous silica matrix by sol-gel methods have been investigated as function of iron oxide mass fraction. The structural properties of γ-Fe₂O₃ phase were carefully examined by X-ray diffraction and transmission electron microscopy. It has been shown that γ-Fe₂O₃ nanocrystals are isolated from each other and uniformly dispersed in silica matrix. The phase stability of maghemite nanocrystals was examined in situ under laser irradiation by Raman spectroscopy and compared with that resulting from heat treatment by X-ray diffraction. It was concluded that ε-Fe₂O₃ is an intermediate phase between γ-Fe₂O₃ and α-Fe₂O₃ and a series of distinct Raman vibrational bands were identified with the ε-Fe₂O₃ phase. The structural transformation of γ-Fe₂O₃ into α-Fe₂O₃ occurs either directly or via ε-Fe₂O₃, depending on the rate of nanocrystal agglomeration, the concentration of iron oxide in the nanocomposite and the properties of silica matrix. A phase diagram is established as a function of laser power density and concentration.     

Enhancement investigations on thermal properties of PMMA/PE composite film reinforced with nano ɤ-Fe2O3 nanoparticles

ABSTRACT

In the present study, PMMA/PE-?-Fe₂O₃ nanocomposites of various compositions were produced through ultrasound-assisted technique. Thermogravimetric analysis and UV-visible results indicated that the thermal stability is enhanced distinctly, without a sacrifice in optical clarity. The improvement of thermal properties was attributed to the homogeneous and good dispersion of ?-Fe₂O₃ nanoparticles in PMMA/PE/?-Fe₂O₃. And the excellent thermal properties performance of the ?-Fe₂O₃ fillers improved the tribological properties of PMMA/PE composites.     

Fabrication of shape-controlled α-Fe2O3 nanostructures by sonoelectrochemical anodization for visible light photocatalytic application

In this study, various α-Fe₂O₃ (hematite) nanostructures were prepared on Fe foils by sonoelectrochemical anodization method. The principal component of the electrolyte was ethylene glycol contained 0.3 wt.% NH₄F. The α-Fe₂O₃ surface shapes have been controlled by varying the water volume ratios (WVR) in electrolyte solution. The α-Fe₂O₃ samples were characterized by field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, grazing incidence x-ray diffraction, and UV-vis absorbance spectra. As the variation of WVR, the α-Fe₂O₃ samples showed different surface morphologies of nanoparticles, nanorods, nanoporous, and nanoleaflets. The visible light photocatalytic activity of the α-Fe₂O₃ nanostructures was investigated by degradation of methylene blue, and the α-Fe₂O₃ nanoporous sample showed the best photocatalytic performance.     

Fabrication and structure characterization of MnCO3/α-Fe2O3 nanocrystal heterostructures

Novel MnCO₃/α-Fe₂O₃ nanocrystal heterostructures, with MnCO₃ nanorods 5-10 nm in diameter and 15-50 nm in length, grown onto the surfaces of the α-Fe₂O₃ nanohexahedrons sized around 30-50 nm, were fabricated via a two-step solvothermal route. The coalescent planes of the heterostructure for the MnCO₃ nanorod and the α-Fe₂O₃ nanohexahedron were determined to be (01?4) and (110), respectively. The formation of the MnCO₃ nanorods from the Mn contained amorphous flakes was tracked by transmission electron microscopy observations at various reaction stages, which suggested a rolling-broken-growth process. Evidenced by the comparative experimental result, the α-Fe₂O₃ nanohexahedrons played an important role in inducing the nucleation and growth of the hexagonal MnCO₃ nanorods on their surfaces.     

Preparation and characterization of hollow α-Fe2O3 irregular microspheres

Hollow α-Fe₂O₃ irregular microspheres were prepared at 160 °C from a hydrolyzing Fe(ClO₄)₃ solution by adding sodium polyanethol sulphonate. The particles were characterized by ⁵⁷Fe Mössbauer, X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The walls of these hollow particles consisted of elongated subunits composed of elongated and thin α-Fe₂O₃ rods. The precipitation of hollow α-Fe₂O₃ irregular microspheres was governed by the preferential adsorption of sulphonate/sulphate groups. The lateral aggregation of elongated thin rods and subunits also played an important role in the formation of hollow α-Fe₂O₃ irregular microspheres.     

Preparation and characterization of α-Fe2O3 nanorod-thin film by metal-organic chemical vapor deposition

Alpha iron oxide (α-Fe₂O₃) films were grown on catalyst-free silicon substrate using a vertical type metal-organic chemical vapor deposition process. X-ray powder diffraction and field-emission transmission electron microscopy measurements showed that these α-Fe₂O₃ films consisted of bundles of one dimensional (1D) nanorods and the nanorods in these α-Fe₂O₃ films were single crystalline with a well-ordered rhombohedral structure. The nanorods showed a preferred growth orientation in the [104] direction. Magnetic force microscopy image suggests that spin domains were formed in the α-Fe₂O₃ nanorods. Photo-catalytic property of these nanorod films was confirmed through the photo-degradation of Rhodamine B by UV irradiation. These α-Fe₂O₃ film/nanorod materials could be used as building blocks for nanodevice applications.     

Hydrothermal synthesis and characterization of monodisperse α-Fe2O3 nanoparticles

Monodisperse α-Fe₂O₃ nanoparticles have been successfully prepared by hydrothermal synthetic route using FeCl₃, CH₃COONa as reagents and reacted at 200 °C for 12 h. The morphology and structure of products were characterized by powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the α-Fe₂O₃ nanoparticles were single-crystalline hexagonal structure and average diameters were about 80 nm. Magnetic properties have been detected by a vibrating sample magnetometer at room temperature. The nanoparticles exhibited a ferromagnetic behavior with the coercive force (Hc), saturation magnetization (Ms) and remanent magnetization (Mr) was 185.28 Oe and 0.494 emu/g, 0.077 emu/g.     

Fabrication of nanostructured α-Fe2O3 electrodes using ferrocene for solar hydrogen generation

Nanostructured thin films of α-Fe₂O₃ were prepared through atmospheric chemical vapour deposition (APCVD) using ferrocene and iron pentacarbonyl as precursors. Higher optical absorption was observed for hematite films prepared using ferrocene, which was attributed to the higher packing density. Photoelectrochemical (PEC) studies of the films prepared using ferrocene showed superior performance to that of iron pentacarbonyl. Photocurrent density of 540 µA/cm² and 1.5 µA/cm² at 1.23 V_RHE was achieved for hematite films prepared using ferrocene and iron pentacarbonyl, respectively. Our findings suggest that ferrocene can be used as a promising alternative to iron pentacarbonyl to prepare hematite photoelectrodes using APCVD.     

Uses of α-Fe2O3 and fly ash as solid adsorbents

Solid adsorbents have shown great promise for control of particulate and non-particulate matter and as gas sensing devices in recent times. In the present study, adsorption of environmental toxic pollutant such as lead ions on solid adsorbents viz. α-Fe₂O₃ and fly ash, are reported. Considerable adsorption was observed on fly ash when compared to α-Fe₂O₃ surface. These studies are characterized by employing solid state and solution studies.