Magnetic Properties Of Hematite Research Articles

Annealing Temperature Dependent of the Structural and Magnetic Properties in Hematite Prepared by Sol-Gel Method

The annealing temperature dependent on the structural and magnetic properties of hematite (α-Fe2O3) powders synthesized via the sol-gel method was studied. The sol-gel method is used to prepare nanoparticles for this experiment. The annealing treatment of 200°C, 400°C, 600°C, and 800°C has been carried out to modify the physical properties. The obtained nanoparticles are characterized by their structural properties using X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Then, magnetic properties were evaluated using Vibrating Sample Magnetometer (VSM). XRD results have shown an increase in crystallite size with an increase in annealing temperature from 35.10 nm to 60.17 nm. The increase in crystallite size can be attributed to the increase in the crystal structure’s internal energy, which promotes atomic diffusion. The FTIR results show an absorption that appears at the peak around ~530 cm-1. It indicates that the Fe3+ cation has successfully formed. The VSM results show an increase in the value of Hc with an increase in the annealing temperature from 117 Oe to 461.5 Oe. It is supported by the increase of anisotropy constant and increasing temperature annealing.

Structure, morphology and magnetic properties of hematite and maghemite nanopowders produced from rolling scale

The work is devoted to development of cost-efficient method of processing of metallurgical waste – oily rolling scale formed during hot-rolled steel strip mechanical cleaning in descaling mills. The most significant parameters of chemical metallurgical process for producing expensive and highly marketed products – α-Fe 2 O 3 and γ-Fe 2 O 3 nanopowders – have been experimentally determined. The properties of initial materials and nanodispersed products were studied by X-ray diffractometry, energy dispersive spectroscopy, scanning and transmission microscopy, and Mossbauer spectrometry. Temperature and field dependences of powders magnetization were built according to vibration magnetometer measurements. It is shown that rolling scale consists of three main phases: wustite, magnetite and hematite in a ratio of 6:8:7 by weight, respectively. The initial scale was activated in magnetic mill in stream of hydrogen and dissolved in mixture of hydrochloric and nitric acids. The resulting solutions were used to obtain α-Fe 2 O 3 nanocrystalline hematite by chemical-metallurgical method, the main stages of which were hydroxide precipitation with alkali at constant p H , washing, drying, and dehydration. γ-Fe 2 O 3 maghemite was obtained from hematite in two stages. At the first stage, hydrogen reduction was carried out, and at the second stage, the magnetite obtained was oxidized in air. Particles of synthesized nanodispersed oxide powders are in aggregated state. Particles of α-Fe 2 O 3 are spherical, and γ-Fe 2 O 3 are rod-shaped. According to Mossbauer spectroscopy, the lattices of both oxides contain magnesium, aluminum, silicon, chromium, and manganese that have passed from the initial scale. These elements determine magnetic properties of α-Fe 2 O 3 and γ-Fe 2 O 3 nanopowders. Set of properties of nanodispersed hematite and maghemite powders obtained from metallurgical waste (rolling scale) allows us to recommend their application as catalysts, in industrial wastewater heavy metal ions treatment systems, and in production of blood analysis markers.

Structure, Morphology and Magnetic Properties of Hematite and Maghemite Nanopowders Produced from Rolling Mill Scale

Structure, Morphology and Magnetic Properties of Hematite and Maghemite Nanopowders Produced from Rolling Mill Scale

Substrate effect on the structural phase formation and magnetic properties of α-Fe2O3 and Ti doped α-Fe2O3 thin films

We report the synthesis and magnetic properties of hematite (α-Fe2O3) and Ti doped hematite (α-Fe1.4Ti0.6O3) films. The films have been grown at 400 °C on different substrates by using Pulsed Laser Deposition technique. The as-grown film has been heated in the temperature range 600–730 °C either in air or vacuum. Microstructure of the films has been studied using X-ray diffraction pattern, Atomic force microscope, Field effect Scanning Electron Microscope, and magneto-optic Kerr effect (MOKE). Crystalline structure of the films has been stabilized either in rhombohedral phase or in cubic spinel phase depending on the type of substrates. The crystalline films have been found highly oriented on specific directions. Magnetic order of the films at room temperature has been studied using MOKE. The films on selected substrates have been used for a detailed study of low temperature magnetic properties. The temperature dependent magnetization of the films has exhibited bifurcation between zero field cooled and field cooled magnetic curves at all measurement temperatures (5–350 K). Magnetic spin order of the films has been affected by the nature of substrates. Some of the films with room temperature ferromagnetism or canted antiferromagnetism seem to be useful for spintronics applications.

Sol–gel combustion synthesis, particle shape analysis and magnetic properties of hematite (α-Fe2O3) nanoparticles embedded in an amorphous silica matrix

We report the synthesis and magnetic properties of hematite/amorphous silica nanostructures. Raman spectroscopy showed the formation of a hematite phase. A transmission electron microscopy (TEM) revealed spherically shaped hematite nanoparticles, well-dispersed in an amorphous silica matrix. In order to quantitatively describe morphological properties of nanoparticles, we use the circularity of shapes as a measure of how circular a shape is. Diameters of about 5nm and a narrow size distribution of nanoparticles are observed. The obtained hematite nanoparticles exhibit superparamagnetic properties at room temperature (SPION). The sample does not display the Morin transition. The FC hysteresis loop at 5K has shown an exchange bias effect. These results have been compared to those previously reported for α-Fe2O3/SiO2 nanosystems in the literature. These comparisons reveal that the sol–gel combustion method yields hematite nanoparticles with a higher magnetization and magnetic moment. These data indicate the existence of an additional factor that contributes to magnetization. We suggest that the increased magnetization is due to an increased number of the surface spins caused by the breaking of large numbers of exchange bonds between surface atoms (disordered structure). This leads to an increase in the magnetic moment per a hematite nanoparticle and an exchange bias effect. We have concluded that the combustion-related part of this synthesis method enhances surface effects, i.e. it promotes the breaking of bonds and surface disordered layers, which results in these magnetic properties. Such interesting structural and magnetic properties of hematite might be important in future practical applications and fundamental research.

Effect of microwave pre-treatment on the magnetic properties of iron ore and its implications on magnetic separation

The use of microwave heating is a potential means of energy savings and is a more effective alternative to the conventional thermal processing of minerals. The effect of microwave treatment on Egyptian iron ore samples was investigated. Changing the microwave exposure time and power as well as their reflection on the magnetic properties of iron ore before and after microwave pretreatment was analyzed using different techniques. Microwave treatment was found to be more efficient at larger particle sizes and longer exposure times for a fixed value of the applied power intensity. Magnetic separation of microwave treated and untreated iron ore indicated that iron recovery increased from 39.54% in the untreated sample to 97.95% in the microwave-treated sample. The results indicated that microwave radiation has a significant effect on the magnetic properties of hematite through the formation of new and more magnetic phases that facilitate their separation from non-magnetic minerals, thereby obtaining high recovery, reaching ca. 98%.

Synthesis, characterization and magnetic properties of hematite (α-Fe2O3) nanoparticles on polysaccharide templates and their antibacterial activity

The present study is to synthesize iron oxide nanoparticles on different polysaccharide templates calcined at controlled temperature, characterizing them for spectroscopic and magnetic studies leading to evaluate their antibacterial property. The synthesized iron oxide nanoparticles were characterized by X-ray diffractometer (XRD), Fourier transform infrared spectroscopy, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer. The iron oxide nanoparticles were tested for antibacterial activity against gram-positive and gram-negative bacterial species. The XRD confirms the crystalline nature of iron oxide nanoparticles with the mean crystallite size of 10 nm. The functional groups of the synthesized iron oxide nanoparticles were 547, 543 and 544 cm–1 characterizing the Fe–O and the broad bands at 3,398, 3,439 and 3,427 cm–1 were attributed to the stretching vibrations of hydroxyl group absorbed by iron oxide nanoparticles. HRTEM analyses revealed that the average particle size of the hematite nanoparticles are about 85, 92 and 77 nm for AF, DF and GF, respectively, which was a coincident with the results obtained from the HRSEM analysis. Magnetic measurement exhibited ferromagnetic behavior of the α-Fe2O3 at the room temperature with higher coercivity of HC = 2,303, 2,333 and 1,019 Oe for AF, DF and GF, respectively. Antibacterial test showed the inhibition against Aeromonas hydrophila and Escherichia coli with significant antagonistic activity.

A Density Functional Theory Study of the Adsorption of Benzene on Hematite (α-Fe2O3) Surfaces

The reactivity of mineral surfaces in the fundamental processes of adsorption, dissolution or growth, and electron transfer is directly tied to their atomic structure. However, unraveling the relationship between the atomic surface structure and other physical and chemical properties of complex metal oxides is challenging due to the mixed ionic and covalent bonding that can occur in these minerals. Nonetheless, with the rapid increase in computer processing speed and memory, computer simulations using different theoretical techniques can now probe the nature of matter at both the atomic and sub-atomic levels and are rapidly becoming an effective and quantitatively accurate method for successfully predicting structures, properties and processes occurring at mineral surfaces. In this study, we have used Density Functional Theory calculations to study the adsorption of benzene on hematite (α-Fe2O3) surfaces. The strong electron correlation effects of the Fe 3d-electrons in α-Fe2O3 were described by a Hubbard-type on-site Coulomb repulsion (the DFT+U approach), which was found to provide an accurate description of the electronic and magnetic properties of hematite. For the adsorption of benzene on the hematite surfaces, we show that the adsorption geometries parallel to the surface are energetically more stable than the vertical ones. The benzene molecule interacts with the hematite surfaces through π-bonding in the parallel adsorption geometries and through weak hydrogen bonds in the vertical geometries. Van der Waals interactions are found to play a significant role in stabilizing the absorbed benzene molecule. Analyses of the electronic structures reveal that upon benzene adsorption, the conduction band edge of the surface atoms is shifted towards the valence bands, thereby considerably reducing the band gap and the magnetic moments of the surface Fe atoms.

Effect of the polymeric matrix on the structural and magnetic properties of hematite/polymer composites

The magnetic properties of hematite (α-Fe2O3) nanoparticles synthesized by in situ thermal decomposition of an iron-mercaptide precursor in polymeric matrices are studied. In Polystyrene, nanoparticles with average size ~20 nm can be produced that show ferromagnetic behavior with no Morin transition for temperatures as low as 10 K. Poly(9-vinylcarbazole)-based nanocomposites, produced by the same synthesis process, show a different magnetic behavior with a clear Morin transition. The effect of the polymeric matrix on the structural and magnetic properties of dispersed hematite nanoparticles is discussed. It is concluded that, in heavily viscous medium, the ability to control the particle growth and distribution is compromised.

Ferromagnetic hematite@graphene nanocomposites for removal of rhodamine B dye molecules from water

In this communication, we report for the first time the synthesis and magnetic properties of hematite (α-Fe2O3) nanocubes anchored on polymer PVP-modified rGO nanosheet (termed HPG) nanocomposites prepared from ferric ions (Fe3+). The HPG exhibited weak ferromagnetic properties with an obviously suppressed Morin temperature of 189 K, much lower than that of hematite nanocubes (257 K), which is attributed to the decrease of the particle size and the coexistence of graphene in the HPG system. Also HPG presents excellent adsorption performance for rhodamine B (RhB) dye molecules.

Synthesis, morphology, microstructure and magnetic properties of hematite submicron particles

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe 2O 3) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ∼500 nm whereas thickness is ∼100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe 2O 3 particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H C = 1140 Oe, remanent magnetization M r = 0.125 emu/g and saturation magnetization M S = 2.15 emu/g as well as the Morin transition at T M ∼ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample.

Preparation of nanoparticles and hollow spheres of α-Fe2O3 and their properties

Uniform nanoparticles and hollow microspheres of hematite (α-Fe2O3) were obtained via a hydrothermal method by using iron (III) chloride as a precursor. The effects of reactant concentration, reaction time and temperature on the morphology of the samples were studied. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and superconducting quantum interference device magnetometer (SQUID) measurement. α-Fe2O3 nanoparticles show a superparamagnetic behavior and the average size of the spherical particles was around 60 nm. However, hollow microspheres show a normal ferromagnetic behavior at room temperature with remanent magnetization and coercivity of 0.2482 emu/g and 2,516 Oe, respectively, and their average diameter was around 2 μm. The effects of reactant concentration and reaction temperature on the formation of the products were investigated. The experimental results reveal that the magnetic properties of hematite can be tuned by controlling the morphology.

Mechanochemical and magnetomechanical synthesis of hematite nanoparticles

Samples of hematite were exposed to mechanochemical activation by high energy ball milling for 0–27 h. The milling-induced changes to the structural and magnetic properties of hematite were characterized by X-ray diffraction (XRD) and Mossbauer spectroscopy. The particle size was found to decrease from 80 to 16.5 nm after 8 h of ball milling time, followed by a small increase to 19.8 nm at the end of the milling period. An overall expansion of the crystalline lattice parameters a and c with the milling time was deduced. The magnetic hyperfine field decreased with the ball milling time, from 51.46 down to 50.68 T after 27 h of grinding. Magnetite and traces of iron were observed at the longest milling time employed. The recoilless fraction (f ) was measured simultaneously using a dual Mossbauer absorber consisting of hematite and a stainless steel etalon. The f factor first decreased with the milling time due to occurrence of nanoparticles in the system, had a maximum at 12 h due to agglomerations of nanoparticles and exhibited a second maximum at 27 h, due to the appearance of magnetite in the system. More samples of hematite were subjected to magnetomechanical activation by magnetic ball milling for 52 and 134 h. A phase mixture of hematite and magnetite was observed.

Effects of milling-induced disorder on the lattice parameters and magnetic properties of hematite

A ball-milling treatment in air for 30 min is enough to reduce anhydrous bulk hematite (α-Fe 2O 3) grains to nanometric sizes. For milling times, t m, of 15, 30 min, 1 and 2 h, the crystals suffer an anisotropic lattice dilation, which is more pronounced for the smaller average grain sizes attained. Mössbauer and susceptibility results show that the process alters the effective Morin temperatures, T M. The transition occurs less sharply than for the non-milled material and spreads over a maximum extent of 50 K for t m=30 min. The susceptibility data indicate that the T M for the fraction of material undergoes the transition shifts toward values not lower than 235 K. For t m=10 h the transition is suppressed down to 12 K. Our results do not allow distinguishing bulk from surface regions of the grains. In addition, the disorder brought about by the milling reduces the magnetic response in the weak ferromagnetic state of α-Fe 2O 3. The modification of T M seems to depend mainly on the anisotropic dilation of the unit cell that affects the whole grain and it is related to the nanometric grain sizes achieved.

Magnetic properties of hematite nanoparticles

The magnetic properties of hematite $(\ensuremath{\alpha}\ensuremath{-}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3})$ particles with sizes of about 16 nm have been studied by use of M\ossbauer spectroscopy, magnetization measurements, and neutron diffraction. The nanoparticles are weakly ferromagnetic at temperatures at least down to 5 K with a spontaneous magnetization that is only slightly higher than that of weakly ferromagnetic bulk hematite. At $T\ensuremath{\gtrsim}100\mathrm{K}$ the M\ossbauer spectra contain a doublet, which is asymmetric due to magnetic relaxation in the presence of an electric field gradient in accordance with the Blume-Tjon model. Simultaneous fitting of series of M\ossbauer spectra obtained at temperatures from 5 K to well above the superparamagnetic blocking temperature allowed the estimation of the pre-exponential factor in N\'eel's expression for the superparamagnetic relaxation time, ${\ensuremath{\tau}}_{0}=(6\ifmmode\pm\else\textpm\fi{}4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\mathrm{s}$ and the magnetic anisotropy energy barrier, ${E}_{\mathrm{bm}}{/k=590}_{\ensuremath{-}120}^{+150}\mathrm{K}.$ A lower value of the pre-exponential factor, ${\ensuremath{\tau}}_{0}{=1.8}_{\ensuremath{-}1.3}^{+3.2}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\mathrm{s},$ and a significantly lower anisotropy energy barrier ${E}_{\mathrm{bm}}^{\mathrm{magn}}/k=305\ifmmode\pm\else\textpm\fi{}20\mathrm{K}$ was derived from simultaneous fitting to ac and dc magnetization curves. The difference in the observed energy barriers can be explained by the presence of two different modes of superparamagnetic relaxation which are characteristic of the weakly ferromagnetic phase. One mode involves a rotation of the sublattice magnetization directions in the basal (111) plane, which gives rise to superparamagnetic behavior in both M\ossbauer spectroscopy and magnetization measurements. The other mode involves a fluctuation of the net magnetization direction out of the basal plane, which mainly affects the magnetization measurements.

Improved method for prediction of heavy metal recoveries from soil using high intensity magnetic separation (HIMS)

In recent years the soil cleaning industry has developed a number of cleaning strategies mostly based on classification techniques. Sometimes, however, those strategies fail for a number of reasons and as a result cleaning targets are not met. Therefore, some soil cleaning facilities have experimented with HIMS as an alternative process step. This paper describes a prediction method based on magnetic separation techniques for use of HIMS separators in soil cleaning plants. Two types of HIMS separators were used. First a (dry) Frantz isodynamic separator (FIS) and secondly a (wet) Jones high gradient magnetic separator (model P40 KHD and model DP 90 Humboldt Wedag). The FIS was used to separate heavy metals from soil and for observation of heavy metal behaviour in magnetic fields. With the Jones P40, pilot-scale experiments were performed to confirm the FIS results. In total six soil samples uncleanable by soil washing plants and three soil samples prepared by laboratory classification were used in the experiments. Furthermore, three soils were treated on full plant scale. FIS experiments indicated that soils can be distinguished by their different magnetic properties and that each soil shows its own characteristic magnetic susceptibility fingerprint. A similarity, however, was observed between the magnetic properties of soils and the magnetic properties of hematite which is a strong indication for the importance of iron in removing heavy metals from contaminated soil. The Jones P40 experiments showed a similar removal efficiency as the FIS for iron but not for the heavy metals. Soils treated with wet HIMS, however, showed considerably lower heavy metal contents than soils only treated with conventional washing techniques, indicating the usefulness of HIMS in cleaning heavy-metal-contaminated soils. Plant-scale treatment of three polluted soils showed that the Jones separator is a feasible technique for soil washing and treatment of heavy metals.

Wet High Intensity Magnetic Separation of Iron Minerals

Four different iron minerals were selected for study, and five size fractions of each mineral were prepared. The magnetic properties of these minerals were measured. The effect of particle size and magnetic susceptibility on wet high intensity magnetic separation was studied simultaneously. It was found that hematite—1 was a strongly paramagnetic mineral, and the effect of particle size in WHIMS was not significant. Goethite and limonite were weakly paramagnetic minerals, and could not be effectively recovered by WHIMS. The magnetic properties of hematite—2 were between hematite—1 and goethite and limonite, and the effect of particle size on WHIMS for hematite—2 was significant.

Magnetic properties of hematite in lava flows from Iceland: Response to hydrothermal alteration

The present study investigates changes in the magnetic properties of hematite, more precisely low‐Ti titanohematite, in Icelandic subaerial basalts during low‐temperature metamorphism (<300°C). The results have implications for detection of secondary magnetization directions in basalts and perhaps for seafloor magnetic anomaly modeling. Samples were collected both from outcrops and from the Iceland Research Drilling Project (IRDP) core and represent 3.6 km of crust. The natural remanent magnetization (NRM) unblocked below 590°C during thermal demagnetization was assigned to magnetite and that unblocked above 610°C to hematite. Unblocking temperatures of hematite gradually increased in the laumontite zeolite zone from the original low range of 610°–650°C to 650°–680°C. We attribute this increase to the migration of a small amount of initial Ti out of the hematite lattice. Titanium migration is consistent with microprobe analyses. The intensity of the hematite magnetization correlated with that of magnetite until the top of the laumontite zeolite zone (1.8 km depth). Below this depth, the intensity of the magnetite magnetization decreased and correlation became poor due to alteration of magnetite to nonmagnetic minerals. Both magnetite and hematite appeared to retain their primary directions of magnetization to the bottom of the laumontite zeolite zone even though Ti had migrated out of the lattices. If field‐controlled chemical remanent magnetization is not produced during Ti migration, then seafloor basalts undergoing the same processes may also faithfully retain primary directions of remanence. Below 3.1 km depth in the epidote metamorphic zone, large secondary components in some samples could not be completely removed by thermal demagnetization to 550°C and were attributable to a thermo‐viscous remanent magnetization (thermo‐VRM) in magnetite. The durability of the hematite magnetization suggests that the identification of hematite components in subaerial basalts may help reveal subtle secondary components contained in magnetite directions of subaerial basalts.

The influence of domain structure on the magnetic properties of hematite

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Superparamagnetism in hematite

It is well known that small particles of ferromagnetic material show superparamagnetic behavior. The magnetic properties of hematite, which has a weak spontaneous magnetization show superparamagnetic behavior in grains which are as large as 1/4 to 1/2 μ in diameter. This is shown to be the case by the use of magnetic tests, including hysteresis and Curie temperature effects and by the use of X-ray diffraction and optical determination of particle sizes.