Iron Oxide Samples Research Articles

The mechanism of reduction of iron oxide by hydrogen

Precipitated iron oxide samples were characterized using temperature-programmed reduction. H 2 was used as the reduction agents. The two-stage reduction was observed: Fe 2O 3 was reduced to Fe 3O 4 and then reduced to metallic Fe. The activation energy for the two reduction steps of iron oxide are 89.13 and 70.412 (kJ mol −1), respectively. The simulation by reduction models of the TPR patterns presents well fitting of unimolecular model for Fe 2O 3→Fe 3O 4 reduction and two-dimensional nucleation according to Avarmi–Erofeev model for Fe 3O 4→Fe.

Synthesis, structural and chemical properties of iron oxide–silica aerogelsElectronic supplementary information (ESI) available: cumulative pore volumes and t-plots of the calcined aerogels prepared by different sol–gel methods, and of aerogels with different iron loadings. See http://www.rsc.org/suppdata/jm/b1/b108120a/

Iron oxide aerogels were synthesized from tetramethoxysilicon(IV) (TMOS) or tetraethoxysilicon(IV) (TEOS) and iron nitrate using an acid-catalyzed solution–sol–gel method combined with subsequent extraction of the alcoholic solvent with supercritical CO2. The main parameters varied in the sol–gel synthesis were: the type of N-base used as the gelation agent (N,N-diethylaniline, trihexylamine, ammonium carbonate, ammonia), the concentration of the iron precursor, and the water content. The silicon precursor was prehydrolyzed to improve its reactivity. After calcination at 600 °C, the structural and chemical properties of the aerogels containing 0–20wt% nominal Fe2O3 were characterized by means of nitrogen adsorption, X-ray diffraction (XRD), transmission and scanning electron microscopy, temperature programmed reduction, X-ray photoelectron spectroscopy (XPS), UV-Vis, DRIFT and EPR spectroscopy. XRD and electron microscopy indicated that all aerogels were amorphous, irrespective of the sol–gel conditions used. The aerogels were predominantly mesoporous, with pore size maxima ranging between 20–50 nm, but also exhibited some microporosity. For the 10 wt% iron oxide samples, the specific pore volumes ranged from 0.7 to 2 cm3 g−1 and BET-surface areas from 150 to 636 m2 g−1, depending on conditions. With increasing iron content, the BET surface area decreased from 740 to 340 m2 g−1, accompanied by increasing microporosity. XPS revealed significant silicon enrichment on the surface. Spectroscopic investigations (UV-Vis, EPR) uncovered different iron-containing species, ranging from tetrahedrally coordinated iron atoms incorporated in the silica matrix to iron oxide nanoclusters. Formation of isolated iron atoms was favored with low iron content samples. The N-base used to force gelation had a significant effect on the morphology and population density of Fe(OH)Si in the aerogels.

Heating Potential of Iron Oxides for Therapeutic Purposes in Interventional Radiology

Rationale and Objectives In addition to their diagnostic applications, iron oxides could be used therapeutically to eliminate tumors with heat if their heating powers are adequate. The authors therefore examined the specific absorption rate (SAR) of different iron oxide (magnetite) samples suspended in water and in liquid or solidified gel. Materials and Methods The authors compared two ferromagnetic fine powders (total particle size, >350 nm and 100 nm), five superparamagnetic ferrofluidic samples (total particle size, 10–280 nm), and a commercially available contrast medium (ferumoxides injectable solution, Endorem). The SARs of the magnetic material—suspended in distilled water or in liquid or solid agar—were estimated from time-dependent calorimetric measurements during exposure to an alternating-current magnetic field (amplitude, 6.5 kA/m; frequency, 400 kHz). Results SARs varied considerably between the different iron oxide samples. The highest value was found for a ferrofluidic sample (>93 W/g), while Endorem had little heating power (<0.1 W/g). The SAR was clearly dependent on the aggregation state of the matrix only for the large-particle–size ferromagnetic sample, yielding the highest values for particle suspensions in water (74 W/g) and lowest for solid agar (8 W/g). The heating power of the smaller-particle–size ferromagnetic sample did not exceed 8 W/g. Conclusion Heating powers differed according to the interaction of multiple physical parameters. Iron oxides should be selected carefully for therapeutic applications in magnetic heating.

Evaluation of temperature increase with different amounts of magnetite in liver tissue samples.

The biologic effects of magnetically induced heating effects using iron oxide, magnetite, were examined in vitro in liver tissue samples as a first step toward potential applications in cancer therapy. For the determination of the temperature profile around an iron oxide sample, a cylinder containing 170 mg of magnetite was constructed and placed into pureed liver tissue from pig, together with thermocouples of copper and constantan wires positioned at defined distances from it. Temperature measurements were performed during the exposure to an alternating magnetic field (frequency: 400 kHz; amplitude: approximately 6.5 kA/m) generated by a circular coil (90 mm of diameter). Moreover, variable amounts of magnetite (dissolved in approximately 0.2 mL physiologic saline) were injected directly into carrageenan gels. During the exposure to a magnetic field for 4 minutes the temperature increase was determined in the area of iron oxide deposition using a thermocouple. Additionally, variable amounts of magnetite were injected directly into isolated liver tissue samples (diameter: 20 mm; height: 30 mm) and exposed to a magnetic field for 2 minutes. The extent of the induced macroscopically visible tissue alterations (light brown colorations caused by heating) was examined by means of volume estimations. The degrees of cellular necrosis were investigated by histopathologic studies. The temperature profile around a magnetite cylinder revealed a significant decrease of temperature difference between the beginning and the end of heating, depending on increasing distance from the sample center. The extent of the temperature difference correlated with increasing heating time. No significant variations of temperature were observed at a distance of approximately 12 mm from the sample center. A good correlation (r = 0.98) between the injected amounts (31 to 200 mg) and the temperature increase since the start of heating (6.8-33.7 degrees C) in the area of iron oxide deposits was detected. The volume of damaged liver tissue was approximately seven times higher than the injected volume of iron oxide dispersion. Histologically different degrees of cellular necrosis were observed. The parameters determined in this article show that iron oxides are able to induce considerable heating effects in the surroundings. After an adequate optimization of the technical procedure, it is conceivable that heating properties of magnetites can be used in future cancer treatments.

The detection of single-domain greigite (Fe3S4) using rotational remanent magnetization (RRM) and the effective gyro field (Bg): mineral magnetic and palaeomagnetic applications

SUMMARY The intensity of rotational remanent magnetization (RRM) acquired by single-domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization (ARM) to calculate the effective biasing field (Bg) that produced the RRM. Samples of single-domain greigite had Bg values between -137 and -84 μT, and a MDFRRM of c. 80 mT. By contrast, a suite of natural and synthetic ferrimagnetic iron oxide samples, including single-domain magnetite and yFe3O4 tape particles, acquired Bg values between -3 and -14 μT, and MDFRRM ranged between 43 and 68 mT (when RRM was acquired). Multidomain magnetite did not acquire a RRM. Bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes, which revealed a minimum Bg value of -24 μT and a MDFRRM of 57 mT for the finest fraction (0.2-0.8 μm in diameter). In a geological example, measurements of Bg and MDFRRM were used to detect the presence of greigite in a 4 m long Late Weichselian sediment core. Variations in inclination, declination and the intensity of the natural remanent magnetization (NRM) correlate with changes in magnetic mineralogy.

Natural Iron and Manganese Oxide Samples by XPS

XPS analyses of naturally formed iron and manganese oxide surfaces reveals important information used for interpreting mineral surface reactivity in our environment. Specifically, these oxides and oxyhydroxides give us details about the oxidation state of manganese phases commonly found during heterogeneous reactions. This type of analysis is also useful for interpreting the formation history of natural mineral surfaces. In this submission we present XPS data on the mineral surfaces hematite (α-Fe2O3), goethite (α-FeOOH), pyrolusite (β-MnO2), and manganite (α-MnOOH).

In Situ Dynamic Measurement of Polydisperse Chain Aggregate Aerosols Using Photocorrelation Spectroscopy Technique

An experimental technique was developed to perform in situ photo correlation spectroscopy measurements on length distribution of dynamic polydisperse iron oxide aerosols with diameters ranging from 0.01 to 0.05 μm. The cumulant analytical method is used to determine the average length of the chain aggregate. The experimental results show that the average length of the iron oxide aerosols obtained by the photo correlation spectroscopy technique is basically consistent with the results obtained by TEM. Results indicate that the length of the iron oxide samples increases as the liquid carbonyl temperature increases and the gas flow dilution ratio decrease.

Magnetic characterization of iron oxides for magnetic resonance imaging

The OMP particle and four additional iron oxide samples were investigated in terms of zero field cooled magnetization (ZFCM) curves and hysteresis loops. The observation of superparamagnetic blocking and the absence of magnetic remanence demonstrated that the samples are superparamagnetic at room temperature. The magnitude of the ZFCM peak temperatures are in qualitative agreement with the iron oxide crystal size. One sample deviated from the remaining four in that it had a significantly lower magnetic moment and an irregular ZFCM curve showing the presence of various less magnetic phases. The similar results obtained with the OMP particles and the individual OMP crystallites without the polymer support show that the superparamagnetic properties of the individual OMP crystallites are retained on the OMP particle. Depending on the application, the ZFCM experiment may be viewed as an alternative or a supplement to Mössbauer spectroscopy in studies of the superparamagnetic blocking of iron oxides.

Study on SnO 2-Fe 2O 3 gas-sensing system by a.c. impedance technique

A.c. complex impedance measurement has been used in a mixed system of tin oxide and iron oxide in an attempt to obtain more information about the gas-sensitive mechanism of semiconducting metallic oxide gas sensors. The impedance spectra in air, liquid petroleum gas (LPG) and acetylene have been obtained for the thick-film elements at different temperatures. A simple equivalent circuit, which contains the contributions from grain bulks and grain boundaries, is proposed to account for the spectra. The results show that both the grain bulks and grain boundaries of tin oxide (doped with a small amount of antimony oxide) are responsible for the reducing-gas sensitivities. For the iron oxide sample, the grain-boundary resistance is dominant in the total resistance and its change in various atmospheres is the main origin of the sensitivity to reducing gases. For the mixed system, the role of grain boundaries is also found to be more important than that of grain bulks. Some structural analyses and direct-current (d.c.) measurement have also been performed. This preliminary study indicates that a.c. complex impedance measurement might be a powerful tool in studying chemical sensors.

State analysis and relationship between lattice constants and compositions including minor elements of synthetic magnetite and maghemite

Chemical formulae were constructed after the determination of the composition including the minor elements in commercially available synthetic magnetite and maghemite, which gave similar x-ray diffraction patterns with close diffraction lines. The contents of FeO in reagent grade magnetite and high-purity magnetite powders were about 8 mol% less and that in a needle-shaled magnetite powder was about 24 mol% less than the 50 mol% in the expected composition (FeO · Fe2O4) of magnetite. They were solid solutions of magnetite-maghemite (γ-Fe2O3) including minor elements in the lattice. A linear relationship was found between the total mole percentage if divalent iron, manganese and zinc oxides and their lattice constants ac corrected by increments of the lattice constant based on the replacement of divalent iron with manganese and zinc atoms. The possibility of a non-destructive total analysis of the same iron oxide samples by an x-ray method is discussed. It was found that magnetite was considerably oxidized in air even at 110°C to form a solid solution, but not to form any separated compound.

On the crystalline structures of iron oxides formed during the removal process of iron in water

The iron oxide samples collected from both filtration and batch reactors were analysed by X-ray diffraction and Mössbauer spectroscopy. In the filtration of water containing iron, the oxidized form of iron was determined to be ferrihydrite. In contrast, in the batch experiment without filtration, iron was oxidized to microcrystalline goethite.

Reduction of supported iron oxide studied by temperature-programmed reduction combined with mössbauer spectroscopy and X-ray diffraction

The reduction of iron oxide supported on alumina, anatase and rutile and the interactions between iron oxides and these supports have been studied using temperature-programmed reduction, Mossbauer spectroscopy and X-ray diffraction. The intermediates formed during reduction depend strongly on the nature of the support, the iron loading and the reduction conditions used. Several iron species such as bulk α-Fe2O3, superparamagnetic α-Fe2O3 and surface iron–aluminium oxides are found in the alumina-supported iron oxide samples. The iron–aluminium species can be formed either by incorporation of Al3+ into the structure of iron oxide in acidic solution during the preparation of the samples or by incorporation of Fe2+ into the structure of the alumina support under high-temperature reduction. For the as-prepared Fe/TiO2 samples, the anatase and rutile have only weak interactions with the iron oxide as only bulk α-Fe2O3 species have been detected. However, some intermediates such as (1 –x)FeTiO3–xFe2O3 solid solution, surface iron–titanium oxide and bulk FeTiO3 phase can be formed during reduction because of the reducibility and mobility of titanium ions on the surface. Surface titanium ions can act as an electron-transfer medium for the reduction of Fe3+ to Fe2+ and can even be substituted for Fe3+ ions in the octahedral sites of magnetite formed during the reduction. In all cases, when the loading of iron oxide is low, Fe3+ and Fe2+ ions are stable during reduction due to the formation of iron oxide–support intermediates by strong interactions between iron oxides and the supports.

Oxygen-isotope systematics in a multiphase weathering system in Haiti

Physical and chemical (partial dissolution) techniques have been applied to a suite of young karst bauxite and laterite samples from the southern peninsula of Haiti. The δ 18O values have been obtained for nine mineral species and range from + 1.0‰ for anatase/rutile to +33.4‰ for authigenic quartz. On one hand, results for quartz, calcite, kaolinite, gibbsite and boehmite compare favourably with δ 18O values predicted from accepted mineral-water fractionation factors, assuming modern temperatures (25 ± 2° C) and water δ 18O values ( −3.1 ± 0.5‰). On the other hand, the δ 18O values measured for anatase, illite/smectite, chlorite/smectite, and some iron oxide samples do not compare favourably with predicted values. Departures from expected values for these minerals may be related to crystallization from water with a different δ 18O value than modern water, an imprecise knowledge of some mineralwater fractionation factors under surficial conditions, or nonattainment of isotopic equilibrium between mineral and water during formation. Partial dissolution techniques hold considerable promise for obtaining quantitative δ 18O values of individual minerals in single samples of complex, fine-grained regolith material.

Powdered mixtures reactivity by thermal analysis

Two less common methods of thermal analysis, namely amperometric and emanation thermal analysis (ATA and ETA, respectively), were used to evaluate the reactivity of various Fe 2O 3 materials. The reactivity was measured using the onset temperature ( t p) of the reaction Fe 2O 3 and ZnO. The ATA method described here can be connected to a personal computer to give the exact determination of t p values. The possible applications of the ATA and ETA methods are demonstrated by means of several examples (the reactivities of various iron oxide samples or Fe 2O 3+ZnO reaction mixtures treated with milling). Both methods are suitable for use in cases where the studied processes proceed separately without any overlapping.

Transverse susceptibility and anisotropy fields of iron-oxide pigments

The transverse susceptibility of oriented iron oxide samples was measured. The results are in qualitative agreement with theoretical curves. From singular points of the transverse susceptibility the anisotropy fields of the pigments were determined. For Co-free pigments these agree well with the chain of spheres model. The anisotropy fields of the Co-modified pigments depend significantly on the kind of modification. This is interpreted with differences in the strength of uniaxiality of the anisotropy. >

Influence of the magnetic interactions on the reversal mode of magnetic recording particles

In an assembly of particles, as used in magnetic recording media, there are always magnetic interactions. The magnetic properties of the media are modified as a consequence of the effect of such interactions on the magnetic behavior of the particles. In this work an attempt is made to find an experimental correlation between the presence and strength of the interactions and the magnetization reversal of the particles. The reversal mode is investigated by rotational hysteresis measurements and by the evolution of the angular dependence of the coercivity in samples of iron oxides at different dilution degrees. The magnetic interactions are evaluated with measurements of the remanence curves. It is found that when the magnetic interactions among the particles increase, the parameters used to study the reversal mode evolve from the behavior typical of the incoherent magnetization processes to behaviors which can be considered as intermediate between coherent and incoherent reversal modes. This evolution can be attributed to the tendency of the magnetic interactions to increase the percentage of particles in the aggregate, which reverse with coherent rotation, particularly in the agglomerates often present in closely packed assemblies.

Use of flow injection flame atomic absorption spectrometry for slurry atomization. Determination of copper, manganese, chromium and zinc in iron oxide pigments

A procedure for the determination of copper, manganese, chromium and zinc in slurries of commercial iron oxide pigments using flame atomic absorption spectrometry is described. The samples are suspended in water and introduced directly into the spectrometer using a flow injection manifold with air-compensation of the difference between the peristaltic pump flow-rate and the nebulizer uptake rate. In order to avoid matrix effects, calibration is achieved by using slurries prepared from previously analysed iron oxide samples. Excellent agreement was found between the results of the slurry procedure and those obtained by conventional acid-dissolution.

Solubilities and stabilities of ferric arsenate compounds

Basic ferric arsenates precipitated from hydrometallurgical liquors by hydrolysis are shown to be very insoluble over a range of pHs. The stability range (solubilities <1 mg l −1) becomes wider with increasing Fe/As ratios. Precipitates with Fe/As ratio=8 have solubilities <1 mg l −1 between Ph=3 and 8. The As solubility did not increase during aging over a 2–3.7 yr period. Naturally occurring iron oxide samples with Fe/As ratios=3–4 show even lower As solubilities than precipitates with the same Ar/As ratios. The solubility of crystalline scorodite, FeAsO 42H 2O, was found to be about two orders of magnitude lower than reported in the literature for apparently amorphous FeAsO 4H 2O. The solubility and the free energy of formation were recalculated for crystalline scorodite. This investigation shows that basic ferric arsenates appear to be suitable for safe disposal of arsenic.

Determination of trace metals in commercial iron oxide by X-ray fluorescence spectrometry

A method is described for the simultaneous determination of low concentrations of chromium, copper, manganese, and zinc in commercial iron oxide samples by X-ray fluorescence spectrometry, without the use of chemical treatment. Synthetic standards are prepared from highly pure iron oxide and appropriate solutions of the elements to be tested. Precision at each concentration of the standards and theoretical minimum detection limits and quantitation limits are calculated. The results for the analysis of eight commercial iron oxide samples agree with those obtained using atomic absorption spectrophotometry.

Magnetic studies of fine iron and iron-oxide particles

The magnetic and structural properties of fine iron and iron-oxide particles have been studied. The samples of iron oxide were prepared by the aerosol method and those of pure iron were prepared by the vapor deposition technique. Electron micrographs showed the size of aerosol particles to be 200 nm and that of vapor deposition particles to be 10–20 nm. The maximum coercivity at 10 K obtained for aerosol particles was approximately 700 Oe, and for vapor deposited particles it was 1540 Oe.