Mixture Of Iron Oxides Research Articles

Catalytic activity and magnetic properties of barium hexaferrite prepared from barite ore

Barium hexaferrite (BaFe 12O 19) has traditionally been used in permanent magnets and more recently used for high density magnetic recording. The classical ceramic method for the preparation of barium hexaferrite consists of firing mixture of chemical grade iron oxide and barium carbonate at high temperature. In this paper a mixture of chemical grade hematite, barium oxide and predetermined mixtures of iron oxide ore and barite ore containing variable amounts of coke were used to prepare barium hexaferrite (BaFe 12O 19) as a permanent magnetic material. The mixtures were mixed in a ball mill and fired for 20 h in a tube furnace at different temperatures (1100, 1150, 1200 and 1250 °C). XRD, magnetic properties, porosity measurements and catalytic activity were used for characterization of the produced ferrite. The results of experiments showed that the optimum conditions for the preparation of barium hexaferrite are found at 1200 °C for the mixture of chemical grade hematite and barium oxide. It was also found that the barium hexaferrite can be prepared from the iron and barite ores at 1200 °C. The addition of coke enhanced the yield of barium hexaferrite and improved its physicochemical properties. Samples prepared from ores with coke% = 0 show the most acidic active sites, they show a higher catalytic activity towards H 2O 2 decomposition. With addition of coke the catalytic activity decreases due to the poisoning effect of carbon on the available active site.

Reduction behaviour of MgFe2O4 with the synthesis of Fe/MgO nanocomposite

Magnesioferrite (MgFe2O4) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of magnesium oxide and iron oxide. The produced powders of MgFe2O4 were isothermally reduced in pure hydrogen at 800–1000°C. Based on thermogravimetric analysis, the reduction behaviour of magnesioferrite and the kinetics reaction mechanism were studied. The initial ferrite powder and the various reduction products were characterised by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) analysis to reveal the effect of hydrogen reduction on composition, microstructure and magnetic properties of produced samples. Completely homogenous nanocrystalline (77 nm) Fe/MgO composite was obtained by the reduction of MgFe2O4 powders. Depending on the kinetics obtained data from reduction process, the reduction rate was found to be controlled by interfacial chemical reaction mechanism. The magnetic characterisation of the formed Fe/MgO nanocomposite were enhanced under the effect of reaction temperature whereas the coercivity values decreased from 57·99 to 33·58 Oe while the saturation magnetisation increased from 110·7 to 148·1 emu g−1.

Preparation and properties of Fe and Fe3O4 nanoparticles in ZrO2 matrix

Iron and magnetite nanoparticles in zirconium oxide matrix have been prepared by a heat treatment of a mixture of nanocrystalline iron oxide and zirconium oxide or zirconium hydride powders. Changes in the phase composition of the as-mixed powders during annealing in vacuum or in hydrogen were monitored using thermomagnetic curves. Structure and phase composition of the final products were characterized by X-ray powder diffraction and 57Fe Mossbauer spectroscopy. Influence of the composition of the original mixture and quality of the annealing atmosphere on the final properties of the composites are discussed.

Effects of pH on the morphology of iron oxides synthesized under gamma-irradiation

Gamma-irradiation has been applied to synthesize pure iron oxide nanorod particles in acid medium of pH 5.0, pure submicron sized particles of ferriferrous oxide with bullet-shaped morphology in alkaline medium at pH 12 and a mixture of iron oxide and ferriferous oxide fanlike morphology in nearly neutral medium of pH 7.2. It has been proven that the morphology of the prepared oxides is strongly dependent on the pH value of the solution before irradiation. The mechanism of formation of these oxides is also suggested.

Chemical environment of iron atoms in iron oxynitride films synthesized by reactive magnetron sputtering

An iron oxynitride film was deposited on silicon and glass substrates by magnetron sputtering in an Ar–N2–O2 reactive mixture. Rutherford back-scattering spectrometry was used to determine the film composition (Fe1.06O0.35N0.65). X-ray diffraction revealed the formation of a face-centred cubic (fcc) structure with a lattice parameter close to that of γ‴-FeN. X-ray photoelectron spectroscopy showed the occurrence of Fe–N and Fe–O bonds in the film. The local environment of iron atoms studied by 57Fe Mossbauer spectrometry at both 300 and 77 K gives clear evidence that the Fe1.06O0.35N0.65 is not a mixture of iron oxide and iron nitride phases. Despite a small amount of an iron nitride phase, the main sample consists of an iron oxynitride phase with an NaCl-type structure where oxygen atoms partially substitute for nitrogen atoms, thus indicating the formation of a iron oxynitride with an fcc structure.

The reactivity of iron oxides towards reductive dissolution with ascorbic acid in a shallow sandy aquifer (Rømø, Denmark)

The pool of iron oxides, available in sediments for reductive dissolution, is usually estimated by wet chemical extraction methods. Such methods are basically empirically defined and calibrated against various synthetic iron oxides. However, in natural sediments, iron oxides are present as part of a complex mixture of iron oxides with variable crystallinity, clays and organics etc. Such a mixture is more accurately described by a reactive continuum covering a range from highly reactive iron oxides to non-reactive iron oxide. The reactivity of the pool of iron oxides in sediment can be determined by reductive dissolution in 10 mM ascorbic acid at pH 3. Parallel dissolution experiments in HCl at pH 3 reveal the release of Fe(II) by proton assisted dissolution. The difference in Fe(II)-release between the two experiments is attributed to reductive dissolution of iron oxides and can be quantified using the rate equation J/ m 0 = k′( m/ m 0) γ , where J is the overall rate of dissolution (mol s −1), m 0 the initial amount of iron oxide, k′ a rate constant (s −1), m/ m 0 the proportion of undissolved mineral and γ a parameter describing the change in reaction rate over time. In the Rømø aquifer, Denmark, the reduction of iron oxides is an important electron accepting process for organic matter degradation and is reflected by the steep increase in aqueous Fe 2+ over depth. Sediment from the Rømø aquifer was used for reductive dissolution experiments with ascorbic acid. The rate parameters describing the reactivity of iron oxides in the sediment are in the range k′ = 7·10 −6 to 1·10 −3 s −1 and γ = 1 to 2.4. These values are intermediate between a synthetic 2-line ferrihydrite and a goethite. The rate constant increases by two orders of magnitude over depth suggesting an increase in iron oxide reactivity with depth. This increase was not captured by traditional oxalate and dithionite extractions.

Reduction behavior of barium hexaferrite into metallic iron nanocrystallites

Barium hexaferrite (BaFe 12O 19) powder was prepared through the ceramic route by calcination of a stoichiometric mixture of barium carbonate and iron oxide at 1200 °C for 2 h. Compacts of synthesized BaFe 12O 19 powder were isothermally reduced in hydrogen atmosphere at 600–1000 °C. Based on thermogravimetric analysis, the reduction behavior of BaFe 12O 19 and reaction kinetics and mechanism were studied. The initial ferrite powder and the various reduction products were characterized by X-ray diffraction analysis,a scanning electron microscope and a vibrating sample magnetometer to reveal the effect of hydrogen reduction on composition, microstructure and magnetic properties. The reduction rate was found to be controlled by interfacial chemical reaction mechanism. Metallic iron was formed in nanosized regimes while grain growth and coalescence were observed at higher reduction temperatures. Magnetic measurements show diluted magnetic properties for the formed metallic iron, whereas coercivity values were in the range 14.1–55 Oe and saturation magnetization varied from 24.79 to 36.15 emu/g. These values have been ascribed to the formation and growth of nanosized metallic iron particles as the reduction treatment proceeded.

Oxidation of two ternary Fe-Cu-5Al alloys in 1×10 5 Pa pure oxygen at 700 °C

The oxidation of two two-phase ternary Fe-Cu-Al alloys containing about 5% Al(mole fraction), one Fe-rich and one Cu-rich, were studied at 700 °C in 1 × 10 5 Pa pure oxygen. The Fe-rich alloy (Fe-15Cu-5Al) shows two quasi-parabolic stages, with a large increase of the parabolic rate constant after about 4 h. The presence of 5% Al does not change greatly the oxidation rate of Fe-15Cu-5Al with respect to a binary Fe-Cu alloy of similar composition, which was quite different from the situation of the same alloys oxidized at 800 °C. Oxidation of Fe-15Cu-5Al at 700 °C produced an outer layer of iron oxides and an inner layer containing a mixture of copper metal, iron and aluminium oxide. On the contrary, the Cu-rich Fe-85Cu-5Al alloy presents a rather irregular kinetic behavior, with formation of an inner continuous alumina thin layer and a rather irregular outer layer. The outer layer with a rather irregular thickness was mainly composed of a matrix of copper oxides plus some aluminium and iron oxides presenting in the deep part of the layer at certain locations. As a result of the formation of a protective alumina layer, the presence of 5% Al greatly reduced the oxidation rate of Fe-85Cu-5Al with respect to a binary Fe-Cu alloy of similar composition, which was also quite different from the situation of the same alloys oxidized at 800 °C. Moreover, the oxidation rate at 700 °C of the Fe-85Cu-5Al alloy was much lower than that of Fe-15Cu-5Al alloy due to the same reason.˙

Processing of nano-structured barium hexaferrite by self-propagating high temperature synthesis (SHS) using nitrate precursor

Barium hexaferrite magnetic powder was produced by self propagating high temperature synthesis (SHS) route through putting a hot filament on top of the compact mixture of iron, iron oxide and barium nitrate powders with a Fe (total)/Ba molar ratio of 12. Morphology, particle size distribution, thermal behavior, phase evolution, chemical analysis and magnetic properties of the products were investigated by SEM, LPSA, DTA/TGA, XRD, EDS and VSM techniques, respectively. EDS analysis confirmed the presence of barium hexaferrite in as-SHS sample. An exothermic peak appeared at 814 °C in DTA/TGA traces seems to be due to the formation of barium hexaferrite. Single-phase barium hexaferrite was formed after annealing of SHS product at 1150 °C for 2 h. SEM micrograph of the sample annealed at 1150 °C for 2 h showed plate-like hexagonal particles of barium hexaferrite with mean size of 2 μm. Saturation magnetization (Ms) and coercivity (Hc) for sample annealed at 1150 °C for 2 h were obtained 66 emu/g and 192 kA/m, respectively. The microstructure of as-SHS sample after it was pressed and then sintered at 1250 °C for 3 h exhibited nano-grains of barium hexaferrite with mean diameter of 200 nm.

Study on the iron–silica interaction of a co-precipitated Fe/SiO 2 Fischer–Tropsch synthesis catalyst

The structural properties and iron–silica interaction of the precipitated iron catalysts incorporated with or without silica have been investigated by powder X-ray diffraction (XRD), Mössbauer spectroscopy, and temperature-programmed reduction (TPR) with H 2 consumption quantitative analysis. The Fischer–Tropsch synthesis (FTS) performances of the catalysts were carried out in a slurry-phase continuously stirred tank reactor (CSTR). It was found that, for as-prepared samples, nano-particles of iron oxide mixtures (α- and/or γ-Fe 2O 3) formed on the silica-incorporated catalyst, whereas well-crystallized hematite (α-Fe 2O 3) is the only phase on the silica-free catalyst. After reduction in H 2, the observed phase in the silica-free catalyst is α-Fe, whereas wüstite (Fe x O) and iron (II) silicate (Fe 2SiO 4) are the main phases in the silica-incorporated catalyst. In H 2-TPR, the Fe 3+ ions in the silica-incorporated catalyst are reduced to Fe (0) via Fe 2+ ions as intermediate and the reduction extent of iron oxides obviously decreased comparing with the silica-free catalyst. The differences in structural properties and reduction behavior between the silica-free and the silica-incorporated catalysts may be due to the high dispersion effect of silica and the iron–silica interaction. The iron–silica interaction also decreases the FTS activity and improves the light hydrocarbon selectivity.

Red ochre decorations in Spanish Neolithic ceramics: a mineralogical and technological study

Some Neolithic ceramics from south-eastern Spain have red to brown external decorations called “almagras” (red ochre). The pigment layer is essentially composed of a mixture of clay and iron oxides: haematite (red) and maghemite (brown). It is suggested that maghemite was formed during the firing process of ceramic in a reducing atmosphere. Several laboratory tests have been carried out to obtain maghemite by adding charcoal or pinewood sawdust to similar ceramic pastes. In fact, maghemite was formed, even when the piece was simply covered with pinewood sawdust before firing. The diverse original red colours are due to variations in iron oxide (or calcite) content and to redox conditions in the firing procedure. Brown- coloured ceramics owe their colour to maghemite and must be considered as a “fabrication defect”, due to the position of the ceramic piece in a zone where a reducing atmosphere prevailed in the course of firing.

Laboratory study related to the production and properties of pig iron nuggets

Pig iron nuggets were produced in a laboratory-scale furnace at Michigan Technological University. The process was intended to replicate Kobe Steel's ITmk3 direct ironmaking process. These nuggets were produced from pellets that were made from a mixture of iron oxide, coal, flux and a binder and heated in a furnace with a chamber temperature of 1450{sup o}C. The pellets then self-reduced to produce a solid, high-density, highly metallized (96.5% Fe) pig iron. During the nugget production process, a separate liquid slag phase formed that cleanly separated from the molten metal. The physical and chemical properties of the pig iron nuggets were similar to pig iron produced by blast furnaces, which is distinct from direct reduced iron (DRI).

Effects of iron surface pretreatment on kinetics of aqueous nitrate reduction

Using hydrogen gas at 400 °C to activate iron surface was proposed to remove nitrate (40 mg N L −1) in a HEPES buffer solution at pH value between 6.5 and 7.5. Compared with the nonpretreated iron, the first-order reaction rate constant ( k obs) was increased 4.7 times by pretreated iron, and the lag of the early period disappeared. Normalized to iron surface area concentration, the specific rate constant ( k SA) was increased approximately by a factor of 6 using hydrogen reduction (0.0020 min −1 m −2 L for nonpretreated iron and 0.0128 min −1 m −2 L for pretreated iron). The reactivity of aged iron covered by a complex mixture of iron oxides (soaking in nitrate solution for 60 days) were restored by hydrogen gas at 400 °C. Scanning electron microscopy (SEM) and temperature-programmed reduction (TPR) exhibited visibly cleaner without pitting and cracking and less oxygen fraction on pretreated iron surface relative to nonpretreated iron. Activation energies ( E a) of nitrate reduction over the temperature range of 10–45 °C were 46.0 kJ mol −1 for nonpretreated iron, and 32.0 kJ mol −1 for pretreated iron, indicating chemical reaction control, rather than diffusion. The results indicated that this enhancement was attributed to the increase in active site concentration on iron surface by hydrogen reduction.

WEATHERING OF BASALTIC ROCKS FROM THE FRENCH MASSIF CENTRAL: ORIGIN AND FATE OF Ni, Cr, Zn AND Cu

We have examined the behavior of Cr, Ni, Cu and Zn during the weathering of basaltic rocks in a moderate temperate climate. Samples of unweathered basaltic rocks, moderately weathered and strongly weathered equivalents were studied at six sites from the Massif Central of France. Unweathered basaltic rocks and basanites are rich in Cr (248–455 mg/kg) and Ni (126–237 mg/kg); all four elements are present in similar amounts in all three categories of sample. The location of these trace elements was investigated by optical and electron microscopy (EMPA, SEM–EDS). In unweathered basaltic rocks, Cr bearing phases are: chromian spinel (4–42 wt%), Fe–Ti spinel (0.12–1.24 wt%) and titanian augite (200–8000 mg/kg), whereas nickel is incorporated into forsterite (830–3600 mg/kg) and the spinel-group minerals (0.11–0.14 wt%). Copper and Zn are found at lower concentrations, but regularly distributed in the phases studied. In weathered samples, authigenic phases fi ll fractures and also replace the primary minerals. They are composed of mixtures of clays, iron oxides and organic compounds. Authigenic phases contain lower amounts of those trace elements than primary minerals. Under conditions of moderate weathering, only 20 to 40% of the total content in Cr, Ni, Cu and Zn appears to be mobile during the weathering of the basaltic rocks. As spinel-group minerals are not affected by strong weathering under a temperate climate, only the fraction of Cr, Ni and Zn present in the silicates of the unweathered basaltic rocks is released.

Irradiation Temperature Dependence of the Efficiency of Radiation-Thermal Synthesis of Lithium Ferrite

Investigations are performed of the synthesis of lithium pentaferrite in the course of isochronous ferritizing annealing of a mixture of lithium carbonate and iron oxide of stoichiometric composition under irradiation by electrons. Within the temperature range 650–950 °C, an increase in the rate of synthesis is observed compared to that under thermal ferritizing annealing. The content of residual inclusions of orthoferrite, which is an intermediate phase, is found to be lower in the specimens synthesized by the radiation-thermal procedure. A model describing the radiation-enhanced process of synthesis is proposed.

Catalytic oxidation of carbon monoxide over gold/iron hydroxide catalyst at ambient conditions

Catalytic oxidation of carbon monoxide at ambient conditions has been studied over gold/iron hydroxide catalysts. The catalyst was prepared by a precipitation method, in which the HAuCl4 was precipitated onto a suspension of the iron hydroxide support, with a low calcination temperature. The support was composed of the mixture of iron hydroxide and iron oxide, the specific surface area was greater than 200m2/g. The catalytic activity of the oxidized gold species was more efficient than zero-valent gold atoms (Au0). The requirements of gold catalyst to have high oxidation activity are small particle size, a reductive support with high surface area, low calcination temperature, and gold particles in intimate contact with the support. The catalysts showed high activity for the oxidation of CO within 10,000ppm at ambient temperature under a very high space velocity of 5,00,000h−1. This catalyst had the lifetime of at least 200h. It was resistant to moisture and high concentration of CO2.

Influence of iron (56Fe2O3 or 54Fe2O3) in the upregulation of cytochrome P4501A1 by benzo[a]pyrene in the respiratory tract of Sprague-Dawley rats.

Any influence of iron in polycyclic aromatic hydrocarbon (PAH)/iron oxide mixtures on the capacity of PAHs to induce metabolizing enzymes will be one of the ways that iron oxides can affect PAH carcinogenicity. Because cytochromes P450 (CYPs) are haemoproteins, it will be of interest to investigate the possible involvement of Fe(2)O(3) in benzo[a]pyrene (BaP)/Fe(2)O(3) mixtures on the induction of CYP1A1 enzymes in the lung. Male Sprague-Dawley rats were instilled intratracheally with haematite ((56)Fe(2)O(3) or (54)Fe(2)O(3), 3 mg), BaP (3 mg) or BaP (3 mg) coated onto haematite ((56)Fe(2)O(3) or (54)Fe(2)O(3)) particles (3 mg). Firstly, mRNA expressions of cyp1a1 were studied. Secondly, protein concentrations and catalytic activities (7-ethoxyresorufin O-deethylase: EROD) of CYP1A1 were determined. Thirdly, (54)Fe from BaP/(54)Fe(2)O(3) mixtures in microsomal proteins was studied using time-of- flight laser microprobe mass spectrometry (ToF-LMMS). Statistically significant increases in mRNA expressions, protein concentrations and catalytic activities of CYP1A1 were observed in animals exposed to BaP, to BaP coated onto (56)Fe(2)O(3) particles or to BaP coated onto (54)Fe(2)O(3) particles versus controls. Both of the BaP/Fe(2)O(3) mixtures induced higher CYP1A1 protein levels and EROD activities than BaP alone. Iron oxide particles per se did not affect mRNA levels of cyp1a1 but only enhanced BaP-mediated increases of CYP1A1 protein levels and activity. The ToF-LMMS spectrum pro fi les showed that the (54)Fe/(56)Fe ratio in the microsomes of BaP coated onto (54)Fe(2)O(3) particle-instilled animals was 1.3 instead of the theoretical ratio (i.e. 0.063) observed in BaP coated onto (56)Fe(2)O(3) particle-instilled animals. Taken together, these novel data support the hypothesis that the Fe(2)O(3)-induced increases of the metabolic activation of BaP might rely on the property of Fe(2)O(3) particles to enhance the BaP-induced translation rate of the cyp1a1 gene into functional haemoproteins.

Cadmium complexation by bacteriogenic iron oxides from a subterranean environment

This study quantifies the metal sorption characteristics of subterranean bacteriogenic iron oxides (BIOS) and their organic phases (intermixed intact and fragmented bacteria). A Cd 2+ ion-selective electrode was used to generate high-resolution metal sorption data as a function of increasing pH. A multisite Langmuir model, along with a linear programming regression method (LPM), was applied to fit experimental data. This approach found two discrete Cd 2+ binding sites for the BIOS with average −log 10 equilibrium constants (p K S, j ) of 1.06±0.19 and 2.24±0.28. Three discrete sites were obtained for the bacterial fraction, with p K S, j values of −0.05±0.12, 1.18±0.02, and 3.81±0.16. This indicated that the BIOS surface had a lower affinity for Cd 2+ than that of the bacteria. p K S, j values for the BIOS were similar to those reported for pure iron oxide phases, while the organic fraction p K S, j spectrum was consistent with previous spectra for intact bacteria. Individual binding site densities of 0.04±0.01 and 0.05±0.02 and 0.29±0.05, 0.11±0.01, and 0.09±0.02 μmol/mg of BIOS corresponded to the iron oxide mixture and bacteria fraction, respectively. These values indicated high concentrations of strong affinity Cd 2+ complexing groups on the bacterial surface. Comparison of total site densities of 0.08±0.02 and 0.48±0.06 μmol/mg of BIOS for the mixture and the bacterial phase, respectively, suggested a nonadditive character for the BIOS surface reactivity. This was emphasized by a higher affinity for Cd 2+, as well as an increase in total site concentration observed for the bacterial phase. LPM was able to distinguish between the BIOS mixture and its organic fraction Cd 2+ complexation characteristics. This approach is therefore a useful tool for the study of natural sorbent materials controlling metal partitioning in contaminated and pristine environments.

Biological treatment of Mn(II) and Fe(II) containing groundwater: kinetic considerations and product characterization

In the present article, the treatment of groundwater containing Mn(II) and Fe(II) has been investigated. The biological oxidation of Mn(II) and Fe(II) in upflow filtration units comprised the applied experimental technique. The oxidation processes were mediated by specific bacteria, namely the Leptothrix ochracea and Gallionella ferruginea, which belong to the general category of manganese and iron oxidizing bacteria. This work was focused on the characterization of the products of biological oxidation and to the examination of the kinetics of Mn(II) removal as compared with Fe(II) removal from groundwaters. The products of biological oxidation were characterized using the spectroscopic techniques XRD, XPS and SEM-EDS and comprised a mixture of biogenic hydrous manganese and iron oxides. The oxidation state of manganese in the precipitates was found to be between 3 and 4. Iron oxides were mainly in the form of amorphous ferrihydrite. The kinetic results indicated that the rates of manganese and iron oxidation were several orders of magnitude greater than the respective for abiotic oxidation. The bacterially mediated oxidation of iron was faster than manganese oxidation, presenting half-lives of reaction 0.9 and 3.98 min, respectively.

Combustion synthesis of zinc ferrite powders in oxygen

The synthesis of zinc ferrite powders is carried out by combustion of a mixture of iron, iron oxides and zinc oxide powders in oxygen. An increase of oxygen pressure increases both the combustion temperature and velocity. The combustion reaction can not be self-sustained when the oxygen pressure is below 0.3 MPa. The results of XRD and Mössbauer spectroscopy show that intermediate phases of iron oxide, Fe 1− x O, Fe 1− z O and crystal defects appear when the oxygen pressure is excessively low or high. An analysis of the dependence of the degree of conversion to ferrite on the oxygen pressure has been made. In addition, the reaction mechanism associated with the combustion synthesis (CS) of ZnFe 2O 4 is proposed.