Iron Oxides Hematite Research Articles

Carbon Coated α-Fe2O3 Nano-Particles as High Performance Anodic Material for Lithium-Ion Batteries

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An Aerosol-Process for the Synthesis of Nanostructured Molybdenum Oxide Catalysts by Integrated Chemical Vapour Synthesis/Chemical Vapour Deposition at Atmospheric Pressure

We report the synthesis of composite nanoparticles by an integrated CVS/CVD process at atmospheric pressure. Iron oxide and silica support particles were generated by chemical vapour synthesis (CVS), using Fe(CO)5 and Si(OC2H5)4 and were directly coated in the aerosol state with molybdenum oxide by chemical vapour deposition of Mo(CO)6. Depending on the CVS temperature hematite (600 degrees C) or maghemite (1500 degrees C) iron oxide phases were determined by XRD and FTIR. Core-shell structures with a coating thickness in the lower nm range were obtained for CVD temperatures below 150 degrees C. Complete encapsulation of the core particles and uniform elemental distribution is shown by TEM and EELS measurements. Higher CVD temperatures lead to unwanted homogenous decomposition of the molybdenum precursor. Additional aerosol temperature treatment was used to reach further oxidation and the formation of a mixed oxide shell, indicated by FTIR measurements. The results show the potential of the process for the synthesis of structured core-shell nanoparticles.

Microstructure Characteristics of the Black-Glazed Shreds Excavated from the Qingliangsi Kiln

The black-glazed shreds from Qingliangsi kiln were studied. The glaze and body micro- structures, compositions and crystal phases were observed and analyzed by field emission scanning electron, microscope multiple functions electron probe-energy spectrum instrument and field emission transmission electron microscope. The iron oxide crystal in oil spot was mainly the ε-Fe2O3 in the orientation of the zone axis [001], and also few content of ε-Fe2O3 in the orientation of the zone axis [412]. The brown oil spots on the glaze surface were aggregations of a great deal of iron oxide hematite crystals. Bodies of black-glazed shreds have high Al2O3(26.47 % ~ 30.48%) and low SiO2 (62.77% ~ 66.20%), which pertained to the typical recipe of north porcelain bodies. The glaze are attributed to calcium-alkali glaze, and according to the ratio of Al2O3:SiO2, it belongs to the crystallization glaze.

Mössbauer, Raman, and Magnetoresistance Study of Aluminum-Based Iron Oxide Thin Films

Thin films of Al-based hematite iron oxide were synthesized by spray pyrolysis in aqueous medium onto the glass microslides. The compact and homogeneous distribution of grains (spindle-shaped hematite nanostructures) with varying sizes has been observed in surface morphological studies. The room temperature Mossbauer study has been carried out to monitor the local environment around Fe cations and valence state of Fe ions. Mossbauer and micro-Raman (low temperature) results suggest that oxygen vacancies cause cation redistribution between the interstitial sites resulting in magnetic ordering. The variation of magnetoresistance in low magnetic field (<3 kOe) is also reported.

INFLUENCE OF PREHEATING PARAMETERS ON THE PLASMA-JET OXIDATION OF A LOW-CARBON STEEL

The adhesion/cohesion (A/C) of coatings onto metallic substrates is an important property for most service conditions. Preheating the substrate before spraying the powder is a way to improve its A/C. It results in a surface oxidation of the substrate due to the high temperature of the gas close to the substrate surface and consequently to the high level of atomic oxygen. This study is devoted to the estimation of the influence of this oxide layer onto the A/C values. A precise monitoring of the preheating process by presetting values of the heating rate, temperature level, and heating time allows producing oxide layers with controlled composition and thickness. In the studied case of low carbon steel a specific choice in the heating rate and temperature leads to the production of an oxide layer with a low or high content of hematite layers in a duplex layer of hematite and magnetite iron oxides.

A magnetic zeolitic nanocomposite from occlusion of silica-coated iron species by crystalline titanosilicate-1

This paper examines the preparation of novel magnetic zeolitic nanocomposites from the occlusion of silica-coated iron species by crystalline titanosilicate-1. The results revealed that well-crystallized TS-1 could be synthesized in the presence of silica-hematite nanoparticles. Each as-made nanocomposite particle exhibited a compact and monolithic ‘brick-like’ morphology with a size of ca. 400 nm × 200 nm × 200 nm. The non-magnetic hematite (iron oxide) in such an as-made nanocomposite can be reduced by hydrogen to produce ferrimagnetic iron oxides and ferromagnetic elemental iron. The resultant nanocomposite consists of TS-1 as outer shell, which occludes a small portion of silica-iron species as the core with a total magnetization value of 3.7 emu/g. The silica coating and size of hematite nanoparticles, the presence of ammonium carbonate as the crystallization-mediating agent for nucleation and growth of TS-1 are critical factors when preparing such nanocomposites.

Formation of nanoscale platinum and iron oxide structures using electron beam induced deposition techniques

Electron beam induced deposition (EBID) is a promising technique for fabricating nanometre-sized structures in a position-controlled manner. In this technique, organometallic precursors are decomposed by focused electron beams. Then, the non-volatile part of the decomposed precursor deposits on the substrate. As electron beams can be focused to a subnanometre scale in modern electron microscopes, the resolution of EBID is now reaching down to subnanometres. However, the deposits generally contain a large amount of amorphous carbon. This carbon contamination may be the most serious drawback and is preventing practical uses of EBID in nanodevice technology. In this study, nanostructures, such as nanowires, were fabricated by EBID using methyl cyclopenta dienyl platinum trimethyl (MeCpPtMe3) and iron pentacarbonyl (Fe(CO)5) precursors in a scanning electron microscope with a custom-made gas introduction system. After the deposition, nanostructures were heated at 400°C in air for 30 min. to remove contaminated carbon. Then, the nanostructures were observed using a transmission electron microscope (TEM). TEM observation revealed that a post-deposition heat-treatment in air resulted in the removal of carbon. The nanostructures made from MeCpPtMe3 and Fe(CO)5 became pure Pt and a mixture of hematite and maghemite iron oxides, respectively.

Sorption of selenium(IV) and selenium(VI) onto natural iron oxides: Goethite and hematite

Selenium is a toxic element with a relatively high mobility in the natural waters. Iron oxy-hydroxides might play an important role in the migration of this element as well as on its removal from contaminated water. In this work we study the interaction of Se(IV), and Se(VI) with natural iron oxides hematite and goethite through two series of batch experiments at room temperature. In the first series, sorption as a function of initial selenium concentration is studied and the results have been fitted with Langmuir isotherms. In a second series of experiments, sorption is studied as a function of pH, being the main trend an increase of the sorption at acidic pH. The variation of the sorption with pH has been modelled with a triple layer surface complexation model and using the FITEQL program. The experimental data have been modelled considering for the Se(IV) the formation of the FeOSe(O)O − complex onto the hematite surface, and a mixture of FeOSe(O)O −, and FeOSe(O)OH onto the goethite surface. For Se(VI) the surface complex considered is FeOH 2 +–SeO 4 2− on both goethite and hematite.

Evolution of the bulk structure and surface species on Fe–Ce catalysts during the Fischer–Tropsch synthesis

Two Fe–Ce catalysts were prepared by wet impregnation of Ce onto iron oxyhydroxide (FeOOH) and hematite iron oxide (α-Fe2O3), respectively. Their performance in the Fischer–Tropsch (FT) synthesis was investigated and compared with that obtained with a Ce-free α-Fe2O3 catalyst. It was observed that the behavior of the different catalysts changed along the course of the FT reaction. The catalysts were tested for different periods of time, carefully passivated, recovered from the reactor and characterized by different techniques. The FT activity of the Ce-loaded and Ce-free catalysts decreased initially, but at a certain point the catalytic activity started to increase. The time needed to reach this inflection point depended on the catalyst composition, being shorter for the Ce-promoted catalysts. The catalytic activity of the Ce-free catalyst increased when the Fe3C species were transformed into χ-Fe2.5C, which are suggested to be the carbide phase present when polymerized carbon species (Cβ) are formed. The addition of Ce to the iron oxyhydroxide developed solids with a higher BET surface area. Besides, these samples displayed a higher FT activity at long time-on-stream (TOS). Moreover, Ce addition also facilitated the formation of the Cβ species previous to the evolution of Fe3C into χ-Fe2.5C, and therefore, promoted the FT synthesis reaction.

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A new simple method permits the growth of vertically aligned iron oxide haematite nanowires with potential applications in magnetic storage media

Optical Properties of Hydrothermally Synthesized Hematite Particulate Pigments

Iron oxide hematite particles with various shapes (platelet, polyhedron, pseudocube, and peanut‐like) have been synthesized by hydrothermal treatment of a Fe(OH)xOy precursor under various conditions. The size and shape of hematite particles can be adjusted by carefully controlling the processing parameters such as holding time, temperature, and adsorption ions present in the system. The nearly monosized α‐Fe2O3 platelets possess face diameters of approximately 3 μm and a thickness of 0.5 μm under a scanning electron microscope. The apparent color of the particles changes as particle size and shape varies. Munsell color notation was employed to compare the color of hematite particles with various sizes and shapes. Diffuse reflectance spectra show that a “red‐shift” of 40 nm is observed in platelet, pseudocube, and peanut‐like particles compared with conventional particles. The band at 850 nm for the 6A1→4T1 transition was split in the pseudocubic and peanut‐like particles. Raman spectra of the hematite particles also reveal that the vibrational modes of α‐Fe2O3 particles diminish as particle size decreases, and dependence of vibrational band intensity on frequency is also observed. The spectral profiles demonstrate significant difference as excitation radiation lines changes from blue (457 nm) to red (647 nm). Possible mechanisms responsible for the optical properties of hematite particles are postulated based on the findings of the experiments.

Interpreting fracture development from diagenetic mineralogy and thermoelastic contraction modeling

Four sets of thin-section scale, Mode I (open mode), cemented microfractures are present in sandstone from the Eocene Misoa Formation, Maracaibo basin, Venezuela. The first set of microfractures is intragranular (F1), formed early during compaction and are filled with quartz cement precipitated at temperatures equal to or higher than 100 °C. The second set of microfractures (F2) is cemented by bituminite–pyrite, formed at temperatures between 60 and 100 °C, and are associated with kerogen maturation and hydrocarbon migration from underlying overpressured source rocks. The third set of microfractures (F3) is fully cemented by either quartz cement or calcite cement. The former has fluid inclusion homogenization temperatures between 149 and 175 °C. These temperatures are mostly higher than maximum burial temperatures (∼160 °C), suggesting that upward flow, caused by a pressure gradient, transported silica vertically which crystallized into the fractures. Upward decompression may have also caused a P CO 2 drop, which, at constant temperature, allowed simultaneous carbonate precipitation into the third microfracture set. The fourth set of thin-section scale microfractures (F4) is open or partially cemented by siderite–hematite and other iron oxides. The presence of hematite and iron oxides in microfractures is evidence for oxidizing conditions that may be associated with the uplift of the Misoa formation. In order to time and place constraints on the depth of formation of the fourth set of microfractures, we have coupled published quartz cementation kinetic algorithms with uniaxial strain equations and determined if, in fact, they could be associated with the uplift of the formation. Our results suggest that thermoelastic contraction, caused by the formation's uplift, erosion, and consequent cooling is a feasible mechanism for the origin of the last fracture set. Hence, we infer that meteoric water invasion into the fractures, at the end of the uplift, cause the precipitation of oxides and the transformation of siderite to hematite.

Multiple scattering analysis of O K-edge NEXAFS in iron oxides

We report a detailed analysis of O K-edges near edge x-ray absorption of maghemite, hematite and magnetite iron oxides. Measurements were performed on powder in Fluorescence Yield mode of detection.Iron forms several stable oxides and its phase diagram is more complicated than that of other transition metal as Ni or Co. The differences in the local symmetry of the three iron oxides are related with the distinguishable NEXAFS spectra. In particular the spectra are characterized by a sharp doublet ascribable to transitions to the empty metal d-bands involving the t2g and eg states whose energy splitting and intensities depend on the structure and state of ionicity.The NEXAFS spectra have been simulated and fitted by MXAN code. The aim of these simulations was the test of light Z element NEXAFS spectra calculation performed by phenomenological no-self-consistent potential in the near edge region, the most sensible to electronic properties details; a fit procedure of the potential parameters was performed in the extended NEXAFS photon energy range and subsequently used for near edge calculations. The MXAN simulations obtained in this way, reproduce the experimental data with good agreement and evidentiate the differences in the spectra of the three compounds. In particular maghemite, that has oxygen in two different sites, has been well simulated using potential details found for the other oxides hematite and magnetite.

A Mössbauer spectroscopic study of the iron redox transition in eastern Mediterranean sediments

Fe cycling at two sites in the Mediterranean Sea (southwest of Rhodes and in the North Aegean) has been studied, combining the pore water determination of nutrients, manganese, and iron, citrate-bicarbonate-dithionite (CDB) and total sediment extractions, X-ray diffraction, and 57Fe Mössbauer spectroscopy (MBS). At the Rhodes site, double peaks in the CDB-extractable Mn and Fe profiles indicate non-steady-state diagenesis. The crystalline iron oxide hematite, identified at both sites by room temperature (RT) MBS, appears to contribute little to the overall Fe reduction. MBS at liquid helium temperature (LHT) revealed that the reactive sedimentary Fe oxide phase was nanophase goethite, not ferrihydrite as is usually assumed. The pore water data at both sites indicates that upon reductive dissolution of nanophase goethite, the upward diffusing dissolved Fe 2+ is oxidized by Mn oxides, rather than by nitrate or oxygen. The observed oxidation of Fe 2+ by Mn oxides may be more common than previously thought but not obvious in sediments where the nitrate penetration depth coincides with the Mn oxide peak. At the Rhodes site, the solid-phase Fe(II) increase occurred at a shallower depth than the accumulation of dissolved Fe 2+ in the pore water. The deeper relict Mn oxide peak acts as an oxidation barrier for the upward diffusing dissolved Fe 2+, thereby keeping the pore water Fe 2+ at depth. At the North Aegean site, the solid-phase Fe(II) increase occurs at approximately the same depth as the increase in dissolved Fe 2+ in the pore water. Overall, the use of RT and cryogenic MBS provided insight into the solid-phase Fe(II) gradient and allowed identification of the sedimentary Fe oxides: hematite, maghemite, and nanophase goethite.

The Falémé Iron District, Senegal

The Faleme iron district in the Kedougou-Kenieba inlier of the Paleoproterozoic Birimian Supergroup of West Africa consists of nine major and 19 minor orebodies, distributed in a belt 65 km long and 15 km wide. Two major exoskarn orebodies have total reserves of 320 million metric tons (Mt) magnetite ore with 42 percent Fe, and seven major supergene-enriched orebodies, which overlie endoskarn, have reserves of 310 Mt with 59 percent Fe. Previous workers advocated an (exhalative)-sedimentary origin for the primary ore. In this paper, however, we present strong evidence for contact-metasomatic skarn mineralization associated with microdiorite intrusions, with an emphasis on the Karakaene-Ndi and Goto deposits. The ore deposits of the Faleme district are the only major Precambrian magnetite skarn deposits worldwide that have not been subjected to postore metamorphism. The deposits of the Faleme district have many similarities to Phanerozoic magnetite skarn deposits that are associated with dioritic intrusions and also lack postore metamorphism. The endoskarn of the Karakaene-Ndi deposit is hosted by microdiorite with pervasive albitization. Garnet (And 56 –100 Grs 0 –43 Alm 0 –2 Sps 0 –1 Pyr 0 –1 ) and clinopyroxene (Di 58 –100 Hed 2 –42 ) are early phases. Individual grains of garnet and clinopyroxene commonly are inhomogeneous, with Fe being concentrated at the margin of the grains rather than in the core. Fe-rich zones in clinopyroxene are also enriched in Na. Biotite and magnetite precipitated relatively late, followed by pyrite (2 vol %) ± chalcopyrite ± pyrrhotite ± iss. Aqueous-carbonic fluid inclusions in quartz from one sample have CO 2 concentrations of 5 to 14 mol percent and indicate pressures of 300 to 900 bars and temperatures of 281° to 373°C at total homogenization. The magnesian exoskarn of the Goto deposit is hosted by dolomitic and calcitic marble, which locally contains graphite. Magnetite is associated with prograde clinopyroxene (Di 89 –100 Hed 0 –11 ) and phlogopite-rich biotite (Mg/(Mg + Fe)~0.89) as well as retrograde serpentine. Garnet is scarce. Sulfur concentrations average 1 wt percent. Pyrrhotite and subordinate pyrite ± chalcopyrite ± arsenopyrite ± pentlandite ± cobaltite postdate most of the magnetite. The exoskarn formed under more reducing conditions and at lower temperatures than the endoskarn. Magnetite in the exoskarn has trace element concentrations similar to those of magnetite in the endoskarn but is distinguished from igneous magnetite in granodiorite and magnetite in andesite (possibly of igneous origin) by low concentrations of Cr 2 O 3 and V 2 O 5 . Microdiorite is the most likely source of iron although no igneous magnetite in microdiorite could be identified. Microdiorite with only moderate hydrothermal alteration has lower iron concentrations (1.6–4.5% Fe 2 O 3(total) ) than unaltered granodiorite and weakly altered andesite in the area (avg ~7% Fe 2 O 3(total) ). Iron was probably leached from the moderately altered microdiorite and transferred into zones of intense alteration in microdiorite and host-rock marble. The low degree of hydrothermal alteration of granodiorite and small areal extent of andesite argue against a granodioritic or andesitic source of iron. The supergene ore is derived from endoskarn with about 30 percent Fe and consists of hematite and hydrous iron oxides. The largest orebodies have a thickness of 100 m and are located in the central part of hills that rise 250 m above the surrounding peneplain; the bottom of the enrichment zone usually is centered deep below the top of the hills. The absence of supergene enrichment in exoskarn orebodies probably is due to unfavorable structural conditions. Supergene enrichment of endoskarn was probably not exclusively by residual enrichment, in which Ca, Mg, Na, and Si were removed from the orebody, but also involved addition of Fe from descending solutions to the site of enrichment. Exploration for new supergene iron ore should be focused outside the exoskarn belt between Goto and Safa, as the deposits in this area are unlikely to have experienced major supergene enrichment. The Faleme district has some similarities to the geologic setting of iron oxide-copper-gold districts in which the deposits are hosted by dioritic rocks and may be representative of an iron oxide-rich end member of the iron oxide-copper-gold class. However, only about 3 t of gold have been mined from alluvial deposits in the area and the district is relatively poor in copper.

Effect of the surfactant and precipitant on the synthesis of pink coral by a microemulsion method

The use of hematite and other iron oxides as a natural red ceramic pigment has been known since prehistoric times and, probably, is the first ceramic pigment to have been employed by humanity. However, hematite crystals grow with temperature and the colour shade becomes unstable. The best red shades are obtained by the inclusion of hematite in silica or in zircon (pink coral) casings. A microemulsion method has been applied in order to improve the inclusion efficiency of hematite into zircon crystals; the effects of several parameters on the synthesis, such as the precipitating agent (ammonia or alkaline hydroxides), the surfactant (anionic or cationic) and the flux agent (NaF or NaF.2NaCl), have been studied.

Deposition of epitaxial α-Fe2O3 layers for exchange bias studies by reactive dc magnetron sputtering

Abstract We describe the deposition and characterization of epitaxial thin films of the iron oxide haematite (α-Fe2O3), a promising candidate for fundamental studies of exchange anisotropy as well as for high thermal stability applications. The films were deposited by reactive dc magnetron sputtering. Structural characterization was by large-angle X-ray diffraction and grazing-incidence reflectivity (with the scattering vector normal to the sample piane), in-plane grazing-incidence diffraction (scattering vector in the sample piane) and reflection high-energy electron diffraction. Optimized sputtering conditions result in good epitaxy both in the growth direction and in the piane, as well as very smooth surfaces.

Deposition of epitaxial α-Fe2O3 layers for exchange bias studies by reactive dc magnetron sputtering

Abstract We describe the deposition and characterization of epitaxial thin films of the iron oxide haematite (α-Fe2O3), a promising candidate for fundamental studies of exchange anisotropy as well as for high thermal stability applications. The films were deposited by reactive dc magnetron sputtering. Structural characterization was by large-angle X-ray diffraction and grazing-incidence reflectivity (with the scattering vector normal to the sample piane), in-plane grazing-incidence diffraction (scattering vector in the sample piane) and reflection high-energy electron diffraction. Optimized sputtering conditions result in good epitaxy both in the growth direction and in the piane, as well as very smooth surfaces.

Narrow Mie Optical Cavity Resonances from Individual 100 nm Hematite Crystallites

Rhombohedral single crystallites of hematite (iron oxide, α-Fe2O3) in the size range of 20−200 nm have been synthesized by forced hydrolysis in water. The optical Rayleigh scattering and AFM topography of individual crystallites have been recorded on an inverted microscope based apparatus. Individual crystallites show narrow Mie “optical cavity” resonances across the visible spectrum as the particle size increases. These spectra are far sharper than the size broadened extinction spectra of the parent colloid. In the blue region near the intense band gap optical absorption, the resonances are also significantly sharper than calculated from simple scattering theory. This unexpected structure is discussed in terms of single crystallite birefringence, and uncertainties in hematite bulk optical properties.

Fractography, Fluidity,and Tensile Properties of Aluminum/Hematite Particulate Composites

This paper examines the effect of hematite (iron oxide) particles on the fluidity of the molten composite as well as the tensile properties and fracture behavior of the solidified as-cast aluminum composites. The percentage of hematite in the composite was varied from 1 to 7% in steps of 2% by weight. The vortex method was employed to prepare the composites. It followed from the results obtained that the ultimate tensile strength and Young’s modulus of the composite increased while the liquid fluidity and solid ductility decreased with the increase in hematite content in the composite specimens. The fluidity of the liquid was greater in a metal mold than in a sand mold, and it decreased with an increase in reinforcing particle size and increased with pouring temperature. The presence of the reinforcing particles altered the fracture behavior of the solid composites considerably. Final fracture of the composite occurred due to the propagation of cracks through the matrix between the reinforcing particles.