Showing papers on "Magnetite published in 1999"
TL;DR: In this paper, the micro-Raman spectra of hematite, magnetite and other iron oxides were compared with literature data and compared with a Stokes-Anti-Stokes procedure was used to control the local temperature during the measurement and also for calibration of the wavenumbers.
Abstract: Films and powders of iron oxide (Fe2O3) prepared by two different sol–gel syntheses, starting from Fe(NO3)3·9H2O or FeCl3·6H2O, were investigated by Raman microscopy. Different phases with different morphology were produced according to the preparation. The spectra obtained in the micro-Raman configuration were compared with the ambiguous data in the literature given by conventional Raman techniques. The principal difficulty in the correct interpretation of the Raman spectrum of the iron oxides is the co-existence of different phases. Contradictory results are also explained by laser–induced thermal effects which easily change the wavenumbers and lineshapes of the phonons. A Stokes–Anti-Stokes procedure was utilized to control the local temperature during the measurement and also for calibration of the wavenumbers. The micro-Raman spectra of hematite, magnetite and other iron oxides are presented and compared with literature data. Copyright © 1999 John Wiley & Sons, Ltd.
471 citations
TL;DR: In this paper, a comparative study of the specific loss power generated by an external magnetic field in superparamagnetic as well as ferromagnetic magnetite particles suspended in molten and solidified gel is presented.
380 citations
TL;DR: In this article, the magnetite core and polymeric shell were synthesized in a single inverse microemulsion and the particle size was varied in the range 80−320 nm by changing of the monomer concentration and water/surfactant ratio.
Abstract: A novel approach to prepare magnetic polymeric nanoparticles by synthesis of the magnetite core and polymeric shell in a single inverse microemulsion is reported. Stable magnetic nanoparticles colloid dispersion with narrow size distribution can thus be produced. The microemulsion seed copolymerization of methacrylic acid, hydroxyethyl methacrylate, and cross-linker results in a stable hydrophilic polymeric shell of the nanoparticles. The preparation of the nanoparticles was carried out also by the two-stage microemulsion process and the seed precipitation polymerization. The particle size was varied in the range 80−320 nm by changing of the monomer concentration and water/surfactant ratio. The magnetic properties and the size distribution of the nanoparticles synthesized by these three methods were compared. The polymeric nanoparticles synthesized in single microemulsion have superparamagnetic properties and the narrowest size distribution.
357 citations
340 citations
01 Apr 1999
TL;DR: The variation in the polymeric shell size and the polymer net density can be useful tools for evaluation of the polymer-coated magnetite particles as effective contrast agents.
Abstract: The properties of polymer-coated magnetite nanoparticles, which have the potential to be used as effective magnetic resonance contrast agents, have been studied. The magnetite particles were synthesized by using continuous synthesis in an aqueous solution. The polymer-coated magnetite nanoparticles were synthesized by seed precipitation polymerization of methacrylic acid and hydroxyethyl methacrylate in the presence of the magnetite nanoparticles. The particle size was measured by laser light scattering. It was shown that the particle size, variance, magnetic properties, and stability of aqueous magnetite colloidal dispersion strictly depend on the nature of the stabilizing agent. The average hydrodynamic radius of the magnetite particles was found to be 5.7 nm in the stable aqueous colloidal dispersion. An inclusion of the magnetite particle into a hydrophilic polymeric shell increases the stability of the dispersion and decreases the influence of the stabilizing agent on the magnetic and structural properties of the magnetite particles as was shown by X-ray diffraction and Mossbauer and IR spectroscopy, as well as by vibrating sample magnetometry. The variation in the polymeric shell size and the polymer net density can be useful tools for evaluation of the polymer-coated magnetite particles as effective contrast agents.
285 citations
TL;DR: The advantage of this method lies in the formation of a red intermediate during the reduction process, which enables us to prevent the reoxidation of the ferrous ions by adding precipitation agents at the end of the reduction reaction without the protection of nitrogen or argon.
239 citations
TL;DR: The main mechanism responsible for the transfer of ferric iron towards the Earth's mantle is the production of magnetite during the hydrothermal alteration of the oceanic crust.
152 citations
TL;DR: In this article, detailed mineral magnetic measurements were conducted on a 9000-year varved lake sediment sequence in northern Sweden (Lake Sarsjon) and the results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments, which is controlled to a large extent by the intensity of the spring snow melt.
Abstract: Detailed mineral magnetic measurements were conducted on a 9000-year varved lake sediment sequence in northern Sweden (Lake Sarsjon). The results demonstrate that the paramagnetic susceptibility reflects the concentration of detrital minerogenic material in the lake sediments, which is controlled to a large extent by the intensity of the spring snow melt. In contrast, the concentration of ferrimagnetic magnetite (reflected by initial magnetic susceptibility and magnetic hysteresis parameters) is positively correlated to the concentration of organic carbon, which is most likely of an autochthonous origin. This magnetite has magnetic properties that are characteristic of stable single-domain magnetite grains produced by magnetotactic bacteria. The paramagnetic susceptibility record clearly points to a climatic excursion in the early Holocene between 6100± 174 bc and 5700± 167 bc, which can be correlated to an d18O excursion (a cold event) in the Greenland ice cores and lake sediments in southern Germany, an...
142 citations
TL;DR: With the fractionation curve established in this report, oxygen-18 isotope values of bacterial Fe(3)O(4) may be useful in paleoenvironmental studies for determining the oxygen- 18 isotopevalues of formation waters and for inferring paleotemperatures.
Abstract: A series of carefully controlled laboratory studies was carried out to investigate oxygen and iron isotope fractionation during the intracellular production of magnetite (Fe 3 O 4 ) by two different species of magnetotactic bacteria at temperatures between 4° and 35°C under microaerobic and anaerobic conditions. No detectable fractionation of iron isotopes in the bacterial magnetites was observed. However, oxygen isotope measurements indicated a temperature-dependent fractionation for Fe 3 O 4 and water that is consistent with that observed for Fe 3 O 4 produced extracellularly by thermophilic Fe 3+ -reducing bacteria. These results contrast with established fractionation curves estimated from either high-temperature experiments or theoretical calculations. With the fractionation curve established in this report, oxygen-18 isotope values of bacterial Fe 3 O 4 may be useful in paleoenvironmental studies for determining the oxygen-18 isotope values of formation waters and for inferring paleotemperatures.
134 citations
TL;DR: In this paper, the effects of water chemistry and surface precipitate buildup on the removal of soluble uranium by zero valent iron were investigated, and the results indicated that the rate of uranium removal is not strongly dependent on the thickness of the adsorbed uranium layer.
Abstract: Removal of uranium from contaminated ground water using zero valent iron is currently under evaluation at several U.S. Department of Energy (DOE) facilities. Uranium removal by zero valent iron may occur via adsorption onto iron corrosion products, and by reduction to less soluble valence states by reactions with elemental iron. This research investigated the effects of water chemistry and surface precipitate buildup on the removal of soluble uranium by zero valent iron. Batch testing was performed to assess solution chemistry effects on uranium adsorption to the potential iron corrosion products, magnetite and a mixed valent amorphous iron oxide. Uranium adsorption to the simulated iron corrosion products was highly dependent on pH, and the concentration and speciation of the background electrolyte solution. Uranium removal via reduction by elemental iron closely approximated pseudo-first-order removal kinetics, despite the buildup of up to 40,000 monolayers of precipitated uranium on the iron surfaces. This indicates that the rate of uranium removal is not strongly dependent on the thickness of the adsorbed uranium layer. Short-term rates of uranium reduction were similar for all solutions tested, but long-term rates were highly dependent on water chemistry. Compared to deionized water, uranium removal rates were increased in sodium chloride containing solutions and reduced in sodium nitrate solutions. The strong influence of water chemistry on long-term reduction rates indicates that system design will require extnded testing with the ground water of interest.
100 citations
TL;DR: The ability of the iron minerals hematite and magnetite to catalyze the decomposition of hydrogen peroxide (H2O2) and initiate the Fenton-like oxidation of pentachlorophenol (PCP) was investigated in batch, bench-scale systems in which PCP was spiked onto silica sand as discussed by the authors.
Abstract: The ability of the iron minerals hematite and magnetite to catalyze the decomposition of hydrogen peroxide (H2O2) and initiate the Fenton-like oxidation of pentachlorophenol (PCP) was investigated in batch, bench-scale systems in which PCP was spiked onto silica sand. Pentachlorophenol degradation was documented in silica sand–mineral–H2O2 systems by the release of chloride and the loss of total organic carbon. The most efficient oxidation stoichiometry was the magnetite-catalyzed reaction over the first 8 h with 490 mol H2O2 consumed/mol PCP degraded. After 8 h, the peroxide efficiency decreased significantly; amorphous iron hydroxide formation on the magnetite surface may have catalyzed the decomposition of H2O2 to oxygen species other than hydroxyl radicals. Mineral-catalyzed Fenton-like treatment in two natural soils was demonstrated after spiking the soils with PCP; the contaminant was degraded with no iron addition. The oxidation stoichiometry in the two soils was 1,100 and 2,930 mol H2O2 c...
TL;DR: In this paper, the authors conclude that the magnetic particles present in the airborne dust particles are most likely Maghemite (γ-Fe2O3) or magnetite (Fe3O4).
Abstract: The Mars Pathfinder lander carried two magnet arrays, each containing five small permanent magnets of varying strength. The magnet arrays were passively exposed to the wind borne dust on Mars. By the end of the Mars Pathfinder mission a bull's-eye pattern was visible on the four strongest magnets of the arrays showing the presence of magnetic dust particles. From the images we conclude that the dust suspended in the atmosphere is not solely single phase particles of hematite (α-Fe2O3) and that single phase particles of the ferrimagnetic minerals maghemite (γ-Fe2O3) or magnetite (Fe3O4) are not present as free particles in any appreciable amount. The material on the strongest magnets seems to be indistinguishable from the bright surface material around the lander. From X-ray fluorescence it is known that the soil consists mainly of silicates. The element iron constitutes about 13% of the soil. The particles in the airborne dust seem to be composite, containing a few percent of a strongly magnetic component. We conclude that the magnetic phase present in the airborne dust particles is most likely maghemite. The particles thus appear to consist of silicate aggregates stained or cemented by ferric oxides, some of the stain and cement being maghemite. These results imply that Fe2+ ions were leached from the bedrock, and after passing through a state as free Fe2+ ions in liquid water, the Fe2+ was oxidized to Fe3+ and then precipitated. It cannot, however, be ruled out that the magnetic particles are titanomagnetite (or titanomaghemite) occurring in palagonite, having been inherited directly from the bedrock.
TL;DR: In this paper, a fly ash from a high-sulfur coal source was wet-sieved at 100, 200, 325, and 500 mesh and each of the five size fractions was then magnetically separated.
TL;DR: In this paper, the structure and unitcell parameters of the magnetite and host olivine and intergrowth relations were determined using a newly developed X-ray diffraction microprobe technique employing synchrotron radiation.
Abstract: Ultrahigh-pressure (UHP) minerals of the Maowu mafic-ultramafic complex in the Dabieshan, east-central China exhibit many exsolution textures. Magnetite lamellae are common in olivines and Ti clinohumites from harzburgite and garnet pyroxenite. Monazite-(Ce) lamellae occur in apatites from the garnet pyroxenite. Independent P-T estimates suggest that these ultramafic rocks formed at P > 5 GPa and T = 700 ± 50 °C. The lamellae-bearing minerals are believed to preserve an earlier, higher P-T record prior to exsolution. Compositions and unit-cell parameters of the magnetite and host olivine and intergrowth relations were determined using a newly developed X-ray diffraction microprobe technique employing synchrotron radiation. The host olivine and magnetite lamellae bear a topotaxial relation with [220] Mag | | [200] Ol, [111]Mag | | [3 3 1]Ol, [11 1] Mag | | [331] Ol, [242]Mag | | [2 2 0]Ol. The recalculated composition of primary olivine may contain up to 1.5 wt% Fe 2O3. Four hypotheses may explain the observed intergrowths of oriented magnetite lamellae in olivine: (1) oxidation of olivine; (2) decomposition of Fe 3+ -bearing olivine formed at >6 GPa; (3) exsolution of a spinel (wadsleyite) solid-solution Fe 3O4-(Fe,Mg)2SiO4 during decompression; and (4) breakdown of phase A [Mg7Si2(OH)6] + enstatite. The third hypothesis appears to be the most likely inasmuch as no additional silicate phase occurs as associated inclusions in the olivine host. However, the actual mechanism for exsolution of magnetite from olivine remains to be studied experimentally.
TL;DR: In this article, the speciation of chromium in overlayers on atomically clean surfaces of single crystal magnetite (Fe 3 O 4 ) and hematite (α-Fe 2 O 3 ) were studied using Cr L-edge, Fe Ledge, and O K-edge X-ray absorption spectra collected with synchrotron radiation.
TL;DR: In this paper, the recovery of hematite fines from quartz and corundum using selective magnetic coating was studied as a function of pH, particle size, magnetic colloidal concentration, magnetic field strength and ratio of hemetite:quartz Synthetic mixtures assaying around 45-72% Fe2O3 was upgraded to 90-92% with recovery level of 90-96%.
TL;DR: In this paper, the authors investigated the influence of extraction temperature and iron oxide concentration on the dissolution behavior of the samples and found that a lower extraction temperature reduces the dissolution rate for all samples, while a decrease in iron oxide concentrations increases the dissolution performance.
TL;DR: Magnetite and Titanomagnetite exhibit magnetic properties which are attributable to the micro-structures developed during oxidation and exsolution: All magnetite iron ores which are lodestones contain maghemite as mentioned in this paper.
Abstract: Magnetite and Titanomagnetite exhibit magnetic properties which are attributable to the micro-structures developed during oxidation and exsolution: All magnetite iron ores which are lodestones contain maghemite. These lodestones have Hc between 10 and 30 mT, SIRM between 8 and 18 Am²kg¹ and RI between 0.10 and 0.26. Magnetite, titanomagnetite and metals have REM values (ratio of NRM to SIRM) < 0.05. Samples (called fulgarites) obtained from the Smithsonian Institution have REM values ranging from 0.45 to 0.92. The REM value serves as a witness parameter to the magnetic fields associated with the lightning bolt. If a high REM value (say ≫ 0.1) can be verified as not to be due to contamination by man and does not contain MD hematite then the rock has LRM (lightning remanent magnetization). The magnetic field associated with lightning can be revealed from an isothermal remanent acquisition (RA) curve.
TL;DR: In this paper, the authors presented the synthesis of magnetite nanoparticles by precipitation with forced mixing, which was easy to obtain a high product saturation degree and the constant pH value of the reaction system.
Abstract: Synthesis of magnetite nanoparticles by precipitation with forced mixing is presented. Using this method it is easy to obtain a high product saturation degree and the constant pH value of the reaction system. The TEM and XRD measurments show that the average size of the product magnetite particles is less than 6.0-nm in the condition of [Fe2+]/[Fe3+]=0.5. The magnetic properties of the samples are discussed.
TL;DR: In this article, the magnetic properties of a para-brown earth from Southern Germany were analyzed using scanning and transmission electron microscopy, and it was shown that these magnetic properties rather indicate particles that are at the boundary between superparamagnetic and single domain behavior.
TL;DR: Modification of chemical and magnetic extraction techniques has yielded biogenic magnetite/maghemite from human hippocampal tissue, the first direct observation of magnetic biominerals from the hippocampus.
01 Jan 1999
TL;DR: In this article, anisotropy of low-field magnetic susceptibility (AMS) was measured in 83 sites, and for many sites from central and southern parts of the intrusive body a large scatter was noticed.
TL;DR: In this article, a magnetic polyamine-epichlorohydrin (MPE) resin resorbent was used to remove actinides (plutonium and americium) from pH 12 wastewater using a 0.3tesla magnetic field.
Abstract: A new magnetic adsorbent material, called magnetic polyamine-epichlorohydrin (MPE) resin, was prepared by attaching activated magnetite to the outer surface of polyamine-epichlorohydrin resin beads. Experiments were carried out in the presence of a 0.3-tesla magnetic field to investigate the removal of actinides (plutonium and americium) from pH 12 wastewater using this new resin. The results demonstrated that the MPE resin has a significantly enhanced capacity for actinides over conventional ferrite-based surface complexation adsorption processes (where no field is applied) and over traditional high-gradient magnetic separation (HGMS) processes that remove suspended particles. This enhancement was attributed to the presence and subsequent removal of suspended actinide nanoparticles through an HGMS effect, with the magnetite acting as a very effective HGMS element. A theoretical analysis verified this supposition by showing that under adequate pHs and particle-particle separations, the attractive...
TL;DR: A microbial biofilm consortium enriched from Shield surface water is able to mediate geochemical cycling of iron within a biofilm as discussed by the authors, which can be leached from Fe(II) containing minerals such as magnetite, biotite and ilmenite to generate a colloidal Fe(III) suspension.
TL;DR: The average particle sizes of samples A and B were calculated by Brunauer-Emmett-Teller analysis and are 8.16 and 2.24 nm, respectively as discussed by the authors.
Abstract: Coprecipitation and microemulsion were used to prepare nanosized magnetite. The average particle sizes of samples A and B were calculated by Brunauer–Emmett–Teller analysis and are 8.16 and 2.24 nm, respectively. The saturation magnetization of sample A at 300 K was 57.2 emu/g, but sample B was not saturated even 7.0 T. The blocking temperature for sample B was 17 K and the crystalline anisotropy energy was 1.2×105 J/m3. At 5 K, sample B is ferrimagnetic with σs=7.62 emu/g. This value is much lower than the σs=65.4 emu/g of the crystallized sample A at 50 K. Mossbauer spectra showed that sample A was ferrimagnetic at room temperature, but sample B was superparamagnetic at T>Tb (critical blocking temperature).
TL;DR: In this paper, the authors show that the most recent sediments from the Bay of Vidy, close to Lausanne on the north shore of Lake Geneva, Switzerland, are rich in superparamagnetic magnetite and the 137C dated increase in magnetite concentration coincides with the beginning of sewage dephosphatization by the addition of iron chloride.
TL;DR: It is proposed that carbonates originally formed in ALH84001 from aqueous fluids and were subsequently shock heated and vaporized, suggesting that the ALH 84001 carbonates have a unique origin.
Abstract: A review of the mineralogical, isotopic, and chemical properties of the carbonates and associated submicrometer iron oxides and sulfides in Martian meteorite ALH84001 provides minimal evidence for microbial activity. Some magnetites resemble those formed by magnetotactic microorganisms but cubic crystals <50 nm in size and elongated grains <25 nm long are too small to be single-domain magnets and are probably abiogenic. Magnetites with shapes that are clearly unique to magnetotactic bacteria appear to be absent in ALH84001. Magnetosomes have not been reported in plutonic rocks and are unlikely to have been transported in fluids through fractures and uniformly deposited where abiogenic magnetite was forming epitaxially on carbonate. Submicrometer sulfides and magnetites probably formed during shock heating. Carbonates have correlated variations in Ca, Mg, and 18O/16O, magnetite-rich rims, and they appear to be embedded in pyroxene and plagiociase glass. Carbonates with these features have not been identified in carbonaceous chondrites and terrestrial rocks, suggesting that the ALH84001 carbonates have a unique origin. Carbonates and hydrated minerals in ALH84001, like secondary phases in other Martian meteorites, have O and H isotopic ratios favoring formation from fluids that exchanged with the Martian atmosphere. I propose that carbonates originally formed in ALH84001 from aqueous fluids and were subsequently shock heated and vaporized. The original carbonates were probably dolomite-magnesite-siderite assemblages that formed in pores at interstitial sites with minor sulfate, chloride, and phyllosilicates. These phases, like many other volatile-rich phases in Martian meteorites, may have formed as evaporate deposits from intermittent floods.
TL;DR: In this article, the reduction of Fe 2 O 3 to Fe 3 O 4 in approximately 5% H 2 around the Curie transition temperature of 575°C of Fe O 4.
TL;DR: In this article, the surface of a coprecipitated magnetite has been coated with amorphous silica in aqueous sodium silicate solution and the particle magnetization curve exhibited a saturation value of 1.57×10 −4 ǫ Wbm/kg including silicate as a coating material.