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Magnetite

About: Magnetite is a research topic. Over the lifetime, 10277 publications have been published within this topic receiving 278071 citations.


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01 Jan 1974
TL;DR: The products of air oxidation of mixed Fe(II)-Fe(III) chloride solutions at pH 6 and 7, at 20 and 60~ and at normal pressure contain green rust, maghemite, lepidocrocite, goethite, and a paracrystalline ferric hydroxide (ferrihydrite) as mentioned in this paper.
Abstract: AB S T R ACT: The products of air oxidation of mixed Fe(II)-Fe(III) chloride solutions at pH 6 and 7, at 20 and 60~ and at normal pressure contain green rust, maghemite, lepidocrocite, goethite and a paracrystalline ferric hydroxide (ferrihydrite). Among these maghemite, a cubic ferromagnetic iron oxide (Fe203) found in many soils, is favoured by slow oxidation rate, high total Fe concentration, the presence of small amounts of Fe(IlI) in the original predominantly Fe(lI) solution, higher temperature and at pH 7 rather than pH 6. The green rust is believed to be an essential precursor of maghemite. On slow oxidation it will form maghemite probably via magnetite. Fast oxidation prevents the cubic phase from being formed and lepidocrocite is the end product. At higher Fe(III) proportions ferrihydrite can be formed which under certain influences converts to goethite and/or hematite. The common iron oxides are seen to form from the same system from small variations in environment which is to be expected from their common associations in soils.

101 citations

Journal Article
TL;DR: It is shown that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature, and the signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage.

101 citations

Journal ArticleDOI
TL;DR: In this paper, a co-precipitation method was used to synthesize 6-13 nm sized 0D superparamagnetic Fe3O4 nanocrystals under a N2 atmosphere as a function of temperature.
Abstract: Uniform 6–13 nm sized 0D superparamagnetic Fe3O4 nanocrystals were synthesized by an aqueous ‘co-precipitation method’ under a N2 atmosphere as a function of temperature to understand the growth kinetics. The crystal phases, surface charge, size, morphology and magnetic characteristics of as-synthesized nanocrystals were characterized by XRD, Raman spectroscopy, FTIR, TG-DTA, BET surface area, dynamic light scattering along with zeta potential, HR-TEM, EDAX, vibrating sample magnetometry and Mossbauer spectroscopy. TEM investigation revealed highly crystalline spherical magnetite particles in the 8.2–12.5 nm size range. The kinetically controlled as-grown nanoparticles were found to possess a preferential (311) orientation of the cubic phase, with a highest magnetic susceptibility of ∼57 emu g−1. The Williamson–Hall technique was employed to evaluate the mean crystallite size and microstrain involved in the as-synthesized nanocrystals from the X-ray peak broadening. In addition to FTIR and Raman spectra, Rietveld structural refinement of XRD confirms the magnetite phase with 5–20% maghemite in the sample. VSM and Mossbauer spectral data allowed us to fit the magnetite/maghemite content to a core–shell model where the shell is 0.2–0.3 nm thick maghemite over a magnetite core. The activation energy of <10 kJ mol−1 calculated from an Arrhenius plot for the complex process of nucleation and growth by diffusion during synthesis shows the significance of the precipitation temperature in the size controlled fabrication processes of nanocrystals. Brunauer–Emmett–Teller (BET) results reveal a mesoporous structure and a large surface area of 124 m2 g−1. Magnetic measurement shows that the particles are ferromagnetic at room temperature with zero remanence and zero coercivity. This method produced highly crystalline and dispersed 0D magnetite nanocrystals suitable for biological applications in imaging and drug delivery.

101 citations

Journal ArticleDOI
TL;DR: In this paper, the use of microcontact printing (μCP) and capillary filling (CF) was demonstrated to pattern the deposition of iron oxides on a surface with feature sizes of microns.
Abstract: This paper demonstrates the use of microcontact printing (μCP) and capillary filling (CF) to pattern the deposition of iron oxides on a surface with feature sizes of microns. Selective wetting of both self-assembled monolayers (SAMs) of alkanethiolates on gold and alkylsiloxanes on Si/SiO2 formed by microcontact printing limited the deposition of the iron oxides to the hydrophilic areas on the surfaces; thereby, the chemical functionality of the hydrophilic SAM had only a minor influence on the wetting behavior and the deposition. The iron oxides were deposited either as magnetite particles from colloidal solution, by precipitation of the oxide from previously deposited drops of water containing an iron(III) salt, or by ferrite plating. The size of the metal oxide patterns was limited to the size of the areas that could be patterned using μCP. Capillary filling using a colloidal solution of magnetite could also be used to fabricate continuous, interconnected structures of magnetite. The magnetic properties of the deposited iron oxides were characterized by magnetic force measurement (MFM) and by measurement of the magnetization. The magnetite particles deposited in these experiments showed superparamagnetic behavior; they were too small individually to support a permanent magnetization.

100 citations

Journal ArticleDOI
TL;DR: In this paper, groundmass spinel grains in 46 kimberlite and related rocks have been analyzed and compared, and the majority of the spinel analyses are classified as high-chromium chromite (Chr) and magnesioulvo« spinel^magnetite (Mum) and represent two significant stages of spinel growth.
Abstract: Groundmass spinel grains in 46 kimberlite and related rocks have been analyzed and compared. The majority of the spinel analyses are classified as high-chromium chromite (Chr) and magnesioulvo« spinel^magnetite (Mum) and represent two significant stages of spinel growth. There are also a significant number of spinel grains that are classified as xenocryst spinel (Xen), pleonaste spinel (Ple) and magnetite (Mag). Eight different spinel zoning trends are identified.The majority of the Chr spinel grains are interpreted as a primary phase that crystallized as small octahedra from kimberlite magma on the journey from the upper mantle to the final resting place in the upper crust. Three zoning trends lead directly away from primary chromite. The major zoning trend, Trend 1, is from chromite to magnesio-ulvo« spinel^magnetite. This zoning trend is unique to spinel in kimberlite, carbonatites and lamprophyres. We suggest that this somewhat oxidizing, and more magnesian, trend was influenced by the high carbonate content of Group I kimberlites and the rapid crystallization of the minerals during the evolution of volatiles.The zoningTrend 2 involves increasing titanium and ferric iron as a function of increasing Fe 2þ /(Fe 2þ þ Mg). This trend is similar to the zoning of spinel in basalt and is thought to be due to co-crystallization of magnesium- and aluminum-rich silicate minerals such as olivine and phlogopite in kimberlites, or pyroxene and plagioclase in basalt. Zoning Trend 3 in kimberlite leads away from primary chromite and towards an aluminous pleonaste (Ple) spinel. This trend is characterized by a large decease of Cr/(Cr þAl) parallel to so-called olivine^spinel iso-potential lines. Similar trends of lesser magnitude and cyclic Al^Cr zoning have been identified in basaltic spinel. This trend is thought to be due to very rapid crystallization under conditions of supersaturation where the crystallization of spinel affects the local environment ahead of the growing spinel crystal (i.e. diffusion-controlled crystallization). The tendency for immiscibility between ferrite- or titanate-rich spinel, and aluminate-rich spinel (pleonaste) has a great influence on Trends 1 and 3 zoning and also on atoll-spinel formation. Very local conditions such as nucleation, or lack of nucleation, of other minerals can influence both the textural environment and composition of kimberlitic spinel.

100 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023570
20221,277
2021367
2020478
2019494
2018446