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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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Journal ArticleDOI
TL;DR: On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low‐density polymer‐coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin, it appears that diffusion through intracellular gradients determines 1/T2.
Abstract: Since 1/T2 of protons of tissue water is generally much greater than 1/T1 at typical imaging fields, small single-ion contrast agents--such as Gd(DTPA), which make comparable incremental contributions and therefore smaller fractional contributions to 1/T2 compared to 1/T1--are not as desirable for contrast-enhancement as agents that could enhance 1/T2 preferentially. In principle, such specialized agents will only be effective at higher fields because the field dependence (dispersion) of 1/T1 is such that it approaches zero at high fields whereas 1/T2 approaches a constant value. The residual 1/T2 is called the "secular" contribution and arises from fluctuations in time--as sensed by the protons of diffusing solvent or tissue water molecules--of the component of the magnetic field parallel to the static applied field. For solutions or suspensions of sufficiently large paramagnetic or ferromagnetic particles (greater than or equal to 250 A diameter), the paramagnetic contributions to the relaxation rates satisfy 1/T2 much greater than 1/T1 at typical imaging fields. We examine the theory of secular relaxation in some detail, particularly as it applies to systems relevant to magnetic resonance imaging, and then analyze the data for solutions, suspensions, or tissue containing ferritin, erythrocytes, agar-bound magnetite particles, and liver with low-density composite polymer-coated magnetite. In most cases we can explain the relaxation data, often quantitatively, in terms of the theory of relaxation of protons (water molecules) diffusing in the outer sphere environments of magnetized particles. The dipolar field produced by these particles has a strong spatial dependence, and its apparent fluctuations in time as seen by the diffusing protons produce spin transitions that contribute to both 1/T1 and /T2 comparably at low fields; for the larger particles, because of dispersion, the secular term dominates at fields of interest. On the basis of the agreement of theory with data for solutions of small paramagnetic complexes, large magnetite particles, and liver containing low-density polymer-coated magnetite agglomerates, it is argued that the theory is sufficiently reliable so that, e.g., for ferritin--for which 1/T2 is unexpectedly large--the source of its large relaxivity must reside in nonideal chemistry of the ferritin core. For blood, it appears that diffusion through intracellular gradients determines 1/T2.

360 citations

Journal ArticleDOI
TL;DR: In this article, a simple one-pot reaction process was applied for the preparation of nanocrystalline magnetite, where iron(III) acetylacetonate was dissolved in benzyl alcohol and treated in an autoclave between 175 and 200 °C.
Abstract: A novel nonaqueous route has been applied for the preparation of nanocrystalline magnetite. In a simple one-pot reaction process, iron(III) acetylacetonate was dissolved in benzyl alcohol and treated in an autoclave between 175 and 200 °C. This approach leads to monocrystalline magnetite particles with sizes ranging from 12 to 25 nm, as evidenced by X-ray analysis, HRTEM, and Raman and Mossbauer spectroscopy. The isolated particles can be redispersed either in polar or nonpolar solvents by coating them just after synthesis with undecanoic acid or dopamine. Simple sedimentation after redispersion in hexane can be used to lower the polydispersity of the sample.

360 citations

Journal ArticleDOI
17 Feb 1999-Langmuir
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

Journal ArticleDOI
TL;DR: The substitution of Fe3+ ions by Al3+ ion in the solid surface has been observed, indicating an alternative removal mechanism of arsenic in these metal hydroxides and oxyhydroxides by providing larger surface area for arsenic adsorption via retarding the crystalline formation of iron oxides.

356 citations

Journal ArticleDOI
11 Jan 1990-Nature
TL;DR: It is suggested that magnetic bacteria and their magnetofossils14 can contribute to the magnetic properties of soils.
Abstract: ENRICHMENT of the ferrimagnetic minerals magnetite and maghemite is frequently observed in the top layer of soil horizons1–5. Although both inorganic6,7and organic8,9processes are known to produce magnetite, magnetite in soils has been ascribed to an inorganic origin6. We report here the discovery of living magnetic bacteria, similar to those found in salt- and fresh-water sediments8,10–2, in the A horizon of a well developed soil profile in a typical meadow environment in southern Bavaria. The bacteria were detected in fresh samples using an optical microscope equipped with a rotating magnetic field13 and a volumetrically calibrated depression slide, permitting accurate counts of the volume density of the organisms. We suggest that magnetic bacteria and their magnetofossils14 can contribute to the magnetic properties of soils.

351 citations


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