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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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TL;DR: For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction and it is shown that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosites are slightly oxidized.
Abstract: Magnetosome biomineralization and chain formation in magnetotactic bacteria are two processes that are highly controlled at the cellular level in order to form cellular magnetic dipoles. However, even if the magnetosome chains are well characterized, controversial results about the microstructure of magnetosomes were obtained and its possible influence in the formation of the magnetic dipole is to be specified. For the first time, the microstructure of intracellular magnetosomes was investigated using high-resolution synchrotron X-ray diffraction. Significant differences in the lattice parameter were found between intracellular magnetosomes from cultured magnetotactic bacteria and isolated ones. Through comparison with abiotic control materials of similar size, we show that this difference can be associated with different oxidation states and that the biogenic nanomagnetite is stoichiometric, i.e. structurally pure whereas isolated magnetosomes are slightly oxidized. The hierarchical structuring of the magnetosome chain thus starts with the formation of structurally pure magnetite nanoparticles that in turn might influence the magnetic property of the magnetosome chains.
77 citations
TL;DR: In this paper, the Cs+ sorption ability of the Prussian-blue-modified magnetite (PB-Fe3O4) was evaluated by batch magnetic separation.
Abstract: Prussian-blue-modified magnetite (PB-Fe3O4) was prepared by a simple method. The Cs+ sorption ability of PB-Fe3O4 was evaluated by batch magnetic separation. As a result, the maximum sorption amoun...
77 citations
TL;DR: In this article, a method for determining the oxidation state of Fe using the electron microprobe was described. But the sensitivity achieved with this "flank method" is about 3-4 times higher than with the conventional peak shift method or peak intensity ratio method.
Abstract: A method is described which allows the determination of Fe 2+ /Fe 3+ ratios with the electron microprobe by analyzing the FeLα and FeLβ X-ray emission spectra. We use the ratios of intensities measured on the high energy flank of the Lα and the low energy flank of the Lβ peak. The sensitivity achieved with this «flank method» is about 3-4 times higher than with the conventional peak shift method or peak intensity ratio method. The method was calibrated with the iron oxides wustite, magnetite and hematite and was then applied to a synthetic spinel solid solution series magnetite-hercynite (Fe 3 O 4 -FeAl 2 O 4 ) and to several natural olivines (Mg 2 SiO 4 -Fe 2 SiO 4 solid solutions). The results obtained by the flank method vary not only with Fe 3+ , but also with total iron content. A quantitative method for determining the oxidation state of Fe must therefore not only be based on a method with a high resolution but must also include corrections for self-absorption and matrix effects. Our method can be applied, if the bulk composition and crystal structure of the samples are known and working curves are established with similar materials
77 citations
Abstract: Low temperature magnetic techniques provide useful tools to detect the presence of magnetite and pyrrhotite in sediments through identification of their low temperature transitions, to determine the amount of ultrafine-grained (superparamagnetic) material in sediments, and can potentially detect the presence of certain types of magnetotactic bacteria. Application of these types of experiments to nannofossil chalks from beneath the Barbados accretionary prism led to some unusual results, which are attributed to the presence of siderite. Thermal demagnetization of low-temperature remanence after cooling in zero field and in a 2.5 T field both displayed large remanence losses from 20 K to 40 K. Below 40 K, the magnetization of the chalks was much higher in the field-cooled experiments than in the zero-field-cooled experiments. Low temperature hysteresis experiments, made after cooling in a 2.5 T field, displayed offsets in magnetization parallel to the direction of the initial applied field, when measured below 40 K. The offset loops can be due to either an exchange anisotropy between siderite and magnetite phases in the sediments, a defect moment in the siderites, or a canted moment in the siderites. Apparent similarity between the low-temperature thermal demagnetization results from these siderite-bearing sediments, pure siderite, and pure rhodochrosite samples and the well-known 34 K transition in pyrrhotite should lead to caution in identification of pyrrhotite in marine sediments based on low-temperature remanence studies alone.
77 citations
TL;DR: In this paper, the authors conducted long term heating experiments with surface sediment slurries to model burial and the associated temperature increase in sub-surface sediments, and found that even after 300 days at constant temperature (30 or 60°C) incremental heating to 90°C continuously stimulated bacterial activity, indicating temperature related activation of recalcitrant organic matter.
77 citations