Topic
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: In this paper, the phase transformations in two types of catalysts, a model supported catalyst with a nonporous silica support and a precipitated catalyst with no support, were investigated under identical CO-TPR conditions.
229 citations
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TL;DR: Electron microscopic studies on magnetosomes in magnetotactic bacteria have revealed much information on their composition, structure, and even the formation of their mineral phase.
Abstract: Electron microscopic studies on magnetosomes in magnetotactic bacteria have revealed much information on their composition, structure, and even the formation of their mineral phase. The mineral phases of the magnetosomes are of two general types: iron oxides and iron sulfides. Iron oxide-type magnetosomes contain particles of the ferrimagnetic mineral magnetite (Fe3O4) while the iron sulfide-type contain ferrimagnetic greigite (Fe3S4), greigite and non-magnetic pyrite (FeS2), or possibly ferrimagnetic pyrrhotite (Fe7S8). Regardless of their composition, the crystalline particles in magnetosomes have a narrow size range: approximately 35 to 120 nm. Magnetite crystals in this size range are single-magnetic-domains and confer a permanent magnetic dipole moment to the cell. The single-domain size range for greigite is not known but is probably similar to that for magnetite. The morphology of the particles in the bacterial magnetosomes appears to be species-specific. Morphologies of magnetite crystals in different species of magnetotactic bacteria include cubo-octahedra, parallelepipedal (truncated hexahedral or octahedral prisms), and tooth- or bullet-shaped (anisotropic). Morphologies of greigite particles include cubo-octahedra and rectangular prismatic. The greigite-pyrite particles are generally pleomorphic with no consistent crystalline morphology. A membrane has been shown to surround the particles in some organisms and may be involved in the formation of the crystalline phase while also providing physical constraints on the size and the shape of the crystal. These results clearly indicate that the biomineralization process involved in the bacterial magnetosome, a good example of a self-assembled structure on a nanometer scale, is highly controlled by the organism.
229 citations
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TL;DR: In this paper, the formation of the porosity of hematite was due to the decomposition of FeCO 3 and FeOOH, which played a key role in the forming of the iron oxide nanorods.
228 citations
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TL;DR: In this article, Maghemite is transformed into hematite, which is the iron oxide that gives red color to soil, and it is shown that the maghemite/hematite ratio is influenced by the particular environment and the degree of soil development.
Abstract: [1] Soil formation usually increases magnetic susceptibility, most often by increasing the concentrations of magnetite and maghemite, which are two ferrimagnetic iron oxides. Here we provide evidence that magnetic enhancement in aerobic soils not affected by detrital magnetic inputs or thermal transformation of other iron oxides is mostly due to the formation of maghemite, which is later transformed into hematite—the iron oxide that gives red color to soil. We show that the maghemite/hematite ratio is influenced by the particular environment and the degree of soil development, so it constitutes an effective tool for paleoenvironmental and planetary studies.
227 citations