Magnetite

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

Ferrous hydroxy carbonate is a stable transformation product of biogenic magnetite

Abstract: A ~1:1 mixture of ferrihydrite and nanocrystalline akaganeite (β-FeOOH; 10-15 nm) was incubated with Shewanella putrefaciens (strain CN32) under anoxic conditions with lactate as an electron donor and anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. The incubation was carried out in a 1,4-piperazinediethanesulfonic acid (PIPES)-buffered medium, without PO³⁻₄ at circumneutral pH. Iron reduction was measured as a function of time (as determined by 0.5 N HCl extraction), and solids were characterized by X-ray diffraction (XRD), electron microscopy, and Mossbauer spectroscopy. The biogenic reduction of Fe3+ was rapid; with 60% of the total Fe (Feтот) reduced in one day. Only an additional 10% of Feтот was reduced over the next three years. A fine-grained (10 nm), cation-excess (CE) magnetite with a Fe²⁺/Feтот ratio of 0.5-0.6 was the sole biogenic product after one day of incubation. The CE magnetite was unstable and partially transformed to micron-sized ferrous hydroxy carbonate [FHC; Fe₂ (OH)₂CO3(s)], a rosasite-type mineral, with time. Ferrous hydroxy carbonate dominated the mineral composition of the three year incubated sample. The Fe²⁺/Feтот ratio of the residual CE magnetite after three years of incubation was lower than the day 1 sample and was close to that of stochiometric magnetite (0.33). To best of ourmore » knowledge, this is the first report of biogenic FHC, and only the third observation of this material in nature. Ferrous hydroxy carbonate appeared to form by slow reaction of microbially produced carbonate with Fe²⁺-excess magnetite. The FHC may be an overlooked mineral phase that explains the infrequent occurrence of fine-grained, biogenic magnetite in anoxic sediments.« less

Identification of magnetite and hematite in rocks by magnetic observation at low temperature

Abstract: A method of identification of coarse-grained hematite and magnetite based on the recognition of their distinctive low-temperature transitions is presented. Specimens are magnetized to saturation, first at room temperature and then at −196°C. The transitions are observed as discontinuities in the curve of the change of isothermal remanent magnetization (IRM) with increasing temperature, from −196°C to 20°C. At −140°C the low-temperature IRM of magnetite is almost completely lost. At −20°C about one-half of the room-temperature IRM of hematite is recovered owing to the memory effect of hematite. The basic characteristics of the memory effects, upon which the method of identification is based, have been investigated with a vibration magnetometer. The memory of room-temperature magnetization has been described previously for hematite and magnetite. It has also been found that under the conditions of the present experiments there is a reciprocal relationship across the transition temperature between the low- and ordinary-temperature IRM of magnetite. On passing through the transition from high to low temperature, the remanence from the preceding cycle of high-temperature events is alone memorized; all earlier magnetizations are lost. Similarly, the last low-temperature IRM is alone memorized when magnetite is heated through the transition temperature. The method of identification has revealed the presence of hematite in a lightly metamorphosed red sediment and of magnetite in a red sediment baked by an igneous intrusion and in a red arkose, but neither coarse hematite nor magnetite has yet been found in unmetamorphosed red sandstones. The detection of both hematite and magnetite by this method is limited by the dependence of the magnetic transitions upon grain size and the presence of impurities.

Magnetic properties of marine magnetotactic bacteria in a seasonally stratified coastal pond (Salt Pond, MA, USA)

Abstract: SUMMARY Magnetic properties of suspended material in the water columns of freshwater and marine environments provide snapshots of magnetic biomineralization that have yet to be affected by the eventual time-integration and early diagenetic effects that occur after sediment deposition. Here, we report on the magnetism, geochemistry and geobiology of uncultured magnetite- and greigite-producing magnetotactic bacteria (MB) and magnetically responsive protists (MRP) in Salt Pond (Falmouth, MA, USA), a small coastal, marine basin (∼5 m deep) that becomes chemically stratified during the summer months. At this time, strong inverse O2 and H2S concentration gradients form in the water column and a well-defined oxic–anoxic interface (OAI) is established at a water depth of about 3.5 m. At least four morphological types of MB, both magnetite and greigite producers, and several species of magnetically responsive protists are found associated with the OAI and the lower sulphidic hypolimnion. Magnetic properties of filtered water were determined through the water column across the OAI and were consistent with the occurrence of magnetite- and greigite-producing MB at different depths. Sharp peaks in anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM) and single-domain (SD) values of ARM/SIRM occur within the OAI corresponding to high concentrations of MB and MRP with magnetically derived cell densities of 10 4 –10 6 ml −1 . Low-temperature ( 1 per cent) is present within magnetite magnetosomes, produced either

Bioinspired synthesis of magnetite nanoparticles

Abstract: Magnetite (Fe3O4) is a widespread magnetic iron oxide encountered in many biological and geological systems, and also in many technological applications. The magnetic properties of magnetite crystals depend strongly on the size and shape of its crystals. Hence, engineering magnetite nanoparticles with specific shapes and sizes allows tuning their properties to specific applications in a wide variety of fields, including catalysis, magnetic storage, targeted drug delivery, cancer diagnostics and magnetic resonance imaging (MRI). However, synthesis of magnetite with a specific size, shape and a narrow crystal size distribution is notoriously difficult without using high temperatures and non-aqueous media. Nevertheless, living organisms such as chitons and magnetotactic bacteria are able to form magnetite crystals with well controlled sizes and shapes under ambient conditions and in aqueous media. In these biomineralization processes the organisms use a twofold strategy to control magnetite formation: the mineral is formed from a poorly crystalline precursor phase, and nucleation and growth are controlled through the interaction of the mineral with biomolecular templates and additives. Taking inspiration from this biological strategy is a promising route to achieve control over the kinetics of magnetite crystallization under ambient conditions and in aqueous media. In this review we first summarize the main characteristics of magnetite and what is known about the mechanisms of magnetite biomineralization. We then describe the most common routes to synthesize magnetite and subsequently will introduce recent efforts in bioinspired magnetite synthesis. We describe how the use of poorly ordered, more soluble precursors such as ferrihydrite (FeH) or white rust (Fe(OH)2) can be employed to control the solution supersaturation, setting the conditions for continued growth. Further, we show how the use of various organic additives such as proteins, peptides and polymers allows for either the promotion or inhibition of magnetite nucleation and growth processes. At last we discuss how the formation of magnetite-based organic–inorganic hybrids leads to new functional nanomaterials.