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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: In this article, the authors evaluate the candidate minerals responsible for strong magnetic anomalies in the Terra Sirenum and Terra Cimmeria regions of Mars' southern highlands, assuming an early dynamo field similar in strength to the present Earth's field, enduring about 500 Myr after accretion and core formation, and a basaltic crust containing no more than 4-7 weight% of magnetic minerals.
Abstract: [1] Using rock magnetism and thermal modeling, we evaluate the candidate minerals responsible for strong magnetic anomalies in the Terra Sirenum and Terra Cimmeria regions of Mars' southern highlands. We assume an early global dynamo field similar in strength to the present Earth's field, enduring about 500 Myr after accretion and core formation, and a basaltic crust containing no more than 4-7 weight% of magnetic minerals. Thermal evolution models with a wide variety of initial crustal thicknesses, distributions of radioactive elements, and thermal expansion coefficients all yield similar thermal histories for the crust: warming in the first ∼1000 Myr (due mainly to radioactive heating) followed by monotonic cooling for the remainder of Mars' history. Primary thermoremanent magnetization (TRM) acquired by intrusive and extrusive bodies during the first 500 Myr was in part thermally demagnetized by general crustal warming after the dynamo field disappeared, from 500 to 1000 Myr. The Curie point isotherms around 1000 Myr established the maximum depth of TRM-bearing crust. Shock and heating due to impacts demagnetized the uppermost ∼10 km of the crust around the same time, resulting in potential magnetic layer thicknesses of 15-20 km for pyrrhotite, 40-50 km for magnetite, and 50-60 km for hematite. Other magnetic phases, such as iron and finely exsolved low-Ti titanohematite, are possible but less likely in a basaltic crust under oxidizing conditions. The prime candidates, in order of likelihood, are single-domain magnetite (0.2-0.4 volume% or 0.4-0.8 weight% required), single-domain pyrrhotite (1-2 volume% or 2-4 weight%), and either multidomain (>15 μm) or 5-15 μm single-domain hematite or a mixture of both (1.5-3 volume% or 3-6 weight%). A composite source with different combinations of these minerals at different depths is entirely possible. Viscous decay of TRM is difficult to assess without detailed knowledge of the distribution of minerals and blocking temperatures with depth but would increase the amounts of magnetic material required.
82 citations
TL;DR: Magnetite nanorods were successfully synthesized from ferric chloride (FeCl 3 ) and diamine hydrate (H 4 N 2 ·H 2 O) reagents via a simple, mild reduction-oxidization hydrothermal process in the presence of polyethylene glycol as mentioned in this paper.
82 citations
TL;DR: In this paper, an X-ray absorption near edge spectroscopy study at the Fe K- and L2,3-edges was performed on nominal magnetite nanoparticles synthesized by different methods.
Abstract: When studying nominal magnetite nanoparticles, it is mandatory to obtain a precise structural characterization to get an accurate relationship with their physiochemical properties. The great deal of information accumulated to date on the characterization of nominal magnetite and maghemite NPs does not clarify if the synthesized materials are single o multiphase systems involving bulk-like stoichiometric oxides (Fe3O4, γ-Fe2O3, α-Fe2O3, ...), or single or multiphase entities formed by nonstoichiometric oxides. In this work we propose a new approach to determine the structure of Fe oxide NPs by using the Fe K-edge X-ray absorption near edge spectroscopy. We report here an X-ray absorption near edge spectroscopy study at the Fe K- and L2,3-edges, on nominal magnetite nanoparticles synthesized by different methods. In addition, X-ray magnetic circular dichroism was recorded at the Fe L2,3-edges, in selected samples. We have found that the experimental spectra are not well reproduced by any linear combination ...
82 citations
TL;DR: In this paper, a study was conducted on the behavior as Fenton catalysts of three commercial mixed iron oxides: copper ferrite, magnetite, and ilmenite, using H2O2 for the degradation and mineralization of gallic acid (GA) at temperatures between 15 and 35°C and pH of 4.3.
Abstract: A study was conducted on the behavior as Fenton catalysts of three commercial mixed iron oxides: copper ferrite, magnetite, and ilmenite, using H2O2 for the degradation and mineralization of gallic acid (GA) at temperatures between 15 and 35 °C and pH of 4.3. Investigation of the activity of the catalysts was complemented by study of the metal ion leaching under reaction conditions. GA was completely mineralized with the three mixed iron oxides in the following order of catalytic activity: CuFe2O4 > Fe3O4 > FeTiO3, and the ferrites could be quickly and completely separated after the reaction by a magnetic field. According to these results, there appears to be a synergic effect between Cu and Fe ions placed in octahedral sites, and Cu ions may be the main active sites for HO radical generation. The efficiency of H2O2 utilization followed the inverse order of the catalytic activity of the mixed iron oxides, likely because the excess hydroxyl radicals generated during the reaction were quenched by hydrogen peroxide, yielding the less reactive hydroperoxide radicals. A very large amount of Cu and Fe ions leached from copper ferrite and decreased at higher reaction temperatures. These leached ions also acted as homogeneous Fenton catalysts in GA degradation and mineralization. A much lower amount of Fe ions was leached from magnetite and ilmenite in comparison to copper ferrite. From the perspective of long-term applications, magnetite with intermediate catalytic activity but with higher efficiency and much lower Fe ion leaching in comparison to copper ferrite may be more appropriate for GA removal.
82 citations
TL;DR: The different relative orientation of the clay-magnetite particles are discussed in order to predict the most favored flocculi configuration, and van der Waals and dipole-dipole magnetic attractions between magnetite-covered clay particles dominate the flocculation processes.
Abstract: This work is devoted to the preparation of magnetite-covered clay particles in aqueous medium. For this purpose, magnetite nanoparticles were synthesized by a coprecipitation method. These magnetic particles are adhered to sodium montmorillonite (NaMt) particles in aqueous suspensions of both materials, by appropriate control of the electrolyte concentrations. The best condition to produce such heteroaggregation corresponds to acid pH and approximately 1 mol/L ionic strength, when the electrokinetic potentials (zeta-potential) of both NaMt and Fe3O4 particles have high enough and opposite sign, as demonstrated from electrophoresis measurements. When a layer of magnetite re-covers the clay particles, the application of an external magnetic field induces a magnetic moment in clay-magnetite particles parallel to the external magnetic flux density. The sedimentation behavior of such magnetic particles is studied in the absence or presence of an external magnetic field in a vertical direction. The whole sedimentation behavior is also strongly affected by the formation of big flocculi in the suspensions under the action of internal colloidal interactions. van der Waals and dipole-dipole magnetic attractions between magnetite-covered clay particles dominate the flocculation processes. The different relative orientation of the clay-magnetite particles (edge-to-edge, face-to-edge, and face-to-face) are discussed in order to predict the most favored flocculi configuration.
82 citations