Sample records for pure magnetite crystals

  1. Thermal Decomposition of an Impure (Roxbury) Siderite: Relevance to the Presence of Chemically Pure Magnetite Crystals in ALH84001 Carbonate Disks

    NASA Technical Reports Server (NTRS)

    McKay, D.S.; Gibson, E.K.; Thomas-Keprta, K.L.; Clemett, S.J.; Wentworth, S.J.

    2009-01-01

    The question of the origin of nanophase magnetite in Martian meteorite ALH84001 has been widely debated for nearly a decade. Golden et al. have reported producing nearly chemically pure magnetite from thermal decomposition of chemically impure siderite [(Fe, Mg, Mn)CO3]. This claim is significant for three reasons: first, it has been argued that chemically pure magnetite present in the carbonate disks in Martian meteorite ALH84001 could have formed by the thermal decomposition of the impure carbonate matrix in which they are embedded; second, the chemical purity of magnetite has been previously used to identify biogenic magnetite; and, third, previous studies of thermal decomposition of impure (Mg,Ca,Mn)-siderites, which have been investigated under a wide variety of conditions by numerous researchers, invariably yields a mixed metal oxide phase as the product and not chemically pure magnetite. The explanation for this observation is that these siderites all possess the same crystallographic structure (Calcite; R3c) so solid solutions between these carbonates are readily formed and can be viewed on an atomic scale as two chemically different but structurally similar lattices.

  2. Formation of "Chemically Pure" Magnetite from Mg-Fe-Carbonates Implications for the Exclusively Inorganic Origin of Magnetite and Sulfides in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, Douglas W.; Lauer, H. V., Jr.; Morris, R. V.; Trieman, A. H.; McKay, G. A.

    2006-01-01

    Magnetite and sulfides in the black rims of carbonate globules in Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al. that they are biogenic in origin. However, exclusively inorganic (abiotic) processes are able to account for the occurrence of carbonate-sulfide-magnetite assemblages in the meteorite. We have previously precipitated chemically zoned and sulfide-bearing carbonate globules analogous to those in ALH84001 (at less than or equal to 150 C) from multiple fluxes of variable-composition Ca-Mg-Fe-CO2-S-H2O solutions. Brief heating of precipitated globules to approx. 470 C produced magnetite and pyrrhotite within the globules by thermal decomposition of siderite and pyrite, respectively. We have also shown that morphology of magnetite formed by inorganic thermal decomposition of Fe-rich carbonate is similar to the morphology of so-called biogenic magnetite in the carbonate globules of ALH84001. Magnetite crystals in the rims of carbonate globules in ALH84001 are chemically pure [Note: "Chemically pure" is defined here as magnetite with Mg at levels comparable or lower than Mg detected by [8] in ALH84001 magnetite]. A debate continues on whether or not chemically pure magnetite can form by the thermal decomposition of mixed Mg-Fe-carbonates that have formed under abiotic conditions. Thomas-Keprta et al. argue that it is not possible to form Mg-free magnetite from Mg-Fe-carbonate based on thermodynamic data. We previously suggested that chemically pure magnetite could form by the thermal decomposition of relatively pure siderite in the outer rims of the globules. Mg-Fe-carbonates may also thermally decompose under conditions conducive for formation of chemically pure magnetite. In this paper we show through laboratory experiments that chemically pure magnetite can form by an inorganic process from mixed Mg-Fe-carbonates.

  3. Non-chemically Pure Magnetites Produced from Thermal Decomposition of Ankerites

    NASA Astrophysics Data System (ADS)

    Jiménez López, C.; Romanek, C.; Rodríguez-Navarro, A.; Pérez-González, T.; Rodríguez Navarro, C.

    2008-12-01

    It has been claimed that chemically pure magnetites (Fe3O4) can be obtained from thermal decomposition of (Fe, Mg, Ca)CO3 (Golden et al., 2004). Such an observation is critical, since it opens the possibility of an inorganic way of formation of the magnetites found on Martian meteorite ALH84001. Such a chemical purity is one of the parameters used, so far, to recognize bacterial origin of natural magnetites (Thomas-Keptra et al., 2001), since it has been demonstrated that biologically-controlled magnetites are chemically pure (Bazylinski and Frankel, 2004) . However, while Golden et al. (2004) obtained pure magnetite from an almost pure precursor, the ankerite cores in ALH84001 in which magnetites are embedded are far from being chemically pure, since they contain considerable amounts of Ca and Mg (Kopp and Humayun, 2003). In this study we have performed several experiments to analyze the chemical purity of magnetites produced by thermal decomposition of four ankerite samples sinthetized in the laboratory, and containing different amounts of Ca, Fe and Mg. Such a thermal decomposition was achieved by two procedures: (1) by heating the samples at 470°C under CO2 pressure and (2) by decomposing the ankerite "in situ" under the TEM (Transmission electron Microscopy) electron beam. Magnetite produced by the first procedure was analyzed by XRD to determine whether or not the resulting solid was a mixture of oxides or rather a solid solution of (Ca, Fe and Mg)oxide. Magnetites formed by the two methods were studied by High Resolution TEM. The chemical composition of about 20 crystals of each experiment was analyzed by EDAX. Under our experimental conditions, ankerites decomposed in magnetite crystals of about 5 nanometers in size. Magentite crystals arranged to keep the morphology of the precursor. Our results confirm that any of these magnetites is chemically pure, but rather, each one of them is a solid solution of Ca and Mg. Therefore, chemically pure magnetites found in the meteorite ALH84001 cannot be obtained, as Golden et al. (2004) proposed, just by the thermal decomposition of the (Fe, Ca, Mg)CO3 precursor in which they were embedded.

  4. Magnetite Crystal Orientation in Magnetosome Chains

    PubMed Central

    Körnig, André; Winklhofer, Michael; Baumgartner, Jens; Gonzalez, Teresa Perez; Fratzl, Peter; Faivre, Damien

    2014-01-01

    One-dimensional magnetic nanostructures have magnetic properties superior to non-organized materials due to strong uniaxial shape anisotropy. Magnetosome chains in magnetotactic bacteria represent a biological paradigm of such magnet, where magnetite crystals synthesized in organelles called magnetosomes are arranged into linear chains. Two-dimensional synchrotron X-ray diffraction (XRD) is applied to cells of magnetotactic bacteria that are pre-aligned with a magnetic field to determine the crystallographic orientation of magnetosomes relative to the chain axis. The obtained pole figure patterns reveal a [111] fiber texture along the chain direction for magnetospirilla strains MSR-1 and AMB-1, whereas a [100] fiber texture is measured for Desulfovibrio magneticus strain RS-1. The [100] axis appears energetically unfavorable because it represents a magnetic hard axis in magnetite, but can be turned into an effective easy axis by particle elongation along [100] for aspect ratios higher than 1.25, consistent with aspect ratios in RS-1 magnetosomes determined earlier. The pronounced fiber textures can be explained either by a strain-specific biological control on crystal orientation at the chain level or by physical alignment effects due to intra-chain magnetic interactions. In this case, biological control of the axis of elongation would be sufficient to influence the crystallographic texture of the magnetosome chain.

  5. Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures

    PubMed Central

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, Hojatollah; Gibson, Everett K.; McKay, Mary Fae; Romanek, Christopher S.

    2001-01-01

    McKay et al. [(1996) Science 273, 924–930] suggested that carbonate globules in the meteorite ALH84001 contained the fossil remains of Martian microbes. We have characterized a subpopulation of magnetite (Fe3O4) crystals present in abundance within the Fe-rich rims of these carbonate globules. We find these Martian magnetites to be both chemically and physically identical to terrestrial, biogenically precipitated, intracellular magnetites produced by magnetotactic bacteria strain MV-1. Specifically, both magnetite populations are single-domain and chemically pure, and exhibit a unique crystal habit we describe as truncated hexa-octahedral. There are no known reports of inorganic processes to explain the observation of truncated hexa-octahedral magnetites in a terrestrial sample. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless there is an unknown and unexplained inorganic process on Mars that is conspicuously absent on the Earth and forms truncated hexa-octahedral magnetites, we suggest that these magnetite crystals in the Martian meteorite ALH84001 were likely produced by a biogenic process. As such, these crystals are interpreted as Martian magnetofossils and constitute evidence of the oldest life yet found. PMID:11226210

  6. Process for Making Single-Domain Magnetite Crystals

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, Douglas W.; Morris, Richard V.; Lofgren, Gary E.; McKay, Gordan A.; Schwandt, Craig S.; Lauer, Howard V., Jr.; Socki, Richard A.

    2004-01-01

    A process for making chemically pure, single-domain magnetite crystals substantially free of structural defects has been invented as a byproduct of research into the origin of globules in a meteorite found in Antarctica and believed to have originated on Mars. The globules in the meteorite comprise layers of mixed (Mg, Fe, and Ca) carbonates, magnetite, and iron sulfides. Since the discovery of the meteorite was announced in August 1996, scientists have debated whether the globules are of biological origin or were formed from inorganic materials by processes that could have taken place on Mars. While the research that led to the present invention has not provided a definitive conclusion concerning the origin of the globules, it has shown that globules of a different but related chemically layered structure can be grown from inorganic ingredients in a multistep precipitation process. As described in more detail below, the present invention comprises the multistep precipitation process plus a subsequent heat treatment. The multistep precipitation process was demonstrated in a laboratory experiment on the growth of submicron ankerite crystals, overgrown by submicron siderite and pyrite crystals, overgrown by submicron magnesite crystals, overgrown by submicron siderite and pyrite. In each step, chloride salts of appropriate cations (Ca, Fe, and Mg) were dissolved in deoxygenated, CO2- saturated water. NaHCO3 was added as a pH buffer while CO2 was passed continuously through the solution. A 15-mL aliquot of the resulting solution was transferred into each of several 20 mL, poly(tetrafluoroethylene)-lined hydrothermal pressure vessels. The vessels were closed in a CO2 atmosphere, then transferred into an oven at a temperature of 150 C. After a predetermined time, the hydrothermal vessels were removed from the oven and quenched in a freezer. Supernatant solutions were decanted, and carbonate precipitates were washed free of soluble salts by repeated decantations with deionized water.

  7. Elongated prismatic magnetite crystals in ALH84001 carbonate globules

    Microsoft Academic Search

    Kathie L. Thomas-Keprta; Dennis A. Bazylinski; Joseph L. Kirschvink; Simon J. Clemett; David S. McKay; Susan J. Wentworth; Hojatollah Vali; Everett K. Gibson Jr.; Christopher S. Romanek

    2000-01-01

    Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like.As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these

  8. Studies of Inorganic Crystals in Biological Tissue: Magnetite in Human

    E-print Network

    of Technology, Division of Geological & Planetary Sciences, 170-25 Pasadena Ca. 91125. Received October 28, 1996 bacteria, polyplacophoran mollusks (chitons), salmons, tuna and recently tissues of the human brain ethmoid a chain of magnetite crystals is contained6) . The color of teeth of chiton gradually changes

  9. Elongated prismatic magnetite crystals in ALH84001 carbonate globules: potential Martian magnetofossils.

    PubMed

    Thomas-Keprta, K L; Bazylinski, D A; Kirschvink, J L; Clemett, S J; McKay, D S; Wentworth, S J; Vali, H; Gibson, E K; Romanek, C S

    2000-12-01

    Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we compared these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we examined 206 magnetites recovered from strain MV-1 cells. Natural (Darwinian) selection in terrestrial magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having the physical and chemical properties that optimize their magnetic moment. In this study, we describe six properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria), properties that, collectively, are not observed in any known population of inorganic magnetites. These criteria can be used to distinguish one of the modes of origin for magnetites from samples with complex or unknown histories. Of the ALH84001 magnetites that we have examined, the elongated prismatic magnetite particles (similar to 27% of the total) are indistinguishable from the MV-1 magnetites in five of these six characteristics observed for biogenically controlled mineralization of magnetite crystals. PMID:11543573

  10. Iron et al.: Incorporation of Manganese in the Crystal Lattice of Magnetosome Magnetite

    Microsoft Academic Search

    Tanya Prozorov; Teresa Perez-Gonzalez; Concepcion Jimenez-Lopez; Surya K. Mallapragada; Paul Howse; Dennis A. Bazylinski; Ruslan Prozorov

    2010-01-01

    Incorporation of foreign metal into the crystal matrix of the magnetotactic bacterial magnetite has been attempted worldwide. Recently, presence of small amounts of cobalt and manganese in magnetosome magnetite crystals in cultured and uncultured magnetotactic bacteria, respectively, was reported. Magnetization of the uncultured cells and their magnetosomes were not determined, while only marginal changes in the magnetic properties of the

  11. Ferromagnetic resonance of intact cells and isolated crystals from cultured and uncultured magnetite-producing magnetotactic bacteria

    NASA Astrophysics Data System (ADS)

    Abraçado, Leida G.; Wajnberg, Eliane; Esquivel, Darci M. S.; Keim, Carolina N.; Silva, Karen T.; Moreira, Emílio T. S.; Lins, Ulysses; Farina, Marcos

    2014-06-01

    Most magnetotactic bacteria (MB) produce stable, single-domain magnetite nanocrystals with species-specific size, shape and chain arrangement. In addition, most crystals are elongated along the [111] direction, which is the easy axis of magnetization in magnetite, chemically pure and structurally perfect. These special characteristics allow magnetite crystal chains from MB to be recognized in environmental samples including old sedimentary rocks. Ferromagnetic resonance (FMR) has been proposed as a powerful and practical tool for screening large numbers of samples possibly containing magnetofossils. Indeed, several studies were recently published on FMR of cultured MB, mainly Magnetospirillum gryphiswaldense. In this work, we examined both uncultured magnetotactic cocci and the cultured MB M. gryphiswaldense using transmission electron microscopy (TEM) and FMR from 10 K to room temperature (RT). The TEM data supported the FMR spectral characteristics of our samples. The FMR spectra of both bacteria showed the intrinsic characteristics of magnetite produced by MB, such as extended absorption at the low field region of the spectra and a Verwey transition around 100 K. As previously observed, the spectra of M. gryphiswaldense isolated crystals were more symmetrical than the spectra obtained from whole cells, reflecting the loss of chain arrangement due to the small size and symmetrical shape of the crystals. However, the FMR spectra of magnetic crystals isolated from magnetotactic cocci were very similar to the FMR spectra of whole cells, because the chain arrangement was maintained due to the large size and prismatic shape of the crystals. Our data support the use of FMR spectra to detect magnetotactic bacteria and magnetofossils in samples of present and past environments. Furthermore, the spectra suggest the use of the temperature transition of spectral peak-to-peak intensity to obtain the Verwey temperature for these systems.

  12. Ferromagnetic resonance of intact cells and isolated crystals from cultured and uncultured magnetite-producing magnetotactic bacteria.

    PubMed

    Abraçado, Leida G; Wajnberg, Eliane; Esquivel, Darci M S; Keim, Carolina N; Silva, Karen T; Moreira, Emílio T S; Lins, Ulysses; Farina, Marcos

    2014-06-01

    Most magnetotactic bacteria (MB) produce stable, single-domain magnetite nanocrystals with species-specific size, shape and chain arrangement. In addition, most crystals are elongated along the [111] direction, which is the easy axis of magnetization in magnetite, chemically pure and structurally perfect. These special characteristics allow magnetite crystal chains from MB to be recognized in environmental samples including old sedimentary rocks. Ferromagnetic resonance (FMR) has been proposed as a powerful and practical tool for screening large numbers of samples possibly containing magnetofossils. Indeed, several studies were recently published on FMR of cultured MB, mainly Magnetospirillum gryphiswaldense. In this work, we examined both uncultured magnetotactic cocci and the cultured MB M. gryphiswaldense using transmission electron microscopy (TEM) and FMR from 10 K to room temperature (RT). The TEM data supported the FMR spectral characteristics of our samples. The FMR spectra of both bacteria showed the intrinsic characteristics of magnetite produced by MB, such as extended absorption at the low field region of the spectra and a Verwey transition around 100 K. As previously observed, the spectra of M. gryphiswaldense isolated crystals were more symmetrical than the spectra obtained from whole cells, reflecting the loss of chain arrangement due to the small size and symmetrical shape of the crystals. However, the FMR spectra of magnetic crystals isolated from magnetotactic cocci were very similar to the FMR spectra of whole cells, because the chain arrangement was maintained due to the large size and prismatic shape of the crystals. Our data support the use of FMR spectra to detect magnetotactic bacteria and magnetofossils in samples of present and past environments. Furthermore, the spectra suggest the use of the temperature transition of spectral peak-to-peak intensity to obtain the Verwey temperature for these systems. PMID:24828297

  13. MMS6 Protein Regulates Crystal Morphology during Nano-sized Magnetite Biomineralization in Vivo*

    PubMed Central

    Tanaka, Masayoshi; Mazuyama, Eri; Arakaki, Atsushi; Matsunaga, Tadashi

    2011-01-01

    Biomineralization, the process by which minerals are deposited by organisms, has attracted considerable attention because this mechanism has shown great potential to inspire bottom-up material syntheses. To understand the mechanism for morphological regulation that occurs during biomineralization, many regulatory proteins have been isolated from various biominerals. However, the molecular mechanisms that regulate the morphology of biominerals remain unclear because there is a lack of in vivo evidence. Magnetotactic bacteria synthesize intracellular magnetosomes that comprise membrane-enveloped single crystalline magnetite (Fe3O4). These nano-sized magnetite crystals (<100 nm) are bacterial species dependent in shape and size. Mms6 is a protein that is tightly associated with magnetite crystals. Based on in vitro experiments, this protein was first implicated in morphological regulation during nano-sized magnetite biomineralization. In this study, we analyzed the mms6 gene deletion mutant (?mms6) of Magnetospirillum magneticum (M. magneticum) AMB-1. Surprisingly, the ?mms6 strain was found to synthesize the smaller magnetite crystals with uncommon crystal faces, while the wild-type and complementation strains synthesized highly ordered cubo-octahedral crystals. Furthermore, deletion of mms6 gene led to drastic changes in the profiles of the proteins tightly bound to magnetite crystals. It was found that Mms6 plays a role in the in vivo regulation of the crystal structure to impart the cubo-octahedral morphology to the crystals during biomineralization in magnetotactic bacteria. Magnetotactic bacteria synthesize magnetite crystals under ambient conditions via a highly controlled morphological regulation system that uses biological molecules. PMID:21169637

  14. Analysis of magnetite crystals and inclusion bodies inside magnetotactic bacteria from different environmental locations

    NASA Astrophysics Data System (ADS)

    Oestreicher, Z.; Lower, B.; Lower, S.; Bazylinski, D. A.

    2011-12-01

    Biomineralization occurs throughout the living world; a few common examples include iron oxide in chiton teeth, calcium carbonate in mollusk shells, calcium phosphate in animal bones and teeth, silica in diatom shells, and magnetite crystals inside the cells of magnetotactic bacteria. Biologically controlled mineralization is characterized by biominerals that have species-specific properties such as: preferential crystallographic orientation, consistent particle size, highly ordered spatial locations, and well-defined composition and structure. It is well known that magnetotactic bacteria synthesize crystals of magnetite inside of their cells, but how they mineralize the magnetite is poorly understood. Magnetosomes have a species-specific morphology that is due to specific proteins involved in the mineralization process. In addition to magnetite crystals, magnetotactic bacteria also produce inclusion bodies or granules that contain different elements, such as phosphorus, calcium, and sulfur. In this study we used the transmission electron microscope to analyze the structure of magnetite crystals and inclusion bodies from different species of magnetotactic bacteria in order to determine the composition of the inclusion bodies and to ascertain whether or not the magnetite crystals contain elements other than iron and oxygen. Using energy dispersive spectroscopy we found that different bacteria from different environments possess inclusion bodies that contain different elements such as phosphorus, calcium, barium, magnesium, and sulfur. These differences may reflect the conditions of the environment in which the bacteria inhabit.

  15. PII S0016-7037(00)00481-6 Elongated prismatic magnetite crystals in ALH84001 carbonate globules

    E-print Network

    these magnetites with those produced by the terrestrial magnetotactic bacteria strain MV-1. By TEM again, we magnetotactic bacteria appears to have resulted in the formation of intracellular magnetite crystals having properties of magnetite produced by biologically controlled mechanisms (e.g., magnetotactic bacteria

  16. The Origin of Magnetite Crystals in ALH84001 Carbonate Disks

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, K. L.; Clemett, S. J.; Wentworth, S. J.; McKay, D. S.; Gibson, E. K., Jr.

    2012-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks believed to have formed approx 3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships between the carbonate disks, their associated magnetites and the orthopyroxene matrix in which they are embedded. Comparison of these results with experimental thermal decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in the ALH84001 carbonate disks are not the products of thermal decomposition.

  17. Elongated prismatic magnetite crystals in ALH84001 carbonate globules: Potential Martin magnetofoss

    Microsoft Academic Search

    K. L. Thomas-keprta; B. A. Bazylinski; J. L. Kirchvink; S. J. Clemett; D. S. Mckay; S. J. Wentworth; H. Vali; C. S. Romanek

    2000-01-01

    Abstract—Using transmission electron microscopy (TEM), we have analyzed magnetite (Fe 3O4) crystals acid-extracted from carbonate globules in Martian meteorite ALH84001. We studied 594 magnetites from ALH84001 and grouped them into three populations on the basis of morphology: 389 were irregularly shaped, 164 were elongated prisms, and 41 were whisker-like. As a possible terrestrial analog for the ALH84001 elongated prisms, we

  18. Crystal growth of bullet-shaped magnetite in magnetotactic bacteria of the Nitrospirae phylum.

    PubMed

    Li, Jinhua; Menguy, Nicolas; Gatel, Christophe; Boureau, Victor; Snoeck, Etienne; Patriarche, Gilles; Leroy, Eric; Pan, Yongxin

    2015-02-01

    Magnetotactic bacteria (MTB) are known to produce single-domain magnetite or greigite crystals within intracellular membrane organelles and to navigate along the Earth's magnetic field lines. MTB have been suggested as being one of the most ancient biomineralizing metabolisms on the Earth and they represent a fundamental model of intracellular biomineralization. Moreover, the determination of their specific crystallographic signature (e.g. structure and morphology) is essential for palaeoenvironmental and ancient-life studies. Yet, the mechanisms of MTB biomineralization remain poorly understood, although this process has been extensively studied in several cultured MTB strains in the Proteobacteria phylum. Here, we show a comprehensive transmission electron microscopy (TEM) study of magnetic and structural properties down to atomic scales on bullet-shaped magnetites produced by the uncultured strain MYR-1 belonging to the Nitrospirae phylum, a deeply branching phylogenetic MTB group. We observed a multiple-step crystal growth of MYR-1 magnetite: initial isotropic growth forming cubo-octahedral particles (less than approx. 40 nm), subsequent anisotropic growth and a systematic final elongation along [001] direction. During the crystal growth, one major {111} face is well developed and preserved at the larger basal end of the crystal. The basal {111} face appears to be terminated by a tetrahedral-octahedral-mixed iron surface, suggesting dimensional advantages for binding protein(s), which may template the crystallization of magnetite. This study offers new insights for understanding magnetite biomineralization within the Nitrospirae phylum. PMID:25566884

  19. Variation in trace element content of magnetite crystallized from a fractionating sulfide liquid, Sudbury, Canada

    E-print Network

    , Ti, V, Al, Mn, Sc, Nb, Ga, Ge, Ta, Hf, W and Zr) are compatible into Fe- oxide. The concentrations by the crystallization of the sulfide minerals with only Ni, Co, Zn, Mo, Sn and Pb present above detection limit in magnetite. Nickel, Mo and Co are compatible in Fe-rich MSS and thus the co-crystallizing Fe

  20. Co-ordinated functions of Mms proteins define the surface structure of cubo-octahedral magnetite crystals in magnetotactic bacteria.

    PubMed

    Arakaki, Atsushi; Yamagishi, Ayana; Fukuyo, Ayumi; Tanaka, Masayoshi; Matsunaga, Tadashi

    2014-08-01

    Magnetotactic bacteria synthesize magnetosomes comprised of membrane-enveloped single crystalline magnetite (Fe3 O4 ). The size and morphology of the nano-sized magnetite crystals (magnetite crystal morphology remain largely unknown. The group of proteins, called Mms (Mms5, Mms6, Mms7, and Mms13), was previously isolated from the surface of cubo-octahedral magnetite crystals in Magnetospirillum magneticum strain AMB-1. Analysis of an mms6 gene deletion mutant suggested that the Mms6 protein plays a major role in the regulation of magnetite crystal size and morphology. In this study, we constructed various mms gene deletion mutants and characterized the magnetite crystals formed by the mutant strains. Comparative analysis showed that all mms genes were involved in the promotion of crystal growth in different manners. The phenotypic characterization of magnetites also suggested that these proteins are involved in controlling the geometries of the crystal surface structures. Thus, the co-ordinated functions of Mms proteins regulate the morphology of the cubo-octahedral magnetite crystals in magnetotactic bacteria. PMID:24961165

  1. Chains of Magnetite Crystals in the Meteorite ALH84001: Evidence of Biological Origin

    NASA Technical Reports Server (NTRS)

    Friedmann, E. I.; Wierzchos, J.; Ascaso, C.; Winklhofer, M.

    2001-01-01

    The presence of magnetite crystal chains, missing evidence for their biological origin, as well as five morphological characteristics incompatible with a nonbiological origin are demonstrated by high-power stereo backscattered scanning electron microscopy. Additional information is contained in the original extended abstract.

  2. Microstructural characterization of metamorphic magnetite crystals with implications for oxygen isotope distribution

    SciTech Connect

    Sitzman, S.D.; Banfield, J.F.; Valley, J.W.

    2000-01-01

    The microstructures of magnetite crystals in three samples from a single outcrop of granulite-facies marble were characterized by transmission electron microscopy (TEM) to determine how exsolution history can affect physical properties and mineral reactivity during retrograde metamorphism. The microstructure of sample 90LP9 consists of dislocation, dislocation arrays (with dislocation spacings of 100 to 500 nm), and linear channels filled with layer silicates. Acid etching and ion milling of polished 90LP9 magnetite grains show dislocation arrays clustered near grain boundaries with rheologically hard magnetite, diopside, and monticellite, but rarely near grain boundaries with softer calcite. Samples LP204-1 magnetite grains contain coherent {l{underscore}brace}100{r{underscore}brace} Al-Mn-Fe-spinel precipitates ({approximately}40 nm diameter, {approximately}1--3 nm thick, {approximately}10{sup 4} platelets/{micro}m{sup 3}) and very few dislocations. Larger, more widely spaced spinel precipitates are present in a third sample, 94AK3. Extremely low dislocation densities in powders of LP204-1 and intermediate dislocation densities in powders of 94AK3, compared with extremely high dislocation densities in powders of 90LP9, are related to strong dislocation pinning effects by precipitates. The different exsolution behavior of the three magnetite samples is attributed to small, but important, differences in Al content. Because dislocations can provide fast pathways for exchange that enhance diffusion, especially in very slowly cooled rocks, these microstructural results may explain previously reported subgrain-scale oxygen isotopic heterogeneity in 90LP9 magnetite compared with relative isotopic homogeneity in LP204-1 magnetite.

  3. Hysteresis of Magnetite, Hematite and Pyrrhotite Crystals at High and Low Temperatures

    NASA Astrophysics Data System (ADS)

    Dunlop, D. J.

    2008-12-01

    Alternating gradient force magnetometers and sensitive vibrating-sample magnetometers operating above, at, and below room temperature have enabled rapid reliable measurements of hysteresis and remanence curves. The hysteresis parameters Ms, Mrs, Hc, plus the remanence coercivity Hcr, are routinely determined, at room temperature at least, and reported in the form of a Day plot as an indication of domain state and inferred grain size. Yet our knowledge of the hysteresis and remanence properties of individual crystals or sized crystal aggregates of magnetite, titanomagnetite, hematite, pyrrhotite and other important magnetic minerals has scarcely advanced beyond what was known at the end of the 1980's. Applications have indeed outstripped fundamental studies. This presentation will focus on new hysteresis measurements for well-sized magnetites of a variety of origins; magnetite inclusions in plagioclase, pyroxene, amphiboles and biotite; hematite; and pyrrhotite. Measurements were made at 20oC intervals from 25oC to the Curie point for all magnetites and hematites and at 10oC intervals for pyrrhotite. For one set of sized magnetites (0.6, 3, 6, 9, 14 and 110 micrometers), hysteresis and back-field remanence curves were also measured below room temperature (every 10 K from 10 K to 70 K, every 5 K from 80 K to 140 K, and every 10 K from 150 K to 300 K). These data give a wealth of information about the individual mineral crystals and trends linking crystals of common origin but different sizes. From Ms(T) we obtain precise Curie points and transition temperatures. Mrs(T)/Ms(T) tracks sometimes subtle changes in domain structure with changing temperature. Hc(T) gives an indication of the mechanism(s) of anisotropy, important for understanding TRM acquisition in crystals above single-domain size. Mrs(T) and Hc(T) often show substantial irreversible changes in the first heating- cooling cycle, particularly but not exclusively for synthetic crystals, stabilizing in subsequent cycles. Finally, Mrs(T)/Ms(T) vs. Hcr(T)/Hc(T) data trace curves on a Day plot showing unmistakable differences in domain structure between monoclinic and cubic magnetite, as well as more subtle changes away from the Verwey transition.

  4. Truncated Hexa-Octahedral Magnetite Crystals in Martian Meteorite ALH84001: Evidence of Biogenic Activity on Early Mars

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, K.; Clemett, S. J.; Schwartz, C.; McIntosh, J. R.; Bazylinski, D. A.; Kirschvink, J.; McKay, D. S.; Gibson, E. K.; Vali, H.; Romanek, C. S.

    2004-01-01

    The landmark paper by McKay et al. [1] cited four lines of evidence associated with the Martian meteorite ALH84001 to support the hypothesis that life existed on Mars approximately 4 Ga ago. Now, more than five years later, attention has focused on the ALH84001 magnetite grains embedded within carbonate globules in the ALH84001 meteorite. We have suggested that up to approx.25% of the ALH84001 magnetite crystals are products of biological activity [e.g., 2]. The remaining magnetites lack sufficient characteristics to constrain their origin. The papers of Thomas Keprta et al. were criticized arguing that the three dimensional structure of ALH84001 magnetite crystals can only be unambiguously determined using electron tomographic techniques. Clemett et al. [3] confirmed that magnetites produced by magnetotactic bacteria strain MV-I display a truncated hexa-octahedral geometry using electron tomography and validated the use of the multi-tilt classical transmission microscopy technique used by [2]. Recently the geometry of the purported martian biogenic magnetites was shown be identical to that for MV-1 magnetites using electron tomography [6].

  5. Pressure-induced crystal structure and spin-state transitions in magnetite (Fe3O4).

    PubMed

    Ju, Sheng; Cai, Tian-Yi; Lu, Hai-Shuang; Gong, Chang-De

    2012-08-22

    High pressure is an important dimension for the emergent phenomena in transition metal oxides, including high-temperature superconductivity, colossal magnetoresistance, and magnetoelectric coupling. In these multiply correlated systems, the interplay between lattice, charge, orbital, and spin is extremely susceptible to external pressure. Magnetite (Fe(3)O(4)) is one of the oldest known magnetic materials and magnetic minerals, yet its high pressure behaviors are still not clear. In particular, the crystal structure of the high-pressure phase has remained contentious. Here, we investigate the pressure-induced phase transitions in Fe(3)O(4) from first-principles density-functional theory. It is revealed that the net magnetic moment, arising from two ferrimagnetically coupled sublattices in Fe(3)O(4), shows an abrupt drop when entering into the high-pressure phase but recovers finite value when the pressure is beyond 65.1 GPa. The origin lies in the redistribution of Fe 3d orbital occupation with the change of crystal field, where successive structural transitions from ambient pressure phase Fd3[combining overline]m to high pressure phase Pbcm (at 29.7 GPa) and further to Bbmm (at 65.1 GPa) are established accurately. These findings not only explain the experimental observations on the structural and magnetic properties of the highly compressed Fe(3)O(4) but also suggest the existence of highly magnetized magnetite in the Earth's lower mantle. PMID:22823905

  6. Variation in trace element content of magnetite crystallized from a fractionating sulfide liquid, Sudbury, Canada: Implications for provenance discrimination

    NASA Astrophysics Data System (ADS)

    Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges

    2012-07-01

    Laser ablation ICP-MS analysis has been applied to many accessory minerals in order to understand better the process by which the rock formed and for provenance discrimination. We have determined trace element concentrations of Fe-oxides in massive sulfides that form Ni-Cu-PGE deposits at the base of the Sudbury Igneous Complex in Canada. The samples represent the crystallization products of fractionating sulfide liquids and consist of early-forming Fe-rich monosulfide solution (MSS) cumulates and residual Cu-rich intermediate solid solution (ISS). This study shows that Fe-oxide geochemistry is a sensitive petrogenetic indicator for the degree of fractionation of the sulfide liquid and provides an insight into the partitioning of elements between sulfide and Fe-oxide phases. In addition, it is useful in determining the provenance of detrital Fe-oxide. In a sulfide melt, all lithophile elements (Cr, Ti, V, Al, Mn, Sc, Nb, Ga, Ge, Ta, Hf, W and Zr) are compatible into Fe-oxide. The concentrations of these elements are highest in the early-forming Fe-oxide (titanomagnetite) which crystallized with Fe-rich MSS. Upon the continual crystallization of Fe-oxide from the sulfide liquid, the lithophile elements gradually decrease so that late-forming Fe-oxide (magnetite), which crystallized from the residual Cu-rich liquid, is depleted in these elements. This behavior is in contrast with Fe-oxides that crystallized from a fractionating silicate melt, whereby the concentration of incompatible elements, such as Ti, increases rather than decreases. The behavior of the chalcophile elements in magnetite is largely controlled by the crystallization of the sulfide minerals with only Ni, Co, Zn, Mo, Sn and Pb present above detection limit in magnetite. Nickel, Mo and Co are compatible in Fe-rich MSS and thus the co-crystallizing Fe-oxide is depleted in these elements. In contrast, magnetite that crystallized later from the fractionated liquid with Cu-rich ISS is enriched in Ni, Mo and Co because Fe-rich MSS is absent. The concentrations of Sn and Pb, which are incompatible with Fe-rich MSS, are highest in magnetite that formed from the fractionated Cu-rich liquid. At subsolidus temperatures, ilmenite exsolved from titanomagnetite whereas Al-spinel exsolved from the cores of some magnetite, locally redistributing the trace elements. However, during laser ablation ICP-MS analysis of these Fe-oxides both the magnetite and its exsolution products are ablated so that the analysis represents the original magmatic composition of the Fe-oxide that crystallized from the sulfide melt.

  7. Molarity (Aromic Density) of the Elements as Pure Crystals.

    ERIC Educational Resources Information Center

    Pauling, Linus; Herman, Zelek S.

    1985-01-01

    Provides background information for teachers on the atomic density of the elements as pure crystals. Atomic density is defined as the reciprocal of the atomic volume. Includes atomic-density diagrams which were prepared using the atomic-volume values given by Singman, supplemented by additional values for some allotropes. (JN)

  8. A magnetosome-associated cytochrome MamP is critical for magnetite crystal growth during the exponential growth phase.

    PubMed

    Taoka, Azuma; Eguchi, Yukako; Mise, Shingo; Oestreicher, Zachery; Uno, Fumio; Fukumori, Yoshihiro

    2014-09-01

    Magnetotactic bacteria use a specific set of conserved proteins to biomineralize crystals of magnetite or greigite within their cells in organelles called magnetosomes. Using Magnetospirillum magneticum AMB-1, we examined one of the magnetotactic bacteria-specific conserved proteins named MamP that was recently reported as a new type of cytochrome c that has iron oxidase activity. We found that MamP is a membrane-bound cytochrome, and the MamP content increases during the exponential growth phase compared to two other magnetosome-associated proteins on the same operon, MamA and MamK. To assess the function of MamP, we overproduced MamP from plasmids in wild-type (WT) AMB-1 and found that during the exponential phase of growth, these cells contained more magnetite crystals that were the same size as crystals in WT cells. Conversely, when the heme c-binding motifs within the mamP on the plasmid was mutated, the cells produced the same number of crystals, but smaller crystals than in WT cells during exponential growth. These results strongly suggest that during the exponential phase of growth, MamP is crucial to the normal growth of magnetite crystals during biomineralization. PMID:25048532

  9. Sub-Micrometer-Scale Mapping of Magnetite Crystals and Sulfur Globules in Magnetotactic Bacteria Using Confocal Raman Micro-Spectrometry

    PubMed Central

    Eder, Stephan H. K.; Gigler, Alexander M.; Hanzlik, Marianne; Winklhofer, Michael

    2014-01-01

    The ferrimagnetic mineral magnetite is biomineralized by magnetotactic microorganisms and a diverse range of animals. Here we demonstrate that confocal Raman microscopy can be used to visualize chains of magnetite crystals in magnetotactic bacteria, even though magnetite is a poor Raman scatterer and in bacteria occurs in typical grain sizes of only 35–120 nm, well below the diffraction-limited optical resolution. When using long integration times together with low laser power (<0.25 mW) to prevent laser induced damage of magnetite, we can identify and map magnetite by its characteristic Raman spectrum (303, 535, 665 ) against a large autofluorescence background in our natural magnetotactic bacteria samples. While greigite (cubic ; Raman lines of 253 and 351 ) is often found in the Deltaproteobacteria class, it is not present in our samples. In intracellular sulfur globules of Candidatus Magnetobacterium bavaricum (Nitrospirae), we identified the sole presence of cyclo-octasulfur (: 151, 219, 467 ), using green (532 nm), red (638 nm) and near-infrared excitation (785 nm). The Raman-spectra of phosphorous-rich intracellular accumulations point to orthophosphate in magnetic vibrios and to polyphosphate in magnetic cocci. Under green excitation, the cell envelopes are dominated by the resonant Raman lines of the heme cofactor of the b or c-type cytochrome, which can be used as a strong marker for label-free live-cell imaging of bacterial cytoplasmic membranes, as well as an indicator for the redox state. PMID:25233081

  10. Sub-micrometer-scale mapping of magnetite crystals and sulfur globules in magnetotactic bacteria using confocal Raman micro-spectrometry.

    PubMed

    Eder, Stephan H K; Gigler, Alexander M; Hanzlik, Marianne; Winklhofer, Michael

    2014-01-01

    The ferrimagnetic mineral magnetite Fe3O4 is biomineralized by magnetotactic microorganisms and a diverse range of animals. Here we demonstrate that confocal Raman microscopy can be used to visualize chains of magnetite crystals in magnetotactic bacteria, even though magnetite is a poor Raman scatterer and in bacteria occurs in typical grain sizes of only 35-120 nm, well below the diffraction-limited optical resolution. When using long integration times together with low laser power (<0.25 mW) to prevent laser induced damage of magnetite, we can identify and map magnetite by its characteristic Raman spectrum (303, 535, 665 cm(-1)) against a large autofluorescence background in our natural magnetotactic bacteria samples. While greigite (cubic Fe3S4; Raman lines of 253 and 351 cm(-1)) is often found in the Deltaproteobacteria class, it is not present in our samples. In intracellular sulfur globules of Candidatus Magnetobacterium bavaricum (Nitrospirae), we identified the sole presence of cyclo-octasulfur (S8: 151, 219, 467 cm(-1)), using green (532 nm), red (638 nm) and near-infrared excitation (785 nm). The Raman-spectra of phosphorous-rich intracellular accumulations point to orthophosphate in magnetic vibrios and to polyphosphate in magnetic cocci. Under green excitation, the cell envelopes are dominated by the resonant Raman lines of the heme cofactor of the b or c-type cytochrome, which can be used as a strong marker for label-free live-cell imaging of bacterial cytoplasmic membranes, as well as an indicator for the redox state. PMID:25233081

  11. New Insights into the Origin of Magnetite Crystals in ALH84001 Carbonate Disks

    NASA Technical Reports Server (NTRS)

    Thomas-Keptra, Katie L.; Clemett, S. J.; Wentworth S. J.; Mckay, D. S.; Gibson, E. K., Jr.

    2010-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks believed to have formed approx.3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose ori gins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of magnetite and carbonate may be unrelated: that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships between the carbonate disks, their associated magnetites and the orthopyroxene matrix in which they are embedded [1]. Comparison of these results with experimental thermal decomposition studies of sideritic carbonates conducted under a range of heating scenarios suggests that the magnetite nanocrystals in the ALH84001 carbonate disks are not the products of thermal decomposition.

  12. Growth and Thermal Studies of Doped and Pure Crystals of L-Argininium Dinitrate

    NASA Astrophysics Data System (ADS)

    Thomas, Preema C.; Sagayaraj, P.

    2015-02-01

    Single crystals of pure and Cu2+ doped semiorganic L-argininium dinitrate (LADN) crystals were grown by slow solvent evaporation technique, with the vision to improve the physicochemical properties of the sample. Single crystal XRD studies of both pure and doped samples were carried out. The thermal (DTA, TGA and DSC) studies were carried out and the results are compared.

  13. Hybrid density functional theory applied to magnetite: Crystal structure, charge order, and phonons

    NASA Astrophysics Data System (ADS)

    Rowan, Andrew D.; Patterson, Charles H.; Gasparov, L. V.

    2009-05-01

    The electronic structure and equilibrium structure of magnetite (Fe3O4) in the high temperature cubic Fd3¯m and low temperature monoclinic P2/c unit cells have been computed using the Perdew-Wang generalized gradient approximation (GGA) to density functional theory (DFT) and the B3LYP hybrid density functional. The ground state for the GGA-DFT is an itinerant electron metallic state in the cubic unit cell and the ground state for the B3LYP functional is a charge ordered semiconducting state in the monoclinic unit cell. The equilibrium structure predicted by the B3LYP functional for Fe3O4 in the P2/c unit cell has been calculated with lattice parameters fixed at values obtained in recent x-ray diffraction work and with the lattice fully relaxed. Bond lengths obtained with lattice parameters fixed at experimental values are in excellent agreement with x-ray measurements [J. P. Wright , Phys. Rev. B 66, 214422 (2002)]. The degree of charge order, measured as disproportionation of charge on octahedral B sites, is considerably less than unity and in reasonable agreement with values from resonant x-ray diffraction measurements. However, conduction electrons are found to be fully localized on B1 and B4 sites in orbitally ordered t2g states. This shows that they are formally Fe2+ ions while Fe B2 and B3 sites are formally Fe3+ sites. Therefore Verwey’s original conjecture regarding charge localization in Fe3O4 applies, even though the specific pattern of charge order is different. GGA-DFT and B3LYP density functionals were used to calculate phonons at the ? point of the Brillouin zone. Phonon frequencies predicted for these crystal structures are compared to frequencies from infrared conductivity and Raman scattering experiments. Charge ordering causes symmetry breaking of force constants on symmetry lowering from the cubic Fd3¯m unit cell to the P2/c unit cell. This produces frequency splitting of modes which are degenerate in the cubic unit cell and concentration of ion displacements in phonon eigenvectors on particular Fe octahedral B site chains, especially in the highest frequency bands.

  14. New insights into the origin of magnetite crystals in ALH84001 carbonate disks

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, K. L.; Clemett, S. J.; Wentworth, S. J.; McKay, D. S.; Gibson, E. K.

    2009-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks which are believed to have precipitated approximately 3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these Fe3O4 are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of Fe3O4 and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. We focus this discussion on the composition of ALH84001 magnetites and then compare these observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios.

  15. Origin of Magnetite Crystals in Martian Meteorite ALH84001 Carbonate Disks

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, K.L.; Clemett, S.J.; McKay, D.S.; Gibson, E. K.; Wentworth, S. J.

    2010-01-01

    Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks which are believed to have precipitated approx.3.9 Ga ago at beginning of the Noachian epoch. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these Fe3O4 are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of Fe3O4 and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. We have sought to resolve between these hypotheses through the detailed characterized of the compositional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded [1]. We focus this discussion on the composition of ALH84001 magnetites and then compare these observations with those from our thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios.

  16. Truncated hexa-octahedral magnetite crystals in ALH84001: Presumptive biosignatures

    E-print Network

    - restrial, biogenically precipitated, intracellular magnetites pro- duced by magnetotactic bacteria strain. In bacteria strain MV-1 their presence is therefore likely a product of Natural Selection. Unless intracellularly by the marine magnetotactic bacterium strain MV-1 (2­7); natural selection has optimized

  17. Field Ion Microscopy and Atom Probe Tomography of Metamorphic Magnetite Crystals

    NASA Technical Reports Server (NTRS)

    Kuhlman, K.; Martens, R. L.; Kelly, T. F.; Evans, N. D.; Miller, M. K.

    2001-01-01

    Magnetite has been analysed using Field Ion Microscopy (FIM) and Atom Probe Tomography (APT), highly attractive techniques for the nanoanalysis of geological materials despite the difficulties inherent in analyzing semiconducting and insulating materials. Additional information is contained in the original extended abstract.

  18. Micromagnetic study of the influence of crystal defects on coercivity in magnetite

    NASA Astrophysics Data System (ADS)

    Moskowitz, Bruce M.

    1993-10-01

    A one-dimensional micromagnetic model is used to calculate the thermal dependence of microcoercivity (h(sub c)) produced by the unpinning of a domain wall (DW) from various types of defects in magnetite. Equilibrium solutions are found that minimize the magnetoelastic, anisotropy, exchange, magnetostatic, and external field energies with respect to the wall width (w) and position of the wall relative to the defect. The defect may be a single dislocation, dislocation dipole, planar defect, or planar defect bounded by two parallel dislocations. Wall pinning is produced by (1) microstress fields of dislocations, (2) local changes in exchange and anisotropy constants within a planar defect region, or (3) a combination of both effects. The calculations, using temperature-dependent parameters, predict the thermal dependence of h(sub c)(T) as a function of grain size, domain wall width, defect spacing, and type of defect. Results show that, for grain sizes between 1 and 100 micrometers, h(sub c)(T) is usually a function of the wall width raised to some power n. The particular value of n is found to be a function of the DW-defect interaction spacing (d/w), type of defect, and grain size. Also, within this sizerange, the wall width expands with temperature moregradually than classical theory predicts. The microcoercivity results are used with the theory of Xu and Merrill (1990) to predict the thermal dependence of the macroscopic coercivitysub c) in magnetite. For grains with low defect densities, such as recrystallized magnetites, negative dislocation dipoles with d/w approximately = 0.1-1 produce a thermal dependence of coercivity that agress with experimental results. In the high defect density limit, a population of positive and negative dislocation dipoles with distribution of dipole widths produce an H(sub c)(T) dependence consistent with experimental data from crushed and glass ceramic magnetites.

  19. Characterization and phylogenetic identification of a species of spherical multicellular magnetotactic prokaryotes that produces both magnetite and greigite crystals.

    PubMed

    Zhang, Rui; Chen, Yi-Ran; Du, Hai-Jian; Zhang, Wen-Yan; Pan, Hong-Miao; Xiao, Tian; Wu, Long-Fei

    2014-09-01

    Magnetotactic bacteria (MTB) are a group of Gram-negative bacteria synthesizing magnetic crystals that allow them aligning along magnetic field lines. They have diverse morphologies including cocci, rods, vibrio, spirilla, and multicellular magnetotactic prokaryotes (MMPs). MMPs are composed of 10-57 cells with peritrichous flagella on their outer surfaces and swim as an entire unit. Here, we describe a species of spherical MMPs isolated from intertidal sediments of Lake Yuehu (Yellow Sea, China). They were mainly found in the subsurface layer of gray-black sediments. Microscopy revealed that these spherical MMPs were 5.6 ± 0.9 ?m in diameter and composed of approximately 16-32 ovoid cells with a helical arrangement and peritrichous flagellation. High-resolution transmission electron microscopy showed that the MMPs contained both bullet-shaped magnetite and irregular greigite magnetosomes that were arranged in chains or clusters. These MMPs displayed typical escape motility and negative phototaxis. The 16S rRNA genes of micromanipulation-purified spherical MMPs were cloned and sequenced. Phylogenetic analysis revealed that the MMP species was affiliated with Deltaproteobacteria and displayed >2.8% sequence divergence with respect to previously reported MMPs. This is the first phylogenetic identification of a spherical MMP that produces both magnetite and greigite magnetosomes. PMID:25086260

  20. Growth and characterization of gel grown pure and mixed iron-manganese levo-tartrate crystals

    Microsoft Academic Search

    S. J. Joshi; B. B. Parekh; K. D. Vohra; M. J. Joshi

    2006-01-01

    Several applications of iron tartrate and manganese tartrate compounds are reported in the literature. In the present investigation,\\u000a we have grown pure and mixed iron (II)-manganese levo-tartrate crystals by single diffusion gel growth technique. Crystals\\u000a with spherulitic morphology were harvested. The colouration of the crystals changed from black to pinkish brown upon increasing\\u000a the content of manganese in the crystals.

  1. Influence of Growth Conditions on Magnetite Nanoparticles Electro-Crystallized in the Presence of Organic Molecules

    PubMed Central

    Mosivand, Saba; Monzon, Lorena M. A.; Kazeminezhad, Iraj; Coey, J. Michael D.

    2013-01-01

    Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am2kg?1, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe3??O4, with a small excess of Fe3+, 0.05 ? ? ? 0.15. PMID:23685871

  2. Influence of growth conditions on magnetite nanoparticles electro-crystallized in the presence of organic molecules.

    PubMed

    Mosivand, Saba; Monzon, Lorena M A; Kazeminezhad, Iraj; Coey, J Michael D

    2013-01-01

    Magnetite nanoparticles were synthesized by electrocrystallization in the presence of thiourea or sodium butanoate as an organic stabilizer. The synthesis was performed in a thermostatic electrochemical cell containing two iron electrodes with an aqueous solution of sodium sulfate as electrolyte. The effects of organic concentration, applied potential and growth temperature on particle size, morphology, structure and magnetic properties were investigated. The magnetite nanoparticles were characterized by X-ray diffraction, electron microscopy, magnetometry and Mössbauer spectrometry. When the synthesis is performed in the presence of sodium butanoate at 60 °C, a paramagnetic ferric salt is obtained as a second phase; it is possible to avoid formation of this phase, increase the specific magnetization and improve the structure of the oxide particles by tuning the growth conditions. Room-temperature magnetization values range from 45 to 90 Am2kg-1, depending on the particle size, type of surfactant and synthesis conditions. Mössbauer spectra, which were recorded at 290 K for all the samples, are typical of nonstoichiometric Fe3-?O4, with a small excess of Fe3+, 0.05 ? ? ? 0.15. PMID:23685871

  3. Growth and characterization of pure and glycine doped cadmium thiourea sulphate (GCTS) crystals.

    PubMed

    Lawrence, M; Thomas Joseph Prakash, J

    2012-06-01

    The pure and glycine doped cadmium thiourea sulphate (GCTS) single crystals were grown successfully by slow evaporation method at room temperature. The concentration of dopant in the mother solution was 1 mol%. There is a change in unit cell. The Fourier transform infrared spectroscopy study confirms the incorporation of glycine into CTS crystal. The doped crystals are optically better and more transparent than the pure ones. The dopant increases the hardness value of the material. The grown crystals were also subjected to thermal and NLO studies. PMID:22349889

  4. Growth and characterization of pure and glycine doped cadmium thiourea sulphate (GCTS) crystals

    NASA Astrophysics Data System (ADS)

    Lawrence, M.; Thomas Joseph Prakash, J.

    2012-06-01

    The pure and glycine doped cadmium thiourea sulphate (GCTS) single crystals were grown successfully by slow evaporation method at room temperature. The concentration of dopant in the mother solution was 1 mol%. There is a change in unit cell. The Fourier transform infrared spectroscopy study confirms the incorporation of glycine into CTS crystal. The doped crystals are optically better and more transparent than the pure ones. The dopant increases the hardness value of the material. The grown crystals were also subjected to thermal and NLO studies.

  5. Optical, thermal and electrical properties of pure and doped bis-thiourea cadmium formate (BTCF) crystal

    NASA Astrophysics Data System (ADS)

    Shejwal, N. N.; Anis, Mohd; Hussaini, S. S.; Shirsat, M. D.

    2014-12-01

    A glycine doped bis-thiourea cadmium formate (BTCF) crystal has been grown by a slow solution evaporation technique. The shifts in vibrational frequencies of different functional groups of BTCF were identified by Fourier transform infrared (FT-IR) spectral analysis. UV-visible studies were employed to assess the optical transparency of pure and doped BTCF crystals. The optical band gap of doped BTCF is found to be 5.16 eV. The optical constants, refractive index, reflectance, and optical conductivity have been evaluated, using the transmission data. The dielectric characteristics of pure and doped BTCF were investigated by employing dielectric studies. The decomposition temperature of pure and doped BTCF crystals was determined by using thermogravimetric analysis. The encouraging third-order nonlinear optical properties of pure and doped BTCF crystals were examined by employing the Z-scan technique at 632.8 nm.

  6. Morphological Evidence for an Exclusively Inorganic Origin for Magnetite in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Morris, R. V.; Brearley, A. J.; Lauer, H. V., Jr.; Treiman, A.; Zolensky, M. E.; Schwandt, C. S.; Lofgren, G. E.; McKay, G. A.

    2003-01-01

    The origin of magnetite crystals in Martian Meteorite ALH84001 is the focus of a debate about the possibility of past (and present) life on Mars. McKay et al. originally suggested that some of the magnetite crystals associated with carbonate globules in Martian Meteorite ALH84001 are biogenic in ori-gin, because they are single magnetic domain, free of crystalline defects, chemically pure, and coexist with other metastable phases in apparent disequilibrium. Thomas-Keprta et al. reported that a subpopulation of magnetite crystals (approx. 25%) associated with carbonate globules in ALH84001 and magnetite crystals produced by magnetotactic bacterial strain MV-1 have similar morphologies with crystal elongation along the [111] crystallographic axis that they describe as "truncated hexa-octahedral" ([111-THO]) magnetite. Along with several other properties, the [111]-THO morphology has been proposed to constitute a biomarker (i.e., formed only in biogenic processes), so that the presence of [111]-THO magnetite in ALH84001 may be evidence for past life on Mars.

  7. Tuning the properties of colloidal magneto-photonic crystals by controlled infiltration with superparamagnetic magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Demeyer, P. J.; Bloemen, M.; Verbiest, T.; Clays, K.

    2012-06-01

    The performance of magnetic-field sensors and optical isolators is largely determined by the efficiency of the active materials. This efficiency could be dramatically increased by integrating Faraday materials in photonic crystals. For this purpose, monodisperse nanospheres were self-assembled into a colloidal photonic crystal and magnetic functionality was introduced by dipping the photonic crystal in a suspension containing superparamagnetic nanoparticles. Reflection and absorbance measurements of these magneto-photonic crystals revealed clear relationships between the time spent in suspension and the position and strength of the photonic band gap. When additional magnetic material was introduced, the band gap was red shifted and the strength of the band gap was decreased. Using Bragg's law and the Maxwell-Garnet approximation for effective media, the filling fraction of the magneto-photonic crystals was calculated from the observed red shift. While superparamagnetic nanoparticles did confer magneto-optical properties to the photonic crystal, they also increased the absorption, which can be detrimental as the Faraday effect is measured in transmission. Therefore a trade-off exists in the optical regime between the amount of Faraday rotation and the absorption. By carefully controlling the filling fraction, this trade-off was investigated and optimized for photonic crystals with different band gaps. Both polystyrene and silica photonic crystals were filled with superparamagnetic nanoparticles. In case of the polystyrene photonic crystals, it was found that the maximum achievable filling fraction was influenced by the size of the polystyrene nanospheres. Smaller polystyrene nanospheres gave rise to smaller pore diameters and a faster onset of pore blocking when filled with superparamagnetic nanoparticles. As a result, the maximum achievable filling fraction was also lower. Pore blocking was found to be negligible in silica photonic crystals. Together with a higher mechanical strength, this makes silica photonic crystals more suited for the fabrication of colloidal magneto-photonic crystals. In this paper, a nanoscale engineering approach is described to carefully control the filling fraction of magneto-photonic crystals. This allows fine-tuning the absorption and the position and strength of the photonic band gap. By tailoring the properties of magneto-photonic crystals, the means for application-specific designs and a better description of Faraday effects in 3D magneto-photonic crystals are provided.

  8. Optical, dosimetric, and scintillation properties of pure sapphire crystals

    NASA Astrophysics Data System (ADS)

    Futami, Yoshisuke; Yanagida, Takayuki; Fujimoto, Yutaka

    2014-02-01

    Optical, dosimetric, and scintillation properties of undoped sapphire (Al2O3) single crystals fabricated by different methods of the Czochralski (Cz) and the Bridgman were investigated. In X-ray induced radioluminescence spectra, they showed emission peaks at 240 and 300 nm due to exciton and F+ centers, respectively. Scintillation decay times of F+ center was fast around few ns. As a dosimetric property, from 0.01 to 2 Gy X-ray was exposed to them and they exhibited a thermally stimulated luminescence (TSL) with a good linearity. The glow peaks of them were similar, 150, 250, and 325 °C. In TSL, the Bridgeman sample represented only F+-center emission while the Cz sample showed F at 400 nm and F+ at 300 nm centers emission.

  9. Measurement of z-direction component of electron spins field-emitted from a single-crystal magnetite whisker.

    PubMed

    Nagai, S; Sakakibara, H; Hata, K; Okada, M; Mimura, H

    2011-05-01

    A 90° sector type spin rotator was developed for measurement of the z-direction component of a spin polarization, which is parallel to the emitter axis. The rotator enables us to measure all components of electron spins field-emitted from a single crystalline magnetite. In-plane component of spin polarization dominated of field-emitted electrons from single crystalline magnetite whisker, thus it is suggested that the magnetization of the magnetite whisker results from the anisotropy of crystalline structure rather than its shape. PMID:21664540

  10. Phenomenological crystal plasticity modeling and detailed micromechanical investigations of pure magnesium

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Joshi, Shailendra P.

    2012-05-01

    We present a single crystal plasticity model for pure Mg incorporating slip and deformation twinning. The model uses the basic framework of Kalidindi (1998), but proposes constitutive descriptions for the slip and twin evolution and their interactions that are motivated by experimental observations. Based on compelling experimental evidences, we distinguish between the constitutive descriptions of the tension and compression twinning to better represent their roles in the overall hardening of Mg single crystals. With these improved phenomenological descriptions, we first calibrate material parameters for the different slip and twin modes by performing three-dimensional simulations mimicking the plane-strain compression experiments by Kelley and Hosford (1967, 1968) on single crystal pure Mg. In doing so, these computational responses are critically compared with their corresponding orientation-dependent microscopic (slip and twin activities) and macroscopic (stress-strain responses) experimental observations. Then, the calibrated parameters are used to predict several other experimental results on pure single- and poly-crystal Mg under different loading conditions. We also investigate the role of pre-existing heterogeneities such as initial twin population and stiff, elastic inclusions on the single crystal macroscopic and microscopic responses. Microstructural characteristics show that such heterogeneities strongly influence the local and global evolution of the slip and twin activities, and in some cases modulate the strength anisotropy that is commonly observed in monolithic single crystals. These results may provide useful indicators toward designing novel composite Mg microstructures.

  11. Structure and morphology of magnetite anaerobically-produced by a marine magnetotactic bacterium and a dissimilatory iron-reducing bacterium

    USGS Publications Warehouse

    Sparks, N.H.C.; Mann, S.; Bazylinski, D.A.; Lovley, D.R.; Jannasch, H.W.; Frankel, R.B.

    1990-01-01

    Intracellular crystals of magnetite synthesized by cells of the magnetotactic vibroid organism, MV-1, and extracellular crystals of magnetite produced by the non-magnetotactic dissimilatory iron-reducing bacterium strain GS-15, were examined using high-resolution transmission electron microscopy, electron diffraction and 57Fe Mo??ssbauer spectroscopy. The magnetotactic bacterium contained a single chain of approximately 10 crystals aligned along the long axis of the cell. The crystals were essentially pure stoichiometric magnetite. When viewed along the crystal long axis the particles had a hexagonal cross-section whereas side-on they appeared as rectangules or truncated rectangles of average dimension, 53 ?? 35 nm. These findings are explained in terms of a three-dimensional morphology comprising a hexagonal prism of {110} faces which are capped and truncated by {111} end faces. Electron diffraction and lattice imaging studies indicated that the particles were structurally well-defined single crystals. In contrast, magnetite particles produced by the strain, GS-15 were irregular in shape and had smaller mean dimensions (14 nm). Single crystals were imaged but these were not of high structural perfection. These results highlight the influence of intracellular control on the crystallochemical specificity of bacterial magnetites. The characterization of these crystals is important in aiding the identification of biogenic magnetic materials in paleomagnetism and in studies of sediment magnetization. ?? 1990.

  12. Magnetite as a prokaryotic biomarker: A review

    NASA Astrophysics Data System (ADS)

    Jimenez-Lopez, Concepcion; Romanek, Christopher S.; Bazylinski, Dennis A.

    2010-06-01

    Over the years, nanometer-sized magnetite (Fe3O4) crystals have been recovered from many modern and ancient environments including sediments and soils and even meteorites. In some cases these crystals have been used as "magnetofossils" for evidence of the past presence of specific microbes. Magnetite nanocrystals can be formed by a number of different biological and inorganic mechanisms resulting in crystals with different physical and magnetic characteristics. Prokaryotes (bacteria) biomineralize magnetite through two methods that differ mechanistically, including: biologically induced mineralization (BIM) and biologically controlled mineralization (BCM). Magnetite nanocrystals produced by BIM are known to be synthesized by the dissimilatory iron-reducing bacteria, are deposited external to the cell, and generally are physically indistinguishable from magnetite particles formed inorganically. BCM magnetites, in contrast, are synthesized by the magnetotactic bacteria and some higher organisms and are precipitated intracellularly as membrane-bounded structures called magnetosomes. These magnetites appear to have unique crystal morphologies and a narrow size range leading to their original use as magnetofossils. Because of the discovery of nanometer-sized crystals of magnetite in the Martian meteorite ALH84001, the use of these criteria for the determination of whether magnetite crystals could constitute a prokaryotic biomarker was questioned. Thus, there is currently great debate over what criteria to use in the determination of whether specific magnetite crystals are biogenic or not. In the last decade, additional criteria have been established (e.g., the Magnetite Assay for Biogenicity), and new tools and technologies have been developed to determine the origin of specific types of magnetite crystals.

  13. Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: inorganic, abiotic formation by shock and thermal metamorphism.

    PubMed

    Treiman, Allan H

    2003-01-01

    Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe(3)O(4), reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered). PMID:14577885

  14. Formation of tabular single-domain magnetite induced by Geobacter metallireducens GS-15

    E-print Network

    at high temperatures (3). Magnetite crystals formed by magnetotactic bacteria (mag- netosomes) also have morphological characteristics of magnetite formed intra- cellularly by magnetic bacteria (magnetosome of magnetite produced extracellularly by a variety of bacteria including Geobacter metallireducens GS-15

  15. Growth and characterization of pure and doped KHP NLO single crystals

    NASA Astrophysics Data System (ADS)

    Thilagavathy, S. R.; Rajesh, P.; Ramasamy, P.; Ambujam, K.

    2014-06-01

    Single crystals of Potassium Hydrogen Phthalate doped with amino acid L-lysine were grown successfully by slow evaporation method. The concentration of dopant in the mother solution was 0.5 mol%, 1 mol% and 2 mol%. There is a drastic change in the morphology due to variation in doping rates which is also reflected in the X-ray diffraction data. The Fourier Transform infrared spectroscopy study confirms the incorporation of L-lysine into Potassium Hydrogen Phthalate crystal. The thermal study indicates the dissociating nature of the crystal. The nonlinear optical property of the grown crystal has been confirmed by Kurtz-powder second harmonic generation test. The dopant of 0.5 mol% and 1 mol% shows higher second harmonic generation result than pure Potassium Hydrogen Phthalate. Results are discussed.

  16. Design of a broadband highly dispersive pure silica photonic crystal fiber

    Microsoft Academic Search

    Harish Subbaraman; Tao Ling; Yongqiang Jiang; Maggie Y. Chen; Peiyan Cao; Ray T. Chen

    2007-01-01

    A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps\\/(nm km) around the 1.56 mum wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The

  17. Trace elements in magnetite as petrogenetic indicators

    NASA Astrophysics Data System (ADS)

    Dare, Sarah A. S.; Barnes, Sarah-Jane; Beaudoin, Georges; Méric, Julien; Boutroy, Emilie; Potvin-Doucet, Christophe

    2014-10-01

    We have characterized the distribution of 25 trace elements in magnetite (Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb), using laser ablation ICP-MS and electron microprobe, from a variety of magmatic and hydrothermal ore-forming environments and compared them with data from the literature. We propose a new multielement diagram, normalized to bulk continental crust, designed to emphasize the partitioning behavior of trace elements between magnetite, the melt/fluid, and co-crystallizing phases. The normalized pattern of magnetite reflects the composition of the melt/fluid, which in both magmatic and hydrothermal systems varies with temperature. Thus, it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts. The crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in Ti or Cu, respectively. The chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite (e.g., Si and Ca). Magnetite formed from low-temperature fluids has the lowest overall abundance of trace elements due to their lower solubility. Chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning, which records the changing conditions and composition of the fluid during magnetite growth. This new way of plotting all 25 trace elements on 1 diagram, normalized to bulk continental crust and elements in order of compatibility into magnetite, provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments. It has applications in both petrogenetic and provenance studies, such as in the exploration of ore deposits and in sedimentology.

  18. Growth and characterization of pure and 1, 10 phenanthraline doped potassium penta borate (KB5) single crystals

    NASA Astrophysics Data System (ADS)

    Prabha, K.; Babu, M. Ramesh; Sagayaraj, P.

    2013-05-01

    We concentrate on the low temperature slow solvent evaporation method and characterization of pure and 1, 10 phenanthraline doped KB5 and describe its potential as a non-linear optical material. The grown crystal has been subjected to single crystal X-ray diffraction analysis to identify the unit cell parameters and crystal system. The presence of carbon, hydrogen and oxygen content were confirmed by CHN analysis. The Kurtz's-Perry powder SHG efficiency was determined for both pure and 1,10 phenanthraline doped KB5 crystals as 1.6 and 2.2 times than that of pure KDP. Surface morphology of the pure and doped KB5 crystals has been found to be Scanning Electron Microscopic technique (SEM).

  19. Design of a broadband highly dispersive pure silica photonic crystal fiber

    NASA Astrophysics Data System (ADS)

    Subbaraman, Harish; Ling, Tao; Jiang, Yongqiang; Chen, Maggie Y.; Cao, Peiyan; Chen, Ray T.

    2007-06-01

    A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 ?m wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays.

  20. Design of a broadband highly dispersive pure silica photonic crystal fiber.

    PubMed

    Subbaraman, Harish; Ling, Tao; Jiang, YongQiang; Chen, Maggie Y; Cao, Peiyan; Chen, Ray T

    2007-06-01

    A highly dispersive dual-concentric-core pure silica photonic crystal fiber is designed with a maximum chromatic dispersion value of about -9500 ps/(nm km) around the 1.56 microm wavelength region and a full width at half-maximum (FWHM) of 55 nm. The change in the dispersion-bandwidth product as a function of period is carefully studied by using the plane wave expansion method. The coupled mode theory matches well with the plane wave expansion method that was used to simulate the chromatic dispersion. This kind of a photonic crystal fiber structure is suitable for high-dispersion application in phased array antenna systems based on photonic crystal fiber arrays. PMID:17514284

  1. Rheology of Pure Glasses and Crystal Bearing Melts: from the Newtonian Field to the Brittle Onset

    NASA Astrophysics Data System (ADS)

    Cordonnier, B.; Caricchi, L.; Pistone, M.; Castro, J. M.; Hess, K.; Dingwell, D. B.

    2010-12-01

    The brittle-ductile transition remains a central question of modern geology. If rocks can be perceived as a granular flow on geological time-scale, their behavior is brittle in dynamic areas. Understanding rock failure conditions is the main parameter in mitigating geological risks, more specifically the eruptive style transitions from effusive to explosive. If numerical simulations are the only way to fully understanding the physical processes involved, we are in a strong need of an experimental validation of the proposed models. here we present results obtained under torsion and uni-axial compression on both pure glasses and crystal bearing melts. We characterized the brittle onset of two phases magmas from 0 to 65% crystals. The strain-rates span a 5 orders magnitude range, from the Newtonian flow to the Brittle field (10-5 - 100 s-1). We particularly emphasize the time dependency of the measured rheology. The materials tested are a borosilicate glass from the National Bureau of Standards, a natural sample from Mt Unzen volcano and a synthetic sample. The lattest is an HPG8 melt with 7% sodium mole excess. The particles are quasi-isometric corundum crystalschosen for their shape and integrity under the stress range investigated. The crystal fraction ranges from 0 to 0.65. Concerning pure magmas, we recently demonstrated that the material passes from a Newtonian to a non-Nemtonian behavior with increasing strain-rate. This onset can mostly be explained by viscous-heating effects. However, for even greater strain-rates, the material cracks and finally fail. The brittle onset is here explained with the visco-elastic theory and corresponds to a Deborah number greater than 10-2. Concerning crystal bearing melts the departure from the Newtonian state is characterized by two effects: a shear-thinning and a time weakening effect. The first one is instantaneous and loading-unloading cyclic tests suggest an elastic contribution of the crystal network. The second one reflects a structural modification of the material (e.g. crystal reorganization, crystal failure, micro-cracking). In the special case presented here, the time weakening effect is the translation of plagioclase breaking during the magma flow. About the ultimate failure of the sample, crystal bearing melts appear to follow the general visco -elastic theory. However a crystal contribution has been here detected and corelate with smaller Deborah numbers before failure. Our observation offer a new vision on volcanic transition and an implication on the 90-95 eruptive crisis of Mt Unzen volcano is presented here.

  2. Growth, structural, spectroscopic and optical studies of pure and amino acid (glycine) doped methyl-para-hydroxy benzoate single crystals.

    PubMed

    Selvaraju, K; Kirubavathi, K; Kumararaman, S

    2009-05-01

    Methyl-para-hydroxy benzoate is a potential organic nonlinear optical (NLO) material. The pure and amino acid (glycine) doped MHB crystals are grown by slow evaporation solution growth technique. Single crystal X-ray diffraction studies of both pure and amino acid doped samples are carried out and the results are compared. FTIR studies are performed to identify the presence of various functional groups in the grown crystal. The UV-vis spectra confirm the improvement in the transparency of these crystals on doping amino acid. The amino acid doping improves the NLO properties. The dopant increases the hardness value of the material. PMID:19157962

  3. A simple synthesis of size-reduce magnetite nano-crystals via aqueous to toluene phase-transfer method

    NASA Astrophysics Data System (ADS)

    Abu Bakar, M.; Tan, W. L.; Abu Bakar, N. H. H.

    2007-07-01

    A simple one-step liquid-liquid phase-transfer synthesis of magnetite nanocrystals affording enhanced size reduction is described. One- and two-step particle transfer methods are compared. In the one-step method, particles are synthesized in a biphasic medium where the particles are formed in the microdroplets and migrate to the organic phase simultaneously, whereas in the two-step method, particles are first prepared in an aqueous phase and subsequently transferred to the organic phase. In both methods, CTAB was used as both a stabilizer and a transferring agent. Data from FTIR and XRD suggest invariably that the particles obtained are of magnetite, Fe 3O 4. The aqueous to organic phase-transfer efficiency is >99.5% for both methods. In the one-step method the average particle size and standard deviation (?) is half of that afforded in the two-step method (ca. 18.3+7.7 nm cf. 42.2+17.6 nm). This reduction in particle size is attributed to the formation of water in oil droplets that act as nanoreactors for the synthesis of magnetite particles.

  4. Magnetism in nanometer-thick magnetite

    NASA Astrophysics Data System (ADS)

    Monti, Matteo; Santos, Benito; Mascaraque, Arantzazu; Rodríguez de La Fuente, Oscar; Niño, Miguel Angel; Mente?, Tevfik Onur; Locatelli, Andrea; McCarty, Kevin F.; Marco, José F.; de La Figuera, Juan

    2012-01-01

    The oldest known magnetic material, magnetite, is of current interest for use in spintronics as a thin film. An open question is how thin can magnetite films be and still retain the robust ferrimagnetism required for many applications. We have grown 1-nm-thick magnetite crystals and characterized them in situ by electron and photoelectron microscopies including selected-area x-ray circular dichroism. Well-defined magnetic patterns are observed in individual nanocrystals up to at least 520 K, establishing the retention of ferrimagnetism in magnetite two unit cells thick.

  5. Magnetic moment and susceptibility measurements of pure Nd and mixed rare-earth (Di) tartrate crystals

    Microsoft Academic Search

    P. N. Kotru; K. K. Raina

    1986-01-01

    Magnetic characteristics of gel-grown pure neodymium tartrate and mixed rare-earth tartrate (didymium tartrate) crystals, using Gouy's balance method are reported. The experimental values of molar susceptibility for Nd2(C4H4O6)3.5H20 and Di2(C4H4O6)35H2O are 4876.787*10-6 and 4411.887*10-6 respectively, and the values of effective magnetic moments are 3.474 and 3.305 Bohr magnetrons respectively. The effective magnetic moments calculated on theoretical grounds are in reasonably

  6. Statistical Analyses Comparing Prismatic Magnetite Crystals in ALH84001 Carbonate Globules with those from the Terrestrial Magnetotactic Bacteria Strain MV-1

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, H.; Gibson, Everett K.

    2000-01-01

    Here we use rigorous mathematical modeling to compare ALH84001 prismatic magnetites with those produced by terrestrial magnetotactic bacteria, MV-1. We find that this subset of the Martian magnetites appears to be statistically indistinguishable from those of MV-1.

  7. Antimicrobial activity and second harmonic studies on organic non-centrosymmetric pure and doped ninhydrin single crystals.

    PubMed

    Prasanyaa, T; Jayaramakrishnan, V; Haris, M

    2013-03-01

    In this paper, we report the successful growth of pure, Cu(2+) ions and Cd(2+) ions doped on ninhydrin single crystals by slow solvent evaporation technique. The presence of Cu(2+) and Cd(2+) ions in the specimen of ninhydrin single crystal has been determined by atomic absorption spectroscopy. The powder X-ray diffraction analysis was done to calculate the lattice parameters of the pure and doped crystals. The percentage of transmittance of the crystal was recorded using the UV-Vis Spectrophotometer. Thermal behaviors of the grown crystals have been examined by the thermal gravimetric/differential thermal analysis. The hardness of the grown crystals was assessed and the results show the minor variation in the hardness value for the pure and doped ninhydrin samples. The value of the work hardening coefficient n was found to be 2.0, 1.0 and 1.06 for pure, copper and cadmium doped ninhydrin crystals respectively. The second harmonic generation efficiency of Cd(2+) and Cu(2+) doped ninhydrin is 8.3 and 6.3 times greater than well known nonlinear crystal of potassium dihydrogen phosphate respectively. The antibacterial and antifungal activities of the title compound were performed by disk diffusion method against the standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillis niger and Aspergillus flavus. PMID:23266683

  8. Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing.

    PubMed

    Liao, Ting-Wei; Chen, Hung-Ming; Shen, Kuan-Yuan; Kuan, Chieh-Hsiung

    2015-04-24

    In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm(-2), the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm(-1) at 300.7 cm(-1), which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities. PMID:25815515

  9. Growth and characterization of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals

    NASA Astrophysics Data System (ADS)

    Krishnan, C.; Selvarajan, P.; Freeda, T. H.; Mahadevan, C. K.

    2009-02-01

    Single crystals of pure and potassium iodide (KI)-doped zinc tris-thiourea sulphate (ZTS) were grown from aqueous solutions by the slow evaporation method. The grown crystals were transparent. The lattice parameters of the grown crystals were determined by the single-crystal X-ray diffraction technique. The grown crystals were also characterized by recording the powder X-ray diffraction pattern and by identifying the diffracting planes. The FT-IR spectrum was recorded in the range 400-4500 cm -1. Second harmonic generation (SHG) was confirmed by the Kurtz powder method. The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) studies reveal that the materials have good thermal stability. Atomic absorption studies confirm the presence of dopant in ZTS crystals. The electrical measurements were made in the frequency range 10 2-10 6 Hz and in the temperature range 40-130 °C along a-, b- and c-directions of the grown crystals. The present study shows that the electrical parameters viz. dc conductivity, dielectric constant, dielectric loss factor and ac conductivity increase with increase in temperature. Activation energy values were also determined for the ac conduction process in grown crystals. The dc conductivity, dielectric constant, dielectric loss factor and ac conductivity of KI-doped ZTS crystal were found to be more than those of pure ZTS crystals.

  10. Panning for Gold and Magnetite

    NSDL National Science Digital Library

    Eleanora Robbins

    In this activity, students can learn to pan for gold and magnetite. They will learn skills such as making observations under field conditions and watching out for poison ivy. They will see the effects of stream flow on sediments and observe sedimentary structures such as stream bars and islands, observe that different sizes of sediment are located in different parts of the stream, distinguish between different sizes of sediment, and recognize that different minerals are different colors. In addition, they can estimate and weigh the content of magnetite and nonmagnetite, observe crystal shapes of some of the mineral grains, and discuss why magnets pick up magnetite but not nonmagnetic grains. Choose desired title from main listing of activities to access individual exercises.

  11. Growth and Characterization of Pure and Cd-Doped Zinc Tris-Thiourea Sulfate (ZTS) Single Crystals

    NASA Astrophysics Data System (ADS)

    Muley, G. G.

    2014-02-01

    Single crystals of pure and Cd-doped zinc tris-thiourea sulfate (ZTS) were grown for frequency conversion applications by a low temperature solution growth method, allowing slow evaporation of the water solvent at a constant temperature. The solubility of ZTS was found to increase with the concentration of Cd in the aqueous solution. The optical transparency was found to increase in the Cd-doped crystals as compared to that in the undoped crystals. The doping of Cd was confirmed quantitatively by the atomic absorption spectroscopy and qualitatively by Fourier transform infrared spectroscopy. From the powder x-ray diffraction study, it was found that the lattice constants (a, b and c) decrease with the concentration of Cd in ZTS, but the change in the crystal symmetry and space group has not been reported. A?change in growth habit of Cd-doped crystals has been observed. Thermo-gravimetric and differential thermal analysis was employed to learn the thermal stability of the grown crystals, and 2 mol% Cd-doped ZTS crystal was found to thermally stable up to 230 °C. The second harmonic generation (SHG) efficiency measurement reveals improvement in the SHG efficiency, as 4 mol% Cd-doped ZTS crystal has 1.36 times more SHG efficiency as compared to the pure ZTS crystal.

  12. Characterization of a natural magnetite

    NASA Astrophysics Data System (ADS)

    Doriguetto, A. C.; Fernandes, N. G.; Persiano, A. I. C.; Filho, E. Nunes; Grenèche, J. M.; Fabris, J. D.

    Single crystals of a rock magnetite were separated from steatite cobbles collected in a geological site near the city of Serro (18° 36' 47'' S 43° 22' 46'' W), Minas Gerais, Brazil. A typically well-shaped magnetite single crystal was characterized by chemical analysis, 57Fe Mössbauer spectrometry at 300, 77 and 4 K and under an applied magnetic field of 6 T at 10 K, magnetization measurements and electronic microprobe. From Mössbauer data, the sample is stoichiometric with a tetrahedral and octahedral site occupancy ratio of 1:2. Elemental chemical analysis and point-to-point electron microscope probing show some inclusions of lamellar ilmenite (<= 1 mass%) randomly distributed throughout the magnetite matrix, and also that the magnetite matrix is constituted only by Fe2+ and Fe3+, with no isomorphic substitution. Results are discussed on the basis of the magnetization curve and of the temperature dependence of the AC magnetic susceptibility. The Verwey transition occurs in the temperature range of 100-115 K, observed by a sudden change in the temperature dependence of the magnetization.

  13. Growth and studies of pure and potassium iodide-doped zinc tris-thiourea sulphate (ZTS) single crystals

    NASA Astrophysics Data System (ADS)

    Krishnan, C.; Selvarajan, P.; Freeda, T. H.

    2008-12-01

    Single crystals of pure and potassium iodide (KI)-doped Zinc Tris-thiourea Sulphate (ZTS) were grown from aqueous solutions by slow evaporation technique. The grown crystals have been subjected to single crystal X-ray diffraction to determine the unit cell dimensions. The grown crystals were also characterized by recording the powder X-ray diffraction patterns and by identifying the diffracting planes. The Fourier Transform Infrared (FT-IR) spectra have been recorded in the range 400-4500 cm -1. Second harmonic generation (SHG) for the materials of this work was confirmed using Nd:YAG laser. The UV-visible spectra show that the grown crystals have wide optical transparency in the entire visible region. The Thermogravimetric/Differential Thermal Analyses (TG/DTA) thermograms reveal that the materials have good thermal stability. Atomic absorption study reveals the presence of potassium in the doped f crystals. The electrical measurements were made in the temperature range 40-130 °C along c-direction of the grown crystals. The dielectric studies show that there may be a ferroelectric transition at 50 °C for both pure and KI-doped ZTS crystals. DC conductivity for both the samples is found to be increasing with increase in temperature. Activation energy values were also determined for both AC and DC conduction processes in the samples.

  14. Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the

    E-print Network

    Dunin-Borkowski, Rafal E.

    Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling of ferrimagnetic magnetite crystals in magnetotactic bacteria provide a model system for studying the fundamental

  15. Magnetite in Chitons

    Microsoft Academic Search

    Manabu Mizota; Yutaka Maeda

    1985-01-01

    Radular teeth of chitons were studied using Mössbauer spectroscopy. Their spectra gave clear evidence of the presence of magnetite and a small amount of paramagnetic substance. These are characteristic features in biogenic magnetite. Measurements on the teeth at different locations along the radular were also performed. The results show that the magnetite in the radular teeth of chitons changes considerably

  16. Biogenic Magnetite and EMF Effects

    NASA Astrophysics Data System (ADS)

    Kirschvink, Joseph L.

    1996-03-01

    Magnetite biomineralization is a genetically-controlled biochemical process through which organisms make perfect ferrimagnetic crystals, usually of single magnetic domain size. This process is an ancient one, having evolved about 2 billion years ago in the magnetotactic bacteria, and presumably was incorporated in the genome of higher organisms, including humans. During this time, DNA replication, protein synthesis, and many other biochemical processes have functioned in the presence of strong static fields of up to 400 mT adjacent to these magnetosomes without any obvious deleterious effects. Recent behavioral experiments using short but strong magnetic pulses in honeybees and birds demonstrates that ferromagnetic materials are involved in the sensory transduction of geomagnetic field information to the nervous system, and both behavioral and direct electrophysiological experiments indicate sensitivity thresholds to DC magnetic fields down to a few nT. However, far more biogenic magnetite is present in animal tissues than is needed for magnetoreception, and the biological function of this extra material is unknown. The presence of ferromagnetic materials in biological systems could provide physical transduction mechanisms for ELF magnetic fields, as well for microwave radiation in the .5 to 10 GHz band where magnetite has its peak ferromagnetic resonance. Elucidation of the cellular ultrastructure and biological function(s) of magnetite might help resolve the question of whether anthropogenic EMFs can cause deleterious biological effects. This work has been supported by grants from the NIH and EPRI.

  17. Spectroscopic and optical studies on pure and doped single crystals of sulphate-mixed ?-arginine phosphate monohydrate—a nonlinear optical crystal

    NASA Astrophysics Data System (ADS)

    Dhanuskodi, S.; Angeli Mary, P. A.; Vasantha, K.

    2003-03-01

    Single crystals of pure and transition metal ions (Cu 2+ and VO 2+)-doped L-arginine sulpho phosphate monohydrate (sulphate-mixed L-arginine phosphate monohydrate, abbreviated as LASP) have been grown by solvent evaporation of the saturated aqueous solution at room temperature and characterized by single-crystal XRD, FT-IR, UV-Vis-NIR and EPR (single-crystal rotation) spectral studies. Kurtz powder technique shows an enhanced second harmonic generation (SHG) efficiency for LASP and its doped analogues than pure LAP. The EPR studies on LASP:VO 2+ reveal that the in-plane ?-bonding is moderately covalent and the out-of-plane ?-bonding is highly covalent, which could be attributed to the cause of enhanced powder efficiency.

  18. The I-Xe Age of Orgueil Magnetite: New Results

    NASA Technical Reports Server (NTRS)

    Pravdivtseva, O. V.; Hohenberg, C. M.; Meshik, A. P.

    2003-01-01

    I-Xe ages of Murchison and Orgueil magnetites were reported to be the oldest [1] and interpreted as the condensation time of the solar nebula. More recent measurements, conducted on a highly magnetic separate from Orgueil (but not pure magnetite), gave much younger I-Xe ages [2]. We have since performed new studies on two pure separates of Orgueil magnetite, confirming the later closing time of the I-Xe system in this mineral phase. In the previous work of Lewis and Anders [1] special attention was paid to the purity of the analyzed material. It was shown, that the trapped Xe resided mostly in hydrated silicates and the radiogenic 129Xe in magnetite [3]. Therefore, Orgueil was finely ground and stirred with a saturated LiCl solution for 8 days at 60 C to remove the silicate-magnetite intergrowth. Although this procedure yields magnetic fractions that are at least 90% pure [1], it could potentially contaminate the magnetite with iodine and produce noncorrelated 128Xe and spurious I-Xe ages. To avoid this possibility, in our first work with Orgueil we deliberately omitted separation in LiCl solution. Instead, the meteorite was ground into a fine powder and the highly magnetic fraction was separated with a hand magnet and was confirmed to be largely magnetite [2]. The new work, reported here, was done in order to confirm our previous results and investigate the effects of the LiCl treatment on the I-Xe system in magnetite.

  19. Growth and characterization of pure and KCl doped zinc thiourea chloride (ZTC) single crystals

    NASA Astrophysics Data System (ADS)

    Ruby Nirmala, L.; Thomas Joseph Prakash, J.

    2013-02-01

    Potassium Chloride (KCl) as an additive is added into zinc thiourea chloride solution in a small amount (1 M%) by the method of slow evaporation solution growth technique at room temperature to get a new crystal. Due to the doping of the impurities on the crystals, remarkable changes in the physical properties were obtained. The grown crystals have been subjected to different instrumentation methods. The incorporation of the amount of potassium and zinc in the crystal lattices has been determined by AAS method. The lattice dimensions have been identified from single crystal X-ray diffraction measurements. The presence of functional group for the grown crystals has been identified by FTIR analysis. The optical, thermal and mechanical behaviors have been assessed by UV-Vis, TG/DTA and Vickers hardness methods respectively. The presence of dislocations of atoms has been identified by etching studies.

  20. Growth and characterization of pure and KCl doped zinc thiourea chloride (ZTC) single crystals.

    PubMed

    Ruby Nirmala, L; Thomas Joseph Prakash, J

    2013-02-01

    Potassium Chloride (KCl) as an additive is added into zinc thiourea chloride solution in a small amount (1M%) by the method of slow evaporation solution growth technique at room temperature to get a new crystal. Due to the doping of the impurities on the crystals, remarkable changes in the physical properties were obtained. The grown crystals have been subjected to different instrumentation methods. The incorporation of the amount of potassium and zinc in the crystal lattices has been determined by AAS method. The lattice dimensions have been identified from single crystal X-ray diffraction measurements. The presence of functional group for the grown crystals has been identified by FTIR analysis. The optical, thermal and mechanical behaviors have been assessed by UV-Vis, TG/DTA and Vickers hardness methods respectively. The presence of dislocations of atoms has been identified by etching studies. PMID:23220671

  1. Magnetite biomineralization induced by Shewanella oneidensis

    NASA Astrophysics Data System (ADS)

    Perez-Gonzalez, Teresa; Jimenez-Lopez, Concepcion; Neal, Andrew L.; Rull-Perez, Fernando; Rodriguez-Navarro, Alejandro; Fernandez-Vivas, Antonia; Iañez-Pareja, Enrique

    2010-02-01

    Shewanella oneidensis is a dissimilatory iron reducing bacterium capable of inducing the extracellular precipitation of magnetite. This precipitation requires a combination of passive and active mechanisms. Precipitation occurs as a consequence of active production of Fe 2+(aq) when bacteria utilize ferrihydrite as a terminal electron acceptor, and the pH rise probably due to the bacterial metabolism of amino acids. As for passive mechanisms, the localized concentration of Fe 2+(aq) and Fe 3+(aq) at the net negatively charged cell wall, cell structures and/or cell debris induces a local rise of supersaturation of the system with respect to magnetite, triggering the precipitation of such a phase. These biologically induced magnetites are morphologically identical to those formed inorganically in free-drift experiments (closed system; 25 °C, 1 atm total pressure), both from aqueous solutions containing Fe(ClO 4) 2, FeCl 3, NaHCO 3, NaCO 3 and NaOH, and also from sterile culture medium added with FeCl 2. However, organic material becomes incorporated in substantial amounts into the crystal structure of S. oneidensis-induced magnetites, modifying such a structure compared to that of inorganic magnetites. This structural change and the presence of organic matter are detected by Raman and FT-IR spectroscopic analyses and may be used as a biomarker to recognize the biogenic origin of natural magnetites.

  2. Microbial Magnetite Formation: Interaction of Biotic and Abiotic Factors

    NASA Astrophysics Data System (ADS)

    Popa, R.; Nealson, K.

    2003-04-01

    Microbial magnetite formation occurs in two known modes - intracellular magnetite in the form of single domain magnetite crystals, usually (but not always) arranged in chains, and extracellular magnetite minerals. The former mode is apparently highly controlled with regard to crystal growth, and the resulting magnetosomes are used by the bacteria for orientation purposes. The latter mode is uncontrolled except by environmental geochemical conditions, and is the result of respiratory iron reduction by bacteria that respire iron under anaerobic conditions (i.e. so called dissimilatory iron reducing bacteria, or DIRB). The studies reported here indicate that the synthesis of magnetite and magnetosomes by a magnetotactic bacterium (Magnetospirillum magnetotacticum strain AMB1) is strongly dependent on the presence of a stable magnetic field. When AMB1 is grown with an external magnetic field (between 0.5 to 400 Gauss) that oscillates or is otherwise unstable, the synthesis of magnetite is nearly completely abolished. In contrast, when grown under sitting or (magnetically) stable conditions, magnetite formation is optimal. Growth in a mu-metal shielded space (which lowers the magnetic field to 80 to 140 nT) resulted in less magnetite formation, but did not inhibit synthesis to the degree that occurred with an unstable large magnetic field. These results show that both the magnitude and changes in the magnetic field can affect intracellular biological magnetite formation. Apparently AMB1 can sense the magnetic field over a wide range of values, and interact with the magnetic field to mediate (or inhibit) magnetite synthesis. Similar effects on magnetite synthesis have not been reported for extracellular magnetite synthesis by DIRB, which are under study now.

  3. Mme GODEFROY G. AND M. COUSON B. CONDUCTIVITY OF BaTiO, . PURE SINGLE CRYSTALS

    E-print Network

    Paris-Sud XI, Université de

    ) SINGLE CRYSTALS Abstract. -When single crystals of barium titanate are placed under d. c. voltage barium titanate. We only cite the most recent :that of Tredgold and his co-workers [I], [2], 131, [4 of barium titanate, we have resumed conductivity measurements and speci- fied conditions of current

  4. Anisotropy of Silicate-Hosted Magnetite Inclusions

    NASA Astrophysics Data System (ADS)

    Scott, G. R.; Feinberg, J. M.; Renne, P. R.

    2004-12-01

    Anisotropy of magnetic properties is a hallmark of silicate crystals with oriented iron-oxide inclusions. Strongly magnetic magnetite-bearing silicates (10-1 A m-1) are common components of gabbros and layered intrusions, contributing to local and regional magnetic anomalies. Additionally, these iron-oxide silicates hold the promise of being exceptional paleomagnetic recorders owing to their features of: physical/chemical isolation from altering fluids, chemical equilibrium with their silicate host, and long relaxation times (enhanced coercivity). However, anisotropy of remanence must be understood before these advantageous features can be utilized. Measurements of single crystals of clinopyroxene and plagioclase (10-4 g) show anisotropy in direction and intensity that directly reflect the crystallography of the silicate host. The host controls both the crystallographic orientation of the magnetite (magnetocrystalline anisotropy) and the elongation direction of the magnetite inclusion (shape anisotropy). We have found another source of anisotropy that involves an internal exsolution of ulvöspinel within titanomagnetite inclusions. This also reflects a host control as this second exsolution occurs along the magnetite \\{100\\}. This fixed wall shape anisotropy creates an array of interacting single domain magnetite parallelepipeds, parallel to \\{100\\}. Each of these anisotropies contributes to enhanced coercivity of remanence, which significantly exceeds the IRM saturation magnetization for magnetite (300 mT). The anisotropy of IRM (aIRM@ 1.1 T) of magnetite-bearing clinopyroxene and plagioclase shows clustering of directions, reflecting the mixture of variables that include: inclusion elongation direction and abundance, orientation of magnetite easy axes relative to the applied field, inclusion aspect ratio and diameter, and pre-existing magnetic domain structure. For pyroxene (monoclinic) with two arrays of needle-shaped magnetite inclusions, the aIRM is strongly planar, showing two sets of antipodal direction clusters. The total intensity is uniform over ˜60% of the remanence plane. The component of magnetization perpendicular to the applied IRM (transverse remanence) exceeds the parallel remanence in some crystallographic directions. For plagioclase (triclinic) with three to five arrays of needle-shaped magnetite inclusions (see Feinberg, et al. this conference), the aIRM is subspherical with numerous minor clusters of directions. Transverse remanence is less important than parallel remanence in plagioclase. Thus, the greater number of inclusion arrays in plagioclase decreases the severity of the IRM anisotropy relative to the two arrays in pyroxene.

  5. Magnetite thin films

    Microsoft Academic Search

    J. Feng; C. Bajorek; M.-A. Nicolet

    1972-01-01

    A low temperature process for converting hematite (?-Fe2O3) thin films into magnetite (Fe3O4is described. The films produced are unambiguously identified as magnetite by several complementary methods of analysis. These include ?-backscattering spectrography, X-ray powder diffractometry, and observations of electrical, magnetic, and optical properties.

  6. Stoichiometric magnetite grown by infrared nanosecond pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Sanz, Mikel; Oujja, Mohamed; Rebollar, Esther; Marco, José F.; de la Figuera, Juan; Monti, Matteo; Bollero, Alberto; Camarero, Julio; Pedrosa, Francisco J.; García-Hernández, Mar; Castillejo, Marta

    2013-10-01

    Pulsed laser deposition (PLD) is a versatile technique for the fabrication of nanostructures due to the possibilities it offers to control size and shape of nanostructured deposits by varying the laser parameters. Magnetite nanostructures are currently promising materials to be used in computing, electronic devices and spintronic applications. For all these uses the fabrication of uniform nanostructured pure magnetite thin films is highly advantageous. In PLD of magnetite, the laser irradiation wavelength and substrate temperature crucially affect the composition, crystallinity, surface structure and the magnetic properties of the grown samples. This work shows that the use of nanosecond IR laser at 1064 nm enhances the quality of the resulting magnetite thin films, compared to the extensively used UV wavelengths. Deposition at 1064 nm, upon heating the substrate at 750 K, produces thin films constituted by stoichiometric magnetite nanoparticles with sharp edges and sizes ranging from 80 to 150 nm, with a Verwey transition at 119 K and a coercivity of 232 Oe at room temperature, close to those of pure bulk magnetite. Thus, IR-PLD of self-prepared hematite sintered targets constitutes a low-cost procedure of fabrication of pure magnetite nanostructured thin films.

  7. Spherulitic crystallization of pure (Nd and Dy) and mixed (Di) rare earth tartrates in silica gel

    NASA Astrophysics Data System (ADS)

    Kotru, P. N.; Raina, K. K.

    1988-08-01

    Spherulites of pure Nd 2(C 4H 4O 6) 3·5H 2O, Dy 2(C 4H 4O 6) 3·11H 2O and mixed Di 2(C 4H 4O 3·5H 2O * were grown from silica gels by the reaction of the corresponding rare-earth nitrate with tartaric acid. The outer morphology of the spherulites is observed to be different for pure and mixed rare-earth tartrates respectively. The internal structure of these spherulites suggest a new formation mechanism - unlike the ones reported in the literature.

  8. Resistance switching in electrodeposited magnetite superlattices.

    PubMed

    Switzer, Jay A; Gudavarthy, Rakesh V; Kulp, Elizabeth A; Mu, Guojun; He, Zhen; Wessel, Andrew J

    2010-02-01

    Defect-chemistry magnetite superlattices and compositional superlattices in the magnetite/zinc ferrite system are electrodeposited as epitaxial films onto single-crystal Au(111). The defect-chemistry superlattices have alternating nanolayers with different Fe(III)/Fe(II) ratios, whereas the compositional superlattices have alternating nanolayers with different Zn/Fe ratios. The electrochemical/chemical (EC) nature of the electrodeposition reaction is exploited to deposit the superlattices by pulsing the applied potential during deposition. The defect-chemistry superlattices show low-to-high and high-to-low resistance switching that may be applicable to the fabrication of resistive random access memory (RRAM). PMID:20055488

  9. Growth conditions, structure and superconductivity of pure and metal-doped FeTe1 - xSex single crystals

    NASA Astrophysics Data System (ADS)

    Gawryluk, D. J.; Fink-Finowicki, J.; Wi?niewski, A.; Pu?niak, R.; Domukhovski, V.; Diduszko, R.; Koz?owski, M.; Berkowski, M.

    2011-06-01

    Superconducting single crystals of pure FeTe1 - xSex and FeTe0.65Se0.35 doped with Co, Ni, Cu, Mn, Zn, Mo, Cd, In, Pb, Hg, V, Ga, Mg, Al, Ti, Cr, Sr or Nd into Fe ion sites have been grown applying Bridgman's method. It has been found that the sharpness of the transition to the superconducting state in FeTe1 - xSex is evidently inversely correlated with the crystallographic quality of the crystals. Among all of the studied dopants only Co, Ni and Cu substitute Fe ions in FeTe0.65Se0.35 crystals. The remaining ions examined do not incorporate into the crystal structure. Nevertheless, they form inclusions together with selenium, tellurium and/or iron, which change the chemical composition of the host matrix and therefore influence the Tc value. The small disorder introduced into the magnetic sublattice, by partial replacement of Fe ions by a slight amount of nonmagnetic ions of Cu (~1.5 at.%) or by magnetic ions of Ni (~2 at.%) and Co (~5 at.%) with spin values different than that of the Fe ion, completely suppresses superconductivity in the FeTe1 - xSex system. This indicates that, even if superconductivity is observed in the system containing magnetic ions, it cannot survive when the disorder in the magnetic ion sublattice is introduced, most likely because of magnetic scattering of Cooper pairs.

  10. Growth, optical, mechanical and dielectric studies on NLO active pure and metal ion doped single crystals of bis-thiourea zinc chloride

    NASA Astrophysics Data System (ADS)

    Parasuraman, K.; Sakthi Murugesan, K.; Uthrakumar, R.; Jerome Das, S.; Milton Boaz, B.

    2011-10-01

    Good quality single crystals of pure and metal ion (Ni 2+) doped bis-thiourea zinc chloride (BTZC) possessing excellent nonlinear optical properties have been grown from aqueous solution by the slow solvent evaporation technique. The lattice parameters of the grown crystals are determined by single crystal X-ray analysis. The well defined sharp peaks in the powder X-ray diffraction pattern reveals the crystalline perfection and the EDAX spectrum confirms the presence of dopant in the lattice of the parent crystal. The DRS UV-visible spectral study reveals improved transparency for the doped crystal, ascertaining the inclusion of metal ion in the lattice. The optical band gap of the pure and doped crystals was calculated to be 4.8 and 5.2 eV respectively from the UV transmission spectrum. The vickers hardness test brings forth higher hardness value for Ni 2+doped BTZC as compared to pure BTZC crystal. The dielectric measurement exhibits very low dielectric constant and dielectric loss at higher frequencies for both the pure and Ni 2+doped BTZC. The existence of second harmonic generation signals in the crystal also has been confirmed by performing the Kurtz powder test.

  11. Kinetics and mechanism of crystallization of gehlenite glass pure and doped with Co 2+, Eu 3+, Cr 3+ and Th 4+

    Microsoft Academic Search

    Andrzej Ma?ecki; Ryszard Gajerski; Stanis?aw ?abu?; Barbara Prochowska-Klisch; Jan Ob?

    1997-01-01

    The crystallization of glasses of gehlenite composition, 2CaO · Al2O3 · SiO2, pure and doped with 0.02 mol cobalt, europium, chromium and thorium per one mole of gehlenite, was studied using differential thermal analysis. The kinetics of crystallization of all examined glasses are described by the Avrami equation: ? = 1 ? exp(?ktn). The activation energy of the crystallization process

  12. Zeeman Effect of the Purely Cubic Field Fluorescence Line of MgO: Cr3+ Crystals

    Microsoft Academic Search

    S. Sugano; A. L. Schawlow; F. Varsanyi

    1960-01-01

    Both transverse and longitudinal Zeeman effects are studied of the most conspicuous red emission line (14 319 cm-1) of a MgO: Cr3+ single crystal. The Zeeman patterns are examined experimentally, with a magnetic field parallel to the [001], [110] and [111] axes, with linear polarizations parallel and perpendicular to each direction of the magnetic field and with circular polarizations around

  13. Laser-assisted one-pot fabrication of calcium phosphate-based submicrospheres with internally crystallized magnetite nanoparticles through chemical precipitation.

    PubMed

    Nakamura, Maki; Oyane, Ayako; Sakamaki, Ikuko; Ishikawa, Yoshie; Shimizu, Yoshiki; Kawaguchi, Kenji

    2015-04-14

    In this paper, we have further developed our simple (one-pot) and rapid (short irradiation time) laser fabrication process of submicrometer spheres composed of amorphous calcium iron phosphate. In our previous process, laser irradiation was applied to a calcium phosphate (CaP) reaction mixture supplemented with ferric ions (Fe(3+)) as a light-absorbing agent. Because the intention of the present study was to fabricate magnetite-encapsulated CaP-based submicrometer spheres, ferrous ions (Fe(2+)) were used as a light-absorbing agent rather than ferric ions. The ferrous ions served as a light-absorbing agent and facilitated the fabrication of submicrometer and micrometer spheres of amorphous calcium iron phosphate. The sphere formation and growth were better promoted by the use of ferrous ions as compared with the use of ferric ions. The chemical composition of the spheres was controllable through adjustment of the experimental conditions. By the addition of sodium hydroxide to the CaP reaction mixture supplemented with ferrous ions, fabrication of CaP-based magnetic submicrometer spheres was successfully achieved. Numerous magnetite and wüstite nanoparticles were coprecipitated or segregated into the CaP-based spherical amorphous matrix via light-material interaction during the CaP precipitation process. The magnetic properties of the magnetite and wüstite formed in the CaP-based spheres were investigated by magnetization measurements. The present process and the resulting CaP-based spheres are expected to have great potential for biomedical applications. PMID:25742691

  14. Scaffold of Asymmetric Organic Compounds - Magnetite Plaquettes

    NASA Technical Reports Server (NTRS)

    Chan, Q. H. S.; Zolensky, M. E.; Martinez, J.

    2015-01-01

    Life on Earth shows preference towards the set of organics with particular spatial configurations, this 'selectivity' is a crucial criterion for life. With only rare exceptions, life prefers the left- (L-) form over the right- (D-) form of amino acids, resulting in an L-enantiomeric excess (L-ee). Recent studies have shown Lee for alpha-methyl amino acids in some chondrites. Since these amino acids have limited terrestrial occurrence, the origin of their stereoselectivity is nonbiological, and it seems appropriate to conclude that chiral asymmetry, the molecular characteristic that is common to all terrestrial life form, has an abiotic origin. A possible abiotic mechanism that can produce chiral asymmetry in meteoritic amino acids is their formation with the presence of asymmetric catalysts, as mineral crystallization can produce spatially asymmetric structures. Magnetite is shown to be an effective catalyst for the formation of amino acids that are commonly found in chondrites. Magnetite 'plaquettes' (or 'platelets'), first described by Jedwab, show an interesting morphology of barrel-shaped stacks of magnetite disks with an apparent dislocation-induced spiral growth that seem to be connected at the center. A recent study by Singh et al. has shown that magnetites can self-assemble into helical superstructures. Such molecular asymmetry could be inherited by adsorbed organic molecules. In order to understand the distribution of 'spiral' magnetites in different meteorite classes, as well as to investigate their apparent spiral configurations and possible correlation to molecular asymmetry, we observed polished sections of carbonaceous chondrites (CC) using scanning electron microscope (SEM) imaging. The sections were also studied by electron backscattered diffraction (EBSD) in order to reconstruct the crystal orientation along the stack of magnetite disks.

  15. Crystal nucleation in glass-forming alloy and pure metal melts under containerless and vibrationless conditions

    NASA Technical Reports Server (NTRS)

    Spaepen, F.; Turnbull, D.

    1982-01-01

    The undercooling behavior of large spheroids of Pd40Ni40P40 was investigated. By surface etching, supporting the specimens on a fused silica substrate, and successive heating and cooling, crystallization can be eliminated, presumable due to the removal of surface heterogeneities. By this method samples up to 3.2g with a 0.53 mm minor diameter, were made entirely glassy, except for some superficial crystals comprising less than 0.5% of the volume. These experiments show that a cooling rate of approximately 1 K/sec is adequate to avoid copious homogeneous nucleation in the alloy, and that by eliminating or reducing the effectiveness of heterogeneous nucleation sites, it is possible to form bulk samples of this metallic glass with virtually unlimited dimensions.

  16. Water-soluble porphyrin detection in a pure-silica photonic crystal fiber

    Microsoft Academic Search

    Cicero Martelli; John Canning; Danial Stocks; Maxwell J. Crossley

    2006-01-01

    Aqueous solutions of the water-soluble porphyrin 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinatomanganese(III) acetate were inserted into the holes of a photonic crystal fiber, and the porphyrin absorption bands were identified. Results were obtained for three concentrations. The porphyrins in water show no surface interactions with the silica walls of the capillary channels. We discuss the implications for future hybrid electronic and photonic fiber devices.

  17. Oriented inclusions of magnetite in clinopyroxene: Source of stable remanent magnetization in gabbros of the Messum Complex, Namibia

    Microsoft Academic Search

    Paul R. Renne; Gary R. Scott; Jonathan M. G. Glen; Joshua M. Feinberg

    2002-01-01

    Crystallographically oriented and highly elongate magnetite inclusions in clinopyroxene are the dominant source of highly stable remanent magnetization in gabbros of the Early Cretaceous Messum Complex, Namibia. Rock magnetic properties determined for individual pyroxene crystals indicate a high proportion of single-domain magnetite, consistent with the observed sizes and shape anisotropy of the magnetite inclusions. As in previous studies of similar

  18. Optical damage dynamics in reduced nominally pure LiNbO3 crystals

    NASA Astrophysics Data System (ADS)

    Kostritskii, S. M.; Aillerie, M.; Chikh-Bled, B.; Sevostyanov, O. G.

    2010-11-01

    The dynamics of the optical damage in the chemically reduced LiNbO3 has been investigated, when a laser beam is externally focused into a bulk crystal. The temporal evolution of the transmitted power P was recorded, using the closed-aperture pseudo-Z-scan method. We define the three specific levels of the transmitted power that occur at different times during experiment: P0 and P1 are the initial and minimal values of the transmitted power during first stage of experiment, when the usual fast rise of optical damage causes decrease of the transmitted power due to laser beam defocusing, while P2 is the steady-state value after the long-term exposure, when a sequent slow increase of the transmitted power is observed, indicating on the self-compensation of optical damage. This compensation becomes undetectable, when the input light intensity I within focal area is smaller than some specific value ranged from 4 to 90 W/cm2 (? = 644 nm), depending on the chemical reduction degree. At intensities above such a threshold the self-compensation increases monotonically with I.

  19. Optimize the modulation response of twisted-nematic liquid crystal displays as pure phase spatial light modulators

    NASA Astrophysics Data System (ADS)

    Ma, Baiheng; Peng, Fei; Kang, Mingwu; Zhou, Jiawu

    2014-11-01

    Twisted-nematic liquid crystal displays (TN-LCD) are widely used in numerous research fields of optics working as spatial light modulators. Approaches to obtaining desired intensity or phase modulation by TN-LCD have been extensively studied based on the knowledge of TN-LCD's internal structure parameters, e.g., the orientation of LC molecules at the surfaces, the twist angle, the thickness of the LC layer, and the birefringence of the material. Generally TN-LCD placed between two linear polarizers (P) produces coupled intensity and phase modulation. To obtain the commonly used pure phase modulation, quarter wave plates (QWP) are often used in front of and/or behind the LCD. In this paper, we present a method to optimize the optical modulation properties of the TN-LCD to obtain pure phase modulation in the configuration of P-QWP-LCD-QWP-P each with proper orientation. Firstly an improved method for determining the Jones matrix of the TN-LCD without knowing its internal parameters is presented, which is based on the macroscopical Jones matrix descriptions for TN-LCD, linear polarizer and QWP. Only three sets of intensity measurements are needed for the complete determination of the TN-LCD's Jones matrix for a single wavelength. Then Jones matrix calculations are carried out to determine the orientations of the polarizers and QWPs for pure phase modulation response. In addition, we prove that the phase modulation depth (PMD) of the TN-LCD can be further increased provided that the mean intensity transmission is decreased to a lower level, which is very useful when the TN-LCD is used as a phase modulator and the ratio between the intensities of the desired diffracted order relative to the other diffracted orders is required higher. Experimental results coincide well with the optical modulation properties of the TN-LCD predicted by our determined Jones matrix. In contrast to the traditional method which requires knowledge of the TN-LCD's internal structure parameters, our method simplified the complicated theory analysis and intensity measurement, and can work in the absence of information on the TN-LCD's internal structure parameters which are usually not available for commercial products.

  20. Nanophase Magnetite and Pyrrhotite in ALH84001 Martian Meteorite: Evidence for an Abiotic Origin

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Lauer, H. V., Jr. III; Ming, D. W.; Morris, R. V.

    2006-01-01

    The nanophase magnetite crystals in the black rims of pancake-shaped carbonate globules of the Martian meteorite ALH84001 have been studied extensively because of the claim by McKay et al.that they are biogenic in origin. A subpopulation of these magnetite crystals are reported to conform to a unique elongated shape called "truncated hexa-octahedral" or "THO" by Thomas-Keprta et al. They claim these THO magnetite crystals can only be produced by living bacteria thus forming a biomarker in the meteorite. In contrast, thermal decomposition of Fe-rich carbonate has been suggested as an alternate hypothesis for the elongated magnetite formation in ALH84001 carbonates. The experimental and observational evidence for the inorganic formation of nanophase magnetite and pyrrhotite in ALH84001 by decomposition of Fe-rich carbonate in the presence of pyrite are provided.

  1. Exsolution of Iron-Titanium Oxides in Magnetite in Miller Range (MIL) 03346 Nakhlite: Evidence for Post Crystallization Reduction in the Nakhlite Cumulate Pile

    NASA Technical Reports Server (NTRS)

    Righter, Kevin; Keller, L. P.; Rahman, Z.; Christoffersen, R.

    2012-01-01

    MIL 03346 is one of the most mesostasis-rich nakhlites [1] and thought to have equilibrated at oxygen fugacities near the fayalite-magnetite-quartz oxygen (FMQ) buffer ([2,3]). Studies of FeTi oxides in nakhlites have led to additional constraints on their equilibration temperatures and fO2s [4,5,6,7]. Comparison of these results to fO2s calculated for shergottites indicates that nakhlites are among the most oxidized samples from the martian meteorite suite [2]. The mesostasis of MIL 03346 contains skeletal titanomagnetite. Several scientists noticed several years ago (e.g. [8]) that this titanomagnetite contains very fine oxidation-driven exsolution lamellae (Figure 1). However, the lamellae are so small that they cannot be characterized by electron microprobe analysis (EMPA). Here we select several areas for focused ion beam (FIB) extraction, prepare transmission electron microscopy (TEM) foils, and identify and analyze the lamellae using TEM at the Johnson Space Center (JSC). The resulting analyses are combined with previous work on nakhlites to interpret the thermal and oxidation history of this meteorite group.

  2. Magnetite: What it reveals about the origin of the banded iron formations. [Abstract only

    NASA Technical Reports Server (NTRS)

    Schwartz, D. E.; Mancinelli, R. L.; White, M. R.

    1994-01-01

    Magnetite, Fe3O4 is produced abiotically and biotically. Abiotically, magnetite is a late magmatic mineral and forms as a consequence of the cooling of iron rich magma. Biotically, magnetite is produced by several organisms, including magnetotactic bacteria. Hematite, Fe2O3, is also produced abiotically and biotically. Abiotically, hematite rarely occurs as a primary mineral in igneous rocks, but is common as an alteration product, fumarole deposit, and in some metamorphosed Fe-rich rocks. Biotically, hematite is produced by several types of microorganisms. Biologically-produced magnetite and hematite are formed under the control of the host organism, and consequently, have characteristics not found in abiotically produced magnetite and hematite crystals. To determine if the magnetite and hematite in the Banded Iron Formation was biologically or abiotically produced, the characteristics of biologically-produced magnetite and hematite (concentrated from Aquaspirillum magnetotacticum) and abiotically-produced magnetite and hematite obtained from Wards Scientific Supply Company, were compared with characteristics of magnetite and hematite concentrated from the Gunflint Banded Iron Formation (Ontario, Canada) using thermal and crystallographic analytical techniques. Whole rock analysis of the Gunflint Banded Iron Formation by x-ray diffraction (XRD) and differential thermal analysis (DTA) revealed the presence of quartz, hematite, siderite and dolomite as the major minerals, and magnetite, greenalite, pyrite, pyrrhotite and apatite as the minor minerals. Analysis of a crude magnetic fraction of the Gunflint showed the minerals quartz, hematite, siderite, dolomite, and magnetite. Analysis of the crude magnetic fraction from Aquaspirillum magnetotacticum revealed organic compounds plus hematite and magnetite. The mineral identification and particle size distribution data obtained from the DTA along with XRD data indicate that the magnetite and hematite from the Gunflint BIF share some similarities with biologically formed magnetite and hematite.

  3. Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation

    E-print Network

    Higgins, Darren

    of magnetotactic bacteria. Together, these results suggest that the magnetosome precisely coordinates magnetite and archaea. The magnetosome compartments of magnetotactic bacteria, however, appear to possess many of magnetite or greigite crystals (Fig. 1A), form a magnet that allows magnetotactic bacteria to orient

  4. Ferromagnetic resonance and low-temperature magnetic tests for biogenic magnetite

    Microsoft Academic Search

    Benjamin P. Weiss; Soon Sam Kim; Joseph L. Kirschvink; Robert E. Kopp; Mohan Sankaran; Atsuko Kobayashi; Arash Komeili

    2004-01-01

    Magnetite is both a common inorganic rock-forming mineral and a biogenic product formed by a diversity of organisms. Magnetotactic bacteria produce intracellular magnetites of high purity and crystallinity (magnetosomes) arranged in linear chains of crystals. Magnetosomes and their fossils (magnetofossils) have been identified using transmission electron microscopy (TEM) in sediments dating back to ?510–570 Ma, and possibly in 4 Ga

  5. Synthesis, characterization and anti-microbial activity of pure, Cu2+ and Cd2+ doped organic NLO l-arginine trifluoroacetate single crystals

    NASA Astrophysics Data System (ADS)

    Prasanyaa, T.; Haris, M.; Jayaramakrishnan, V.; Amgalan, M.; Mathivanan, V.

    2013-10-01

    Optically transparent Cu2+ and Cd2+ doped l-arginine trifluoroacetate (LATF) single crystals were grown from its aqueous solution using the slow solvent evaporation technique. The grown crystals were characterized by powder x-ray diffraction to confirm the monoclinic crystal structure. The percentage of transmittance measured using the ultraviolet-visible-near infrared spectrophotometer was found to be more than 80% for doped crystals. The functional group analysis of the grown crystals has been made by Fourier transform infrared spectroscopy. Thermogravimetric/differential thermal analysis was performed for the grown crystals. An atomic absorption study was carried out to determine the presence of Cu2+ and Cd2+. The hardness of the grown crystals was assessed and the results show a significant variation in the hardness value between the pure and doped LATF crystals. The second harmonic generation measurements show that Cu2+ doped LATF is 2.8 times greater and Cd2+ doped is 2.6 times greater than KDP. The anti-bacterial and anti-fungal activities of the title compound were performed using the disc diffusion method against standard bacteria Escherichia coli, Xanthomonas oryzae and against the fungus Aspergillus niger and Aspergillus flavus.

  6. Experimental low-grade alteration of biogenic magnetite indicates microbial involvement in generation of banded iron formations

    NASA Astrophysics Data System (ADS)

    Li, Yi-Liang; Konhauser, Kurt O.; Kappler, Andreas; Hao, Xi-Luo

    2013-01-01

    During the deposition of banded iron formation (BIF), the downward flux of ferric oxyhydroxides and phytoplankton biomass should have facilitated Fe(III) reduction during burial, with the end product being ferrous iron-containing minerals including magnetite. Although earlier studies have attempted to quantify the significance of this pathway based on models of the ancient Fe cycle, the only direct evidences of a biological role in magnetite formation in BIF are their iron isotope compositions and unique crystallography which are reminiscent of biologically-generated magnetite. However, the biogenesis hypothesis lacks an explanation as to why modern biogenic magnetite crystals are generally a few hundred nm or smaller in size, yet the magnetite crystals in BIF are mostly tens of micrometers or larger in size. In this study, we demonstrate that biogenic magnetite crystals can grow in size upon reaction between oxyhydroxide and microbial biomass after compression and heating to 1 kbar and 150 °C, respectively. The magnetite crystals previously produced by Thermoanaerobacter spp. TOR39 reach sizes in excess of 700 nm after the P-T experiments, while new magnetite grains >400 nm formed from the superparamagnetic magnetite-dominated end product of Shewanella sp. culture. This study indicates that the large magnetite crystals observed in BIF can be derived through a three-stage sequence, beginning with dissimilatory iron reduction of an initial ferric iron-rich sediment coupled to the oxidation of dead phytoplankton biomass, followed by magnetite crystal aging, and ultimately pressure-temperature induced abiotic alteration of the biogenic magnetite during metamorphism.

  7. Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001.

    PubMed

    Barber, David J; Scott, Edward R D

    2002-05-14

    Crystals of magnetite (Fe(3)O(4)) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size approximately equal to 3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals approximately equal to 50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO(2). Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites. PMID:12011420

  8. Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001

    PubMed Central

    Barber, David J.; Scott, Edward R. D.

    2002-01-01

    Crystals of magnetite (Fe3O4) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size ?3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals ?50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO2. Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites. PMID:12011420

  9. Formation of single-domain magnetite by a thermophilic bacterium

    SciTech Connect

    Zhang, C.; Phelps, T.J. [Oak Ridge National Lab., TN (United States). Environmental Sciences Div.; Vali, H. [McGill Univ., Montreal, Quebec (Canada). Electron Microscopy Center; Romanek, C.S. [Univ. of Georgia, Aiken, SC (United States); Liu, S.V. [Allegheny Univ. of the Health Sciences, Philadelphia, PA (United States). Dept. of Microbiology and Immunology

    1998-11-01

    Magnetite is a common product of bacterial iron reduction and may serve as a potential physical indicator of biological activity in geological settings. Here the authors report the formation of single-domain magnetite under laboratory conditions by a thermophilic fermentative bacterial strain TOR-39 that was isolated from the deep subsurface. Time-course analyses were performed at 65 C to study the effect of bacterial activity on solution chemistry and magnetite formation during the growth of TOR-39. Run products were examined by transmission electron microscopy. Magnetite particles formed exclusively outside of bacterial cells and exhibited octahedral shapes having relatively equal length and width (<15% difference). Tiny magnetite particles (<12 nm) nucleated between 10 and 11 h of incubation and increased to average lengths of 55.4 {+-} 26.8 nm after 24 h of incubation. Between 24 h and 22 d of incubation, magnetite particles maintained average lengths of 56.2 {+-} 24.8 nm. Based on size constraints, greater than 85% of the particles observed fell within the magnetic single domain. Little to no magnetite was detected in abiotic controls at 65 or 95 C, or in TOR-39 cultures whose activity was suppressed. Unlike mesophilic iron-reducing bacteria (e.g., GS-15), TOR-39 produced crystals having shapes and sizes similar to some particles produced intracellularly by magnetotactic bacteria. Thus the single-domain magnetite produced by thermophiles such as TOR-39 may represent a heretofore unrecognized biological contribution to natural remanent magnetization in sedimentary basins and other geothermal environments.

  10. Electrically driven phase transition in magnetite nanostructures.

    PubMed

    Lee, Sungbae; Fursina, Alexandra; Mayo, John T; Yavuz, Cafer T; Colvin, Vicki L; Sofin, R G Sumesh; Shvets, Igor V; Natelson, Douglas

    2008-02-01

    Magnetite (Fe3O4), an archetypal transition-metal oxide, has been used for thousands of years, from lodestones in primitive compasses to a candidate material for magnetoelectronic devices. In 1939, Verwey found that bulk magnetite undergoes a transition at TV approximately 120 K from a high-temperature 'bad metal' conducting phase to a low-temperature insulating phase. He suggested that high-temperature conduction is through the fluctuating and correlated valences of the octahedral iron atoms, and that the transition is the onset of charge ordering on cooling. The Verwey transition mechanism and the question of charge ordering remain highly controversial. Here, we show that magnetite nanocrystals and single-crystal thin films exhibit an electrically driven phase transition below the Verwey temperature. The signature of this transition is the onset of sharp conductance switching in high electric fields, hysteretic in voltage. We demonstrate that this transition is not due to local heating, but instead is due to the breakdown of the correlated insulating state when driven out of equilibrium by electrical bias. We anticipate that further studies of this newly observed transition and its low-temperature conducting phase will shed light on how charge ordering and vibrational degrees of freedom determine the ground state of this important compound. PMID:18084295

  11. Magnetic response of microbially synthesized transition metal- and lanthanide-substituted nano-sized magnetites

    NASA Astrophysics Data System (ADS)

    Moon, Ji-Won; Yeary, Lucas W.; Rondinone, Adam J.; Rawn, Claudia J.; Kirkham, Melanie J.; Roh, Yul; Love, Lonnie J.; Phelps, Tommy J.

    2007-06-01

    The magnetic susceptibility ( ?RT) and saturation magnetization ( MS) of microbially synthesized magnetites were systematically examined. Transition metal (Cr, Mn, Co, Ni and Zn)- and lanthanide (Nd, Gd, Tb, Ho and Er)-substituted magnetites were microbially synthesized by the incubation of transition metal (TM)- and lanthanide (L)-mixed magnetite precursors with either thermophilic (TOR-39) or psychrotolerant (PV-4) metal-reducing bacteria (MRB). Zinc incorporated congruently into both the precursor and substituted magnetite, while Ni and Er predominantly did not. Microbially synthesized Mn- and Zn-substituted magnetites had higher ?RT than pure biomagnetite depending on bacterial species and they exhibited a maximum ?RT at 0.2 cationic mole fraction (CMF). Other TMs' substitution linearly decreased the ?RT with increasing substitution amount. Based on the MS values of TM- and L-substituted magnetite at 0.1 and 0.02 CMF, respectively, Zn (90.7 emu/g for TOR-39 and 93.2 emu/g for PV-4)- and Mn (88.3 emu/g by PV-4)-substituted magnetite exhibited higher MS than standard chemical magnetite (84.7 emu/g) or pure biomagnetite without metal substitution (76.6 emu/g for TOR-39 and 80.3 emu/g for PV-4). Lanthanides tended to decrease MS, with Gd- and Ho-substituted magnetites having the highest magnetization. The higher magnetization of microbially synthesized TM-substituted magnetites by the psychrotroph, PV-4 may be explained by the magnetite formation taking place at low temperatures slowing mechanics, which may alter the magnetic properties compared to the thermophile, through suppression of the random distribution of substituted cations.

  12. Evidence for exclusively inorganic formation of magnetite in Martian meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Morris, R. V.; Brearley, A. J.; Lauer, H. V., Jr.; Treiman, A. H.; Zolensky, M. E.; Schwandt, C. S.; Lofgren, G. E.

    2004-01-01

    Magnetite crystals produced by terrestrial magnetotactic bacterium MV-1 are elongated on a [111] crystallographic axis, in a so-called truncated hexa-Octahedral shape. This morphology has been proposed to constitute a biomarker (i.e., formed only in biogenic processes). A subpopulation of magnetite crystals associated with carbonate globules in Martian meteorite ALH84001 is reported to have this morphology, and the observation has been taken as evidence for biological activity on Mars. In this study, we present evidence for the exclusively inorganic origin of [111]-elongated magnetite crystals in ALH84001. We report three-dimensional(3-D) morphologies for approx.1000 magnetite crystals extracted from: (1) thermal decomposition products of Fe-rich carbonate produced by inorganic hydrothermal precipitation in laboratory experiments; (2) carbonate globules in Martian meteoriteeALH84001; and (3) cells of magnetotactic bacterial strain MV-1. The 3-D morphologies were derived by fitting 3-D shape models to two-dimensional bright-field transmission-electron microscope (TEAM) images obtained at a series of viewing angles. The view down the {110} axes closest to the [111] elongation axis of magnetite crystals ([111]x{110) not equal to 0) provides a 2-D projection that uniquely discriminates among the three [111]-elongated magnetite morphologies found in these samples: [111]-elongated truncated hexaoctahedron ([111]-THO), [111]-elongated cubo-octahedron ([111]-ECO), and [111]-elongated simple octahedron ([111]-ESO). All [111] -elongated morphologies are present in the three types of sample, but in different proportions. In the ALH84001 Martian meteorite and in our inorganic laboratory products, the most common [111]-elongated magnetite crystal morphology is [111]-ECO. In contrast, the most common morphology for magnetotactic bacterial strain MV-1 is [111]-THO. These results show that: (1) the morphology of [111]-elongated magnetite crystals associated with the carbonate globules in Martian meteorite ALH84001 is replicated by an inorganic process; and (2) the most common crystal morphology for biogenic (MV-1) magnetite is distinctly different from that in both ALH84001 and our inorganic laboratory products. Therefore, [111]-elongated magnetite crystals in ALH84001 do not constitute, as previously claimed, a robust biosignature and, in fact, an exclusively inorganic origin for the magnetite is fully consistent with our results. Furthermore, the inorganic synthesis method, i.e., the thermal decomposition of hydrothermally precipitated Fe-rich carbonate, is a process analogue for formation of the magnetite on Mars. Namely, precipitation of carbonate globules from carbonate-rich hydrothermal solutions followed at some later time by a thermal pulse, perhaps in association with meteoritic impact or volcanic processes on the Martian surface.

  13. Controlled biomineralization of magnetite (Fe3O4) by Magnetospirillum gryphiswaldense

    E-print Network

    Benning, Liane G.

    true biominerals, magnetotactic bacteria (or MTB) are considered to be model species for studying the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high, chemical and micro- structural characteristics of biogenic magnetite crystals produced by the magnetotactic

  14. Oxygen Isotopes in Semarkona Magnetite

    Microsoft Academic Search

    J. M. Saxton; I. C. Lyon; G. Turner; R. Hutchison

    1995-01-01

    Magnetite is a phase that may form by aqueous alteration and may therefore offer insights into processes of aqueous alteration in the early solar system. Rowe et al [1] have used oxygen isotopes of magnetite and other phases to constrain conditions of aqueous alteration of the CM and CI chondrites. Semarkona is one of the few ordinary chondrites known to

  15. Magnetite morphology and life on Mars Peter R. Buseck*

    E-print Network

    Dunin-Borkowski, Rafal E.

    are ``indistinguishable'' from those produced by a particular strain of terrestrial magnetotactic bacteria. Both are indeed magnetite crystals. Moreover, magnetotactic bacteria are ubiquitous on Earth, and yet intact within frac- tures in which it is most unlikely that aquatic magnetotactic bacteria ever lived

  16. Magnetite-bubble aggregates at mixing interfaces in andesite magma bodies

    E-print Network

    Edmonds, M.; Brett, A.; Herd, R. A.; Humphreys, M. C. S.; Woods, A.

    2014-08-14

    to a bubble by surface forces (Gualda and Ghioso, 2007). 80 81 An association between magnetites and a bubble has been recognised previously: a pre-eruptive 82 aggregate of multiple magnetite crystals and a single bubble was observed in a pumice sample... the same hand specimen. Pumice samples were not used in this study as the exceedingly high 144 vesicularity meant that crystals were too sparse and bubbles not separated sufficiently for 145 meaningful statistical analysis. 146 147 Scanning electron...

  17. Zero-dimensional magnetite

    NASA Astrophysics Data System (ADS)

    Arredondo, Melissa Gayle

    Low-dimensional magnetic systems are of interest due to several new effects and modifications that occur at sizes below the average domain grain boundary within the bulk material. Molecule-like magnetite (Fe3O4) nanoparticles, with sizes ranging from one to two nm were synthesized and characterized in order to investigate new properties arising from quantum size effects. These small systems will provide opportunities to investigate magnetism of zero-dimension systems. A zero-dimensional object is usually called a quantum dot or artificial atom because its electronic states are few and sharply separated in energy, resembling those within an atom. Since the surface to volume ratio is the highest for zero-dimensional systems, most of the changes to magnetic behavior will be observed in ultra-fine magnetic particles. Chemically functional magnetic nanoparticles, comprised of a Fe 3O4 magnetite core encased in a thin aliphatic carboxylate, have been prepared by sequential high temperature decomposition of organometallic compounds in a coordinating solvent. In this work, aliphatic carboxylic acid chain length, reaction temperature and duration were varied to produce small core diameters. In order to correlate size effects with changes in particle formation, it is important to have a through understanding of the structural components. This includes studies of the core size, surface effects, decomposition, electronic properties and magnetic behavior. Quantum size effects were observed in the (Fe3O4)X(carboxylate)Y monolayer protected clusters (MPCs) when the average core diameter was ?2.0 nm, evidenced by a blue shifted absorbance band maxima, suggesting the onset of quantum confinement. These (Fe3O4)X(carboxylate) Y MPCs also posses a complex interplay between surface and finite size effects, which govern the magnetic properties of these zero-dimensional systems. These MPCs are all superparamagnetic above their blocking temperatures with total magnetic anisotropy values greater than the bulk value due to an increase in surface and magnetocrystalline anisotropy. A non-linear decrease in saturation magnetization (MS) (muB per cluster) as a function of the reciprocal of core radius have been attributed to surface effects such as a magnetically inactive layer or an increase in spin disorder as core diameter decreases. The reduced core dimensions of these MPCs make them ideal candidates for further investigation of quantum magnetic systems. Chapter 1 provides a brief introduction to magnetic properties on the quantum scale and methods to examine those properties. Chapter 2 is an introduction to nanostructured magnetic systems including metals and oxides. Specific instrumentation and methodologies needed to provide insight about nanoparticles are discussed. Chapter 3 is an investigation of zero-dimensional magnetite monolayer protected clusters. The aim of this research is the preparation, isolation, and characterization of sub-colloidal (diameter ?2.0 nm) magnetite (Fe3O4) nanocrystals. The synthetic procedures within are the first reports of 1.0--2.0 nm (Fe 3O4)x(carboxylate)y materials, approaching the scale of single-molecule magnets. Appendix A includes some of the common units and formulas used in magnetism while Appendix B summarizes the Langevin model of paramagnetism and how it relates to quantum effects, and Appendix C presents a table of values pertaining to photon energies in various units.

  18. A Comparison between Chemical Synthesis Magnetite Nanoparticles and Biosynthesis Magnetite.

    PubMed

    Kahani, Seyed Abolghasem; Yagini, Zahra

    2014-01-01

    The preparation of Fe3O4 from ferrous salt by air in alkaline aqueous solution at various temperatures was proposed. The synthetic magnetites have different particle size distributions. We studied the properties of the magnetite prepared by chemical methods compared with magnetotactic bacterial nanoparticles. The results show that crystallite size, morphology, and particle size distribution of chemically prepared magnetite at 293?K are similar to biosynthesis of magnetite. The new preparation of Fe3O4 helps to explain the mechanism of formation of magnetosomes in magnetotactic bacteria. The products are characterized by X-ray powder diffraction (XRD), infrared (IR) spectra, vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM). PMID:24982609

  19. A Comparison between Chemical Synthesis Magnetite Nanoparticles and Biosynthesis Magnetite

    PubMed Central

    Kahani, Seyed Abolghasem; Yagini, Zahra

    2014-01-01

    The preparation of Fe3O4 from ferrous salt by air in alkaline aqueous solution at various temperatures was proposed. The synthetic magnetites have different particle size distributions. We studied the properties of the magnetite prepared by chemical methods compared with magnetotactic bacterial nanoparticles. The results show that crystallite size, morphology, and particle size distribution of chemically prepared magnetite at 293?K are similar to biosynthesis of magnetite. The new preparation of Fe3O4 helps to explain the mechanism of formation of magnetosomes in magnetotactic bacteria. The products are characterized by X-ray powder diffraction (XRD), infrared (IR) spectra, vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM). PMID:24982609

  20. Synthesis of stabilized myrrh-capped hydrocolloidal magnetite nanoparticles.

    PubMed

    Atta, Ayman M; Al-Lohedan, Hamad A; Al-Hussain, Sami A

    2014-01-01

    Herein we report a new method for synthesizing stabilized magnetic nanoparticle (MNP) colloids. A new class of monodisperse water-soluble magnetite nano-particles was prepared by a simple and inexpensive co-precipitation method. Iron ions and iodine were prepared by the reaction between ferric chloride and potassium iodide. The ferrous and ferric ions were hydrolyzed at low temperature at pH 9 in the presence of iodine to produce iron oxide nanoparticles. The natural product myrrh gum was used as capping agent to produce highly dispersed coated magnetite nanoparticles. The structure and morphology of the magnetic nanogel was characterized by Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM), and X-ray diffraction (XRD) was used to examine the crystal structure of the produced magnetite nanoparticles. PMID:25090117

  1. JOURNAL DE PHYSIQUE Colloque C 3, supplkment au no 7-8, Tome 27, juilbet-aodt 1966, page C 3-193 THE PLASTICITY OF PURE NIOBIUM SINGLE CRYSTALS

    E-print Network

    Paris-Sud XI, Université de

    -193 THE PLASTICITY OF PURE NIOBIUM SINGLE CRYSTALS M. S. DUESBERY,R. A. FOXALLand P. B. HIRSCH Cavendish Laboratory, University of Cambridge. R6sumb. - On ktudie la dkformation de monocristaux de niobium purifiks par recuit of single crystals of niobium purified by annealing in ultra-high vacua is studied. The stress-strain curves

  2. Correlation between magnetic spin structure and the three-dimensional geometry in chemically synthesized nanoscale magnetite rings

    E-print Network

    Dunin-Borkowski, Rafal E.

    synthesized nanoscale magnetite rings M. Eltschka,1,a M. Kläui,1,b U. Rüdiger,1 T. Kasama,2 L. Cervera% spin polarization at the Fermi level. An example is magnetite Fe3O4 , which has been extensively The magnetic properties of thin films of vari- ous thicknesses and bulk single crystal Fe3O4 have been in

  3. Incorporation and retention of 99-Tc(IV) in magnetite under high pH conditions.

    PubMed

    Marshall, Timothy A; Morris, Katherine; Law, Gareth T W; Mosselmans, J Frederick W; Bots, Pieter; Parry, Stephen A; Shaw, Samuel

    2014-10-21

    Technetium incorporation into magnetite and its behavior during subsequent oxidation has been investigated at high pH to determine the technetium retention mechanism(s) on formation and oxidative perturbation of magnetite in systems relevant to radioactive waste disposal. Ferrihydrite was exposed to Tc(VII)(aq) containing cement leachates (pH 10.5-13.1), and crystallization of magnetite was induced via addition of Fe(II)aq. A combination of X-ray diffraction (XRD), chemical extraction, and X-ray absorption spectroscopy (XAS) techniques provided direct evidence that Tc(VII) was reduced and incorporated into the magnetite structure. Subsequent air oxidation of the magnetite particles for up to 152 days resulted in only limited remobilization of the incorporated Tc(IV). Analysis of both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) data indicated that the Tc(IV) was predominantly incorporated into the magnetite octahedral site in all systems studied. On reoxidation in air, the incorporated Tc(IV) was recalcitrant to oxidative dissolution with less than 40% remobilization to solution despite significant oxidation of the magnetite to maghemite/goethite: All solid associated Tc remained as Tc(IV). The results of this study provide the first direct evidence for significant Tc(IV) incorporation into the magnetite structure and confirm that magnetite incorporated Tc(IV) is recalcitrant to oxidative dissolution. Immobilization of Tc(VII) by reduction and incorporation into magnetite at high pH and with significant stability upon reoxidation has clear and important implications for limiting technetium migration under conditions where magnetite is formed including in geological disposal of radioactive wastes. PMID:25236360

  4. Sonoelectrochemical synthesis of magnetite

    NASA Astrophysics Data System (ADS)

    Cabrera, L.; Gutiérrez, S.; Herrasti, P.; Reyman, D.

    2010-01-01

    The effects of ultrasound (US) on the direct electrosynthesis of magnetite (Fe3O4) nanoparticles are investigated. The electrochemical system consists of two electrodes; anode and cathode, both of iron, and 99.5% purity. The anode is a sacrificial electrode, which when oxidized generates the desired Fe3O4. Cationic surfactants are used in the synthetic system as supporting electrolytes and as a protective layer which covers the obtained nanoparticles in order to avoid aggregation. In order to study the influence of ultrasound in the synthesis of Fe3O4, the experiments were compared to the same systems without the application of ultrasound. Physical properties of the reaction product, such as morphology and particle size, were characterized by means of X-ray diffraction, and transmission electron microscopy. Size distribution studies in function of the application and variation of the US parameters are shown. The effect of US on the magnetic properties of Fe3O4 was studied by means of hysteresis loops. The experimental results were compared to those obtained during the synthesis of Fe3O4 without the US presence.

  5. Reflectance anisotropy spectroscopy of magnetite (110) surfaces

    NASA Astrophysics Data System (ADS)

    Fleischer, K.; Verre, R.; Mauit, O.; Sofin, R. G. S.; Farrell, L.; Byrne, C.; Smith, C. M.; McGilp, J. F.; Shvets, I. V.

    2014-05-01

    Reflectance anisotropy spectroscopy (RAS) has been used to measure the optical anisotropies of bulk and thin-film Fe3O4(110) surfaces. The spectra indicate that small shifts in energy of the optical transitions, associated with anisotropic strain or electric field gradients caused by the (110) surface termination or a native oxide layer, are responsible for the strong signal observed. The RAS response was then measured as a function of temperature. A distinct change in the RAS line-shape amplitude was observed in the spectral range from 0.8 to 1.6 eV for temperatures below the Verwey transition of the crystal. Finally, thin-film magnetite was grown by molecular beam epitaxy on MgO(110) substrates. Changes in the RAS spectra were found for different film thickness, suggesting that RAS can be used to monitor the growth of magnetite (110) films in situ. The thickness dependence of the RAS is discussed in terms of various models for the origin of the RAS signal.

  6. Thickness dependence of the resistivity tensor in epitaxial magnetite thin films

    NASA Astrophysics Data System (ADS)

    Naftalis, N.; Shperber, Y.; Moyer, J. A.; Ahn, C. H.; Klein, L.

    2013-07-01

    We report a systematic study of the thickness dependence of the resistivity tensor of epitaxial thin films of magnetite (Fe3O4). We find that decreasing film thickness decreases the relative magnitude of the terms related to crystal symmetry but increases their field dependence. We attribute this behavior to the presence of antiphase boundaries in thin films of magnetite and the dependence of their density on the film thickness.

  7. Site-specific magnetization reversal studies of magnetite

    SciTech Connect

    Cady, A.; Haskel, D.; Lang, J. C.; Islam, Z.; Srajer, G. [Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Ankudinov, A. [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Subias, G.; Garcia, J. [Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, Pza. San Francisco s/n 50009 Zaragoza (Spain)

    2006-04-01

    The mechanism of magnetization reversal in magnetite (Fe{sub 3}O{sub 4}) single crystals was studied using site-specific magnetic sensitive diffraction anomalous near-edge structure. By exploiting the angular dependence of the cross section, we are able to show that the mechanism of reversal involves a mixture of coherent rotation and domain formation. The results reveal additional details to that provided by XMCD measurements, which average over nonequivalent sites.

  8. Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

    SciTech Connect

    Kaur, Maninder; Jiang, Weilin; Qiang, You; Burks, Edward; Liu, Kai; Namavar, Fereydoon; Mccloy, John S.

    2014-11-03

    Iron oxide films were deposited onto Si substrates using ion-beam-assisted deposition. The films were ~300 nm thick polycrystalline magnetite with an average crystallite size of ~6 nm. Additionally, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite. However, Raman spectroscopy and x-ray diffraction both indicate that the films are single-phase magnetite. Since no direct evidence of a second phase could be found, exchange bias likely arises due to defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples have such small grains, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field. The high energy deposition process results in an oxygen-rich, argon-containing magnetite film with low temperature exchange bias due to defects at the high concentration of grain boundaries.

  9. Structural insight into magnetochrome-mediated magnetite biomineralization

    NASA Astrophysics Data System (ADS)

    Siponen, Marina I.; Legrand, Pierre; Widdrat, Marc; Jones, Stephanie R.; Zhang, Wei-Jia; Chang, Michelle C. Y.; Faivre, Damien; Arnoux, Pascal; Pignol, David

    2013-10-01

    Magnetotactic bacteria align along the Earth's magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(II) and iron(III) is clear, little is known about the biological mechanisms controlling their ratio. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(II) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(III) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization.

  10. Structural insight into magnetochrome-mediated magnetite biomineralization.

    PubMed

    Siponen, Marina I; Legrand, Pierre; Widdrat, Marc; Jones, Stephanie R; Zhang, Wei-Jia; Chang, Michelle C Y; Faivre, Damien; Arnoux, Pascal; Pignol, David

    2013-10-31

    Magnetotactic bacteria align along the Earth's magnetic field using an organelle called the magnetosome, a biomineralized magnetite (Fe(II)Fe(III)2O4) or greigite (Fe(II)Fe(III)2S4) crystal embedded in a lipid vesicle. Although the need for both iron(II) and iron(III) is clear, little is known about the biological mechanisms controlling their ratio. Here we present the structure of the magnetosome-associated protein MamP and find that it is built on a unique arrangement of a self-plugged PDZ domain fused to two magnetochrome domains, defining a new class of c-type cytochrome exclusively found in magnetotactic bacteria. Mutational analysis, enzyme kinetics, co-crystallization with iron(II) and an in vitro MamP-assisted magnetite production assay establish MamP as an iron oxidase that contributes to the formation of iron(III) ferrihydrite eventually required for magnetite crystal growth in vivo. These results demonstrate the molecular mechanisms of iron management taking place inside the magnetosome and highlight the role of magnetochrome in iron biomineralization. PMID:24097349

  11. Some Properties of Magnetite Nanoparticles Produced Under Different Conditions

    NASA Astrophysics Data System (ADS)

    Khan, Umar Saeed; Khattak, Nazir Shah; Manan, Abdul; Rahman, Aminur; Khan, Faridullah; Rahim, Abdur

    2015-01-01

    Temperature, stirring rate, stirring time, reaction pH, and concentration of precursors during synthesis were found to be crucial in determining the size of the magnetite nanoparticles (NPs) obtained. The relationship between synthetic conditions and the crystal structure, particle size, and size distribution of the NPs was studied. Surface coating of iron oxide NPs was performed in two steps. Magnetite NPs were prepared by coprecipitation then coated with silica by use of a sol-gel process. Saturation magnetization of the magnetite NPs increased from 47.23 to 49.12 emu/g when their size was increased from 8.89 to 9.39 nm. Magnetite NPs in the size range 11-12 nm, coated with silica, are monodispersed and their corresponding saturation magnetization is 40.67 emu/g (11 nm) and 34.65 emu/g (12 nm). The decrease in the saturation magnetization of the coated samples is attributed to the increase in the amount of tetraethyl orthosilicate.

  12. Coherent optical phonons in pure and Pr3+ doped YAG crystal studied by Optical Kerr Effect spectroscopy: Temperature and concentration dependence

    NASA Astrophysics Data System (ADS)

    Polok, K.; Ratajska-Gadomska, B.; Konarska, J.; Gadomski, W.

    2014-10-01

    Herewith we present the results of the investigation of coherent phonons in pure and Pr3+ doped YAG crystals, by means of the femtosecond Optical Kerr Effect spectroscopy. In the experiment we have followed the dynamics of the Raman-active phonon modes at different temperatures in range between 263 K and 373 K and for different dopant concentrations. We found that the temperature dependence of phonon frequencies and lifetimes is linear, which is characteristic for 3-phonon relaxation process. We have used our fit results to calculate the widths of homogeneously broadened Raman lines and to find the anharmonic coupling constants. The observed dependence of phonon frequency and lifetime on dopant concentration is interpreted in terms of small, dopant induced alterations in the crystal structure, where the most influenced modes involve motion of the substituted ion. High precision of the OKE experiment is of great value, as such changes are small and thus hard to measure, when only low doping is possible, which is the case for Pr:YAG.

  13. Pure- and mixed-crystal optical studies of the Jahn-Teller effect for the d/sup 6/ hexafluoroplatinate (IV) ion

    SciTech Connect

    Laurent, M.P.; Patterson, H.H.; Pike, H.; Engstrom, H.

    1981-02-01

    Measurements have been made of the low-temperature luminescence and Raman spectra of pure Cs/sub 2/PtF/sub 6/ crystals and Cs/sub 2/PtF/sub 6/-Cs/sub 2/GeF/sub 6/ crystals in which PtF/sub 6//sup 2 -/ is doped into the Cs/sub 2/SiF/sub 6/ lattice. In both environments, the Raman spectra at liquid-helium temperature show sharp lines assigned to the a/sub 1g/, e/sub g/, and t/sub 2g/ internal modes of the PtF/sub 6//sup 2 -/ ion. A comparison of the low-temperature Raman and sharp-line luminescence spectra indicates that in the luminescence spectra a Jahn-Teller e/sub g/-type progression occurs with a small degree of anharmonicity present. The luminescence can be assigned as a transition from the t/sub 2//sup 5/e/sub g/GAMMA/sub 3/(/sup 3/T/sub 1g/) twofold degenerate excited electronic state to the t/sub 2g//sup 6/GAMMA/sub 1/(/sup 1/A/sub 1g/) nondegenerate ground electronic state.

  14. Raman study of the Verwey transition in magnetite thin films

    NASA Astrophysics Data System (ADS)

    Baghaie Yazdi, M.; Choi, K.-Y.; Wulferding, D.; Lemmens, P.; Alff, L.

    2013-10-01

    We have grown epitaxial thin films of magnetite on MgO and Al2O3 substrates with sharp and distinct signatures of the Verwey transition in resistivity and magnetization. We have used Raman scattering to separate the footprint of purely structural changes from the effect of additional charge and orbital order. Raman modes related to the structural phase transition occur first at temperatures above the Verwey transition temperature. In contrast, newly emerging modes indicating additional charge and orbital order appear at the Verwey transition. These results suggest that the completion of the structural phase transition in magnetite is a necessary precursor triggering a transition into a complex charge and orbitally ordered state.

  15. Magnetite-Based Magnetoreceptor Cells in the Olfactory Organ of Rainbow Trout and Zebrafish

    NASA Astrophysics Data System (ADS)

    Kirschvink, J. L.; Cadiou, H.; Dixson, A. D.; Eder, S.; Kobayashi, A.; McNaughton, P. A.; Muhamad, A. N.; Raub, T. D.; Walker, M. M.; Winklhofer, M.; Yuen, B. B.

    2011-12-01

    Many vertebrate and invertebrate animals have a geomagnetic sensory system, but the biophysics and anatomy of how magnetic stimuli are transduced to the nervous system is a challenging problem. Previous work in our laboratories identified single-domain magnetite chains in olfactory epithelium in cells proximal to the ros V nerve, which, in rainbow trout, responds to magnetic fields. Our objectives are to characterize these magnetite-containing cells and determine whether they form part of the mechanism of magnetic field transduction in teleost fishes, as a model for other Vertebrates. Using a combination of reflection mode confocal microscopy and a Prussian Blue technique modified to stain specifically for magnetite, our Auckland group estimated that both juvenile rainbow trout (ca. 7 cm total length) olfactory rosettes have ~200 magnetite-containing cells. The magnetite present in two types of cells within the olfactory epithelium appears to be arranged in intracellular chains. All of our groups (Munich, Auckland, Cambridge and Caltech) have obtained different types of structural evidence that magnetite chains closely associate with the plasma membrane in the cells, even in disaggregated tissues. In addition, our Cambridge group used Ca2+ imaging to demonstrate a clear response by individual magnetite-containing cells to a step change in the intensity of the external magnetic field and a slow change in Ca2+ activity when the external magnetic field was cancelled. In the teleost, zebrafish (Danio rerio), a small (~4 cm adult length in captivity) genetic and developmental biology model organism, our Caltech group detected ferromagnetic material throughout the body, but concentrated in the rostral trunk, using NRM and IRM scans of whole adults. Our analysis suggests greater than one million, 80-100 nm crystals, with Lowrie-Fuller curves strongly consistent with single-domain magnetite in 100-100,000 magnetocytes. Ferromagentic resonance (FMR) spectra show crystals with narrow particle size distribution concentrated in the trunk, similar to biogenic magnetofossils. In SQUID microscopy images numerous dipole spots are widely distributed throughout the flank, not correlated with skin pigments or the spinal cord and neural arches. We interpret this to indicate a lateral line location for trunk magnetite in zebrafish. In contrast to trout in which rock magnetic experiments and TEM suggest highly interacting bundled ropes of crystals, similar to those in the large magnetotactic bacterium, M. bavaricum, zebrafish magnetic aggregates apparently arrange in clumps or mixed chains and clumps. We report trout olfactory epithelium containing magnetite magnetoreceptors that transduce the external magnetic field, then encode and transmit it to the brain, while zebrafish contain magnetite in the lateral line region.

  16. Biophysics of Magnetic Orientation: Radical Pairs, Biogenic Magnetite, or both?

    NASA Astrophysics Data System (ADS)

    Kirschvink, Joe

    2011-03-01

    Two major biophysical mechanisms for magnetoreception in terrestrial animals, one based on biogenic magnetite and another on radical-pair biochemical reactions, have been the subject of experiment and debate for the past 30 years. The magnetite hypothesis has stood the test of time: biogenic magnetite is synthesized biochemically in Bacteria, Protists, and numerous Animal phyla, as well as in some plants. Chains of single-domain crystals have been detected by clean-lab based SQUID magnetometry in animal tissues in all major phyla, followed by high-resolution TEM in selected model organisms, as well as by electrophysiological studies demonstrating the role of the ophthalmic branch of the trigeminal nerve in the magnetoreceptive process. Pulse-remagnetization - configured to uniquely flip the polarity of single-domain ferromagnets - has dramatic effects on the behavior of many birds, honeybees, mole rats, turtles, and bats, to cite a growing list. Magnetite-containing cells in the vicinity of these neurons in fish are now the subject of intense study by our consortium. The existence of a specialized class of magnetite-containing magnetoreceptor cells in animal tissues is no longer controversial. In contrast, less success has been achieved in gaining experimental support across a range of taxa for the radical-pair hypothesis. Although this mechanism was proposed to explain an early observation that birds would not respond to complete inversion of the magnetic vector, many organisms (even some birds) do indeed respond to the field polarity. We also note that few, if any, of these critical experiments have been done using fully double-blind methods. This is joint work with: M. M. Walker (University of Auckland, New Zealand) and M. Winklhofer (LMU Munich, Germany).

  17. Dissolution and reduction of magnetite by bacteria

    NASA Technical Reports Server (NTRS)

    Kostka, J. E.; Nealson, K. H.

    1995-01-01

    Magnetite (Fe3O4) is an iron oxide of mixed oxidation state [Fe(II), Fe(III)] that contributes largely to geomagnetism and plays a significant role in diagenesis in marine and freshwater sediments. Magnetic data are the primary evidence for ocean floor spreading and accurate interpretation of the sedimentary magnetic record depends on an understanding of the conditions under which magnetite is stable. Though chemical reduction of magnetite by dissolved sulfide is well known, biological reduction has not been considered likely based upon thermodynamic considerations. This study shows that marine and freshwater strains of the bacterium Shewanella putrefaciens are capable of the rapid dissolution and reduction of magnetite, converting millimolar amounts to soluble Fe(II)in a few days at room temperature. Conditions under which magnetite reduction is optimal (pH 5-6, 22-37 degrees C) are consistent with an enzymatic process and not with simple chemical reduction. Magnetite reduction requires viable cells and cell contact, and it appears to be coupled to electron transport and growth. In a minimal medium with formate or lactate as the electron donor, more than 10 times the amount of magnetite was reduced over no carbon controls. These data suggest that magnetite reduction is coupled to carbon metabolism in S. putrefaciens. Bacterial reduction rates of magnetite are of the same order of magnitude as those estimated for reduction by sulfide. If such remobilization of magnetite occurs in nature, it could have a major impact on sediment magnetism and diagenesis.

  18. Thermoremanent Magnetization in Submicroscopic Magnetite

    Microsoft Academic Search

    D. J. Dunlop

    1973-01-01

    titano- magnetite particles in igneous rocks. Although hysteresis properties indicate that the magne- tites are above single-domain (SD) size, their weak-field TRM are SD-like. TRM intensity, for a 1-oe inducing field, ranges from 6 to 12 emu\\/cm 8. Median alternating demagnetization fields are between 275 and 400 oe, while blocking temperatures are generally within 50øC of the Curie point. However,

  19. The origin and stability of lunar goethite, hematite and magnetite.

    NASA Technical Reports Server (NTRS)

    Williams, R. J.; Gibson, E. K.

    1972-01-01

    Extra-lunar contamination, fumarolic activity, and exposure to oxidizing gases from comet or carbonaceous meteorite impacts have been previously proposed as the causes of magnetite, hematite, and goethite in lunar materials. However, these minerals can occur in the stable low-temperature gas-solid equilibrium assemblages of lunar rocks. Below 600 C magnetite is in equilibrium with C-O-H gases with compositions compatible with high-temperature equilibrium with metallic iron; below 150 C hematite is stable in these same gases. Goethite is not stable in carbonaceous gases at low total pressure, and thus gases from impacting carbonaceous material cannot have produced it. Goethite is stable at low temperatures and pressures in almost pure H2-H2O gases. Its minimum stability against hematite is 2 bars total pressure at 130 C and 0.001 bars at 30 C for H2 to H2O ratios compatible with the high-temperature redox state of lunar materials. Thus the traces of magnetite, hematite, and goethite in lunar materials may be the result of normal low-temperature processes indigenous to the moon and not special processes.

  20. Biogenic Magnetite in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, K. L.; Bazylinski, Dennis; Wentworth, Susan J.; McKay, David S.; Kirschvink, Joseph L.; Clemett, SImon J.; Bell, Mary Sue; Golden, D. C.; Gibson, Everett K., Jr.

    1999-01-01

    Fine-grained magnetite (Fe3O4) in martian meteorite ALH84001, generally less than 200 nm in size, is located primarily in the rims that surround the carbonate globules. There are two populations of ALH84001 magnetites, which are likely formed at low temperature by inorganic and biogenic processes. Nearly 27% of ALH84001 magnetite particles, also called elongated prisms, have characteristics which make them uniquely identifiable as biological precipitates. Additional information is contained in the original extended abstract.

  1. Magnetite in the radular teeth of chitons

    Microsoft Academic Search

    Manabu Mizota; Yutaka Maeda

    1986-01-01

    To understand the process by which living organisms synthesize magnetite, we measured the Mössbauer spectra on the teeth at\\u000a different maturation stages along the radula of chitons. Our results show that magnetite is progressively mineralized from\\u000a hydrous ferric oxide precursor in the early stage of maturation. As the denticles become fully mineralized, a part of magnetite\\u000a is oxidized to maghemite

  2. From iron(III) precursor to magnetite and vice versa

    SciTech Connect

    Gotic, M., E-mail: gotic@irb.hr [Division of Materials Chemistry, Ruder Boskovic Institute, P.O. Box 180, HR-10002 Zagreb (Croatia); Jurkin, T.; Music, S. [Division of Materials Chemistry, Ruder Boskovic Institute, P.O. Box 180, HR-10002 Zagreb (Croatia)

    2009-10-15

    The syntheses of nanosize magnetite particles by wet-chemical oxidation of Fe{sup 2+} have been extensively investigated. In the present investigation the nanosize magnetite particles were synthesised without using the Fe(II) precursor. This was achieved by {gamma}-irradiation of water-in-oil microemulsion containing only the Fe(III) precursor. The corresponding phase transformations were monitored. Microemulsions (pH {approx} 12.5) were {gamma}-irradiated at a relatively high dose rate of {approx}22 kGy/h. Upon 1 h of {gamma}-irradiation the XRD pattern of the precipitate showed goethite and unidentified low-intensity peaks. Upon 6 h of {gamma}-irradiation, reductive conditions were achieved and substoichiometric magnetite ({approx}Fe{sub 2.71}O{sub 4}) particles with insignificant amount of goethite particles found in the precipitate. Hydrated electrons (e{sub aq}{sup -}), organic radicals and hydrogen gas as radiolytic products were responsible for the reductive dissolution of iron oxide in the microemulsion and the reduction Fe{sup 3+} {yields} Fe{sup 2+}. Upon 18 h of {gamma}-irradiation the precipitate exhibited dual behaviour, it was a more oxidised product than the precipitate obtained after 6 h of {gamma}-irradiation, but it contained magnetite particles in a more reduced form ({approx}Fe{sub 2.93}O{sub 4}). It was presumed that the reduction and oxidation processes existed as concurrent competitive processes in the microemulsion. After 18 h of {gamma}-irradiation the pH of the medium shifted from the alkaline to the acidic range. The high dose rate of {approx}22 kGy/h was directly responsible for this shift to the acidic range. At a slightly acidic pH a further reduction of Fe{sup 3+} {yields} Fe{sup 2+} resulted in the formation of more stoichiometric magnetite particles, whereas the oxidation conditions in the acidic medium permitted the oxidation Fe{sup 2+} {yields} Fe{sup 3+}. The Fe{sup 3+} was much less soluble in the acidic medium and it hydrolysed and recrystallised as goethite. The {gamma}-irradiation of the microemulsion for 25 h at a lower dose rate of 16 kGy/h produced pure substoichiometric nanosize magnetite particles of about 25 nm in size and with the stoichiometry of Fe{sub 2.83}O{sub 4}.

  3. Vortex magnetic structure in framboidal magnetite reveals existence of water droplets in an ancient asteroid.

    PubMed

    Kimura, Yuki; Sato, Takeshi; Nakamura, Norihiro; Nozawa, Jun; Nakamura, Tomoki; Tsukamoto, Katsuo; Yamamoto, Kazuo

    2013-01-01

    The majority of water has vanished from modern meteorites, yet there remain signatures of water on ancient asteroids. How and when water disappeared from the asteroids is important, because the final fluid-concentrated chemical species played critical roles in the early evolution of organics and in the final minerals in meteorites. Here we show evidence of vestigial traces of water based on a nanometre-scale palaeomagnetic method, applying electron holography to the framboids in the Tagish Lake meteorite. The framboids are colloidal crystals composed of three-dimensionally ordered magnetite nanoparticles and therefore are only able to form against the repulsive force induced by the surface charge of the magnetite as a water droplet parches in microgravity. We demonstrate that the magnetites have a flux closure vortex structure, a unique magnetic configuration in nature that permits the formation of colloidal crystals just before exhaustion of water from a local system within a hydrous asteroid. PMID:24149376

  4. Understanding the biological stabilization of ferrihydrite and its transformation to magnetite

    NASA Astrophysics Data System (ADS)

    Gordon, Lyle; Joester, Derk

    2013-03-01

    The biosynthesis of magnetite in the chiton tooth begins with the formation of ferrihydrite, which is transformed into magnetite. This strategy, which employs crystallization of a precursor into the desired polymorph, is generalized across a range of organisms. However, the specific biological factors that control the transformation are not known. Our results employing atom probe tomography of chiton tooth magnetite revealed the presence of acidic proteins binding sodium and magnesium ions associated with chitin nanofibers. Using a model system we are investigating the influence of organic and inorganic additives on the stabilization of ferrihydrite and the transformation to magnetite. I will discuss the influence of a range of organic and inorganic additives on the formation and transformation of ferrihydrite within the gel. We have found that acidic polymers stabilize ferrihydrite and prevent the formation of the crystalline polymorphs. Transformation of the ferrihydrite to magnetite upon addition of ferrous iron is observed as early as 30 minutes. Taken together, the contribution of these factors to magnetite biomineralization in the presence of an organic matrix will help to elucidate biological mechanisms for nucleation, stabilization, and transformation of iron oxides.

  5. Experimental study of magnetic interactions between individual biogenic magnetite nanocrystals

    NASA Astrophysics Data System (ADS)

    Simpson, E. T.; Kasama, T.; Posfai, M.; Faivre, D.; Scheffel, A.; Schuler, D.; Buseck, P. R.; Harrison, R. J.; Dunin-Borkowski, R. E.

    2006-12-01

    We present an electron holographic study of magnetostatic interactions between magnetite nanocrystals from wild-type and mutant magnetotactic bacteria of the Magnetospirillum gryphiswaldense (M. gryph) strain. The results are discussed with reference to their implications for the superparamagnetic limit, magnetic moments of arrays of magnetic nanocrystals, and the threshold of magnetotaxis. The size and spacing of magnetite nanocrystals in M. gryph was carefully adjusted through control of iron provision and growth time. Examination of these cultured cells provided data on the magnetic properties ranging from isolated superparamagnetic crystals to fully assembled magnetosome chains. A magnetic state phase diagram was created showing empirically how the superparamagnetic threshold is influenced by the effect of inter-particle interactions within the chains. This experimental data was compared with analytical models of superparamagnetism which account for size, spacing and crystal shape. Further to this, we also studied two-dimensional arrays of magnetite particles produced by bacteria whose mamJ protein had been removed through genetic modification. In unmodified bacteria this protein is responsible for producing magnetosomes in linear arrangements. The mutant bacteria's non-linear assemblages had much lower magnetic moments per unit volume than bacteria with intact chains, and also displayed more complex magnetic microstructures such as vortex states. These complex magnetic states were metastable, as the states were sensitive to subtle changes in experimental conditions. The magnetic moments of all the samples examined, both wild-type and mutant cells, were compared to that necessary for alignment in the geomagnetic field, showing the threshold at which the crystal sizes, arrangement and numbers led to effective magnetotaxis.

  6. Novel environmentally friendly synthesis of superparamagnetic magnetite nanoparticles using mechanochemical effect

    SciTech Connect

    Iwasaki, Tomohiro, E-mail: iwasaki@chemeng.osakafu-u.ac.jp [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan)] [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan); Kosaka, Kazunori; Watano, Satoru [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan)] [Department of Chemical Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan); Yanagida, Takeshi; Kawai, Tomoji [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)] [Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)

    2010-04-15

    A novel method for synthesizing superparamagnetic magnetite nanoparticles in water system via coprecipitation under an environmentally friendly condition has been developed. In this method, an almost neutral suspension containing ferrous hydroxide and goethite is used as the starting suspension and subjected to a ball-milling treatment. The product was characterized by transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering, superconducting quantum interference device magnetometry, and Moessbauer spectroscopy. The mechanochemical effect generated by the ball-milling treatment promoted the reaction between ferrous hydroxide and goethite even at room temperature, resulting in the formation of homogeneous magnetite nanoparticles. Simultaneously, it also contributed to crystallize the formed magnetite nanoparticles while inhibiting the particle growth. This resulted in the formation of ultrafine magnetite nanoparticles of about 10 nm having a single crystal structure. This method could provide ferromagnetic magnetite nanoparticles with superparamagnetism under the moderate condition without neither heating nor any additives such as surfactant and organic solvent.

  7. Crystal phases, defects, and dynamics of adsorbed hyroxyl groups and water in pure and lanthanide-modified zirconia: A neutron-scattering study

    SciTech Connect

    Loong, C.K; Richardson, J.W. Jr. [Argonne National Laboratory, IL (United States)] [Argonne National Laboratory, IL (United States); Ozawa, Masakuni [Nagoya Inst. of Technology, Gifu (Japan)] [Nagoya Inst. of Technology, Gifu (Japan)

    1995-12-01

    The role of lanthanide doping in zirconia as a means of stabilizing and promoting catalytic reactions was studied by neutron spectroscopy. The crystal structure of high-surface-area Ln{sub 0.1}Zr{sub 0.9}O{sub 1.95}(Ln = La and Nd) powders prepared by a coprecipitation method were found to be composed of mixed phases of tetragonal and cubic symmetry, which can be stabilized over a temperature range (up to {approximately}1000{degrees}C) pertinent to catalytic applications. A real-space correlation function, obtained from a Fourier transform of the filtered residual diffuse scattering, showed evidence of static, oxygen vacancy-induced atomic displacements along the pseudocubic <111> and other directions. The dynamics of hydrogen atoms associated with the surface hydroxyl groups and adsorbed water molecules on Ln{sub 0.1}Zr{sub 0.9}O{sub 1.95} and pure ZrO{sub 2} over a frequency range of 0-4400 cm{sup -1} was investigated by neutron inelastic scattering. The stretch vibrations of surface hydroxyl groups on monoclinic ZrO{sub 2} were found to have slightly higher frequencies than those for Ln{sub 0.1}Zr{sub 0.9}O{sub 1.95}. At a submonolayer coverage of water the O-H stretch bands broaden and shift to lower energies. At higher coverage three bands, corresponding to the O-H stretch, H-O-H bend, and librational motion of water molecules, were observed, indicating the influence of hydrogen bonding. The neutron results were compared with infrared data and ab initio calculations for similar zirconia systems found in the literature. 55 refs., 7 figs., 2 tabs.

  8. e-publishing Biogenic magnetite in the

    E-print Network

    be strongly influenced by the presence of magnetite. Caenorhabditis elegans is a soil nematode of ca. 1 mmFirstCite e-publishing Biogenic magnetite in the nematode Caenorhabditis elegans Charles G.01.04; Accptd 21.04.04; Published online The nematode Caenorhabditis elegans is widely used as a model system

  9. Metal-doped magnetite thin films.

    PubMed

    Abe, Seishi; Ping, De Hai; Nakamura, Shintaro; Ohnuma, Masato; Ohnuma, Shigehiro

    2012-06-01

    This paper investigates magnetite (Fe3O4) thin film containing a small amount of a metal element. The films are prepared by rf sputtering with a composite target of ceramic iron oxide with metal chips. Low-temperature magnetization of magnetite containing 5.3%Ge reveals that the film contains some magnetically weak coupling grains. The metal element Mg reduces both hematite (alpha-Fe2O3) and magnetite, resulting in single-phase wüstite (Fe1-xO). In contrast, adding Ge selectively reduces hematite, while magnetite remains unreactive. According to the free energy of reaction, the element Ge is able to reduce hematite only, whereas the element Mg is capable of reducing both hematite and magnetite. This property is in good agreement with the experiment results. PMID:22905582

  10. Crystals

    NSDL National Science Digital Library

    Lawrence Hall of Science

    2009-01-01

    In this earth science/math/art activity, learners use simple ingredients to grow crystals and examine the repeating geometric shapes and patterns. Learners compare the growth of crystals from four types of crystal-starters (table salt, Borax, sand, and Epsom salt) to see which starter grows the most crystals in 14 days. Learners report their results online and find out what other learners discovered. Afterward, learners can use the crystals they grew to create works of art.

  11. Three-Dimensional Morphological Analysis of ALH84001 Magnetite Using Electron Tomography

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Shimmin, Joel; Morphew, Mary; McIntosh, J. Richard; Bazylinski, Dennis A.; Kirschvink, Joseph L.; Wentworth, Susan J.; McKay, David S.; Vali, Hojatollah

    2003-01-01

    We report here the crystal morphologies of MV-1 and ALH84001 magnetites as calculated by back-projection using electron tomography. In the present study, we used a 300 keV TEM with a field emission gun (Tecnai F-30 from FEI Inc.), equipped with a 2048 x 2048 pixel CCD camera from Gatan Inc. to image magnetite crystals over tilt ranges of approx. +/- 72 deg in 2 deg tilt intervals. The images were aligned for back-projection, either manually, or through the use of fiducial 5 nm Au spheres affixed to the specimen prior to microscopy. Three-dimensional (3-D) reconstructions were computed using weighted back-projection of the tilted views. The tomograms were viewed and analyzed as a series of slices 1.0 nm thick, taken parallel to the specimen-supporting grid, using the IMOD software package. The shape of each magnetite crystal was determined by defining the external contour of a given magnetite in each slice and assembling a stack of these contours in 3-D. To aid in visualization, the stacked contour array was reduced to an optimal mesh by Delaunay triangulation. The surface normal to each of the triangles in the mesh was calculated and the triangle faces colored according to the orientation of that surface normal relative to the principal crystallographic axis of magnetite. Green surfaces correspond to {111} orientations, blue surfaces to {100} orientations, and red surfaces to {110} orientations. Triangles whose surface normal did not correspond to one of the principal axes were colored gray. Within the experimental and numerical uncertainties of the deconvolution, the tomographic reconstruction of both MV-1 and ALH84001 magnetites are equivalent and correspond to a truncated hexa-octahedral morphology.

  12. Magnetite and magnetite/silver core/shell nanoparticles with diluted magnet-like behavior

    SciTech Connect

    Garza-Navarro, Marco [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Torres-Castro, Alejandro, E-mail: alejandro.torrescs@uanl.edu.m [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600 (Mexico); Gonzalez, Virgilio; Ortiz, Ubaldo [Facultad de Ingenieria Mecanica y Electrica, Universidad Autonoma de Nuevo Leon, Av. Universidad s/n, Cd. Universitaria, San Nicolas de los Garza, Nuevo Leon 66450 (Mexico); Centro de Innovacion, Investigacion y Desarrollo en Ingenieria y Tecnologia, Universidad Autonoma de Nuevo Leon, Apodaca, Nuevo Leon 66600 (Mexico); De la Rosa, Elder [Centro de Investigaciones en Optica, A.P. 1-948, Leon Gto. 37160 (Mexico)

    2010-01-15

    In the present work is reported the use of the biopolymer chitosan as template for the preparation of magnetite and magnetite/silver core/shell nanoparticles systems, following a two step procedure of magnetite nanoparticles in situ precipitation and subsequent silver ions reduction. The crystalline and morphological characteristics of both magnetite and magnetite/silver core/shell nanoparticles systems were analyzed by high resolution transmission electron microscopy (HRTEM) and nanobeam diffraction patterns (NBD). The results of these studies corroborate the core/shell morphology and the crystalline structure of the magnetite core and the silver shell. Moreover, magnetization temperature dependent, M(T), measurements show an unusual diluted magnetic behavior attributed to the dilution of the magnetic ordering in the magnetite and magnetite/silver core/shell nanoparticles systems. - Graphical abstract: Biopolymer chitosan was used as stabilization media to synthesize both magnetite and magnetite/silver core/shell nanoparticles. Results of HRTEM and NBD patterns confirm core/shell morphology of the obtained nanoparticles. It was found that the composites show diluted magnet-like behavior.

  13. Rock magnetism of tiny exsolved magnetite in plagioclase from a Paleoarchean granitoid in the Pilbara craton

    NASA Astrophysics Data System (ADS)

    Usui, Yoichi; Shibuya, Takazo; Sawaki, Yusuke; Komiya, Tsuyoshi

    2015-01-01

    are widespread in Precambrian terranes as well as the Phanerozoic orogenic belts, but they have garnered little attention in paleomagnetic studies, because granitoids often contain abundant coarse-grained, magnetically unstable oxides. In this study, the first example of tiny, needle-shaped, exsolved oxides in plagioclase in a Paleoarchean granitoid is reported. The magnetic properties of single plagioclase crystals with the exsolved oxide inclusions have been studied to determine their paleomagnetic recording fidelity. Demagnetization experiments and hysteresis parameters indicate that the oxide inclusions are near stoichiometric magnetite and magnetically very stable. First-order reversal curve (FORC) diagrams reveal negligible magnetostatic interactions. Minimal interactions are also reflected by very efficient acquisition of anhysteretic remanent magnetization. Single plagioclase crystals exhibit strong magnetic remanence anisotropies, which require corrections to their paleodirectional and paleointensity data. Nonetheless, quantitative consideration of anisotropy tensors of the single plagioclase crystals indicates that the bias can be mitigated by properly averaging data from a few tens of single crystals. From the nonlinear thermoremanence acquisition of the plagioclase crystals, we estimate that the plagioclase crystals can reconstruct paleointensity up to 50 ?T. Local metamorphic condition suggests that those magnetite may carry remanence of ˜3.2 to 3.3 Ga. We suggest that exsolved magnetite in granitoids is potentially a suitable target for the study of the early history of the geomagnetic field, and prompt detailed microscopic investigations as well as paleomagnetic tests to constrain the age of remanence.

  14. Novel magnetite-producing magnetotactic bacteria belonging to the Gammaproteobacteria

    PubMed Central

    Lefèvre, Christopher T; Viloria, Nathan; Schmidt, Marian L; Pósfai, Mihály; Frankel, Richard B; Bazylinski, Dennis A

    2012-01-01

    Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin–Benson–Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments. PMID:21776027

  15. Novel magnetite-producing magnetotactic bacteria belonging to the Gammaproteobacteria.

    PubMed

    Lefèvre, Christopher T; Viloria, Nathan; Schmidt, Marian L; Pósfai, Mihály; Frankel, Richard B; Bazylinski, Dennis A

    2012-02-01

    Two novel magnetotactic bacteria (MTB) were isolated from sediment and water collected from the Badwater Basin, Death Valley National Park and southeastern shore of the Salton Sea, respectively, and were designated as strains BW-2 and SS-5, respectively. Both organisms are rod-shaped, biomineralize magnetite, and are motile by means of flagella. The strains grow chemolithoautotrophically oxidizing thiosulfate and sulfide microaerobically as electron donors, with thiosulfate oxidized stoichiometrically to sulfate. They appear to utilize the Calvin-Benson-Bassham cycle for autotrophy based on ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) activity and the presence of partial sequences of RubisCO genes. Strains BW-2 and SS-5 biomineralize chains of octahedral magnetite crystals, although the crystals of SS-5 are elongated. Based on 16S rRNA gene sequences, both strains are phylogenetically affiliated with the Gammaproteobacteria class. Strain SS-5 belongs to the order Chromatiales; the cultured bacterium with the highest 16S rRNA gene sequence identity to SS-5 is Thiohalocapsa marina (93.0%). Strain BW-2 clearly belongs to the Thiotrichales; interestingly, the organism with the highest 16S rRNA gene sequence identity to this strain is Thiohalospira alkaliphila (90.2%), which belongs to the Chromatiales. Each strain represents a new genus. This is the first report of magnetite-producing MTB phylogenetically associated with the Gammaproteobacteria. This finding is important in that it significantly expands the phylogenetic diversity of the MTB. Physiology of these strains is similar to other MTB and continues to demonstrate their potential in nitrogen, iron, carbon and sulfur cycling in natural environments. PMID:21776027

  16. Formation of single domain magnetite by green rust oxidation promoted by microbial anaerobic nitrate-dependent iron oxidation

    NASA Astrophysics Data System (ADS)

    Miot, Jennyfer; Li, Jinhua; Benzerara, Karim; Sougrati, Moulay Tahar; Ona-Nguema, Georges; Bernard, Sylvain; Jumas, Jean-Claude; Guyot, François

    2014-08-01

    Biomineralization of magnetite is a central geomicrobiological process that might have played a primordial role over Earth’s history, possibly leaving traces of life in the geological record or controlling trace metal(loid)s and organic pollutants mobility in modern environments. Magnetite biomineralization has been attributed to two main microbial pathways to date (namely magnetotactic bacteria and dissimilatory iron-reducing bacteria). Here, we uncover a new route of magnetite biomineralization involving the anaerobic nitrate-reducing iron(II) oxidizing bacterium Acidovorax sp. strain BoFeN1. Using transmission electron microscopy, scanning transmission X-ray microscopy, transmission Mössbauer spectroscopy and rock magnetic analyses, this strain is shown to promote the transformation of hydroxychloride green rust in equilibrium with dissolved Fe(II) to (1) periplasmic lepidocrocite (?-FeOOH) and (2) extracellular magnetite, thus leading to strong redox heterogeneities at the nanometer scale. On the one hand, lepidocrocite was associated with protein moieties and exhibited an anisotropic texture, with the elongated axis parallel to the cell wall. On the other hand, magnetite crystals exhibited grain sizes and magnetic properties consistent with stable single domain particles. By comparison, abiotic controls led to a very slow (4 months vs. 2 days in BoFeN1 cultures) and incomplete oxidation of hydroxychloride green rust towards magnetite. As this abiotic magnetite exhibited the same size and magnetic properties (stable single domain particles) as magnetite produced in BoFeN1 cultures, only the co-occurrence of textured Fe(III)-oxides and magnetite, associated with the persistence of organic carbon molecules, might constitute valuable biosignatures to be looked for in the geological record. Our results furthermore contribute to a more complex picture of Fe redox cycling in the environment, providing an additional process of Fe(II)-bearing phase biomineralization that is not specific of Fe bio-reduction, but can also result from Fe bio-oxidation.

  17. Mineralogical and microfabric characteristics of magnetite in the Wuyang Precambrian BIFs, southern North China Craton: Implications for genesis and depositional processes of the associated BIFs

    NASA Astrophysics Data System (ADS)

    Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Yang, Zhijun; Kapsiotis, Argyrios; Zhou, Yongzhang; He, Junguo; Wang, Changle; Liang, Jin

    2014-11-01

    Precambrian Banded Iron Formations (BIFs) are widely distributed in the North China Craton (NCC). Among them, the Wuyang BIFs located in the southern margin of NCC occur in the Late Archaean Tieshanmiao Formation and can be subdivided in two different sub-types: (i) quartz-magnetite BIFs (QMB), consisting of magnetite, fine-microcrystalline quartz and minor calcite and (ii) pyroxene-magnetite BIFs (PMB), composed of pyroxene, fine-microcrystalline quartz and subordinate feldspars. Both sub-types display apparent discrepancies in terms of petrography and mineral composition. As shown in Electron BackScattered Diffraction (EBSD) images and micrographs, magnetite grains from the QMB range in size from tens up to hundreds of ?m, whereas magnetite crystals from the PMB can be up to a few tens of ?m across. The X-ray diffraction (XRD) structural data indicate that magnetite from both BIF sub-types is equiaxed (cubic) and was generated by sedimentary metamorphic processes. The cell parameters of magnetite in the QMB are a = b = c = 8.396 Å and Z = 8, which deviate slightly from these of magnetite in the PMB: a = b = c = 8.394 Å and Z = 8. The analytical results of Raman spectroscopy analysis revealed micro-structural signatures of both magnetite (Raman shifts near 552 cm-1 and 673 cm-1) and hematite (Raman shifts near 227 cm-1, 295 cm-1 and 413 cm-1). In magnetite from both QMB and PMB, the crystallinity degree is similar for magnetite micro-structures but varies significantly for hematite micro-structures. Oxygen fugacity (fO2) conditions fluctuated during the recrystallization of magnetite in the QMB, whereas no evident variation of fO2 occurred during the formation of magnetite in the PMB. Analytical results of laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) show that the Si, Al and Mg abundances are higher in magnetite from the QMB, whereas the Ti and Mn contents are more elevated in magnetite from the PMB. Magnetite composition also denotes that both BIF sub-types are sedimentary-metamorphic origin, whereas the deposition of PMB was also affected by volcanic activities. Overall data indicate that the differences in the depositional environment of each BIF sub-type are due to the involvement of volcanic eruption processes in the genesis of the PMB. Thus, this paper indicated that the QMB was deposited by chemical deposition at the long-term interval of volcanic eruptions, and the PMB were the product of chemical deposition affected by the volcanic eruption.

  18. Biogenic Magnetite in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Bazylinski, Dennis; Wentworth, Susan J.; McKay, David S.; Kirschvink, Joseph L.; Clemett, Simon J.; Bell, Mary Sue; Golden, D. C.

    1999-01-01

    Fine-grained magnetite (Fe3O4) in martian meteorite ALH84001, generally less than 200 microns in size, is located primarily in the rims that surround the carbonate globules. There are two populations of ALH84001 magnets, which are likely formed at low temperature by inorganic and biogenic processes. Nearly 27/o of ALH84001 magnetite particles. also called elongated prisms, have characteristics which make them uniquely identifiable as biological precipitates.

  19. Phagocytosis of bacterial magnetite by leucocytes

    Microsoft Academic Search

    Tadashi Matsunaga; Kohji Hashimoto; Noriyuki Nakamura; Kayoko Nakamura; Shozo Hashimoto

    1989-01-01

    Magnetotactic bacteria were introduced into granulocytes and monocytes by phagocytosis. The number of phagocytes containing bacterial magnetites (magneto-sensitive cells) became constant after 1.5 h incubation, and viable phagocytes contained about 20–40 cells of magnetotactic bacteria. Granulocytes and monocytes containing bacterial magnetites were separated by magnet a Samarium-cobalt from lymphocytes. After separation, 89% of lymphocytes were recovered and 95% of the

  20. Thermal Analysis of Acicular Shaped Magnetite

    NASA Technical Reports Server (NTRS)

    Lauer, H. V., Jr.; Ming, D. W.; Golden, D. C.

    2003-01-01

    We are in the process of developing a database on the thermal properties of well-characterized Martian analog materials in support of future Mars surface missions. The database contains the thermal behaviors of these analog materials under reduced and Earth ambient pressures. Magnetite in planetary materials has received considerable attention in recent years since the identification of fine grain single-domain magnetite in Martian meteorite ALH84001 and their possible link to past life on Mars (i.e., possible biominerals of magnetotactic bacteria). Because of its possible importance to Mars science, we report here the thermal properties of magnetite particles with acicular morphology, i.e., needle-shaped magnetite. Acicular shaped magnetite can be commercially produced from goethite (FeOOH) as the starting material via a H2 reduction process. However, instead of using this process or procedure, we report here on the thermal characterization of acicular magnetite formed under reducing conditions from well-characterized needle-shaped goethite at low temperature in controlled CO-CO2 1-bar atmosphere gas mixing furnaces.

  1. Synthesis, characterization and applications of magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Kanmukhla, Vikram Kumar

    In the past few years, the synthesis of magnetic nanoparticles has received considerable attention due to their potential use in clinical applications. Since the properties of these nanoparticles depend strongly on their size, shape and crystallinity, there is a need for a general method to produce these particles with a controlled size, shape and crystal type. Of the many magnetic materials (Co, Ni, and Fe), the magnetite (Fe3O 4) is least toxic and hence most promising for applications in medical diagnostics. Microemulsion-based synthesis utilizes the local aqueous environment within a reverse micelle as a nano-scale reactor and allows synthesizing nanoparticles with a hydrophilic surface for subsequent functionalization. By controlling the water-to-surfactant ratio, the type of surfactants, and the ionic strength of the aqueous core, one can control the size and shape of the resulting particles. We developed such a system that allows the multi-step synthesis of surface-functionalized, magnetic nanoparticles in a one-pot synthesis reaction. By altering the system chemistry, we were further able to produce either spheres or cylinders of controlled dimension in the size range of 5 nm to 30 nm. Using standard bio-conjugation techniques, we successfully immobilized an enzyme onto the nanoparticles. We also developed a theoretical model for the separation and fractionation of nanoparticles based on their size and magnetic properties. Using the multiphysics and finite element modeling capabilities of FEMLAB(TM), we solved the coupled system of PDEs describing the interaction of magnetic particles within a magnetic field for either static (cylindrical beaker) or convective flow (capillary) conditions. A net retention time as high as 310 s is achieved for 200 nm particles at field strength of 1250 kA/m. The model allows the design of a magnetic, field-flow fractionation (MFFF) system to separate nanoparticles by size.

  2. Experimental Study on Mixtures of Superparamgnetic and Single-Domain Magnetite with Respect to Day-Dunlop Plots

    NASA Astrophysics Data System (ADS)

    Hirt, A. M.; Kumari, M.; Senn, N.; Uebe, R.; Schueler, D.

    2013-12-01

    Day-Dunlop plots are widely used as a diagnostic of domain state: superparamagnetic (SP), stable single-domain (SD), pseudo-single-domain (PSD), multi-domain (MD) and mixture of these. A n earlier experimental study on mixtures of SP and SD magnetite showed that ratios of saturation remanent magnetization to saturation magnetization and the coercivity of remanence to coercivity are lower than the expected theoretical mixing trend (Dunlop & Carter-Stiglitz, J. Geophys. Res., 111, B12S09). This study reexamines Day-Dunlop plots with experimentally determined mixtures of SD and SP magnetite grains. The starting materials that are used in this study are biogenic magnetite with SD and SP particle size, and a commercial ferrofluid. The SD-biogenic magnetite is from magnetotactic bacteria that are arranged in chains. The average magnetosome size is 45 mm; however, there is also a minor amount of SP material among the magnetosomes. The SP component consists either of: 1) SP-biogenic magnetite, which occurs as isolated particles within the bacteria with an average size of 18 nm, or 2) Chemicell ferrofluid, magnetite with 10 nm particle size and hydrodynamic diameter of 45 nm. The magnetic properties of the pure materials were first characterized by measurements of hysteresis, acquisition of an isothermal remanent magnetization, and first-order reversal curves. The magnetic properties of the SD magnetite are typical for magnetotactic bacteria. The SP samples show no remanence. Two samples were prepared from the SD-magnetite to serve as the starting material. The SP-component was then added incrementally to the SD samples. Experimental results from these tests show that the magnetization and coercivity ratios are lower than the theoretical prediction for both sample mixtures. The reasons for this discrepancy will be discussed.

  3. Geochemistry of magnetite from Proterozoic Fe-Cu deposits in the Kangdian metallogenic province, SW China

    NASA Astrophysics Data System (ADS)

    Chen, Wei Terry; Zhou, Mei-Fu; Gao, Jian-Feng; Hu, Ruizhong

    2015-01-01

    Fe-Cu deposits in the Kangdian Fe-Cu metallogenic province, SW China, are hosted in Paleoproterozoic meta-volcanic-sedimentary sequences and are spatially associated with coeval mafic intrusions. Several well-known examples are the giant Lala, Dahongshan, and Yinachang deposits. They have a common paragenetic sequence of an early Fe-oxide stage associated with sodic alteration and a late Cu-sulfide stage associated with potassic-carbonate alteration. Magnetite dominates the Fe-oxide stage of these deposits but is also present in the Cu-sulfide stage of the Lala deposit. This study uses trace element compositions of magnetite to examine the nature and origin of the ore-forming fluids. The magnetite has variable concentrations of Ti, Al, Mg, Mn, Si, V, Cr, Ca, Co, Ni, Sc, Zn, Cu, Mo, Sn, and Ga, which are thought to have been controlled mainly by fluid compositions and/or intensive parameters (e.g., temperature and oxygen fugacity (fO2)). Fluid-rock interaction and coprecipitating mineral phases appear to be less important in controlling the magnetite compositions. Magnetite grains in the Fe-oxide stage of the Lala and Dahongshan deposits have comparable trace element compositions and were likely precipitated from chemically similar fluids. High Ni contents of magnetite in both deposits, coupled with previous isotopic data and the fact that the two deposits are spatially associated with coeval mafic intrusions, strongly suggest that the ore-forming fluids were genetically related to the mafic magmas that formed the intrusions. Magnetite grains in the Fe-oxide stage of the Yinachang deposit have much lower V and Ni but higher Sn and Mo contents than those of the Lala and Dahongshan deposits and are thus thought to have precipitated from more oxidized and Mo-Sn-rich fluids that may have evolved from relatively felsic magmas. Magnetite grains from the Cu-sulfide and Fe-oxide stages of the Lala deposit are broadly similar in composition, but those in the Cu-sulfide stage have slightly higher Cu, Zn, and Mn and are thought to have crystallized from relatively low-temperature and Cu-Zn-Mn-rich fluids evolved from the fluids of the early Fe-oxide stage. Our results show that magnetite from the Fe-Cu deposits in the Kangdian Province, banded iron formation, Fe skarn deposits, diabase-hosted hydrothermal Fe deposits, and magmatic deposits has significantly different compositions. We propose that covariations of Co-Ni, Zn-Sn, and Co/Ni-Mn can be used to effectively discriminate different deposit types.

  4. Magnetic anisotropy modulation of magnetite in Fe3O4/BaTiO3(100) epitaxial structures

    NASA Astrophysics Data System (ADS)

    Vaz, C. A. F.; Hoffman, J.; Posadas, A.-B.; Ahn, C. H.

    2009-01-01

    Temperature dependent magnetometry and transport measurements on epitaxial Fe3O4 films grown on BaTiO3(100) single crystals by molecular beam epitaxy show a series of discontinuities, due to changes in the magnetic anisotropy induced by strain from the different crystal phases of BaTiO3. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO3 at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with the magnetoelastic anisotropies. These results demonstrate the possibility of using the piezoelectric response of BaTiO3 to modulate the magnetic anisotropy of magnetite films.

  5. Thermal, dielectric studies on pure and amino acid ( l-glutamic acid, l-histidine, l-valine) doped KDP single crystals

    Microsoft Academic Search

    P. Kumaresan; S. Moorthy Babu; P. M. Anbarasan

    2008-01-01

    Amino acids (l-glutamic acid, l-histidine, l-valine) doped potassium dihydrogen phospate crystals are grown by solution growth technique. Slow cooling as well as slow evaporation methods were employed to grow these crystals. The concentration of dopants in the mother solution was varied from 0.1mol% to 10mol%. The solubility data for all dopants concentration were determined. There is variation in pH value

  6. Magnetite: a search for the half-metallic state.

    PubMed

    Fonin, M; Dedkov, Yu S; Pentcheva, R; Rüdiger, U; Güntherodt, G

    2007-08-01

    We present a detailed study of the spin-dependent electronic structure of thin epitaxial magnetite films of different crystallographic orientations. Using spin- and angle-resolved photoelectron spectroscopy at room temperature, we determine for epitaxial Fe(3)O(4)(111) films a maximum spin polarization value of -(80 ± 5)% near E(F). The spin-resolved photoelectron spectra for binding energies between 1.5 eV and E(F) show good agreement with the spin-split band structure from density functional theory (DFT) calculations which predict an overall energy gap in the spin-up electron bands in high symmetry directions, thus providing evidence for the half-metallic ferromagnetic state of Fe(3)O(4) in the [111] direction. In the case of the Fe(3)O(4)(100) surface, both the spin-resolved photoelectron spectroscopy experiments and the DFT density of states give evidence for a half-metal to metal transition: the measured spin polarization of about -(55 ± 10)% at E(F) and the theoretical value of -40% are significantly lower than the -100% predicted by local spin density approximation (LSDA) calculations for the bulk magnetite crystal as well as the -(80 ± 5)% obtained for the Fe(3)O(4)(111) films. The experimental findings were corroborated by DFT calculations as due to a surface reconstruction leading to the electronic states in the majority-spin band gap and thus to the reduced spin polarization. PMID:21694117

  7. Evaluating the cytotoxicity of palladium/magnetite nano-catalysts intended for wastewater treatment.

    PubMed

    Hildebrand, Heike; Kühnel, Dana; Potthoff, Annegret; Mackenzie, Katrin; Springer, Armin; Schirmer, Kristin

    2010-01-01

    Palladium/magnetite nanoparticulate catalysts were developed for efficient elimination of halogenated organic pollutants from contaminated wastewater. Particle recovery from treated water can be ensured via magnetic separation. However, in worst-case scenarios, this catalyst removal step might fail, leading to particle release into the environment. Therefore, a toxicological study was conducted to investigate the impact of both pure magnetite and palladium/magnetite nanoparticle exposure upon human skin (HaCaT) and human colon (CaCo-2) cell lines and a cell line from rainbow trout gills (RTgill-W1). To quantify cell viability after particle exposure, three endpoints were examined for all tested cell lines. Additionally, the formation of reactive oxygen species was studied for the human cells. The results showed only minor effects of the particles on the tested cell systems and support the assumption that palladium/magnetite nano-catalysts can be implemented for a new wastewater treatment technology in which advantageous catalyst properties outweigh the risks. PMID:19783337

  8. Actinide removal from aqueous solution with activated magnetite

    SciTech Connect

    Kochen, R.L.; Thomas, R.L. (ed.)

    1987-08-10

    An actinide aqueous waste treatment process using activated magnetite has been developed at Rocky Flats. The use and effectiveness of various magnetites in lowering actinide concentrations in aqueous solution are described. Experiments indicate that magnetite particle size and pretreatment (activation of the magnetite surface with hydroxyl ions greatly influence the effective use of magnetite as an actinide adsorbent. With respect to actinide removal, Ba(OH)/sub 2/-activated magnetite was more effective over a broader pH range than was NaOH-activated magnetite. About 50% less Ba(OH)/sub 2/-activated magnetite was required to lower plutonium concentration from 10/sup -4/ to 10/sup -8/ g/l. 7 refs., 8 tabs.

  9. crystal

    NASA Astrophysics Data System (ADS)

    Yu, Yi; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Sun, Shijia; Wang, Guofu

    2014-07-01

    A Nd3+:Na2La4(WO4)7 crystal with dimensions of ? 17 × 30 mm3 was grown by the Czochralski method. The thermal expansion coefficients of Nd3+:Na2La4(WO4)7 crystal are 1.32 × 10-5 K-1 along c-axis and 1.23 × 10-5 K-1 along a-axis, respectively. The spectroscopic characteristics of Nd3+:Na2La4(WO4)7 crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 × 10-20 cm2 with a full width at half maximum (FWHM) of 15 nm for ?-polarization, and 2.29 × 10-20 cm2 with a FWHM of 14 nm for ?-polarization. The emission cross sections are 3.19 × 10-20 cm2 for ?-polarization and 2.67 × 10-20 cm2 for ?-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd3+:Na2La4(WO4)7 crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd3+:Na2La4(WO4)7 crystal as a promising laser crystal fit for laser diode pumping.

  10. Oxidation of pyrite in coal to magnetite

    USGS Publications Warehouse

    Thorpe, A.N.; Senftle, F.E.; Alexander, C.C.; Dulong, F.T.

    1984-01-01

    When bituminous coal is heated in an inert atmosphere (He) containing small amounts of oxygen at 393-455 ??C, pyrite (FeS2) in coal is partially converted to magnetite (Fe304). The maximum amount of Fe304 formed during the time of heating corresponds to 5-20% of the total pyrite present, depending on the coal sample. The magnetite forms as an outer crust on the pyrite grains. The fact that the magnetic properties of the pyrite grains are substantially increased by the magnetite crust suggests that pyrite can be separated from coal by use of a low magnetic field. In a laboratory test, 75% removal is obtained by means of a 500 Oe magnet on three samples, and 60% on a fourth sample. ?? 1984.

  11. Spin state of iron in Fe3O4 magnetite and h-Fe3O4

    NASA Astrophysics Data System (ADS)

    Bengtson, Amelia; Morgan, Dane; Becker, Udo

    2013-04-01

    The high-pressure behavior of magnetite has been widely debated in the literature. Experimental measurements have found conflicting high-pressure transitions: a charge reordering in magnetite from inverse-spinel to normal-spinel [Pasternak , J. Phys. Chem. Solids0022-369710.1016/j.jpcs.2003.12.013 65, 1531 (2004); Rozenberg , Phys. Rev. B10.1103/PhysRevB.75.020102 75, 020102 (2007)], iron high-spin to intermediate-spin transition in magnetite [Ding , Phys. Rev. Lett.0031-900710.1103/PhysRevLett.100.045508 100, 045508 (2008)], electron delocalization in magnetite [Baudelet , Phys. Rev. B1098-012110.1103/PhysRevB.82.140412 82, 140412 (2010); Glazyrin , Am. Mineral.0003-004X10.2138/am.2011.3862 97, 128 (2012)], and a structural phase transition from magnetite to h-Fe3O4 [Dubrovinsky , J. Phys.: Condens. Matter0953-898410.1088/0953-8984/15/45/009 15, 7697 (2003); Fei , Am. Mineral. 84, 203 (1999); Haavik , Am. Mineral. 85, 514 (2000)]. We present ab initio calculations of iron's spin state in magnetite and h-Fe3O4, which help resolve the high-pressure debate. The results of the calculations find that iron remains high spin in both magnetite and h-Fe3O4; intermediate-spin iron is not stable. In addition, magnetite remains inverse-spinel but undergoes a phase transition to h-Fe3O4 near 10 GPa. Magnetite has a complex magnetic ordering, multiple valence states (Fe2+ and Fe3+), charge ordering, and different local Fe site environments, all of which were accounted for in the calculations. The lack of intermediate-spin iron in magnetite helps resolve the spin state of iron in perovskite, the major mineral in the lower mantle. In both magnetite and perovskite, x-ray emission spectroscopy (XES) measurements in the literature show a drop in satellite peak intensity by approximately half, which is interpreted as intermediate-spin iron. In both minerals, calculations give no indication of intermediate-spin iron and predict high-spin iron to be stable for defect-free crystals. The results question the interpretation of a nonzero drop in XES satellite peak intensities as intermediate-spin iron.

  12. Origin of magnetite and pyrrhotite in carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Herndon, J. M.; Rowe, M. W.; Larson, E. E.; Watson, D. E.

    1975-01-01

    It is proposed that a substantial fraction of the magnetite, at least, resulted from the oxidation of troilite. Pyrrhotite is expected as a direct consequence of magnetite formation through this reaction. During thermomagnetic experiments on troilite, magnetite formation was observed at temperatures as low as 373 K, provided that the oxygen fugacity was held in the magnetite stability field, and that the troilite was sufficiently finely divided.

  13. Magnetotransport anisotropy effects in epitaxial magnetite (Fe3O4) thin films

    Microsoft Academic Search

    S. B. Ogale; K. Ghosh; R. P. Sharma; R. L. Greene; R. Ramesh; T. Venkatesan

    1998-01-01

    Epitaxial films of magnetite (Fe3O4) have been grown on SrTiO3 (100) and sapphire (alpha-Al2O3, 0001) substrates by pulsed laser deposition, and they exhibit crystal orientations of [100] and [111], respectively. Films of both orientations show a clear Verwey transition near 120 K. The temperature dependence of magnetoresistance of the films is examined at fields up to 8.5 T applied parallel

  14. Transport and magnetic properties of epitaxial and polycrystalline magnetite thin films

    Microsoft Academic Search

    X. W. Li; A. Gupta; Gang Xiao; G. Q. Gong

    1998-01-01

    The transport and magnetic properties of magnetite (Fe3O4) thin films grown epitaxially on single crystal MgO(100) and SrTiO3(100) substrates, and with multiple grain orientations on polycrystalline SrTiO3 substrates, have been investigated. The films are grown using pulsed laser deposition and their epitaxial quality determined using ion channeling measurements. Transport and magnetic studies of Fe3O4 films as a function of thickness

  15. Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films

    Microsoft Academic Search

    N. Naftalis; A. Kaplan; M. Schultz; C. A. F. Vaz; J. A. Moyer; C. H. Ahn; L. Klein

    2011-01-01

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system.

  16. Immobilization of Peroxidase onto Magnetite Modified Polyaniline

    PubMed Central

    Barbosa, Eduardo Fernandes; Molina, Fernando Javier; Lopes, Flavio Marques; García-Ruíz, Pedro Antonio; Caramori, Samantha Salomão; Fernandes, Kátia Flávia

    2012-01-01

    The present study describes the immobilization of horseradish peroxidase (HRP) on magnetite-modified polyaniline (PANImG) activated with glutaraldehyde. After the optimization of the methodology, the immobilization of HRP on PANImG produced the same yield (25%) obtained for PANIG with an efficiency of 100% (active protein). The optimum pH for immobilization was displaced by the effect of the partition of protons produced in the microenvironment by the magnetite. The tests of repeated use have shown that PANImG-HRP can be used for 13 cycles with maintenance of 50% of the initial activity. PMID:22489198

  17. Rock magnetism linked to human brain magnetite

    NASA Astrophysics Data System (ADS)

    Kirschvink, Joseph L.

    Magnetite has a long and distinguished career as one of the most important minerals in geophysics, as it is responsible for most of the remanent magnetization in marine sediments and the oceanic crust. It may come as a surprise to discover that it also ranks as the third or fourth most diverse mineral product formed biochemically by living organisms, and forms naturally in a variety of human tissues [Kirschvink et al., 1992].Magnetite was discovered in teeth of the Polyplacophora mollusks over 30 years ago, in magnetotactic bacteria nearly 20 years ago, in honey bees and homing pigeons nearly 15 years ago, but only recently in human tissue.

  18. Determination of the Three-Dimensional Morphology of ALH84001 and Biogenic MV-1 Magnetite: Comparison of Results from Electron Tomography and Classical Transmission Electron Microscopy

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Schwartz, Cindy; Morphew, Mary; McIntosh, J. Richard; Bazylinski, Dennis A.; Kirschvink, Joseph L.; Wentworth, Susan J.; McKay, David S.; Vali, Hojatollah

    2004-01-01

    Dated at approximately 3.9 billion years of age, carbonate disks, found within fractures of the host rock of Martian meteorite ALH84001, have been interpreted as secondary minerals that formed at low temperature in an aqueous medium. Heterogeneously distributed within these disks are magnetite nanocrystals that are of Martian origin. Approximately one quarter of these magnetites have morphological and chemical similarities to magnetite particles produced by magnetotactic bacteria strain MV-1, which are ubiquitous in aquatic habitats on Earth. Moreover, these types of magnetite particles are not known or expected to be produced by abiotic means either through geological processes or synthetically in the laboratory. The remaining three quarters of the ALH84001 magnetites are likely products of multiple processes including, but not limited to, precipitation from a hydrothermal fluid, thermal decomposition of the carbonate matrix in which they are embedded, and extracellular formation by dissimilatory Fe-reducing bacteria. We have proposed that the origins of magnetites in ALH84001 can be best explained as the products of multiple processes, one of which is biological. Recently the three-dimensional (3-D) external morphology of the purported biogenic fraction of the ALH84001 magnetites has been the subject of considerable debate. We report here the 3-D geometry of biogenic magnetite crystals extracted from MV-1 and of those extracted from ALH84001 carbonate disks using a combination of high resolution classical and tomographic transmission electron microscopy (TEM). We focus on answering the following questions: (1) which technique provides adequate information to deduce the 3-D external crystal morphology?; and, (2) what is the precise 3-D geometry of the ALH84001 and MV-1 magnetites?

  19. Biomimetic Magnetite Formation: From Biocombinatorial Approaches to Mineralization Effects

    PubMed Central

    2014-01-01

    Biological materials typically display complex morphologies and hierarchical architectures, properties that are hardly matched by synthetic materials. Understanding the biological control of mineral properties will enable the development of new synthetic approaches toward biomimetic functional materials. Here, we combine biocombinatorial approaches with a proteome homology search and in vitro mineralization assays to assess the role of biological determinants in biomimetic magnetite mineralization. Our results suggest that the identified proteins and biomimetic polypeptides influence nucleation in vitro. Even though the in vivo role cannot be directly determined from our experiments, we can rationalize the following design principles: proteins, larger complexes, or membrane components that promote nucleation in vivo are likely to expose positively charged residues to a negatively charged crystal surface. In turn, components with acidic (negatively charged) functionality are nucleation inhibitors, which stabilize an amorphous structure through the coordination of iron. PMID:24499323

  20. Magnetite Biomineralization: Fifty years of progress, from beach-combing to the SQUID microscope

    NASA Astrophysics Data System (ADS)

    Kirschvink, J. L.; Dixson, A. D.; Raub, T.

    2012-12-01

    Magnetite biomineralization was first discovered 50 years ago as a hardening agent in the teeth of the Polyplacophoran molluscs (chitons) by the late Prof. Heinz A. Lowenstam of Caltech, when he noticed unusual erosional effects produced by their grazing in the intertidal zones of Palau (Lowenstam, 1962). Since then, biogenic magnetite has been detected in a broad range of organisms, including magnetotactic bacteria, protists, insects, fish, amphibians, reptiles, birds, and mammals including humans. In many species, the role of ferromagnetic material as a neurophysiological transducer is demonstrated clearly through the effects of pulse-remagnetization on behavior. A brief (1 uS), properly configured magnetic discharge from a rectified LC circuit, tailored to exceed the coercivity of the magnetite, will often abolish a magnetic behavioral response, or in some cases make the organism go the wrong way. This is a unique ferromagnetic effect. The genes controlling magnetite biomineralization are well characterized in several species of bacteria, and the ability of some of these bacterial genes to initiate magnetite precipitation in mammalian cell lines argues for a common descent, probably via a magnetotactic mitochondrial ancestor. Previous studies in fish reported the presence of single-domain magnetite crystals in cells near projections of the trigeminal nerve, co-located in the olfactory epithelium. Although the cells are rare, the recent development of a spinning magnetic field technique allows easy identification and isolation of these cells for individual study (Eder et al., 2012). The cells are surprisingly magnetic, with moments hundreds of times larger than typical magnetotactic bacteria. Subsequent efforts to identify the anatomical seat of magnetoreceptors have focused on the same locations in new organisms, excluding other areas. Using SQUID moment magnetometry and SQUID scanning microscopy, we report here the unexpected presence of biogenic magnetite in the lateral line region of the zebrafish, Danio rerio. We suspect that the magnetic field receptor cells of the trigeminal system in animals may be co-located within a variety of other sensory tissues (olfaction, lateral line, vision, hearing, taste, etc.) as a means of spatially dispersing cells with large magnetic moments to prevent magnetostatic interactions between them. References: Eder et al., Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells. Proc. Natl. Acad. Sci. USA 2012; 109:12022-12027. Lowenstam, H.A., 1962. Magnetite in denticle capping in recent chitons (Polyplacophora). Bulletin of the Geological Society of America 73, 435-438.

  1. Title: Biogenic Magnetite Prevails in Oxic Pelagic Red Clay Core in the South Pacific Gyre

    NASA Astrophysics Data System (ADS)

    Shimono, T.; Yamazaki, T.

    2012-12-01

    Magnetotactic bacteria have been observed in wide variety of environments, including soils, freshwater lakes, and marine sediments, since Blakemore (1975) first described in 1975. Magnetotactic bacteria, which most commonly live within the oxic-anoxic transition zone (OATZ) of aquatic environments, produce intracellular crystals of magnetic minerals, specifically magnetite or greigite. It is considered that the magnetite/greigite crystals facilitate the bacteria's search for optimal conditions within the sharp chemical gradients of the OATZ. Petermann and Bleil (1993) reported living magnetotactic bacteria in pelagic and hemipelagic sediments near OATZ in the eastern South Atlantic at water depths to about 3,000 m, but they couldn't find actively swimming magnetotactic bacteria in sediments of deeper water depths. The South Pacific Gyre (SPG) is far from continents and the lowest productivity region on Earth. IODP site U1365 (water depth ~5,700 m) cored pelagic red clay of 75.5 m thick above ~100 Ma basement (except for the chart layer from ~42 to 63.5 m) in the western edge of the SPG. The core mainly consists of iron rich clay. The color is dark reddish and/or dark brown throughout the core. We conducted a paleomagnetic and environmental rock magnetic study of the pelagic clay core. The magnetostratigraphy revealed the top 5 m sediments cover the last 5 My, and sedimentation rate decreases downward from 1.7 to 0.6 m/m.y. Geochemical measurements of pore water indicate that dissolved oxygen was present throughout the core (>50 ?M). Thus oxygen penetrates through the entire sediment column to the sediment/basalt interface, and there is no OATZ. Magnetic mineral assemblage of this core is dominated by biogenic magnetite despite no OATZ. First-order reversal curve (FORC) diagrams of all specimens have a narrow central ridge along the Hc axis with very small vertical spread. This indicates very weak magnetostatic interaction (Roberts et al., 2000), and is the characteristic of biogenic magnetite (Egli et al., 2010; Roberts et al., 2011). Presence of biogenic magnetite was confirmed by TEM observation. Occurrence of biogenic magnetite was reported also in pelagic red clay of the North Pacific with TEM observations (Yamazaki and Ioka, 1997), and these samples also display the characteristic FORC diagrams. These observations suggest that biogenic magnetites commonly occur in oxic pelagic red clay without OATZ.

  2. Partial oxidation as a rational approach to kinetic control in bioinspired magnetite synthesis.

    PubMed

    Altan, Cem L; Lenders, Jos J M; Bomans, Paul H H; de With, Gijsbertus; Friedrich, Heiner; Bucak, Seyda; Sommerdijk, Nico A J M

    2015-04-13

    Biological systems show impressive control over the shape, size and organization of mineral structures, which often leads to advanced physical properties that are tuned to the function of these materials. Such control is also found in magnetotactic bacteria, which produce-in aqueous medium and at room temperature-magnetite nanoparticles with precisely controlled morphologies and sizes that are generally only accessible in synthetic systems with the use of organic solvents and/or the use of high-temperature methods. The synthesis of magnetite under biomimetic conditions, that is, in water and at room temperature and using polymeric additives as control agents, is of interest as a green production method for magnetic nanoparticles. Inspired by the process of magnetite biomineralization, a rational approach is taken by the use of a solid precursor for the synthesis of magnetite nanoparticles. The conversion of a ferrous hydroxide precursor, which we demonstrate with cryo-TEM and low-dose electron diffraction, is used to achieve control over the solution supersaturation such that crystal growth can be regulated through the interaction with poly-(?,?)-dl-aspartic acid, a soluble, negatively charged polymer. In this way, stable suspensions of nanocrystals are achieved that show remanence and coercivity at the size limit of superparamagnetism, and which are able to align their magnetic moments forming strings in solution as is demonstrated by cryo-electron tomography. PMID:25740708

  3. Ferromagnetic resonance and low-temperature magnetic tests for biogenic magnetite

    NASA Astrophysics Data System (ADS)

    Weiss, Benjamin P.; Sam Kim, Soon; Kirschvink, Joseph L.; Kopp, Robert E.; Sankaran, Mohan; Kobayashi, Atsuko; Komeili, Arash

    2004-07-01

    Magnetite is both a common inorganic rock-forming mineral and a biogenic product formed by a diversity of organisms. Magnetotactic bacteria produce intracellular magnetites of high purity and crystallinity (magnetosomes) arranged in linear chains of crystals. Magnetosomes and their fossils (magnetofossils) have been identified using transmission electron microscopy (TEM) in sediments dating back to ˜510-570 Ma, and possibly in 4 Ga carbonates in Martian meteorite ALH84001. We present the results from two rock magnetic analyses—the low-temperature Moskowitz test and ferromagnetic resonance (FMR)—applied to dozens of samples of magnetite and other materials. The magnetites in these samples are of diverse composition, size, shape, and origin: biologically induced (extracellular), biologically controlled (magnetosomes and chiton teeth), magnetofossil, synthetic, and natural inorganic. We confirm that the Moskowitz test is a distinctive indicator for magnetotactic bacteria and provide the first direct experimental evidence that this is accomplished via sensitivity to the magnetosome chain structure. We also demonstrate that the FMR spectra of four different strains of magnetotactic bacteria and a magnetofossil-bearing carbonate have a form distinct from all other samples measured in this study. We suggest that this signature also results from the magnetosomes' unique arrangement in chains. Because FMR can rapidly identify samples with large fractions of intact, isolated magnetosome chains, it could be a powerful tool for identifying magnetofossils in sediments.

  4. Surface spin disorder effects in magnetite and poly(thiophene)-coated magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Cótica, Luiz F.; Santos, Ivair A.; Girotto, Emerson M.; Ferri, Elidia V.; Coelho, Adelino A.

    2010-09-01

    Chemically synthesized magnetite and poly(thiophene)-coated magnetite nanoparticles and the correlations between their magnetic, structural, and microstructural properties are investigated. A typical superparamagnetic behavior was observed for faceted nanoparticle agglomerates of magnetite and nanocomposite. In nanocomposites, the polymer layer causes a sharp decrease in the spin disorder, which reduces the anisotropy constant significantly. This happens because the intimate contact between magnetite and poly(thiophene) leads to charge transfer from the polymer to the core via polaron interactions, causing a structural rearrangement of the nanoparticles and suppression of the spin movement at the surface. As this dynamic interaction can tune the core dimensions, the magnetic properties of nanocomposites can be tuned by controlling the core size through polymer coating. These characteristics can be exploited to design high-performance magnetically tunable nanodevices and applied in many areas of biomedicine (DNA separation, drug targeting, immune detection, and magnetic nanoparticle hyperthermia in cancer treatment).

  5. Influence of magnetite stoichiometry on U(VI) reduction.

    PubMed

    Latta, Drew E; Gorski, Christopher A; Boyanov, Maxim I; O'Loughlin, Edward J; Kemner, Kenneth M; Scherer, Michelle M

    2012-01-17

    Hexavalent uranium (U(VI)) can be reduced enzymatically by various microbes and abiotically by Fe(2+)-bearing minerals, including magnetite, of interest because of its formation from Fe(3+) (oxy)hydroxides via dissimilatory iron reduction. Magnetite is also a corrosion product of iron metal in suboxic and anoxic conditions and is likely to form during corrosion of steel waste containers holding uranium-containing spent nuclear fuel. Previous work indicated discrepancies in the extent of U(VI) reduction by magnetite. Here, we demonstrate that the stoichiometry (the bulk Fe(2+)/Fe(3+) ratio, x) of magnetite can, in part, explain the observed discrepancies. In our studies, magnetite stoichiometry significantly influenced the extent of U(VI) reduction by magnetite. Stoichiometric and partially oxidized magnetites with x ? 0.38 reduced U(VI) to U(IV) in UO(2) (uraninite) nanoparticles, whereas with more oxidized magnetites (x < 0.38) and maghemite (x = 0), sorbed U(VI) was the dominant phase observed. Furthermore, as with our chemically synthesized magnetites (x ? 0.38), nanoparticulate UO(2) was formed from reduction of U(VI) in a heat-killed suspension of biogenic magnetite (x = 0.43). X-ray absorption and Mössbauer spectroscopy results indicate that reduction of U(VI) to U(IV) is coupled to oxidation of Fe(2+) in magnetite. The addition of aqueous Fe(2+) to suspensions of oxidized magnetite resulted in reduction of U(VI) to UO(2), consistent with our previous finding that Fe(2+) taken up from solution increased the magnetite stoichiometry. Our results suggest that magnetite stoichiometry and the ability of aqueous Fe(2+) to recharge magnetite are important factors in reduction of U(VI) in the subsurface. PMID:22148359

  6. Nuclear quadrupole alignment of 176Lum and 177Lu in a lutetium single crystal at low temperatures and systematics of electric field gradients in pure hexagonal transition metals

    Microsoft Academic Search

    H. Ernst; E. Hagn; E. Zech; G. Eska

    1979-01-01

    The quadrupole frequencies for 176Lum and 177Lu nuclei in a Lu single crystal have been determined by nuclear orientation at temperatures down to 6 mK as -128(16) MHz and +294(37) MHz, respectively. From the observed gamma anisotropies several gamma-ray multipole mixing ratios could be derived. With the known ground-state quadrupole moment of Q=3.39(2) b for 177Lu the electric field gradient

  7. Pure low-frequency flexural mode of [011]c poled relaxor-PbTiO3 single crystals excited by k32 mode

    E-print Network

    Cao, Wenwu

    Gang Liu, Wenhua Jiang, Jiaqi Zhu, and Wenwu Cao Citation: Appl. Phys. Lett. 100, 213501 (2012); doi/2)O3­Pb(Mg1/3Nb2/3)O3­PbTiO3 single crystals J. Appl. Phys. 112, 126102 (2012) Influence of electric mode Gang Liu,1,2 Wenhua Jiang,2 Jiaqi Zhu,1 and Wenwu Cao2,a) 1 Center for Composite Materials, Harbin

  8. Crystal Phases, Defects, and Dynamics of Adsorbed Hydroxyl Groups and Water in Pure and Lanthanide-Modified Zirconia: A Neutron-Scattering Study

    Microsoft Academic Search

    C. K. Loong; J. W. Jr. Richardson; Masakuni Ozawa

    1995-01-01

    The role of lanthanide doping in zirconia as a means of stabilizing and promoting catalytic reactions was studied by neutron spectroscopy. The crystal structure of high-surface-area Ln0.1Zr0.9O1.95 (Ln = La and Nd) powders prepared by a coprecipitation method were found to be composed of mixed phases of tetragonal and cubic symmetry, which can be stabilized over a temperature range (up

  9. Charge ordering and ferroelectricity in magnetite

    NASA Astrophysics Data System (ADS)

    Khomskii, Daniel

    2007-03-01

    Magnetite Fe3O4 is one of the most fascinating material in solid state physics. Besides being the first magnetic material known to the mankind, it is also the first example of an insulator-metal transition in transition metal oxides -- the famous Verwey transition [1]. One usually connects this transition with the charge ordering of Fe^2+ and Fe^3+. However the detailed pattern of CO in Fe3O4 is still a matter of debate. Another aspect, which is not so widely known and which did not yet receive sufficient attention, is that below TV, besides being completely spin polarised, magnetite apparently is also ferroelectric (FE) [2]. Thus it seems that magnetite, besides being the first magnetic material and the first transition metal oxide with an insulator-metal transition, is also the first multiferroic material. Using the idea of a coexistence of site-centred and bond-centred charge ordering [3], I suggest a novel type of ordering in magnetite which explains the observed FE in Fe3O4 and which agrees with the structural data. [1] Verwey E.J.W., Nature 144, 327 (1939) [2] Rado G.T. and Ferrari J.M., Phys.Rev.B 12, 5166 (1975); Kato K. and Iida S., J.Phys.Soc.Japan 50, 2844 (1981) [3] Efremov D.V., van den Brink J. and Khomskii D.I., Nature Mater. 3, 853 (2004)

  10. Biogenic magnetite in the nematode Caenorhabditis

    E-print Network

    Dunin-Borkowski, Rafal E.

    is a soil nematode of ca. 1 mm in length, which is readily grown in culture on a diet of bac- teria, usuallyBiogenic magnetite in the nematode Caenorhabditis elegans Charles G. Cranfield1 , Adam Dawe2.04.04; Published online 28.06.04 The nematode Caenorhabditis elegans is widely used as a model system in biological

  11. The metal-insulator transition in magnetite.

    NASA Technical Reports Server (NTRS)

    Cullen, J. R.; Callen, E.

    1972-01-01

    We describe an electronic model for the low temperature transition in magnetite, in which the average number of electrons on a site is non-integral. The solution of the one-dimensional problem is reviewed, and the connection of the model with the Verwey ordering is discussed. Some of the implication of the three dimensional problem are discussed.

  12. Self-assembly of liquid crystal block copolymer PEG-b-smectic polymer in pure state and in dilute aqueous solution

    E-print Network

    B. Xu; R. Pinol; M. Nono-Djamen; S. Pensec; P. Keller; P. -A. Albouy; D. Levy; M. -H. Li

    2009-09-03

    A series of amphiphilic LC block copolymers, in which the hydrophobic block is a smectic polymer poly(4-methoxyphenyl 4-(6-acryloyloxy-hexyloxy)-benzoate) (PA6ester1) and the hydrophilic block is polyethyleneglycol (PEG), were synthesized and characterized. The self-assembly of one of them in both the pure state and the dilute aqueous solution was investigated in detail. Nano-structures in the pure state were studied by SAXS and WAXS on samples aligned by a magnetic field. A hexagonal cylindrical micro-segregation phase was observed with a lattice distance of 11.2 nm. The PEG blocks are in the cylinder, while the smectic polymer blocks form a matrix with layer spacing 2.4 nm and layer normal parallel to the long axis of the cylinders. Faceted unilamellar polymer vesicles, polymersomes, were formed in water, as revealed by cryo-TEM. In the lyotropic bilayer membrane of these polymersomes, the thermotropic smectic order in the hydrophobic block is clearly visible with layer normal parallel to the membrane surface.

  13. Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

    NASA Astrophysics Data System (ADS)

    Kaur, Maninder; Jiang, Weilin; Qiang, You; Burks, Edward C.; Liu, Kai; Namavar, Fereydoon; McCloy, John S.

    2014-11-01

    Iron oxide films were produced using ion-beam-assisted deposition, and Raman spectroscopy and x-ray diffraction indicate single-phase magnetite. However, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite, suggesting greater than normal disorder. Low temperature magnetometry and first-order reversal curve measurements show strong exchange bias, which likely arises from defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples contain grains ˜6 nm, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field.

  14. Exchange bias in polycrystalline magnetite films made by ion-beam assisted deposition

    SciTech Connect

    Kaur, Maninder; Qiang, You [Department of Physics, University of Idaho, Moscow, Idaho 83844 (United States); Jiang, Weilin [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Burks, Edward C.; Liu, Kai [Department of Physics, University of California, Davis, California 95616 (United States); Namavar, Fereydoon [University of Nebraska Medical Center, Omaha, Nebraska 68198 (United States); McCloy, John S. [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington 98163 (United States)

    2014-11-07

    Iron oxide films were produced using ion-beam-assisted deposition, and Raman spectroscopy and x-ray diffraction indicate single-phase magnetite. However, incorporation of significant fractions of argon in the films from ion bombardment is evident from chemical analysis, and Fe/O ratios are lower than expected from pure magnetite, suggesting greater than normal disorder. Low temperature magnetometry and first-order reversal curve measurements show strong exchange bias, which likely arises from defects at grain boundaries, possibly amorphous, creating frustrated spins. Since these samples contain grains ?6?nm, a large fraction of the material consists of grain boundaries, where spins are highly disordered and reverse independently with external field.

  15. Occurrence of gigantic biogenic magnetite during the Paleocene-Eocene Thermal Maximum

    NASA Astrophysics Data System (ADS)

    Schumann, D.; Raub, T. D.; Kopp, R. E.; Guerquin-Kern, J. L.; Wu, T. D.; Rouiller, I.; Smirnov, A. V.; Sears, S. K.; Lücken, U.; Tikoo, S. M.; Hesse, R.; Kirschvink, J. L.; Vali, H.

    2009-04-01

    The Paleocene-Eocene Thermal Maximum (PETM) is one of the most severe climatic events of the Cenozoic Era. A massive injection of light carbon into the oceans and atmosphere over a few thousand of years triggered drastic perturbation of Earth's climate resulting in abrupt global warming of ~5-9oC [Sluijs et al., 2007] that persisted for ~180,000 years. This episode is marked by the diversification and radiation of terrestrial plants and mammals while in the marine realm numerous deep-sea benthic foraminifera species disappeared and new forms evolved. Sediments deposited during the PETM are clay-rich and contain distinct evidence of these climatic changes. Kopp et al., (2007) and Lippert & Zachos (2007) report an extraordinary magnetofossil ‘Lagerstätte' in lowermost Eocene kaolinite-rich clay sediments deposited at subtropical paleolatitude in the Atlantic Coastal Plain of New Jersey, USA. Magnetofossils are magnetic particles produced most abundantly by magnetotactic bacteria. Kopp et al. (2007) and Lippert & Zachos (2007) used ferromagnetic resonance (FMR) spectroscopy, other rock magnetic methods, and transmission electron microscopy (TEM) of magnetic separates to characterize sediments from boreholes at Ancora (ODP Leg 174AX) and Wilson Lake, NJ, respectively. These sediments contain abundant ~40- to 300-nm cuboidal, elongate-prismatic and bullet-shaped magnetofossils, sometimes arranged in short chains, resembling crystals in living magnetotactic bacteria. Despite the scarcity of intact magnetofossil chains, the asymmetry ratios of the FMR spectra reflects a profusion of elongate single domain (SD) crystals and/or chains. Here we address both conundrums by reporting the discovery from these same sediments of exceptionally large and novel biogenic magnetite crystals unlike any previously reported from living organisms or from sediments. Aside from abundant bacterial magnetofossils, electron microscopy reveals novel spearhead-like and spindle-like magnetite crystals up to 4 ?m long (eight times larger than magnetite produced by magnetotactic bacteria) and elongated hexaoctahedra up to 1.4 ?m long. Similar to magnetite produced by magnetotactic bacteria, these single-crystal particles exhibit chemical composition and lattice perfection consistent with a biogenic origin. The oxygen isotopic composition of indiviual particles supports a low temperature aquatic origin. Electron holography indicates single-domain magnetization despite the large crystal size. In a few cases, we observed apparently intact, tip-outward spherical assemblages of spearhead-like particles that possibly represent the preserved original biological arrangement of these crystals in a hitherto unknown magnetite producing organism. The discovery of these exceptionally large biogenic magnetite crystals that possibly represent the remains of a new microorganism that appeared and disappeared with the PETM sheds some light upon the ecological response to biogeochemical changes that occurred during this warming event. The abundance of fossil magnetotactic bacteria on the Atlantic Coastal Plain during the PETM could be explained by enhanced production, enhanced preservation, or both. The presence of novel magnetofossils, however, argues that changes in growth conditions are a major part of the explanation. Considering that other bacterial magnetofossils are present (although less abundant) and well-preserved in sediments below and above the PETM clay, as well as in a sand lens within the PETM clay [Kopp et al., 2007], suggests that the new magnetofossils are unlikely to be a preservation artefact. We conclude, therefore, that the development of a thick suboxic zone with high iron bioavailability - a product of dramatic changes in weathering and sedimentation patterns driven by severe global warming - resulted in diversification of magnetite-forming organisms, likely including eukaryotes. In this study we extended the search for these new magnetofossils [Schumann et al. 2008] to other PETM locations of the Atlantic margin and to a possible modern

  16. The magnetosome membrane protein, MmsF, is a major regulator of magnetite biomineralization in Magnetospirillum magneticum AMB-1

    PubMed Central

    Murat, Dorothée; Falahati, Veesta; Bertinetti, Luca; Csencsits, Roseann; Körnig, André; Downing, Kenneth; Faivre, Damien; Komeili, Arash

    2013-01-01

    Summary Magnetotactic bacteria (MTB) use magnetosomes, membrane bound crystals of magnetite or greigite, for navigation along geomagnetic fields. In Magnetospirillum magneticum sp. AMB-1, and other MTB, a magnetosome gene island (MAI) is essential for every step of magnetosome formation. An 8-gene region of the MAI encodes several factors implicated in control of crystal size and morphology in previous genetic and proteomic studies. We show that these factors play a minor role in magnetite biomineralization in vivo. In contrast, MmsF, a previously uncharacterized magnetosome membrane protein encoded within the same region plays a dominant role in defining crystal size and morphology and is sufficient for restoring magnetite synthesis in the absence of the other major biomineralization candidates. In addition, we show that the 18 genes of the mamAB gene cluster of the MAI are sufficient for the formation of an immature magnetosome organelle. Addition of MmsF to these 18 genes leads to a significant enhancement of magnetite biomineralization and an increase in the cellular magnetic response. These results define a new biomineralization protein and lay down the foundation for the design of autonomous gene cassettes for the transfer of the magnetic phenotype in other bacteria. PMID:22716969

  17. An experimental study of the mechanism of the replacement of magnetite by pyrite up to 300 °C

    NASA Astrophysics Data System (ADS)

    Qian, Gujie; Brugger, Joël; Skinner, William M.; Chen, Guorong; Pring, Allan

    2010-10-01

    We present the results of an experimental study into the sulfidation of magnetite to form pyrite/marcasite under hydrothermal conditions (90-300 °C, vapor saturated pressures), a process associated with gold deposition in a number of ore deposits. The formation of pyrite/marcasite was studied as a function of reaction time, temperature, pH, sulfide concentration, solid-weight-to-fluid-volume ratio, and geometric surface area of magnetite in polytetrafluoroethylene-lined autoclaves (PTFE) and a titanium and stainless steel flow-through cell. Marcasite was formed only at pH 21°C <4 and was the dominant Fe disulfide at pH 21°C 1.11, while pyrite predominated at pH 21°C >2 and formed even under basic conditions (up to pH 21°C 12-13). Marcasite formation was favored at higher temperatures. Fine-grained pyrrhotite formed in the initial stage of the reaction together with pyrite in some experiments with large surface area of magnetite (grain size <125 ?m). This pyrrhotite eventually gave way to pyrite. The transformation rate of magnetite to Fe disulfide increased with decreasing pH (at 120 °C; pH 120°C 0.96-4.42), and that rate of the transformation increased from 120 to 190 °C. Scanning electron microscope (SEM) imaging revealed that micro-pores (0.1-5 ?m scale) existed at the reaction front between the parent magnetite and the product pyrite, and that the pyrite and/or marcasite were euhedral at pH 21°C <4 and anhedral at higher pH. The newly formed pyrite was micro-porous (0.1-5 ?m); this micro-porosity facilitates fluid transport to the reaction interface between magnetite and pyrite, thus promoting the replacement reaction. The pyrite precipitated onto the parent magnetite was polycrystalline and did not preserve the crystallographic orientation of the magnetite. The pyrite precipitation was also observed on the PTFE liner, which is consistent with pyrite crystallizing from solution. The mechanism of the reaction is that of a dissolution-reprecipitation reaction with the precipitation of pyrite being the rate-limiting step relative to magnetite dissolution under mildly acidic conditions (e.g., pH 155°C 4.42). The experimental results are in good agreement with sulfide phase assemblage and textures reported from sulfidized Banded Iron Formations: pyrite, marcasite and pyrrhotite have been found to exist or co-exist in different sulfidized Banded Iron Formations, and the microtextures show no evidence of sub-?m-scale pseudomorphism of magnetite by pyrite.

  18. Remanent and Induced Magnetic Anomalies over the Bjerkreim-Sokndal Layered Intrusion: Effects from Crystal Fractionation and Magma Recharge

    NASA Astrophysics Data System (ADS)

    McEnroe, S. A.; Brown, L. L.; Robinson, P.

    2013-12-01

    The Bjerkreim-Sokndal (BKS) norite-quartz mangerite layered intrusion is part of the early Neoproterozoic Rogaland Anorthosite Province intruded into the Fennoscandian shield in south Norway at ~930 Ma. The BKS is exposed over an area of 230 km2 with a thickness of ~7000m and is of economic interest for hemo-ilmenite, magnetite and apatite deposits. From the point of view of magnetic minerals, in the course of fractional crystallization and magma evolution, the ilmenite becomes less Fe3+-rich reflected by a change from ilmenite with hematite exsolution to nearly pure ilmenite. Magnetite starts to crystallize relatively late in the intrusive history, but its crystallization is interrupted by influxes of more primitive magma containing hemo-ilmenite. The variations in aeromagnetic and ground-magnetic anomalies measured over the BKS can be explained in terms of the magnetic properties of NRM, susceptibility, and hysteresis. Magnetic properties are correlated with the oxide mineralogy and mineral chemistry. Early layers in the intrusion contain hemo-ilmenite. As the magma evolved and magnetite started to crystallize, this caused a distinct change over the layering from remanence-controlled negative anomalies to induced positive anomalies. When new, more primitive magma was injected into the system, hemo-ilmenite returned as the major oxide and the resulting magnetic anomalies are again negative. The most dramatic change in the magnetic signature is in the upper part of the intrusion in MCU IVe, where magnetite became a well established cumulate phase as indicated by susceptibility, but its induced magnetization is overcome by large NRM's associated either with hemo-ilmenite or with hemo-ilmenite and magnetite exsolved from pyroxenes. The average natural remanent magnetizations change from ~3 A/m in MCU IVd, to 15 A/m in MCU IVe, and back to 2 A/m in the overlying MCU IVf, producing a strong negative remanent anomaly that has been followed along strike for at least 20 km by ground-magnetic measurements. The highly varied magnetic properties of this intrusion, caused by varied magmatic crystallization of combinations of oxide minerals illustrate some of the possibilities to be considered in evaluating crustal magnetic anomalies.

  19. crystal

    NASA Astrophysics Data System (ADS)

    Bai, Fen; Wang, Qingpu; Tao, Xutang; Li, Ping; Zhang, Xingyu; Liu, Zhaojun; Shen, Hongbin; Lan, Weixia; Gao, Liang; Gao, Zeliang; Zhang, Junjie; Fang, Jiaxiong

    2014-08-01

    An eye-safe Raman laser is realized with BaTeMo2O9 (BTM) nonlinear crystal for the first time. By using a diode-end-pumped acousto-optically Q-switched Nd:YVO4 laser as the pumping source, the BTM crystal converts the fundamental laser at 1,342 nm to first-Stokes laser at 1,531 nm successfully. With an incident power of 10.8 W and a pulse repetition rate of 25 kHz, the average output power at 1,531 nm is obtained to be 0.83 W, corresponding to a diode-to-Stokes conversion efficiency of 7.7 %. The pulse width is 11 ns, and the peak power is 3.0 kW.

  20. In-depth investigation of EPR spectra of Mn(2+) ions in ZnS single crystals with pure cubic structure.

    PubMed

    Nistor, S V; Stefan, M

    2009-04-01

    The X (9.8 GHz)-band electron paramagnetic resonance (EPR) properties of substitutional Mn(2+) ions in high quality cubic ZnS single crystals grown from PbCl(2) flux have been thoroughly investigated. Accurate spin Hamiltonian (SH) parameters: g = 2.002?25 ± 0.000?06; a = (7.987 ± 0.008) × 10(-4) cm(-1) and A = -(63.88 ± 0.02) × 10(-4) cm(-1) were obtained by simulation and fitting to the experimentally allowed transitions recorded for the magnetic field aligned within ± 0.25° along the main crystal axes. The normally forbidden hyperfine [Formula: see text], ?m = ± 1 transitions were also observed. Their position was found to be in agreement, within the experimental accuracy of ?H = ± 0.01 mT, with calculations using the same SH parameters. The angular variation of the ratios of the intensities of the central forbidden to the allowed transitions could be accounted for only by including an additional constant contribution. The observed line broadening of the [Formula: see text] and [Formula: see text] fine structure transitions and their line width variation in a (110) plane have been quantitatively described by considering a random distribution of lattice strains at the Mn(2+) impurity ions. The influence of the forbidden transitions and line broadening on the EPR spectra line shape of the Mn(2+) ions in cubic ZnS crystalline powders is also examined. PMID:21825339

  1. Hexagonal Platelet-like Magnetite as a Biosignature of Thermophilic Iron-Reducing Bacteria and Its Applications to the Exploration of the Modern Deep, Hot Biosphere and the Emergence of Iron-Reducing Bacteria in Early Precambrian Oceans

    PubMed Central

    2012-01-01

    Abstract Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120?nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. Key Words: Biosignatures—Magnetite—Iron-reducing bacteria—Deep subsurface biosphere—Banded iron formation. Astrobiology 12, 1100–1108. PMID:23145573

  2. Habits of Magnetosome Crystals in Coccoid Magnetotactic Bacteria

    Microsoft Academic Search

    Ulysses Lins; Martha R. McCartney; Marcos Farina; Richard B. Frankel; Peter R. Buseck

    2005-01-01

    High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control. Magnetotactic bacteria (MB) contain magnetosomes com- prising nanoscale magnetic iron mineral crystals in membrane vesicles

  3. The oxidation state and microstructural environment of transition metals (V, Co, and Ni) in magnetite: an XAFS study

    NASA Astrophysics Data System (ADS)

    Liang, Xiaoliang; He, Zisen; Tan, Wei; Liu, Peng; Zhu, Jianxi; Zhang, Jing; He, Hongping

    2014-12-01

    Transition metal-substituted magnetite minerals have attracted increasing attention for their wide application in industry and environmental protection. In this study, the valence and atomic environment of some substituting metals in magnetites (Fe3-x M x O4, M = V, Co, and Ni) were investigated using X-ray absorption fine structure spectroscopy. The results deduced from X-ray absorption near-edge structure spectroscopy indicated that the valences of V, Co, and Ni in Fe3-x M x O4 were +3, +2, and +2, respectively. The valences did not change as the substitution extent increased. Extended X-ray absorption fine structure spectroscopy suggested that the substituting cations occupied octahedral sites in the magnetite structure. The M-O and M-M/Fe distances were consistent with the Feoct-O and Feoct-Fe distances, respectively, in the magnetite (Fe3O4) structure. The occupancy of the substituting cations was assessed by crystal-field theory. We also considered the relationship between the chemical environment of substituting cations and their effects on the physicochemical properties of magnetite, including thermal stability, surface properties, and catalytic reactivity.

  4. Field-dependent anisotropic magnetoresistance and planar Hall effect in epitaxial magnetite thin films

    NASA Astrophysics Data System (ADS)

    Naftalis, N.; Kaplan, A.; Schultz, M.; Vaz, C. A. F.; Moyer, J. A.; Ahn, C. H.; Klein, L.

    2011-09-01

    A systematic study of the temperature and magnetic field dependence of the longitudinal and transverse resistivities of epitaxial thin films of magnetite (Fe3O4) is reported. The anisotropic magnetoresistance (AMR) and the planar Hall effect are sensitive to the in-plane orientation of current and magnetization with respect to crystal axes in a way consistent with the cubic symmetry of the system. We also show that the AMR exhibits a sign reversal as a function of temperature, and that it shows significant field dependence without saturation up to 9 T. Our results provide a unified description of the anisotropic magnetoresistance effects in epitaxial magnetite films and illustrate the need for a full determination of the resistivity tensor in crystalline systems.

  5. Quantifying magnetite magnetofossil contributions to sedimentary magnetizations

    NASA Astrophysics Data System (ADS)

    Heslop, David; Roberts, Andrew P.; Chang, Liao; Davies, Maureen; Abrajevitch, Alexandra; De Deckker, Patrick

    2013-11-01

    Under suitable conditions, magnetofossils (the inorganic remains of magnetotactic bacteria) can contribute to the natural remanent magnetization (NRM) of sediments. In recent years, magnetofossils have been shown to be preserved commonly in marine sediments, which makes it essential to quantify their importance in palaeomagnetic recording. In this study, we examine a deep-sea sediment core from offshore of northwestern Western Australia. The magnetic mineral assemblage is dominated by continental detritus and magnetite magnetofossils. By separating magnetofossil and detrital components based on their different demagnetization characteristics, it is possible to quantify their respective contributions to the sedimentary NRM throughout the Brunhes chron. In the studied core, the contribution of magnetofossils to the NRM is controlled by large-scale climate changes, with their relative importance increasing during glacial periods when detrital inputs were low. Our results demonstrate that magnetite magnetofossils can dominate sedimentary NRMs in settings where they are preserved in significant abundances.

  6. Encapsulated magnetite particles for biomedical application

    NASA Astrophysics Data System (ADS)

    Landfester, Katharina; Ramírez, Liliana P.

    2003-04-01

    The process of miniemulsification allows the generation of small, homogeneous, and stable droplets containing monomer or polymer precursors and magnetite which are then transferred by polymer reactions to the final polymer latexes, keeping their particular identity without serious exchange kinetics involved. It is shown that the miniemulsion process can excellently be used for the formulation of polymer-coated magnetic nanoparticles which can further be used for biomedical applications. The use of high shear, appropriate surfactants, and the addition of a hydrophobe in order to suppress the influence of Ostwald ripening are key factors for the formation of the small and stable droplets in miniemulsion and will be discussed. Two different approaches based on miniemulsion processes for the encapsulation of magnetite into polymer particles will be presented in detail.

  7. Experimental Shock Decomposition of Siderite to Magnetite

    NASA Technical Reports Server (NTRS)

    Bell, M. S.; Golden, D. C.; Zolensky, M. E.

    2005-01-01

    The debate about fossil life on Mars includes the origin of magnetites of specific sizes and habits in the siderite-rich portions of the carbonate spheres in ALH 84001 [1,2]. Specifically [2] were able to demonstrate that inorganic synthesis of these compositionally zoned spheres from aqueous solutions of variable ion-concentrations is possible. They further demonstrated the formation of magnetite from siderite upon heating at 550 C under a Mars-like CO2-rich atmosphere according to 3FeCO3 = Fe3O4 + 2CO2 + CO [3] and they postulated that the carbonates in ALH 84001 were heated to these temperatures by some shock event. The average shock pressure for ALH 84001, substantially based on the refractive index of diaplectic feldspar glasses [3,4,5] is some 35-40 GPa and associated temperatures are some 300-400 C [4]. However, some of the feldspar is melted [5], requiring local deviations from this average as high as 45-50 GPa. Indeed, [5] observes the carbonates in ALH 84001 to be melted locally, requiring pressures in excess of 60 GPa and temperatures > 600 C. Combining these shock studies with the above inorganic synthesis of zoned carbonates it seems possible to produce the ALH 84001 magnetites by the shock-induced decomposition of siderite.

  8. Hybrid DFT calculation of Fe57 NMR resonances and orbital order in magnetite

    NASA Astrophysics Data System (ADS)

    Patterson, C. H.

    2014-08-01

    The crystal structure and charge and orbital order of magnetite below the Verwey temperature are calculated using a first-principles hybrid density functional theory (DFT) method. The initial atomic positions in the crystal-structure calculation are those recently refined from x-ray diffraction data for the Cc space-group unit cell [Senn, Wright, and Attfield, Nature (London) 481, 173 (2012), 10.1038/nature10704]. Fermi contact and magnetic dipolar contributions to hyperfine fields at Fe57 nuclei obtained from hybrid DFT calculations are used to obtain NMR resonance frequencies for magnetite for a range of external magnetic field directions in a relatively weak field. NMR frequencies from hybrid density functional theory calculations are compared to NMR data [M. Mizoguchi, J. Phys. Soc. Jpn. 70, 2333 (2001), 10.1143/JPSJ.70.2333] for a range of applied magnetic field directions. NMR resonance frequencies of B-site Fe ions show large relative variations with applied field direction owing to anisotropic hyperfine fields from charge and orbital ordered Fe 3d minority-spin electrons at those sites. Good agreement between computed and measured NMR resonance frequencies confirms the pattern of charge and orbital order obtained from calculations. The charge and orbital order of magne-tite in its low-temperature phase obtained from hybrid DFT calculations is analyzed in terms of one-electron bonds between Fe ions. The Verwey transition in magnetite therefore resembles Mott-Peierls transitions in vanadium oxides which undergo symmetry-breaking transitions owing to electron-pair bond formation.

  9. Disappearing Crystals

    NSDL National Science Digital Library

    2012-06-26

    Learners experiment with water gel crystals, or sodium polyacrylate crystals, which absorb hundreds of times their weight in water. When in pure water, the water gel crystals cannot be seen. However, when learners place the crystals in solutions of Splenda and water, the crystals can be seen. Learners use this property to determine how much Splenda is in 4 different cups of water. This is one of four activities learners can complete related to PhysicsQuest 2008. Each activity gives a clue to solve a puzzle in the accompanying comic book, "Nikola Tesla and the Electric Fair."

  10. Functional Analysis of the Magnetosome Island in Magnetospirillum gryphiswaldense: The mamAB Operon Is Sufficient for Magnetite Biomineralization

    PubMed Central

    Lohße, Anna; Ullrich, Susanne; Katzmann, Emanuel; Borg, Sarah; Wanner, Gerd; Richter, Michael; Voigt, Birgit; Schweder, Thomas; Schüler, Dirk

    2011-01-01

    Bacterial magnetosomes are membrane-enveloped, nanometer-sized crystals of magnetite, which serve for magnetotactic navigation. All genes implicated in the synthesis of these organelles are located in a conserved genomic magnetosome island (MAI). We performed a comprehensive bioinformatic, proteomic and genetic analysis of the MAI in Magnetospirillum gryphiswaldense. By the construction of large deletion mutants we demonstrate that the entire region is dispensable for growth, and the majority of MAI genes have no detectable function in magnetosome formation and could be eliminated without any effect. Only <25% of the region comprising four major operons could be associated with magnetite biomineralization, which correlated with high expression of these genes and their conservation among magnetotactic bacteria. Whereas only deletion of the mamAB operon resulted in the complete loss of magnetic particles, deletion of the conserved mms6, mamGFDC, and mamXY operons led to severe defects in morphology, size and organization of magnetite crystals. However, strains in which these operons were eliminated together retained the ability to synthesize small irregular crystallites, and weakly aligned in magnetic fields. This demonstrates that whereas the mamGFDC, mms6 and mamXY operons have crucial and partially overlapping functions for the formation of functional magnetosomes, the mamAB operon is the only region of the MAI, which is necessary and sufficient for magnetite biomineralization. Our data further reduce the known minimal gene set required for magnetosome formation and will be useful for future genome engineering approaches. PMID:22043287

  11. Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites

    NASA Astrophysics Data System (ADS)

    Marquez-Linares, F.; Uwakweh, O. N. C.; Lopez, N.; Chavez, E.; Polanco, R.; Morant, C.; Sanz, J. M.; Elizalde, E.; Neira, C.; Nieto, S.; Roque-Malherbe, R.

    2011-03-01

    The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Mössbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications.

  12. Deformation microstructures and magnetite texture development in synthetic shear zones

    NASA Astrophysics Data System (ADS)

    Till, Jessica L.; Moskowitz, Bruce M.

    2014-08-01

    We present observations of deformation features in magnetite from synthetic magnetite-bearing silicate aggregates deformed between 1000 °C and 1200 °C in transpressional shear experiments with strains of up to 300%. Anisotropy of magnetic susceptibility and shape preferred orientation (SPO) analysis were combined with electron backscatter diffraction (EBSD) to characterize the magnetite deformation fabrics and intragrain microstructures. Crystallographic preferred orientation (CPO) in magnetite is very weak in all deformed samples and does not vary as a function of either temperature or shear strain. Magnetic anisotropy and SPO increase strongly with both strain and deformation temperature and indicate that strain partitioning between magnetite and the plagioclase matrix decreases at higher temperatures. EBSD orientation mapping of individual magnetite particles revealed substantial dispersions in intragrain orientation, analogous to undulose extinction, after deformation at 1000 and 1100 °C, indicating that dislocation creep processes were active in magnetite despite the lack of a well-developed CPO. Geometrical analysis of crystallographic orientation dispersions from grain map data indicates that low-angle grain boundary formation in magnetite could have been accommodated by slip on {110} or {100} planes, but no evidence for dominant slip on the expected {111} planes was found. Evidence for activation of multiple slip systems was seen in some magnetite grains and could be partially responsible for the lack of CPO in magnetite. These results suggest that, at least in polyphase rocks, crystallographic textures in magnetite may be inherently weak or slow to develop and CPO alone is not an adequate indicator of magnetite deformation mechanisms. These results may aid in the interpretation of deformation textures in other spinel-structured phases such as chromite and ringwoodite.

  13. Electrodeposition of copper–magnetite magnetic composite films

    Microsoft Academic Search

    A. Roldan; E. Gómez; S. Pané; E. Vallés

    2007-01-01

    Electrodeposition was demonstrated to be useful for the preparation of copper–magnetite magnetic composites. An acidic bath\\u000a was tested for the incorporation of nanometric magnetite (Fe3O4) particles into an electrodeposited copper matrix. Cationic surfactant (dodecyltrimethylammonium chloride—DTAC) was used\\u000a to keep particles suspended in the electrolyte as well as to assist magnetite incorporation. The influence of several parameters\\u000a (bath temperature, deposition technique,

  14. Zinc and Arsenic Immobilization and Magnetite Formation Upon Maghemite Reduction by Shewanella putrefaciens ATCC 8071

    NASA Astrophysics Data System (ADS)

    Cismasu, C.; Ona-Nguema, G.; Bonnin, D.; Menguy, N.; Brown, G. E.

    2007-12-01

    Dissimilatory reduction of ferric iron oxides is recognized as an important component of the iron biogeochemical cycle, causing the dissolution of iron oxide minerals and the possible formation of Fe(II)-bearing minerals such as magnetite, green rusts, siderite, etc. These mineralogical transformations affect the mobility of surface- associated toxic metal(loid)s, which may be released into solution, adsorbed, or incorporated into newly formed minerals. Maghemite (?-Fe2O3) is an iron oxide mineral that is found in certain tropical soils and as isolated deposits in more temperate regions. In these settings, maghemite may play an important role in the biogeochemical cycling of iron and of surface-associated trace metal(loids). However, the reduction of maghemite by iron-respiring bacteria, the impact of reductive dissolution on the release of associated contaminants, and the nature of biogenic Fe(II)-containing reaction products are not well documented. In the present study, we incubated samples of pure maghemite and As(V)- and Zn-adsorbed maghemite with an iron reducing bacterium, Shewanella putrefaciens strain ATCC 8071, in a batch system under anoxic conditions. As a result of Fe(III) bioreduction, all mineral suspensions turned from brown to black during the first hour of incubation, indicating the onset of magnetite formation. The presence of this mineral was confirmed by transmission Mössbauer spectroscopy at room temperature, which showed the formation of an almost stoichiometric magnetite. High-resolution transmission electron microscopy images indicate that the parent maghemite and the biogenic magnetite particles are octahedral in shape and of similar size (5 to 20 nm). The presence of 50 mg/L adsorbed Zn(II) did not affect the initial rate of iron reduction with respect to the Zn-free maghemite sample (0.62 mM Fe(II)/h and 0.66 mM Fe(II)/h, respectively). However, adsorption of 50 and 100 mg/L As(V) on maghemite decreased the initial iron reduction rate to 0.35 mM Fe(II)/h and 0.16 mM Fe(II)/h, respectively. Results show that before inoculation, the proportion of As(V) adsorbed on the maghemite surface is significantly higher (90%) than Zn(II) (50%) after a two-day equilibration period. During bioreduction, the remaining soluble zinc and arsenic content decreases progressively as a function of time, possibly as a result of coprecipitation or adsorption reactions on the newly formed biogenic magnetite. Overall, this study shows that magnetite formation induced by the bioreduction of maghemite is particularly effective for the removal of zinc and arsenic from solution.

  15. Magnetic properties of ilmenite-hematite single crystals from the Ecstall pluton near Prince Rupert, British Columbia

    Microsoft Academic Search

    Sarah J. Brownlee; Joshua M. Feinberg; Takeshi Kasama; Richard J. Harrison; Gary R. Scott; Paul R. Renne

    2011-01-01

    Single crystal magnetic properties affected by reheating in the Ecstall plutonEvidence for magnetite growth in reheated single crystals of ilmenite-hematitePaleomagnetic directions from eastern Ecstall pluton were reset during reheating

  16. Magnetic anisotropy modulation of magnetite in Fe{sub 3}O{sub 4}/BaTiO{sub 3}(100) epitaxial structures

    SciTech Connect

    Vaz, C. A. F.; Hoffman, J.; Posadas, A.-B.; Ahn, C. H. [Department of Applied Physics and CRISP, Yale University, New Haven, Connecticut 06520 (United States)

    2009-01-12

    Temperature dependent magnetometry and transport measurements on epitaxial Fe{sub 3}O{sub 4} films grown on BaTiO{sub 3}(100) single crystals by molecular beam epitaxy show a series of discontinuities, due to changes in the magnetic anisotropy induced by strain from the different crystal phases of BaTiO{sub 3}. The magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO{sub 3} at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with the magnetoelastic anisotropies. These results demonstrate the possibility of using the piezoelectric response of BaTiO{sub 3} to modulate the magnetic anisotropy of magnetite films.

  17. Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites

    SciTech Connect

    Marquez-Linares, F. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Uwakweh, O.N.C. [Engineering Science and Materials Department, College of Engineering, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9044 (Puerto Rico); Lopez, N. [Chemical Engineering Department, College of Engineering, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9000 (Puerto Rico); Chavez, E. [Physics Department, University of Puerto Rico-Mayagueez Campus, Mayaguez, PR 00681-9000 (Puerto Rico); Polanco, R. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Morant, C.; Sanz, J.M.; Elizalde, E. [Department of Applied Physics, C-XII, Universidad Autonoma de Madrid, Cantoblanco, 28049-Madrid (Spain); Neira, C.; Nieto, S. [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico); Roque-Malherbe, R., E-mail: RRoque@suagm.ed [Institute for Physical Chemical Applied Research, School of Science, University of Turabo, PO Box 3030, Gurabo, PR 00778-3030 (Puerto Rico)

    2011-03-15

    The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Moessbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications. -- Graphical abstract: A large amount of Lewis acid sites were found in the highly dispersed magnetite which is supported on the SWCNT outer surface. Display Omitted Research highlights: {yields} The obtained materials were completely characterized with XRD, Raman and SEM-TEM. {yields} DRIFT, TGA and adsorption of the composites allowed understand the material formation. {yields} This is the first report of a study of Lewis sites by Moessbauer spectroscopy.

  18. Ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites: diffusive exchange as a guide to cooling history

    NASA Astrophysics Data System (ADS)

    Valley, John W.; Graham, Colin M.

    1991-03-01

    Ion microprobe analysis of magnetites from the Adirondack Mountains, NY, yields oxygen isotope ratios with spatial resolution of 2 8 ?m and precision in the range of 1‰ (1 sigma). These analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of ?18O at this scale. High precision micro-analyses of this sort will permit wide-ranging new applications in stable isotope geochemistry. The analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite. Textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite. Magnetites are near to Fe3O4 in composition, and optically and chemically homogeneous. A combination of ion probe plus conventional BrF5 analysis shows that individual grains are homogeneous with ?18O=8.9±1‰ SMOW from the core to near the rim of 0.1 1.2 mm diameter grains. Depth profiling into crystal growth faces of magnetites shows that rims are 9‰ depleted in ?18O. These low ?18O values increase in smooth gradients across the outer 10 ?m of magnetite rims in contact with calcite. These are the sharpest intracrystalline gradients measured to date in geological materials. This discovery is confirmed by bulk analysis of 150 350 ?m diameter magnetites which average 1.2‰ lower in ?18O than coarse magnetites due to low ?18O rims. Conventional analysis of coexisting calcite yields °18O=18.19, suggesting that bulk ?18O (Cc-Mt)=9.3‰ and yielding an apparent equilibration “temperature” of 525° C, over 200° C below the temperature of regional metamorphism. Consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories. The data for oxygen in calcite under hydrothermal conditions at high P(H2O) indicates that diffusion is faster in magnetite and modelling of the low ?18O rims on magnetite would suggest that the Adirondacks experienced slow cooling after Grenville metamorphism, followed by a brief period of rapid cooling, possibly related to uplift. Conversely, the data for calcite at low P(H2O) show slower oxygen diffusion than in magnetite. Modelling based on these data is consistent with geochronology that shows slow cooling through the blocking temperature of both minerals, suggesting that the low ?18O rims form by exchange with late, low temperature fluids similar to those that infiltrated the rock to serpentinize monticellite and which infiltrated adjacent anorthosite to form late calcite veinlets. In either case, the ion microprobe results indicate that two distinct events are recorded in the post-metamorphic exchange history of these magnetites. Recognition of these events is only possible through microanalysis and has important implications for geothermometry.

  19. Genes Necessary for Bacterial Magnetite Biomineralization Identified by Transposon Mutagenesis

    NASA Astrophysics Data System (ADS)

    Nash, C. Z.; Komeili, A.; Newman, D. K.; Kirschvink, J. L.

    2004-12-01

    Magnetic bacteria synthesize nanoscale crystals of magnetite in intracellular, membrane-bounded organelles (magnetosomes). These crystals are preserved in the fossil record at least as far back as the late Neoproterozoic and have been tentatively identified in much older rocks (1). This fossil record may provide deep time calibration points for molecular evolution studies once the genes involved in biologically controlled magnetic mineralization (BCMM) are known. Further, a genetic and biochemical understanding of BCMM will give insight into the depositional environment and biogeochemical cycles in which magnetic bacteria play a role. The BCMM process is not well understood, though proteins have been identified from the magnetosome membrane and genetic manipulation and biochemical characterization of these proteins are underway. Most of the proteins currently thought to be involved are encoded within the mam cluster, a large cluster of genes whose products localize to the magnetosome membrane and are conserved among magnetic bacteria (2). In an effort to identify all of the genes necessary for bacterial BCMM, we undertook a transposon mutagenesis of Magnetospirillum magneticum AMB-1. Non-magnetic mutants (MNMs) were identified by growth in liquid culture followed by a magnetic assay. The insertion site of the transposon was identified two ways. First MNMs were screened with a PCR assay to determine if the transposon had inserted into the mam cluster. Second, the transposon was rescued from the mutant DNA and cloned for sequencing. The majority insertion sites are located within the mam cluster. Insertion sites also occur in operons which have not previously been suspected to be involved in magnetite biomineralization. None of the insertion sites have occurred within genes reported from previous transposon mutagenesis studies of AMB-1 (3, 4). Two of the non-mam cluster insertion sites occur in operons containing genes conserved particularly between MS-1 and MC-1. We are undertaking a complementation strategy to demonstrate the necessity of these novel genes in BCMM as well as characterizing the phenotypes of the mutants. 1. S. B. R. Chang, J. F. Stolz, J. L. Kirschvink, S. M. Awramik, Precambrian Res. 43, 305-315 (1989). 2. K. Grünberg, C. Wawer, B. M. Tebo, D. Schüler, Appl. Environ. Microbiol. 67, 4573-4582 (2001). 3. A. T. Wahyudi, H. Takeyama, T. Matsunaga, Appl. Biochem. Biotechnol. 91-3, 147-154 (2001). 4. T. Matsunaga, C. Nakamura, J. G. Burgess, K. Sode, J. Bacteriol. 174, 2748-2753 (1992).

  20. Fe atom exchange between aqueous Fe2+ and magnetite.

    PubMed

    Gorski, Christopher A; Handler, Robert M; Beard, Brian L; Pasakarnis, Timothy; Johnson, Clark M; Scherer, Michelle M

    2012-11-20

    The reaction between magnetite and aqueous Fe(2+) has been extensively studied due to its role in contaminant reduction, trace-metal sequestration, and microbial respiration. Previous work has demonstrated that the reaction of Fe(2+) with magnetite (Fe(3)O(4)) results in the structural incorporation of Fe(2+) and an increase in the bulk Fe(2+) content of magnetite. It is unclear, however, whether significant Fe atom exchange occurs between magnetite and aqueous Fe(2+), as has been observed for other Fe oxides. Here, we measured the extent of Fe atom exchange between aqueous Fe(2+) and magnetite by reacting isotopically "normal" magnetite with (57)Fe-enriched aqueous Fe(2+). The extent of Fe atom exchange between magnetite and aqueous Fe(2+) was significant (54-71%), and went well beyond the amount of Fe atoms found at the near surface. Mössbauer spectroscopy of magnetite reacted with (56)Fe(2+) indicate that no preferential exchange of octahedral or tetrahedral sites occurred. Exchange experiments conducted with Co-ferrite (Co(2+)Fe(2)(3+)O(4)) showed little impact of Co substitution on the rate or extent of atom exchange. Bulk electron conduction, as previously invoked to explain Fe atom exchange in goethite, is a possible mechanism, but if it is occurring, conduction does not appear to be the rate-limiting step. The lack of significant impact of Co substitution on the kinetics of Fe atom exchange, and the relatively high diffusion coefficients reported for magnetite suggest that for magnetite, unlike goethite, Fe atom diffusion is a plausible mechanism to explain the rapid rates of Fe atom exchange in magnetite. PMID:22577839

  1. Spin-Dependent Transport For Magnetite (Fe3O4) Thin Films On SiO2Glass, MgO And MgAl2O4 Substrates

    Microsoft Academic Search

    H. Kobori; D. Shimizu; A. Yamasaki; A. Sugimura; T. Taniguchi; H. Kawanaka; A. Ando; T. Shimizu

    2008-01-01

    Spin-dependent-transport was studied for magnetite (Fe3O4) thin films on SiO2-glass, MgO (100) and MgAl2O4 (100) single crystal substrates prepared by RF-magnetron sputtering. The magnetite thin film was found to be composed of nano-sized grains. The magnetoresistance is mainly dominated by the crystallinity of the thin film rather than the grain-size.

  2. Cryptic grain-scale heterogeneity of oxygen isotope ratios in metamorphic magnetite.

    PubMed

    Valley, J W; Graham, C M

    1993-03-19

    Oxygen isotope ratios measured by ion microprobe in magnetite from granulite-facies marble of the Adirondack Mountains, New York, range from +2 to +11 per mil (standard mean ocean water) across a single grain that measures 3 millimeters by 5 millimeters. Low values are concentrated in irregular domains near the grain boundary but also occur in the grain's interior. In contrast, grains 1 millimeter in diameter that are from a second nearby sample show no significant heterogeneity, except within 10 micrometers of the grain boundary. These data, including large gradients of up to 9 per mil per 10 micrometers, provide important new constraints on the nature and origins of intragrain isotopic heterogeneity and on oxygen isotope thermometry. The differences between these magnetite grains result from contrasting mechanisms of isotope exchange with fluids after the peak of regional metamorphism. Volume diffusion of oxygen through the crystal structure of magnetite contributed to isotope exchange in the rims of small grains, but larger grains are crosscut by healed cracks that are not readily detected and that short-circuited diffusion. PMID:17816891

  3. Hyperfine field and electronic structure of magnetite below the Verwey transition

    NASA Astrophysics Data System (ADS)

    ?ezní?ek, R.; Chlan, V.; Št?pánková, H.; Novák, P.

    2015-03-01

    Magnetite represents a prototype compound with a mixed valence of iron cations. Its structure and electron ordering below the Verwey transition have been studied for decades. A recently published precise crystallographic structure [Senn et al., Nature (London) 481, 173 (2012), 10.1038/nature10704] accompanied by a suggestion of a "trimeron" model has given a new impulse to magnetite research. Here we investigate hyperfine field anisotropy in the C c phase of magnetite by quantitative reanalysis of published measurements of the dependences of the 57Fe nuclear magnetic resonance frequencies on the external magnetic field direction. Further, ab initio density-functional-theory-based calculations of hyperfine field depending on the magnetization direction using the recently reported crystal structure are carried out, and analogous hyperfine anisotropy data linked to particular crystallographic sites are determined. These two sets of data are compared, and mutually matching groups of the iron B sites in the 8:5:3 ratio are found. Moreover, information on electronic structure is obtained from the ab initio calculations. Our results are compared with the trimeron model and with an alternative analysis [Patterson, Phys. Rev. B 90, 075134 (2014), 10.1103/PhysRevB.90.075134] as well.

  4. Hexagonal platelet-like magnetite as a biosignature of thermophilic iron-reducing bacteria and its applications to the exploration of the modern deep, hot biosphere and the emergence of iron-reducing bacteria in early precambrian oceans.

    PubMed

    Li, Yi-Liang

    2012-12-01

    Dissimilatory iron-reducing bacteria are able to enzymatically reduce ferric iron and couple to the oxidation of organic carbon. This mechanism induces the mineralization of fine magnetite crystals characterized by a wide distribution in size and irregular morphologies that are indistinguishable from authigenic magnetite. Thermoanaerobacter are thermophilic iron-reducing bacteria that predominantly inhabit terrestrial hot springs or deep crusts and have the capacity to transform amorphous ferric iron into magnetite with a size up to 120?nm. In this study, I first characterize the formation of hexagonal platelet-like magnetite of a few hundred nanometers in cultures of Thermoanaerobacter spp. strain TOR39. Biogenic magnetite with such large crystal sizes and unique morphology has never been observed in abiotic or biotic processes and thus can be considered as a potential biosignature for thermophilic iron-reducing bacteria. The unique crystallographic features and strong ferrimagnetic properties of these crystals allow easy and rapid screening for the previous presence of iron-reducing bacteria in deep terrestrial crustal samples that are unsuitable for biological detection methods and, also, the search for biogenic magnetite in banded iron formations that deposited only in the first 2 billion years of Earth with evidence of life. PMID:23145573

  5. Vibrational Spectroscopic Characterization of Hematite, Maghemite, and Magnetite Thin

    E-print Network

    Vibrational Spectroscopic Characterization of Hematite, Maghemite, and Magnetite Thin Films University, 100 West 18th Avenue, Columbus, Ohio 43210 ABSTRACT Thin films of three iron oxide polymorphs, hematite, maghemite, and magnetite, were produced on KBr substrates using a conventional electron beam

  6. College of Engineering Electromagnetically Enhanced Hydrocyclone for Magnetite Separation during

    E-print Network

    Demirel, Melik C.

    magnetite The current technology uses permanent magnet drum separators which achieve a 99.4% recovery rate, but pose a safety risk due to the constant magnetic field. The Spring 2011 team des electromagnetic of it has become important to recycle magnetite efficiently. The current technology uses permanent magnet

  7. Magnetic process for removing heavy metals from water employing magnetites

    DOEpatents

    Prenger, F. Coyne; Hill, Dallas D.; Padilla, Dennis D.; Wingo, Robert M.; Worl, Laura A.; Johnson, Michael D.

    2003-07-22

    A process for removing heavy metals from water is provided. The process includes the steps of introducing magnetite to a quantity of water containing heavy metal. The magnetite is mixed with the water such that at least a portion of, and preferably the majority of, the heavy metal in the water is bound to the magnetite. Once this occurs the magnetite and absorbed metal is removed from the water by application of a magnetic field. In most applications the process is achieved by flowing the water through a solid magnetized matrix, such as steel wool, such that the magnetite magnetically binds to the solid matrix. The magnetized matrix preferably has remnant magnetism, but may also be subject to an externally applied magnetic field. Once the magnetite and associated heavy metal is bound to the matrix, it can be removed and disposed of, such as by reverse water or air and water flow through the matrix. The magnetite may be formed in-situ by the addition of the necessary quantities of Fe(II) and Fe(III) ions, or pre-formed magnetite may be added, or a combination of seed and in-situ formation may be used. The invention also relates to an apparatus for performing the removal of heavy metals from water using the process outlined above.

  8. Magnetic process for removing heavy metals from water employing magnetites

    DOEpatents

    Prenger, F. Coyne; Hill, Dallas D.

    2006-12-26

    A process for removing heavy metals from water is provided. The process includes the steps of introducing magnetite to a quantity of water containing heavy metal. The magnetite is mixed with the water such that at least a portion of, and preferably the majority of, the heavy metal in the water is bound to the magnetite. Once this occurs the magnetite and absorbed metal is removed from the water by application of a magnetic field. In most applications the process is achieved by flowing the water through a solid magnetized matrix, such as steel wool, such that the magnetite magnetically binds to the solid matrix. The magnetized matrix preferably has remnant magnetism, but may also be subject to an externally applied magnetic field. Once the magnetite and associated heavy metal is bound to the matrix, it can be removed and disposed of, such as by reverse water or air and water flow through the matrix. The magnetite may be formed in-situ by the addition of the necessary quantities of Fe(II) and Fe(III) ions, or pre-formed magnetite may be added, or a combination of seed and in-situ formation may be used. The invention also relates to an apparatus for performing the removal of heavy metals from water using the process outlined above.

  9. No evidence for intracellular magnetite in putative vertebrate magnetoreceptors identified by magnetic screening

    PubMed Central

    Edelman, Nathaniel B.; Fritz, Tanja; Nimpf, Simon; Pichler, Paul; Lauwers, Mattias; Hickman, Robert W.; Papadaki-Anastasopoulou, Artemis; Ushakova, Lyubov; Heuser, Thomas; Resch, Guenter P.; Saunders, Martin; Shaw, Jeremy A.; Keays, David A.

    2015-01-01

    The cellular basis of the magnetic sense remains an unsolved scientific mystery. One theory that aims to explain how animals detect the magnetic field is the magnetite hypothesis. It argues that intracellular crystals of the iron oxide magnetite (Fe3O4) are coupled to mechanosensitive channels that elicit neuronal activity in specialized sensory cells. Attempts to find these primary sensors have largely relied on the Prussian Blue stain that labels cells rich in ferric iron. This method has proved problematic as it has led investigators to conflate iron-rich macrophages with magnetoreceptors. An alternative approach developed by Eder et al. [Eder SH, et al. (2012) Proc Natl Acad Sci USA 109(30):12022–12027] is to identify candidate magnetoreceptive cells based on their magnetic moment. Here, we explore the utility of this method by undertaking a screen for magnetic cells in the pigeon. We report the identification of a small number of cells (1 in 476,000) with large magnetic moments (8–106 fAm2) from various tissues. The development of single-cell correlative light and electron microscopy (CLEM) coupled with electron energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) permitted subcellular analysis of magnetic cells. This revealed the presence of extracellular structures composed of iron, titanium, and chromium accounting for the magnetic properties of these cells. Application of single-cell CLEM to magnetic cells from the trout failed to identify any intracellular structures consistent with biogenically derived magnetite. Our work illustrates the need for new methods to test the magnetite hypothesis of magnetosensation. PMID:25535350

  10. No evidence for intracellular magnetite in putative vertebrate magnetoreceptors identified by magnetic screening.

    PubMed

    Edelman, Nathaniel B; Fritz, Tanja; Nimpf, Simon; Pichler, Paul; Lauwers, Mattias; Hickman, Robert W; Papadaki-Anastasopoulou, Artemis; Ushakova, Lyubov; Heuser, Thomas; Resch, Guenter P; Saunders, Martin; Shaw, Jeremy A; Keays, David A

    2015-01-01

    The cellular basis of the magnetic sense remains an unsolved scientific mystery. One theory that aims to explain how animals detect the magnetic field is the magnetite hypothesis. It argues that intracellular crystals of the iron oxide magnetite (Fe3O4) are coupled to mechanosensitive channels that elicit neuronal activity in specialized sensory cells. Attempts to find these primary sensors have largely relied on the Prussian Blue stain that labels cells rich in ferric iron. This method has proved problematic as it has led investigators to conflate iron-rich macrophages with magnetoreceptors. An alternative approach developed by Eder et al. [Eder SH, et al. (2012) Proc Natl Acad Sci USA 109(30):12022-12027] is to identify candidate magnetoreceptive cells based on their magnetic moment. Here, we explore the utility of this method by undertaking a screen for magnetic cells in the pigeon. We report the identification of a small number of cells (1 in 476,000) with large magnetic moments (8-106 fAm(2)) from various tissues. The development of single-cell correlative light and electron microscopy (CLEM) coupled with electron energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) permitted subcellular analysis of magnetic cells. This revealed the presence of extracellular structures composed of iron, titanium, and chromium accounting for the magnetic properties of these cells. Application of single-cell CLEM to magnetic cells from the trout failed to identify any intracellular structures consistent with biogenically derived magnetite. Our work illustrates the need for new methods to test the magnetite hypothesis of magnetosensation. PMID:25535350

  11. Habits of Magnetosome Crystals in Coccoid Magnetotactic Bacteria

    PubMed Central

    Lins, Ulysses; McCartney, Martha R.; Farina, Marcos; Frankel, Richard B.; Buseck, Peter R.

    2005-01-01

    High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control. PMID:16085893

  12. Three-dimensional domain observations of magnetite and titanomagnetites using the dried colloid SEM method

    NASA Astrophysics Data System (ADS)

    Soffel, H. C.; Aumüller, C.; Hoffmann, V.; Appel, E.

    Dried colloid scanning electron microscopy (SEM) has been applied for the study of Bitter patterns on unpolished and uneven surfaces of microcrystals of natural ferrites (hydrothermally grown magnetite, synthetic TM70 and TM50 removed from a basaltic rock matrix). By the simultaneous observation of domain walls on crystal surfaces of different orientation with high resolution, information is obtained on the volume domain structure underneath. The observation confirms the presence of lamellae-shaped volume domains associated with closure domains on the surface for the reduction of the magnetic stray field energy.

  13. Pyroelectric detection of spontaneous polarization in magnetite thin films

    NASA Astrophysics Data System (ADS)

    Takahashi, R.; Misumi, H.; Lippmaa, M.

    2012-10-01

    We have investigated the spontaneous polarization in Fe3O4 thin films by using dynamic and static pyroelectric measurements. The magnetic and dielectric behavior of Fe3O4 thin films grown on Nb:SrTiO3(001) substrates was consistent with bulk crystals. The well-known metal-insulator (Verwey) transition was observed at 120 K. The appearance of a pyroelectric response in the Fe3O4 thin films just below the Verwey temperature shows that spontaneous polarization appeared in Fe3O4 at the charge-ordering transition temperature. The polar state characteristics are consistent with bond- and site-centered charge ordering of Fe2+ and Fe3+ ions sharing the octahedral B sites. The pyroelectric response in Fe3O4 thin films was dependent on the dielectric constant. Quasistatic pyroelectric measurement of Pd/Fe3O4/Nb:SrTiO3 junctions showed that magnetite has a very large pyroelectric coefficient of 735 nC cm-2 K-1 at 60 K.

  14. Production of substantially pure fructose

    SciTech Connect

    Hatcher, H.J.; Gallian, J.J.; Leeper, S.A.

    1990-05-22

    This patent describes a process for the production of a substantially pure product containing greater than 60% fructose. It comprises: combining a sucrose-containing substrate with effective amounts of a levansucrase enzyme preparation to form levan and glucose; purifying the levan by at least one of the following purification methods: ultrafiltration, diafiltration, hyperfiltration, reverse osmosis, liquid--liquid partition, solvent extraction, chromatography, and precipitation; hydrolyzing the levan to form fructose substantially free of glucose and sucrose; and recovering the fructose by at least one of the following recovery methods: hyperfiltration, reverse osmosis, evaporation, drying, crystallization, and chromatography.

  15. Superparamagnetic magnetite nanocrystals-graphene oxide nanocomposites: facile synthesis and their enhanced electric double-layer capacitor performance.

    PubMed

    Wang, Qihua; Wang, Dewei; Li, Yuqi; Wang, Tingmei

    2012-06-01

    Superparamagnetic magnetite nanocrystals-graphene oxide (FGO) nanocomposites were successfully synthesized through a simple yet versatile one-step solution-processed approach at ambient conditions. Magnetite (Fe3O4) nanocrystals (NCs) with a size of 10-50 nm were uniformly deposited on the surfaces of graphene oxide (GO) sheets, which were confirmed by transmission electron microscopy (TEM) and high-angle annular dark field scanning transmission election microscopy (HAADF-STEM) studies. FGO with different Fe3O4 loadings could be controlled by simply manipulating the initial weight ratio of the precursors. The M-H measurements suggested that the as-prepared FGO nanocomposites have a large saturation magnetizations that made them can move regularly under an external magnetic field. Significantly, FGO nanocomposites also exhibit enhanced electric double-layer capacitor (EDLC) activity compared with pure Fe3O4 NCs and GO in terms of specific capacitance and high-rate charge-discharge. PMID:22905504

  16. Field-induced decoupling of NiO-magnetite multilayers

    SciTech Connect

    Erwin, R.W.; Borchers, J.A. [National Inst. of Standards and Technology, Gaithersburg, MD (United States). Reactor Radiation Div.; Berry, S.D.; Lind, D.M.; Lochner, E.; Shaw, K.A. [Florida State Univ., Tallahassee, FL (United States). Dept. of Physics

    1995-12-31

    NiO-magnetite multilayers exhibit long range antiferromagnetic order with the magnetite ferrimagnetic correlations confined to a single layer due to stacking faults of the spinel structure at the interfaces. A systematic study of the field-dependence of the interlayer coupling in a series of NiO-magnetite multilayers has been made using neutron diffraction. Both NiO and magnetite single thin films were included in the measurements for comparison. In the magnetite film, intensity changes with magnetic field are consistent with domain reorientation of the net ferrimagnetic moments, while in the NiO film there are essentially no intensity changes. There is no significant field dependence of the magnetic correlation lengths in either film. For multilayers where the ratio of NiO to magnetite layer thickness is far from unity, the field dependence approximates that of the bulk films. However, for a Fe{sub 3}O{sub 4} (68{angstrom}){vert_bar}NiO (34{angstrom}) multilayer the NiO antiferromagnetic intensity decreases with increasing field, and there is a broadening of the NiO peak on the order of 30%. Concomitantly, the magnetite spins rotate collinear with the field, as expected, due to the net 4.2 {micro}{sub B} moment per unit-cell. The NiO moments appear to rotate into domains where the direction of propagation of the ferromagnetic sheets is closer to the field direction.

  17. LA-ICP-MS of magnetite: Methods and reference materials

    USGS Publications Warehouse

    Nadoll, P.; Koenig, A.E.

    2011-01-01

    Magnetite (Fe3O4) is a common accessory mineral in many geologic settings. Its variable geochemistry makes it a powerful petrogenetic indicator. Electron microprobe (EMPA) analyses are commonly used to examine major and minor element contents in magnetite. Laser ablation ICP-MS (LA-ICP-MS) is applicable to trace element analyses of magnetite but has not been widely employed to examine compositional variations. We tested the applicability of the NIST SRM 610, the USGS GSE-1G, and the NIST SRM 2782 reference materials (RMs) as external standards and developed a reliable method for LA-ICP-MS analysis of magnetite. LA-ICP-MS analyses were carried out on well characterized magnetite samples with a 193 nm, Excimer, ArF LA system. Although matrix-matched RMs are sometimes important for calibration and normalization of LA-ICP-MS data, we demonstrate that glass RMs can produce accurate results for LA-ICP-MS analyses of magnetite. Cross-comparison between the NIST SRM 610 and USGS GSE-1G indicates good agreement for magnetite minor and trace element data calibrated with either of these RMs. Many elements show a sufficiently good match between the LA-ICP-MS and the EMPA data; for example, Ti and V show a close to linear relationship with correlation coefficients, R2 of 0.79 and 0.85 respectively. ?? 2011 The Royal Society of Chemistry.

  18. Reduction of Hg(II) to Hg(0) by Magnetite

    SciTech Connect

    Wiatrowski, Heather A.; Das, Soumya; Kukkadapu, Ravi K.; Ilton, Eugene S.; Barkay, Tamar; Yee, Nathan

    2009-06-12

    Mercury (Hg) is a highly toxic element, and its contamination of groundwater presents a significant threat to terrestrial ecosystems. Understanding the geochemical processes that mediate mercury transformations in the subsurface is necessary to predict its fate and transport. In this study, we investigated the redox transformation of mercuric Hg (Hg[II]) in the presence of the Fe(II)/Fe(III) mixed valence iron oxide mineral magnetite. Kinetic and spectroscopic experiments were performed to elucidate reaction rates and mechanisms. The experimental data demonstrated that reaction of Hg(II) with magnetite results in the loss of Hg(II) and the formation of volatile elemental Hg (Hg[0]). Kinetic experiments showed that Hg(II) reduction occurred within minutes, with reaction rates increasing with increasing magnetite suspension density (0.05 to 0.2 g/L) and solution pH (4.8 to 6.7), and decreasing with increasing chloride concentration (10-6 to 10-2 mol/L). Mössbauer spectroscopic analysis of reacted magnetite samples revealed a decrease in Fe(II) content, corresponding the oxidation of Fe(II) to Fe(III) in the magnetite structure. X-ray photoelectron spectroscopy detected the presence of Hg(II) on magnetite surfaces, suggesting that adsorption is involved in the electron transfer process. These results suggest that Hg(II) reaction with solid-phase Fe(II) is a kinetically favorable pathway for Hg(II) reduction in magnetite-bearing environmental systems.

  19. Bats Use Magnetite to Detect the Earth's Magnetic Field

    PubMed Central

    Holland, Richard A.; Kirschvink, Joseph L.; Doak, Thomas G.; Wikelski, Martin

    2008-01-01

    While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a “compass organelle” containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic cues for compass orientation but the method by which they detect the Earth's magnetic field remains unknown. Here we use the classic “Kalmijn-Blakemore” pulse re-magnetization experiment, whereby the polarity of cellular magnetite is reversed. The results demonstrate that the big brown bat Eptesicus fuscus uses single domain magnetite to detect the Earths magnetic field and the response indicates a polarity based receptor. Polarity detection is a prerequisite for the use of magnetite as a compass and suggests that big brown bats use magnetite to detect the magnetic field as a compass. Our results indicate the possibility that sensory cells in bats contain freely rotating magnetite particles, which appears not to be the case in birds. It is crucial that the ultrastructure of the magnetite containing magnetoreceptors is described for our understanding of magnetoreception in animals. PMID:18301753

  20. Comparative genomic analysis of magnetotactic bacteria from the Deltaproteobacteria provides new insights into magnetite and greigite magnetosome genes required for magnetotaxis.

    PubMed

    Lefèvre, Christopher T; Trubitsyn, Denis; Abreu, Fernanda; Kolinko, Sebastian; Jogler, Christian; de Almeida, Luiz Gonzaga Paula; de Vasconcelos, Ana Tereza R; Kube, Michael; Reinhardt, Richard; Lins, Ulysses; Pignol, David; Schüler, Dirk; Bazylinski, Dennis A; Ginet, Nicolas

    2013-10-01

    Magnetotactic bacteria (MTB) represent a group of diverse motile prokaryotes that biomineralize magnetosomes, the organelles responsible for magnetotaxis. Magnetosomes consist of intracellular, membrane-bounded, tens-of-nanometre-sized crystals of the magnetic minerals magnetite (Fe3O4) or greigite (Fe3S4) and are usually organized as a chain within the cell acting like a compass needle. Most information regarding the biomineralization processes involved in magnetosome formation comes from studies involving Alphaproteobacteria species which biomineralize cuboctahedral and elongated prismatic crystals of magnetite. Many magnetosome genes, the mam genes, identified in these organisms are conserved in all known MTB. Here we present a comparative genomic analysis of magnetotactic Deltaproteobacteria that synthesize bullet-shaped crystals of magnetite and/or greigite. We show that in addition to mam genes, there is a conserved set of genes, designated mad genes, specific to the magnetotactic Deltaproteobacteria, some also being present in Candidatus Magnetobacterium bavaricum of the Nitrospirae phylum, but absent in the magnetotactic Alphaproteobacteria. Our results suggest that the number of genes associated with magnetotaxis in magnetotactic Deltaproteobacteria is larger than previously thought. We also demonstrate that the minimum set of mam genes necessary for magnetosome formation in Magnetospirillum is also conserved in magnetite-producing, magnetotactic Deltaproteobacteria. Some putative novel functions of mad genes are discussed. PMID:23607663

  1. Nucleation and growth of magnetite from solution

    NASA Astrophysics Data System (ADS)

    Baumgartner, Jens; Dey, Archan; Bomans, Paul H. H.; Le Coadou, Cécile; Fratzl, Peter; Sommerdijk, Nico A. J. M.; Faivre, Damien

    2013-04-01

    The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite—a magnetic iron oxide with numerous bio- and nanotechnological applications—proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

  2. Controlled cobalt doping in biogenic magnetite nanoparticles.

    PubMed

    Byrne, J M; Coker, V S; Moise, S; Wincott, P L; Vaughan, D J; Tuna, F; Arenholz, E; van der Laan, G; Pattrick, R A D; Lloyd, J R; Telling, N D

    2013-06-01

    Cobalt-doped magnetite (CoxFe3 -xO4) nanoparticles have been produced through the microbial reduction of cobalt-iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe(2+) site with Co(2+), with up to 17 per cent Co substituted into tetrahedral sites. PMID:23594814

  3. Controlled cobalt doping in biogenic magnetite nanoparticles

    PubMed Central

    Byrne, J. M.; Coker, V. S.; Moise, S.; Wincott, P. L.; Vaughan, D. J.; Tuna, F.; Arenholz, E.; van der Laan, G.; Pattrick, R. A. D.; Lloyd, J. R.; Telling, N. D.

    2013-01-01

    Cobalt-doped magnetite (CoxFe3 ?xO4) nanoparticles have been produced through the microbial reduction of cobalt–iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe2+ site with Co2+, with up to 17 per cent Co substituted into tetrahedral sites. PMID:23594814

  4. Verwey transition in single magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Yu, Q.; Mottaghizadeh, A.; Wang, H.; Ulysse, C.; Zimmers, A.; Rebuttini, V.; Pinna, N.; Aubin, H.

    2014-08-01

    We present a tunnel spectroscopy study of the electronic spectrum of single magnetite Fe3O4 nanoparticles trapped between nanometer-spaced electrodes. The Verwey transition is clearly identified in the current-voltage characteristics where we find that the transition temperature is electric field dependent. The data show the presence of localized states at high energy, ? ˜0.6 eV, which can be attributed to polaron states. At low energy, the density of states (DOS) is suppressed at the approach of the Verwey transition. Below the Verwey transition, a gap, ? ˜300 meV, is observed in the spectrum. In contrast, no gap is observed in the high temperature phase, implying that electronic transport in this phase is possibly due to polaron hopping with activated mobility.

  5. Graphite-magnetite aggregates in ordinary chondritic meteorites

    NASA Technical Reports Server (NTRS)

    Scott, E. R. D.; Taylor, G. J.; Rubin, A. E.; Keil, K.; Okada, A.

    1981-01-01

    The graphite-magnetite component has been found (1) as abundant isolated inclusions in eight ordinary-chondritic, regolith breccias; (2) as the sole matrix in a new kind of unequilibrated chondrite that forms clasts in these regolith breccias; and (3) together with a Huss matrix in six unequilibrated ordinary chondrites. It is suggested that the component was formed by low-temperature, gas-solid reactions before the accretion of the meteorite, and that the isolated inclusions of graphite-magnetite in regolith breccias were derived from bodies composed of the new kind of chondrite that has graphite-magnetite as its sole matrix.

  6. The case against UV photostimulated oxidation of magnetite. [on Mars

    NASA Technical Reports Server (NTRS)

    Morris, R. V.; Lauer, H. V., Jr.

    1980-01-01

    The kinetics of magnetite oxidation in O2-bearing atmospheres in the presence of electromagnetic radiation was studied. No perceptible oxidation of magnetite by ultraviolet (UV) photostimulation occurred. These results do not corroborate previous conclusions by Huguenin (1973, 1974) as to the occurrence of this process. Therefore, although the possibility that the process actually occurs cannot be ruled out, it is concluded that there is not yet a basis in laboratory experiments for inferring that UV photostimulated oxidation of magnetite occurs naturally on the surface of Mars.

  7. Day plots of mixtures of superparamagnetic, single-domain, pseudosingle-domain, and multidomain magnetites

    NASA Astrophysics Data System (ADS)

    Dunlop, David J.; Carter-Stiglitz, Brian

    2006-12-01

    We test how well a few hysteresis parameters (saturation remanence Mrs, coercive force Hc and remanent coercivity Hcr) serve to determine the proportions of end-members in binary mixtures. Our end-members are six magnetites whose grain sizes are within the superparamagnetic (SP), stable single-domain (SD, three samples), pseudo-SD (PSD), and multidomain (MD) ranges (Carter-Stiglitz et al., 2001). The three SD magnetites have contrasting origins and properties: (1) bacterial magnetite crystals of a single size and coercivity, arranged in chains; (2) natural volcanic magnetites with a narrow distribution of coercivities; and (3) synthetic magnetites precipitated in glass, with a broader coercivity distribution. Our parameter mixing theory assumes linear magnetization curves of the end-members between zero field and the largest coercive force Hc (that of the SD phase, if present). Similarly remanent hysteresis curves should be linear up to the maximum remanent coercive force Hcr. Three of our mixtures (SP plus bacterial SD, PSD plus bacterial SD, MD plus volcanic SD) had acceptable agreement between predicted and measured dependences of Hc, Hcr and the curve of Mrs/Ms versus. Hcr/Hc (Day plot) on end-member concentrations. A nonlinear approximation to remanent hysteresis curves gave a reasonable fit to MD plus glass SD results. In this case, Hcr/Hc for the most MD-rich mixture is larger than Hcr/Hc of either end-member. Such behavior is characteristic of bimodal mixtures in which Hcr is largely determined by the hard (SD) phase and Hc by the soft (MD) phase. The only mixture that could not be modeled by linear or nonlinear parameter theory was MD plus bacterial SD. The bacterial SD hysteresis loop descends almost vertically at -Hc because of the extremely narrow range of particle sizes and coercivities. In general, linear and nonlinear parameter mixing models are adequate if only an approximate fit to real data is needed. An inversion method using complete magnetization curves as end-member basis functions is preferable as an unmixing technique. However, comparison of measured data to type curves, for example, on a Day plot, gives a quick indication of what end-member phases might be involved in the mix and provides additional insight before beginning an inversion.

  8. Magnetic anisotropy modulation of magnetite in Fe3O4/BaTiO3(100) epitaxial structures

    NASA Astrophysics Data System (ADS)

    Vaz, Carlos A. F.; Hoffman, Jason; Posadas, Agham; Ahn, Charles

    2009-03-01

    Temperature dependent magnetometry and transport measurements on epitaxial Fe3O4 films grown on BaTiO3(100) single crystals by molecular beam epitaxy show a series of discontinuities that are attributed to changes in the magnetic anisotropy induced by strain in the different crystal phases of BaTiO3. High resolution x-ray diffraction measurements show that the magnetite film is under tensile strain at room temperature, which is ascribed to the lattice expansion of BaTiO3 at the cubic to tetragonal transition, indicating that the magnetite film is relaxed at the growth temperature. From the magnetization versus temperature curves, the variation in the magnetic anisotropy is determined and compared with numerical estimates for the magnetoelastic anisotropies. In particular, the tensile strain in the Fe3O4 films is shown to give rise to a strong perpendicular magnetic anisotropy, as observed experimentally. These results demonstrate the possibility of using the piezoelectric response of BaTiO3 to modulate the magnetic anisotropy of magnetite films.

  9. Effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} nucleating agents on crystallization behavior and magnetic properties of ferromagnetic glass-ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2}

    SciTech Connect

    Abdel-Hameed, Salwa A.M., E-mail: Salwa_NRC@hotmail.com [Glass Research Department, National Research Center, Dokki, Cairo (Egypt); Elwan, Rawhia L. [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)] [Glass Research Department, National Research Center, Dokki, Cairo (Egypt)

    2012-05-15

    Highlights: Black-Right-Pointing-Pointer Crystallization of magnetic glass ceramic with different nucleating agents. Black-Right-Pointing-Pointer The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was studied. Black-Right-Pointing-Pointer XRD for as prepared samples revealed crystallization of pure magnetite. Black-Right-Pointing-Pointer Heat treatment revealed minor calcium silicate, hematite and cristobalite. Black-Right-Pointing-Pointer TEM revealed crystallization of crystallite size in the range 50-100 nm. -- Abstract: Preparation and characterization of ferromagnetic glass ceramic in the system Fe{sub 2}O{sub 3}{center_dot}CaO{center_dot}ZnO{center_dot}SiO{sub 2} with different nucleating agents was studied. The effect of La{sub 2}O{sub 3}, CoO, Cr{sub 2}O{sub 3} and MoO{sub 3} as nucleating agents was investigated. Differential thermal analysis; X-ray diffraction and transmission electron microscope were used to investigate thermal behavior, sequence of crystallization and microstructure of the samples. XRD analysis for as prepared samples revealed the crystallization of single magnetite phase. Heat treatment at 900 Degree-Sign C/2 h revealed the appearance of minor amounts of calcium silicate, hematite and cristobalite beside magnetite. TEM revealed crystallization of crystallite size in the range 50-100 nm. Lattice parameters, cell volume and crystallite size were stimulated from XRD data. Magnetic properties of quenched samples were measured under 20 kG.

  10. Uniaxial anisotropy in magnetite thin film—Magnetization studies

    Microsoft Academic Search

    A. Wiechec; J. Korecki; B. Handke; Z. Kakol; D. Owoc; D. A. Antolak; A. Kozlowski

    2006-01-01

    Magnetization and electrical resistivity measurements have been performed on a stoichiometric single crystalline magnetite Fe3O4 thin film (thickness of ca. 500nm) MBE deposited on MgO (100) substrate. The aim of these studies was to check the influence of preparation method and sample form (bulk vs. thin film) on magnetic anisotropy properties in magnetite. The film magnetization along ?001? versus applied

  11. Parametric investigation for direct chemical vapour deposition of magnetite films

    Microsoft Academic Search

    Sandip Dhara; B. R. Awasthy; A. C. Rastogi; B. K. Das; N. V. Gelfond; N. E. Fedotova; A. F. Bykov; I. K. Igumenov

    1994-01-01

    A direct growth of magnetite (Fe3O4) phase has been obtained by a low-pressure chemical vapour deposition (LPCVD) technique using metal-organic ferric dipivaloylmethanate (Fe(DPM)3) as precursor. On oxidation these films are converted to gamma-Fe2O3 phase which give superior magnetic coercivity values. Crystallographic structures are determined by small-angle XRD analysis. As deposited magnetite and oxidized gamma-Fe2O3 films are reported with coercivity values

  12. Study of pulsed laser deposited magnetite thin film

    Microsoft Academic Search

    Murtaza Bohra; N. Venkataramani; Shiva Prasad; N. Kumar; D. S. Misra; S. C. Sahoo; R. Krishnan

    2007-01-01

    Magnetite thin film with a predominant (110) texture has been deposited by pulsed laser ablation of ?-Fe2O3 target onto fused quartz substrate. Spontaneous magnetization of 5400G and room temperature electrical resistivity of 4.2×10?3?cm were measured for an annealed magnetite thin film. Zero-field-cooled magnetization data clearly show the Verwey transition near 120K through an abrupt change, and is consistent with the

  13. Deposition of magnetite films by reactive sputtering of iron

    Microsoft Academic Search

    J. Heller

    1976-01-01

    Iron is sputtered reactively in an argon-oxygen glow discharge to form deposits of magnetite. Cycling the oxygen partial pressure between a low and a high value during sputtering causes deposition of alternating layers of Fe-metal and Fe2O3-oxide. Depending on the cycle length, a layered structure results or homogeneous films form. For all films pronounced magnetite peaks were found by X-ray

  14. Electrophoretic mobility of magnetite particles in high temperature water

    SciTech Connect

    Vidojkovic, Sonja [Pennsylvania State University; Rodriguez-Santiago, V [Oak Ridge National Laboratory (ORNL); Fedkin, Mark V. [Pennsylvania State University; Wesolowski, David J [ORNL; Lvov, Serguei N. [Pennsylvania State University

    2011-01-01

    Magnetite(Fe3O4) isoneofthemostcommonoxidesformingdepositsandparticulatephasesin industrialhightemperaturewatercircuits.Itscolloidalcharacteristicsplayaprincipalroleinthe mechanismofdepositformationandcanbeusedascontrollingfactorstopreventorminimizedeposit formationanddamageofindustrialpipelinesduetounder-depositcorrosion.Inthisstudy,ahigh temperatureparticleelectrophoresistechniquewasemployedtomeasurethezetapotentialatthe magnetite/waterinterface the parameterthatcontrolscolloidalstabilityofparticles,theiraggrega- tion, anddeposition.Themeasurementsweremadeattemperaturesupto200 1C overawiderangeofpH. The isoelectricpointsofmagnetite,atwhichthedepositionofparticlesisincreased,weredeterminedatpH 6.35, 6.00,5.25,and5.05fortemperatures25,100,150,and200 1C, respectively.Theobserved temperaturedependenceofzetapotentialandtheisoelectricpHpointofmagnetitecanhelptoexplain the extentofinteractionsbetweenthecolloidalparticlesandthesteelwallsurfacesunderhydro- thermalconditions,andindicatemethodsforcontrollingandmitigatingoxidedepositioninhigh temperaturewatercycles.

  15. Structure of the magnetite-oleic acid-decalin magnetic fluid from small-angle neutron scattering data

    NASA Astrophysics Data System (ADS)

    Nagornyi, A. V.; Petrenko, V. I.; Bulavin, L. A.; Avdeev, M. V.; Almásy, L.; Rosta, L.; Aksenov, V. L.

    2014-01-01

    Structural parameters of the magnetite-oleic acid-decalin magnetic fluid at various excesses of oleic acid (up to 25 vol %) have been determined using small-angle neutron scattering. Based on the comparison of the behavior of oleic acid in the magnetic fluid and in the pure solvent (decalin), it has been concluded that the interaction between the molecules of free (unadsorbed) surfactant changes in the presence of magnetic nanoparticles. However, the system remains stable and does not form aggregates of magnetic particles or free oleic acid. These results are compared with the previously presented data for similar benzene-based magnetic fluids.

  16. Toward pure electronic spectroscopy

    E-print Network

    Petrovi?, Vladimir, 1978-

    2009-01-01

    In this thesis is summarized the progress toward completing our understanding of the Rydberg system of CaF and developing Pure Electronic Spectroscopy. The Rydberg system of CaF possesses a paradigmatic character due to ...

  17. Geomorphology: Pure and applied

    SciTech Connect

    Hart, M.G.

    1986-01-01

    The book summarizes the history of intellectual debate in geomorphology and describes modern developments both ''pure'' and ''applied.'' The history begins well before W.M. Davis and follows through to such debates as those concerned with the Pleistocene. Modern developments in pure geomorphology are cast in terms of chapters on form, process, materials, and methods analysis. The applied chapters concentrate on environmental hazards and resources, and their management.

  18. Origins of Magnetite Nanocrystals in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Mckay, David S.; Gibson, Everett K.; Wentworth, Susan J.

    2009-01-01

    The Martian meteorite ALH84001 preserves evidence of interaction with aqueous fluids while on Mars in the form of microscopic carbonate disks. These carbonate disks are believed to have precipitated 3.9 Ga ago at beginning of the Noachian epoch on Mars during which both the oldest extant Martian surfaces were formed, and perhaps the earliest global oceans. Intimately associated within and throughout these carbonate disks are nanocrystal magnetites (Fe3O4) with unusual chemical and physical properties, whose origins have become the source of considerable debate. One group of hypotheses argues that these magnetites are the product of partial thermal decomposition of the host carbonate. Alternatively, the origins of mag- netite and carbonate may be unrelated; that is, from the perspective of the carbonate the magnetite is allochthonous. For example, the magnetites might have already been present in the aqueous fluids from which the carbonates were believed to have been deposited. We have sought to resolve between these hypotheses through the detailed characterized of the compo- sitional and structural relationships of the carbonate disks and associated magnetites with the orthopyroxene matrix in which they are embedded. Extensive use of focused ion beam milling techniques has been utilized for sample preparation. We then compared our observations with those from experimental thermal decomposition studies of sideritic carbonates under a range of plausible geological heating scenarios. We conclude that the vast majority of the nanocrystal magnetites present in the car- bonate disks could not have formed by any of the currently proposed thermal decomposition scenarios. Instead, we find there is considerable evidence in support of an alternative allochthonous origin for the magnetite unrelated to any shock or thermal processing of the carbonates.

  19. Magnetite colloidal nanocrystals: a facile pathway to prepare mesoporous hematite thin films for photoelectrochemical water splitting.

    PubMed

    Gonçalves, Ricardo H; Lima, Bruno H R; Leite, Edson R

    2011-04-20

    In this study, we demonstrate an alternative and promising way to produce hematite photoanodes with high performance and without the addition of doping or catalytic coating. In this approach, we processed hematite thin films using a colloidal dispersion of magnetite nanocrystals as the precursor. The photoelectrochemical characterization shows that the colloidal approach used to process an undoped hematite photoanode produced a high-performance electrode for water photooxidation with an onset potential as low as 0.8 V(RHE). This value is comparable to the best results reported in the literature for a hematite photoanode modified with catalytic materials. We demonstrate that pure hematite thin films reach 1.1 mA·cm(-2) at 1.23 V(RHE) with back-side illumination. PMID:21443221

  20. 7 CFR 917.8 - Pure grower or pure producer.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...Vegetables, Nuts), DEPARTMENT OF AGRICULTURE FRESH PEARS AND PEACHES GROWN IN CALIFORNIA Order Regulating Handling Definitions § 917.8 Pure grower or pure producer. (a) For peaches, pure grower means any grower: (1) Who...

  1. Electrochemistry and dissolution kinetics of magnetite and ilmenite

    USGS Publications Warehouse

    White, A.F.; Peterson, M.L.; Hochella, M.F., Jr.

    1994-01-01

    Natural samples of magnetite and ilmenite were experimentally weathered in pH 1-7 anoxic solutions at temperatures of 2-65 ??C. Reaction of magnetite is described as [Fe2+Fe23+]O4(magnetite) + 2H+ ??? ??[Fe23+]O3(maghemite) + Fe2+ + H2O. Dynamic polarization experiments using magnetite electrodes confirmed that this reaction is controlled by two electrochemical half cells, 3[Fe2+Fe23+]O4(magnetite) ??? 4??[Fe23+]O3(maghemite) + Fe2+ + 2e- and [Fe2+Fe23+]O4(magnetite) + 8 H+ + 2e- ??? 3Fe2+ + 4H2O, which result in solid state Fe3+ reduction, formation of an oxidized layer and release of Fe(II) to solution. XPS data revealed that iron is present in the ferric state in the surfaces of reacted magnetite and ilmenite and that the Ti Fe ratio increased with reaction pH for ilmenite. Short-term (<36 h) release rates of Fe(II) were linear with time. Between pH 1 and 7, rates varied between 0.3 and 13 ?? 10-14 mol ?? cm-2 ?? s-1 for magnetite and 0.05 and 12.3 ?? 10-14 mol ?? cm-2 ?? s-1 for ilmenite. These rates are two orders of magnitude slower than electrochemical rates determined by Tafel and polarization resistance measurements. Discrepancies are due to both differences in geometric and BET surface area estimates and in the oxidation state of the mineral surface. In long-term closed-system experiments (<120 days), Fe(II) release slowed with time due to the passivation of the surfaces by increasing thicknesses of oxide surface layers. A shrinking core model, coupling surface reaction and diffusion transport, predicted that at neutral pH, the mean residence time for sand-size grains of magnetite and ilmenite will exceed 107 years. This agrees with long-term stability of these oxides in the geologic record. ?? 1994.

  2. Production Rate of Cosmogenic 10Be in Magnetite

    NASA Astrophysics Data System (ADS)

    Granger, D. E.; Rogers, H. E.; Riebe, C. S.; Lifton, N. A.

    2013-12-01

    Cosmogenic 10Be is widely used for determining exposure ages, soil production rates, and catchment-wide erosion rates. To date, measurements have been almost exclusively in the mineral quartz (SiO2), which is resistant to weathering and easily cleaned of meteoric 10Be contamination. However, this limits the method to quartz-bearing rocks and requires specialized laboratories due to the need for large quantities of hydrofluoric acid (HF). Here, we present initial results for 10Be production in the mineral magnetite (Fe3O4). Magnetite offers several advantages over quartz; it is (1) present in mafic rocks, (2) easily collected in the field, (3) quickly and easily separated in the lab, and (4) digested without HF. In addition, 10Be can be measured in both detrital quartz and magnetite from the same catchment to yield information about the intensity of chemical weathering (Rogers et al., this conference). The 10Be production rate in magnetite relative to quartz was determined for a granitic boulder from Mt. Evans, Colorado, USA. The boulder was crushed and homogenized to facilitate production rate comparisons among various minerals. We separated magnetite using a combination of hand magnets, froth flotation, and a variety of selective chemical dissolutions in dithionite-citrate-bicarbonate solution, 5% nitric acid (HNO3) and 1% HF/HNO3. Six aliquots of magnetite were analyzed for 10Be and compared to quartz. Three aliquots that were not exposed to 1% HF/HNO3 were contaminated with meteoric 10Be, probably associated with residual mica. Three aliquots that were exposed to 1% HF/HNO3 treatments agreed to within 2% measurement uncertainty. Our preliminary results indicate that the relative production rate by mass of 10Be in magnetite and quartz is 0.462 × 0.012. Our results are similar to theoretically predicted values. Recently updated excitation functions for neutron and proton spallation reactions allow us to partition 10Be production in quartz and magnetite among silicon, oxygen, and iron. While most of the production in both magnetite and quartz is from spallation of oxygen, our experimental results indicate that approximately (13 × 3)% of 10Be in the Mt. Evans quartz sample is produced from silicon.

  3. Study of cerium doped magnetite (Fe 3O 4:Ce)/PMMA nanocomposites

    NASA Astrophysics Data System (ADS)

    Padalia, Diwakar; Johri, U. C.; Zaidi, M. G. H.

    2012-03-01

    The paper presents the synthesis and properties of polymer nanocomposite material based on cerium doped magnetite (Fe 3O 4) as filler material and poly methyl methacrylate (PMMA) as host matrix. The magnetite (Fe 3O 4) particles were synthesized by co-precipitation route using stable ferrous and ferric salts with ammonium hydroxide as precipitating agent. Further, they doped by cerium oxide (CeO 2) non-stoichiometrically. The composite material was fabricated by solvent evaporation method. Here 2.4 GHz microwaves were used to study the effect of microwaves heating on polymerization. The phase and crystal structure is determined by X-ray diffraction (XRD). The average crystallite size of the composites varies from 28 to 35 nm. The chemical structure is confirmed by Fourier transform infrared (FTIR) spectroscopy. The magnetic and thermal properties are investigated by vibrating sample magnetometer (VSM) and differential scanning calorimetry (DSC). The thermal study shows that the microwave heated samples possess higher glass transition temperature ( Tg). The magnetic results suggest that coercivity ( HC) and squareness ( Mr/ Ms) of the loop increases with increasing doping percent of cerium.

  4. Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures

    PubMed Central

    Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H.; Leu, Bogdan M.; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi

    2014-01-01

    Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20?GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5?GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8?GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8?GPa and room temperature. PMID:25186916

  5. Abnormal elastic and vibrational behaviors of magnetite at high pressures.

    PubMed

    Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H; Leu, Bogdan M; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi

    2014-01-01

    Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe(2+)-Fe(3+)-Fe(2+) ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature. PMID:25186916

  6. Abnormal Elastic and Vibrational Behaviors of Magnetite at High Pressures

    NASA Astrophysics Data System (ADS)

    Lin, Jung-Fu; Wu, Junjie; Zhu, Jie; Mao, Zhu; Said, Ayman H.; Leu, Bogdan M.; Cheng, Jinguang; Uwatoko, Yoshiya; Jin, Changqing; Zhou, Jianshi

    2014-09-01

    Magnetite exhibits unique electronic, magnetic, and structural properties in extreme conditions that are of great research interest. Previous studies have suggested a number of transitional models, although the nature of magnetite at high pressure remains elusive. We have studied a highly stoichiometric magnetite using inelastic X-ray scattering, X-ray diffraction and emission, and Raman spectroscopies in diamond anvil cells up to ~20 GPa, while complementary electrical conductivity measurements were conducted in a cubic anvil cell up to 8.5 GPa. We have observed an elastic softening in the diagonal elastic constants (C11 and C44) and a hardening in the off-diagonal constant (C12) at ~8 GPa where significant elastic anisotropies in longitudinal and transverse acoustic waves occur, especially along the [110] direction. An additional vibrational Raman band between the A1g and T2g modes was also detected at the transition pressure. These abnormal elastic and vibrational behaviors of magnetite are attributed to the occurrence of the octahedrally-coordinated Fe2+-Fe3+-Fe2+ ions charge-ordering along the [110] direction in the inverse spinel structure. We propose a new phase diagram of magnetite in which the temperature for the metal-insulator and distorted structural transitions decreases with increasing pressure while the charge-ordering transition occurs at ~8 GPa and room temperature.

  7. Functionalization of magnetite nanoparticles as oil spill collector.

    PubMed

    Atta, Ayman M; Al-Lohedan, Hamad A; Al-Hussain, Sami A

    2015-01-01

    In the present study, a new magnetic powder based on magnetite can be used as a petroleum crude oil collector. Amidoximes based on rosin as a natural product can be prepared from a reaction between hydroxylamine and rosin/acrylonitrile adducts. The produced rosin amidoximes were used as capping agents for magnetite nanoparticles to prepare hydrophobic coated magnetic powders. A new class of monodisperse hydrophobic magnetite nanoparticles was prepared by a simple and inexpensive co-precipitation method. Iron ions and iodine were prepared by the reaction between ferric chloride and potassium iodide. The structure and morphology of magnetite capped with rosin amidoxime were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, thermogravimetric analysis (TGA) and dynamic light scattering (DLS). The magnetic properties were determined from vibrating sample magnetometer (VSM) analyses. These prepared magnetite nanoparticles were tested as bioactive nanosystems and their antimicrobial effects were investigated. The prepared nanomaterials were examined as a crude oil collector using magnetic fields. The results show promising data for the separation of the petroleum crude oil from aqueous solution in environmental pollution cleanup. PMID:25822876

  8. Magnetic Separations with Magnetite: Theory, Operation, and Limitations

    SciTech Connect

    G. B. Cotten

    2000-08-01

    This dissertation documents the theory development and experimental plan followed to describe how a magnetite-based column under the influence of an external magnetic field functions as a magnetic separator. Theoretical simulations predict that weekly paramagnetic particles in the sub-micron range can be magnetically separated while diamagnetic particles as large as 2 microns in diameter may pass. Magnetite-based columns were evaluated as magnetically-controllable enhanced filtration devices. There was no evidence of enhanced filtration for diamagnetic particles by the magnetite-based bed. Magnetite-based magnetic separators have proven to be effective in specific laboratory experiments, indicating a potential feasibility for scale-up operations. Column media-filter type filtration effects indicate a magnetite-based column would not be suitable for treatment of a waste stream with a high diamagnetic solids content or high volume throughput requirements. Specific applications requiring removal of sub-micron para- or ferromagnetic particles under batch or Stokes flow conditions would be most applicable.

  9. A Magnetite Colloid System Studied by Mössbauer Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kuzmann, E.; Homonnay, Z.; Németh, Z.; Vértes, A.; Garg, V. K.; Zrínyi, M.

    2005-04-01

    Magnetite loaded polyvinyl alcohol and polystyrol hydrogels were investigated by the help of 57Fe Mössbauer spectroscopy, XRD and transmission electron microscopy. Chemically cross-linked polyvinyl alcohol hydrogels filled with magnetite particles were prepared from magnetite sol obtained from FeCl2 and FeCl3 in aqueous solution. At near room temperature, the Mössbauer spectrum has hyperfine fields smaller than those characteristic of bulk magnetite. The temperature dependent collapse of the hyperfine splitting can be associated with paramagnetism rather than superparamagnetism. This indicates that a special magnetic interaction occurs between the small particles. This may be interpreted in the terms of dynamic magnetic phenomenon in fine particle magnetite incorporated into swollen elastic polymer network by supposing magnetic ordering of clusters (after Boquet et al.) created by high concentration of defects when the hyperfine field distribution is mainly influenced by the slow relaxation of the magnetic moments of the clusters. Nevertheless, the effect of monodispersity of the colloid system may also contribute to the unusual relaxation shape of the Mössbauer spectra.

  10. The Verwey transition in nanostructured magnetite produced by a combination of chimie douce and spark plasma sintering

    SciTech Connect

    Gaudisson, T.; Nowak, S.; Ammar, S. [ITODYS, Université Paris Diderot, PRES Sorbonne Paris Cité, CNRS-UMR 7086, 75205 Paris Cedex (France); Vázquez-Victorio, G.; Valenzuela, R., E-mail: raulvale@yahoo.com [Depto Materiales Metálicos y Cerámicos, Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Mexico 04510 (Mexico); Bañobre-López, M.; Rivas, J. [International Iberian Nanotechnology Laboratory, 4715-310 Braga (Portugal); Mazaleyrat, F. [SATIE, ENS Cachan, CNRS, UniverSud, F-94230 Cachan (France)

    2014-05-07

    Magnetite nanoparticles about 10?nm sized were synthesized by the polyol method. Zero-field-cooled (ZFC)-FC measurements showed a blocking temperature ?170?K and the absence of the Verwey transition. They were subsequently consolidated by spark plasma sintering at 750?°C for 15?min, leading to a high density (92% of the theoretical density), solid body, with grains in the 150?nm range. X-ray diffraction patterns exhibited a spinel single phase with cell parameters corresponding to the magnetite structure. Magnetic measurements showed a decrease of coercivity from 685?Oe (54.5?kA/m) at 118?K to 90?Oe (7.2?kA/m) at 139?K. ZFC measurements at 25?Oe presented a three-fold magnetization increase as temperature increased; a small transition between 116 and 117.5?K, followed by a larger one from 117.6 to 124?K. The first transition can be associated with a complex crystallographic transition and delocalization of Fe{sup 2+}-Fe{sup 3+}, while the second one can be attributed to spin reorientation due to the magnetocrystalline anisotropy constant (K{sub 1}) change of sign as previously observed only in magnetite single crystals.

  11. Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers.

    PubMed

    Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

    2012-01-01

    New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization. PMID:22038075

  12. The microstructure and characteristics of magnetite thin films prepared by ultrasound-enhanced ferrite plating

    Microsoft Academic Search

    Chun-Young Oh; Jae-Hee Oh; Tae-Kyung Ko

    2002-01-01

    Summary form only given. In this study, magnetite (Fe3O4) thin films were prepared by ultrasound-enhanced ferrite plating. The effects of ferrite plating condition on the microstructure and magnetic properties of magnetite thin films were investigated.

  13. Simple and Rapid Synthesis of Magnetite/Hydroxyapatite Composites for Hyperthermia Treatments via a Mechanochemical Route

    PubMed Central

    Iwasaki, Tomohiro; Nakatsuka, Ryo; Murase, Kenya; Takata, Hiroshige; Nakamura, Hideya; Watano, Satoru

    2013-01-01

    This paper presents a simple method for the rapid synthesis of magnetite/hydroxyapatite composite particles. In this method, superparamagnetic magnetite nanoparticles are first synthesized by coprecipitation using ferrous chloride and ferric chloride. Immediately following the synthesis, carbonate-substituted (B-type) hydroxyapatite particles are mechanochemically synthesized by wet milling dicalcium phosphate dihydrate and calcium carbonate in a dispersed suspension of magnetite nanoparticles, during which the magnetite nanoparticles are incorporated into the hydroxyapatite matrix. We observed that the resultant magnetite/hydroxyapatite composites possessed a homogeneous dispersion of magnetite nanoparticles, characterized by an absence of large aggregates. When this material was subjected to an alternating magnetic field, the heat generated increased with increasing magnetite concentration. For a magnetite concentration of 30 mass%, a temperature increase greater than 20 K was achieved in less than 50 s. These results suggest that our composites exhibit good hyperthermia properties and are promising candidates for hyperthermia treatments. PMID:23629669

  14. Pure red cell aplasia.

    PubMed

    Skikne, B S; Lynch, S R; Bezwoda, W R; Bothwell, T H; Bernstein, R; Katz, J

    1976-08-14

    The presentation and clinical course of pure red cell aplasia in 5 patients are described. In 3 of them no concomitant diseases were present, in 1 the condition was associated with the presence of a thymoma, and the remaining patient was suffering from a lymphocytic lymphoma. Pregnancy led to a recurrence of the disorder in 2 patients. The fact that 4 of the patients exhibited unequivocal evidence of other auto-immune disturbances adds further support to the concept that pure red cell aplasia itself has an auto-immune basis. PMID:989625

  15. Nanoparticulate magnetite thin films as electrode materials for the fabrication of electrochemical capacitors

    Microsoft Academic Search

    Suh Cem Pang; Wai Hwa Khoh; Suk Fun Chin

    2010-01-01

    Magnetite nanoparticles in stable colloidal suspension were prepared by the co-precipitation method. Nanoparticulate magnetite\\u000a thin films on supporting stainless steel plates were prepared by drop-coating followed by heat treatment under controlled\\u000a conditions. The effects of calcination temperature and atmosphere on the microstructure and electrochemical properties of\\u000a nanoparticulate magnetite thin films were investigated. Nanoparticulate magnetite thin films prepared under optimized conditions

  16. Relationship between altered pyroxene diorite and the magnetite mineralization in the Chilean Iron Belt, with emphasis on the El Algarrobo iron deposits (Atacama region, Chile)

    Microsoft Academic Search

    J.-J. Ménard

    1995-01-01

    North of El Algarrobo (one of the four main deposits of the Chilean Iron Belt), the iron-mineralization (magnetite-etrmolite\\/actinolite-apatite) is related to clinoand orthopyroxene diorite intrusions which have crystallized at shallow depth (4km) under increasing oxygen fugacities. The supercritical fluid phase exsolved during cooling after the consolidation of the plutons (800–900°C), results in a H+, Cl- and sodic enrichment, and in

  17. Surface modification of superparamagnetic magnetite nanoparticles and their intracellular uptake

    Microsoft Academic Search

    Y Zhang; Nathan Kohler; Miqin Zhang

    2002-01-01

    Superparamagnetic magnetite nanoparticles were surface-modified with\\u000a poly (ethylene glycol) (PEG) and folic acid, respectively, to improve\\u000a their intracellular uptake and ability to tat-get specific cells. PEG\\u000a and folic acid were successfully immobilized on the surfaces of\\u000a magnetite nanoparticles and characterized using fourier transform\\u000a infrared spectra. The nanoparticle internalization into mouse macrophage\\u000a (RAW 264.7) and human breast cancer (BT20) cells was

  18. Synthesis of pure RDX

    SciTech Connect

    Pagoria, P.F.

    1994-03-25

    For the bioremediation of explosives, there is the need for RDX uncontaminated by HMX. (In the Bachmann process, RDX always has residual HMX.) There are two methods for synthesizing pure RDX: one involving oxidation of R-salt, the other nitration of hexamine. Absence of HMX in the RDX samples was confirmed by NMR and melting points.

  19. Ab initio study of the half-metal to metal transition in strained magnetite

    E-print Network

    does not lead to a metallic state for magnetite films grown on (111)-oriented substrates. 3 PresentAb initio study of the half-metal to metal transition in strained magnetite Martin Friák1 of magnetite under different strain conditions. The effects of volume relaxation and internal degrees

  20. The relationship between magnetic microstructure and anti-phase domain size in epitaxial magnetite thin films

    E-print Network

    Dunin-Borkowski, Rafal E.

    -axis electron holography Thin films of magnetite (Fe3O4) that have been grown epitaxially on MgO exhibit unusual suggested that 50-nm-thick magnetite films contain distinct magnetic regions that are 2-4 times the anti induction and the positions of the APBs, we have examined a 25-nm-thick magnetite film using off

  1. Dissolution behaviour of magnetite film formed over carbon steel in dilute organic acid media

    Microsoft Academic Search

    A. A. M. Prince; S. Velmurugan; S. V. Narasimhan; C. Ramesh; N. Murugesan; P. S. Raghavan; R. Gopalan

    2001-01-01

    Magnetite is the major corrosion product formed over the carbon steel in the primary heat transport system of the pressurized heavy water reactor (PHWR). This magnetite usually accumulates radioactivity during reactor operation. The dissolution of the host magnetite is achieved by chemical formulations in order to get rid of the radioactivity trapped in the oxide; the underlying base metal also

  2. Magnetite composition in Ni-Cu-PGE deposits worldwide: application to mineral exploration

    E-print Network

    Magnetite composition in Ni-Cu-PGE deposits worldwide: application to mineral exploration Emilie October 2013 Accepted 13 May 2014 Available online 21 May 2014 Keywords: Magnetite Ni Cu Sulfides Mineral in the exploration of ore deposits. Magnetite is a common accessory mineral in magmatic Ni­Cu­Platinum-Group Element

  3. Synthesis and Magnetorheological Characterization of Magnetite Nanoparticle and Poly(Vinyl Butyral) Composite

    Microsoft Academic Search

    Bong Jun Park; Jae Lim You; Hyoung Jin Choi; Seong Yong Park; Byoung Yoon Lee

    2009-01-01

    Iron oxide nanoparticle of magnetite, one of well-known soft magnetic materials, has been investigated due to their various potential applications. In order to apply it as a magnetorheological (MR) material, composite of poly(vinyl butyral) and magnetite nanoparticles was prepared via solvent evaporation method using synthesized magnetite nanoparticles because of their proper magnetic characteristics and dispersion stability in a viscous medium.

  4. Magnetite in Desert Varnish and Applications to Rock Varnish on Mars

    NASA Technical Reports Server (NTRS)

    Mancinelli, R. L.; Bishop, J. L.; De, S.

    2002-01-01

    Magnetite in desert varnish is characterized here using DTA, IR and SEM. The presence of magnetite in desert varnish is significant because of the oxidizing environment. This situation is similar to that of Mars where magnetite may also be present. Additional information is contained in the original extended abstract.

  5. Intensified magneto-resistance by rapid thermal annealing in magnetite (Fe3O4) thin film on SiO2 glass substrate

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Morii, K.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

    2012-12-01

    We have observed large magneto-resistance (MR) intensified by rapid thermal annealing (RTA) in magnetite (Fe3O4) thin film (MTF) on SiO2 glass (a-SiO2) substrate. The MTF was produced by the RF magnetron sputtering method by using a magnetite target. The electrical resistivity (ER) of as-grown MTF (AG-MTF) showed the Mott's variable range hopping behavior, which implies that the AG-MTF is amorphous-like. Although the magneto-resistance (MR) ratio of bulk single crystal is very small except around the Verwey transition temperature (VTT), that of the AG-MTF showed moderately large below room temperature. Due to RTA of the AG-MTF by use of an IR image furnace, the MR ratio of MTFs was intensified, and especially by the annealing around the Curie temperature (585°C) of magnetite. Furthermore the ER of the rapid thermally annealed MTF (RTA-MTF) showed a slight kink at around the VTT, which indicates that the crystallinity of the RTA-MTF is higher than that of the AG-MTF The MTF produced by the RF magnetron sputtering method are composed of magnetite fine particles (MFPs). We consider that the directions of magnetic moments of MFPs in the MTF were spatially randomized by the RTA and the strong spin scattering of itinerant electrons transferring between adjacent MFPs caused the intensification of the MR ratio.

  6. Exsolved magnetite inclusions in silicates: Features determining their remanence behavior

    Microsoft Academic Search

    Joshua M. Feinberg; Gary R. Scott; Paul R. Renne; Hans-Rudolf Wenk

    2005-01-01

    Submicroscopic, needle-shaped titanomagnetite inclusions exsolved in silicate minerals commonly occur in mafic intrusive rocks and are protected from alteration by their silicate hosts, making them excellent candidates for paleomagnetic studies. A suite of samples containing clinopyroxene- and plagioclase-hosted magnetite inclusions from five geologically diverse sites was examined using magnetic force microscopy to image the inclusions' magnetic domain state. Alternating field

  7. Experimental study of magnetic interactions between individual biogenic magnetite nanocrystals

    E-print Network

    Dunin-Borkowski, Rafal E.

    nanocrystals from wild-type and mutant magnetotactic bacteria of the Magnetospirillum gryphiswaldense (M. gryph studied two-dimensional arrays of magnetite particles produced by bacteria whose mamJ protein had been removed through genetic modification. In unmodified bacteria this protein is responsible for producing

  8. Magnetic and magnetotransport properties of magnetite films with step edges

    Microsoft Academic Search

    M. Ziese; R. Höhne; H. C Semmelhack; K. H Han; P. Esquinazi; K. Zimmer

    2004-01-01

    The magnetoresistance of step edges in magnetite films was systematically studied. An enhancement of the magnetoresistance by the introduction of step edges was observed, especially in the high-field regime. This was modelled by spin-disorder scattering. The analysis revealed magnetic cluster formation at the step edges.

  9. Avian magnetite-based magnetoreception: a physiologist's perspective

    PubMed Central

    Cadiou, Hervé; McNaughton, Peter A.

    2010-01-01

    It is now well established that animals use the Earth's magnetic field to perform long-distance migration and other navigational tasks. However, the transduction mechanisms that allow the conversion of magnetic field variations into an electric signal by specialized sensory cells remain largely unknown. Among the species that have been shown to sense Earth-strength magnetic fields, birds have been a model of choice since behavioural tests show that their direction-finding abilities are strongly influenced by magnetic fields. Magnetite, a ferromagnetic mineral, has been found in a wide range of organisms, from bacteria to vertebrates. In birds, both superparamagnetic (SPM) and single-domain magnetite have been found to be associated with the trigeminal nerve. Electrophysiological recordings from cells in the trigeminal ganglion have shown an increase in action potential firing in response to magnetic field changes. More recently, histological evidence has demonstrated the presence of SPM magnetite in the subcutis of the pigeon's upper beak. The aims of the present review are to review the evidence for a magnetite-based mechanism in birds and to introduce physiological concepts in order to refine the proposed models. PMID:20106875

  10. 26 CURA REPORTER Hydrogen Generation Using Magnetite to Store

    E-print Network

    Levinson, David M.

    26 CURA REPORTER Hydrogen Generation Using Magnetite to Store Energy from Alternative Sources by J. Woods Halley, Andy Schofield, and Bjorn Berntson D emand for alternative energy sources arises from foreign sources. The leading alternative energy sources, wind and solar, however, are intermittent

  11. Bats Use Magnetite to Detect the Earth's Magnetic Field

    Microsoft Academic Search

    Richard A. Holland; Joseph L. Kirschvink; Thomas G. Doak; Martin Wikelski

    2008-01-01

    While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a ''compass organelle'' containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic

  12. Bats Use Magnetite to Detect the Earth's Magnetic Field

    Microsoft Academic Search

    Richard A. Holland; Joseph L. Kirschvink; Thomas G. Doak; Martin Wikelski; Sarah Frances Brosnan

    2008-01-01

    While the role of magnetic cues for compass orientation has been confirmed in numerous animals, the mechanism of detection is still debated. Two hypotheses have been proposed, one based on a light dependent mechanism, apparently used by birds and another based on a “compass organelle” containing the iron oxide particles magnetite (Fe3O4). Bats have recently been shown to use magnetic

  13. Benefaction studies on the Hasan Celebi magnetite deposit, Turkey

    USGS Publications Warehouse

    Pressler, Jean W.; Akar, Ali

    1972-01-01

    Bench-scale and semicontinuous tests were performed on surface, trench, and diamond drill core samples from the Hasan Celebi low-grade magnetite deposit to determine the optimum benefication procedures utilizing wet magnetic separation techniques. Composite core samples typically contain about 27 percent recoverable magnetite and require crushing and grinding through 1 mm in size to insure satisfactory separation of the gangue from the magnetite. Regrinding and cleaning the magnetite concentrate to 80 percent minus 150-mesh is necessary to obtain an optimum of 66 percent iron. Semicontinuous pilot-plant testing with the wet magnetic drum using the recycled middling technique indicates that as much as 83 percent of the acid-soluble iron can be recovered into a concentrate containing 66 percent iron, with minimum deleterious elements. This represents 27 weight percent of the original ore. Further tests will continue when the Maden Tetkik ve Arama Enstitusu (MTA) receives 24 tons of bulk sample from an exploratory drift and cross-cut now being driven through a section of the major reserve area.

  14. Magnetite-sulfide-metal complexes in the Allende meteorite

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E.; Mcmahon, B. M.

    1979-01-01

    A model of liquid immiscibility is presented that seemingly accounts for the sulfide-oxide-metal complexes that are present in olivine-rich chondrules in the Allende meteorite. The four major assemblages that are identified are: (1) magnetite + Ni-Fe metal; (2) magnetite + troilite + Ni-Fe metal; (3) magnetite + troilite + pentlandite + Ni-Fe metal; and (4) troilite + or - pentlandite. Specific attention is focused on oxide-metal associations and experimental data confirm earlier suggestions that magnetite results from the oxidation of an initially high-Fe-content metal alloy. Oxidation decreases the modal abundance of the Fe metal and this is accompanied by substantial increases in Ni contents which reach a maximum of approximately 70 wt % Ni. The proposed oxidation mechanism is entirely consistent with condensation of Fe-metal + olivine (Fa5) that subsequently reequilibrated at lower temperatures. Although the sulfide constituents could also have formed by the reaction of Fe-Ni metal + gaseous H2S, sulfide immiscibility under increased conditions of partial O2 pressure is the preferred process.

  15. Magnetite and Carbonate Textures in ALH84001: Experimental Insights

    NASA Technical Reports Server (NTRS)

    Koziol, Andrea M.

    2001-01-01

    Synthetic siderite and synthetic siderite-magnesite carbonates were equilibrated with hematite, magnetite, and CO2 at elevated pressure and temperature. Comparisons are made to textures seen in the carbonate globules in ALH84001. Additional information is contained in the original extended abstract.

  16. Pure and Applied Chemistry

    NSDL National Science Digital Library

    Established in 1960, the journal Pure and Applied Chemistry is committed to publishing notable research papers arising from various international scientific events and projects that are sponsored by the International Union of Pure and Applied Chemistry (IUPAC). First-time visitors can view the "News" area to learn about the most recent work published in the journal, and then they may wish to move on to the embedded search engine displayed prominently on the homepage. Other sections on the site include "Editorial Board", "Notes For Authors", and "Publication Policy". Visitors with a deep and abiding interest in the journal may also wish to consult their RSS feeds, which include those related to the publication of new articles and reports from the IUPAC. Finally, the site also contains a drop down menu titled "PAC Archives" where visitors can browse the contents of each volume.

  17. Cellular interactions of lauric acid and dextran-coated magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Pradhan, Pallab; Giri, Jyotsnendu; Banerjee, Rinti; Bellare, Jayesh; Bahadur, Dhirendra

    2007-04-01

    In vitro cytocompatibility and cellular interactions of lauric acid and dextran-coated magnetite nanoparticles were evaluated with two different cell lines (mouse fibroblast and human cervical carcinoma). Lauric acid-coated magnetite nanoparticles were less cytocompatible than dextran-coated magnetite nanoparticles and cellular uptake of lauric acid-coated magnetic nanoparticles was more than that of dextran-coated magnetite nanoparticles. Lesser cytocompatibility and higher uptake of lauric acid-coated magnetite nanoparticles as compared to dextran-coated magnetic nanoparticles may be due to different cellular interactions by coating material. Thus, coating plays an important role in modulation of biocompatibility and cellular interaction of magnetic nanoparticles.

  18. Pressure effect on the low-temperature remanences of multidomain magnetite: Change in the Verwey transition temperature

    NASA Astrophysics Data System (ADS)

    Sato, M.; Yamamoto, Y.; Nishioka, T.; Kodama, K.; Mochizuki, N.; Tsunakawa, H.

    2011-12-01

    The Verwey transition of magnetite is the basic issues for the rock magnetism, since main magnetic mineral of terrestrial rocks is magnetite and its associates. One of the most important issues concerning the Verwey transition is the change in transition temperature (Tv) due to pressure, which is thought to improve our understanding of its electric and magnetic nature in relation to the phase diagram. Recently, the opposite pressure effects of the transition temperature were reported applying the different experimental method. Measuring the electrical resistivity of single crystalline samples, Môri et al. [2002] reported that Tv becomes lower with increasing pressure by 9 GPa. In contrast, Pasternak et al. [2003] reported from Mössbauer experiment that transition temperature becomes higher with increasing pressure by 30 GPa. Thus the change in transition temperature with pressure has been controversial, and nature of the Verwey transition is still unclear. The magnetic property measurements using low temperature cycle are a powerful tool for identifying the state of magnetic minerals. Carporzen and Gilder [2010] conducted the thermal demagnetization experiment of low-temperature remanences of magnetite, and observed an increase in Tv with increasing pretreated pressure. From this result, they suggested that the Verwey transition of magnetite have the potential of a geobarometer. Modern techniques of high-pressure experiments enable us to measure sample magnetizations under pressure [Gilder et al., 2002; Kodama and Nishioka, 2005; Sadykov et al., 2008]. In the present study, systematic experiments of low-temperature remanences have been conducted for powder samples of stoichiometric magnetite under pressure up to 0.7 GPa using the high-pressure cell specially designed for MPMS, which was made of CuBe and ZrO2 [Kodama and Nishioka, 2005]. Natural magnetite of large single crystals were crushed by hand and sieved in an ultrasonic bath to be ~50 ?m in size. For relaxation of internal stress, powder samples were annealed in vacuum at 700 C with carbon buffer for several hours. The magnetite powders were dispersed in the glass wool and it was then placed in a Teflon capsule, which was filled by a pressure transmitting fluid. The high-pressure cell was connected with the end of the sample rod of MPMS and measured in a regular manner. We precisely measured thermal demagnetization curves of low-temperature isothermal remanent magnetization imparted at 20 K after cooling in zero-field and remanence acquired by cooling in 2.5 T DC field. The magnetite samples showed decrease in Tv under high-pressure, although decompressed samples exhibited the increase in Tv. Negative Clapeyron slope of the transition boundary is calculated to be -2.5 K/GPa to -4.0 K/GPa, supporting the results obtained by recent electrical resistivity measurement [Môri et al., 2002] and magnetic susceptibility measurement [Wieche? et al., 2005]. Decompressed samples also showed similar results obtained by thermal demagnetization experiment of low-temperature remanences [Carporzen and Gilder, 2010].

  19. Reproducible Crystallite Size of Mono-Dispersed and Scalable Biologically Produced Metal-Substituted Nanometer-Sized Magnetites

    Microsoft Academic Search

    J. Moon; C. Rawn; A. Rondinone; L. Love; Y. Roh; R. Lauf; T. Phelps

    2008-01-01

    Our previous research demonstrated that biosynthesized magnetite (biomagnetite) exhibited similar properties as chemically synthesized magnetite. To complement uses of the traditional chemically synthesized magnetite (chem-magnetite) biomagnetite must be exhibit highly reproducible sizes and be available in scalable qualities. Here we emphasize potentially advantageous properties of biomagnetite regarding size, reproducibility and scaling availability. Average crystallite size (ACS) of biomagnetites ranging from

  20. Magnetite Formation from Thermal Decomposition of Siderite: Implications for Inorganic Magnetite Formation in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Morris, RIchard V.

    2002-01-01

    A biogenic mechanism for formation of a subpopulation magnetite in Martian meteorite ALH84001 has been suggested [McKay et al., 1996; Thomas-Keprta, et al., 2000]. We are developing experimental evidence for an alternating working hypothesis, that the subpopulation was produced inorganically by the thermal decomposition of siderite [Golden et al., 2000].

  1. Magnetite-based Magnetoreception in Animals: 25+ Years of Theory & Experimentation

    NASA Astrophysics Data System (ADS)

    Kirschvink, J. L.; Walker, M. M.

    2005-12-01

    Living organisms ranging from bacteria through higher vertebrates rely on orientation, navigation, and homing to survive. Any sensory cue that enhances these behaviors will be subject to intense natural selection over geological time. Reproducible behavioral responses to earth-strength magnetic fields(1) have been documented in Bacteria, Protoctists, and in nearly every major group of animals, and are possibly also present in the Archaea. Several groups of animals, including birds and cetaceans, respond behaviorally to magnetic anomalies below 100 nT in magnitude, implying that their magnetoreception ability approaches the thermal noise limit. This approach to thermal noise is commonly observed in other sensory systems, including hearing, olfaction, and electroreception. The hypothesis of magnetite-based magnetoreception(2) is the only theory proposed so far that is capable of explaining all of the magnetic behavioral data. Tiny crystals of single-domain magnetite (or in some bacteria, greigite) rotate the cells of microorganisms passively like a simple compass needle. The initial detection of biogenic magnetite with rock magnetic techniques in birds and bees over 25 years ago has led progressively to the identification of a group of specialized cells in fish and birds which contain organized magnetite-containing structures. In these animals (and presumably all vertebrates) magnetic signals are transmitted to the brain via the ophthalmic branch of the trigeminal nerve(3, 4). Experiments with pulse-remagnetization, like those that convert North-seeking bacteria into South-seekers, have dramatic effects on animal behavior, confirming the role of magnetite in the sensory system. This is therefore a general mechanism for a highly sensitive magnetic sense, the origin of which probably dates to the ancestral metazoan, and perhaps earlier. The largest debate presently occurring in the field concerns the interpretation of magnetic compass responses that vary with intensity and color of light. Some biologists interpret the tendency of birds and amphibians to orient randomly under red lights, but not under shorter wavelengths, as evidence for the existence of a separate compass receptor involving light. However, even some magnetotactic bacteria change their behavior in red light,(5) and all such effects reported to date in animals can be explained simply as a visual influence on an animal's choice of behavior. Although the light-dependent mechanism might be physically plausible for a compass (but not for a high-resolution magnetic), natural selection cannot develop it without a separation from the visual system (exaptation), for which there is no evidence. 1. R. Wiltschko, W. Wiltschko, Magnetic orientation in animals, Zoophysiology (Springer, Berlin, 1995), pp. 297. 2. J. L. Kirschvink, Ph.D. Thesis, Princeton University (1979). 3. J. L. Kirschvink, M. M. Walker, C. Deibel, Current Opinion in Neurobiology 11, 462 (2001). 4. M. M. Walker, T. E. Dennis, J. L. Kirschvink, Current Opinion in Neurobiology 12, 735 (Dec, 2002). 5. R. B. Frankel, D. A. Bazylinski, M. S. Johnson, B. L. Taylor, Biophysical Journal 73, 994 (1997).

  2. Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States

    NASA Astrophysics Data System (ADS)

    Nadoll, Patrick; Mauk, Jeffrey L.; Leveille, Richard A.; Koenig, Alan E.

    2014-08-01

    A combination of petrographic observations, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and statistical data exploration was used in this study to determine compositional variations in hydrothermal and igneous magnetite from five porphyry Cu-Mo and skarn deposits in the southwestern United States, and igneous magnetite from the unmineralized, granodioritic Inner Zone Batholith, Japan. The most important overall discriminators for the minor and trace element chemistry of magnetite from the investigated porphyry and skarn deposits are Mg, Al, Ti, V, Mn, Co, Zn, and Ga—of these the elements with the highest variance for (I) igneous magnetite are Mg, Al, Ti, V, Mn, Zn, for (II) hydrothermal porphyry magnetite are Mg, Ti, V, Mn, Co, Zn, and for (III) hydrothermal skarn magnetite are Mg, Ti, Mn, Zn, and Ga. Nickel could only be detected at levels above the limit of reporting (LOR) in two igneous magnetites. Equally, Cr could only be detected in one igneous occurrence. Copper, As, Mo, Ag, Au, and Pb have been reported in magnetite by other authors but could not be detected at levels greater than their respective LORs in our samples. Comparison with the chemical signature of igneous magnetite from the barren Inner Zone Batholith, Japan, suggests that V, Mn, Co, and Ga concentrations are relatively depleted in magnetite from the porphyry and skarn deposits. Higher formation conditions in combination with distinct differences between melt and hydrothermal fluid compositions are reflected in Al, Ti, V, and Ga concentrations that are, on average, higher in igneous magnetite than in hydrothermal magnetite (including porphyry and skarn magnetite). Low Ti and V concentrations in combination with high Mn concentrations are characteristic features of magnetite from skarn deposits. High Mg concentrations (<1,000 ppm) are characteristic for magnetite from magnesian skarn and likely reflect extensive fluid/rock interaction. In porphyry deposits, hydrothermal magnetite from different vein types can be distinguished by varying Ti, V, Mn, and Zn contents. Titanium and V concentrations are highly variable among hydrothermal and igneous magnetites, but Ti concentrations above 3,560 ppm could only be detected in igneous magnetite, and V concentrations are on average lower in hydrothermal magnetite. The highest Ti concentrations are present in igneous magnetite from gabbro and monzonite. The lowest Ti concentrations were recorded in igneous magnetite from granodiorite and granodiorite breccia and largely overlap with Ti concentrations found in hydrothermal porphyry magnetite. Magnesium and Mn concentrations vary between magnetite from different skarn deposits but are generally greater than in hydrothermal magnetite from the porphyry deposits. High Mg, and low Ti and V concentrations characterize hydrothermal magnetite from magnesian skarn deposits and follow a trend that indicates that magnetite from skarn (calcic and magnesian) commonly has low Ti and V concentrations.

  3. Physics with chemically and isotopically pure semiconductors

    SciTech Connect

    Haller, E.E.

    1993-05-01

    Chemically and isotopically pure semiconductors offer a wealth of interesting physics. We review a number of impurity complexes which were discovered in ultrapure Germanium. The have led the way to the widely pursued studies of hydrogen in numerous semiconductors. Isotope related effects and processes include neutron transmutation doping, a technique used for a number of silicon and germanium devices. Isotopically pure and deliberately mixed crystals of germanium have been grown recently and have been used to study the dependence of the indirect bandgap and phonon properties on the mass and mass disorder of the nuclei. The large number of stable isotopes of the various semiconductors present a great potential for basic and applied studies. Semi-conductor isotope engineering may become a reality because of the new economic and political world order.

  4. X-ray diffraction study on size effects in epitaxial magnetite thin films on MgO(0?0?1)

    NASA Astrophysics Data System (ADS)

    Bertram, F.; Deiter, C.; Hoefert, O.; Schemme, T.; Timmer, F.; Suendorf, M.; Zimmermann, B.; Wollschläger, J.

    2012-10-01

    Epitaxial ultrathin iron oxide films of different thicknesses were grown by reactive molecular beam epitaxy in 10-6 mbar oxygen atmosphere on MgO(0?0?1) single crystal substrates at room temperature. Afterwards, the films were studied by x-ray diffraction, x-ray reflectivity and x-ray photoelectron spectroscopy to provide information regarding film structure as well as chemical composition of the films. Except for a very thin interface layer of subnanometre thickness, the iron oxide films have magnetite stoichiometry and structure and Mg does not diffuse from the substrate into the iron oxide film. The interface layer has a wuestite structure as determined by kinematic diffraction analysis. The magnetite films exhibit very homogeneous thickness while the vertical lattice constant decreases gradually towards its bulk value.

  5. Investigation of heteroepitaxial growth of magnetite thin films.

    SciTech Connect

    Sterbinsky, G. E.; Cheng, J.; Chiu, P. T.; Wessels, B. W.; Keavney, D. J.; X-Ray Science Division; Northwestern Univ.

    2007-07-01

    Epitaxial magnetite (Fe{sub 3}O{sub 4}) thin films were deposited by molecular beam epitaxy using molecular oxygen as the oxidant. Films deposited on (001) SrTiO{sub 3}, (001) MgO, and (001) BaTiO{sub 3} surfaces are epitaxial with the film (001) parallel to the substrate (001) and the film <100> parallel to the substrate <100>. X-ray magnetic circular dichroism was used to determine the relative Fe{sup 2+}/Fe{sup 3+} stoichiometry of the magnetite films, which was nearly independent of oxygen partial pressure over the range studied. All films show no in-plane magnetic anisotropy. Coercive fields ranged from 0.019 to 0.039 T and depended on film roughness.

  6. Iron spin transitions in high-pressure magnetite

    NASA Astrophysics Data System (ADS)

    Bengtson, A. K.; Morgan, D.; Becker, U.

    2009-12-01

    The spin state of iron (Fe) in materials deep within Earth’s mantle (primarily ferropericlase (Mg,Fe)O and (Mg,Fe)(Si,Fe,Al)O3 perovskite) has been of recent interest. The Fe high- to low-spin transition in ferropericlase is now well supported by both experiment and theory. However, the spin changes in perovskite are not as well understood, in part because perovskite contains more variables than ferropericlase: different valences (Fe3+ and Fe2+), substitutions (such as Al), two possible Fe sites, and varying Fe content. Experimental evidence using X-ray emission spectroscopy suggests the presence of intermediate-spin Fe in perovskite, but ab initio studies have not found intermediate-spin Fe to be stable with respect to high- or low-spin. In order to better understand these inconsistencies between experimental and computational results, we use ab initio methods to calculate the stable spin state in Fe3O4 magnetite, which also has X-ray emission spectroscopy evidence for a high- to intermediate-spin transition between 12-16 GPa [1]. Magnetite has two Fe sites, a tetrahedral site occupied by Fe3+ and an octahedral site, which has an average valence of 2.5+. At ambient pressure there is a charge ordering transition at 120K, where the low-temperature charge-ordered phase has valences [Fe3+]TET[Fe2+Fe3+]OCTO4 and the high-temperature charge-averaged phase has valences [Fe3+]TET[Fe2.5+Fe2.5+]OCTO4. We use ab initio methods to calculate the spin transition pressure for high- to intermediate-spin, high- to low-spin, and intermediate- to low-spin transitions in magnetite as a function of site (tetrahedral and octahedral), valence (2+, 2.5+, 3+), and charge state (charge averaged and charge ordered). Our results find that the charge-averaged symmetry (Fd-3m) has a spin collapse from high to low-spin on the octahedral site at 50 GPa and a gradual loss of moment on the tetrahedral site between 70 to 150 GPa. Fe in magnetite with charge ordering on the octahedral site (Imma and Pmca symmetries) is stable as high-spin up to 70 GPa (highest pressure of our study). Our calculations do not find intermediate-spin Fe to be stable with respect to high- or low-spin in magnetite. There now exist two systems, magnetite and perovskite, where experimental X-ray emission spectroscopy suggests Fe is in the intermediate-spin state but computational results do not find intermediate-spin Fe to be the most stable spin state. The results on spin transitions in magnetite are important for understanding Fe’s spin behavior in the lower mantle and better characterizing high-pressure regimes like subduction zones or other Fe-rich regions. The results could impact magnetotelluric measurements and geodynamic models. [1] Ding Y., et al Novel Pressure-Induced Magnetic Transition in Magnetite (Fe3O4). PRL. 100, 045508 (2008)

  7. Magnetite from magnetotactic bacteria: Size distributions and twinning

    Microsoft Academic Search

    BERTRAND DEVOUARD; MIHALY POSFAI; XIN HUA; DENNIS A. BAZYLINSKI; RICHARD B. FRANKEL; PETER R. BUSECK

    1998-01-01

    We studied intracellular magnetite particles produced by several morphological types of magnetotactic bacteria including the spirillar (helical) freshwater species, Magnetospirillum magnetotacticum,and four incompletely characterized marine strains: MV-1, a curved rod- shaped bacterium; MC-1 and MC-2, two coccoid (spherical) microorganisms; and MV-4, a spirillum. Particle morphologies, size distributions, and structural features were examined using conventional and high-resolution transmission electron microscopy. The

  8. Photoemission electronic states of epitaxially grown magnetite films

    Microsoft Academic Search

    R. Zalecki; A. Ko?odziejczyk; J. Korecki; N. Spiridis; M. Zaj?c; A. Koz?owski; Z. K?kol; D. Antolak

    2007-01-01

    The valence band photoemission spectra of epitaxially grown 300? single crystalline magnetite films were measured by the angle-resolved ultraviolet photoemission spectroscopy (ARUPS) at 300K. The samples were grown either on MgO(001) (B termination) or on (001) Fe (iron-rich A termination), thus intentionally presenting different surface stoichiometry, i.e. also different surface electronic states. Four main features of the electron photoemission at

  9. Investigation of magnetite thin films produced by pulsed laser deposition

    Microsoft Academic Search

    S. P. Sena; R. A. Lindley; H. J. Blythe; Ch. Sauer; M. Al-Kafarji; G. A. Gehring

    1997-01-01

    Thin films of magnetite (Fe3O4) with thicknesses in the range 10–1000 nm have been produced by the XeCl excimer laser (? = 308 nm) ablation of both Fe3O4 and metallic 57Fe targets. Deposition conditions have been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablation of metallic Fe has

  10. UV pulsed laser deposition of magnetite thin films

    Microsoft Academic Search

    M. L. Paramês; J. Mariano; M. S. Rogalski; N. Popovici; O. Conde

    2005-01-01

    Magnetite thin films were grown by pulsed laser deposition in O2 reactive atmosphere from Fe3O4 targets. The ablated material was deposited onto Si(100) substrates at various temperatures up to 623K. The temperature dependence of structure and stoichiometry was investigated by X-ray diffraction (XRD) and conversion electron Mössbauer spectroscopy (CEMS). The XRD results show that films grown between 483 and 623K

  11. Magnetite films grown directly on organic semiconductor layers

    Microsoft Academic Search

    V. Dediu; E. Arisi; I. Bergenti; A. Riminucci; M. Murgia; G. Ruani

    2006-01-01

    Magnetite (Fe3O4) films were grown directly on thin layers of two organic semiconductors (p-conjugated oligomers), 8-hydroxyquinoline aluminium (Alq3) and sexitiophene (T6) by pulsed electron beam deposition, also called channel spark ablation (CSA), for which spin injection effects have been demonstrated at low and room temperatures. The room temperature ferromagnetism for both kind of films found by magneto-optical Kerr rotation (MOKE)

  12. Investigation of heteroepitaxial growth of magnetite thin films

    Microsoft Academic Search

    G. E. Sterbinsky; J. Cheng; P. T. Chiu; B. W. Wessels; D. J. Keavney

    2007-01-01

    Epitaxial magnetite (FeO) thin films were deposited by molecular beam epitaxy using molecular oxygen as the oxidant. Films deposited on (001) SrTiO, (001) MgO, and (001) BaTiO surfaces are epitaxial with the film (001) parallel to the substrate (001) and the film <100> parallel to the substrate <100>. X-ray magnetic circular dichroism was used to determine the relative Fe{sup 2+}\\/Fe{sup

  13. Investigation of magnetite thin films produced by pulsed laser deposition

    Microsoft Academic Search

    H. J. Blythe; S. P. Sena; R. A. Lindley; G. A. Gehring; Ch. Sauer; M. Al-Kafarji

    1997-01-01

    Thin films of magnetite (Fe3O4) with thicknesses in the range 10-1000 nm have been produced by the XeCl excimer laser (lambda = 308 nm) ablation of both Fe3O4 and metallic e57Fe targets. Deposition conditions have been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablation of metallic Fe has

  14. Magnetic and transport properties of magnetite thin films

    Microsoft Academic Search

    Guomin Zhang; Chongfei Fan; Liqing Pan; Fengping Wang; Ping Wu; Hong Qiu; Yousong Gu; Yue Zhang

    2005-01-01

    Magnetite (Fe3O4) films were prepared by DC reactive magnetron sputtering at various oxygen partial pressures with the ratio ? of oxygen to argon changing from 0.50:50 to 0.70:50 at room temperature, and then the Fe3O4 films were annealed at 480°C for 80min. The properties of the films were studied by X-ray diffraction, scanning electron microscopy, magnetic hysteresis loops, magnetoresistance (MR),

  15. Magnetization and susceptibility of ion-irradiated granular magnetite films

    Microsoft Academic Search

    Weilin Jiang; John S. McCloy; Alan S. Lea; J. A. Sundararajan; Qi Yao; Y. Qiang

    2011-01-01

    Porous granular films of magnetite (Fe3O4) with grains of ˜3 nm in size were prepared using a state-of-the-art nanocluster deposition system. The films are initially superparamagnetic but become magnetized following Si2+ ion irradiation. A significant increase in the grain size and a dramatic change in the microstructure are observed. There are dipolar interactions between the nanoparticles in both the unirradiated

  16. Patterned magnetite films prepared via soft lithography and thermal decomposition

    Microsoft Academic Search

    Lijuan An; Zhaoqiang Li; Wei Li; Yaru Nie; Zhimin Chen; Yanping Wang; Bai Yang

    2006-01-01

    A method for the fabrication of patterned magnetite (Fe3O4) films is presented. We first prepared an ordered 2D array of Fe(acac)3 through a selective deposition technique on patterned self-assembled monolayers. Using thermal decomposition at elevated temperature (300°C), we transformed the patterned Fe(acac)3 into patterned Fe3O4 films in a short reaction time. These patterned films have been confirmed by using optical

  17. Magnetoresistance at grain boundaries artificially introduced into magnetite films

    Microsoft Academic Search

    M. Ziese; R. Höhne; N. H Hong; J. Dienelt; K. Zimmer; P. Esquinazi

    2002-01-01

    Magnetotransport data of step-edge junctions fabricated in magnetite (Fe3O4) films are presented. An enhancement of the low field magnetoresistance of these step-edge junctions as evidenced by measurements with the electrical current along and across the step edges was observed. This is especially pronounced in a film on patterned MgAl2O4 which additionally shows a significant geometrically induced resistivity anisotropy. The enhanced

  18. Adsorption of naphthenic acid on magnetite at different temperatures

    NASA Astrophysics Data System (ADS)

    Balmasova, O. V.; Ramazanova, A. G.; Korolev, V. V.

    2015-03-01

    Isotherms of naphthenic acid adsorption from heptane solutions on highly dispersed magnetite are studied using the adsorption equilibrium approach. The isosteric heats of naphthenic acid adsorption from heptane solutions are calculated over a temperature range of 293-308 K. The adsorption isotherms can be approximated using the equation for a straight line. Experimental adsorption isotherms are shown to be linear in the coordinates of the equation for the theory of volume filling of micropores (TVFM).

  19. Photostimulated Oxidation of Magnetite 1. Kinetics and Alteration Phase Identification

    Microsoft Academic Search

    Robert L. Huguenin

    1973-01-01

    It has been demonstrated that magnetite (PesOs) becomes oxidized upon exposure to ultra- violet and visible radiation in 02-bearing atmospheres. X ray diffraction and diffuse reflectance studies of the oxidation product indicate that hematite (.a-Fe20a) is the principal reaction phase, although some maghemite ('y-Fe2Oa) may also be produced. A_ set of kinetic constraints on the photostimulated oxidation mechanism has been

  20. Recovery of recombinant Escherichia coli by chitosan-conjugated magnetite

    Microsoft Academic Search

    Hiroyuki Honda; Atsushi Kawabe; Masashige Shinkai; Takeshi Kobayashi

    1999-01-01

    Magnetic separation of a recombinant Escherichia coli harboring the ?-galactosidase gene was investigated. We prepared a chitosan-conjugated magnetite (chitosan-mag) that disperses well in aqueous solution. After adding it to a cell suspension, it can recover various microorganisms including E. coli as the precipitant within only 1min. Over 90% of E. coli cells were recovered in a wide pH range from

  1. Electrical impedance spectroscopy investigation of surfactant–magnetite–polypyrrole particles

    Microsoft Academic Search

    H. P. de Oliveira; C. A. S. Andrade; C. P. de Melo

    2008-01-01

    We report an electrical impedance spectroscopy (EIS) characterization of composite systems formed by emulsion polymerization of polypyrrole (PPY) in concentrated aqueous solutions of sodium dodecyl sulfate (SDS) containing dispersed magnetite particles. SDS–(Fe3O4)–(conducting polymer) microaggregates with different iron contents were prepared by varying in a reciprocal manner the relative amounts of the metal oxide and PPY. We have measured the zeta-potential

  2. SIZE-OPTIMIZED MAGNETITE NANOPARTICLES FOR MAGNETIC PARTICLE IMAGING

    SciTech Connect

    Ferguson, R. Matthew; Khandhar, Amit P.; Minard, Kevin R.; Krishnan, Kannan M.

    2010-06-01

    We present experimental results to demonstrate that there is an optimum size for magnetite nanoparticles that are used to generate MPI signal, where the signal is detected as the third harmonic of nanoparticle magnetization, M, for any driving field frequency, ?. Our experimental results, for an arbitrarily chosen ? = 250 kHz, agree with predictions for a nanoparticle magnetization model based on the Langevin theory of superparamagnetism.

  3. Hematite Versus Magnetite as the Signature for Planetary Magnetic Anomalies?

    NASA Technical Reports Server (NTRS)

    Kletetshka, Gunther; Taylor, Patrick T.; Wasilewski, Peter J.

    1999-01-01

    Crustal magnetic anomalies are the result of adjacent geologic units having contrasting magnetization. This magnetization arises from induction and/or remanence. In a planetary context we now know that Mars has significant crustal magnetic anomalies due to remanent magnetization, while the Earth has some anomalies where remanence can be shown to be important. This picture, however, is less clear because of the nature and the magnitude of the geomagnetic field which is responsible for superimposed induced magnetization. Induced magnetization assumes a magnetite source, because of its much greater magnetic susceptibility when compared with other magnetic minerals. We investigated the TRM (thermoremanent magnetization) acquisition of hematite, in weak magnetic fields up to 1 mT, to determine if the remanent and induced magnetization of hematite could compete with magnetite. TRM acquisition curves of magnetite and hematite show that multi-domain hematite reaches TRM saturation (0.3 - 0.4 A sq m/kg) in fields as low as 100 microT. However, multi-domain magnetite reaches only a few percent of its TRM saturation in a field of 100 microT (0.02 - 0.06 A sq m/kg). These results suggest that a mineral such as hematite and, perhaps, other minerals with significant remanence and minor induced magnetization may play an important role in providing requisite magnetization contrast. Perhaps, and especially for the Mars case, we should reevaluate where hematite and other minerals, with efficient remanence acquisition, exist in significant concentration, allowing a more comprehensive explanation of Martian anomalies and better insight into the role of remanent magnetization in terrestrial crustal magnetic anomalies.

  4. Magnetite-Alginate-AOT nanoparticles based drug delivery platform

    NASA Astrophysics Data System (ADS)

    Regmi, R.; Sudakar, C.; Dixit, A.; Naik, R.; Lawes, G.; Toti, U.; Panyam, J.; Vaishnava, P. P.

    2008-03-01

    Iron oxide having the magnetite structure is a widely used biomaterial, having applications ranging from cell separation and drug delivery to hyperthermia. In order to increase the efficacy of drug treatments, magnetite nanoparticles can be incorporated into a composite system with a surfactant-polymer nanoparticle, which can act as a platform for sustained and enhanced cellular delivery of water-soluble molecules. Here we report a composite formulation based on magnetite and Alginate-aerosol OT (AOT) nanoparticles formulated using an emulsion-cross-linking process loaded with Rhodamine 6G [1]. We prepared two set of nanoparticles by using Ca^2+ or Fe^2+ to cross-link the alginate polymer. Additionally, we added ˜8 nm diameter Fe3O4 magnetic nanoparticles prepared by a soft chemical method to these alginate-AOT nanoparticles. The resulting composites were superparamagnetic at room temperature, with a saturation magnetization of approximately 0.006 emu/g of solution. We will present detailed studies on the structural and magnetic properties of these samples. We will also discuss HPLC measurements on Rhodamine uploading in these composites. [1] M.D.Chavanpatil, Pharmaceutical Research, vol.24, (2007) 803.

  5. Magnetostatic interactions in a natural magnetite-ulvöspinel system

    NASA Astrophysics Data System (ADS)

    Evans, Michael E.; KráSa, David; Williams, Wyn; Winklhofer, Michael

    2006-12-01

    Magnetostatic interactions have been investigated in an intergrown material consisting of ˜200-nm magnetite blocks separated by ˜30-nm-wide ulvöspinel lamellae. First-order reversal curve (FORC) measurements provide a direct measure of the interaction fields, giving a value for the full width at half maximum (FWHM) of 30 mT (atHc = 20 mT). Hysteresis parameters are Mrs/Ms = 0.22, Hcr/Hc = 1.98 and transient energy dissipation (TED) = 0.18. Elimination of the intergrowth structure (by heating in vacuo) causes the FORC contours to shrink down toward the origin, yielding FWHM = 14 mT (at Hc = 6 mT) with corresponding changes in Mrs/Ms, Hcr/Hc and TED to 0.11, 2.73 and 0.28, respectively. All these characteristics reveal the strong influence of particle-to-particle magnetostatic interactions between the magnetite blocks in the starting material and demonstrate the change from single-domain/pseudosingle-domain to multidomain behavior due to the fundamental structural change brought about by the experimental homogenization. Micromagnetic calculations of particle assemblages representative for the intergrown structure confirm that the magnetite blocks will interact by assuming a supervortex magnetization structure.

  6. Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria

    E-print Network

    Dunin-Borkowski, Rafal E.

    Magnetic Microstructure of Closely-Spaced Ferrimagnetic Crystals in Magnetotactic Bacteria R. E of Cambridge, Pembroke Street, Cambridge CB2 3QZ, United Kingdom Magnetotactic bacteria migrate along of magnetite and greigite crystals in air-dried cells of magnetotactic bacteria, with sub-10-nm spatial

  7. Production of nano zinc, zinc sulphide and nanocomplex of magnetite zinc oxide by Brevundimonas diminuta and Pseudomonas stutzeri.

    PubMed

    Mirhendi, Mansoureh; Emtiazi, Giti; Roghanian, Rasoul

    2013-12-01

    ZnO (Zincite) nanoparticle has many industrial applications and is mostly produced by chemical reactions, usually prepared by decomposition of zinc acetate or hot-injection and heating-up method. Synthesis of semi-conductor nanoparticles such as ZnS (Sphalerite) by ultrasonic was previously reported. In this work, high-zinc tolerant bacteria were isolated and used for nano zinc production. Among all isolated microorganisms, a gram negative bacterium which was identified as Brevundimonas diminuta could construct nano magnetite zinc oxide on bacterial surface with 22 nm in size and nano zinc with 48.29 nm in size. A piece of zinc metal was immersed in medium containing of pure culture of B. diminuta. Subsequently, a yellow-white biofilm was formed which was collected from the surface of zinc. It was dried at room temperature. The isolated biofilm was analysed by X-ray diffractometer. Interestingly, the yield of these particles was higher in the light, with pH 7 at 23°C. To the best of the authors knowledge, this is the first report about the production of nano zinc metal and nano zinc oxide that are stable and have anti-bacterial activities with magnetite property. Also ZnS (sized 12 nm) produced by Pseudomonas stutzeri, was studied by photoluminescence and fluorescent microscope. PMID:24206770

  8. Bench-Scale Testing of the Micronized Magnetite Process

    SciTech Connect

    Edward R. Torak; Peter J. Suardini

    1997-11-01

    A recent emphasis of the Department of Energy's (DOE's), Coal Preparation Program has been the development of high-efficiency technologies that offer near-term, low-cost improvements in the ability of coal preparation plants to address problems associated with coal fines. In 1992, three cost-shared contracts were awarded to industry, under the first High-Efficiency Preparation (HEP I) solicitation. All three projects involved bench-scale testing of various emerging technologies, at the Federal Energy Technology Center*s (FETC*s), Process Research Facility (PRF). The first HEP I project, completed in mid-1993, was conducted by Process Technology, Inc., with the objective of developing a computerized, on-line system for monitoring and controlling the operation of a column flotation circuit. The second HEP I project, completed in mid-1994, was conducted by a team led by Virginia Polytechnic Institute to test the Mozely Multi-Gravity Separator in combination with the Microcel Flotation Column, for improved removal of mineral matter and pyritic sulfur from fine coal. The last HEP I project, of which the findings are contained in this report, was conducted by Custom Coals Corporation to evaluate and advance a micronized-magnetite-based, fine-coal cycloning technology. The micronized-magnetite coal cleaning technology, also know as the Micro-Mag process, is based on widely used conventional dense-medium cyclone applications, in that it utilizes a finely ground magnetite/water suspension as a separating medium for cleaning fine coal, by density, in a cyclone. However, the micronized-magnetite cleaning technology differs from conventional systems in several ways: ! It utilizes significantly finer magnetite (about 5 to 10 micron mean particle size), as compared to normal mean particle sizes of 20 microns. ! It can effectively beneficiate coal particles down to 500M in size, as compared to the most advanced, existing conventional systems that are limited to a particle bottom size of about 28M - 100 M. ! Smaller diameter cyclones, 4 to 10 inches, are used to provide the higher G-force required to separate the finer feed coal. ! Cyclone feed pressures up to 10 times greater than those used in conventional cleaning systems are employed to enhance the separating forces.

  9. Magnetite nanoparticle-loaded anti-HER2 immunoliposomes for combination of antibody therapy with hyperthermia

    Microsoft Academic Search

    Akira Ito; Yuko Kuga; Hiroyuki Honda; Hiroyuki Kikkawa; Atsushi Horiuchi; Yuji Watanabe; Takeshi Kobayashi

    2004-01-01

    Anti-HER2 antibody can induce antitumor responses, and can be used in delivering drugs to HER2-overexressing cancer. Previously, we produced hyperthermia using magnetite nanoparticles that generate heat in an alternating magnetic field. In the present study, we constructed anti-HER2 immunoliposomes containing magnetite nanoparticles, which act as tumor-targeting vehicles, combining anti-HER2 antibody therapy with hyperthermia. The magnetite nanoparticle-loaded anti-HER2 immunoliposomes exerted HER2-mediated

  10. Force interactions between magnetite, silica, and bentonite studied with atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Dobryden, I.; Potapova, E.; Holmgren, A.; Weber, H.; Hedlund, J.; Almqvist, N.

    2015-04-01

    Iron ore pellets consist of variety of mineral particles and are an important refined product used in steel manufacturing. Production of high-quality pellets requires good understanding of interactions between different constituents, such as magnetite, gangue residues, bentonite, and additives. Much research has been reported on magnetite, silica, and bentonite surface properties and their effect on pellet strength but more scant with a focus on a fundamental particle-particle interaction. To probe such particle interaction, atomic force microscopy (AFM) using colloidal probe technique has proven to be a suitable tool. In this work, the measurements were performed between magnetite-magnetite, bentonite-magnetite, silica-bentonite, and silica-magnetite particles in 1 mM CaCl2 solution at various pH values. The interaction character, i.e., repulsion or attraction, was determined by measuring and analyzing AFM force curves. The observed quantitative changes in interaction forces were in good agreement with the measured zeta-potentials for the particles at the same experimental conditions. Particle aggregation was studied by measuring the adhesion force. Absolute values of adhesion forces for different systems could not be compared due to the difference in particle size and contact geometry. Therefore, the relative change of adhesion force between pH 6 and 10 was used for comparison. The adhesion force decreased for the magnetite-magnetite and bentonite-silica systems and slightly increased for the magnetite-bentonite system at pH 10 as compared to pH 6, whereas a pronounced decrease in adhesion force was observed in the magnetite-silica system. Thus, the presence of silica particles on the magnetite surface could have a negative impact on the interaction between magnetite and bentonite in balling due to the reduction of the adhesion force.

  11. Diagenetic magnetite carries ancient yet secondary remanence in some Paleozoic sedimentary carbonates

    NASA Astrophysics Data System (ADS)

    McCabe, Chad; van der Voo, Rob; Peacor, Donald R.; Scotese, Christopher R.; Freeman, Roy

    1983-04-01

    Many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite. When such magnetizations are observed, it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition. However, paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the Helderberg and Bonneterre carbonates (United States) indicate that the magnetite present in these rocks is most likely of diagenetic (i.e., postdepositional) origin.

  12. Experimental Shock Decomposition of Siderite and the Origin of Magnetite in Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Bell, Mary Sue

    2007-01-01

    Shock recovery experiments to determine whether magnetite could be produced by the decomposition of iron-carbonate were initiated. Naturally occurring siderite was first characterized by electron microprobe (EMP), transmission electron microscopy (TEM), Mossbauer spectroscopy, and magnetic susceptibility measurements to be sure that the starting material did not contain detectable magnetite. Samples were shocked in tungsten-alloy holders (W=90%, Ni=6%, Cu=4%) to further insure that any iron phases in the shock products were contributed by the siderite rather than the sample holder. Each sample was shocked to a specific pressure between 30 to 49 GPa. Previously reported results of TEM analyses on 49 GPa experiments indicated the presence of nano-phase spinel-structured iron oxide. Transformation of siderite to magnetite as characterized by TEM was found in the 49 GPa shock experiment. Compositions of most magnetites are greater than 50% Fe sup(+2) in the octahedral site of the inverse spinel structure. Magnetites produced in shock experiments display the same range of single-domain, superparamagnetic sizes (approx. 50 100 nm), compositions (100% magnetite to 80% magnetite-20% magnesioferrite), and morphologies (equant, elongated, euhedral to subhedral) as magnetites synthesized by Golden et al. (2001) or magnetites grown naturally by MV1 magnetotactic bacteria, and as the magnetites in Martian meteorite ALH84001. Fritz et al. (2005) previously concluded that ALH84001 experienced approx. 32 GPa pressure and a resultant thermal pulse of approx. 100 - 110 C. However, ALH84001 contains evidence of local temperature excursions high enough to 1 melt feldspar, pyroxene, and a silica-rich phase. This 49 GPa experiment demonstrates that magnetite can be produced by the shock decomposition of siderite as a result of local heating to greater than 470 C. Therefore, magnetite in the rims of carbonates in Martian meteorite ALH84001 could be a product of shock devolatilization of siderite as well.

  13. Soft X-ray Spectroscopy Study of the Electronic Structure of Oxidized and Partially Oxidized Magnetite Nanoparticles

    SciTech Connect

    Gilbert, Benjamin; Katz, Jordan E.; Denlinger, Jonathan D.; Yin, Yadong; Falcone, Roger; Waychunas, Glenn A.

    2010-10-24

    The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed-valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, and soft X-ray absorption and emission spectroscopy to characterize the products of oxidizing uncoated and oleic acid-coated magnetite nanoparticles in air. The oxidization of uncoated magnetite nanoparticles creates a material that is structurally and electronically indistinguishable from maghemite. By contrast, while oxidized oleic acid-coated nanoparticles are also structurally indistinguishable from maghemite, Fe L-edge spectroscopy revealed the presence of interior reduced iron sites even after a 2-year period. We used X-ray emission spectroscopy at the O K-edge to study the valence bands (VB) of the iron oxide nanoparticles, using resonant excitation to remove the contributions from oxygen atoms in the ligands and from low-energy excitations that obscured the VB edge. The bonding in all nanoparticles was typical of maghemite, with no detectable VB states introduced by the long-lived, reduced-iron sites in the oleic acid-coated sample. However, O K-edge absorption spectroscopy observed a 0.2 eV shift in the position of the lowest unoccupied states in the coated sample, indicating an increase in the semiconductor band gap relative to bulk stoichiometric maghemite that was also observed by optical absorption spectroscopy. The results show that the ferrous iron sites within ferric iron oxide nanoparticles coated by an organic ligand can persist under ambient conditions with no evidence of a distinct interior phase and can exert an effect on the global electronic and optical properties of the material. This phenomenon resembles the band gap enlargement caused by electron accumulation in the conduction band of TiO2.

  14. Reaction of U-VI with titanium-substituted magnetite: Influence of Ti on U-IV speciation

    SciTech Connect

    Latta, Drew; Pearce, Carolyn I.; Rosso, Kevin M.; Kemner, Kenneth M.; Boyanov, Maxim I.

    2013-07-01

    Reduction of hexavalent uranium (UVI) to less soluble tetravalent uranium (UIV) through enzymatic or abiotic redox reactions has the potential to alter U mobility in subsurface environments. As a ubiquitous natural mineral, magnetite (Fe3O4) is of interest because of its ability to act as a rechargeable reductant for UVI. Natural magnetites are often impure with titanium, and structural Fe3+ replacement by TiIV yields a proportional increase in the relative Fe2+ content in the metal sublattice to maintain bulk charge neutrality. In the absence of oxidation, the Ti content sets the initial bulk Fe2+/Fe3+ ratio (R). Here, we demonstrate that Ti-doped magnetites (Fe3 xTixO4) reduce UVI to UIV. The UVI-Fe2+ redox reactivity was found to be controlled directly by R, but was otherwise independent of Ti content (xTi). However, in contrast to previous studies with pure magnetite where UVI was reduced to nanocrystalline uraninite (UO2), the presence of structural Ti (xTi = 0.25 0.53) results in the formation of UIV species that lack the bidentate U-O2-U bridges of uraninite. Extended x-ray absorption fine structure spectroscopic analysis indicated that the titanomagnetite-bound UIV phase has a novel UIV-Ti binding geometry, different from the coordination of UIV in the mineral brannerite (UIVTi2O6). The observed UIV-Ti coordination at a distance of 3.43 Å suggests a binuclear corner-sharing adsorption/incorporation UIV complex with the solid phase. Furthermore, we explored the effect of oxidation (decreasing R) and solids-to-solution ratio on the reduced UIV phase. The formation of the non-uraninite UIV-Ti phase appears to be controlled by availability of surface Ti sites, rather than R. Our work highlights a previously unrecognized role of Ti in the environmental chemistry of UIV and suggests that further work to characterize the long-term stability of UIV phases formed in the presence of Ti is warranted.

  15. Tuning of multiferroic orders correlated to oxygen stoichiometry in magnetite films

    NASA Astrophysics Data System (ADS)

    Dey, K.; Ghosh, A.; Modak, P.; Indra, A.; Majumdar, S.; Giri, S.

    2014-10-01

    Magnetite films are grown on Si(100) substrate using pulsed laser deposition technique. The deposition is performed at three fixed oxygen pressures of 0.4 × 10-6, 4.0 × 10-6, and 10 × 10-6 Torr keeping other conditions fixed. Raman and x-ray photoemission spectroscopies confirm formation of single magnetite phase for the first two pressures and a mixed phase composed of magnetite and hematite for the highest pressure. A trivial change in oxygen stoichiometry of magnetite is found crucial for the multiferroic orders at room temperature and below the charge ordering temperature. Possible mechanisms of multiferroic orders driven by change in oxygen stoichiometry are discussed.

  16. Synthesis of chiral hybrid nanotubes of magnetite nanoparticles and conducting polymers

    NASA Astrophysics Data System (ADS)

    Mitsumori, Masashi; Nakahodo, Tsukasa; Fujihara, Hisashi

    2011-12-01

    New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization.New chiral magnetite nanoparticles with a polymerizable group produced polymer composite films on an electrode surface and the hybrid nanotubes of magnetite nanoparticles and polythiophene from their template-based electropolymerization. Electronic supplementary information (ESI) available: Synthesis of a chiral stabilizer 1 and the spectral data. See DOI: 10.1039/c1nr11312g

  17. Synthesis, characterization and magnetoresistance properties study of magnetite thin films by electroless plating in aqueous solution

    Microsoft Academic Search

    Jianrong Sun; Zhiguang Wang; Yuyu Wang; Yabin Zhu; Kongfang Wei; Tielong Shen; Fashen Li

    Polycrystalline half-metallic Fe3O4 films with 1 ?m in thickness were synthesized on glass substrates directly by electroless plating in aqueous solution at 90 °C without heat treatment. The films have single pure spinal phase structure and the well-crystallized columnar grains grow perpendicularly to the substrates, as revealed by XRD, XPS and SEM. At room temperature, the films exhibit negative magnetoresistance (MR) ratio

  18. Typical pure nonequilibrium steady states

    NASA Astrophysics Data System (ADS)

    Monnai, Takaaki; Yuasa, Kazuya

    2014-08-01

    We show that typicality holds for a class of nonequilibrium systems, i.e., nonequilibrium steady states (NESSs): almost all the pure states properly sampled from a certain Hilbert space well represent a NESS and characterize its intrinsic thermal nature. We clarify the relevant Hilbert space from which the pure states are to be sampled, and construct practically all the typical pure NESSs. The scattering approach leads us to the natural extension of the typicality for equilibrium systems. Each pure NESS correctly yields the expectation values of observables given by the standard ensemble approach. It means that we can calculate the expectation values in a NESS with only a single pure NESS. We provide an explicit construction of the typical pure NESS for a model with two reservoirs, and see that it correctly reproduces the Landauer-type formula for the current flowing steadily between the reservoirs.

  19. Typical Pure Nonequilibrium Steady States

    E-print Network

    Takaaki Monnai; Kazuya Yuasa

    2014-08-12

    We show that typicality holds for a class of nonequilibrium systems, i.e., nonequilibrium steady states (NESSs): almost all the pure states properly sampled from a certain Hilbert space well represent a NESS and characterize its intrinsic thermal nature. We clarify the relevant Hilbert space from which the pure states are to be sampled, and construct practically all the typical pure NESSs. The scattering approach leads us to the natural extension of the typicality for equilibrium systems. Each pure NESS correctly yields the expectation values of observables given by the standard ensemble approach. It means that we can calculate the expectation values in a NESS with only a single pure NESS. We provide an explicit construction of the typical pure NESS for a model with two reservoirs, and see that it correctly reproduces the Landauer-type formula for the current flowing steadily between the reservoirs.

  20. Crystal structures of carbonates up to Mbar pressures determined by single crystal synchrotron radiation diffraction

    NASA Astrophysics Data System (ADS)

    Merlini, M.

    2013-12-01

    The recent improvements at synchrotron beamlines, currently allow single crystal diffraction experiments at extreme pressures and temperatures [1,2] on very small single crystal domains. We successfully applied such technique to determine the crystal structure adopted by carbonates at mantle pressures. The knowledge of carbon-bearing phases is in fact fundamental for any quantitative modelling of global carbon cycle. The major technical difficulty arises after first order transitions or decomposition reactions, since original crystal (apx. 10x10x5 ?m3) is transformed in much smaller crystalline domains often with random orientation. The use of 3D reciprocal space visualization software and the improved resolution of new generation flat panel detectors, however, allow both identification and integration of each single crystal domain, with suitable accuracy for ab-initio structure solution, performed with direct and charge-flipping methods and successive structure refinements. The results obtained on carbonates, indicate two major crystal-chemistry trends established at high pressures. The CO32- units, planar and parallel in ambient pressure calcite and dolomite structures, becomes non parallel in calcite- and dolomite-II and III phases, allowing more flexibility in the structures with possibility to accommodate strain arising from different cation sizes (Ca and Mg in particular). Dolomite-III is therefore also observed to be thermodynamically stable at lower mantle pressures and temperatures, differently from dolomite, which undergoes decomposition into pure end-members in upper mantle. At higher pressure, towards Mbar (lowermost mantle and D'' region) in agreement with theoretical calculations [3,4] and other experimental results [5], carbon coordination transform into 4-fold CO4 units, with different polymerisation in the structure depending on carbonate composition. The second important crystal chemistry feature detected is related to Fe2+ in Fe-bearing magnesite, which spontaneously oxidises at HP/HT, forming Fe3+ carbonates, Fe3+ oxides and reduced carbon (diamonds). Single crystal diffraction approach allowed full structure determination of these phases, yielding to the discovery of few unpredicted structures, such as Mg2Fe2C4O13 and Fe13O19, which can be well reproduced in different experiments. Mg2Fe2C4O13 carbonate present truncated chain C4O13 groups, and Fe13O19 oxide, whose stoichiometry is intermediate between magnetite and hematite, is a one-layer structure, with features encountered in superconducting materials. The results fully support the ideas of unexpected complexities in the mineralogy of the lowermost mantle, and single crystal technique, once properly optimized in ad-hoc synchrotron beamlines, is fundamental for extracting accurate structural information, otherwise rarely accessible with other experimental techniques. References: [1] Merlini M., Hanfland M. (2013). Single crystal diffraction at Mbar conditions by synchrotron radiation. High Pressure Research, in press. [2] Dubrovinsky et al., (2010). High Pressure Research, 30, 620-633. [3] Arapan et al. (1997). Phys. Rev. Lett., 98, 268501. [4] Oganov et al. (2008) EPSL, 273, 38-47. [5] Boulard et al. (2011) PNAS, 108, 5184-5187.

  1. Magnetorheological behavior of magnetite covered clay particles in aqueous suspensions

    NASA Astrophysics Data System (ADS)

    Galindo-Gonzalez, C.; Lopez-Lopez, M. T.; Duran, J. D. G.

    2012-08-01

    Montmorillonite clay particles coated with magnetite nanoparticles suspended in aqueous media behave as magnetorheological fluids with enhanced stability as compared to conventional ones. In this work, the study of the magnetorheological behavior of these suspensions of magnetite-clay composite particles has been carried out. For this purpose, both steady and dynamic rheological measurements were carried out in the absence and in the presence of external magnetic fields. In the first kind of experiments, the rheograms of the suspensions (shear stress versus shear rate plot) are analyzed as a function of the strength of the magnetic field applied. In the second one, oscillatory stresses are applied to the system, and the storage modulus is studied as a function of the external magnetic field. In the absence of magnetic field, the suspensions develop a weak yield stress due to the aggregation of the magnetite covered clay particles. In the presence of magnetic field, the yield stress is strongly dependent on the magnetic field strength inside the samples, demonstrating that the suspensions experience a magnetorheological effect, moderate when the magnetic field strength is weak and stronger for values of magnetic field higher than 150-200 kA/m. Actually, the most intriguing result is the change of the trend in the dependence of the yield stress with the field. This dependence is approximately linear with the field for strength values smaller than 150-200 kA/m. On the other hand, for higher values, the yield stress increases with magnetic field following a power law with exponent 4.5.The results are interpreted by means of a model that relates the structure of the particles in the suspensions to the magnetic field applied and using the interaction energy between particles calculated by the extended DLVO theory to include magnetic interaction.

  2. Mechanism of fast growth of magnetite on carbon steel

    SciTech Connect

    Macdonald, D.D.

    1985-07-01

    The corrosion of and the growth of magnetite on carbon steel in chloride-containing aqueous solutions at temperatures from 200 to 270/sup 0/C and for times up to 400 hours have been studied using ac impedance and scanning electron microscopy techniques. Thick and porous magnetite films form in solutions which are acidic because of the presence of HCL or by hydrolysis of cupric, ferric, nickelous and ferrous chlorides. The reciprocal of the polarization resistance, which is proportional to the corrosion rate, increases with time (i.e., autocatalysis), but eventually tends to a constant value (i.e., a linear rate law). Autocatalytic corrosion is attributed to the gradual development of a highly aggressive solution within the porous film due to the hydrolysis of ferrous ions dissolved from the base metal and the transport of chloride ions from the bulk solution into the pores. However, the reciprocal decreases with time (i.e., self-passivation) when thin and compact magnetite films form in neutral or slightly acidic chloride solutions. The frequency dispersion of the impedance of the growing film has been successfully accounted for by a finite electrical transmission line model. Numerical analysis has shown that the total impedance is a sensitive function of the film geometry and of the inter-facial impedances along the pore wall and at the base of the pore. These analyses have demonstrated that the ac impedance technique is well suited for studying the corrosion of metals and the growth of corrosion product films in aqueous systems. 39 refs., 25 figs., 1 tab.

  3. Synthesis of monodispersed magnetite nanoparticles from iron pivalate clusters.

    PubMed

    Abdulwahab, Khadijat; Malik, Mohammad A; O'Brien, Paul; Govender, Kuveshni; Muryn, Christopher A; Timco, Grigore A; Tuna, Floriana; Winpenny, Richard E P

    2013-01-01

    The iron pivalate clusters [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu (1), [Fe(8)(OH)(4)(O(2)C(t)Bu)(12)(OC(6)H(4)C(6)H(5))(8)] (2) and [Fe(3)O(O(2)C(t)Bu)(6)(C(5)H(5)N)(3)] (3) have been used as single source precursors to synthesise iron oxide nanoparticles by a hot injection thermal decomposition method in oleylamine, hexadecanol, oleic acid, oleylamine/oleic acid with dodecanol or octyl ether as solvent. The effect of the different reaction parameters such as temperature, reaction time and capping agents on the phase and morphology were studied. The reaction time was studied for (1) by thermolysis in a mixture of oleylamine, oleic acid, hexadecanol and dodecanol (solvent) at 260 °C. The results obtained showed that a mixture of maghemite-C (Fe(2)O(3)) and magnetite (Fe(3)O(4)) were obtained for aliquots withdrawn for reaction times of less than 30 minutes whilst only magnetite was obtained after one hour. The nanoparticles were characterised by p-XRD, TEM and magnetic measurements. TEM showed that monodispersed magnetite particles were obtained when the precursor was injected at the boiling point of the solvent. The diameter of the monodispersed nanoparticles obtained by the thermolysis of [Fe(3)O(O(2)C(t)Bu)(6)(H(2)O)(3)](O(2)C(t)Bu)·HO(2)C(t)Bu (1) in oleylamine, hexadecanol, oleic acid with dodecanol or octyl ether as solvent were 4.3 ± 0.4 and 4.9 ± 0.5 nm respectively. Magnetic measurements revealed that all the particles are superparamagnetic. PMID:23132230

  4. Superexchange coupling on oleylsarcosine-coated magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Bakuzis, A. F.; Pereira, A. R.; Santos, J. G.; Morais, P. C.

    2006-04-01

    Room temperature ferromagnetic resonance was used to investigate particle-particle interaction in magnetic fluid samples containing magnetite nanoparticles surface coated with dimercaptosuccinic acid (DMSA) or oleylsarcosine (OLEL). The DMSA sample showed a decrease of the magnetic resonance field (MRF) increasing the nanoparticle concentration (phi), whereas the OLEL sample showed the opposite behavior. The DMSA MRF concentration dependence was explained using a dipolar interaction model beyond the point dipole approximation. In addition, the magnetic resonance spectra of the OLEL sample showed an optical mode suggesting an antiferromagnetic superexchange coupling between magnetic nanoparticles forming dimers.

  5. Sticking polydisperse hydrophobic magnetite nanoparticles to lipid membranes.

    PubMed

    Paulus, Michael; Degen, Patrick; Brenner, Thorsten; Tiemeyer, Sebastian; Struth, Bernd; Tolan, Metin; Rehage, Heinz

    2010-10-19

    The formation of a layer of hydrophobic magnetite (Fe(3)O(4)) nanoparticles stabilized by lauric acid is analyzed by in situ X-ray reflectivity measurements. The data analysis shows that the nanoparticles partially disperse their hydrophobic coating. Consequently, a Langmuir layer was formed by lauric acid molecules that can be compressed into an untilted condensed phase. A majority of the nanoparticles are attached to the Langmuir film integrating lauric acid residue on their surface into the Langmuir film. Hence, the particles at the liquid-gas interface can be identified as so-called Janus beads, which are amphiphilic solids having two sides with different functionality. PMID:20873726

  6. Surface site density, silicic acid retention and transport properties of compacted magnetite powder

    NASA Astrophysics Data System (ADS)

    Mayant, C.; Grambow, B.; Abdelouas, A.; Ribet, S.; Leclercq, S.

    In France, within the framework of investigations of the feasibility of deep geological disposal of high-level radioactive waste, studies on corrosion products of steel over packs are ongoing. Such studies concern silica and radionuclide retention. The objective of the present work is to study sorption of silicic acid on compacted magnetite in percolation cells to attempt to simulate confined site conditions. Potentiometric titration of commercial magnetite was carried out with both dispersed and compacted magnetite. The titration of the magnetite suspension has been made with two different methods: a batch method (several suspensions) and a direct fast method (one suspension). The Gran’s function gave 1.7 (±0.4) and 2.4 (±0.5) sorption sites nm -2 with these respective methods but site densities as high as 20/nm 2 could be obtained by modelling. The titration of magnetite compacted at 120 bars showed that the evolution of charge density on magnetite surfaces is similar for compacted and dispersed magnetite. Silicic acid sorption onto dispersed and compacted magnetite was similar with sorption site densities ranging between 2.2 and 4.4/nm 2.

  7. Morphology of thin nanocomposite films of asymmetric diblock copolymer and magnetite nanoparticles

    E-print Network

    Morphology of thin nanocomposite films of asymmetric diblock copolymer and magnetite nanoparticles nanocomposite films of asymmetric diblock copolymer and magnetite nanoparticles Valeria Lauter1,3 , Peter M films of an asymmetric diblock copolymer and nanoparticles are fabricated. The morphologies of the films

  8. Magnetite (Fe3O4) Core-Shell Nanowires: Synthesis and

    E-print Network

    Zhou, Chongwu

    Magnetite (Fe3O4) Core-Shell Nanowires: Synthesis and Magnetoresistance Daihua Zhang,,§ Zuqin Liu. As has been theoretically predicted on the basis of electron band structure calculations, magnetite (Fe3O films,13-17 nanocluster assemblies,18-21 and compacted powders,14 where the MR was ascribed

  9. Characterization of interfacial reactions in magnetite tunnel junctions with transmission electron microscopy

    E-print Network

    Laughlin, David E.

    Characterization of interfacial reactions in magnetite tunnel junctions with transmission electron of Physics. DOI: 10.1063/1.1688535 I. INTRODUCTION Half metallic magnetite (Fe3O4) has been thought to be one is also discussed. II. EXPERIMENT Thin films were deposited onto Si or oxidized Si wafers by either rf

  10. In situ formation of magnetite reactive barriers in soil for waste stabilization

    Microsoft Academic Search

    Robert C

    2003-01-01

    Reactive barriers containing magnetite and methods for making magnetite reactive barriers in situ in soil for sequestering soil contaminants including actinides and heavy metals, organic materials, iodine and technetium are disclosed. According to one embodiment, a two-step reagent introduction into soil takes place. In the first step, free oxygen is removed from the soil by separately injecting into the soil

  11. Dislocations in magnetite: Experimental observations of their structural, magnetic, and low-temperature effects

    NASA Astrophysics Data System (ADS)

    Lindquist, Anna K.

    Magnetite (Fe3O4) is the most important mineral to the rock magnetic and paleomagnetic communities and is ubiquitous in igneous, sedimentary, and metamorphic rocks. Larger multidomain (MD) magnetite grains are more common than single domain grains, so understanding how they record paleomagnetic fields would be a boon to paleomagnetists. MD magnetite grains are divided into multiple domains, regions with uniform magnetization, separated by domain walls. Domain walls sweep through magnetite grains easily, so slight changes in ambient magnetic fields can alter the magnetization of MD magnetite. Because of this, MD magnetite is not considered reliable for paleomagnetic studies, and the mechanisms by which MD grains may record past magnetic fields are not well understood. Dislocations, linear crystallographic defects, may increase magnetic coercivity by pinning domain walls in place. This study, for the first time, experimentally investigates this pinning behavior by using a transmission electron microscope (TEM) to simultaneously image magnetic domain walls, dislocations, and low-temperature twin structures. Magnetite grains were deformed in the dislocation glide regime, which is active in natural magnetite grains. Dislocations were not uniformly distributed throughout the sample, but regions with more and longer dislocations pinned domain walls more strongly. First-order reversal curve diagrams demonstrate the presence of regions with pinning strengths of over 125 mT. The strength of domain wall pinning at dislocations was found experimentally and theoretically to be proportional to dislocation length, with longer dislocations pinning more strongly. Average pinning fields were around 0.2 mT. Magnetite grains with more uniformly distributed dislocations would likely have coercivities that were high enough to enable MD magnetite to record geomagnetic fields over geologic timescales. Further, low-temperature TEM and magnetic studies demonstrated that dislocations can affect twin growth in magnetite below the Verwey transition. Deformed magnetite samples had more soft-shouldered Verwey transitions and were able to retain more remanence after low-temperature demagnetization (LTD). Therefore, MD magnetite grains may be able to retain relevant magnetizations, even after LTD. Dislocation length, density, and distribution are then all important considerations when investigating the ways in which MD magnetite may retain a stable record of paleomagnetic field characteristics, even after LTD.

  12. Structure-Disorder induced MagnetoResistance intensification on spin-dependent-conduction in magnetite (Fe3O4) thin film produced by RF magnetron sputtering method

    Microsoft Academic Search

    H. Kobori; D. Shimizu; A. Sugimura; T. Taniguchi; A. Ando; H. Kawanaka; Y. Naitoh; T. Shimizu

    2009-01-01

    The intensification of magneto-resistance (MR) caused by structure-disorder has been observed in magnetite (Fe3O4) thin film (MTF) produced by the rf magnetron sputtering method. The MTFs with the thickness of 20nm, 50nm and 100nm were deposited on the substrates of SiO2-glass, MgAl2O4 (100) and MgO (100) single crystals. We have observed that the MR of the MTF on SiO2-glass substrate

  13. Synthesizing cysteine-coated magnetite nanoparticles as MRI contrast agent: Effect of pH and cysteine addition on particles size distribution

    NASA Astrophysics Data System (ADS)

    Ahmadi, R.; Ranjbarnodeh, E.; Gu, N.

    2012-12-01

    Cysteine capped magnetite nanoparticles (10 to 20 nm) were synthesized via coprecipitation method under ultrasonic irradiation. The influence of pH value of the solution and cysteine addition on the size distribution and hydrodynamic size of nanoparticles were studied via TEM and PCS methods, respectively. The crystal structure and magnetic properties of the nanoparticles were characterized by XRD and VSM techniques, respectively. Coating density was calculated using TGA and TEM results. Cytotoxicity assessment performed by incubation of L929 cells, confirmed that ferrofluids are biocompatible. MRI studies conducted on rats demonstrated suitability of synthesized nanoparticles as contrast agents, especially for imaging of the lymph nodes.

  14. Simple and facile approach to synthesize magnetite nanoparticles and assessment of their effects on blood cells

    NASA Astrophysics Data System (ADS)

    Cótica, Luiz F.; Freitas, Valdirlei F.; Dias, Gustavo S.; Santos, Ivair A.; Vendrame, Sheila C.; Khalil, Najeh M.; Mainardes, Rubiana M.; Staruch, Margo; Jain, Menka

    2012-02-01

    In this paper, a very simple and facile approach for the large scale synthesis of uniform and size-controllable single-domain magnetite nanoparticles is reported. These magnetite nanoparticles were synthesized via thermal decomposition of a ferric nitrate/ethylene glycol solution. The structural and morphological properties of the synthesized nanoparticles were carefully studied. Nearly spherical nanoparticles with inverted spinel structure and average particle and crystallite sizes smaller than 20 nm were obtained. The magnetic measurements revealed that magnetite nanoparticles have a magnetic saturation value near that of the bulk magnetite. The erythrocyte cytotoxicity assays showed no hemolytic potential of the samples containing magnetite nanoparticles, indicating no cytotoxic activity on human erythrocytes, which makes these interesting for biotechnological applications.

  15. Avian orientation: the pulse effect is mediated by the magnetite receptors in the upper beak

    PubMed Central

    Wiltschko, Wolfgang; Munro, Ursula; Ford, Hugh; Wiltschko, Roswitha

    2009-01-01

    Migratory silvereyes treated with a strong magnetic pulse shift their headings by approximately 90°, indicating an involvement of magnetite-based receptors in the orientation process. Structures containing superparamagnetic magnetite have been described in the inner skin at the edges of the upper beak of birds, while single-domain magnetite particles are indicated in the nasal cavity. To test which of these structures mediate the pulse effect, we subjected migratory silvereyes, Zosterops l. lateralis, to a strong pulse, and then tested their orientation, while the skin of their upper beak was anaesthetized with a local anaesthetic to temporarily deactivate the magnetite-containing structures there. After the pulse, birds without anaesthesia showed the typical shift, whereas when their beak was anaesthetized, they maintained their original headings. This indicates that the superparamagnetic magnetite-containing structures in the skin of the upper beak are most likely the magnetoreceptors that cause the change in headings observed after pulse treatment. PMID:19324756

  16. Magnetite and Silicate Spherules from the GISP2 Core at the 536 A.D. Horizon

    NASA Astrophysics Data System (ADS)

    Abbott, D. H.; Biscaye, P.; Cole-Dai, J.; Breger, D.

    2008-12-01

    We examined the solid fraction of melt water from a depth of 361.45-361.55 meters in the GISP2 ice core. This subbottom depth covers the time from 536.15 to 536.66 A.D. roughly from February 24th to August 28th, 536 A.D.[1,2]. Earlier work measured a Cl value of 64 ppb from 535.9 to 536.2 A.D. roughly from November 24th, 535 A.D. to March 14th, 536 A.D. [3]. This is the highest nonvolcanic Cl value in the last 2000 years. The Cl value of 48 ppb from 536.2 to 536.5 A.D. or roughly from March 14th to July 1st, 536 A.D. is the third highest nonvolcanic Cl value in the last 2000 years. These high Cl values are at the same time as the beginning of an 18-month long period starting in March of 536 A.D. when ' the sun gave no more light than the moon' [4]. Because there is no evidence for a volcanic eruption during this 18-month time period, some authors have proposed a cosmogenic origin for the dust veil [5]. Our data supports the latter hypothesis. We have found 5 perfectly round, smooth spherules at the depth corresponding to early 536 A.D. Three of the spherules are pure iron oxide. They range in size from 0.3 to 1.3 micrometers in diameter. One spherule is mixed silicate plus iron oxide, with a diameter of 0.5 micrometers. One spherule is Na-K aluminum silicate, with a diameter of 2.6 micrometers. The spherules occur in association with crystals of titanium oxide and zircon, and partially crystalline Ca-Na feldspar. Associated K-Na feldspar and quartz grains have sharp edges. The largest grains in the sample are translucent C-O spheroids of volatile material that is sensitive to the electron beam. The translucent C-O spheroids often contain small amounts (0.2 to 2 percent) of Na and Cl. We also found some calcium carbonate precipitate. We interpret the perfectly round FeO and silicate spherules as impact spherules. The associated crystalline and sharp edged grains are also impact ejecta. The mixed chemistry of the spherules and the lack of Ni are inconsistent with their origin as ablation products from meteorites (i.e. cosmic spherules). Instead they must have originated from a terrestrial impact event. We have found an impact ejecta layer in the Gulf of Carpentaria, Australia that contains abundant magnetite spherules with quench textures and ablated surfaces. Using existing carbon-14 ages, the spherule horizon is from an impact that occurred prior to 900 A.D. and after 70 A.D [6]. The most likely source craters in the Gulf formed from an impactor that was about 640 meters in diameter, in line with the 600-meter estimate of [5] for the diameter of the impactor needed to produce the dust veil event of 536-537 A.D. Because the age and impactor size are both a good match within the errors of our data, the Carpentaria impact event is our best candidate for the source of the impact spherules in the GISP2 ice core. However, much more work remains before we can be certain that the impact into the Gulf of Carpentaria was the source of the dust veil event that began in March of 536 A.D. [1]. Meese et al., 1994. Science, 266:1680-1682. [2]. Sowers et al., 1993. Paleoceanography 8:737-766. [3]. Mayewski et al., 1997. J. Geophys. Res., 102:26345-26366. [4]. Stothers, 1984. Nature 307:344-345. [5] Rigby et al., 2004. Astron. Geophys. 45:1.23-1.26. [6] Abbott et al., submitted, Geophys. Res. Lett.

  17. Off-axis electron holography observation of magnetic microstructure in a magnetite (001) thin film containing antiphase domains

    E-print Network

    Dunin-Borkowski, Rafal E.

    Off-axis electron holography observation of magnetic microstructure in a magnetite (001) thin film; published 21 March 2006 Magnetic remanent states in a self-supporting 25-nm-thick magnetite 001 film for use in spin valve devices, attempts to integrate magnetite films into multilayer structures using Mg

  18. Department of Earth and Mineral Sciences Spring 2012 Magnetically Enhanced Hydro Cyclone for Magnetite Recovery During Coal

    E-print Network

    Demirel, Melik C.

    for Magnetite Recovery During Coal Beneficiation Overview Magnetite is employed in a water slurry during the coal beneficiation process. The slurry has a density in between that of coal and that of unwanted material so that only coal floats and can be scraped off. Magnetite has tripled in price so recovering

  19. Biomimetic Control of Magnetite Shape and Morphology using Polyaminoacids

    NASA Astrophysics Data System (ADS)

    Altan, Cem Levent; Bucak, Seyda; Sommerdijk, Nico

    2012-02-01

    Inspired by nature, this work explores the use of randomly sequenced poly(aminoacids)s to control the size, morphology and magnetic properties of magnetite via synthetic methods in a controlled manner as in the case of magnetotactic bacteria. Aqueous partial oxidation and chemical precipitation methods are employed for the synthesis of 7 - 50 nm iron oxide nanoparticles at room temperature. X -- ray diffraction (XRD) and Transmission Electron Microscopy (TEM) revealed formation of iron oxide nanoparticles both in the presence and absence of poly(amino acids). In the presence of random poly(amino acid)s with different compositions consisting of E, K and A amino acids the mean particle size for the chemical precipitation method is decreased regardless of amino acid composition. For partial oxidation method, mean particle size is also decreased and nanoparticle strings are observed while synthesized in the presence of poly(aspartic acid). Magnetic properties of particles obtained via different routes are also investigated. This provides a bio-inspired route for control over size, morphology and magnetic properties of magnetite nanoparticles.

  20. Low temperature oxidation mechanisms of nanocrystalline magnetite thin film

    SciTech Connect

    Bourgeois, F.; Gergaud, P.; Feuillet, G. [CEA, LETI, MINATEC Campus, 17 rue des Martyrs, 38054 GRENOBLE, Cedex 9 (France); Renevier, H.; Leclere, C. [Grenoble INP Minatec, LMGP, 3 parvis Louis Neel, 38016 Grenoble (France)

    2013-01-07

    A detailed investigation of the mechanisms related to the low temperature oxidation of nanocrystalline magnetite thin films into maghemite is presented. Despite strong differences in the functional properties of these two phases, structural similarities make it difficult to distinguish between them, and to quantify the oxidation process, particularly in the case of nanostructured polycrystalline layers. Contrary to the case of bulk materials or monocrystalline films and particles, the oxidation processes in nanocrystalline thin film have only scarcely been studied. In this work, structural and optical techniques, including X-ray diffraction (XRD), EXAFS/X-ray absorption near edge structure, FTIR, and Raman scattering, have been used to estimate the oxidation rate of magnetite. The overall oxidation reaction rates are discussed in the framework of two limiting cases corresponding to intra grain diffusion and to grain boundary diffusion. SIMS profiling and electrical measurements were also carried out to better assess the oxidation quantification in order to conclude on the predominant oxidation mechanisms in this heterogeneous material. We propose a qualitative model for the structure, in terms of insulating zone distribution, for partially oxidized films.

  1. Low temperature oxidation mechanisms of nanocrystalline magnetite thin film

    NASA Astrophysics Data System (ADS)

    Bourgeois, F.; Gergaud, P.; Renevier, H.; Leclere, C.; Feuillet, G.

    2013-01-01

    A detailed investigation of the mechanisms related to the low temperature oxidation of nanocrystalline magnetite thin films into maghemite is presented. Despite strong differences in the functional properties of these two phases, structural similarities make it difficult to distinguish between them, and to quantify the oxidation process, particularly in the case of nanostructured polycrystalline layers. Contrary to the case of bulk materials or monocrystalline films and particles, the oxidation processes in nanocrystalline thin film have only scarcely been studied. In this work, structural and optical techniques, including X-ray diffraction (XRD), EXAFS/X-ray absorption near edge structure, FTIR, and Raman scattering, have been used to estimate the oxidation rate of magnetite. The overall oxidation reaction rates are discussed in the framework of two limiting cases corresponding to intra grain diffusion and to grain boundary diffusion. SIMS profiling and electrical measurements were also carried out to better assess the oxidation quantification in order to conclude on the predominant oxidation mechanisms in this heterogeneous material. We propose a qualitative model for the structure, in terms of insulating zone distribution, for partially oxidized films.

  2. Speed limit of the insulator-metal transition in magnetite

    NASA Astrophysics Data System (ADS)

    de Jong, S.; Kukreja, R.; Trabant, C.; Pontius, N.; Chang, C. F.; Kachel, T.; Beye, M.; Sorgenfrei, F.; Back, C. H.; Bräuer, B.; Schlotter, W. F.; Turner, J. J.; Krupin, O.; Doehler, M.; Zhu, D.; Hossain, M. A.; Scherz, A. O.; Fausti, D.; Novelli, F.; Esposito, M.; Lee, W. S.; Chuang, Y. D.; Lu, D. H.; Moore, R. G.; Yi, M.; Trigo, M.; Kirchmann, P.; Pathey, L.; Golden, M. S.; Buchholz, M.; Metcalf, P.; Parmigiani, F.; Wurth, W.; Föhlisch, A.; Schüßler-Langeheine, C.; Dürr, H. A.

    2013-10-01

    As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown, magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible. Recently, three-Fe-site lattice distortions called trimerons were identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase. Here we investigate the Verwey transition with pump-probe X-ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two-step process. After an initial 300?fs destruction of individual trimerons, phase separation occurs on a 1.5±0.2?ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics.

  3. Characterization of Modified Magnetite Nanoparticles for Albumin Immobilization

    PubMed Central

    Bordbar, A. K.; Rastegari, A. A.; Amiri, R.; Ranjbakhsh, E.; Abbasi, M.; Khosropour, A. R.

    2014-01-01

    Magnetite Fe3O4 nanoparticles (NPs) were prepared by chemical coprecipitation method. Silica-coated magnetite NPs were prepared by sol-gel reaction, subsequently coated with 3-aminopropyltriethoxysilane (APTES) via silanization reaction, and then were activated with 2,4,6-trichloro-1,3,5-triazine (TCT) and covalently immobilized with bovine serum albumin (BSA). The size and structure of the particles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and dynamic light scattering (DLS) techniques. The immobilization was confirmed by Fourier transform infrared spectroscopy (FT-IR). XRD analysis showed that the binding process has not done any phase change to Fe3O4. The immobilization time for this process was 4?h and the amount of immobilized BSA for the initial value of 1.05?mg BSA was about 120?mg/gr nanoparticles. Also, the influences of three different buffer solutions and ionic strength on covalent immobilization were evaluated. PMID:24963410

  4. Magnetite nanoparticles for biosensor model based on bacteria fluorescence

    NASA Astrophysics Data System (ADS)

    Poita, A.; Creanga, D.-E.; Airinei, A.; Tupu, P.; Goiceanu, C.; Avadanei, O.

    2009-06-01

    Fluorescence emission of pyoverdine - the siderophore synthesized by iron scavenger bacteria - was studied using in vitro cultures of Pseudomonas aeruginosa with the aim to design a biosensor system for liquid sample iron loading. Diluted suspensions of colloidal magnetite nanoparticles were supplied in the culture medium (10 microl/l and 100 microl/l) to simulate magnetic loading with iron oxides of either environmental waters or human body fluids. The electromagnetic exposure to radiofrequency waves of bacterial samples grown in the presence of magnetic nanoparticles was also carried out. Cell density diminution but fluorescence stimulation following 10 microl/l ferrofluid addition and simultaneous exposure to radiofrequency waves was evidenced. The inhibitory influence of 100 microl/l ferrofluid combined with RF exposure was evidenced by fluorescence data. Mathematical model was proposed to approach quantitatively the dynamics of cell density and fluorescence emission in relation with the consumption of magnetite nanoparticle supplied medium. The biosensor scheme was shaped based on the response to iron loading of bacterial sample fluorescence.

  5. Synthesis and characterization of magnetite nanoparticles coated with lauric acid

    SciTech Connect

    Mamani, J.B., E-mail: javierbm@einstein.br [Instituto do Cérebro-InCe, Hospital Israelita Albert Einstein-HIAE, 05651-901 São Paulo (Brazil); Costa-Filho, A.J. [Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto (Brazil); Cornejo, D.R. [Instituto de Física Universidade de São Paulo, USP, São Paulo (Brazil); Vieira, E.D. [Instituto de Física, Universidade Federal de Goiás, Goiânia (Brazil); Gamarra, L.F. [Instituto do Cérebro-InCe, Hospital Israelita Albert Einstein-HIAE, 05651-901 São Paulo (Brazil)

    2013-07-15

    Understanding the process of synthesis of magnetic nanoparticles is important for its implementation in in vitro and in vivo studies. In this work we report the synthesis of magnetic nanoparticles made from ferrous oxide through coprecipitation chemical process. The nanostructured material was coated with lauric acid and dispersed in aqueous medium containing surfactant that yielded a stable colloidal suspension. The characterization of magnetic nanoparticles with distinct physico-chemical configurations is fundamental for biomedical applications. Therefore magnetic nanoparticles were characterized in terms of their morphology by means of TEM and DLS, which showed a polydispersed set of spherical nanoparticles (average diameter of ca. 9 nm) as a result of the protocol. The structural properties were characterized by using X-ray diffraction (XRD). XRD pattern showed the presence of peaks corresponding to the spinel phase of magnetite (Fe{sub 3}O{sub 4}). The relaxivities r{sub 2} and r{sub 2}* values were determined from the transverse relaxation times T{sub 2} and T{sub 2}* at 3 T. Magnetic characterization was performed using SQUID and FMR, which evidenced the superparamagnetic properties of the nanoparticles. Thermal characterization using DSC showed exothermic events associated with the oxidation of magnetite to maghemite. - Highlights: • Synthesis of magnetic nanoparticles coated with lauric acid • Characterization of magnetic nanoparticles • Morphological, structural, magnetic, calorimetric and relaxometric characterization.

  6. Solution voltammetry of 4 nm magnetite iron oxide nanoparticles.

    PubMed

    Roberts, Joseph J P; Westgard, John A; Cooper, Laura M; Murray, Royce W

    2014-07-30

    The voltammetry of solution-dispersed magnetite iron oxide Fe3O4 nanoparticles is described. Their currents are controlled by nanoparticle transport rates, as shown with potential step chronoamperometry and rotated disk voltammetry. In pH 2 citrate buffer with added NaClO4 electrolyte, solution cyclic voltammetry of these nanoparticles (average diameter 4.4 ± 0.9 nm, each containing ca. 30 Fe sites) displays an electrochemically irreversible oxidation with E(PEAK) at ca. +0.52 V and an irreversible reduction with E(PEAK) at ca. +0.2 V vs Ag/AgCl reference electrode. These processes are presumed to correspond to the formal potentials for one-electron oxidation of Fe(II) and reduction of Fe(III) at their different sites in the magnetite nanoparticle structure. The heterogeneous electrode reaction rates of the nanoparticles are very slow, in the 10(-5) cm/s range. The nanoparticles are additionally characterized by a variety of tools, e.g., TEM, UV/vis, and XPS spectroscopies. PMID:25046101

  7. Magnetite deposits near Klukwan and Haines, southeastern Alaska

    USGS Publications Warehouse

    Robertson, Eugene C.

    1956-01-01

    Low-grade iron ore is found in magnetite-bearing pyroxenite bodies near Klukwan and Haines in Southeastern Alaska. An alluvial fan at Haines also contains magnetite-bearing rock of possible economic significance. The Haines-Klukwan area is underlain by rocks of Mesozoic Including epidote diorite, quartz diorite, and alaskite of the Coast Range batholith, metabasalt (recrystallized lava flows and pyroclastic rocks), and, in the southern part, interbedded slate and limestone. Layering and foliation, where perceptible, generally strike northwest and dip steeply northeast. The iron deposits are found at or near the contact between the metabasalt and epidote diorite; they appear to represent highly-altered lava flows that were metamorphosed during the emplacement of the batholith. Several billion tens of rock containing about 13 percent magnetic iron are included in the pyroxenite body at Klukwan. Sampling and dip-needle data suggest the presence there of two or three tabular aches in which the rock has an average magnetic iron content of 20 percent or more. Pyroxenite bodies outcropping in three areas near Haines apparently are lower in grade than the Klukwan deposit; lack of exposures prevented thorough sampling but reconnaissance traverses with a dip needle failed to reveal important zones of high-grade iron ore. An alluvial fan adjoining the pyroxenite body at Klukwan contains several hundred million tons of broken rock having a magneticiron content of about 10 percent.

  8. Carbon nanotubes/magnetite hybrids prepared by a facile synthesis process and their magnetic properties

    NASA Astrophysics Data System (ADS)

    Zhang, Li; Ni, Qing-Qing; Natsuki, Toshiaki; Fu, Yaqin

    2009-07-01

    In this paper, a facile synthesis process is proposed to prepare multiwalled carbon nanotubes/magnetite (MWCNTs/Fe 3O 4) hybrids. The process involves two steps: (1) water-soluble CNTs are synthesized by one-pot modification using potassium persulfate (KPS) as oxidant. (2) Fe 3O 4 is assembled along the treated CNTs by employing a facile hydrothermal process with the presence of hydrazine hydrate as the mineralizer. The treated CNTs can be easily dispersed in aqueous solvent. Moreover, X-ray photoelectron spectroscopy (XPS) analysis reveals that several functional groups such as potassium carboxylate (-COOK), carbonyl (-C dbnd O) and hydroxyl (-C-OH) groups are formed on the nanotube surfaces. The MWCNTs/Fe 3O 4 hybrids are characterized with respect to crystal structure, morphology, element composition and magnetic property by X-ray diffraction (XRD), transmission electron microscopy (TEM), XPS and superconducting quantum interference device (SQUID) magnetometer. XRD and TEM results show that the Fe 3O 4 nanoparticles with diameter in the range of 20-60 nm were firmly assembled on the nanotube surface. The magnetic property investigation indicated that the CNTs/Fe 3O 4 hybrids exhibit a ferromagnetic behavior and possess a saturation magnetization of 32.2 emu/g. Further investigation indicates that the size of assembled Fe 3O 4 nanoparticles can be turned by varying experiment factors. Moreover, a probable growth mechanism for the preparation of CNTs/Fe 3O 4 hybrids was discussed.

  9. Cell-surface interactions involving immobilized magnetite nanoparticles on flat magnetic substrates.

    PubMed

    Loichen, Juliane; Hartmann, Uwe

    2009-09-01

    A new method to affect cells by cell-surface interaction is introduced. Biocompatible magnetic nanobeads are deposited onto a biocompatible magnetic thin layer. The particles are composed of small magnetite crystals embedded in a matrix which can be functionalized by different molecules, proteins or growth factors. The magnetic interaction between surface and beads prevents endocytosis if the setup is utilized for cell culturing. The force acting between particles and magnetic layer is calculated by a magnetostatic approach. Biocompatibility is ensured by using garnet layers which turned out to be nontoxic and stable under culturing conditions. The garnet thin films exhibit spatially and temporally variable magnetic domain configurations in changing external magnetic fields and depending on their thermal pretreatment. Several patterns and bead deposition methods as well as the cell-surface interactions were analyzed. In some cases the cells show directed growth. Theoretical considerations explaining particular cell behavior on this magnetic material involve calculations of cell growth on elastic substrates and bending of cell membranes. PMID:19488746

  10. Charge ordered structure of magnetite Fe3O4 below the Verwey transition

    NASA Astrophysics Data System (ADS)

    Wright, Jon P.; Attfield, J. Paul; Radaelli, Paolo G.

    2002-12-01

    The crystal structure of highly stoichiometric magnetite (Fe3O4) below the Verwey transition has been refined from high-resolution neutron and synchrotron x-ray powder-diffraction data. The refined model has a monoclinic P2/c symmetry cell with orthorhombic Pmca pseudosymmetry constraints on the atomic positions, and contains four independent octahedral B site iron atoms. Charge ordering is evidenced by the presence of expanded and contracted BO6 octahedra, and by the distribution of B-B distances resulting from unequal Coulombic repulsions between the different B site charges. The B-B distances are inconsistent with dimer formation. Competition between the B-O and B-B interactions results in polar displacements of two of the B site cations. The charge ordering has a predominant [001] density modulation, which relieves a nesting instability in the electronic density of states, but a second [001/2] phase modulation also occurs. The monoclinic distortion at the Verwey transition is consistent with a macroscopic rhombohedral magnetostriction, driven by the localization of orbitally degenerate Fe2+, coincident with the microscopic charge ordering distortions that have an orthorhombic lattice symmetry.

  11. Synthesis of magnetite particles by pulsed alexandrite laser processing of metallic glass precursors

    SciTech Connect

    Sorescu, M. [Duquesne Univ., Pittsburgh, PA (United States). Physics Dept.; Schafer, S.A.; Knobbe, E.T. [Oklahoma State Univ., Stillwater, OK (United States)

    1996-12-31

    Samples of Fe{sub 78}B{sub 13}Si{sub 9} and Fe{sub 81}B{sub 13.5}Si{sub 3.5}C{sub 2} metallic glasses were irradiated with a pulsed alexandrite laser ({lambda} = 750 nm, {tau} = 60 {micro}s) using different laser fluences. Kinetics of laser-induced phase transformations and fluence dependence of magnetic properties were studied by scanning electron microscopy (SEM) and Moessbauer spectroscopy. Low laser fluences were found to induce changes in magnetic texture and onset of crystallization. High laser fluences, however, correlated with additional oxidation effects and the formation of stoichiometric Fe{sub 3}O{sub 4} particles in the irradiated alloy system. An activation energy of 11.9 eV was estimated for the laser-driven synthesis of magnetite nanoparticles. Pulsed alexandrite laser processing is an intriguing alternative technique for the controlled synthesis of iron oxide phases from ferromagnetic glass precursors.

  12. Surface metal-insulator phase transition of a single crystalline magnetite (0 0 1)

    NASA Astrophysics Data System (ADS)

    Kim-Ngan, N.-T. H.; Soszka, W.; Jag?o, G.; Goc-Jag?o, D.

    2004-01-01

    The single crystalline Fe 3O 4 (0 0 1) surface has been investigated by using a low-energy ion scattering (LEIS) in the temperature range of 85-300 K. An Ar + ion beam with primary energies of 4-8 keV was used. Two distinguished peaks in the LEIS spectra were attributed to the Ar +-Fe scattering and the Fe-recoil atoms. An enormous increase of the Ar +-Fe peak-intensity and an enhanced influence from the azimuthal angle on the Fe-recoil peak were found at low temperature. In the metal-insulator phase transition region, the temperature-dependent curve of the scattering ion yield, R+( T), have revealed two step-like increases. The first step-rise was always found at 138 K. The second step-rise was found at 123 K under 5 keV Ar + ion bombardment, which moved to lower temperature with increasing primary energies implying a widening of the plateau between two steps. The characteristics of the R+( T) curves were explained as a complex interplay between dominant Auger and resonant neutralizations related to the change in the electronic state in the octahedral-Fe sites and the re-ionization of neutralized particles in a collision with atoms in the deeper layers than the surface layer. The later one was influenced largely by the change in the crystal transparency of magnetite at the phase transition.

  13. Synthesis of magnetite nanoparticles for bio- and nanotechnology: genetic engineering and biomimetics of bacterial magnetosomes.

    PubMed

    Lang, Claus; Schüler, Dirk; Faivre, Damien

    2007-02-12

    Magnetotactic bacteria (MTB) have the ability to navigate along the Earth's magnetic field. This so-called magnetotaxis is a result of the presence of magnetosomes, organelles which comprise nanometer-sized intracellular crystals of magnetite (Fe(3)O(4)) enveloped by a membrane. Because of their unique characteristics, magnetosomes have a high potential for nano- and biotechnological applications, which require a specifically designed particle surface. The functionalization of magnetosomes is possible either by chemical modification of purified particles or by genetic engineering of magnetosome membrane proteins. The second approach is potentially superior to chemical approaches as a large variety of biological functions such as protein tags, fluorophores, and enzymes may be directly incorporated in a site-specific manner during magnetosome biomineralization. An alternative to the bacterial production of magnetosomes are biomimetic approaches, which aim to mimic the bacterial biomineralization pathway in vitro. In MTB a number of magnetosome proteins with putative functions in the biomineralization of the nanoparticles have been identified by genetic and biochemical approaches. The initial results obtained by several groups indicate that some of these proteins have an impact on nanomagnetite properties in vitro. In this article the key features of magnetosomes are discussed, an overview of their potential applications are given, and different strategies are proposed for the functionalization of magnetosome particles and for the biomimetism of their biomineralization pathway. PMID:17295401

  14. Operators on Pure Spinor Spaces

    SciTech Connect

    Cederwall, Martin [Fundamental Physics, Chalmers University of Technology, SE 412 96 Goteborg (Sweden)

    2010-06-17

    Pure spinors are relevant to the formulation of supersymmetric theories, and provide the only known way to maintain manifest maximal supersymmetry. The (non-linear) pure spinor constraint makes it nontrivial to find well defined operators on pure spinor wave functions. We discuss how such operators are defined. One application concerns covariant gauge fixing in maximally supersymmetric Yang-Mills (and string theory). Another issue is the construction of a manifestly supersymmetric action for 11-dimensional supergravity in terms of a scalar superfield. We describe some work in progress.

  15. Impact of high energy ball milling on the nanostructure of magnetite–graphite and magnetite–graphite–molybdenum disulphide blends

    SciTech Connect

    Österle, W., E-mail: Werner.oesterle@bam.de [BAM Federal Institute for Materials Research and Testing, 12200 Berlin (Germany); Orts-Gil, G.; Gross, T.; Deutsch, C. [BAM Federal Institute for Materials Research and Testing, 12200 Berlin (Germany); Hinrichs, R. [Instituto de Geociências, UFRGS, P.O. Box 15001, 91501-970 Porto Alegre (Brazil); Vasconcellos, M.A.Z. [Instituto de Física, UFRGS, P.O. Box 15051, 91501-970 Porto Alegre (Brazil); Zoz, H.; Yigit, D.; Sun, X. [Zoz Group, 57482 Wenden (Germany)

    2013-12-15

    Different, partly complementary and partly redundant characterization methods were applied to study the transition of magnetite, graphite and MoS{sub 2} powders to mechanically alloyed nanostructures. The applied methods were: Transmission electron microscopy (TEM), Mössbauer spectroscopy (MS), Raman spectroscopy (RS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The main objective was to prepare a model material providing the essential features of a typical tribofilm forming during automotive braking, and to assess the impact of different constituents on sliding behaviour and friction level. Irrespective of the initial grain size, the raw materials were transferred to a nanocrystalline structure and mixed on a nanoscopic scale during high energy ball milling. Whereas magnetite remained almost unchanged, graphite and molybdenum disulphide were transformed to a nanocrystalline and highly disordered structure. The observed increase of the coefficient of friction was attributed to a loss of lubricity of the latter ingredient due to this transformation and subsequent oxidation. - Highlights: • Characterization of microstructural changes induced by high energy ball milling • Assessment of the potential of different characterization methods • Impact of mechanical alloying on tribological performance revealed by tests • Preparation of an artificial third body resembling the one formed during braking.

  16. Pure Maple Syrup: Nutritive Value.

    PubMed

    Leaf, A L

    1964-02-28

    Variations in concentrations of sugar, nitrogen, phosphorus, potassium, calcium, and magnesium of sap from sugar maple (Acer saccharum, Marsh.) trees are related to the time of sap collection and result in variation of the same components in pure maple syrup. Thirty milliliters (one fluid ounce) of pure maple syrup may contain 3 to 6 mg of phosphorus, 10 to 30 mg of potassium, 40 to 80 mg of calcium, and 4 to 25 mg of magnesium. PMID:17743933

  17. Anaerobic production of magnetite by a dissimilatory iron-reducing microorganism

    USGS Publications Warehouse

    Lovley, D.R.; Stolz, J.F.; Nord, G.L., Jr.; Phillips, E.J.P.

    1987-01-01

    The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2-4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits. ?? 1987 Nature Publishing Group.

  18. Transformation products of submicron-sized aluminum-substituted magnetite: Color and reductant solubility

    NASA Technical Reports Server (NTRS)

    Golden, D. C.; Ming, D. W.; Lauer, H. V., Jr.

    1991-01-01

    Magnetite, when present as fine particles, is soluble in acid ammonium oxalate (pH equals 3). However, the commonly used extractant for free iron oxides (i.e., citrate dithionite-bicarbonate (CDB) is not very effective in dissolving magnetite in soils and geologic materials. Upon oxidation, magnetite transforms to maghemite; at elevated temperatures, maghemite inverts to hematite. This transformation causes a change in color from black to red and may affect the reductant solubility as well. The objectives here were to examine the color and reflectance spectral characteristics of products during the transformation of magnetite to maghemite to hematite and to study the effect of Al-substitution in magnetite on the above process. Reductant solubility of Al-substituted magnetite, maghemite, and hematite was also studied. In summary, the transformation of magnetite to maghemite was accompanied by a change in color from black to red because of the oxidation of Fe2(+) to Fe3(+). The phase change maghemite to hematite had a relatively minor effect on the color and the reflectance spectra.

  19. Electromagnetic nanocomposite of bacterial cellulose using magnetite nanoclusters and polyaniline.

    PubMed

    Park, Minsung; Cheng, Jie; Choi, Jaeyoo; Kim, Jaehwan; Hyun, Jinho

    2013-02-01

    Magnetic BC was biosynthesized by culturing Gluconacetobacter xylinus in a medium containing magnetite nanoparticle (MNP) clusters. The stable dispersion of MNP clusters in an aqueous solution was achieved using amphiphilic comb-like polymer (CLP) stabilizers to disperse the MNPs. Subsequently, a conducting polymer was synthesized on the magnetic BC fibers by the chemical oxidative polymerization of aniline. The BC fiber was fully coated with polyaniline, forming hydrogen bonds. The colloidal stability of the CLP-modified MNPs was characterized by optical imaging and UV-visible spectroscopy. The chemical structure and morphology of the hybrid BC layers were observed using Fourier transform infrared spectroscopy and scanning electron microscopy. Magnetic and conductive properties were measured to confirm the immobilization of MNPs and polyaniline. PMID:23000681

  20. Magnetite-Magnesioferrite Phase Relations and Application to ALH84001

    NASA Technical Reports Server (NTRS)

    Koziol, Andrea M.

    2003-01-01

    Oxygen fugacity (fO2) is an important factor in planetary formation and evolution. Certain minerals or assemblages of minerals are stable only under certain fO2 conditions (at a constant T and P) and can be recorders of ambient fO2 during geologic processes. The best estimate of oxygen fugacity from mineral assemblages has implications, from large-scale models of planetary evolution to interpretation of single meteorites. For example, redox conditions are part of the discussion of the origin and history of shergottites, basaltic rocks in meteorites from Mars [1-4]. In addition oxygen fugacity may be an important factor to consider in the interpretation of the carbonate and magnetite assemblages seen in ALH84001 [5].

  1. Hydrocolloid-Stabilized Magnetite for Efficient Removal of Radioactive Phosphates

    PubMed Central

    Vellora Thekkae Padil, Vinod; Rouha, Michael; ?erník, Miroslav

    2014-01-01

    Liquid radioactive waste is a common by-product when using radioactive isotopes in research and medicine. Efficient remediation of such liquid waste is crucial for increasing safety during the necessary storage of the material. Herein, we present a novel Gum Karaya stabilized magnetite for the efficient removal of radioactive phosphorus 32P from liquid radioactive waste. This environmentally friendly material is well suited to be used as a nanohydrogel for the removal of liquid waste, which can then be stored in a smaller space and without the risk of the spills inherent to the initial liquid material. The maximum adsorption capacity of the GK/M in this study was found to be 15.68?GBq/g. We present a thorough morphological characterization of the synthesised GK/M, as well as a discussion of the possible phosphorus adsorption mechanisms. PMID:24696854

  2. Hydrocolloid-stabilized magnetite for efficient removal of radioactive phosphates.

    PubMed

    Vellora Thekkae Padil, Vinod; Rouha, Michael; Cerník, Miroslav

    2014-01-01

    Liquid radioactive waste is a common by-product when using radioactive isotopes in research and medicine. Efficient remediation of such liquid waste is crucial for increasing safety during the necessary storage of the material. Herein, we present a novel Gum Karaya stabilized magnetite for the efficient removal of radioactive phosphorus (32)P from liquid radioactive waste. This environmentally friendly material is well suited to be used as a nanohydrogel for the removal of liquid waste, which can then be stored in a smaller space and without the risk of the spills inherent to the initial liquid material. The maximum adsorption capacity of the GK/M in this study was found to be 15.68 GBq/g. We present a thorough morphological characterization of the synthesised GK/M, as well as a discussion of the possible phosphorus adsorption mechanisms. PMID:24696854

  3. Paleomagnetism of a new magnetite-rich carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Gattacceca, J.; Rochette, P.; Gounelle, M.; Bonal, L.; Weiss, B. P.; Sonzogni, C.

    2012-12-01

    Recent studies of CV carbonaceous chondrites have led to the conclusion that their parent body was partially differentiated and possessed a convecting core [1]. This possibility has been validated by modeling of asteroid accretion [2]. Were partially differentiated chondritic asteroid the rule or the exception? We will present petrographic and paleomagnetic data obtained on an unusual carbonaceous chondrite that we discovered in 2011 in the Atacama desert. This meteorite is a fully crusted stone with a total weight of 2.4 g. Although classification is still ongoing, its petrography, and oxygen isotopes (d18O=-1.74‰, d17O=-5.15‰, D17O=-4.25‰) point to a C2 ungrouped chondrite. Preliminary Raman spectroscopy data confirm that it has not suffered thermal metamorphism. Magnetic properties show that the meteorite contains ~13 wt.% of pseudo-single domain magnetite, making it a rock with remarkable paleomagnetic recorder. Indeed, this is the most magnetic magnetite-bearing chondrite ever described. Paleomagnetic measurements show that the meteorite possesses a uniform and unidirectional stable component of magnetization unblocked up to 120 mT during alternating field demagnetization. Paleointensity is estimated to a few ?T using normalization techniques [3]. The nature of the magnetizaiton, and the origin of the magnetizing field will be discussed. [1] Carporzen et al., 2011. Proc. National Acad. Sci., 108, 6386-6389. [2] Elkins-Tanton et al., 2011. Earth Planet . Sci. Lett., 305, 1-10. [3] Gattacceca and Rochette P. 2004 Earth Planet . Sci. Lett., 227, 377-393.

  4. Spin-resolved electron spectroscopies of epitaxial magnetite (001) (abstract)

    NASA Astrophysics Data System (ADS)

    Shaw, Kimberly A.; Lochner, Eric; Lind, David M.; DiBari, Rebecca C.; Stoyanov, Plamen; Singer, Brian

    1996-04-01

    We will present the first spin-resolving electron spectroscopic studies of a magnetite (Fe3O4)(001) surface. Magnetite is a semimetal with a high density of states in the minority band, but a large band gap in the majority states at the Fermi energy. The polarization of the secondary emission cascade is measured using spin-resolved secondary electron emission spectroscopy (SRSEES), and reflects the semimetallic spin structure of Fe3O4. The polarization plateau of spin-resolved secondary emission (29.8%) matches the average 3D band polarization of stoichiometric Fe3O4 as determined from spin-resolved band structure calculations (34.2%). An enhancement of the polarization of the secondary electrons at lowest energies will also be discussed. Spin-resolved Auger emission spectroscopy (SRAES) of the Fe3O4 films have been measured and show correlation effects in the valence-valence Auger transitions. Suppressed intensity and polarization of M23M45M45 Auger emission relative to M1M45M45 Auger emission is observed, as well as strong resonant emission with shake-up. Conversely, no spin polarization is detected in the spin-resolved oxygen LMM Auger features, although oxygen Auger emission (in which we can distinguish between adsorbed and bonded oxygen) is used to verify surface cleanliness of the samples. The synthesis of Fe3O4 films grown on magnesium oxide (001) substrates using oxygen plasma-assisted molecular beam epitaxy will be discussed, as will thin-film characterization using SQUID magnetometry and x-ray and electron diffraction. A unique angle-, energy-, and spin-resolved electron spectrometer has been designed and built for the study of magnetic surfaces, and these studies represent its' first use. That spectrometer is based on a tandem configuration of an energy-dispersive energy analyzer and Mott spin polarimeter.

  5. Growth of magnetite nanorods along its easy-magnetization axis of [1 1 0

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Peng, Zhenmeng; Huang, Yujie; Chen, Qianwang

    2004-03-01

    Magnetite nanorods were successfully synthesized from ferric chloride (FeCl3) and diamine hydrate (H4N2·H2O) reagents via a simple, mild reduction-oxidization hydrothermal process in the presence of polyethylene glycol. The magnetite nanorods were characterized by X-ray diffraction, Mössbauer spectroscopy, and magnetization measurements. The nanorods exhibit a ferromagnetic behavior with a high saturation magnetization (90.5 emu/g), a little lower than that of the corresponding bulk material (92 emu/g). The mechanism for the improved magnetic properties of the magnetite nanorods is discussed based on the oriented growth of particles.

  6. Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine V.; Ferry, John M.

    1988-08-01

    Crystal size distributions (CSDs) measured in metamorphic rocks yield quantitative information about crystal nucleation and growth rates, growth times, and the degree of overstepping ( ?T) of reactions during metamorphism. CSDs are described through use of a population density function n=dN/dL, where N is the cumulative number of crystals per unit volume and L is a linear crystal size. Plots of ln ( n) vs. L for olivine+pyroxene and magnetite in high-temperature (1000° C) basalt hornfelses from the Isle of Skye define linear arrays, indicating continuous nucleation and growth of crystals during metamorphism. Using the slope and intercept of these linear plots in conjunction with growth rate estimates we infer minimum mineral growth times of less than 100 years at ?T<10° C, and nucleation rates between 10-4 and 10-1/cm3/s. Garnet and magnetite in regionally metamorphosed pelitic schists from south-central Maine have CSDs which are bell-shaped. We interpret this form to be the result of two processes: 1) initial continuous nucleation and growth of crystals, and 2) later loss of small crystals due to annealing. The large crystals in regional metamorphic rocks retain the original size frequency distribution and may be used to obtain quantitative information on the original conditions of crystal nucleation and growth. The extent of annealing increases with increasing metamorphic grade and could be used to estimate the duration of annealing conditions if the value of a rate constant were known. Finally, the different forms of crystal size distributions directly reflect differences in the thermal histories of regional vs. contact metamorphosed rocks: because contact metamorphism involves high temperatures for short durations, resulting CSDs are linear and unaffected by annealing, similar to those produced by crystallization from a melt; because regional metamorphism involves prolonged cooling from high temperatures, primary linear CSDs are later modified by annealing to bell shapes.

  7. 76 FR 69284 - Pure Magnesium From China

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-08

    ...731-TA-696 (Third Review)] Pure Magnesium From China Determination On the basis...of the antidumping duty order on pure magnesium from China would be likely to lead to...4274 (October 2011), entitled Pure Magnesium from China: Investigation No....

  8. Magnetite nanoparticle-loaded anti-HER2 immunoliposomes for combination of antibody therapy with hyperthermia.

    PubMed

    Ito, Akira; Kuga, Yuko; Honda, Hiroyuki; Kikkawa, Hiroyuki; Horiuchi, Atsushi; Watanabe, Yuji; Kobayashi, Takeshi

    2004-08-30

    Anti-HER2 antibody can induce antitumor responses, and can be used in delivering drugs to HER2-overexpressing cancer. Previously, we produced hyperthermia using magnetite nanoparticles that generate heat in an alternating magnetic field. In the present study, we constructed anti-HER2 immunoliposomes containing magnetite nanoparticles, which act as tumor-targeting vehicles, combining anti-HER2 antibody therapy with hyperthermia. The magnetite nanoparticle-loaded anti-HER2 immunoliposomes exerted HER2-mediated antiproliferative effects on SKBr3 breast cancer cells in vitro. Moreover, 60% of magnetite nanoparticles were incorporated into SKBr3, and the cells were then heated at 42.5 degrees C under an alternating magnetic field, resulting in strong cytotoxic effects. These results suggest that this novel therapeutic tool is applicable to treatment of HER2-overexpressing cancer. PMID:15279897

  9. Magnetite-supported sulfonic acid: a retrievable nanocatalyst for the Ritter reaction and multicomponent reactions

    EPA Science Inventory

    Magnetite-sulfonic acid (NanocatFe-OSO3H), prepared by wet-impregnation method, serves as a magnetically retrievable sustainable catalyst for the Ritter reaction which can be used in several reaction cycles without any loss of activity....

  10. Laboratory verification of submicron magnetite production in pseudotachylytes: relevance for paleointensity studies

    NASA Astrophysics Data System (ADS)

    Nakamura, Norihiro; Hirose, Takehiro; Borradaile, Graham J.

    2002-07-01

    Pseudotachylytes generally possess stable remanent magnetizations but the processes by which pseudotachylytes are magnetized remain poorly understood. Magnetic hysteresis and scanning electron microscope studies reveal that experimental frictional melting of granites produces dispersed submicron inclusions of weakly interacting pseudo-single-domain (PSD) magnetite, in artificial pseudotachylyte. The magnetite inclusions are absent in the undeformed granite protolith and result from oxidation of Fe in melt-susceptible mafic minerals during the melt-quenched event. The pseudotachylytes acquired a stable thermal remanence in fine-grained PSD magnetites during the rapid cooling of the melt, implying that fine-grained magnetite has the potential for paleointensity determinations of contemporaneous magnetic fields with co-seismic faulting in granitoids.

  11. Magnetic and Structural Properties of Magnetite in Radular Teeth of Chiton Acanthochiton Rubrolinestus

    NASA Astrophysics Data System (ADS)

    Han, Y. N.; Liu, C. L.; Yao, L. D.; Wang, Y.; Han, X. F.

    2008-03-01

    The major radular lateral teeth of Polyplacophora Chiton comprise a magnetite biomineral cap.We have investigated the structure and magnetic properties of the biomineralized magnetite crystallites in mature teeth of Chiton Acanthochiton Rubrolinestus. From the measurement of magnetic properties of tooth particles using SQUID magnetometry we find that the saturation magnetization and the Verwey transition temperature (Tv) are 78.4 emu/g and 105 K, respectively. An in situ examination of the structure of magnetite-bearing region within individual tooth using the high resolution TEM, together with electron diffraction (ED) pattern and energy-dispersive X-ray (EDX) analyses indicates magnetite microcrystal form electron-dense polycrystalline sheets with typical length 800 nm and width 150 nm or so. These polycrystalline sheets are arranged regularly along the longitude direction of the tooth cutting surface. Furthermore, the microcrystallites in polycrystalline sheet take on the generally good crystallinity.

  12. Carbonate and Magnetite Parageneses as Monitors of Carbon Dioxide and Oxygen Fugacity

    NASA Technical Reports Server (NTRS)

    Koziol, Andrea M.

    2000-01-01

    The stable coexistence of siderite with other key minerals, such as graphite or magnetite, is only possible under certain restrictive conditions of CO2 and O2 fugacity. Carbonate parageneses in Mars meteorite ALH 84001 are analyzed.

  13. Ferrihydrite Alteration to Magnetite, Maghemite and Hematite; Implications for Iron Oxides on Mars

    NASA Technical Reports Server (NTRS)

    Zent, A. P.; Bishop, J. L.; Mancinelli, R. L.; Olsen, M.; Wagner, P. A.

    2000-01-01

    Synthetic ferrihydrites have been altered to form magnetite, maghemite and hematite through low-temperature heating experiments (some with an organic reductant). Maghemite formed in this manner could become an indicator for Astrobiology on Mars.

  14. Truncated Hexa-Octahedral Magnetites: Biosignatures in Terrestrial Samples and Martian Meteorite ALH84001

    NASA Technical Reports Server (NTRS)

    Thomas-Keprta, Kathie L.; Clemett, Simon J.; Bazylinski, Dennis A.; Kirschvink, Joseph L.; McKay, David S.; Wentworth, Susan J.; Vali, H.; Gibson, Everett K.

    2001-01-01

    We suggest that the observation of truncated hexa-octahedral magnetites in ALH84001 are both consistent with, and in the absence of terrestrial inorganic analogs, likely formed by biogenic processes. Additional information is contained in the original extended abstract.

  15. A unique type 3 ordinary chondrite containing graphite-magnetite aggregates - Allan Hills A77011

    NASA Technical Reports Server (NTRS)

    Mckinley, S. G.; Scott, E. R. D.; Taylor, G. J.; Keil, K.

    1982-01-01

    ALHA 77011, which is the object of study in the present investigation, is a chondrite of the 1977 meteorite collection from Allan Hills, Antarctica. It contains an opaque and recrystallized silicate matrix (Huss matrix) and numerous aggregates consisting of micron- and submicron-sized graphite and magnetite. It is pointed out that no abundant graphite-magnetite aggregates could be observed in other type 3 ordinary chondrites, except for Sharps. Attention is given to the results of a modal analysis, relations between ALHA 77011 and other type 3 ordinary chondrites, and the association of graphite-magnetite and metallic Fe, Ni. The discovery of graphite-magnetite aggregates in type 3 ordinary chondrites is found to suggest that this material may have been an important component in the formation of ordinary chondrites.

  16. Morphological features of elongated-anisotropic magnetosome crystals in magnetotactic bacteria of the Nitrospirae phylum and the Deltaproteobacteria class

    NASA Astrophysics Data System (ADS)

    Lefèvre, Christopher T.; Pósfai, Mihály; Abreu, Fernanda; Lins, Ulysses; Frankel, Richard B.; Bazylinski, Dennis A.

    2011-12-01

    High resolution transmission electron microscopy was used to study the crystallographic habits of the elongated magnetite crystals, variously described as bullet-, tooth- or arrowhead-shaped, in two recently described, uncultured, magnetotactic bacteria belonging to the Nitrospirae phylum designated Candidatus Magnetoovum mohavensis strain LO-1, and Candidatus Thermomagnetovibrio paiutensis strain HSMV-1; and a cultured sulfate-reducing magnetotactic bacterium of the Deltaproteobacteria class of the Proteobacteria phylum designated strain AV-1. The elongation axes of the magnetosomes do not coincide with the easy magnetization axis (which is [111]) but they are parallel to [100] in LO-1 and AV-1 and parallel to [110] in HSMV-1. In all three strains, magnetosome magnetite crystals appear to elongate at constant width, resulting in asymmetric shapes. Idealized crystal morphologies are proposed. Neither the control mechanism over crystal growth, nor the adaptiveness, if any, of such unusual crystal habits are known at the moment. Since similar elongated and asymmetric morphologies are unknown in inorganically-formed magnetite crystals, these forms of magnetosome magnetite appear to be excellent biomarkers.

  17. Dependence of microbial magnetite formation on humic substance and ferrihydrite concentrations

    NASA Astrophysics Data System (ADS)

    Piepenbrock, Annette; Dippon, Urs; Porsch, Katharina; Appel, Erwin; Kappler, Andreas

    2011-11-01

    Iron mineral (trans)formation during microbial Fe(III) reduction is of environmental relevance as it can influence the fate of pollutants such as toxic metal ions or hydrocarbons. Magnetite is an important biomineralization product of microbial iron reduction and influences soil magnetic properties that are used for paleoclimate reconstruction and were suggested to assist in the localization of organic and inorganic pollutants. However, it is not well understood how different concentrations of Fe(III) minerals and humic substances (HS) affect magnetite formation during microbial Fe(III) reduction. We therefore used wet-chemical extractions, magnetic susceptibility measurements and X-ray diffraction analyses to determine systematically how (i) different initial ferrihydrite (FH) concentrations and (ii) different concentrations of HS (i.e. the presence of either only adsorbed HS or adsorbed and dissolved HS) affect magnetite formation during FH reduction by Shewanella oneidensis MR-1. In our experiments magnetite formation did not occur at FH concentrations lower than 5 mM, even though rapid iron reduction took place. At higher FH concentrations a minimum fraction of Fe(II) of 25-30% of the total iron present was necessary to initiate magnetite formation. The Fe(II) fraction at which magnetite formation started decreased with increasing FH concentration, which might be due to aggregation of the FH particles reducing the FH surface area at higher FH concentrations. HS concentrations of 215-393 mg HS/g FH slowed down (at partial FH surface coverage with sorbed HS) or even completely inhibited (at complete FH surface coverage with sorbed HS) magnetite formation due to blocking of surface sites by adsorbed HS. These results indicate the requirement of Fe(II) adsorption to, and subsequent interaction with, the FH surface for the transformation of FH into magnetite. Additionally, we found that the microbially formed magnetite was further reduced by strain MR-1 leading to the formation of either dissolved Fe(II), i.e. Fe 2+, in HEPES buffered medium or Fe(II) carbonate (siderite) in bicarbonate buffered medium. Besides the different identity of the Fe(II) compound formed at the end of Fe(III) reduction, there was no difference in the maximum rate and extent of microbial iron reduction and magnetite formation during FH reduction in the two buffer systems used. Our findings indicate that microbial magnetite formation during iron reduction depends on the geochemical conditions and can be of minor importance at low FH concentrations or be inhibited by adsorption of HS to the FH surface. Such scenarios could occur in soils with low iron mineral or high organic matter content.

  18. Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles

    NASA Astrophysics Data System (ADS)

    Nan, Alexandrina; Turcu, Rodica; Liebscher, Jürgen

    2013-11-01

    In order to contribute to the trend in contemporary research to develop magnetic core shell nanoparticles with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) in straightforward and reproducible methods new core shell magnetic nanoparticles were developed based on polypyrrole shells functionalized with biotin and folic acid. Magnetite nanoparticles stabilized by sebacic acid were used as magnetic cores. The morphology of magnetite was determined by transmission electron microscopy TEM, while the chemical structure investigated by FT-IR.

  19. Effects of the unique shape of submicron magnetite hollow spheres on magnetic properties and domain states

    Microsoft Academic Search

    Quan-Lin Ye; Yasuharu Kozuka; Hirofumi Yoshikawa; Kunio Awaga; Shunji Bandow; Sumio Iijima

    2007-01-01

    Submicron-scale magnetite (Fe3O4) hollow spheres were prepared by a template method using polystyrene beads. The obtained particles were very uniform in size with a diameter of 650±20nm and a shell thickness of 40nm . The temperature dependence of the zero-field cooled magnetizations indicated a broad anomaly at around 110K that was ascribable to the Verwey transition, while the magnetite nanoparticles

  20. Magnetic and magneto-optical properties of heteroepitaxial magnetite thin films

    Microsoft Academic Search

    J. Cheng; G. E. Sterbinsky; B. W. Wessels

    2008-01-01

    The magnetic and magneto-optical properties of heteroepitaxial magnetite (Fe3O4) thin films were investigated. Of interest was the role of misfit strain on determining its magnetic properties. Epitaxial magnetite thin films were deposited by molecular beam epitaxy using molecular oxygen on (100) oriented SrTiO3, BaTiO3 and MgO. Polar spectroscopic magneto-optic Kerr effect (MOKE) measurements on the thin films over near infrared

  1. Optical magnetic circular dichroism in threshold photoemission from a magnetite thin film

    Microsoft Academic Search

    K. Hild; J. Maul; T. Meng; M. Kallmayer; G. Schönhense; H. J. Elmers; R. Ramos; S. K. Arora; I. V. Shvets

    2008-01-01

    Threshold photoemission excited by polarization-modulated ultraviolet femtosecond laser light is exploited for phase-sensitive detection of magnetic circular dichroism (MCD) for a magnetite thin film. Magnetite (Fe3O4) shows a magnetic circular dichroism of ~(4.5 ± 0.3) × 10-3 for perpendicularly incident circularly polarized light and a magnetization vector switched parallel and antiparallel to the helicity vector by an external magnetic field.

  2. CVD synthesis of polycrystalline magnetite thin films: structural, magnetic and magnetotransport properties

    Microsoft Academic Search

    R. Mantovan; A. Lamperti; M. Georgieva; G. Tallarida; M. Fanciulli

    2010-01-01

    Magnetite (Fe3O4) is predicted to be half metallic at room temperature (RT) and it shows the highest Curie temperature among oxides. The use of Fe3O4 thin films is therefore promising for spintronic devices such as magnetic tunnel junctions (MTJs) and magnetoresistive sensors. The structural, magnetic and magnetotransport properties of magnetite are reported to be strongly dependent on the growth conditions.

  3. Enhancement of the magnetization saturation in magnetite (100) epitaxial films by thermo-chemical treatment

    Microsoft Academic Search

    Y. Zhou; Xuesong Jin; I. V. Shvets

    2004-01-01

    The effect of thermo-chemical treatment on the ease of saturation in a magnetic field of epitaxial magnetite (100) thin films grown on MgO (100) substrates was investigated. It was found that the films maintained a fully strained state with the MgO substrate during the treatment in air. No other iron oxide phase apart from the magnetite was observed in the

  4. Squid measurement of the Verwey transition on epitaxial (1 0 0) magnetite thin films

    Microsoft Academic Search

    V. Dediu; E. Arisi; I. Bergenti; A. Riminucci; M. Solzi; C. Pernechele; M. Natali

    2007-01-01

    We report results on epitaxial magnetite (Fe3O4) thin films grown by electron beam ablation on (100) MgAl2O4 substrates. At 120K magnetite undergoes a structural and electronic transition, the so-called Verwey transition, at which magnetic and conducting properties of the material change. We observed the Verwey transition on epitaxial films with a thickness of 50nm by comparing zero-field cooling (ZFC) and

  5. The microstructure and characteristics of magnetite thin films prepared by ultrasound-enhanced ferrite plating

    Microsoft Academic Search

    Chun-Young Oh; Jae-Hee Oh; Taegyung Ko

    2002-01-01

    Magnetite thin films were produced using the ultrasound-enhanced ferrite plating method. The effect of ferrite plating conditions on the microstructure and magnetic properties was investigated. The saturation magnetization (Ms) and the coercive force (Hc) of the magnetic thin films were 465-475 emu\\/cm3 and 60-65 Oe, respectively. Then, the applicability of the magnetite thin films as a CO gas sensor was

  6. Characterization of nanostructured magnetite thin films produced by sol–gel processing

    Microsoft Academic Search

    Ali Erdem Eken; Macit Ozenbas

    2009-01-01

    Nanocrystalline films of magnetite have been prepared by a novel sol–gel route in which, a solution of iron (III) nitrate\\u000a dissolved in ethylene glycol was applied on glass substrates by spin coating. Coating solution showed Newtonian behaviour\\u000a and viscosity was found as 0.0215 Pa.s. Annealing temperature was selected between 291 and 350 °C by DTA analysis in order\\u000a to obtain magnetite films.

  7. Microstructure and magnetic properties of magnetite thin films prepared by reactive sputtering

    Microsoft Academic Search

    Hongmei Qiu; Liqing Pan; Liwei Li; Hao Zhu; Xuedan Zhao; Mei Xu; Liangqiang Qin; John Q. Xiao

    2007-01-01

    Highly oriented magnetite (Fe3O4) thin films have been produced by reactive sputtering in a mixture of hydrogen and argon. While different phases can be achieved by varying the ratio between hydrogen and argon, single phase magnetite films can be achieved with hydrogen concentration gamma=0.75%-1%. For the sample grown at gamma=1.0%, a Verwey transition at about 111 K can be seen

  8. Size control of nanocrystalline magnetite thin films containing a small amount of Ge

    Microsoft Academic Search

    Seishi Abe; De Hai Ping; Hiroyuki Usui; Masato Ohnuma; Shigehiro Ohnuma

    2010-01-01

    This study investigated the preparation and particle size control of nanocrystalline magnetite (Fe3O4) containing a small amount of Ge. Thin films were prepared by radio-frequency sputtering with a composite target of Ge chips set on a Fe3O4 compound target in a mixed atmosphere of Ar and O2. X-ray diffraction revealed that the diffraction peak of magnetite gradually broadened as the

  9. Study of magnetite film formation at metal-scale interface during cooling of steel products

    Microsoft Academic Search

    J. Baud; A. Ferrier; J. Manenct

    1978-01-01

    A thin layer of magnetite is sometimes observed in the scales of hot-rolled sheets and wire rod at the scale-metal interface. The results of this study show that this layer of magnetite is produced, during the cooling of the products, by the wustite decomposition. The time\\/temperature field in which it appears has been defined. This inner layer is composed of

  10. Introduction of biotin or folic acid into polypyrrole magnetite core-shell nanoparticles

    SciTech Connect

    Nan, Alexandrina; Turcu, Rodica [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca (Romania)] [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca (Romania); Liebscher, Jürgen [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca, Romania and Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor 2, D-12489 Berlin (Germany)] [National Institute of Research and Development for Isotopic and Molecular Technologies, Donath 65-103, Cluj-Napoca, Romania and Institute of Chemistry, Humboldt-University Berlin, Brook-Taylor 2, D-12489 Berlin (Germany)

    2013-11-13

    In order to contribute to the trend in contemporary research to develop magnetic core shell nanoparticles with better properties (reduced toxicity, high colloidal and chemical stability, wide scope of application) in straightforward and reproducible methods new core shell magnetic nanoparticles were developed based on polypyrrole shells functionalized with biotin and folic acid. Magnetite nanoparticles stabilized by sebacic acid were used as magnetic cores. The morphology of magnetite was determined by transmission electron microscopy TEM, while the chemical structure investigated by FT-IR.

  11. Surface modification of magnetite nanoparticles using lactobionic acid and their interaction with hepatocytes

    Microsoft Academic Search

    K. M. Kamruzzaman Selim; Yong-Soo Ha; Sun-Jung Kim; Yongmin Chang; Tae-Jeong Kim; Gang Ho Lee; Inn-Kyu Kang

    2007-01-01

    In the current study, superparamagnetic magnetite nanoparticles were surface-modified with lactobionic acid (LA) to improve their intracellular uptake and ability to target hepatocytes. Maltotrionic acid (MA)-modified nanoparticles were also synthesized as a control. Cell culture experiment showed that LA-modified nanoparticles were internalized into hepatocytes and atomic absorption spectrometer (AAS) measurement indicated that the uptake amount of LA-modified magnetite into hepatocytes

  12. Non-stoichiometric magnetite and maghemite in the mature teeth of the chiton Acanthopleura hirtosa

    NASA Astrophysics Data System (ADS)

    St. Pierre, T. G.; Evans, L. A.; Webb, J.

    1992-04-01

    Mature radula pieces from the chiton Acanthopleura hirtosa were studied using Mössbauer spectroscopy. The magnetite present in the radulae was found to have a distribution of Verwey transition temperatures in the range 85-100K. It was deduced that the magnetite was non-stoichiometric with an average formula Fe2.98O3. About 10% of the Fe in the radulae was in the form of maghemite and about 19% was in the form of paramagnetic or superparamagnetic phases.

  13. Magnetic and Structural Properties of Magnetite in Radular Teeth of Chiton Acanthochiton Rubrolinestus

    Microsoft Academic Search

    Y. N. Han; C. L. Liu; L. D. Yao; Y. Wang; X. F. Han

    2008-01-01

    The major radular lateral teeth of Polyplacophora Chiton comprise a magnetite biomineral cap.We have investigated the structure and magnetic properties of the biomineralized magnetite crystallites in mature teeth of Chiton Acanthochiton Rubrolinestus. From the measurement of magnetic properties of tooth particles using SQUID magnetometry we find that the saturation magnetization and the Verwey transition temperature (Tv) are 78.4 emu\\/g and

  14. Using Magnetites to Remediate Heavy Metal Wastewaters from Acid-Mine Drainage

    Microsoft Academic Search

    M. D. Johnson; R. Wingo; M. Valdez

    \\u000a The remediation of heavy metal wastewaters using magnetites, also known as ferrites, has been an area of investigation for\\u000a many years. Early investigators used a synthetic procedure for the production of magnetites at 70 °C. Although quite effective,\\u000a as demonstrated by remediation of small waste streams from universities in Japan, this method is too energy intensive for\\u000a application to large

  15. Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study

    NASA Astrophysics Data System (ADS)

    Smirnov, Aleksey V.

    2009-01-01

    Magnetic measurements at cryogenic temperatures (<300 K) proved to be useful in paleomagnetic and rock magnetic research, stimulating continuous interest to low-temperature properties of magnetite and other magnetic minerals. Here I report new experimental results on a grain size dependence of the ratio ( R LT) between a low-temperature (20 K) saturation isothermal remanent magnetization (SIRM) imparted in magnetite after cooling in a 2.5 T field (field cooling, FC) and in a zero field environment (zero field cooling, ZFC). Synthetic magnetite samples ranged in mean grain size from 0.15 to 100 ?m, representing nearly single-domain (SD), pseudosingle-domain (PSD), and multidomain (MD) magnetic states. The R LT ratio monotonically increases from 0.58 to 1.12 with the decreasing mean grain size, being close to unity for PSD grains (0.15-5 ?m) and smaller than unity for MD magnetite (12-100 ?m). The R LT ratio of 1.27 is observed for acicular magnetite characterized by nearly SD behavior. These observations indicate that within the range of ~0.15 to ~5 ?m, the low-temperature SIRM may be higher than that expected from "normal" magnetic domain wall displacement. Such a behavior can be caused by the presence of a SD-like component in the magnetization of these grains, which origin, however, is uncertain. The natural rocks containing nearly stoichiometric magnetite manifest a dependence of the R LT ratio on magnetic domain state identical to that observed from synthetic magnetites. Therefore, the comparison of FC SIRM and ZFC SIRM at very low temperatures may allow a crude estimate of magnetic domain state in some magnetite-bearing rocks, such as shallow mafic intrusions or some marine sediments.

  16. Theoretical Single-Domain Grain Size Range in Magnetite and Titanomagnetite

    Microsoft Academic Search

    Robert F. Butler; Subir K. Banerjee

    1975-01-01

    A theoretical model of single-domain (SD) grain sizes is applied to magnetite and titanomagnetite. In this model, transition to a two-domain configuration takes place at the SD threshold do. This two-domain configuration is shown to be more applicable to fine-grained magnetites in igneous rocks than previous models involving transition to a circular spin configuration at do. Calculations of the stable

  17. Purely radiative irrotational dust spacetimes

    E-print Network

    N Van den Bergh; B Bastiaensen; H R Karimian; L Wylleman

    2007-02-27

    We consider irrotational dust spacetimes in the full non-linear regime which are "purely radiative" in the sense that the gravitational field satisfies the covariant transverse conditions div(H) = div(E) = 0. Within this family we show that the Bianchi class A spatially homogeneous dust models are uniquely characterised by the condition that $H$ is diagonal in the shear-eigenframe.

  18. Production of substantially pure fructose

    DOEpatents

    Hatcher, Herbert J. (Idaho Falls, ID); Gallian, John J. (Twin Falls, ID); Leeper, Stephen A. (Idaho Falls, ID)

    1990-01-01

    A process is disclosed for the production of substantially pure fructose from sucrose-containing substrates. The process comprises converting the sucrose to levan and glucose, purifying the levan by membrane technology, hydrolyzing the levan to form fructose monomers, and recovering the fructose.

  19. Isolation and pure culture of a freshwater magnetic spirillum in chemically defined medium.

    PubMed Central

    Blakemore, R P; Maratea, D; Wolfe, R S

    1979-01-01

    A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp. The organism was cultured in a chemically defined medium containing ferric quinate and succinate as sources of iron and carbon, respectively. Nonmagnetic variants of this isolate were maintained in chemically defined medium lacking ferric quinate. In contrast to magnetic cells, these had less iron and lacked measurable magnetic remanence and the intracytoplasmic crystals. In other respects, including moles percent guanine plus cytosine content, growth characteristics, nutrition, and physiology, the two types were similar. The isolate reduced nitrate without accumulating nitrite and produced ammonia during growth. Nitrate or ammonium ions served as a nitrogen source. The organism was microaerophilic and did not grow anaerobically with nitrate in the medium. In chemically defined medium, cells synthesized magnetite only if the initial O2 concentration in the atmosphere of sealed cultures was 6% (vol/vol) or less. Images PMID:500569

  20. A comparison of magnetite particles produced anaerobically by magnetotactic and dissimilatory iron-reducing bacteria

    SciTech Connect

    Moskowitz, B.M. (Univ. of California, Davis (USA)); Frankel, R.B. (California Polytechnic State Univ., San Luis Obispo (USA)); Bazylinski, D.A.; Jannasch, H.W. (Woods Hole Oceanographic Institution, MA (USA)); Lovley, D.R.

    1989-07-01

    The authors compare the magnetic properties of fine-grained magnetite produced by two newly isolated anaerobic bacteria, a magnetotactic bacterium (MV-1) and a dissimilatory iron-reducing bacterium (GS-15). Although room-temperature magnetic properties are generally different between the two microorganisms, MV-1 and GS-15 magnetites can be most easily distinguished by the temperature variation of saturation remanence obtained at liquid helium temperatures. Magnetite produced by MV-1 displays a sharp discontinuity in intensity at 100 K related to the Verwey transition. Magnetite produced by GS-15 displays a gradual decrease in intensity with temperature due to the progressive unblocking of magnetization. The differing behavior is due exclusively to different grain size distributions produced by these microorganisms. MV-1 produces magnetite with a narrow grain size distribution that is within the stable single domain size range at room temperature and below. GS-15 produces magnetite with a wide grain size distribution extending into the superparamagnetic (SPM) size range. Results show that a substantial fraction of particles produced by GS-15 are SPM at room temperature.

  1. Selective Product of Magnetite through Addition of Small Amount of Metal Element

    NASA Astrophysics Data System (ADS)

    Abe, Seishi; Hai Ping, De; Ohnuma, Masato; Ohnuma, Shigehiro

    2011-06-01

    In this study, we investigate the transformation mechanism from a phase mixture of magnetite (Fe3O4) and hematite (?-Fe2O3) to a single-phase magnetite through the addition of a specific metal element. The thin films were prepared by rf sputtering with a composite target of metal chips set on a ceramic magnetite (or hematite) target in Ar atmosphere. It is revealed that the addition of Ge to the polycrystalline hematite film obviously produces single-phase magnetite, indicating that the hematite is fully transformed to magnetite through an addition of Ge. Such transformation is also seen with slight additions of Mo, W, Cr, and Mg, whereas the addition of Sn does not affect the phase mixture of magnetite and hematite. According to the free energy of the reaction, elements of Ge, Mo, W, Cr, and Mg are capable of reducing hematite, whereas hematite remains unreactive with addition of Sn. This is in good agreement with the experiment results. This unique technique additionally provides the maximum magnetization of 3.9 kG at 8 ×105 A·m-1(10 kOe) at a Mo concentration of 1.3 at. %.

  2. Estimation of Sintering Kinetics of Oxidized Magnetite Pellet Using Optical Dilatometer

    NASA Astrophysics Data System (ADS)

    Sandeep Kumar, T. K.; Viswanathan, Neelakantan Nurni; Ahmed, Hesham M.; Andersson, Charlotte; Björkman, Bo

    2014-12-01

    The quality of magnetite pellet is primarily determined by the physico-chemical changes the pellet undergoes as it makes excursion through the gaseous and thermal environment in the induration furnace. Among these physico-chemical processes, the oxidation of magnetite phase and the sintering of oxidized magnetite (hematite) and magnetite (non-oxidized) phases are vital. Rates of these processes not only depend on the thermal and gaseous environment the pellet gets exposed in the induration reactor but also interdependent on each other. Therefore, a systematic study should involve understanding these processes in isolation to the extent possible and quantify them seeking the physics. With this motivation, the present paper focusses on investigating the sintering kinetics of oxidized magnetite pellet. For the current investigation, sintering experiments were carried out on pellets containing more than 95 pct magnetite concentrate from LKAB's mine, dried and oxidized to completion at sufficiently low temperature to avoid sintering. The sintering behavior of this oxidized pellet is quantified through shrinkage captured by Optical Dilatometer. The extent of sintering characterized by sintering ratio found to follow a power law with time i.e., Kt n . The rate constant K for sintering was determined for different temperatures from isothermal experiments. The rate constant, K, varies with temperature as ln left( {TK^{(1/n)} } right) = ln K' - Q/RT, and the activation energy (Q) and reaction rate constant (K') are estimated. Further, the sintering kinetic equation was also extended to a non-isothermal environment and validated using laboratory experiments.

  3. Magnetic and structural properties of magnetite in radular teeth of chiton Acanthochiton rubrolinestus.

    PubMed

    Han, Yunan; Liu, Chuanlin; Zhou, Dong; Li, Fashen; Wang, Yong; Han, Xiufeng

    2011-04-01

    The teeth of the Polyplacophora Chiton Acanthochiton Rubrolinestus contain biomineralized magnetite crystallites whose biological functions in relation to structure and magnetic properties are not well understood. Here, using superconducting quantum interference device (SQUID) magnetometry, we find that the saturation magnetization (?(s)) and the Verwey transition temperature (T(v)) of tooth particles are 78.4 emu/g and 105 K, respectively. These values are below those of the stoichiometric magnetite. An in situ examination of the structure of the magnetite-bearing region within an individual tooth using high-resolution transmission electron microscopy indicates magnetite microcrystals form electron dense polycrystalline sheets with typical lengths of about 800 nm and widths of about 150 nm. These polycrystalline sheets are arranged regularly along the longitudinal direction of the tooth cutting surface. In addition, the crystallites in polycrystalline sheets take on generally good crystallinity. The magnetic microstructures of in situ magnetic force microscopy demonstrate that the [111] easy direction of magnetite microcrystals are aligned along the length of the tooth, whereas the [111] direction is parallel to the thickness of the tooth. Both Mössbauer spectra and magnetization versus temperature measurements under field cooled and zero-field cooled conditions do not detect superparamagnetic magnetite crystallites in the mature major lateral tooth particles of this chiton. PMID:21365666

  4. Sorption of nalidixic acid onto micrometric and nanometric magnetites: Experimental study and modeling

    NASA Astrophysics Data System (ADS)

    Usman, M.; Martin, S.; Cimetière, N.; Giraudet, S.; Chatain, V.; Hanna, K.

    2014-04-01

    The sorption of nalidixic acid (NA) was studied onto three kinds of magnetite characterized by different particle sizes (from micrometric to nanometric) and surface properties. Experiments were performed under static batch and dynamic flow conditions. Obtained results indicate that kinetics and extent of sorption was strongly affected by the particle size of tested magnetites. Ionic strength effect was less significant suggesting that aggregation state of the magnetite particles did not affect the sorption. During kinetic sorption experiments, apparent rate constant normalized to solid mass was faster for nanosized magnetite while an opposite trend was observed for the surface area-normalized rate constants. Infrared data suggested the possibility of similar surface interactions on both microsized and nanosized magnetites. Transport of NA in magnetite-packed column was found associated to the instantaneous sorption without any significant effect of kinetic limitation. Breakthrough curves (BC) and sorption extent in columns were calculated by using Thomas, Yan and Yoon-Nelson models. Sorption capacities predicted by Thomas or Yan model were in good agreement with that determined by integrating total area above BC. However, Thomas model failed particularly to predict an accurate concentration at lower and higher time points of the BC. These findings have strong implications in relation to the transport and removal of environmental pollutants in natural and engineered systems.

  5. The synthesis and characterization of poly(?-glutamic acid)-coated magnetite nanoparticles and their effects on antibacterial activity and cytotoxicity

    NASA Astrophysics Data System (ADS)

    Inbaraj, B. Stephen; Kao, T. H.; Tsai, T. Y.; Chiu, C. P.; Kumar, R.; Chen, B. H.

    2011-02-01

    Magnetite nanoparticles (MNPs) modified with sodium and calcium salts of poly(?-glutamic acid) (NaPGA and CaPGA) were synthesized by the coprecipitation method, followed by characterization and evaluation of their antibacterial and cytotoxic effects. Superparamagnetic MNPs are particularly attractive for magnetic driving as well as bacterial biofilm and cell targeting in in vivo applications. Characterization of synthesized MNPs by the Fourier transform infrared spectra and magnetization curves confirmed the PGA coating on MNPs. The mean diameter of NaPGA- and CaPGA-coated MNPs as determined by transmission electron microscopy was 11.8 and 14 nm, respectively, while the x-ray diffraction pattern revealed the as-synthesized MNPs to be pure magnetite. Based on agar dilution assay, both NaPGA- and CaPGA-coated MNPs showed a lower minimum inhibitory concentration in Salmonella enteritidis SE 01 than the commercial antibiotics linezolid and cefaclor, but the former was effective against Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 10832, whereas the latter was effective against Escherichia coli O157:H7 TWC 01. An in vitro cytotoxicity study in human skin fibroblast cells as measured by MTT assay implied the as-synthesized MNPs to be nontoxic. This outcome demonstrated that both ?-PGA-modified MNPs are cytocompatible and possess antibacterial activity in vitro, and thereby should be useful in in vivo studies for biomedical applications.

  6. Magnetite-sulfide chondrules and nodules in CK carbonaceous chondrites - Implications for the timing of CK oxidation

    NASA Technical Reports Server (NTRS)

    Rubin, Alan E.

    1993-01-01

    CK carbonaceous chondrites contain rare (about 0.1 vol pct) magnetite-sulfide chondrules that range from about 240 to 500 microns in apparent diameter and have ellipsoidal to spheroidal morphologies, granular textures, and concentric layering. They resemble the magnetite-sulfide nodules occurring inside mafic silicate chondrules in CK chondrites. It seems likely that the magnetite-sulfide chondrules constitute the subset of magnetite-sulfide nodules that escaped as immiscible droplets from their molten silicate chondrule hosts during chondrule formation. The intactness of the magnetite-sulfide chondrules and nodules implies that oxidation of CK metal occurred before agglomeration. Hence, the pervasive silicate darkening of CK chondrites was caused by the shock mobilization of magnetite and sulfide, not metallic Fe-Ni and sulfide as in shock-darkened ordinary chondrites.

  7. Observing thermomagnetic stability of nonideal magnetite particles: Good paleomagnetic recorders?

    NASA Astrophysics Data System (ADS)

    Almeida, Trevor P.; Kasama, Takeshi; Muxworthy, Adrian R.; Williams, Wyn; Nagy, Lesleis; Dunin-Borkowski, Rafal E.

    2014-10-01

    The thermomagnetic behavior of remanence-induced magnetite (Fe3O4) particles in the pseudo-single-domain (PSD) size range (~0.1-10 µm), which dominate the magnetic signature of many rock lithologies, is investigated using off-axis electron holography. Construction of magnetic induction maps allowed for the visualization of the vortex domain state in an individual Fe3O4 grain (~200 nm in diameter) as a function of temperature. Acquisition of a series of electron holograms at 100°C intervals during in situ heating up to 700°C demonstrates the vortex state of the Fe3O4 grain, in this instance, remains thermally stable close to its unblocking temperature and exhibits a similar in-plane remanent state upon cooling; i.e., the particle is effectively behaving like a uniaxial single-domain particle to temperatures near TC. Such particles are thought to be robust magnetic recorders. It is suggested that evidence for PSD behavior should therefore not preclude paleomagnetic investigation.

  8. Magnetite stability in aqueous sodium phosphate solutions at elevated temperatures

    SciTech Connect

    Ziemniak, S.E.; Opalka, E.P.

    1992-03-01

    Magnetite (Fe{sub 3}O{sub 4}) is shown to transform to a sodium ferric hydroxy-phosphate compound in concentrated, alkaline sodium phosphate solutions at elevated temperatures via 1/3 Fe{sub 3}O{sub 4}(s) + 13/3 Na{sup +} + 2 HPO{sub 4}{sup =} {r_reversible} Na{sub 4}Fe(OH)(PO{sub 4}){sub 2}{center_dot}1/3NaOH(s) + 1/3 H{sup +} + 1/6 H{sub 2}(g). The thermodynamic equilibrium for this reaction was defined in the system Na{sub 2}O-P{sub 2}O{sub 5}Fe{sub 3}O{sub 4}-H{sub 2}O for Na/P molar ratios between 2.1 and 3. Quantitative chemical, infrared and Mossbauer spectroscopic, and X-ray diffraction analyses are employed to verify that the precipitated solid was a single phase having the non-whole number stoichiometric Na/P ratio 2.15 {plus_minus} 0.02. Standard entropy and free energy of formation for sodium ferric hydroxyphosphate were calculated to be 729.2 J/mol-K and {minus}3550.3 kJ/mol, respectively.

  9. Magnetite stability in aqueous sodium phosphate solutions at elevated temperatures

    SciTech Connect

    Ziemniak, S.E.; Opalka, E.P.

    1992-03-01

    Magnetite (Fe[sub 3]O[sub 4]) is shown to transform to a sodium ferric hydroxy-phosphate compound in concentrated, alkaline sodium phosphate solutions at elevated temperatures via 1/3 Fe[sub 3]O[sub 4](s) + 13/3 Na[sup +] + 2 HPO[sub 4][sup =] [r reversible] Na[sub 4]Fe(OH)(PO[sub 4])[sub 2][center dot]1/3NaOH(s) + 1/3 H[sup +] + 1/6 H[sub 2](g). The thermodynamic equilibrium for this reaction was defined in the system Na[sub 2]O-P[sub 2]O[sub 5]Fe[sub 3]O[sub 4]-H[sub 2]O for Na/P molar ratios between 2.1 and 3. Quantitative chemical, infrared and Mossbauer spectroscopic, and X-ray diffraction analyses are employed to verify that the precipitated solid was a single phase having the non-whole number stoichiometric Na/P ratio 2.15 [plus minus] 0.02. Standard entropy and free energy of formation for sodium ferric hydroxyphosphate were calculated to be 729.2 J/mol-K and [minus]3550.3 kJ/mol, respectively.

  10. Novel hybrid nanostructured materials of magnetite nanoparticles and pectin

    NASA Astrophysics Data System (ADS)

    Sahu, Saurabh; Dutta, Raj Kumar

    2011-04-01

    A novel hybrid nanostructured material comprising superparamagnetic magnetite nanoparticles (MNPs) and pectin was synthesized by crosslinking with Ca2+ ions to form spherical calcium pectinate nanostructures, referred as MCPs, which were typically found to be 100-150 nm in size in dried condition, confirmed from transmission electron microscopy and scanning electron microscopy. The uniform size distribution was revealed from dynamic light scattering measurement. In aqueous medium the MCPs showed swelling behavior with an average size of 400 nm. A mechanism of formation of spherical MCPs is outlined constituting a MNP-pectin interface encapsulated by calcium pectinate at the periphery, by using an array of characterization techniques like zeta potential, thermogravimetry, Fourier transformed infrared and X-ray photoelectron spectroscopy. The MCPs were stable in simulated gastrointestinal fluid and ensured minimal loss of magnetic material. They exhibited superparamagnetic behavior, confirmed from zero field cooled and field cooled profiles and showed high saturation magnetization (Ms) of 46.21 emu/g at 2.5 T and 300 K. Ms decreased with increasing precursor pectin concentrations, attributed to quenching of magnetic moments by formation of a magnetic dead layer on the MNPs.

  11. Enhanced thermal stability of phosphate capped magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Muthukumaran, T.; Philip, John

    2014-06-01

    We have studied the effect of phosphate capping on the high temperature thermal stability and magnetic properties of magnetite (Fe3O4) nanoparticles synthesized through a single-step co-precipitation method. The prepared magnetic nanoparticles are characterized using various techniques. When annealed in air, the phosphate capped nanoparticle undergoes a magnetic to non-magnetic phase transition at a temperature of 689 °C as compared to 580 °C in the uncoated nanoparticle of similar size. The observed high temperature phase stability of phosphate capped nanoparticle is attributed to the formation of a phosphocarbonaceous shell over the nanoparticles, which acts as a covalently attached protective layer and improves the thermal stability of the core material by increasing the activation energy. The phosphocarbonaceous shell prevents the intrusion of heat, oxygen, volatiles, and mass into the magnetic core. At higher temperatures, the coalescence of nanoparticles occurs along with the restructuring of the phosphocarbonaceous shell into a vitreous semisolid layer on the nanoparticles, which is confirmed from the small angle X-ray scattering, Fourier transform infra red spectroscopy, and transmission electron microscopy measurements. The probable mechanism for the enhancement of thermal stability of phosphocarbonaceous capped nanoparticles is discussed.

  12. Magnetization and susceptibility of ion-irradiated granular magnetite films

    NASA Astrophysics Data System (ADS)

    Jiang, W.; McCloy, J. S.; Lea, A. S.; Sundararajan, J. A.; Yao, Q.; Qiang, Y.

    2011-04-01

    Porous granular films of magnetite (Fe3O4) with grains of ˜3 nm in size were prepared using a state-of-the-art nanocluster deposition system. The films are initially superparamagnetic but become magnetized following Si2+ ion irradiation. A significant increase in the grain size and a dramatic change in the microstructure are observed. There are dipolar interactions between the nanoparticles in both the unirradiated and irradiated films. The in-phase alternating current magnetic susceptibility of the unirradiated film shows a blocking temperature of ˜150 K, depending on frequency. A broadened Verwey transition for the irradiated film occurs at ˜75 K, above which the susceptibility exhibits unusual behavior: a nearly linear decrease with decreasing temperature. There are irreversible domain rotations in the irradiated film during zero-field cooling and warming cycles between 10 and 300 K. The observed behavior of the irradiated granular films is quite distinct from that of metallic nanostructures after irradiation, and is due to the dramatic change in microstructures.

  13. Magnetization and susceptibility of ion-irradiated granular magnetite films

    SciTech Connect

    Jiang, W.; McCloy, J. S.; Lea, A. S.; Sundararajan, J. A.; Yao, Q.; Qiang, Y. [Pacific Northwest National Laboratory, Richland, Washington 99352 (United States); Physics Department, University of Idaho, Moscow, Idaho 83844 (United States)

    2011-04-01

    Porous granular films of magnetite (Fe{sub 3}O{sub 4}) with grains of {approx}3 nm in size were prepared using a state-of-the-art nanocluster deposition system. The films are initially superparamagnetic but become magnetized following Si{sup 2+} ion irradiation. A significant increase in the grain size and a dramatic change in the microstructure are observed. There are dipolar interactions between the nanoparticles in both the unirradiated and irradiated films. The in-phase alternating current magnetic susceptibility of the unirradiated film shows a blocking temperature of {approx}150 K, depending on frequency. A broadened Verwey transition for the irradiated film occurs at {approx}75 K, above which the susceptibility exhibits unusual behavior: a nearly linear decrease with decreasing temperature. There are irreversible domain rotations in the irradiated film during zero-field cooling and warming cycles between 10 and 300 K. The observed behavior of the irradiated granular films is quite distinct from that of metallic nanostructures after irradiation, and is due to the dramatic change in microstructures.

  14. Magnetization and susceptibility of ion irradiated granular magnetite films

    SciTech Connect

    Jiang, Weilin; McCloy, John S.; Lea, Alan S.; Sundararajan, J. A.; Yao, Qi; Qiang, Y.

    2011-04-26

    Superparamagnetic granular magnetite (Fe3O4) films with an average grain size of 3 nm have been found to be magnetized following 5.5 MeV Si2+ ion irradiation to a fluence of 1.0E16 ions/cm2 near room temperature. The film underwent a phase transition to ferromagnetism after the irradiation. X-ray diffraction study shows that the average grain size increased to 23 nm. There is a dramatic change in the microstructure, featuring particle aggregation and material condensation. Magnetic domains in the irradiated film are observed in the size range of tens to several hundreds of nanometers. The change in the magnetic properties is attributed to irradiation induced grain growth and structural modifications that lead to occurrence of magnetic anisotropy. There are dipolar interactions between the nanoparticles in both the unirradiated and irradiated films. Data fits for the in-phase alternating current magnetic susceptibility of the unirradiated film indicate that the blocking temperature is ~150 K, depending on frequency. A gradual Verwey transition for the irradiated film occurs at ~75 K, above which the susceptibility exhibits unusual behavior: a linear decrease with decreasing temperature. There are irreversible processes of magnetic domains during cooling and warming up between 10 and 300 K.

  15. Lipolytic biocatalyst based on recyclable magnetite-polysiloxane nanoparticles

    NASA Astrophysics Data System (ADS)

    Durdureanu-Angheluta, Anamaria; Ignat, Maurusa-Elena; Maier, Stelian Sergiu; Pricop, Lucia; Coroaba, Adina; Fifere, Adrian; Pinteala, Mariana; Chiriac, Anca

    2014-02-01

    This work presents a novel hydrophobic magnetizable nanosupport able to load and valorize the lipase derived from Candida cylindracea (CCL). Nude magnetite nanoparticles (MP) were coated by covalent binding with an ester-polysiloxane (PS). The chemical composition, dimensions, morphology and magnetic properties of the resulted core-shell nanoparticles (MP-PS-CCL) are analyzed. The amount of immobilized lipase increase when loaded from aqueous solutions of up to 12.8 mg/mL CCL, when a lipolytic activity of 74.76 U/g is achieved. For higher concentrations of the loading solution, the activity of immobilized lipase decreases, probably due to the enzyme steric hindrance. MP-PS-CCL exhibits a good lipolytic activity against 4-nitrophenyl laurate (4-NPL), which allows the kinetic study of lipolysis reaction by measuring the amount of released 4-nitrophenol (4-NP), when working at room temperature, in TRIS buffer (pH 8.2). Even after three months of storage, the product is able to sustain up to 4 reusing cycles.

  16. Enhanced thermal stability of phosphate capped magnetite nanoparticles

    SciTech Connect

    Muthukumaran, T.; Philip, John, E-mail: philip@igcar.gov.in [SMARTS, Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamil Nadu-603 102 (India)

    2014-06-14

    We have studied the effect of phosphate capping on the high temperature thermal stability and magnetic properties of magnetite (Fe{sub 3}O{sub 4}) nanoparticles synthesized through a single-step co-precipitation method. The prepared magnetic nanoparticles are characterized using various techniques. When annealed in air, the phosphate capped nanoparticle undergoes a magnetic to non-magnetic phase transition at a temperature of 689?°C as compared to 580?°C in the uncoated nanoparticle of similar size. The observed high temperature phase stability of phosphate capped nanoparticle is attributed to the formation of a phosphocarbonaceous shell over the nanoparticles, which acts as a covalently attached protective layer and improves the thermal stability of the core material by increasing the activation energy. The phosphocarbonaceous shell prevents the intrusion of heat, oxygen, volatiles, and mass into the magnetic core. At higher temperatures, the coalescence of nanoparticles occurs along with the restructuring of the phosphocarbonaceous shell into a vitreous semisolid layer on the nanoparticles, which is confirmed from the small angle X-ray scattering, Fourier transform infra red spectroscopy, and transmission electron microscopy measurements. The probable mechanism for the enhancement of thermal stability of phosphocarbonaceous capped nanoparticles is discussed.

  17. Optimizing Magnetite Nanoparticles for Mass Sensitivity in Magnetic Particle Imaging

    SciTech Connect

    Ferguson, R. Matthew; Minard, Kevin R.; Khandhar, Amit P.; Krishnan, Kannan M.

    2011-03-01

    Purpose: Magnetic particle imaging (MPI), using magnetite nanoparticles (MNPs) as tracer material, shows great promise as a platform for fast tomographic imaging. To date, the magnetic properties of MNPs used in imaging have not been optimized. As nanoparticle magnetism shows strong size dependence, we explore how varying MNP size impacts imaging performance in order to determine optimal MNP characteristics for MPI at any driving field frequency, ?. Methods: Monodisperse MNPs of varying size were synthesized and their magnetic properties characterized. Their MPI response was measured experimentally, at an arbitrarily chosen ? = 250 kHz, using a custom-built MPI transceiver designed to detect the third harmonic of MNP magnetization. Results were interpreted using a model of dynamic MNP magnetization that is based on the Langevin theory of superparamagnetism and accounts for sample size distribution, and size-dependent magnetic relaxation. Results: Our experimental results show clear variation in the MPI signal intensity as a function of MNP size that is in good agreement with modeled results. A maxima in the plot of MPI signal vs. MNP size indicates there is a particular size that is optimal for the chosen frequency of 250 kHz. Conclusions: For MPI at any chosen frequency, there will exist a characteristic particle size that generates maximum signal amplitude. We illustrate this at 250 kHz with particles of 15 nm core diameter.

  18. Adsorption of copper ion on magnetite-immobilised chitin.

    PubMed

    Wong, K S; Wong, K H; Ng, S; Chung, W K; Wong, P K

    2007-01-01

    The adsorption of Cu2+ from aqueous solution by magnetite-immobilised chitin (MC) was studied in batch mode. Two conventional adsorbents, cation exchange resin (CER) and activated carbon (AC) were used for the comparison. The physicochemical parameters including pH, concentration of adsorbent, temperature and initial Cu2+ concentration were optimised. Under the optimised conditions, the removal efficiencies of Cu2+ for MC, CER and AC were 91.67, 93.36 and 89.16%, respectively. In addition, the removal capacities of Cu2+ for MC, CER and AC were 56.71, 74.84 and 6.55 mg/g, respectively. The adsorption isotherm studies indicated that the adsorptive behaviour of Cu2+ on three adsorbents could be well described by the Langmuir model. The maximum adsorption capacities (qmax) for MC, CER and AC were 53.19, 89.29 and 5.82 mg/g, respectively. The applicability of the kinetic model has been investigated for MC. Experimental results indicated that a pseudo-second-order reaction model provided the best description of the data with a correlation coefficient 0.999 for different initial Cu2+ concentrations. The rate constants were also determined. Various thermodynamic parameters such as standard free energy (DeltaG 0), enthalpy (DeltaH 0) and entropy (DeltaS 0) were calculated for predicting the adsorption nature of MC. The results indicated that this system was a spontaneous and endothermic process. PMID:17951877

  19. Temperature-dependent structure of Tb-doped magnetite nanoparticles

    NASA Astrophysics Data System (ADS)

    Rice, Katherine P.; Russek, Stephen E.; Geiss, Roy H.; Shaw, Justin M.; Usselman, Robert J.; Evarts, Eric R.; Silva, Thomas J.; Nembach, Hans T.; Arenholz, Elke; Idzerda, Yves U.

    2015-02-01

    High quality 5 nm cubic Tb-doped magnetite nanoparticles have been synthesized by a wet-chemical method to investigate tailoring of magnetic properties for imaging and biomedical applications. We show that the Tb is incorporated into the octahedral 3+ sites. High-angle annular dark-field microscopy shows that the dopant is well-distributed throughout the particle, and x-ray diffraction measurements show a small lattice parameter shift with the inclusion of a rare-earth dopant. Magnetization and x-ray magnetic circular dichroism data indicate that the Tb spins are unpolarized and weakly coupled to the iron spin lattice at room temperature, and begin to polarize and couple to the iron oxide lattice at temperatures below 50 K. Broadband ferromagnetic resonance measurements show no increase in magnetic damping at room temperature for Tb-doped nanoparticles relative to undoped nanoparticles, further confirming weak coupling between Fe and Tb spins at room temperature. The Gilbert damping constant, ?, is remarkably low for the Tb-doped nanoparticles, with ? = 0.024 ± 0.003. These nanoparticles, which have a large fixed moment, a large fluctuating moment and optically active rare-earth elements, are potential high-relaxivity T1 and T2 MRI agents with integrated optical signatures.

  20. IDENTIFICATION OF MAGNETITE IN B-TYPE ASTEROIDS

    SciTech Connect

    Yang Bin [Institute for Astronomy, University of Hawaii, Honolulu, HI 96822 (United States); Jewitt, David, E-mail: yangbin@ifa.hawaii.ed, E-mail: jewitt@ucla.ed [Department of Earth and Space Sciences, Institute for Geophysics and Planetary Physics and Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States)

    2010-09-15

    Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example. We conducted a focused, infrared spectroscopic survey of B-type asteroids to search for water-related features in these objects. Our results show that the negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 {mu}m. The 1 {mu}m band can be matched in position and shape using magnetite (Fe{sub 3}O{sub 4}), which is an important indicator of past aqueous alteration in the parent body. Furthermore, our observations of B-type asteroid (335) Roberta in the 3 {mu}m region reveal an absorption feature centered at 2.9 {mu}m, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. The new observations suggest that at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration.

  1. Trichloroethylene degradation by persulphate with magnetite as a heterogeneous activator in aqueous solution.

    PubMed

    Ruan, Xiaoxin; Gu, Xiaogang; Lu, Shuguang; Qiu, Zhaofu; Sui, Qian

    2015-06-01

    Iron oxide-magnetite (Fe3O4) as a heterogeneous activator to activate persulphate anions [Formula: see text] for trichloroethylene (TCE) degradation was investigated in this study. The experimental results showed that TCE could be completely oxidized within 5?h by using 5?g?L(-1) magnetite and 63?mM [Formula: see text] indicating the effectiveness of the process for TCE removal. Various factors of the process, including. [Formula: see text] and magnetite dosages, and initial solution pH, were evaluated, and TCE degradation fitted well to the pseudo-first-order kinetic model. The calculated kinetic rate constant was increased with increasing [Formula: see text] and magnetite dosages, but it was independent of solution pH. In addition, the changes of magnetite morphology examined by scanning electron microscopy and X-ray powder diffraction, respectively, confirmed the slight corrosion with ?-Fe2O3 coated on the magnetite surface. The probe compounds tests clearly identified the generation of the reactive oxygen species in the system. While the free radical quenching studies further demonstrated that [Formula: see text] and •OH were the major radicals responsible for TCE degradation, whereas [Formula: see text] contributed less in the system, and therefore the roles of reactive oxygen species on TCE degradation mechanisms were proposed accordingly. To our best knowledge, this is the first time the performance and mechanism of magnetite-activated persulphate oxidation for TCE degradation are reported. The findings of this study provided a new insight into the heterogeneous catalysis mechanism and showed a great potential for the practical application of this technique in in situ TCE-contaminated groundwater remediation. PMID:25496173

  2. Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization II: Makaopuhi lava lake

    NASA Astrophysics Data System (ADS)

    Cashman, Katharine V.; Marsh, Bruce D.

    1988-07-01

    Crystal size distribution (CSD) theory has been applied to drill core samples from Makaopuhi lava lake, Kilauea Volcano, Hawaii. Plagioclase and Fe-Ti oxide size distribution spectra were measured and population densities (n)were calculated and analyzed using a steady state crystal population balance equation: n=n 0 exp(-L/G?). Slopes on ln( n) versus crystal size ( L) plots determine the parameter G?, a. product of average crystal growth rate ( G) and average crystal growth time ( ?). The intercept is J/G where J is nucleation rate. Known temperature-depth distributions for the lava lake provide an estimate of effective growth time ( ?), allowing nucleation and growth rates to be determined that are independent of any kinetic model. Plagioclase growth rates decrease with increasing crystallinity (9.9-5.4×10-11 cm/s), as do plagioclase nucleation rates (33.9-1.6×10-3/cm3 s). Ilmenite growth and nucleation rates also decrease with increasing crystallinity (4.9-3.4 ×10-10 cm/s and 15-2.2×10-3/cm3 s, respectively). Magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus ( G =2.9×10-10 cm/s, J=7.6×10-2/cm3 s). Moments of the population density function were used to examine the change in crystallization rates with time. Preliminary results suggest that total crystal volume increases approximately linearly with time after ˜50% crystallization; a more complete set of samples is needed for material with <50% crystals to define the entire crystallization history. Comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling. This interpretation is consistent with proposed thermal models of magmatic cooling, where heat loss is balanced by latent heat production to maintain equilibrium cooling.

  3. pureS2HAT: S 2HAT-based Pure E/B Harmonic Transforms

    NASA Astrophysics Data System (ADS)

    Grain, J.; Stompor, R.; Tristram, M.

    2011-10-01

    The pS2HAT routines allow efficient, parallel calculation of the so-called 'pure' polarized multipoles. The computed multipole coefficients are equal to the standard pseudo-multipoles calculated for the apodized sky maps of the Stokes parameters Q and U subsequently corrected by so-called counterterms. If the applied apodizations fullfill certain boundary conditions, these multipoles correspond to the pure multipoles. Pure multipoles of one type, i.e., either E or B, are ensured not to contain contributions from the other one, at least to within numerical artifacts. They can be therefore further used in the estimation of the sky power spectra via the pseudo power spectrum technique, which has to however correctly account for the applied apodization on the one hand, and the presence of the counterterms, on the other. In addition, the package contains the routines permitting calculation of the spin-weighted apodizations, given an input scalar, i.e., spin-0 window. The former are needed to compute the counterterms. It also provides routines for maps and window manipulations. The routines are written in C and based on the S2HAT library, which is used to perform all required spherical harmonic transforms as well as all inter-processor communication. They are therefore parallelized using MPI and follow the distributed-memory computational model. The data distribution patterns, pixelization choices, conventions etc are all as those assumed/allowed by the S2HAT library.

  4. Protein crystallization: from purified protein to diffraction-quality crystal

    Microsoft Academic Search

    Emmanuel Saridakis; Naomi E Chayen

    2008-01-01

    Determining the structure of biological macromolecules by X-ray crystallography involves a series of steps: selection of the target molecule; cloning, expression, purification and crystallization; collection of diffraction data and determination of atomic positions. However, even when pure soluble protein is available, producing high-quality crystals remains a major bottleneck in structure determination. Here we present a guide for the non-expert to

  5. Epitaxial Fe3-xTixO4 films from magnetite to ulvöspinel by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Droubay, T. C.; Pearce, C. I.; Ilton, E. S.; Engelhard, M. H.; Jiang, W.; Heald, S. M.; Arenholz, E.; Shutthanandan, V.; Rosso, K. M.

    2011-09-01

    Epitaxial films along the Fe3-xTixO4 (titanomagnetite) compositional series from pure end-members magnetite (Fe3O4) to ulvöspinel (Fe2TiO4) were successfully grown by pulsed laser deposition on MgO(001) substrates. Characterization, including high-resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism, consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional alteration to a titanomaghemite-like composition and structure. The surfaces of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low-oxygen environments.

  6. Impedimetric sensor for toxigenic Penicillium sclerotigenum detection in yam based on magnetite-poly(allylamine hydrochloride) composite.

    PubMed

    Silva, Gilcelia J L; Andrade, Cesar A S; Oliveira, Idjane S; de Melo, Celso P; Oliveira, Maria D L

    2013-04-15

    We describe a new DNA biosensor for the detection of toxigenic Penicillium sclerotigenum in pure culture or infected yams. The P. sclerotigenum detection takes place on a self-assembled monolayer of a (magnetite)/(poly(allylamine hydrochloride)) (Fe3O4-PAH) composite that serves as an anchoring layer for the DNA hybridization interaction. Electrical impedance spectroscopy (EIS) was used to evaluate and quantify the hybridization degree. The Fe3O4-PAH composite is a good platform for the immobilization of biomolecules, due to the presence of many possible binding sites for nucleotides and to its large surface-to-volume ratio and good biocompatibility. The biosensor was capable of not only qualitatively detecting the presence of the fungus genome at low concentrations, but also shown a good quantitative impedimetric response its electrical resistance was monitored along the time of exposure. A Fe3O4-PAH-probe biosensor would require only small volumes and low concentrations of the analyte when used, for instance, in detecting P. sclerotigenum contamination of food, besides presenting many comparative advantages, such as selectivity, specificity and reproducibility, relative to alternative techniques. PMID:23465186

  7. Epitaxial Fe3-xTixO4 films from magnetite to ulvöspinel by pulsed laser deposition

    SciTech Connect

    Droubay, Timothy C.; Pearce, Carolyn I.; Ilton, Eugene S.; Engelhard, Mark H.; Jiang, Weilin; Heald, Steve M.; Arenholz, Elke; Shutthanandan, V.; Rosso, Kevin M.

    2011-10-13

    Epitaxial films along the Fe3-xTixO4 (titanomagnetite) compositional series from pure end-members magnetite (Fe3O4) to ulvöspinel (Fe2TiO4) were successfully grown by pulsed laser deposition on MgO(100) substrates. Spectroscopic characterization including high resolution x-ray diffraction, x-ray photoelectron spectroscopy, and synchrotron-based x-ray absorption and magnetic circular dichroism consistently shows that Ti(IV) substitutes for Fe(III) in the inverse spinel lattice with a proportional increase in lattice Fe(II) concentration. No evidence of Ti interstitials, spinodal decomposition, or secondary phases was found in the bulk of the grown films. At the uppermost few nanometers of the Ti-bearing film surfaces, evidence suggests that Fe(II) is susceptible to facile oxidation, and that an associated lower Fe/Ti ratio in this region is consistent with surface compositional incompleteness or alteration to a titanomaghemite-like composition and structure. The surface of these films nonetheless appear to remain highly ordered and commensurate with the underlying structure despite facile oxidation, a surface condition that is found to be reversible to some extent by heating in low oxygen environments.

  8. Crystallization Stages of the Bishop Tuff Magma Body Recorded in Crystal Textures in Pumice Clasts

    SciTech Connect

    Pamukcu, Ayla; Gualda, Guilherme A.R.; Anderson, Jr. , Alfred T. (Vanderbilt); (UC)

    2012-07-25

    The Bishop Tuff is a giant silicic ignimbrite erupted at 0.76 Ma in eastern California, USA. Five pumice clasts from the late-erupted Bishop Tuff (Aeolian Buttes) were studied in an effort to better understand the pre- and syn-eruptive history of the Bishop magma body and place constraints on the timescales of its existence. This study complements and expands on a previous study that focused on early-erupted Bishop Tuff pumice clasts. Bulk densities of pumice clasts were measured using an immersion method, and phenocryst crystal contents were determined using a sieving and winnowing procedure. X-ray tomography was used to obtain qualitative and quantitative textural information, particularly crystal size distributions (CSDs). We have determined CSDs for crystals ranging in size from {approx}10 to {approx}1000 {micro}m for three groups of mineral phases: magnetite ({+-}ilmenite), pyroxene + biotite, quartz + feldspar. Similar to early-erupted pumice, late-erupted pumice bulk density and crystal contents are positively correlated, and comparison of crystal fraction vs size trends suggests that the proportion of large crystals is the primary control on crystallinity. Porosity is negatively correlated with crystal content, which is difficult to reconcile with closed-system crystallization. Magnetite and pyroxene + biotite size distributions are fractal in nature, often attributed to fragmentation; however, crystals are mostly whole and euhedral, such that an alternative mechanism is necessary to explain these distributions. Quartz + feldspar size distributions are kinked, with a shallow-sloped log-linear section describing large crystals (> 140 {micro}m) and a steep-sloped log-linear section describing small crystals (< 140 {micro}m). We interpret these two crystal populations as resulting from a shift in crystallization regime. We suggest that the shallow-sloped section describes a pre-eruptive quartz + feldspar growth-dominated regime, whereas the steep-sloped section represents a population that grew during a nucleation-dominated regime that began as a result of decompression at the onset of eruption. Timescales of quartz growth calculated from the slopes of these two segments of the size distributions indicate that the pre-eruptive crystal population grew on timescales on the order of millennia and may describe the timescale of crystallization of the Bishop magma body. The syn-eruptive population gives timescales of < 1-2 years (but possibly much less) and probably marks the onset of eruptive decompression.

  9. Magneto-transport study of magnetite (Fe3O4) nanoparticles between Au nanogap electrodes on surface-oxidized Si substrate

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Takata, N.; Fukutome, N.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

    2013-04-01

    We have studied the magneto-transport of magnetite (Fe3O4) nanoparticles (MNPs) between Au nanogap electrodes (ANGEs) on surface-oxidized Si substrate. The MNP sizes are approximately 40 nm and the 100 nm thick magnetite thin film (which is formed of the MNP aggregation) was prepared between and around the ANGEs by use of the RF reactive magnetron sputtering method. The distance between the ANGEs and the bridge width of the ANGEs are approximately 50 nm and 1.5 ?m, respectively. The ANGEs were produced by the tilted-angle-deposition method. The optical microscope, scanning electron microscope and atomic force microscope were used to observe the sample surface structure and morphology. To investigate the crystal structure and crystallinity of the MNPs, the X-ray diffraction measurement was performed. The electrical resistance and magneto-resistance ratio of the MNPs between the ANGEs were measured as a function of temperature. The magneto-transport mechanism is discussed on the basis of the spin dependent transport.

  10. Direct observations of field-induced assemblies in magnetite ferrofluids

    NASA Astrophysics Data System (ADS)

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ? 10 nm) is studied with an emphasis on examining the effects of particle concentration (?) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ? = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  11. Particle characteristics and reduction behavior of synthetic magnetite

    NASA Astrophysics Data System (ADS)

    Ramadan, Wegdan; Zaki, Mohamed I.; Fouad, Nasr E.; Mekhemer, Gamal A. H.

    2014-04-01

    Two samples (S1 and S2) of magnetite were synthesized, using two different methods, and characterized by means of X-ray powder diffractometry, infrared and Mössbauer spectroscopy, N2 sorptiometry and electron microscopy. Particles of sample-S1 were found to be loosely agglomerated, micro-sized spheroids (200-350 nm) composed almost solely of highly aggregated (fused) crystallites (size averaged at 35 nm) of cubic-Fe3O4. In contrast, particles of sample-S2 were strongly agglomerated, nano-sized spheroids (25-30 nm) composed of slightly aggregated crystallites (size averaged at 11 nm) of cubic-Fe3O4 and noncrystalline domains made-up of FeO(OH) species. Temperature-programed reduction (TPR) profiles obtained for the two samples were similar in monitoring two peaks at >450 °C assignable to a two-step reduction of Fe3O4 (?FeO?Fe), but different in monitoring a peak at<450 °C only for the reduction of FeO(OH) (?Fe3O4) contained in sample-S2. However, curve fitting analysis of the TPR profiles and molecular stoichiometry calculations based on amounts of hydrogen consumed revealed that the two-step reduction of Fe3O4 is not straightforward. That is by resolving two consecutive pathways for each step and, hence, nonstoichiometric intermediate products whose composition was found to be critically controlled by the composition of the reducing gas atmosphere (5 or 80% H2/N2) and characteristics of the starting sample particles (chemical and phase composition, and, but to lesser extents, the agglomeration and average size).

  12. Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin

    NASA Astrophysics Data System (ADS)

    Channell, J. E. T.; Hodell, D. A.; Margari, V.; Skinner, L. C.; Tzedakis, P. C.; Kesler, M. S.

    2013-08-01

    Magnetic properties of late Quaternary sediments on the SW Iberian Margin are dominated by bacterial magnetite, observed by transmission electron microscopy (TEM), with contributions from detrital titanomagnetite and hematite. Reactive hematite, together with low organic matter concentrations and the lack of sulfate reduction, lead to dissimilatory iron reduction and availability of Fe(II) for abundant magnetotactic bacteria. Magnetite grain-size proxies (?ARM/? and ARM/IRM) and S-ratios (sensitive to hematite) vary on stadial/interstadial timescales, contain orbital power, and mimic planktic ?18O. The detrital/biogenic magnetite ratio and hematite concentration are greater during stadials and glacial isotopic stages, reflecting increased detrital (magnetite) input during times of lowered sea level, coinciding with atmospheric conditions favoring hematitic dust supply. Magnetic susceptibility, on the other hand, has a very different response being sensitive to coarse detrital multidomain (MD) magnetite associated with ice-rafted debris (IRD). High susceptibility and/or magnetic grain-size coarsening, mark Heinrich stadials (HS), particularly HS2, HS3, HS4, HS5, HS6 and HS7, as well as older Heinrich-like detrital layers, indicating the sensitivity of this region to fluctuations in the position of the polar front. Relative paleointensity (RPI) records have well-constrained age models based on planktic ?18O correlation to ice-core chronologies, however, they differ from reference records (e.g. PISO) particularly in the vicinity of glacial maxima, mainly due to inefficient normalization of RPI records in intervals of enhanced hematite input.

  13. Small magnetite antiretroviral therapeutic nanoparticle probes for MRI of drug biodistribution

    PubMed Central

    Guo, Dongwei; Li, Tianyuzi; McMillan, JoEllyn; Sajja, Balasrinivasa R; Puligujja, Pavan; Boska, Michael D; Gendelman, Howard E; Liu, Xin-Ming

    2013-01-01

    Aim Drug toxicities, compliance and penetrance into viral reservoirs have diminished the efficacy of long-term antiretroviral therapy (ART) for treatment of HIV infection. Cell-targeted nanoformulated ART was developed to improve disease outcomes. However, rapid noninvasive determination of drug biodistribution is unrealized. To this end, small magnetite ART (SMART) nanoparticles can provide assessments of ART biodistribution by MRI. Materials & methods Poly(lactic-co-glycolic acid), 1,2-distearoyl-sn-glycero-3-phosphocholine- and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-(methoxy-PEG 2000)-encased particles were synthesized with atazanavir (ATV) and magnetite. Uptake and retention of ATV and magnetite administered at 3:1 ratios (weight/weight) were determined in human monocyte-derived macrophages and mice. Results SMART particles were taken up and retained in macrophages. In mice, following parenteral SMART injection, magnetite and drug biodistribution paralleled one another with MRI signal intensity greatest in the liver and spleen at 24 h. Significantly, ATV and magnetite levels correlated. Conclusion SMART can permit rapid assessment of drug tissue concentrations in viral reservoirs. PMID:23905578

  14. Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens

    SciTech Connect

    Byrne, J. M.; Telling, N. D.; Coker, V. S.; Pattrick, R. A. D.; Laan, G. van der; Arenholz, E.; Tuna, F.; Lloyd, J. R.

    2011-08-02

    The bioproduction of nano-scale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens, by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50 nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles has been investigated by X-ray magnetic circular dichroism and indicates the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimised biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently in the less harmful trivalent form.

  15. Control of nanoparticle size, reactivity and magnetic properties during the bioproduction of magnetite by Geobacter sulfurreducens.

    PubMed

    Byrne, J M; Telling, N D; Coker, V S; Pattrick, R A D; van der Laan, G; Arenholz, E; Tuna, F; Lloyd, J R

    2011-11-11

    The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50 nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form. PMID:22020365

  16. Facile one-step fabrication of magnetite particles under mild hydrothermal conditions

    NASA Astrophysics Data System (ADS)

    Keerthana, D. Shanthini; Namratha, K.; Byrappa, K.; Yathirajan, H. S.

    2015-03-01

    Hydrophilic magnetite particles for biological applications were synthesized by hydrothermal method in the presence of D-Glucose as both reducing and capping agent in a facile, one-step, low energy and environmentally friendly route. The role of D-Glucose as a reducing agent in the formation of magnetite particles under mild hydrothermal conditions has been investigated. The absence of D-Glucose results in the formation of hematite. The magnetite particles synthesized were characterized using powder X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, High Resolution Scanning Electron Microscopy (HR-SEM), Dynamic Light Scattering (DLS) and Vibrating Sample Magnetometery (VSM). The influence of the quantity of D-Glucose used and the reaction duration on the formation of magnetite were studied. DLS and HR-SEM results show that the size of the particles was in nano- to micron range. The antioxidant potency of the particles was confirmed using DPPH assay, where 2,2- Diphenyl-1-picrylhydrazyl was used as a source of free radicals. Hence the magnetite particles obtained could be considered for the use in various biological applications.

  17. Universality in Pure Gravity Mediation

    E-print Network

    Jason L. Evans; Masahiro Ibe; Keith A. Olive; Tsutomu T. Yanagida

    2014-05-30

    If low energy supersymmetry is realized in nature, the apparent discovery of a Higgs boson with mass around 125 GeV points to a supersymmetric mass spectrum in the TeV or multi-TeV range. Multi-TeV scalar masses are a necessary component of supersymmetric models with pure gravity mediation or in any model with strong moduli stabilization. Here, we show that full scalar mass universality remains viable as long as the ratio of Higgs vevs, tan beta is relatively small (\\lesssim 2.5). We discuss in detail the low energy (observable) consequences of these models.

  18. Synthesis of Enantiomerically Pure Anthracyclinones

    NASA Astrophysics Data System (ADS)

    Achmatowicz, Osman; Szechner, Barbara

    The anthracycline antibiotics are among the most important clinical drugs used in the treatment of human cancer. The search for new agents with improved therapeutic efficacy and reduced cardiotoxicity stimulated considerable efforts in the synthesis of new analogues. Since the biological activity of anthracyclines depends on their natural absolute configuration, various strategies for the synthesis of enantiomerically pure anthracyclinones (aglycones) have been developed. They comprise: resolution of racemic intermediate, incorporation of a chiral fragment derived from natural and non-natural chiral pools, asymmetric synthesis with the use of a chiral auxiliary or a chiral reagent, and enantioselective catalysis. Synthetic advances towards enantiopure anthracyclinones reported over the last 17 years are reviewed.

  19. Synthesis of magnetite-porphyrin nanocomposite and its application as a novel magnetic adsorbent for removing heavy cations

    SciTech Connect

    Bakhshayesh, Sara, E-mail: s_bakhshayesh@yahoo.com; Dehghani, Hossein, E-mail: dehghani@kashanu.ac.ir

    2013-07-15

    Graphical abstract: Magnetite-porphyrin nanocomposite (MPNC) as a novel magnetic adsorbent for removing heavy cations was synthesized. - Highlights: • Nanosized Fe{sub 3}O{sub 4} was prepared by hydrothermal reaction of iron salt in alkaline media. • The synthesized magnetite and nanocomposite had soft ferromagnetic property. • Magnetic nanocomposite as a novel magnetic adsorbent for heavy cations was prepared. • Satisfactory separation from solutions in the order of Pb{sup 2+} > Cd{sup 2+} > Hg{sup 2+} was obtained. - Abstract: Magnetite-porphyrin nanocomposite (MPNC) was synthesized as a novel magnetic adsorbent for removing heavy cations. Firstly, we prepared nano-sized magnetite using a simple hydrothermal route. The synthesis of nanoscaled magnetite was carried out through reaction between iron source and various amines. In this paper, we studied effective parameters in controlling shape and size of nanoscaled magnetite. These parameters were presence of alkaline, reaction time, kind of amine and iron salt. Morphology, particle size and magnetic properties of the nanoscaled magnetite were obtained by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Fourier transform infrared (FT-IR), diffuse reflectance spectra (DRS) and vibrating sample magnetometer (VSM). Our study showed that the synthesized magnetite from reaction between FeSO{sub 4} and hydrazinum hydrate has spherical shape. The synthesized magnetite was a nanosized compound and used for preparation of magnetite-porphyrin nanocomposite. The synthesized magnetite-porphyrin hybrid material had magnetic property and was used as magnetic adsorbent for removing heavy cations of water. Satisfactory separation from solutions in the order of Pb{sup 2+} > Cd{sup 2+} > Hg{sup 2+} was obtained.

  20. Fayalite Oxidation Processes: Experimental Evidence for the Stability of Pure Ferric Fayalite?

    NASA Technical Reports Server (NTRS)

    Martin, A. M.; Righter, K.; Keller, L. P.; Medard, E.; Devouard, B.; Rahman, Z.

    2011-01-01

    Olivine is one of the most important minerals in Earth and planetary sciences. Fayalite Fe2(2+)SiO4, the ferrous end-member of olivine, is present in some terrestrial rocks and primitive meteorites (CV3 chondrites). A ferric fayalite (or ferri-fayalite), Fe(2+) Fe2(3+)(SiO4)2 laihunite, has been reported in Earth samples (magnetite ore, metamorphic and volcanic rocks...) and in Martian meteorites (nakhlites). Laihunite was also synthesized at 1 atmosphere between 400 and 700 C. We show evidence for the stability of a pure ferrifayalite end-member and for potential minerals with XFe(3+) between 2/3 and 1.

  1. Reflective and magnetic properties of photonic polymer composite materials based on porous silicon and magnetite nanoparticles.

    PubMed

    Kim, Jihoon; Koh, Youngdae; Jang, Seunghyun; Jung, Kyoungsun; Woo, Hee-Gweon; Kim, Sungsoo; Sohn, Honglae

    2010-05-01

    Photonic polymer composite materials exhibiting both reflective and magnetic properties were prepared by the replication of rugate porous silicon (PS) using polystyrene and magnetite nanoparticle (Fe3O4). Rugate PS prepared by applying a computer-generated pseudo-sinusoidal current waveform resulted in a mirror with high reflectivity in a specific narrow spectral region and served as a template for replicating its nanostructure with polystyrene containing the magnetic nanoparticles of magnetite. The composite films replicated a sharp photonic resonance with full-width at half maximum (FWHM) of 20 nm from rugate PS in the reflectivity spectrum as well as displayed a magnetic property of magnetite nanoparticles in SQUID magnetometry. Optical characteristics of composite films indicated that the surface of polymer film had a negative structure of rugate PS. The composite films were stable in aqueous solutions for several days without any degradation. PMID:20358975

  2. Reordering between tetrahedral and octahedral sites in ultrathin magnetite films grown on MgO(001)

    NASA Astrophysics Data System (ADS)

    Bertram, F.; Deiter, C.; Schemme, T.; Jentsch, S.; Wollschläger, J.

    2013-05-01

    Magnetite ultrathin films were grown using different deposition rates and substrate temperatures. The structure of these films was studied using (grazing incidence) x-ray diffraction, while their surface structure was characterized by low energy electron diffraction. In addition to that, we performed x-ray photoelectron spectroscopy and magneto optic Kerr effect measurements to probe the stoichiometry of the films as well as their magnetic properties. The diffraction peaks of the inverse spinel structure, which originate exclusively from Fe ions on tetrahedral sites are strongly affected by the preparation conditions, while the octahedral sites remain almost unchanged. With both decreasing deposition rate as well as decreasing substrate temperature, the integrated intensity of the diffraction peaks originating exclusively from Fe on tetrahedral sites is decreasing. We propose that the ions usually occupying tetrahedral sites in magnetite are relocated to octahedral vacancies. Ferrimagnetic behaviour is only observed for well ordered magnetite films.

  3. Surface modification of magnetite nanoparticles using lactobionic acid and their interaction with hepatocytes.

    PubMed

    Kamruzzaman Selim, K M; Ha, Yong-Soo; Kim, Sun-Jung; Chang, Yongmin; Kim, Tae-Jeong; Ho Lee, Gang; Kang, Inn-Kyu

    2007-02-01

    In the current study, superparamagnetic magnetite nanoparticles were surface-modified with lactobionic acid (LA) to improve their intracellular uptake and ability to target hepatocytes. Maltotrionic acid (MA)-modified nanoparticles were also synthesized as a control. Cell culture experiment showed that LA-modified nanoparticles were internalized into hepatocytes and atomic absorption spectrometer (AAS) measurement indicated that the uptake amount of LA-modified magnetite into hepatocytes was higher than that of unmodified and MA-modified nanoparticles. LA-modified nanoparticle solution was injected in rabbit and the magnetic resonance (MR) images obtained showed that LA-coated nanoparticles were selectively accumulated onto the hepatocytes. This result demonstrates that the LA-modified magnetite nanoparticles have a great potential to be used as contrast agent for liver diagnosis. PMID:17049979

  4. Curious Crystals

    NSDL National Science Digital Library

    James H. Kessler

    2007-01-01

    Learners carefully look at four known household crystals. After observing and describing the crystals, learners are given an unknown crystal, which is chemically the same as one of the four known crystals but looks different. When learners realize that they cannot identify this crystal by its appearance alone, they will suggest other tests and ways to compare the crystals to eventually identify the unknown crystal. The related activities are examples of tests learners can conduct on the crystals. After a series of these tests, learners will gather enough evidence to identify the unknown crystal.

  5. 2, 303331, 2005 Pure stands of

    E-print Network

    Paris-Sud XI, Université de

    BGD 2, 303­331, 2005 Pure stands of temperate forest tree species N. Br¨uggemann et al. Title Page Discussions is the access reviewed discussion forum of Biogeosciences Pure stands of temperate forest tree Pure stands of temperate forest tree species N. Br¨uggemann et al. Title Page Abstract Introduction

  6. Doped TGS crystals for IR detection and sensors

    Microsoft Academic Search

    H. V. Alexandru; C. Berbecaru; F. Stanculescu; L. Pintilie; I Matei; M Lisca

    2004-01-01

    Triglycine sulfate crystals (TGS) doped with l- and d-alanine, respectively, where grown in paraelectric phase at 52°C. They show stable parameters versus pure TGS crystals, lower permittivities and losses, i.e. higher pyroelectric figure of merit. l- and d-alanine-doped crystals show a mirror asymmetry of the growth habit along the ferroelectric axis. Hysteresis loop of pure and doped samples were automatically

  7. Arsenate and Arsenite Sorption on Magnetite: Relations to Groundwater Arsenic Treatment Using Zerovalent Iron and Natural Attenuation

    EPA Science Inventory

    Magnetite (Fe3O4) is a zerovalent iron corrosion product; it is also formed in natural soil and sediment. Sorption of arsenate (As(V)) and arsenite (As(III)) on magnetite is an important process of arsenic removal from groundwater using zerovalent iron-based permeable reactive ba...

  8. ccsd-00105476,version1-11Oct2006 Finite size effects in the Verwey transition of magnetite thin films

    E-print Network

    Paris-Sud XI, Université de

    size effects in the Verwey transition of stress-free magnetite (Fe3O4 ) thin films. A limit thicknessccsd-00105476,version1-11Oct2006 Finite size effects in the Verwey transition of magnetite thin films A.M. Bataille,1, E. Vincent,2 S. Gota,1, and M. Gautier-Soyer1 1 DRECAM/SPCSI, CEA Saclay, 91191

  9. I-XE ANALYSES OF TAGISH LAKE MAGNETITE AND MONAHANS HALITE. A. Busfield1 , J. D. Gil-

    E-print Network

    Grossman, Lawrence

    I-XE ANALYSES OF TAGISH LAKE MAGNETITE AND MONAHANS HALITE. A. Busfield1 , J. D. Gil- mour1 , J. A-Xe dating system is particu- larly applicable to aqueously-formed minerals, notable examples include halite analysis of a magnetite-rich separate from the carbonaceous chondrite Tagish Lake and of a halite grain

  10. In situ monitoring of lepidocrocite bio-reduction and magnetite formation by reflexion1 Mssbauer spectroscopy2

    E-print Network

    Boyer, Edmond

    1 In situ monitoring of lepidocrocite bio-reduction and magnetite formation by reflexion1 Mössbauer II) was used to monitor in situ the12 mineralogical transformation of lepidocrocite (-Fe used in this study could be21 replicated in field experiments when assessing the formation of magnetite

  11. Ferrous Hydroxy Carbonate is a Stable Transformation Product of Biogenic Magnetite

    SciTech Connect

    Kukkadapu, Ravi K.; Zachara, John M.; Fredrickson, Jim K.; Kennedy, David W.; Dohnalkova, Alice; McCready, David E.

    2005-02-02

    A ~1:1 mixture of ferrihydrite and nanocrystalline akaganeite (?-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 PO?³? 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 Mössbauer spectroscopy. The biogenic reduction of Fe(III) was rapid; with 60% of the total Fe (Fe???) reduced in one day. Only an additional 10% of Fe??? was reduced over the next three years. A fine-grained (10 nm), cation-excess (CE) magnetite with a Fe(II)/Fe??? 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?], a rosasite-type mineral, with time. Ferrous hydroxy carbonate dominated the mineral composition of the three year incubated sample. The Fe(II)/Fe??? 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 our 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 Fe(II)-excess magnetite. The FHC may be an overlooked mineral phase that explains the infrequent occurrence of fine-grained, biogenic magnetite in anoxic sediments.

  12. The oxygen sensor MgFnr controls magnetite biomineralization by regulation of denitrification in Magnetospirillum gryphiswaldense

    PubMed Central

    2014-01-01

    Background Magnetotactic bacteria are capable of synthesizing magnetosomes only under oxygen-limited conditions. However, the mechanism of the aerobic repression on magnetite biomineralization has remained unknown. In Escherichia coli and other bacteria, Fnr (fumarate and nitrate reduction regulator) proteins are known to be involved in controlling the switch between microaerobic and aerobic metabolism. Here, we report on an Fnr-like protein (MgFnr) and its role in growth metabolism and magnetite biomineralization in the alphaproteobacterium Magnetospirillum gryphiswaldense. Results Deletion of Mgfnr not only resulted in decreased N2 production due to reduced N2O reductase activity, but also impaired magnetite biomineralization under microaerobic conditions in the presence of nitrate. Overexpression of MgFnr in the WT also caused the synthesis of smaller magnetite particles under anaerobic and microaerobic conditions in the presence of nitrate. These data suggest that proper expression of MgFnr is required for WT-like magnetosome synthesis, which is regulated by oxygen. Analyses of transcriptional gusA reporter fusions revealed that besides showing similar properties to Fnr proteins reported in other bacteria, MgFnr is involved in the repression of the expression of denitrification genes nor and nosZ under aerobic conditions, possibly owing to several unique amino acid residues specific to MTB-Fnr. Conclusions We have identified and thoroughly characterized the first regulatory protein mediating denitrification growth and magnetite biomineralization in response to different oxygen conditions in a magnetotactic bacterium. Our findings reveal that the global oxygen regulator MgFnr is a genuine O2 sensor. It is involved in controlling expression of denitrification genes and thereby plays an indirect role in maintaining proper redox conditions required for magnetite biomineralization. PMID:24915802

  13. Four decades of paleomagnetic studies of magnetite in carbonate rocks: a history of remagnetizations

    NASA Astrophysics Data System (ADS)

    Van Der Voo, R.

    2011-12-01

    With the advent of cryogenic magnetometers in the early 1970's, paleomagnetic studies of carbonate rocks became possible and it was quickly established that magnetite generally was the carrier of an ancient remanence in non-red limestones. For about a decade, this magnetite was thought to be detrital, implying that the magnetizations were primary, i.e., dating back to the time of deposition of the strata. Gray Devonian limestones from Ohio, Arizona's Grand Canyon, Arkansas, and New York revealed directions similar to those of Permian rocks in North America, resulting in APWP loops and erroneous large-scale tectonic conclusions about an "Acadia" displaced terrane and Europe-Laurentia reconstructions. However, when syn-folding magnetizations became documented, the prevailing interpretations quickly changed. Remagnetizations became the rule rather than the exception. The carrier was no longer thought to be detrital, and abundant magnetite in the form of spherules and framboids imaged in scanning electron microscopy (SEM) seemed to be the answer to the quest for a growth mechanism of this mineral. In some cases, magnetite could be seen as oxidation rims to Fe-sulfide cores. Also, at about this time, hysteresis parameters of remagnetized carbonates, plotted in Day diagrams, revealed unique patterns, which did not match the parameters measured on individual spherules. Growth of the magnetite from a superparamagnetic size to single- and pseudo-single-domain size is currently the favored mode of occurrence of the magnetite, and some SEM images support this. Important unresolved questions remain, however. Notably, it remains puzzling why the remagnetizations most often appear to have been acquired at the time the nearest orogeny occurred, and what role fluids played in this process.

  14. The play of light in crystals

    Microsoft Academic Search

    Boris Petrovitch Zakharchenya

    2008-01-01

    And God said: ‘Let there be light’, and there was light. Genesis 1 3 When trapped in a crystal, light interacts with electrons, phonons (crystal lattice vibrations) and defects, generating many effects which are important not only for pure physics, by broadening our comprehension of nature, but also for practical applications. These include: photo-galvanic effects; discrete light scattering on lattice

  15. Single crystal growth of actinide compounds

    Microsoft Academic Search

    J. C. Spirlet; W. Müller; J. van Audenhove

    1985-01-01

    During recent years, the importance of solid state actinide research has been increasingly recognized. Further progress in actinide solid state physics depends on the availability of pure and perfect single crystals. Actinide compounds have large magnetic anisotropy with anisotropy fields of 8 × 107 A.m-1 or higher. Investigation of the mechanism responsible for such unique behaviour requires large single crystals

  16. Physics of water: Crystal-clear transition

    NASA Astrophysics Data System (ADS)

    Starr, Francis W.

    2014-09-01

    Liquid-liquid phase separation is counted among the peculiar phenomena attributed to pure water, but rapid crystallization has rendered its existence hard to prove. Evidence of a 'naked' liquid-liquid transition in a system unencumbered by crystallization encourages us to keep searching.

  17. Magnetic and Mössbauer studies of fucan-coated magnetite nanoparticles for application on antitumoral activity

    NASA Astrophysics Data System (ADS)

    Silva, V. A. J.; Andrade, P. L.; Bustamante, Angel; de los Santos Valladares, L.; Mejia, M.; Souza, I. A.; Cavalcanti, K. P. S.; Silva, M. P. C.; Aguiar, J. Albino

    2014-01-01

    Fucan-coated magnetite (Fe3O4) nanoparticles were synthesized by the co-precipitation method and studied by Mössbauer spectroscopy and magnetic measurements. The sizes of the nanoparticles were 8-9 nm. Magnetization measurements and Mössbauer spectroscopy at 300 K revealed superparamagnetic behavior. The magnetic moment of the Fe3O4 is partly screened by the Fucan coating aggregation. When the magnetite nanoparticles are capped with oleic acid or fucan, reduced particle-particle interaction is observed by Mössbauer and TEM studies. The antitumoral activity of the fucan-coated nanoparticles were tested in Sarcoma 180, showing an effective reduction of the tumor size.

  18. Geochronology and stable isotope signature of alteration related to hydrothermal magnetite ores in Central Anatolia, Turkey

    Microsoft Academic Search

    Robert Marschik; Richard Spikings; Ilkay Kuscu

    2008-01-01

    Hydrothermal iron ores at Divri?i, east Central Anatolia, are contained in two orebodies, the magnetite-rich A-kafa and the\\u000a limonitic B-kafa (resources of 133.8 Mt with 56% Fe and 0.5% Cu). The magnetite ores are hosted in serpentinites of the Divri?i\\u000a ophiolite at the contact with plutons of the Murmano complex. Hydrothermal biotite from the Divri?i A-kafa yield identical\\u000a weighted mean plateau

  19. Novel protocol for the solid-state synthesis of magnetite for medical practices

    NASA Astrophysics Data System (ADS)

    Paiva, D. L.; Andrade, A. L.; Pereira, M. C.; Fabris, J. D.; Domingues, R. Z.; Alvarenga, M. E.

    2015-01-01

    It is reported a novel approach to prepare nanoparticles of magnetite (Fe3O4) by heating a mixture of synthetic commercial maghemite (?Fe2O3) with sucrose. This solid-state reaction leads to the chemical reduction of part of the Fe3+ of the precursor oxide to render Fe2+ and Fe3+ in octahedral and Fe3+ in tetrahedral sites of the Fe-O coordination framework. Powder X-ray diffraction patterns, FTIR and 298 K Mössbauer spectra confirm the conversion of maghemite into magnetite. Based on these results, the optimal sucrose:maghemite rate was found to be 4.

  20. Magnetite (Fe3O4): a new variant of relaxor multiferroic?

    NASA Astrophysics Data System (ADS)

    Ziese, M.; Esquinazi, P. D.; Pantel, D.; Alexe, M.; Nemes, N. M.; Garcia-Hernández, M.

    2012-02-01

    The electric polarization, dielectric permittivity, magnetoelectric effect, heat capacity, magnetization and ac susceptibility of magnetite films and polycrystals were investigated. The electric polarization of magnetite films with saturation values between 4 and 8 µC cm-2 was found to vanish between 32 and 38 K, but in polycrystals no phase transition was detected in this range by heat capacity. Both types of samples showed magnetoelectric effects at low temperatures below a frequency-dependent crossover. This is interpreted as arising from multiferroic relaxor behavior.

  1. Thin magnetite films on an oxidized silicon surface: Raman spectroscopy study

    NASA Astrophysics Data System (ADS)

    Vikulov, V. A.; Balashev, V. V.; Pisarenko, T. A.; Dimitriev, A. A.; Korobtsov, V. V.

    2012-08-01

    Polycrystalline films of magnetite (Fe3O4) formed by the reactive sputtering of iron in oxygen on Si(001) substrates covered by thin (1.4 nm) or thick (1200 nm) SiO2 layers have been studied by Raman spectroscopy. It is established that (i) the ?-Fe2O3 phase is formed due to the laser-induced heating in magnetite films synthesized on thick SiO2 layers and (ii) the formation of ?-Fe2O3 phase depends on the thickness of the buffer SiO2 layer.

  2. Magnetite (Fe3O4): a new variant of relaxor multiferroic?

    PubMed

    Ziese, M; Esquinazi, P D; Pantel, D; Alexe, M; Nemes, N M; Garcia-Hernández, M

    2012-02-29

    The electric polarization, dielectric permittivity, magnetoelectric effect, heat capacity, magnetization and ac susceptibility of magnetite films and polycrystals were investigated. The electric polarization of magnetite films with saturation values between 4 and 8 ?C cm(-2) was found to vanish between 32 and 38 K, but in polycrystals no phase transition was detected in this range by heat capacity. Both types of samples showed magnetoelectric effects at low temperatures below a frequency-dependent crossover. This is interpreted as arising from multiferroic relaxor behavior. PMID:22314835

  3. High-temperature susceptibility of magnetite: a new pseudo-single-domain effect

    NASA Astrophysics Data System (ADS)

    Dunlop, David J.

    2014-11-01

    Remanent magnetizations of magnetites between single-domain (SD) threshold size (?0.1 ?m) and ?20 ?m have SD-like intensities and coercivities. This paper shows for the first time that magnetite's induced magnetization also has pseudo-single-domain behaviour. The first part of the paper reports temperature-dependent initial susceptibility data, k0(T), of sized magnetites and assesses their granulometric potential. The second part transforms coercive force data, Hc(T), for the same magnetites into simulated k0(T) curves. The third part considers k0(T) results of coarse-grained mafic rocks as candidate sources of deep-seated magnetic anomalies. High-temperature susceptibility k0 measured with a Kappabridge for eight fractions of crushed natural magnetites (median sizes of 0.6, 1, 3, 6, 9, 14, 110 and 135 ?m) shows a progressive increase in the height of the Hopkinson peak below the Curie point as grain size decreases. The trend is systematic and has granulometric potential in the 1-14 ?m range. Self-demagnetization should produce almost flat k0(T) in grains larger than SD size but experimentally, well-defined Hopkinson peaks are not limited to the finest grains. 1-?m magnetites have a peak 1.5 times k0 at 20 °C and 14-?m grains have a peak of 1.25. Only 110 and 135 ?m grains have T-independent k0. Using an empirical relationship between coercive force Hc and k0, Hc(T) data for the sized magnetites were used to simulate k0(T) results. A hump in the k0 heating curve around 250 °C was traced to annealing out internal strains, evident in Hc data measured in first heatings. For sizes ?6 ?m, observed Hopkinson peaks were smaller than predicted, possibly because of a previously unrecognized grain-size dependence of the empirical constant relating Hc and k0. Two crystalline rocks, a gabbro and a diabase, combine SD-like Hopkinson peaks and multidomain (MD) flat ramps in their k0(T) data. In the diabase, a Hopkinson peak is prominent in separated plagioclase grains containing submicron magnetite, but is masked in whole-rock data. The gabbro has a clear superposition of SD and MD k0(T) functions in its whole-rock data, with a Hopkinson peak of 1.35. If oceanic layer-3 gabbros have similar susceptibility enhancement above 500 °C, they could be more important magnetic anomaly sources than room-temperature k0 measurements on dredged or fault-uplifted samples would suggest.

  4. How Much Magnetite Have Magnetic Bacteria Made? A Multiple Case Study of Swedish Varved Lake Sediments

    NASA Astrophysics Data System (ADS)

    Snowball, I.; Zillen, L.; Sandgren, P.

    2005-12-01

    Annually laminated (varved) lakes sediments are relatively common in Sweden because the distinct seasonality of climate induces winter ice cover and long periods of anoxia in the deeper parts of lake basins. The preserved annual cycle of sediment accumulation is characterized by a mineral rich layer, which is deposited during the spring snow melt, and an organic rich layer, which accumulates during the summer and winter. Mineral magnetic studies of several varved lake sediment sequences point to a common characteristic - high concentrations of a stable single domain magnetic mineral in the organic rich layers. In fact, in bulk sampled there is often a linear relationship between the amount of organic carbon and mass specific magnetic parameters that indicate the concentrations of ferrimagnetic minerals. The magnetic properties of catchment soils and sub-soils are quite different from the organic rich sediments and point to the production of magnetite in the lake. This magnetite is the carrier of an extremely stable natural remanent magnetization, which we have used to reconstruct the direction and intensity of the Earth's geomagnetic field over the past 9000 years, and it's concentrations in the sediment sequences also appear to be related to known climate changes during the Holocene. At this point of our studies, however, only one definite conclusion can be made: that the fine grained magnetite is produced within the lake, before or after sediment deposition. Where do we go from here? What methods can we use to test our hypothesis that magnetotactic bacteria are indeed responsible for the production of the single-domain magnetite? And how much secondary magnetite does a single lake contain? These are questions posed by this study. We attempt to answer the last one through using magnetic techniques and the known properties of magnetite. For the central parts of the lake basins we derive a conservative estimate in the range between 16 and 18 mg magnetite per square meter per year for the last 9000 years. This estimate implies that a cylinder of sediment with a radius of 50 m and thickness of 4-5 meters would contain approximately 1300 kg of secondary single domain magnetite.

  5. Fabrication of magnetite-based core-shell coated nanoparticles with antibacterial properties.

    PubMed

    Grumezescu, A M; Cristescu, R; Chifiriuc, M C; Dorcioman, G; Socol, G; Mihailescu, I N; Mihaiescu, D E; Ficai, A; Vasile, O R; Enculescu, M; Chrisey, D B

    2015-01-01

    We report the fabrication of biofunctionalized magnetite core/sodium lauryl sulfate shell/antibiotic adsorption-shell nanoparticles assembled thin coatings by matrix assisted pulsed laser evaporation for antibacterial drug-targeted delivery. Magnetite nanoparticles have been synthesized and subsequently characterized by transmission electron microscopy and x-ray diffraction. The obtained thin coatings have been investigated by FTIR and scanning electron microscope, and tested by in vitro biological assays, for their influence on in vitro bacterial biofilm development and cytotoxicity on human epidermoid carcinoma (HEp2) cells. PMID:25797361

  6. Thiol-functionalized magnetite/graphene oxide hybrid as a reusable adsorbent for Hg2+ removal

    PubMed Central

    2013-01-01

    A thiol-functionalized magnetite/graphene oxide (MGO) hybrid as an adsorbent of Hg2+ was successfully synthesized by a two-step reaction. It exhibited a higher adsorption capacity compared to the bare graphene oxide and MGO due to the combined adsorption of thiol groups and magnetite nanocrystals. Its capacity reached 289.9 mg g-1 in a solution with an initial Hg2+ concentration of 100 mg l-1. After being exchanged with H+, the adsorbent could be reused. The adsorption of Hg2+ by the thiol-functionalized MGO fits well with the Freundlich isotherm model and followed pseudo-second-order kinetics. PMID:24252617

  7. Quenched magnetite in cretaceous-tertiary boundary microtekite-like spheroid

    NASA Technical Reports Server (NTRS)

    Smit, J.; Kyte, F. T.; Wasson, J. T.

    1984-01-01

    The magnetite containing spheres collected from a kt boundary localities in Italy were analyzed. It was found that these spheres contain relatively high concentrations of Ir. The spheres were analyzed for siderophile elements Ir, Pt, Au, Pd, Os, and Re. Elements Ir, Pt, Pd, and Au were found in high concentrations in magnetic spheres and their concentrations are similar to those in most meteorites. It is suggested that the magnetite spheres do not contain a meteorite component which may be a relic of the kt event.

  8. Evidence for a ubiquitous, sub-microscopic 'magnetite-like' constituent in the lunar soils

    NASA Technical Reports Server (NTRS)

    Griscom, D. L.; Friebele, E. J.; Marquardt, C. L.

    1973-01-01

    Electron spin resonance (ESR) has been employed in a study of the ferromagnetic constituents of a wide variety of soils from six sampled regions of the moon as well as glasses made to simulate lunar compositions. A significant result has been that magnetite-like phases (magnetic iron spinel) precipitated in and on simulated lunar glasses as a result of sub-solidus oxidation yield room-temperature ESR spectra virtually identical with the line shape predicted for spherical, single domain particles of metallic Fe. It is shown that such magnetite-like phases can nevertheless be distinguished from metallic iron on the basis of the temperature dependence of the ESR intensity.

  9. Pure gauge QCD and holography

    NASA Astrophysics Data System (ADS)

    Trinchero, R. C.

    2014-09-01

    Holographic models for the pure gauge quantum chromodynamics (QCD) vacuum are explored. The holographic renormalization of these models is considered as required by a phenomenological approach that takes the ?-functions of the models as the only input. This approach is done taking the dilaton as the coordinate orthogonal to the border. This choice greatly simplifies the analysis and gives a geometrical interpretation for the fixed points of the renormalization group flow. Examples are constructed that present asymptotic freedom, confinement of static quarks, either with vanishing or nonvanishing gluon condensate G2. The latter models require an extension of the dilaton-gravity models already considered in the literature. This extension is also determined by the only input, i.e. the ?-function. In addition, the restrictions imposed by the trace anomaly equation (TAE) are studied. In doing so, a holographic derivation of this equation is presented.

  10. Magnetotactic bacteria form magnetite from a phosphate-rich ferric hydroxide via nanometric ferric (oxyhydr)oxide intermediates.

    PubMed

    Baumgartner, Jens; Morin, Guillaume; Menguy, Nicolas; Perez Gonzalez, Teresa; Widdrat, Marc; Cosmidis, Julie; Faivre, Damien

    2013-09-10

    The iron oxide mineral magnetite (Fe3O4) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms. PMID:23980143

  11. Magnetotactic bacteria form magnetite from a phosphate-rich ferric hydroxide via nanometric ferric (oxyhydr)oxide intermediates

    PubMed Central

    Baumgartner, Jens; Morin, Guillaume; Menguy, Nicolas; Perez Gonzalez, Teresa; Widdrat, Marc; Cosmidis, Julie; Faivre, Damien

    2013-01-01

    The iron oxide mineral magnetite (Fe3O4) is produced by various organisms to exploit magnetic and mechanical properties. Magnetotactic bacteria have become one of the best model organisms for studying magnetite biomineralization, as their genomes are sequenced and tools are available for their genetic manipulation. However, the chemical route by which magnetite is formed intracellularly within the so-called magnetosomes has remained a matter of debate. Here we used X-ray absorption spectroscopy at cryogenic temperatures and transmission electron microscopic imaging techniques to chemically characterize and spatially resolve the mechanism of biomineralization in those microorganisms. We show that magnetite forms through phase transformation from a highly disordered phosphate-rich ferric hydroxide phase, consistent with prokaryotic ferritins, via transient nanometric ferric (oxyhydr)oxide intermediates within the magnetosome organelle. This pathway remarkably resembles recent results on synthetic magnetite formation and bears a high similarity to suggested mineralization mechanisms in higher organisms. PMID:23980143

  12. Preparation of biocompatible magnetite-carboxymethyl cellulose nanocomposite: Characterization of nanocomposite by FTIR, XRD, FESEM and TEM

    NASA Astrophysics Data System (ADS)

    Habibi, Neda

    2014-10-01

    The preparation and characterization of magnetite-carboxymethyl cellulose nano-composite (M-CMC) material is described. Magnetite nano-particles were synthesized by a modified co-precipitation method using ferrous chloride tetrahydrate and ferric chloride hexahydrate in ammonium hydroxide solution. The M-CMC nano-composite particles were synthesized by embedding the magnetite nanoparticles inside carboxymethyl cellulose (CMC) using a freshly prepared mixture of Fe3O4 with CMC precursor. Morphology, particle size, and structural properties of magnetite-carboxymethyl cellulose nano-composite was accomplished using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) and field emission scanning electron microscopy (FESEM) analysis. As a result, magnetite nano-particles with an average size of 35 nm were obtained. The biocompatible Fe3O4-carboxymethyl cellulose nano-composite particles obtained from the natural CMC polymers have a potential range of application in biomedical field.

  13. Preparation of biocompatible magnetite-carboxymethyl cellulose nanocomposite: characterization of nanocomposite by FTIR, XRD, FESEM and TEM.

    PubMed

    Habibi, Neda

    2014-10-15

    The preparation and characterization of magnetite-carboxymethyl cellulose nano-composite (M-CMC) material is described. Magnetite nano-particles were synthesized by a modified co-precipitation method using ferrous chloride tetrahydrate and ferric chloride hexahydrate in ammonium hydroxide solution. The M-CMC nano-composite particles were synthesized by embedding the magnetite nanoparticles inside carboxymethyl cellulose (CMC) using a freshly prepared mixture of Fe3O4 with CMC precursor. Morphology, particle size, and structural properties of magnetite-carboxymethyl cellulose nano-composite was accomplished using X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR) and field emission scanning electron microscopy (FESEM) analysis. As a result, magnetite nano-particles with an average size of 35nm were obtained. The biocompatible Fe3O4-carboxymethyl cellulose nano-composite particles obtained from the natural CMC polymers have a potential range of application in biomedical field. PMID:24820322

  14. Crystal Creations.

    ERIC Educational Resources Information Center

    Whipple, Nona; Whitmore, Sherry

    1989-01-01

    Presents a many-faceted learning approach to the study of crystals. Provides instructions for performing activities including crystal growth and patterns, creating miniature simulations of crystal-containing rock formations, charcoal and sponge gardens, and snowflakes. (RT)

  15. Highly water-soluble nanocrystal powders of magnetite and maghemite coated with gluconic acid: Preparation, structure characterization, and surface coordination.

    PubMed

    Wei, Xiucheng; Wei, Zhiwei; Zhang, Liping; Liu, Yingqi; He, Deyan

    2011-02-01

    A simple method was developed to prepare highly water-soluble nanocrystal powders of magnetic iron oxides with different oxidation degree from magnetite (Fe(3)O(4)) to maghemite (?-Fe(2)O(3)) coated with gluconic acid (GLA). X-ray diffraction and transmission electron microscopy measurements show that the products have a narrow size distribution, and the cores are inverse spinel iron oxides and completely crystallized. Vibrating sample magnetometry measurements reveal that all the samples exhibit superparamagnetic behavior at room temperature. Fourier transform infrared (FTIR) and Raman spectra were used to identify the products. It is shown that GLA molecules are immobilized on the nanoparticle surface by chemical bonding and the carboxyl is asymmetrically bound to the surface iron atom, and the vacancies in the ?-Fe(2)O(3) cores are disordered. Compared with FTIR, Raman spectrum analysis is a rapid, simple, and accurate method for identifying inverse spinel iron oxides. The chemical stability and the high solubility of the products are explained in terms of the proposed coordination modes of the surface iron atom with GLA. PMID:21084095

  16. 6.2. Pure death processes 6.2.1. Postulates of pure death processes.

    E-print Network

    Chen, Kani

    45 6.2. Pure death processes 6.2.1. Postulates of pure death processes. {X(t) : t [0, )} is called a pure death process with parameters µ0 = 0, µ1, ..., µN , and state space {0, 1, ..., N are equivalent, but Postulate 2 is incomplete and cannot be considered as a definition for pure death process. 6

  17. Application of cellulase and hemicellulase to pure xylan, pure cellulose, and switchgrass solids from leading pretreatments

    E-print Network

    California at Riverside, University of

    Application of cellulase and hemicellulase to pure xylan, pure cellulose, and switchgrass solids-glucosidase, Multifect xylanase, and beta-xylosidase were evaluated for hydrolysis of pure cellulose, pure xylan observed from Avicel, phosphoric acid swollen cellulose (PASC), xylan, and pretreated switchgrass solids

  18. Entanglement purification protocol for a mixture of a pure entangled state and a pure product state

    E-print Network

    Wójcik, Antoni

    Entanglement purification protocol for a mixture of a pure entangled state and a pure product state purification protocol for a mixture of a pure entangled state and a pure product state, which are orthogonal recursive formula for the rate of the protocol for different states, i.e., the number of maximally entangled

  19. Highly dispersive photonic crystal fiber for beamforming

    Microsoft Academic Search

    Maggie Y. Chen; Harish Subbaraman; Ray T. Chen

    2008-01-01

    In this paper, a highly dispersive pure silica photonic crystal fiber is designed and fabricated with maximum chromatic dispersion value of about -600 ps\\/(nm.km) around 1.55 mum wavelength region. This kind of a photonic crystal fiber structure is suitable for high dispersion application in photonic crystal fiber array based phased array antenna systems. A four-element true-time delay module is constructed

  20. Dispersion in photonic crystals

    NASA Astrophysics Data System (ADS)

    Witzens, Jeremy

    2005-11-01

    Investigations on the dispersive properties of photonic crystals, modified scattering in ring-resonators, monolithic integration of vertical-cavity surface-emitting lasers and advanced data processing techniques for the finite-difference time-domain method are presented. Photonic crystals are periodic mesoscopic arrays of scatterers that modify the propagation properties of electromagnetic waves in a similar way as "natural" crystals modify the properties of electrons in solid-state physics. In this thesis photonic crystals are implemented as planar photonic crystals, i.e., optically thin semiconductor films with periodic arrays of holes etched into them, with a hole-to-hole spacing of the order of the wavelength of light in the dielectric media. Photonic crystals can feature forbidden frequency ranges (the band-gaps) in which light cannot propagate. Even though most work on photonic crystals has focused on these band-gaps for application such as confinement and guiding of light, this thesis focuses on the allowed frequency regions (the photonic bands) and investigates how the propagation of light is modified by the crystal lattice. In particular the guiding of light in bulk photonic crystals in the absence of lattice defects (the self-collimation effect) and the angular steering of light in photonic crystals (the superprism effect) are investigated. The latter is used to design a planar lightwave circuit for frequency domain demultiplexion. Difficulties such as efficient insertion of light into the crystal are resolved and previously predicted limitations on the resolution are circumvented. The demultiplexer is also fabricated and characterized. Monolithic integration of vertical-cavity surface-emitting lasers by means of resonantly enhanced grating couplers is investigated. The grating coupler is designed to bend light through a ninety-degree angle and is characterized with the finite-difference time-domain method. The vertical-cavity surface-emitting lasers are fabricated and characterized. A purely theoretical section of the thesis investigates advanced data processing techniques for the finite-difference time-domain method. In particular it is shown that an inner product can be used to filter out specific photonic crystal modes or photonic crystal waveguide modes (Bloch-modes). However it is also shown that the numerical accuracy of this inner product severely worsens for Bloch modes with very low group velocities.