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Now showing items 1 - 16 of 20

  • Casting Nanoporous Platinum in Metal-Organic Frameworks

    Gao, Xiang   Pei, Xiaokun   Gardner, David W.   Diercks, Christian S.   Lee, Seungkyu   Rungtaweevoranit, Bunyarat   Prevot, Mathieu S.   Zhu, Chenhui   Fakra, Sirine   Maboudian, Roya  

    Nanocasting based on porous templates is a powerful strategy in accessing materials and structures that are difficult to form by bottom-up syntheses in a controlled fashion. A facile synthetic strategy for casting ordered, nanoporous platinum (NP-Pt) networks with a high degree of control by using metal-organic frameworks (MOFs) as templates is reported here. The Pt precursor is first infiltrated into zirconium-based MOFs and subsequently transformed to 3D metallic networks via a chemical reduction process. It is demonstrated that the dimensions and topologies of the cast NP-Pt networks can be accurately controlled by using different MOFs as templates. The Brunauer-Emmett-Teller surface areas of the NP-Pt networks are estimated to be >100 m(2) g(-1) and they exhibit excellent catalytic activities in the methanol electrooxidation reaction (MEOR). This new methodology presents an attractive route to prepare well-defined nanoporous materials for diverse applications ranging from energy to sensing and biotechnology.
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  • Casting Nanoporous Platinum in Metal-Organic Frameworks

    Gao, Xiang   Pei, Xiaokun   Gardner, David W.   Diercks, Christian S.   Lee, Seungkyu   Rungtaweevoranit, Bunyarat   Prevot, Mathieu S.   Zhu, Chenhui   Fakra, Sirine   Maboudian, Roya  

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  • Strontium Substitution for Calcium in Lithogenesis

    Blaschko, Sarah D.   Chi, Thomas   Miller, Joe   Flechner, Lawrence   Fakra, Sirine   Kapahi, Pankaj   Kahn, Arnold   Stoller, Marshall L.  

    Purpose: Strontium has chemical similarity to calcium, which enables the replacement of calcium by strontium in biomineralization processes. Incorporating strontium into human bone and teeth has been studied extensively but little research has been performed of the incorporation of strontium into urinary calculi. We used synchrotron based x-ray fluorescence and x-ray absorption techniques to examine the presence of strontium in different types of human kidney stones. Materials and Methods: Multiple unique human stone samples were obtained via consecutive percutaneous nephrolithotomies/ureteroscopies. A portion of each stone was sent for standard laboratory analysis and a portion was retained for x-ray fluorescence and x-ray absorption measurements. X-ray fluorescence and x-ray absorption measurements determined the presence, spatial distribution and speciation of strontium in each stone sample. Results: Traditional kidney stone analyses identified calcium oxalate, calcium phosphate, uric acid and cystine stones. X-ray fluorescence measurements identified strontium in all stone types except pure cystine. X-ray fluorescence elemental mapping of the samples revealed co-localization of calcium and strontium. X-ray absorption measurements of the calcium phosphate stone showed strontium predominately present as strontium apatite. Conclusions: Advanced x-ray fluorescence imaging identified strontium in all calcium based stones, present as strontium apatite. This finding may be critical since apatite is thought to be the initial nidus for calcium stone formation. Strontium is not identified by standard laboratory stone analyses. Its substitution for calcium can be reliably identified in stones from multiple calcium based stone formers, which may offer opportunities to gain insight into early events in lithogenesis.
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  • Microcomposition of Human Urinary Calculi Using Advanced Imaging Techniques

    Blaschko, Sarah D.   Miller, Joe   Chi, Thomas   Flechner, Lawrence   Fakra, Sirine   Kahn, Arnold   Kapahi, Pankaj   Stoller, Marshall L.  

    Purpose: Common methods of commercial urolithiasis analysis, such as light microscopy and Fourier transform infrared spectroscopy, provide limited or no information on the molecular composition of stones, which is vital when studying early stone pathogenesis. We used synchrotron radiation based microfocused x-ray fluorescence, x-ray absorption and x-ray diffraction advanced imaging techniques to identify and map the elemental composition, including trace elements, of urinary calculi on a mu m (0.0001 cm) scale. Materials and Methods: Human stone samples were obtained during serial percutaneous nephrolithotomy and ureteroscopy procedures. A portion of each sample was sent for commercial stone analysis and a portion was retained for synchrotron radiation based advanced imaging analysis. Results: Synchrotron radiation based methods of stone analysis correctly identified stone composition and provided additional molecular detail on elemental components and spatial distribution in uroliths. Resolution was on the order of a few mu m. Conclusions: Knowledge of all elements present in lithogenesis at this detail allows for better understanding of early stone formation events, which may provide additional insight to prevent and treat stone formation.
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  • Formation of Zn-Ca phyllomanganate nanoparticles in grass roots RID A-4207-2009

    Lanson, Bruno   Marcus, Matthew A.   Fakra, Sirine   Panfili, Frederic   Geoffroy, Nicolas   Manceau, Alain  

    It is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33 angstrom in the ab plane and contain only 1.2 layers (similar to 8.6 angstrom) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn-Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere. (C) 2008 Elsevier Ltd. All rights reserved.
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  • Selenium-tolerant diamondback moth disarms hyperaccumulator plant defense RID C-4910-2009

    Freeman, John L.   Quinn, Colin F.   Marcus, Matthew A.   Fakra, Sirine   Pilon-Smits, Elizabeth A. H.  

    Background: Some plants hyperaccumulate the toxic element selenium (Se) to extreme levels, up to 1% of dry weight. The function of this intriguing phenomenon is obscure. Results: Here, we show that the Se in the hyperaccumulator prince's plume (Stanleya pinnata) protects it from caterpillar herbivory because of deterrence and toxicity. In its natural habitat, however, a newly discovered variety of the invasive diamondback moth (Plutella xylostelia) has disarmed this elemental defense. It thrives on plants containing highly toxic Se levels and shows no oviposition or feeding deterrence, in contrast to related varieties. Interestingly, a Se-tolerant wasp (Diadegma insulare) was found to parasitize the tolerant moth. The insect's Se tolerance mechanism was revealed by X-ray absorption spectroscopy and liquid chromatography-mass spectroscopy, which showed that the Se-tolerant moth and its parasite both accumulate methylselenocysteine, the same form found in the hyperaccumulator plant, whereas related sensitive moths accumulate selenocysteine. The latter is toxic because of its nonspecific incorporation into proteins. Indeed, the Se-tolerant diamondback moth incorporated less Se into protein. Additionally, the tolerant variety sequestered Se in distinct abdominal areas, potentially involved in detoxification and larval defense to predators. Conclusions: Although Se hyperaccumulation protects plants from herbivory by some invertebrates, it can give rise to the evolution of unique Se-tolerant herbivores and thus provide a portal for Se into the local ecosystem. In a broader context, this study provides insight into the possible ecological implications of using Se-enriched crops as a source of anti-carcinogenic selenocompounds and for the remediation of Se-polluted environments.
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  • Millisecond kinetics of nanocrystal cation exchange using microfluidic X-ray absorption spectroscopy

    Chan, Emory M.   Marcus, Matthew A.   Fakra, Sirine   ElNaggar, Mariam   Mathies, Richard A.   Alivisatos, A. Paul  

    We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-to-Ag2Se nanocrystal cation exchange reaction using micro-X-ray absorption spectroscopy (mu XAS). The small microreactor dimensions facilitate the millisecond mixing of CdSe nanocrystals and Ag+ reactant solutions, and the transposition of the reaction time onto spatial coordinates enables the in situ observation of the millisecond reaction using mu XAS. Selenium K-edge absorption spectra show the progression of CdSe nanocrystals to Ag2Se over the course of 100 ms without the presence of long-lived intermediates. These results, along with supporting stopped-flow absorption experiments, suggest that this nanocrystal cation exchange reaction is highly efficient and provide insight into how the reaction progresses in individual particles. This experiment illustrates the value and potential of in situ microfluidic X-ray synchrotron techniques for detailed studies of the millisecond structural transformations of nanoparticles and other solution-phase reactions in which diffusive mixing initiates changes in local bond structures or oxidation states.
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  • Chemical forms of calcium in Ca,Zn- and Ca,Cd-containing grains excreted by tobacco trichomes

    Sarret, Geraldine   Isaure, Marie-Pierre   Marcus, Matthew A.   Harada, Emiko   Choi, Yong-Eui   Pairis, Sebastien   Fakra, Sirine   Manceau, Alain  

    Tobacco (Nicotiana tabacum L. cv. Xanthi) plants exposed to toxic levels of zinc and cadmium excrete metals through their leaf trichomes (epidermal hairs) as Zn,Ca- and Cd,Ca-containing grains. Little is known about the nature and formation mechanism of these precipitates. The chemical, crystalline, and noncrystalline compositions of individual grains produced by tobacco were studied by scanning electron microscopy coupled with energy dispersive Xray analysis (SEM-EDX), micro-X-ray diffraction (mu XRD), and calcium K-edge micro X-ray absorption near edge structure (mu XANES) spectroscopy. Zinc is predominantly incorporated in calcite and cadmium in calcite and vaterite. Aragonite, which occurs occasionally, does not seem to contain trace metals. In addition to being precipitated in its three possible polymorphic forms, calcite, aragonite, and vaterite, calcium is also speciated as amorphous CaCO(3) and possibly organic Ca in some grains. Most often, a particular grain consists of two or more crystalline and noncrystalline phases. The observed variability of intra- and inter-grain elemental and phase composition suggests that this biomineralization process is not constrained by biological factors but instead results from thermodynamically and kinetically controlled reactions. This study illustrates the potential of laterally resolved X-ray synchrotron radiation techniques (mu XRD and mu XANES) to study biomineralization and metal immobilization processes in plants.
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  • Selenium accumulation protects plants from herbivory by Orthoptera via toxicity and deterrence RID C-4910-2009

    Freeman, John L.   Lindblom, Stormy Dawn   Quinn, Colin F.   Fakra, Sirine   Marcus, Matthew A.   Pilon-Smits, Elizabeth A. H.  

    To investigate whether selenium (Se) accumulation in plants provides a chemical defense against generalist insect herbivores, the feeding preference and performance of a mix of orthopteran species were investigated. The selenium hyperaccumulator Stanleya pinnata and accumulator Brassica juncea were used in herbivory studies in the laboratory, and S. pinnata was also used in a manipulative field experiment. In laboratory studies, both crickets and grasshoppers avoided plants pretreated with selenate while those given no choice died after eating leaves with elevated Se (447 +/- 68 and 230 +/- 68 pg Se g(-1) DW, respectively). B. juncea has previously been shown to accumulate selenate, while S. pinnata hyperaccumulates methylselenocysteine. Thus, these findings demonstrate that both inorganic and organic forms of selenium protect plants from herbivory. Grasshoppers fed S. pinnata contained methylselenocysteine in their midgut and absorbed this form into surrounding tissues. In a manipulative field experiment, methylselenocysteine protected S. pinnata from invertebrate herbivory and increased its long-term survival rate over an entire growth season. In native habitats of selenium hyperaccumulators, orthopterans represent a major group of insect herbivores. Protection offered by organic selenium accumulation against these herbivores may have promoted the evolution of selenium hyperaccumulation in plants.
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  • Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities

    Yang, Ankun   Zhou, Guangmin   Kong, Xian   Vila, Rafael A.   Pei, Allen   Wu, Yecun   Yu, Xiaoyun   Zheng, Xueli   Wu, Chun-Lan   Liu, Bofei   Chen, Hao   Xu, Yan   Chen, Di   Li, Yanxi   Fakra, Sirine   Hwang, Harold Y.   Qin, Jian   Chu, Steven   Cui, Yi  

    A supercooled liquid phase of elemental sulfur can be grown electrochemically on two-dimensional materials. This phase has a markedly higher areal capacity than solid sulfur, with possible implications for future lithium-sulfur batteries. It has recently been shown that sulfur, a solid material in its elementary form S-8, can stay in a supercooled state as liquid sulfur in an electrochemical cell. We establish that this newly discovered state could have implications for lithium-sulfur batteries. Here, through in situ studies of electrochemical sulfur generation, we show that liquid (supercooled) and solid elementary sulfur possess very different areal capacities over the same charging period. To control the physical state of sulfur, we studied its growth on two-dimensional layered materials. We found that on the basal plane, only liquid sulfur accumulates; by contrast, at the edge sites, liquid sulfur accumulates if the thickness of the two-dimensional material is small, whereas solid sulfur nucleates if the thickness is large (tens of nanometres). Correlating the sulfur states with their respective areal capacities, as well as controlling the growth of sulfur on two-dimensional materials, could provide insights for the design of future lithium-sulfur batteries.
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  • A compact dispersive refocusing Rowland circle X-ray emission spectrometer for laboratory,synchrotron,and XFEL applications

    Holden, William M.   Hoidn, Oliver R.   Ditter, Alexander S.   Seidler, Gerald T.   Kas, Joshua   Stein, Jennifer L.   Cossairt, Brandi M.   Kozimor, Stosh A.   Guo, Jinghua   Ye, Yifan   Marcus, Matthew A.   Fakra, Sirine  

    X-ray emission spectroscopy is emerging as an important complement to x-ray absorption fine structure spectroscopy, providing a characterization of the occupied electronic density of states local to the species of interest. Here, we present details of the design and performance of a compact x-ray emission spectrometer that uses a dispersive refocusing Rowland (DRR) circle geometry to achieve excellent performance for the 2-2.5 keV range, i.e., especially for the K-edge emission from sulfur and phosphorous. The DRR approach allows high energy resolution even for unfocused x-ray sources. This property enables high count rates in laboratory studies, approaching those of insertion-device beamlines at third-generation synchrotrons, despite use of only a low-powered, conventional x-ray tube. The spectrometer, whose overall scale is set by use of a 10-cm diameter Rowland circle and a new small-pixel complementary metal-oxide-semiconductor x-ray camera, is easily portable to synchrotron or x-ray free electron laser beamlines. Photometrics from measurements at the Advanced Light Source show excellent overall instrumental efficiency. In addition, the compact size of this instrument lends itself to future multiplexing to gain large factors in net collection efficiency or its implementation in controlled gas gloveboxes either in the lab or in an endstation. Published by AIP Publishing.
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  • Coupled redox transformations of catechol and cerium at the surface of a cerium(III) phosphate mineral RID E-3182-2010

    Cervini-Silva, Javiera   Gilbert, Benjamin   Fakra, Sirine   Friedrich, Stephan   Banfield, Jillian  

    Highly insoluble Ce-bearing phosphate minerals form by weathering of apatite [Ca(5)(PO(4))(3)center dot(OH,F,Cl)], and are important phosphorous repositories in soils. Although these phases can be dissolved via biologically-mediated pathways, the dissolution mechanisms are poorly understood. In this paper we report spectroscopic evidence to support coupling of redox transformations of organic carbon and cerium during the reaction of rhabdophane (CePO(4)center dot H(2)O) and catechol, a ubiquitous biogenic compound, at pH 5. Results show that the oxic-anoxic conditions influence the mineral dissolution behavior. Under anoxic conditions, the release of P and Ce occurs stoichiometrically. In contrast, under oxic conditions, the mineral dissolution behavior is incongruent, with dissolving Ce(3+) ions oxidizing to CeO(2). Reaction product analysis shows the formation of CO(2), polymeric C, and oxalate and malate. The presence of more complex forms of organic carbon was also confirmed. Near edge X-ray absorption fine structure spectroscopy measurements at Ce-M(4.5) and C-K absorption edges on reacted CePO(4)center dot H(2)O samples in the absence or presence of catechol and dissolved oxygen confirm that (1) the mineral surface converts to the oxide during this reaction, while full oxidation is limited to the near-surface region only; (2) the Ce valence remains unchanged when the reaction between CePO(4)center dot H(2)O and O(2) but in the absence of catechol. Carbon K-edge spectra acquired from rhabdophane reacted with catechol under oxic conditions show spectral features before and after reaction that are considerably different from catechol, indicating the formation of more complex organic molecules. Decreases in intensity of characteristic catechol peaks are accompanied by the appearance of new pi* resonances due to carbon in carboxyl (ca. 288.5 eV) and carbonyl (ca. 289.3 eV) groups, and the development of broad structure in the sigma* region characteristic of aliphatic carbon. Evolution of the C K-edge spectra is consistent with aromatic-ring cleavage and polymerization. These results further substantiate that the presence of catechol, O(2) (aq) causes both the oxidation of structural Ce(3+) and the transformation of catechol to more complex organic molecules. Scanning Transmission X-Ray Microscopy measurements at the C K and Ce M(4.5) edges indicate three dominant organic species, varying in complexity and association with the inorganic phase. Untransformed catechol is loosely associated with CeO(2), whereas more complex organic molecules that exhibit lower aromaticity and stronger C=O pi* resonances of carboxyl-C and carbonyl-C groups are only found in association with the grains. These results further serve as basis to postulate that, in the presence of O(2), CeO(2) can mediate the oxidative polymerization of catechol to form higher molecular weight polymers. The present work provides evidence for a pathway of biologically-induced, non-enzymatic oxidation of cerium and formation of small CeO(2) particles at room temperature. These findings may have implications for carbon cycling in natural and cerium-contaminated soils and aqueous environments. (C) 2008 Published by Elsevier Ltd.
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  • Trichomes of tobacco excrete zinc as zinc-substituted calcium carbonate and other zinc-containing compounds RID A-5107-2009

    Sarret, Geraldine   Harada, Emiko   Choi, Yong-Eui   Isaure, Marie-Pierre   Geoffroy, Nicolas   Fakra, Sirine   Marcus, Matthew A.   Birschwilks, Mandy   Clemens, Stephan   Manceau, Alain  

    Tobacco (Nicotiana tabacum L. cv Xanthi) plants were exposed to toxic levels of zinc (Zn). Zn exposure resulted in toxicity signs in plants, and these damages were partly reduced by a calcium (Ca) supplement. Confocal imaging of intracellular Zn using Zinquin showed that Zn was preferentially accumulated in trichomes. Exposure to Zn and Zn + Ca increased the trichome density and induced the production of Ca/Zn mineral grains on the head cells of trichomes. These grains were aggregates of submicrometer-sized crystals and poorly crystalline material and contained Ca as major element, along with subordinate amounts of Zn, manganese, potassium, chlorine, phosphorus, silicon, and magnesium. Micro x-ray diffraction revealed that the large majority of the grains were composed essentially of metal-substituted calcite (CaCO3). CaCO3 polymorphs (aragonite and vaterite) and CaC2O4 (Ca oxalate) mono- and dihydrate also were identified, either as an admixture to calcite or in separate grains. Some grains did not diffract, although they contained Ca, suggesting the presence of amorphous form of Ca. The presence of Zn-substituted calcite was confirmed by Zn K-edge micro-extended x-ray absorption fine structure spectroscopy. Zn bound to organic compounds and Zn-containing silica and phosphate were also identified by this technique. The proportion of Zn-substituted calcite relative to the other species increased with Ca exposure. The production of Zn-containing biogenic calcite and other Zn compounds through the trichomes is a novel mechanism involved in Zn detoxification. This study illustrates the potential of laterally resolved x-ray synchrotron radiation techniques to study biomineralization and metal homeostasis processes in plants.
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  • Surface structure of CdSe nanorods revealed by combined X-ray absorption fine structure measurements and ab initio calculations

    Aruguete, Deborah M.   Marcus, Matthew A.   Li, Liang-Shi   Williamson, Andrew   Fakra, Sirine   Gygi, Francois   Galli, Giulia A.   Alivisatos, A. Paul  

    We report orientation-specific, surface-sensitive structural characterization of colloidal CdSe nanorods with extended X-ray absorption fine structure spectroscopy and ab initio density functional theory calculations. Our measurements of crystallographically aligned CdSe nanorods show that they have reconstructed Cd-rich surfaces. They exhibit orientation-dependent changes in interatomic distances which are qualitatively reproduced by our calculations. These calculations reveal that the measured interatomic distance anisotropy originates from the nanorod surface.
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  • Evolution of selenium hyperaccumulation in Stanleya (Brassicaceae) as inferred from phylogeny, physiology and X-ray microprobe analysis.

    Cappa, Jennifer J   Yetter, Crystal   Fakra, Sirine   Cappa, Patrick J   DeTar, Rachael   Landes, Corbett   Pilon-Smits, Elizabeth A H   Simmons, Mark P  

    Past studies have identified herbivory as a likely selection pressure for the evolution of hyperaccumulation, but few have tested the origin(s) of hyperaccumulation in a phylogenetic context. We focused on the evolutionary history of selenium (Se) hyperaccumulation in Stanleya (Brassicaceae). Multiple accessions were collected for all Stanleya taxa and two outgroup species. We sequenced four nuclear gene regions and performed a phylogenetic analysis. Ancestral reconstruction was used to predict the states for Se-related traits in a parsimony framework. Furthermore, we tested the taxa for Se localization and speciation using X-ray microprobe analyses. True hyperaccumulation was found in three taxa within the S. pinnata/bipinnata clade. Tolerance to hyperaccumulator Se concentrations was found in several taxa across the phylogeny, including the hyperaccumulators. X-ray analysis revealed two distinct patterns of leaf Se localization across the genus: marginal and vascular. All taxa accumulated predominantly (65-96%) organic Se with the C-Se-C configuration. These results give insight into the evolution of Se hyperaccumulation in Stanleya and suggest that Se tolerance and the capacity to produce organic Se are likely prerequisites for Se hyperaccumulation in Stanleya. =C2=A9 2014 The Authors. New Phytologist =C2=A9 2014 New Phytologist Trust.
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  • Ultrafast growth of wadsleyite in shock-produced melts and its implications for early solar system impact processes RID E-7451-2010

    Tschauner, Oliver   Asimow, Paul D.   Kostandova, Natalya   Ahrens, Thomas J.   Ma, Chi   Sinogeikin, Stanislas   Liu, Zhenxian   Fakra, Sirine   Tamura, Nobumichi  

    We observed micrometer-sized grains of wadsleyite, a high-pressure phase of (Mg,Fe)(2)SiO(4), in the recovery products of a shock experiment. We infer these grains crystallized from shock-generated melt over a time interval of <1 mu s, the maximum time over which our experiment reached and sustained pressure sufficient to stabilize this phase. This rapid crystal growth rate (approximate to 1 m/s) suggests that, contrary to the conclusions of previous studies of the occurrence of high-pressure phases in shock-melt veins in strongly shocked meteorites, the growth of high-pressure phases from the melt during shock events is not diffusion-controlled. Another process, such as microturbulent transport, must be active in the crystal growth process. This result implies that the times necessary to crystallize the high-pressure phases in shocked meteorites may correspond to shock pressure durations achieved on impacts between objects 1-5 m in diameter and not, as previously inferred, approximate to 1-5 km in diameter. These results may also provide another pathway for syntheses, via shock recovery, of some high- value, high-pressure phases.
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