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1.
J Synchrotron Radiat ; 29(Pt 1): 167-179, 2022 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-34985434

RESUMO

Results of the 2018 commissioning and experimental campaigns of the new High Power Laser Facility on the Energy-dispersive X-ray Absorption Spectroscopy (ED-XAS) beamline ID24 at the ESRF are presented. The front-end of the future laser, delivering 15 J in 10 ns, was interfaced to the beamline. Laser-driven dynamic compression experiments were performed on iron oxides, iron alloys and bismuth probed by online time-resolved XAS.

2.
Nat Commun ; 12(1): 2913, 2021 05 18.
Artigo em Inglês | MEDLINE | ID: mdl-34006864

RESUMO

Highly siderophile elements (HSE), including platinum, provide powerful geochemical tools for studying planet formation. Late accretion of chondritic components to Earth after core formation has been invoked as the main source of mantle HSE. However, core formation could also have contributed to the mantle's HSE content. Here we present measurements of platinum metal-silicate partitioning coefficients, obtained from laser-heated diamond anvil cell experiments, which demonstrate that platinum partitioning into metal is lower at high pressures and temperatures. Consequently, the mantle was likely enriched in platinum immediately following core-mantle differentiation. Core formation models that incorporate these results and simultaneously account for collateral geochemical constraints, lead to excess platinum in the mantle. A subsequent process such as iron exsolution or sulfide segregation is therefore required to remove excess platinum and to explain the mantle's modern HSE signature. A vestige of this platinum-enriched mantle can potentially account for 186Os-enriched ocean island basalt lavas.

3.
J Phys Chem Lett ; 12(12): 3246-3252, 2021 Apr 01.
Artigo em Inglês | MEDLINE | ID: mdl-33764078

RESUMO

The ultrafast synthesis of ε-Fe3N1+x in a diamond-anvil cell (DAC) from Fe and N2 under pressure was observed using serial exposures of an X-ray free electron laser (XFEL). When the sample at 5 GPa was irradiated by a pulse train separated by 443 ns, the estimated sample temperature at the delay time was above 1400 K, confirmed by in situ transformation of α- to γ-iron. Ultimately, the Fe and N2 reacted uniformly throughout the beam path to form Fe3N1.33, as deduced from its established equation of state (EOS). We thus demonstrate that the activation energy provided by intense X-ray exposures in an XFEL can be coupled with the source time structure to enable exploration of the time-dependence of reactions under high-pressure conditions.

4.
Proc Natl Acad Sci U S A ; 117(22): 11981-11986, 2020 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-32414927

RESUMO

Properties of liquid silicates under high-pressure and high-temperature conditions are critical for modeling the dynamics and solidification mechanisms of the magma ocean in the early Earth, as well as for constraining entrainment of melts in the mantle and in the present-day core-mantle boundary. Here we present in situ structural measurements by X-ray diffraction of selected amorphous silicates compressed statically in diamond anvil cells (up to 157 GPa at room temperature) or dynamically by laser-generated shock compression (up to 130 GPa and 6,000 K along the MgSiO3 glass Hugoniot). The X-ray diffraction patterns of silicate glasses and liquids reveal similar characteristics over a wide pressure and temperature range. Beyond the increase in Si coordination observed at 20 GPa, we find no evidence for major structural changes occurring in the silicate melts studied up to pressures and temperatures exceeding Earth's core mantle boundary conditions. This result is supported by molecular dynamics calculations. Our findings reinforce the widely used assumption that the silicate glasses studies are appropriate structural analogs for understanding the atomic arrangement of silicate liquids at these high pressures.

5.
Proc Natl Acad Sci U S A ; 112(13): 3916-9, 2015 Mar 31.
Artigo em Inglês | MEDLINE | ID: mdl-25775531

RESUMO

The physical properties of iron (Fe) at high pressure and high temperature are crucial for understanding the chemical composition, evolution, and dynamics of planetary interiors. Indeed, the inner structures of the telluric planets all share a similar layered nature: a central metallic core composed mostly of iron, surrounded by a silicate mantle, and a thin, chemically differentiated crust. To date, most studies of iron have focused on the hexagonal closed packed (hcp, or ε) phase, as ε-Fe is likely stable across the pressure and temperature conditions of Earth's core. However, at the more moderate pressures characteristic of the cores of smaller planetary bodies, such as the Moon, Mercury, or Mars, iron takes on a face-centered cubic (fcc, or γ) structure. Here we present compressional and shear wave sound velocity and density measurements of γ-Fe at high pressures and high temperatures, which are needed to develop accurate seismic models of planetary interiors. Our results indicate that the seismic velocities proposed for the Moon's inner core by a recent reanalysis of Apollo seismic data are well below those of γ-Fe. Our dataset thus provides strong constraints to seismic models of the lunar core and cores of small telluric planets. This allows us to propose a direct compositional and velocity model for the Moon's core.

6.
Proc Natl Acad Sci U S A ; 108(13): 5184-7, 2011 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-21402927

RESUMO

The global geochemical carbon cycle involves exchanges between the Earth's interior and the surface. Carbon is recycled into the mantle via subduction mainly as carbonates and is released to the atmosphere via volcanism mostly as CO(2). The stability of carbonates versus decarbonation and melting is therefore of great interest for understanding the global carbon cycle. For all these reasons, the thermodynamic properties and phase diagrams of these minerals are needed up to core mantle boundary conditions. However, the nature of C-bearing minerals at these conditions remains unclear. Here we show the existence of a new Mg-Fe carbon-bearing compound at depths greater than 1,800 km. Its structure, based on three-membered rings of corner-sharing (CO(4))(4-) tetrahedra, is in close agreement with predictions by first principles quantum calculations [Oganov AR, et al. (2008) Novel high-pressure structures of MgCO(3), CaCO(3) and CO(2) and their role in Earth's lower mantle. Earth Planet Sci Lett 273:38-47]. This high-pressure polymorph of carbonates concentrates a large amount of Fe((III)) as a result of intracrystalline reaction between Fe((II)) and (CO(3))(2-) groups schematically written as 4FeO + CO(2) → 2Fe(2)O(3) + C. This results in an assemblage of the new high-pressure phase, magnetite and nanodiamonds.


Assuntos
Carbono/química , Carbonatos/química , Planeta Terra , Minerais/química , Ferro/química , Magnésio/química , Estrutura Molecular , Pressão , Temperatura , Termodinâmica , Difração de Raios X
7.
Science ; 331(6013): 64-7, 2011 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-21212352

RESUMO

Seismic discontinuities in Earth typically arise from structural, chemical, or temperature variations with increasing depth. The pressure-induced iron spin state transition in the lower mantle may influence seismic wave velocities by changing the elasticity of iron-bearing minerals, but no seismological evidence of an anomaly exists. Inelastic x-ray scattering measurements on (Mg(0.83)Fe(0.17))O-ferropericlase at pressures across the spin transition show effects limited to the only shear moduli of the elastic tensor. This explains the absence of deviation in the aggregate seismic velocities and, thus, the lack of a one-dimensional seismic signature of the spin crossover. The spin state transition does, however, influence shear anisotropy of ferropericlase and should contribute to the seismic shear wave anisotropy of the lower mantle.

8.
Phys Rev Lett ; 100(8): 085501, 2008 Feb 29.
Artigo em Inglês | MEDLINE | ID: mdl-18352634

RESUMO

We performed high-resolution inelastic x-ray scattering measurements on a single crystal of hcp cobalt at simultaneous high pressure and high temperature, obtaining 4 of the 5 independent elements of the elastic tensor. Our experiments indicate that the elasticity of hcp-Co is well described within the quasiharmonic approximation and that anharmonic high-temperature effects on the elastic moduli, sound velocities, and elastic anisotropy are minimal at constant density. These results support the validity of Birch's law and represent an important benchmark for ab initio thermal lattice dynamics and molecular-dynamics simulations.

9.
Science ; 305(5682): 383-6, 2004 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-15256667

RESUMO

We measured the spin state of iron in magnesium silicate perovskite (Mg(0.9),Fe(0.1))SiO(3) at high pressure and found two electronic transitions occurring at 70 gigapascals and at 120 gigapascals, corresponding to partial and full electron pairing in iron, respectively. The proportion of iron in the low spin state thus grows with depth, increasing the transparency of the mantle in the infrared region, with a maximum at pressures consistent with the D" layer above the core-mantle boundary. The resulting increase in radiative thermal conductivity suggests the existence of nonconvecting layers in the lowermost mantle.

10.
Nat Mater ; 3(5): 294-7, 2004 May.
Artigo em Inglês | MEDLINE | ID: mdl-15107839

RESUMO

There has been considerable interest in the synthesis of new nitrides because of their technological and fundamental importance. Although numerous metals react with nitrogen there are no known binary nitrides of the noble metals. We report the discovery and characterization of platinum nitride (PtN), the first binary nitride of the noble metals group. This compound can be formed above 45-50 GPa and temperatures exceeding 2,000 K, and is stable after quenching to room pressure and temperature. It is characterized by a very high Raman-scattering cross-section with easily observed second- and third-order Raman bands. Synchrotron X-ray diffraction shows that the new phase is cubic with a remarkably high bulk modulus of 372(+/-5) GPa.


Assuntos
Modelos Moleculares , Compostos de Nitrogênio/química , Compostos de Platina/química , Simulação por Computador , Teste de Materiais , Metais/síntese química , Metais/química , Conformação Molecular , Compostos de Nitrogênio/síntese química , Compostos de Platina/síntese química , Pressão , Análise Espectral Raman , Propriedades de Superfície
11.
Science ; 300(5620): 789-91, 2003 May 02.
Artigo em Inglês | MEDLINE | ID: mdl-12677070

RESUMO

We measured the spin state of iron in ferropericlase (Mg0.83Fe0.17)O at high pressure and found a high-spin to low-spin transition occurring in the 60- to 70-gigapascal pressure range, corresponding to depths of 2000 kilometers in Earth's lower mantle. This transition implies that the partition coefficient of iron between ferropericlase and magnesium silicate perovskite, the two main constituents of the lower mantle, may increase by several orders of magnitude, depleting the perovskite phase of its iron. The lower mantle may then be composed of two different layers. The upper layer would consist of a phase mixture with about equal partitioning of iron between magnesium silicate perovskite and ferropericlase, whereas the lower layer would consist of almost iron-free perovskite and iron-rich ferropericlase. This stratification is likely to have profound implications for the transport properties of Earth's lowermost mantle.

12.
Phys Rev Lett ; 89(20): 205504, 2002 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-12443487

RESUMO

We present a new method to separate the crystallographic and electronic phase transitions in hematite using x-ray emission spectroscopy and x-ray diffraction. Our observations, based on the behavior of a metastable high-pressure phase in the stability domain of the low-pressure phase, show that the electronic transition is preempted by the crystallographic transition. The former occurs only afterwards in the high-pressure phase, possibly as a result of a Mott transition. The idea that the electronic transition drives the transition in hematite is therefore invalidated. Such methods should help elucidate the mechanics and the driving forces behind a number of first-order high-pressure phase transitions.

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