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Results for “shock compression”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Transformation of shock-compressed graphite to hexagonal diamond in nanoseconds

The graphite-to-diamond transformation under shock compression has been of broad scientific interest since 1961. The formation of hexagonal diamond (HD) is of particular interest because it is expected to be harder than cubic diamond and due to its use in terrestrial sciences as a marker at meteorite impact sites. However, the formation of diamond having a fully hexagonal structure continues to be questioned and remains unresolved. Using real-time (nanosecond), in situ x-ray diffraction measurements, we show unequivocally that highly oriented pyrolytic graphite, shock-compressed along the c axis to 50 GPa, transforms to highly oriented elastically strained HD with the (100)HD plane parallel to the graphite basal plane. These findings contradict recent molecular dynamics simulation results for the shock-induced graphite-to-diamond transformation and provide a benchmark for future theoretical simulations. Additionally, our results show that an earlier report of HD forming only above 170 GPa for shocked pyrolytic graphite may lead to incorrect interpretations of meteorite impact events.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural Transformation and Melting in Gold Shock Compressed to 355 GPa

Gold is believed to retain its ambient crystal structure at very high pressures under static and shock compression, enabling its wide use as a pressure marker. Our in situ x-ray diffraction measurements on shock-compressed gold show that it transforms to the body-centered-cubic (bcc) phase, with an onset pressure between 150 and 176 GPa. A liquid-bcc coexistence was observed between 220 and 302 GPa and complete melting occurs by 355 GPa. Our observation of the lower coordination bcc structure in shocked gold is in marked contrast to theoretical predictions and the reported observation of the hexagonal-close-packed structure under static compression.

phase transitions↗
DOE OSTI2018

In situ X-Ray Diffraction of Shock-Compressed Fused Silica

Because of its widespread applications in materials science and geophysics, SiO 2 has been extensively examined under shock compression. Both quartz and fused silica transform through a so-called “mixed-phase region” to a dense, low compressibility high-pressure phase. For decades, the nature of this phase has been a subject of debate. Proposed structures include crystalline stishovite, another high-pressure crystalline phase, or a dense amorphous phase. Here we use plate-impact experiments and pulsed synchrotron x-ray diffraction to examine the structure of fused silica shock compressed to 63 GPa. In contrast to recent laser-driven compression experiments, we find that fused silica adopts a dense amorphous structure at 34 GPa and below. When compressed above 34 GPa, fused silica transforms to untextured polycrystalline stishovite. Our results can explain previously ambiguous features of the shock-compression behavior of fused silica and are consistent with recent molecular dynamics simulations. Stishovite grain sizes are estimated to be ~5–30 nm for compression over a few hundred nanosecond time scale.

58 GEOSCIENCES↗
DOE OSTI2022

Quantitative measurements of density in shock-compressed silver up to 330 GPa using x-ray diffraction

This work presents a structural study of shock-compressed states in Ag to 331 GPa, accessed via laser shock compression. Structures of the resulting crystalline phases and the average atomic distribution of the liquid state are determined using in situ x-ray diffraction. We employ structure factor analysis, adapted for a non-monochromatic x-ray source, to determine the density of the liquid phase from analysis of x-ray diffraction data for the first time in shock compressed Ag. We also present a detailed analysis of the crystalline phases, which shows good agreement with the phase boundaries reported in previous experimental and theoretical works. We utilize the whole powder pattern fitting approach implemented in the MAUD package to constrain stacking faults in the face centered cubic structure. We observe the ambient fcc structure up to a stress of 146 GPa before a transition to a body-centered cubic structure and liquid phase at 179 GPa, with full melting above 212 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Nanometer-scale characterization of laser-driven compression, shocks, and phase transitions, by x-ray scattering using free electron lasers

In this paper, we study the feasibility of using small angle X-ray scattering (SAXS) as a new experimental diagnostic for intense laser-solid interactions. By using X-ray pulses from a hard X-ray free electron laser, we can simultaneously achieve nanometer and femtosecond resolution of laser-driven samples. This is an important new capability for the Helmholtz international beamline for extreme fields at the high energy density endstation currently built at the European X-ray free electron laser. We review the relevant SAXS theory and its application to transient processes in solid density plasmas and report on first experimental results that confirm the feasibility of the method. Finally, we present results of two test experiments where the first experiment employs ultra-short laser pulses for studying relativistic laser plasma interactions, and the second one focuses on shock compression studies with a nanosecond laser system.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

A direct measurement of the forward shock speed in supernova remnant 0509–67.5: Constraints on the age, ambient density, shock compression factor, and electron–ion temperature equilibration

Two Hubble Space Telescope narrow-band Hα images separated in time by 1.03 years are used for a proper motion measurement of the forward shock of the LMC supernova remnant 0509–67.5, the only spectroscopically confirmed LMC remnant of Ia origin. We measure a global shock speed of 6500 ± 200 km s{sup −1} and constrain the pre-shock neutral hydrogen density to be 0.084 ± 0.003 cm{sup −3}, for a typical mean number of Hα photons produced per neutral hydrogen atom entering the forward shock. Previously published broad Hα line widths from two locations on the rim and our corresponding shock speed measurements are consistent with Balmer shock models that do not include effects of cosmic-ray acceleration. For the northeastern rim location, we limit the post-shock electron temperature to 10% of the proton temperature by also using the broad-to-narrow flux ratio. Hydrodynamic simulations for different initial ejecta density profiles constrain the age and ambient medium density; for an exponential ejecta profile and initial explosion energy of 1.4 × 10{sup 51} erg, the remnant’s age is 310{sub −30}{sup +40} years. For all evolutionary models explored, the expansion parameter falls in the range of 0.41–0.73, indicating that the remnant is still firmly in the ejecta-dominated phase of its evolution. Our measured neutral hydrogen density of the ambient medium, combined with the shocked density obtained in Williams et al., disfavors forward shock compression factors greater than ∼7.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Twinning and Dislocation Evolution during Shock Compression and Release of Single Crystals: Real-Time X-Ray Diffraction

Determining the temporal evolution of twinning and/or dislocation slip, in real time (nanoseconds), in single crystals subjected to plane shock wave loading is a long-standing scientific need. Non-cubic crystals pose special challenges because they have many competing slip and twinning systems. Here, we report on time-resolved, in situ, synchrotron Laue x-ray diffraction measurements during shock compression and release of magnesium single crystals that are subjected to compression along the c-axis. Significant twinning was observed directly during stress release following shock compression; during compression, only dislocation slip was observed. Our measurements unambiguously distinguish between twinning and dislocation slip on nanosecond timescales in a shocked hexagonal-close-packed metal.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Direct Observation of Melting in Shock-Compressed Bismuth With Femtosecond X-ray Diffraction

The melting of bismuth in response to shock compression has been studied using in situ femtosecond x-ray diffraction at an x-ray free electron laser. Both solid-solid and solid-liquid phase transitions are documented using changes in discrete diffraction peaks and the emergence of broad, liquid scattering upon release from shock pressures up to 14 GPa. The transformation from the solid state to the liquid is found to occur in less than 3 ns, very much faster than previously believed. These results are the first quantitative measurements of a liquid material obtained on shock release using x-ray diffraction, and provide an upper limit for the time scale of melting of bismuth under shock loading.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Experimental and theoretical examination of shock-compressed copper through the fcc to bcc to melt phase transitions

Recent studies show a face-centered cubic (fcc) to body-centered cubic (bcc) transformation along the shock Hugoniot for several metals (i.e., Cu, Au, and Ag). Here, we combine laser-shock compression of Cu foils on nanosecond timescales with in situ x-ray diffraction (XRD) to examine the microstructural changes with stress. We study the fcc phase and the phase transition from fcc to bcc (pressures greater than 180 GPa). Textural analysis of the azimuthal intensities from the XRD images is consistent with transformation into the bcc phase through the Pitsch-distortion mechanism. We use embedded atom model molecular dynamics simulations to determine the stability of the bcc phase in pressure–temperature space. Finally, our results indicate that the bcc phase is stabilized only at high temperatures and remains stable at pressures greater than 500 GPa.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Shock compression of strongly correlated oxides: A liquid-regime equation of state for cerium(IV) oxide

Here, the shock Hugoniot for full-density and porous CeO 2 was investigated in the liquid regime using ab initio molecular dynamics (AIMD) simulations with Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 6000 and 100 000 K and densities ranging from ρ = 2.5 to 20 g/cm 3 . The impact of on-site Coulomb interaction corrections +U on the equation of state (EOS) obtained from AIMD simulations was assessed by direct comparison with results from standard density functional theory simulations. Classical molecular dynamics (CMD) simulations were also performed to model atomic-scale shock compression of larger porous CeO 2 models. Results from AIMD and CMD compression simulations compare favorably with Z-machine shock data to 525 GPa and gas-gun data to 109 GPa for porous CeO 2 samples. Using results from AIMD simulations, an accurate liquid-regime Mie-Grüneisen EOS was built for CeO 2 . In addition, a revised multiphase SESAME-type EOS was constrained using AIMD results and experimental data generated in this work. This study demonstrates the necessity of acquiring data in the porous regime to increase the reliability of existing analytical EOS models.

74 ATOMIC AND MOLECULAR PHYSICS↗