A5059829283- High-pressure geophysics and materials
- High-Velocity Impact and Material Behavior
- Diamond and Carbon-based Materials Research
- Laser-Plasma Interactions and Diagnostics
- Energetic Materials and Combustion
- Rock Mechanics and Modeling
- Crystal Structures and Properties
- Geotechnical and Geomechanical Engineering
- Geological and Geochemical Analysis
- X-ray Diffraction in Crystallography
- Force Microscopy Techniques and Applications
- Engineering Applied Research
- Glass properties and applications
- Granular flow and fluidized beds
- Powder Metallurgy Techniques and Materials
- Drilling and Well Engineering
- Ion-surface interactions and analysis
- Scientific Measurement and Uncertainty Evaluation
- Inorganic Fluorides and Related Compounds
- Spectroscopy and Laser Applications
- Advanced Chemical Physics Studies
- Thermodynamic and Structural Properties of Metals and Alloys
- Tunneling and Rock Mechanics
- Earthquake Detection and Analysis
- Structural Analysis of Composite Materials
Lawrence Livermore National Laboratory
2014-2024
Los Alamos National Laboratory
2020
California Institute of Technology
2002-2019
National Security Technologies (United States)
2016
The University of Texas at Austin
2006-2009
We measured the longitudinal sound velocity in Mo shock compressed up to 4.4 Mbars on Hugoniot. Its speed increases linearly with pressure 2.6 Mbars; slope then decreases melting of $\ensuremath{\sim}$3.8 Mbars. This suggests a decrease shear modulus before melt. A linear extrapolation our data 1 bar agrees ambient speed. The results suggest that remains bcc phase Hugoniot pressure. There is no statistically significant evidence for previously reported bcc$\ensuremath{\rightarrow}$hcp transition
A new absolute equation of state measurement technique is described and demonstrated measuring the shock refractive index MgO up to 226 GPa. This utilizes steady waves high-pressure transparency under dynamic compression release. Hugoniot measurements performed using this are consistent with previous measurements. linear dependence shocked density observed GPa, over a magnitude greater in pressure that studies. The along principal higher than any other material reported date. We observe...
Thermal desorption spectroscopy is employed to examine transport mechanisms in structured, nanoscale films consisting of labeled amorphous solid water (ASW, H218O, H216O) and organic spacer layers (CCl4, CHCl3) prior ASW crystallization (T ≈ 150−160 K). Self-transport studied as a function both the layer film thickness, effectiveness these bulk diffusion "barrier" also investigated. Isothermal measurements structured are combined with gas uptake (CClF2H) investigate self-transport changes...
We used several variations of the shock compression method to measure longitudinal sound velocity shocked tantalum over pressure range 37–363 GPa with a typical uncertainty 1.0%. These data are consistent Ta remaining in bcc phase along principal Hugoniot from ambient ≈300 GPa, at which melting occurs. also do not support putative phenomena reported below 100 some static experiments.
Abstract The response of forsterite, Mg 2 SiO 4 , under dynamic compression is fundamental importance for understanding its phase transformations and high‐pressure behavior. Here, we have carried out an in situ X‐ray diffraction study laser‐shocked polycrystalline single‐crystal forsterite ( a ‐, b c ‐orientations) from 19 to 122 GPa using the Matter Extreme Conditions end‐station Linac Coherent Light Source. Under laser‐based shock loading, does not transform equilibrium assemblage MgSiO 3...
We performed experiments combining three-dimensional x-ray diffraction and computed tomography to explore the relationship between microstructure local force strain during quasistatic granular compaction. found that initial void space around a grain contact coordination number before compaction can be used predict regions vulnerable above-average at later stages of also correlations number, stress maximum interparticle force, all Finally, we observed grains fracture have an below-average...
Dynamic compaction of granular materials is a complex process, wherein the material response at continuum scale arises from fracture, comminution, and fragment flow grain scale. Granular have heterogeneity due to variation in properties as well local packing density structure. These heterogeneities may affect dynamic response, producing structured time-varying front. The methodology used characterize shock behavior solid be inappropriate for because this unsteady interactions between...
Graded density impactors (GDIs) are used to dynamically compress materials extreme conditions. Two modifications a previously developed Mg-Cu-W GDI made in this work before using it dynamic compression experiment: Mg is replaced with Al and Ta disk glued the back. The phase by because FCC remains solid higher pressure along its Hugoniot compared Mg. addition of creates constant particle velocity regime facilitates definition peak states. Microstructure analysis, profilometry, ultrasonic...
An outstanding challenge in developing a complete equation of state for materials at elevated pressure and temperature is robust method determining the bulk under dynamic conditions. In metals, determination states by optical pyrometry complicated small depth thermal conduction effects. These effects lead to observed temperatures differing 20% or more from state. this work, we show presence measurements tin iron coatings during compression experiments. We demonstrate that tin, contrast iron,...
Abstract Shockwave data on mineral‐forming compounds such as Mg 2 SiO 4 are essential for understanding the interiors of Earth and other planets, but correct interpretation these depends knowing phase assemblage being probed at high pressure. Hence, direct observations or phases making up measured states along forsterite Hugoniot to assess whether kinetic factors inhibit achievement expected equilibrium, phase‐separated assemblage. Previous shock recovery experiments forsterite, which has...
In this work we provide direct evidence of shock-induced melting and associated kinetics in a porous solid (aluminum powder) using time-resolved x-ray diffraction. Unambiguous 50% aluminum (Al) powder samples, shocked to peak pressures between $\ensuremath{\sim}13\text{\ensuremath{-}}19\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$, was provided by the broadening Debye-Scherrer ring corresponding (111) peak. Shocked Al did not melt completely any our experiments within durations measurement....
Experiments were performed on grooved Sn and Cu samples to study the temporal evolution of microjets. Jets generated by impact gun-launched flyer plates against back targets made from either or (groove depth ∼250 μm). The Hugoniot states in various encompassed conditions where solid phases are maintained throughout (7 16 GPa) also melting occurs upon release compression (25 34 GPa); transition near a pressure 23 GPa. at 27 56 GPa provide comparisons which jets move similar speeds but remain...
We present an equation of state for the solid and liquid phases lithium fluoride that covers a wide range conditions from ambient pressure temperature to high pressures temperatures exhibited in shock- ramp-compression studies. The particular phase we have focused on this work is B1 phase. followed approach where heat-capacity functions both are fit experimental data our own quantum molecular dynamics simulations then integrated thermodynamically consistent way obtain corresponding...
The low-energy, electron-stimulated desorption (ESD) of molecular products from amorphous solid water (ASW) films capped with methanol is investigated versus coverage (0–4×1015 cm−2) at 50 K using 100 eV incident electrons. major ESD a monolayer (ML) on ASW are quite similar to the bulk film: H2, CH4, H2O, C2H6, CO, CH2O, and CH3OH. For 40 ML films, oxygen, hydrogen, yields suppressed increasing coverage, while CH3OH yield increases proportionally coverage. suppression by consistent...
Thermal desorption spectroscopy (TDS) is employed to investigate the effects of dilute HNO3 (0−2.2 mol %) on crystallization-induced fracture/morphology changes that occur in nanoscale amorphous solid water (ASW) films. Gas uptake measurements (CClF2H) annealed pure and HNO3-doped films are conducted film morphology/surface area during annealing crystallization. These demonstrate amounts within thin ASW reduce extent fracture crystallization also accelerate
We respond to the Comment by Errandonea et al. [Phys. Rev. B 92, 026101 (2015)] on their reinterpretation of our published data [Nguyen al., Phys. 89, 174109 (2014)]. In original paper, we argued that there is no solid-solid phase transition along Hugoniot at 2.1 Mbars. There is, however, a softening shear modulus starting 2.6 reinterpreted and concluded structural change near 2.3 Mbars Hugoniot. will explore differences agreements in two interpretations data.
In situ x-ray diffraction was performed on shock-generated microjets composed of Sn and Sn–4Ag. Under low pressure drives (∼21 GPa), a significant fraction the jet volume found to be in β-Sn phase, these crystallites were much smaller than initial grain size material. Significant quantities amorphous (molten) material observed for higher drive pressures (∼25–35 GPa). The extent melting at greater would predicted uniaxial shock loading. Diffraction patterns from Sn–4Ag alloy showed peak that...
This article presents a concept and implementation of calibrated streaked spectral pyrometer (SSP) temperature diagnostic used in dynamically driven shock experiments on two-stage gas gun. system relies upon measuring the total response using tunable monochromator, NIST-traceable power meter, SSP. The performance is validated against previously measured temperatures z-cut quartz at 99 GPa 93 GPa. results are found to agree with literature within 5% discussed this manuscript. experimental...
Diagnostic use of single-pulse x-ray diffraction (XRD) at pulsed power facilities can be challenging due to factors such as the high flux and brightness requirements for geometric constraints experimental platforms. By necessity, source is usually positioned very close, within a few inches sample. On dynamic compression platforms, this puts in debris field. We coupled polycapillary optics single-shot needle-and-washer diode using laser-based alignment scheme obtain high-quality single 16 ns...
We use double pass absorption spectroscopy to examine shock induced reactions in situ cyclohexane and benzene at pressures up 33.1 GPa. Reactions begin by 27 GPa complete are observed 12 18 Absorption spectra indicate that the first reaction occurs within or near front, a metastable local equilibrium is reached post-shock state. A second process may be upon reshock lower pressures, suggesting new post-reshock as well. bands consistent with formation of short radicals fragments decomposition;...
The equation of state glow discharge polymer (GDP) was measured to high precision using the two-stage light gas gun at Lawrence Livermore National Laboratory pressures up 70 GPa. Both absolute measurements and impedance matching techniques were used determine principal secondary Hugoniots. GDP likely reacts about 30 GPa, demonstrated by specific emission 450 nm coupled with changes Hugoniot reshock points. As a result these reactions, shock pressure in evolves time, leading possible decrease...