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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 OSTI2015

Exploring Mbar shock conditions and isochorically heated aluminum at the MEC end station of the LCLS

Recent experiments performed at the Matter in Extreme Conditions end station (MEC) of the Linac Coherent Light Source (LCLS) have demonstrated the first spectrally resolved measurements of plasmons from isochorically heated aluminum. The experiments have been performed using a seeded 8-keV x-ray laser beam as a pump and probe to both volumetrically heat and scatter x-rays from aluminum. Collective x-ray Thomson scattering spectra show a well-resolved plasmon feature that is down-shifted in energy by 19 eV. In addition, Mbar shock pressures from laser-compressed aluminum foils using Velocity Interferometer System for Any Reflector (VISAR) have been measured. The combination of experiments fully demonstrates the possibility to perform warm dense matter studies at the LCLS with unprecedented accuracy and precision.

INST, MATSCI, PHYS, XFEL↗
DOE OSTI2015

A high-transparency, micro-patternable chip for X-ray diffraction analysis of microcrystals under native growth conditions

A highly X-ray-transparent, silicon nitride-based device has been designed and fabricated to harvest protein microcrystals for high-resolution X-ray diffraction data collection using microfocus beamlines and XFELs. Microcrystals present a significant impediment to the determination of macromolecular structures by X-ray diffraction methods. Although microfocus synchrotron beamlines and X-ray free-electron lasers (XFELs) can enable the collection of interpretable diffraction data from microcrystals, there is a need for efficient methods of harvesting small volumes (<2 µl) of microcrystals grown under common laboratory formats and delivering them to an X-ray beam source under native growth conditions. One approach that shows promise in overcoming the challenges intrinsic to microcrystal analysis is to pair so-called ‘fixed-target’ sample-delivery devices with microbeam-based X-ray diffraction methods. However, to record weak diffraction patterns it is necessary to fabricate devices from X-ray-transparent materials that minimize background scattering. Presented here is the design of a new micro-diffraction device consisting of three layers fabricated from silicon nitride, photoresist and polyimide film. The chip features low X-ray scattering and X-ray absorption properties, and uses a customizable blend of hydrophobic and hydrophilic surface patterns to help localize microcrystals to defined regions. Microcrystals in their native growth conditions can be loaded into the chips with a standard pipette, allowing data collection at room temperature. Diffraction data collected from hen egg-white lysozyme microcrystals (10–15 µm) loaded into the chips yielded a complete, high-resolution (<1.6 Å) data set sufficient to determine a high-quality structure by molecular replacement. The features of the chip allow the rapid and user-friendly analysis of microcrystals grown under virtually any laboratory format at microfocus synchrotron beamlines and XFELs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Analysis of TID process, geometry, and bias condition dependence in 14-nm FinFETs and implications for RF and SRAM performance

Here, total ionizing dose results are provided, showing the effects of different threshold adjust implant processes and irradiation bias conditions of 14-nm FinFETs. Minimal radiation-induced threshold voltage shift across a variety of transistor types is observed. Off-state leakage current of nMOSFET transistors exhibits a strong gate bias dependence, indicating electrostatic gate control of the sub-fin region and the corresponding parasitic conduction path are the largest concern for radiation hardness in FinFET technology. The high-Vth transistors exhibit the best irradiation performance across all bias conditions, showing a reasonably small change in off-state leakage current and Vth, while the low-Vth transistors exhibit a larger change in off-state leakage current. The “worst-case” bias condition during irradiation for both pull-down and pass-gate nMOSFETs in static random access memory is determined to be the on-state (Vgs = Vdd). We find the nMOSFET pull-down and pass-gate transistors of the SRAM bit-cell show less radiation-induced degradation due to transistor geometry and channel doping differences than the low-Vth transistor. Near-threshold operation is presented as a methodology for reducing radiation-induced increases in off-state device leakage current. In a 14-nm FinFET technology, the modeling indicates devices with high channel stop doping show the most robust response to TID allowing stable operation of ring oscillators and the SRAM bit-cell with minimal shift in critical operating characteristics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2012

Thickness measurements of nanoscale brine films on silica surfaces under geologic CO 2 sequestration conditions using synchrotron X-ray fluorescence

In reservoirs used for geologic CO 2 sequestration, brine films remaining on mineral surfaces can influence flow, diffusion, and reactions. We have examined how the capillary (disjoining) potential influences the thickness of a KCsI 2 brine film on both smooth and rough SiO 2 surfaces [root mean square roughness (Rrms), 1.6 and 330 nm, respectively], under confinement with supercritical (sc) CO2. The thicknesses of brine films coating interior surfaces of SiO 2 windows in a high-pressure cell were determined through synchrotron X-ray fluorescence of two tracer ions (I - and Cs +) at 7.8 MPa and 40°C (representative of conditions at about 0.78 km below the land surface), with scCO 2 as the immiscible confining fluid. The measured area-averaged film thicknesses on the 330 nm Rrms silica surface ranged from 265 to 249 nm for capillary potentials measured within a narrow range from 0.18 to 3.7 kPa. Over this same range of potentials, film thicknesses measured on the smooth (1.6 nm Rrms) silica surface were about 2 nm, although equilibrium does not seem to have been achieved. The measured average brine film thicknesses were critically controlled by surface roughness, with very weak variation in response to the fairly narrow range of tested capillary potentials.

58 GEOSCIENCES↗
DOE OSTI2019

Physical conditions for UO formation in laser-produced uranium plumes

Laser-induced plasma spectroscopy is a powerful method for elemental detection and analysis, however the broadening and merging of densely packed spectral lines can make it especially challenging for studying high-Z elements such as uranium and other actinides. In order to understand the processes occurring in laser-induced plasma, it is necessary to evaluate the variation of its thermodynamic parameters. We performed spatiotemporal diagnostics of uranium species in plasma plumes produced by nanosecond near-infrared laser pulses in low- pressure environment. Spatially- and temporally-resolved emission spectroscopy experiments are supported by modeling of uranium emission and its persistence in the plume. Saha-Eggert equation as well as Boltzmann diagrams generated from numerous U I transitions are used to infer temperature. We report the rst measurements of uranium Stark broadening parameters for U I 499.01 nm and U II 500.82 nm transitions. The Stark widths of selected U transitions were measured by comparing their linewidths with the broadening of O I 777.19 nm line. Electron density was found to be on the order of 1016 cm??3, while the temperature was found to be in the range of 3000{8000 K. In addition to enhancing the fundamental understanding of high-Z plasmas under reduced-pressure environments, the knowledge of Stark broadening parameters could improve modeling capabilities and analytical performance of techniques that rely on emission plasma spectroscopy.

(140.3440) Laser-induced breakdown, (280.4788) Opt↗
DOE OSTI2014

Theoretical Investigation of H₂ Oxidation on the Sr 2 Fe 1.5 Mo 0.5 O 6 (001) Perovskite Surface Under Anodic Solid Oxide Fuel Cell Conditions

Periodic density functional theory (DFT) calculations and microkinetic modeling are used to investigate the electrochemical oxidation of H₂ fuel on the (001) surface of Sr 2 Fe 1.5 Mo 0.5 O 6 (SFMO) perovskite under anodic solid oxide fuel cell conditions. Three surface models with different Fe/Mo ratios in the topmost layer-identified by ab initio thermodynamic analysis-are used to investigate the H₂ oxidation mechanism. A microkinetic analysis that considers the effects of anode bias potential suggests that a higher Mo concentration in the surface increases the activity of the surface toward H₂ oxidation. At operating voltage and anodic SOFC conditions, the model predicts that water desorption is rate-controlling and that stabilizing the oxygen vacancy structure increases the overall rate for H₂ oxidation. Although we find that Mo plays a crucial role in improving catalytic activity of SFMO, under fuel cell operating conditions, the Mo content in the surface layer tends to be very low. On the basis of these results and in agreement with previous experimental observations, a strategy for improving the overall electrochemical performance of SFMO is increasing the Mo content or adding small amounts of an active transition metal, such as Ni, to the surface to lower the oxygen vacancy formation energy of the SFMO surface.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

Enhancing Uranium Uptake by Amidoxime Adsorbent in Seawater: An investigation for optimum alkaline conditioning parameters

A high-surface-area polyethylene-fiber adsorbent (AF160-2) has been developed at the Oak Ridge National Laboratory (ORNL) by radiation-induced graft polymerization of acrylonitrile and itaconic acid. The grafted nitriles were converted to amidoxime groups by treating with hydroxylamine. The amidoximated adsorbents were then conditioned with potassium hydroxide (KOH) by varying different reaction parameters such as KOH concentration (0.2, 0.44, and 0.6 M), duration (1, 2, and 3 h), and temperature (60, 70, and 80 ºC). Adsorbent screening was then performed with simulated seawater solutions containing sodium chloride and sodium bicarbonate, at concentrations found in seawater, and uranium nitrate at a uranium concentration of ~ 7-8 ppm and pH 8. FTIR and solid state NMR indicated that a fraction of amidoxime groups was hydrolyzed to carboxylate during KOH conditioning. The uranium adsorption capacity in the simulated seawater screening solution gradually increased with conditioning time and temperature for all KOH concentrations. It was also observed that the adsorption capacity increased with an increase in concentration of KOH for all the conditioning times and temperatures. AF160-2 adsorbent samples were also tested with natural seawater using flow-through experiments to determine uranium adsorption capacity with varying KOH conditioning time and temperature. Based on uranium loading capacity values of several AF160-2 samples, it was observed that changing KOH conditioning time from 3 to 1 h at 60, 70, and 80 ºC resulted in increase of the uranium loading capacity in seawater, which did not follow the trend found in laboratory screening with stimulated solutions. Longer KOH conditioning times lead to significantly higher uptake of divalent metal ions, such as calcium and magnesium, which is a result of amidoxime conversion into less selective carboxylate. Scanning electron microscopy showed that long conditioning times may also lead to adsorbent degradation

Das, S.↗
DOE OSTI2019

Reference Natural Gas Flames at Nominally Autoignitive Engine-Relevant Conditions

Laminar natural gas flames are investigated at engine-relevant thermochemical conditions where the ignition delay time r is short due to very high ambient temperatures and pressures. At these conditions, it is not possible to measure or calculate well-defined values for the laminar flame speed S-l, laminar flame thickness delta(l), and laminar flame time scale tau(l) = delta(l)/S-l due to the explosive thermochemical state. Here, the corresponding reference values, S-R, delta(R), and tau(R) = S-R/S-R, that account for the effects of autoignition, are numerically estimated to investigate the enhancement of flame propagation, and the competition with autoignition that arises under nominally autoignitive conditions (characterised here by the number tau/tau(R)). Large values of tau/tau(R) indicate that autoignition is unimportant, values near or below unity indicate that flame propagation is not possible, and intermediate values indicate that a combination of both flame propagation and autoignition may be important, depending upon factors such as device geometry, turbulence, stratification, et cetera. The reference quantities are presented for a wide range of temperatures, equivalence ratios, pressures, and hydrogen concentrations, which includes conditions relevant to stationary gas turbine reheat burners and boosted spark ignition engines. It is demonstrated that the transition from flame propagation to autoignition is only dependent on residence time, when the results are non-dimensionalised by the reference values. The temporal evolution of the reference values are also reported for a modelled boosted SI engine. It is shown that the nominally autoignitive conditions enhance flame propagation, which may be an ameliorating factor for the onset of engine knock. The calculations are performed using a recently-developed, detailed 177 species mechanism for C0-C3 chemistry that is derived from theoretical chemistry and is suitable for a wide range of thermochemical conditions as it is not tuned or optimised for a particular operating condition. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

autoignition↗
DOE OSTI2015

Towards understanding KOH conditioning of amidoxime-based oolymer adsorbents for sequestering uranium from seawater

Conditioning of polymer fiber adsorbents grafted with amidoxime and carboxylic acid groups is necessary to make the materials hydrophilic for sequestering uranium from seawater. In this paper, spectroscopic techniques were employed to study the effectiveness of the traditional KOH conditioning method (2.5% KOH at 80⁰C) on recently developed high-surface-area amidoxime-based polymer fiber adsorbents developed at Oak Ridge National Laboratory. FTIR spectra reveal that the KOH conditioning process removes the proton from the carboxylic acids and also converts the amidoxime groups to carboxylate groups in the adsorbent. With prolonged KOH treatment (>1 hr) at 80⁰C, physical damage to the adsorbent material occurs which can lead to a significant reduction in the adsorbent's uranium adsorption capability in real seawater during extended exposure times (>21 days). The physical damage to the adsorbent can be minimized by lowering KOH conditioning temperature. For the high-surface-area amidoxime-based adsorbents, 20 min of conditioning in 2.5% KOH at 80⁰C or 1 hr of conditioning in 2.5% KOH at 60⁰C appears sufficient to achieve de-protonation of the carboxylic acid with minimal harmful effects to the adsorbent material. Lastly, the use of NaOH instead of KOH can also reduce the cost of the base treatment process required for conditioning the amidoxime-based sorbents with minimal loss of adsorption capacity (≤7%).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effects of surface initial condition on aqueous corrosion of glass-A study with a model nuclear waste glass

Being a nonequilibrium material, the structure of glass varies with the sample history. Thus, the initial surface condition of a glass can vary with the preparation condition and have a large impact on its reactivity. This paper shows that the aqueous corrosion behavior of international simple glass (ISG) varies depending on the initial surface state. The ISG glass samples were prepared as-polished-only and polished-then-annealed and they were immersed in aqueous solution saturated with soluble SiO 2 at 30°C (modeling a mild condition) and at 90°C (modeling a severe condition). Molecular dynamics simulations were performed to obtain coordination numbers of network formers of ISG to assist oxygen speciation calculations. The surface structures of as-prepared and corroded ISG samples were analyzed using various imaging and spectroscopic techniques. Among these analyses, only the oxygen speciation with x-ray photoelectron spectroscopy showed discernable differences between two uncorroded surfaces with different preparation histories; all other methods could not differentiate the surface preparation history before aqueous corrosion. Such minor difference in chemical structures was found to have a profound impact on corrosion behaviors in the mild condition. In the harsh condition, the surface history dependence was not as drastic as the corrosion in the mild condition. The analysis results of the corroded surfaces suggested that the thickness and structure of the alteration layer formed on ISG in aqueous corrosion can vary with the initial surface state.

nuclear, defects, corrosion↗
DOE OSTI2012

Monte Carlo Simulations of the Dissolution of Borosilicate Glasses in Near-Equilibrium Conditions

Monte Carlo simulations were performed to investigate the mechanisms of glass dissolution as equilibrium conditions are approached in both static and flow-through conditions. The glasses studied are borosilicate glasses in the compositional range (80-x)% SiO2 (10+x/2)% B2O3 (10+x/2)% Na2O, where 5 < x < 30%. In static conditions, dissolution/condensation reactions lead to the formation, for all compositions studied, of a blocking layer composed of polymerized Si sites with principally 4 connections to nearest Si sites. This layer forms atop the altered glass layer and shows similar composition and density for all glass compositions considered. In flow-through conditions, three main dissolution regimes are observed: at high flow rates, the dissolving glass exhibits a thin alteration layer and congruent dissolution; at low flow rates, a blocking layer is formed as in static conditions but the simulations show that water can occasionally break through the blocking layer causing the corrosion process to resume; and, at intermediate flow rates, the glasses dissolve incongruently with an increasingly deepening altered layer. The simulation results suggest that, in geological disposal environments, small perturbations or slow flows could be enough to prevent the formation of a permanent blocking layer.

borosilicate glasses↗