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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Processing of tungsten through electron beam melting

Additive manufacturing (AM) presents a new design paradigm for the manufacture of engineering materials through the layer-by-layer approach combined with welding theory. In the instance of difficult to process materials such as tungsten and other refractory metals, AM offers an opportunity for radical redesign of critical components for next-generation energy technologies including fusion. In this work, electron beam powder bed fusion (EB-PBF) is applied to process pure tungsten to study the influence of process parameters on the defect density of the material. Here, an in-situ image analysis algorithm is applied to pure tungsten for the first time, and is used to visualize the defect structure in AM tungsten. Finally, a cracking mechanism for AM tungsten is proposed, and suggestions for suppression of cracks in pure tungsten are offered.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Comparison of the photochemical properties of phthalocyanine and hemiporphyrazine Zn(II) complexes

In DMF (dimethylformamide) solutions containing concentrations of (NEt 4 )Br (Et = ethyl) between 0.001 and 0.05 M both zinc phthalocyanine (Pc) and hemiporphyrazine (Hp) complexes are dissolved and form species [Zn(Hp)(Br)] – , and [Zn(Pc)(Br)] – . The increase in formation of the hemiporphyrazine bromide adduct is revealed by a linear dependence of the UV–Vis absorption spectrum on the Br – concentration whereas, over the same concentration range, absorption measurements indicate the formation of the phthalocyanine bromide adduct in solution. The x-ray and molecular structure of [NEt 4 ][Zn(Pc)(Br)](H 2 O) 0.33 has been determined showing the coordination of the Br – to the metal center. Photo-induced processes of the Zn complexes were investigated with deaerated solutions in a time scale t ≥10 ns. The 355 nm flash irradiation of [Zn(Hp)(Br)] – produced transient spectra which showed a bathochromic shift of the absorption maximum from 460 nm to 440 nm and an increase of the spectrum rate of decay with increasing Br – concentrations. The initial spectrum is attributed to the (nπ*–LLCT Br→Hp )[Zn(Hp)(Br)] – excited state which reacts with H-atom donors forming a radical [Zn(Hp-H)(Br)] •– . On the other hand, a transient spectrum, λ max ~600 nm, grows in a time t ≤0.6 µs when [Zn(Pc)(Br)] – is flash irradiated at 355 nm. The photoreactions of these complexes with SCN – and 2-propanol (IPA) were studied. Despite of the apparent similarity between both complexes, IPA was photo-oxidized by both complexes although by different mechanisms, an electron transfer with [Zn(Pc)(Br)] – and an H atom abstraction with [Zn(Hp)(Br)] – . Finally, the photo-oxidation of SCN– by [Zn(Pc)(Br)] – but not by [Zn(Hp)(Br)] – makes a remarkable difference between the photochemistries of these complexes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Internal short circuit and failure mechanisms of lithium-ion pouch cells under mechanical indentation abuse conditions: An experimental study

Electromechanical structural integrity and thermal stability dictate the safety performance of lithium-ion batteries. Progressive deformation and failure across microscopic and macroscopic lengths scales that are responsible for internal short circuit (ISC) in lithium-ion cells under mechanical abuse conditions remains elusive. In this study, a series of indentation tests were conducted on lithium-ion cells with different capacities up to the occurrence of ISC. The external response and internal configuration of these cells were investigated. It is discovered that cells with different capacities and state of charges exhibited different behaviors. Maximum temperature, which is often regarded as the most important parameter related to thermal runaway (TR), varied considerably due to the complicated contact configurations. X-ray computed tomography (XCT) showed that ISC was a collective result of shear band or other strain-localization modes in the electrode assembly, shear offsets in the granular coatings of electrodes, and the accompanying ductile fracture in the metal foils. We believe that the irregular strain-localization modes (kinks, cusps, and buckles), radical mismatches in mechanical properties of different layers, and geometric features of the indenter eventually lead to the tearing/puncture of cell separator at various locations. Furthermore, the results could provide useful guidance for the micromechanical modeling of lithium-ion cells.

25 ENERGY STORAGE↗
DOE OSTI2020

Effects of charged interfaces on electrolyte decomposition at the lithium metal anode

Lithium–Sulfur batteries are promising candidates to substitute conventional Li-ion batteries due to their higher energy density and reduced cost. However, several challenges related to the reactivity of the lithium metal anode have prevented this technology from becoming broadly commercialized. Lithium's high reactive nature leads to the continuous decomposition of the electrolyte and the formation of the solid-electrolyte interphase (SEI) layer. Thus, a comprehensive understanding of how the SEI film is formed is crucial to help elucidate improvements for this battery technology. In this work, we use density functional theory (DFT) based computational methods to investigate the effect of charged interfaces on the electrolyte degradation at the lithium anode. Here, several electrolyte mixtures were considered including 1,2-dimethoxyethane (DME) and 1,3-dioxolane (DOL) as solvents, and lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as salts. It is found that the extent of salt decomposition is higher when the interface is charged. In addition, two types of solvent reduction mechanisms are identified: C–O bond cleavage and radical attacks. Charge transfer and evolution analysis are characterized in detail. Finally, solvent decomposition reactions are found to become more thermodynamically favorable and their activation barriers to be diminished under the effect of constant potentials and electric fields.

25 ENERGY STORAGE↗
DOE OSTI2022

SEI formation mechanisms and Li + dissolution in lithium metal anodes: Impact of the electrolyte composition and the electrolyte-to-anode ratio

The lithium metal battery is one of today's most promising high-energy-density storage devices. Its full-scale implementation depends on solving operational and safety issues intrinsic to the Li metal high reactivity leading to uncontrolled electrolyte decomposition and uneven Li deposition. In this work, we study the spontaneous formation of the solid electrolyte interphase (SEI) upon contact of Li metal with the electrolyte and describe the heterogeneous SEI morphological features. Multiple electrolyte formulations based on lithium bis(fluorosulfonyl)imide (LiFSI), dimethoxyethane (DME), dimethyl carbonate (DMC), 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) and bis(2,2,2-trifluoroethyl) ether (BTFE) are used. Findings include the description of the SEI evolution from dispersed LiO, LiS, LiN, and LiF clusters to a continuous and compact inorganic phase in which the LiO and LiF content depend on the presence of fluorine diluents. Further, the role of the DME ether solvent helping the growth of a “wet-SEI” is compared to that of the highly unstable carbonate DMC, which decomposes into complex radical oligomers that might contribute to further electrolyte decomposition. The impact of the electrolyte-to-anode ratio on LiFSI decomposition is highlighted. Finally, we suggest the existence of a critical LiFSI concentration and electrolyte-to-anode ratio that could potentially balance the rate of electrolyte depletion and lithium consumption.

25 ENERGY STORAGE↗
DOE OSTI2025

Low-lying states and total internal partition sums of CH

The electronic structure and spin-orbit states of the CH radical have been systematically investigated using multi-reference configuration interaction (MRCI) and single-reference coupled-cluster (CC) methods. These calculations were performed in conjunction with large correlation-consistent basis sets of quadruple-, quintuple-, and sextuple-ζ quality. To achieve high accuracy, electronic energies for all states were extrapolated to the complete basis set (CBS) limit, enabling the detailed construction of potential energy curves and determination of reliable spectroscopic constants. Spin-orbit coupling effects were explicitly incorporated, and vibrational energy levels were computed via Numerov analysis. Furthermore, the resulting values exhibit good to excellent agreement with available experimental data. Dipole moment and transition dipole moment curves were evaluated to assess the opacity characteristics of CH, revealing that transitions such as Χ 2 Π (u′′ = 0) → Α 2 Δ (u′ = 0), Χ 2 Π (u′′ = 0) → Β 2 Σ − (u′ = 0), Χ 2 Π (u′′ = 0) → C 2 Σ + (u′ = 0), and Χ 2 Π (u′′ = 0) → D 2 Σ + (u′ = 3) are particularly probable. Finally, the total internal partition function sum (TIPS) of CH was computed over a broad temperature range (10–30,000 K) based on our high-accuracy ab initio results.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Highly tunable structure-by-design polymer brush membranes for organic solvent nanofiltration

Synthetic polymeric nanofiltration membrane processes offer an alternate low-energy option to energy-intensive distillation to fractionate similar size organic solvents for chemical, petroleum, food and biotechnology industries. Here, in this study, we synthesize and test a new class of structure-by-design hydrophilic polymeric brush membranes, that address the limitations of commercial polymer membranes, are tunable and exhibit commercially relevant filtration performance. Because these brush membranes are grafted by Single Electron Transfer-Living Radical Polymerization (SET-LRP) and replace statistically random phase inversion or interfacial polymerization used for synthesizing commercial polymer membranes, their porous structure can be remodeled by varying their morphology and chemistry. We graft hydroxyethyl methacrylate (HEMA) brush structures with short and long crosslinkers, demonstrate two competing phenomena - pore stiffening and opening - and obtain high selectivity at reasonable permeability for commercially relevant methanol/toluene separation. This new class of stable, tunable, and scalable membranes offers exciting opportunities to reduce energy for separation of organic solvents.

42 ENGINEERING↗
DOE OSTI2021

An organic bifunctional redox active material for symmetric aqueous redox flow battery

Symmetric redox flow batteries utilizing a single redox active material as catholyte and anolyte, offer a plausible and unique strategy to alleviate cross-contamination issues during cycling, making them an ideal energy storage device for large scale applications. In this work, a low-cost riboflavin organic molecule is coupled with a 2,2,6,6-Tetramethylpiperidinyl-N-oxyl (TEMPO) radical molecule to form a single Riboflavin-TEMPO (RIBOTEMPO) bifunctional redox active material, which is used in both aqueous anolyte and catholyte. Cyclic voltammetry analysis of the combined molecule displays electrochemically reversible reactions for the redox couples at 0.72 V and 0.51 V versus Hg/Hg2SO4, leading to a theoretical cell voltage of 1.23 V. A symmetric cell testing demonstrated over 100 consecutive charge/discharge cycles with nearly 80% coulombic efficiency and capacity retention of 44.7% at a current density of 2.5 mA cm(-2). By utilizing a pH neutral supporting electrolyte, a lowcost, safe, and environmental-friendly redox flow battery is achieved. This work provides a pathway for the design and development of bifunctional redox active molecules for symmetric battery applications.

25 ENERGY STORAGE↗
DOE OSTI2021

6 MeV novel hybrid (standing wave - traveling wave) photo-cathode electron gun for a THz superradiant FEL

A novel 6 MeV hybrid photo-injector has been designed and constructed, based on a smaller-scale prototype previously built in UCLA’s Particle Beam Physics Laboratory. It has been commissioned at Ariel University in Israel as an on-going collaboration between the two universities. This unique, new generation design provides a radically simpler approach to RF feeding of a gun/buncher system, leading to a much shorter beam via velocity bunching owed to an attached traveling wave section of the photo-injector. This design offers better performance in beam parameters, providing a high quality electron beam, with energy of 6 MeV. The hybrid photo-injector was designed to provide emittance of approximately 3 μm, and pulse duration of 150 fs at up to 1 nC per pulse. The hybrid gun is driven by a SLAC XK5 klystron as the high power RF source, and third harmonic of a ~35 fs IR Laser amplifier (266 nm) to extract electrons from the photo-cathode. The unique electron gun will produce a bunched electron pulse to drive a THz FEL, which will operate at the super-radiant regime, and therefore requires ambitious beam properties. This paper describes the gun and presents experimental results from the gun and its sub-systems, including energy and charge measurements, compared with the design simulations.

150fs↗
DOE OSTI2024

Performance stability of plastics for neutron-gamma pulse shape discrimination

The introduction of the first commercially available plastic scintillators with pulse shape discrimination (PSD) offered by Eljen Technology marked progress towards potentially replacing liquid scintillators in neutron detection. However, use of these plastics over several recent years has revealed an important flaw in these materials: the eventual degradation of scintillation light output and PSD performance. Here, studies described in this paper considered possible reasons for this degradation. Experiments conducted with numerous lab-prepared and commercial EJ-276 samples showed that the main factor affecting the instability is oxidation that involves highly reactive radicals generated during the polymerization process or from the further breakdown of polymer chains under oxygen/air exposure. Based on the obtained results, the stability of scintillation performance for PPO (2,5-Diphenyloxazole)-based PSD plastics has been improved through modifications of the composition via the utilization of scintillation dyes and compounds with antioxidant properties that diminish the effects of oxidation. Elements of these studies were used in the commercial production of the most recent EJ-276D PSD plastic version for fast neutron detection and 6Li-loaded plastics for thermal neutron and antineutrino detection applications. Performance projections of the new PSD plastics indicate a likely degradation of less than 10 % over 5–10 years in comparison to previous EJ-276 that might lose up to 30–40 % of the scintillation light during 1–2 years of storage or deployment under ambient conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A new-old approach to composite scalars with chiral fermion constituents

We develop a dynamical, Lorentz invariant theory of composite scalars in configuration space consisting of chiral fermions, interacting by the perturbative exchange of a massive “gluon” of coupling g 0 and mass M 0 2 (the coloron model). The formalism is inspired by, but goes beyond, old ideas of Yukawa and the Nambu-Jona-Lasinio (NJL) model. It yields a non-pointlike internal wave-function of the bound state, ϕ ( r ) , which satisfies a Schrödinger-Klein-Gordon (SKG) equation with eigenvalue μ 2 . For super-critical coupling, g 0 2 > g 0 c 2 , we have μ 2 < 0 leading to spontaneous symmetry breaking. The binding of chiral fermions is semiclassical, not loop-level as in NJL. The mass scale is determined by the interaction as in NJL. We mainly focus on the short-distance, large M 0 2 limit, yielding an NJL pointlike interaction, but the bound state internal wave-function, ϕ ( r → ) , remains spatially extended and dilutes ϕ ( 0 ) . This leads to power-law suppression of the induced Yukawa and quartic couplings and requires radically less fine-tuning of a hierarchy than does the NJL model. We include a discussion of loop corrections of the theory. A realistic top condensation model appears possible.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Characterizing mineralization on low carbon steel exposed to aerated and degassed synthetic hydraulic fracture fluids

This study investigates the mineralization occurring at the interface between injected hydraulic fracturing fluids and steel production casing during the shut-in period of unconventional shale wells. Mild steel coupons were reacted with synthetic hydraulic fracturing fluids with varying base fluid and dissolved gas concentrations. Experiments were carried out in an autoclave system set at 50 °C and 2000 PSI for 2 and 14 days. Physical and mineralogical changes to the steel coupons’ surface were characterized using an FEI Quanta 600 field emission gun (FEG) scanning electron microscope (SEM) and a PANalytical XPert Pro diffractometer. Barite precipitation occurred ubiquitously during the first 48 hours in all experimental scenarios. Sulfate radicals created from degradation and reduction of ammonium persulfate breakers facilitate barite formation. Concomitant barite and corrosion related precipitates on the sample surfaces suggest iron hydroxy salts act as nucleation sites for mineral scale growth. These results suggest hydraulic fracturing fluids may have deleterious effects on the wellbore before production of the well begins.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at intermediate temperatures

High temperature proton exchange membrane fuel cells are being lately investigated because of their high energy efficiency, their superior heat/water management, CO tolerance, and electrode reaction kinetics. To further advance this technology, the polymer membrane portfolio and performance should be improved for intermediate or high temperature operation (>100 °C). In this work we present new poly(diallylmethylammonium) proton conducting membranes with high ionic conductivity at 120 °C. First, new protic ionic liquids, hereafter called DAMAH + X - , were synthesized leading to diallylmethylammonium monomers with different counter-anions. By radical cyclopolymerization through thermal and photoinitiation mechanisms, self-standing protic polymeric membranes of poly(diallylmethylammonium X - ) were obtained. Membranes showed good thermal stability (>250 °C) and mechanical properties without the need of additives such as (protic) ionic liquids, solvents or inorganic charges. Great attention was paid to understand the effect of the different counter-anions on the membrane properties. As a general trend, fluorinated anions coming from strong acids confer high ionic conductivity and allow to reduce the hygroscopic properties on the protic polymeric membranes. Proton structural and dynamical stability at different temperatures and humidification conditions were investigated by Neutron Scattering (QENS and NR). The optimized poly(diallylmethylammonium X - ) shows similar ionic conductivity values than Nafion 212 under varying relative humidity conditions at 80 °C. Furthermore, it shows a high ionic conductivity value of 1.9 × 10 -3 Scm -1 at 120 °C under dry conditions.

08 HYDROGEN↗
DOE OSTI2024

Functional stimuli-responsive polymers on micro- and nano-patterned interfaces

Micro- and nano-patterned surfaces offer precise control over morphology and chemical composition, enhancing the stability, durability, and functionality of coating materials. When combined with stimuli-responsive polymers, these surfaces gain dynamic adaptability, enabling reversible binding, reusable sensing, and selective molecular capture. Furthermore, while recent review articles have explored various aspects of stimuli-responsive materials, from hydrogel patterns for bioanalytical applications to shape-morphing hydrogels for soft robotics and sensors, a comprehensive review focused on the integration of smart polymers with micro- or nano-patterned interfaces remains absent. This review addresses key surface patterning techniques, including soft lithography, colloidal lithography, and polymer brush photolithography, as well as advances in surface-initiated polymerization methods, such as surface-initiated controlled radical polymerization (SI-CRP). In addition, we discuss recent progress in integrating stimuli-responsive polymers with patterned surfaces to create advanced, functional materials.

Colloidal lithography↗
DOE OSTI2021

Experimental and computational investigations of ethane and ethylene kinetics with copper oxide particles for Chemical Looping Combustion

In this work, reaction pathways for the oxidation of methane, ethane, and ethylene with CuO was obtained by ReaxFF Molecular Dynamics (MD) simulations between temperatures of 1000 K and 2000 K. Experiments in a fixed-bed flow reactor were preformed with methane, ethane, and ethylene at temperatures ranging from 500 K to 1000 K with time-dependent species measurements from an Electron-Ionization Molecular Beam Mass Spectrometer (MBMS), and species validation with Gas Chromatography (GC) for detection of complete and intermediate combustion products. The MBMS and GC allow for the detection of oxygenated species and larger species produced from radical reformation. The simulation and experiment agree on the production of such species as CH 3 CHO, CH 2 O, CO, and H 2 O, which allow for the creation of simple C1 and C2 reaction pathways, which can be used in kinetic models of C2 species and larger fuels such as biofuels, which inherently depend on C1 and C2 kinetics and reaction pathway. The simulation and experiment disagree on the formation of C 2 H 2 , CH 3 OH, and CO 2 with large amounts of C 2 H 2 being measured in the ethylene oxidation simulations and CH 3 OH being formed in methane oxidation simulations, while neither species were experimentally found. In the case of CO 2 large amounts of CO 2 are rapidly produced in experiments with C2 fuels at 800 K, while little-to-no CO 2 was observed in simulations. This is believed to be resulting from the extremely short timescale of the simulations, preventing total oxidation of the fuel. Here, the differences in products produced between simulation and experiment allow for the potential to modify the ReaxFF potential functions to more accurately model the experimental products of Cu–H–O–C reaction kinetics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Ring Opening in Cycloheptane and Dissociation of 1-Heptene at High Temperatures

Cycloalkanes and alkenes are important components of real fuels but there is little kinetic and mechanistic data on the dissociation of most large cyclic and olefinic molecules at elevated temperatures. We present here the first experimental and theoretical investigation of dissociation of cycloheptane and the initial product from ring opening, 1-heptene. Experiments were performed in a diaphragmless shock tube using laser schlieren densitometry. Pyrolysis of cycloheptane (0.5-4% in Kr) was studied over 1450-2000 K and 30-120 Torr. Experiments with 1-heptene (1-4% in Kr) covered 1200-1650 K and 30-120 Torr. A newly developed chemical kinetic mechanism for pyrolysis of cycloheptane and 1-heptene is presented herein. Simulations are in very good agreement with the experimental measurements. Rate coefficients for the initial ring-opening process in cycloheptane, k 1 , and dissociation of 1-heptene, k 2 , were determined from the experiments. Both k 1 and k 2 are in falloff, and the pressure and temperature dependencies were well reproduced by theoretical calculations allowing extrapolation to conditions beyond the scope of this work. These calculations yielded the following expressions for k 1 and k 2 with the uncertainties estimated as +/- 40% and +/- 50% respectively: k 1 , infinity = 5 . 94 & times; 10 17 exp ( & minus;44 T, 521 ) s & minus;1 and k 2 , infinity = 8 . 86 & times; 10 16 exp ( & minus;35 , 887 T ) s & minus;1 . The results of this study indicate that cycloheptane dissociates similarly to cyclopentane and cyclohexane, i.e. ring-opening via C -C scission to a diradical that rapidly isomerizes to a conjugate 1-alkene. The secondary chemistry is dominated by the dissociation products of the 1-alkenes i.e. allyl and n-alkyl radicals. Furthermore, rates of dissociation of the cycloalkanes are size dependent and k cyclopentane << k cyclohexane < k cycloheptane . (c) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Chemical kinetics↗
DOE OSTI2020

An improved detailed chemical kinetic model for C3-C4 linear and iso-alcohols and their blends with gasoline at engine-relevant conditions

Propanol and butanol isomers have received significant research attention as promising fuel additives or neat biofuels. Robust chemical kinetic models are needed that can provide accurate and efficient predictions of combustion performance across a wide range of engine relevant conditions. Herein, this study seeks to improve the understanding of ignition and combustion behavior of pure C3-C4 linear and iso-alcohols, and their blends with gasoline at engine-relevant conditions. In this work, a kinetic model with improved thermochemistry and reaction kinetics was developed based on recent theoretical calculations of H-atom abstraction and peroxy radical reaction rates. Kinetic model validations are reported, and the current model reproduces the ignition delay times of the C3 and C4 alcohols well. Variations in reactivity over a wide range of temperatures and other operating conditions are also well predicted by the current model. Recent ignition delay time measurements from a rapid compression machine of neat iso-propanol and iso-butanol [Cheng et al., Proc. Combust Inst. (2020)] and blends with a research grade gasoline [Goldsborough et al., Proc. Combust Inst. (2020)] at elevated pressure (20–40 bar) and intermediate temperatures (780–950 K) were used to demonstrate the accuracy of the current kinetic model at conditions relevant to boosted spark-ignition engines. The effects of alcohol blending with gasoline on the autoignition behavior are discussed. The current model captures the suppression of reactivity in the low-temperature and negative-temperature-coefficient (NTC) region when either isopropanol and isobutanol are added to a research grade gasoline. Sensitivity and reaction flux analysis were performed to provide insights into the relevant fuel chemistry of the C3-C4 alcohols.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗