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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Measurements of the reaction e/+/e/-/ yielding gamma-gamma at center-of-mass energies in the range 6.2-7.4 GeV

The cross section for the pair-annihilation reaction e(+)e(-) yields gamma-gamma were measured at center-of-mass energies in the range 6.2-7.4 GeV and at production angles close to 90 deg. The experimental apparatus consisted of two identical spectrometers which were set to view the luminous region at SPEAR-II from opposite directions at an azimuthal angle of 45 deg. In each spectrometer there was a NaI(TI) crystal 20 radiation lengths thick and 30 in. in diameter to measure the gamma-ray energies. Annihilation events were detected by an electronic trigger which required only the observation in coincidence of more than 0.2 GeV in each NaI(TI) crystal within + or - 15 nsec of the crossing beams. The observed rates of pair-annihilation events were found to be in agreement with those expected from quantum electrodynamics (QED) at all the center-of-mass energies used.

Hilger, E.↗
NASA NTRS2005

Reaction Control System Thruster Cracking Consultation: NASA Engineering and Safety Center (NESC) Materials Super Problem Resolution Team (SPRT) Findings

The shuttle orbiter s reaction control system (RCS) primary thruster serial number 120 was found to contain cracks in the counter bores and relief radius after a chamber repair and rejuvenation was performed in April 2004. Relief radius cracking had been observed in the 1970s and 1980s in seven thrusters prior to flight; however, counter bore cracking had never been seen previously in RCS thrusters. Members of the Materials Super Problem Resolution Team (SPRT) of the NASA Engineering and Safety Center (NESC) conducted a detailed review of the relevant literature and of the documentation from the previous RCS thruster failure analyses. It was concluded that the previous failure analyses lacked sufficient documentation to support the conclusions that stress corrosion cracking or hot-salt cracking was the root cause of the thruster cracking and lacked reliable inspection controls to prevent cracked thrusters from entering the fleet. The NESC team identified and performed new materials characterization and mechanical tests. It was determined that the thruster intergranular cracking was due to hydrogen embrittlement and that the cracking was produced during manufacturing as a result of processing the thrusters with fluoride-containing acids. Testing and characterization demonstrated that appreciable environmental crack propagation does not occur after manufacturing.

MacKay, Rebecca A.↗
DOE OSTI2022

Thermonuclear reaction rate of 29 Si(p,γ) 30 P

The thermonuclear rate of the 29 Si(p,γ) 30 P reaction impacts the 29 Si abundance in classical novae. A reliable reaction rate is essential for testing the nova paternity of presolar stardust grains. At present, the fact that no classical nova grains have been unambiguously identified in primitive meteorites among thousands of grains studied is puzzling, considering that classical novae are expected to be prolific producers of dust grains. We investigated the 29 Si + p reaction at center-of-mass energies of 200–420 keV, and present improved values for resonance energies, level excitation energies, resonance strengths, and branching ratios. One new resonance was found at a center-of-mass energy of 303 keV. For an expected resonance at 215 keV, an experimental upper limit could be determined for the strength. We evaluated the level structure near the proton threshold, and present new reaction rates based on all the available experimental information. Our new reaction rates have much reduced uncertainties compared with previous results at temperatures of T ≥ 140 MK, which are most important for classical nova nucleosynthesis. Furthermore, future experiments to improve the reaction rates at lower temperatures are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRSDate not supplied

Carbothermal Reduction Demonstration: Laser Driven Reaction in a Thermal-Vacuum Environment and Project Status

Introduction: Lunar regolith is approximately 45% oxygen by mass. The majority of the oxygen is bound in silicate minerals. The carbothermal reduction process has been proven to be effective at removing oxygen from lunar regolith simulants [1]. The Carbothermal Reduction Demonstration (CaRD) project aims to increase the Technology Readiness Level (TRL) of a combined solar concentrator and carbothermal reduction systemin order to demonstrate this technology on the lunar surface. The CaRD project is divided into two design cycles, a brass board and prototype. The status of both design cycles will be discussed, as well as concepts for how this technology can be applied to the Artemis program in the future. Brassboard Vacuum Test: For the brassboard demonstration, a 2 kW Nd-YAG laser was used to heat lunar regolith simulant within a carbothermal reactor developed by Sierra Space. The reactor was placed inside of a 15 ft thermal vacuum chamber at the Johnson Space Center. The resulting reaction products were analyzed using both a gas chromotograph and mass spectrometer provided by Kennedy Space Center. Thermal data was also collected. Prototype Design: For the prototype, the CaRD team will perform another thermal vacuum test at JSC using the same interfaces and assets developed for the brassboard but will test a new carbothermal reactor design that Sierra Space is developing through the Carbothermal Oxygen Production Reactor (COPR) Tipping Point project that will include a means to autonomously move regolith in and out of the reactor. In addition, a deployable solar concentrator is being developed by Glenn Research Center using mirrors produced by Carbon Mirror Applications. The solar concentrator will be used to deliver solar energy into a carbothermal reactor to melt regolith and extract oxygen. Avionics and software for the concentrator are being developed by Kennedy Space Center. Future Concepts: An ongoing task within the CaRD project is to update models that can be used to determine the mass, power, and size of In-Situ Resource Utilization concepts at various scales. These models can now be used to analyze alternatives for future applications based on the latest available data.

A J Paz↗
NASA NTRS2014

NASA Engineering and Safety Center Technical Bulletin No. 14-02: Aerodynamic Reaction Control System (RCS) Orientation and Jet Interaction (JI) Model Validation

Careful consideration should be given to placement and orientation of RCS jet thrusters on hypersonic entry vehicles in order to minimize adverse RCS JI. Modern state-of-the-art computational fluid dynamics (CFD) tools should be able to predict the RCS effectiveness and JI accurately when coupled with verification and validation studies, including the use of appropriately designed experimental wind tunnel testing.

Aerodynamic Reaction Control System↗
DOE OSTI2024

Finding a common ground for RCM experiments. Part B: Benchmark study on ethanol ignition

Rapid compression machines (RCMs) are widely used to investigate gas phase reaction kinetics of various kind of fuels at application relevant conditions. In principle, the operation of an RCM is based on the idea of compressing a homogenous pre-mixed fuel-air mixture by a piston. Usually creviced pistons ensure a homogenous adiabatic core in the center of the reaction chamber which permits the assumption of an isentropic relation between the measured pressure and gas temperature. Despite the ideal core gas compression, non-ideal effects such as heat loss, differences in the compression behavior, and ultimately non-standardized design and operation of rapid compression machines lead to different experimental results in different facilities at nominally the same end of compression conditions. In this study ignition delay times of ethanol are investigated at four different conditions in five independent RCMs. As expected, the raw results of the different facilities indeed show notable differences at the same end of compression conditions. However, according to the adiabatic core hypothesis the agreement between kinetic simulations and experiments should be consistent for all facilities provided that the facility effects are correctly accounted for. To elaborate upon this hypothesis, a kinetic mechanism is optimized to reflect the experimental results of all facilities. In the end, the optimized mechanism predicts all experimental data within the expected uncertainty. This confirms the reliability of RCM experiments for kinetic investigations and the validity of the effective volume approach in simulating RCM data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Effects of surface species and homogeneous reactions on rates and selectivity in ethane oxidation on oxide catalysts

Selective alkane oxidations on metal oxide catalysts involve complex mechanisms with multiple reactions in series and parallel, different types of reduced and oxidized surface species, and potential contributions from gas-phase reactions. We report kinetics and thermodynamics of elementary steps involved in C 2 H 6 -O 2 reactions on SiO 2 -supported small vanadium oxide domains are determined using density functional theory. These surface reactions together with gas-phase mechanisms are incorporated in kinetic simulations to determine how surface and gaseous reactions interact and contribute to rates and selectivity. The results show that gas-phase reactions within pore volumes in contact with the catalyst contribute significantly to C 2 H 6 activation rates, even at conditions where gas-phase reactions in empty volumes without catalyst are negligible. The majority of C 2 H 6 activations occur on the surface, via H abstraction by vanadium oxo species present at terminal lattice oxygens. The gas-phase activations via H-abstraction by OH radicals also exhibit significant contributions. The reduced centers formed by reactions at vanadium oxo species are re-oxidized rapidly and, therefore, are present in very small concentrations at reaction conditions. The re-oxidation steps lead to the formation of HO 2 radicals and surface peroxo species that are also rapidly consumed and are present in small concentrations. The peroxo species preferentially convert C 2 H 4 to its epoxide product and influence selectivity even at low concentrations. The gas-phase reactions decrease the concentrations of peroxo species and improve selectivity slightly. The effects of reaction conditions and catalyst site density provide further insights into how factors beyond conversions at lattice oxygens influence rates and selectivity in alkane oxidation reactions of significant industrial importance.

42 ENGINEERING↗
DOE OSTI2022

How Bayesian methods can improve R -matrix analyses of data: The example of the d t reaction

The 3 H(d, n) 4 He reaction is of significant interest in nuclear astrophysics and nuclear applications. It is an important, early step in big-bang nucleosynthesis and a key process in nuclear fusion reactors. We use one- and two-level R-matrix approximations to analyze data on the cross section for this reaction at center-of-mass energies below 215 keV. We critically examine the data sets using a Bayesian statistical model that allows for both common-mode and additional point-to-point un- certainties. We use Markov Chain Monte Carlo sampling to evaluate this R-matrix-plus-statistical model and find two-level R-matrix results that are stable with respect to variations in the channel radii. The S factor at 40 keV evaluates to 25.36(19) MeV b (68% credibility interval). We discuss our Bayesian analysis in detail and provide guidance for future applications of Bayesian methods to R-matrix analyses. We also discuss possible paths to further reduction of the S-factor uncertainty.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Hydrosilane σ‐Adduct Intermediates in an Adaptive Zinc‐Catalyzed Cross‐dehydrocoupling of Si−H and O−H Bonds

Abstract Three‐coordinate Ph BOX ZnR ( Ph BOX =phenyl‐(4,4‐dimethyl‐oxazolinato; R=Me: 2 a , Et: 2 b ) catalyzes the dehydrocoupling of primary or secondary silanes and alcohols to give silyl ethers and hydrogen, with high turnover numbers (TON; up to 10 7 ) under solvent‐free conditions. Primary and secondary silanes react with small, medium, and large alcohols to give various degrees of substitution, from mono‐ to tri‐alkoxylation, whereas tri‐substituted silanes do not react with MeOH under these conditions. The effect of coordinative unsaturation on the behavior of the Zn catalyst is revealed through a dramatic variation of both rate law and experimental rate constants, which depend on the concentrations of both the alcohol and hydrosilane reactants. That is, the catalyst adapts its mechanism to access the most facile and efficient conversion. In particular, either alcohol or hydrosilane binds to the open coordination site on the Ph BOX ZnOR catalyst to form a Ph BOX ZnOR(HOR) complex under one set of conditions or an unprecedented σ‐adduct Ph BOX ZnOR(H−SiR′ 3 ) under other conditions. Saturation kinetics provide evidence for the latter species, in support of the hypothesis that σ‐bond metathesis reactions involving four‐centered electrocyclic 2σ–2σ transition states are preceded by σ‐adducts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

A broad specificity β-propeller enzyme from Rhodopseudomonas palustris that hydrolyzes many lactones including γ-valerolactone

Lactones are prevalent in biological and industrial settings, yet there is a lack of information regarding enzymes used to metabolize these compounds. One compound, γ-valerolactone (GVL), is used as a solvent to dissolve plant cell walls into sugars and aromatic molecules for subsequent microbial conversion to fuels and chemicals. Despite the promise of GVL as a renewable solvent for biomass deconstruction, residual GVL can be toxic to microbial fermentation. Here, we identified a Ca 2+ -dependent enzyme from Rhodopseudomonas palustris (Rpa3624) and showed that it can hydrolyze aliphatic and aromatic lactones and esters, including GVL. Maximum-likelihood phylogenetic analysis of other related lactonases with experimentally determined substrate preferences shows that Rpa3624 separates by sequence motifs into a subclade with preference for hydrophobic substrates. Additionally, we solved crystal structures of this β-propeller enzyme separately with either phosphate, an inhibitor, or a mixture of GVL and products to define an active site where calcium-bound water and calcium-bound aspartic and glutamic acid residues make close contact with substrate and product. Our kinetic characterization of WT and mutant enzymes combined with structural insights inform a reaction mechanism that centers around activation of a calcium-bound water molecule promoted by general base catalysis and close contacts with substrate and a potential intermediate. Similarity of Rpa3624 with other β-propeller lactonases suggests this mechanism may be relevant for other members of this emerging class of versatile catalysts.

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

Computational Study of an Iron(II) Polypyridine Electrocatalyst for CO 2 Reduction: Key Roles for Intramolecular Interactions in CO 2 Binding and Proton Transfer

A solar-driven conversion of CO 2 into fuels by artificial photosynthesis would not only mitigate the greenhouse effect but also provide an alternative to obtain fuels in a renewable fashion. To this end, the new iron polypyridine catalyst [Fe(bpy NHEt PY2Me)L 2 ] 2+ (L = H 2 O, CH 3 CN) was recently developed for the electrochemical reduction of CO 2 to CO. Here, we performed density functional theory (DFT) electronic structure calculations to shed light on a possible pathway for CO 2 reduction and the origin of the selectivity between CO 2 reduction versus the hydrogen evolution reaction. The metal center remains Lewis acidic throughout the reduction process due to ligand loss and mainly ligand-based reduction stabilized by antiferromagnetic coupling to a high-spin Fe(II) center. This results in a high barrier for hydride formation but a facile addition and activation of CO 2 via an η 2 coordination and stabilizing hydrogen bonding by the amine group. The second unoccupied equatorial coordination site opens up the possibility for an intramolecular protonation with a coordinated water ligand. This facilitates protonation because not only CO 2 but also the proton source H 2 O is activated and properly aligned for a proton transfer due to the Fe-OH 2 bond; consequently, both protonation steps are facile. The moderate ligand field allows a rapid ligand exchange for a second intramolecular protonation step and facilitates an exergonic CO release. The lower selectivity of the related [Fe(bpy OH PY2Me)L 2 ] 2+ complex can be related to its more acidic second coordination sphere, which enables an intramolecular proton transfer that is kinetically competitive with CO 2 addition.

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

A Covalent Organic Framework for Fast-Charge and Durable Rechargeable Mg Storage

High safety, low cost and high volumetric capacity rechargeable magnesium batteries (RMBs) are promising alternatives to lithium ion batteries. However, lack of high power, high energy and stable cathodes for RMBs hinders their commercialization. Herein, an environmentally benign, low cost and sustainable covalent organic framework (COF) cathode for Mg storage is reported for the first time. It delivers a high power density of 2.8 kW kg -1 , a high specific energy density of 146 Wh kg -1 , and ultra-long cycle life of 3000 cycles with very slow capacity decay rate of 0.0196% per cycle, representing one of the best cathodes to date. The comprehensive electrochemical analysis proves that triazine ring sites in COF are redox centers for reversible reaction with magnesium ions, and the ultra-fast reaction kinetic is mainly attributed to pseudocapacitive behavior. The high-rate Mg storage of COF offers new opportunities for the development of ultra-stable and fast charge RMBs.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Formation Mechanism of Flower-like Polyacrylonitrile Particles

Flower-like polyacrylonitrile (PAN) particles have shown promising performance for numerous applications, including sensors, catalysis, and energy storage. However, the detailed formation process of these unique structures during polymerization has not been investigated. Here, we elucidate the formation process of flower-like PAN particles through a series of in situ and ex situ experiments. We have the following key findings. First, lamellar petals within the flower-like particles were predominantly orthorhombic PAN crystals. Second, branching of the lamellae during the particle formation arose from PAN's fast nucleation and growth on pre-existing PAN crystals, which was driven by the poor solubility of PAN in the reaction solvent. Third, the particles were formed to maintain a constant center-to-center distance during the reaction. The separation distance was attributed to strong electrostatic repulsion, which resulted in the final particles' spherical shape and uniform size. Lastly, we employed the understanding of the formation mechanism to tune the PAN particles' morphology using several experimental parameters including incorporating comonomers, changing temperature, adding nucleation seeds, and adjusting the monomer concentration. Here these findings provide important insights into the bottom-up design of advanced nanostructured PAN-based materials and controlled polymer nanostructure self-assemblies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Impact of Changes in ENDF/B-VII.1 and ENDF/B-VIII.0 235U Nuclear Data Indicated by NDSE Studies on LLNL Pulsed Sphere Simulations

A recent journal article by J.A. Gomez et al. measured gamma-ray die-off curves of three subcritical static highly-enriched uranium (HEU) assemblies driven by an external neutron source with a new detector system. This new detector system was developed for being used in dynamically driven subcritical assemblies as part of the Neutron Diagnosed Subcritical Experiments (NDSE) program. Simulations of these die-off curves with various nuclear data and comparison to experimental data indicated that a decrease of the ENDF/B-VII.1 235 U(n,inl) cross section by a factor 0.8 and 0.85 for ENDF/B-VIII.0 would lead to better predictions of experimental data. Here, we test the proposed changes with another type of measurement response, namely neutron-leakage spectra emitted in LLNL pulsed sphere measurements. These spheres were pulsed by 14-MeV neutrons produced via the D+T reaction in their center. The proposed changes in nuclear data have a distinctly smaller impact on predicting pulsed-sphere neutron-leakage spectra than for the die-off curves; they lead to a worsened prediction of the inelastic valley of LLNL pulsed-sphere neutron spectra indicating that the proposed change could constitute a compensating error. Changes in the inelastic angular distributions along with the cross section might be worthwhile to study

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Biodegradable transient battery built on core-double-shell zinc microparticle networks

A transient or biodegradable battery is provided having a filament structure that limits the speed of reaction allowing for a longer duration of battery power with a controlled current limit. In one embodiment, the filament may be constructed of zinc microparticles or nanoparticles having a thin outer insulation whereby a chemical reaction at the center core results in the progressive disintegration of the insulation revealing more core material. In one embodiment, microparticles or nanoparticles are coated with outer layers of chitosan and Al2O3 nanofilms, respectively, with designable discharge current and battery lifespan by controlling the exposed cross-sectional area of the zinc microparticle center core and the length of the filament, respectively. This novel structure of biodegradable battery provides improved control of battery life and power output, providing a promising solution to power transient medical implants.

Wang, Xudong↗
DOE OSTI2023

Going around the Kok cycle of the water oxidation reaction with femtosecond X-ray crystallography

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO 2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn 4 Ca complex (Mn 4 CaO 5 ) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of O X from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn 4 Ca cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Nature of Zirconia on a Copper Inverse Catalyst Under CO 2 Hydrogenation Conditions

The growing concern over the escalating levels of anthropogenic CO 2 emissions necessitates effective strategies for its conversion to valuable chemicals and fuels. In this research, we embark on a comprehensive investigation of the nature of zirconia on a copper inverse catalyst under the conditions of CO 2 hydrogenation to methanol. We employ density functional theory calculations in combination with the Grand Canonical Basin Hopping method, enabling an exploration of the free energy surface including a variable amount of adsorbates within the relevant reaction conditions. Our focus centers on a model three-atom Zr cluster on a Cu(111) surface decorated with various OH, O, and formate ligands, noted Zr 3 O x (OH) y (HCOO) z /Cu(111), revealing major changes in the active site induced by various reaction parameters such as the gas pressure, temperature, conversion levels, and CO 2 /H 2 feed ratios. Further, through our analysis, we have unveiled insights into the dynamic behavior of the catalyst. Specifically, under reaction conditions, we observe a large number of composition and structures with similar free energy for the catalyst, with respect to changing the type, number, and binding sites of adsorbates, suggesting that the active site should be regarded as a statistical ensemble of diverse structures that interconvert.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗