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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 91 records · Page 5

Galacti chemical evolution: Hygrogen through zinc

Using the output from a grid of 60 Type II supernova models (Woosley & Weaver 1995) of varying mass (11 approx. less than (M/solar mass) approx. less than 40) and metallicity (0, 10(exp -4), 0.01, and 1 solar metallicity), the chemical evolution of 76 stable isotopes, from hydrogen to zinc, is calculated. The chemical evolution calculation employs a simple dynamical model for the Galaxy (infall with a 4 Gyr e-folding timescale onto a exponential dsk and 1/r(exp 2) bulge), and standard evolution parameters, such as a Salpeter initial mass function and a quadratic Schmidt star formation rate. The theoretical results are compared in detail with observed stellar abundances in stars with metallicities in the range -3.0 approx. less than (Fe/H) approx. less than 0.0 dex. While our discussion focuses on the solar neighborhood where there are the most observations, the supernova rates, an intrinsically Galactic quality, are also discussed.

Timmes, F. X.↗

A window on the composition of the early solar nebula: 2014MU69, Pluto, and Phoebe

The initial chemical composition of any solar nebula will depend upon the degree to which 1) organic and ice components form on dust grains, 2) organic and molecular species form in the gas phase, 3) organics and ices are exchanged between the gas and solid state, and 4) the precursor and newly formed (more complex) materials survive and are modified in the developing planetary system. Infrared and radio observations of star-forming regions reveal that complex chemistry occurs on icy grains, sometimes before stars even form. Additional processing, through the protosolar disk and within the solar nebula further modifies most, but probably not all, of the initial materials. In fact, the modern Solar System still carries a fraction of its interstellar inheritance [Alexander et al., 2017]. Here we focus on three examples of small bodies in our Solar System, each containing chemical and dynamical clues to its origin and evolution: the small, cold-classical Kuiper Belt object (KBO) 2014MU69 , Pluto and Saturn’s moon, Phoebe. The New Horizons flyby of 2014 MU69 has given the first view of an unaltered body composed of material originally in the solar nebula at ~45 AU. The spectrum reveals methanol ice (not commonly found), a possible detection of water ice (Stern et al. 2019). Pluto’s internal and surface inventory of volatiles and complex organics, together with active geological processes including cryo-volcanism, indicate a surprising level of activity on a body in the outermost region of the Solar System, and the fluid that emerges from subsurface reservoirs may contain material inherited from the solar nebula (Cruikshank et al. 2019). Meanwhile, Saturn's captured moon, Phoebe, carries high D/H in H2O [Clark et al. 2018)], and complex organics (Cruikshank et al. 2008), both consistent with its formation in, and inheritance from, the outer solar nebula. Together, these objects provide windows on the origin and evolution of our Solar System and constraints to be considered in future chemical and physical models of PPDs. The Spitzer Space telescope discovered the ring of dust around Saturn that emanated from the bombardment of Phoebe in the recent past, dislodging primitive Solar System material from deep within that satellite. In addition, Spitzer has provided detailed studies of the chemistry of star forming regions where methanol and other ices are readily observed. As a result of these and other observations, protoplanetary disk models are beginning to combine both dynamical and chemical complexities into their codes, resulting in new insights for exoplanetary systems.

Yvonne J. Pendleton↗

Numerical study of the transient flow in the driven tube and the nozzle section of a shock tunnel

The initial flow in a shock tunnel was examined numerically using computational fluid dynamics (CFD). A finite-volume total variation diminishing (TVD) scheme was used to calculate the transient flow in a shock tunnel. Both viscous and inviscid, chemically nonreacting flows were studied. The study consisted of two parts, the first dealt with the transient flow in the driven-tube/nozzle interface region (inviscid calculations). The effects of varying the geometry in this region was examined. The second part of the study examined the transient flow in the nozzle (viscous calculations). The results were compared to experimental data.

Tokarcik-Polsky, Susan↗

Size-dependent femtosecond proton transfer in protonated methanol clusters

Methanol clusters (CH 3 OH) n are prototypical hydrogen-bonded systems that bridge isolated molecules and bulk liquid methanol. Strong-field ionization of these clusters can trigger ultrafast charge migration, proton transfer, and isomerization; however, the onset timescales of these pathways remain largely unexplored despite extensive steady-state mass-spectrometric evidence for protonation and chemical rearrangement. Here we use femtosecond time-resolved strong-field ionization and disruptive probing to directly track the early-time dynamics of methanol clusters. Transient mass spectra yield size-dependent timescales for the formation of protonated clusters H + (CH 3 OH) n (n = 1–3) and an associated CHO˙ + radical cation. We find that both proton-transfer and subsequent stabilization become markedly faster with increasing cluster size. These measurements establish methanol clusters as a complementary benchmark to water for understanding ionization-initiated proton motion and chemical reorganization in hydrogen-bonded liquids.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Air Carbon for Algae Production (AirCAP) – Expanding algae resource potential via direct (in-pond) air-CO2 capture.

Microalgae biofuel production potential in the United States is constrained by a lack of suitable cultivation locations within a close proximity to CO2 point-sources. Initial estimates suggest that removing the requirement of a concentrated CO2 source expands resource potential ten-fold, allowing the projection of production levels that approach levels of current U.S. diesel consumption. Decoupling cultivation locations from concentrated CO2 point-sources requires direct capture of air-CO2 into the pond bulk at a rate sufficient to meet maximum expected carbon assimilation rates (10 g C/m2-day and higher). Enhancement of the ingassing rate via chemical reaction, the direct reaction of dissolved CO2 with hydroxide ions, has been proposed as a mechanism to increase the ingassing rate of air-CO2. The central objectives of this project are to validate whether chemically enhanced air-CO2 ingassing rates in large raceway ponds can meet or exceed the level required to support high levels of algae productivity, then subsequently identify alkaliphilic strains able to withstand such conditions while maintaining a biomass productivity that enables process economics. Full scale ponds (~1 acre, unlined) will be used to validate ingassing rates as a function of pH expected at scale in a series of abiotic experiments. To date, mass-transfer dynamics have been characterized in ponds ranging from 1 to 1,000 m2. Initial results will be presented describing the mass transfer coefficient in 1-acre (~4,000 m2), unlined ponds. The maximum expected carbon ingassing rate will be measured during ingassing trials, in which pond pH is displaced from equilibrium via the addition of a strong base, with the subsequent decrease in pH (and increase in dissolved inorganic carbon) corresponding to the air-CO2 absorption rate. A mass-transfer model, validated with experimental results, will be used to project ingassing rates expected at pond scales (10 acres) required for production of commodity chemicals.

09 BIOMASS FUELS↗

Visualizing Crystallization Dynamics and Transformation Pathways of Disordered Rocksalt Oxides During Thermally Activated Sol–Gel Synthesis

Sol–gel synthesis is a wet-chemical processing route for fabricating functional materials with control over composition and microstructure at relatively low temperatures compared to conventional solid-state synthesis. While sol–gel process initiates with intermixed molecular precursors, the early-stage nucleation pathways are insufficiently understood. Here, in this study, the chemical and structural transformation of ion disordered rocksalt (DRX) Li 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO), a promising cathode material for lithium batteries, is studied by multiscale characterizations. In situ heating transmission electron microscopy (TEM) using a liquid cell visualizes and identifies crystallization pathways at the nanoscale. While some regions follow a classical multi-step transition through thermodynamically stable intermediates, others exhibit a kinetic shortcut via a localized amorphous matrix to directly form the DRX structure. Macroscale Fourier transform infrared spectroscopy corroborates the findings and reveals that transition metal ions are more strongly incorporated into the acetate-coordinated network than lithium. Although in situ heating TEM captures diverse local transformation pathways, in situ synchrotron X-ray diffraction indicates that the macroscopic transformation proceeds predominantly through spinel LMTO and lithium titanates toward DRX-LMTO. The findings uncover the spatiotemporal chemical and structural transformations in sol–gel derived DRX-LMTO materials, and call for fine-tuning of such sol–gel chemistries to manipulate the crystallization pathways and achieve target material homogeneity more efficiently.

cathode material↗

An Atmospheric General Circulation Model with Chemistry for the CRAY T3E: Design, Performance Optimization and Coupling to an Ocean Model

The design, implementation and performance optimization on the CRAY T3E of an atmospheric general circulation model (AGCM) which includes the transport of, and chemical reactions among, an arbitrary number of constituents is reviewed. The parallel implementation is based on a two-dimensional (longitude and latitude) data domain decomposition. Initial optimization efforts centered on minimizing the impact of substantial static and weakly-dynamic load imbalances among processors through load redistribution schemes. Recent optimization efforts have centered on single-node optimization. Strategies employed include loop unrolling, both manually and through the compiler, the use of an optimized assembler-code library for special function calls, and restructuring of parts of the code to improve data locality. Data exchanges and synchronizations involved in coupling different data-distributed models can account for a significant fraction of the running time. Therefore, the required scattering and gathering of data must be optimized. In systems such as the T3E, there is much more aggregate bandwidth in the total system than in any particular processor. This suggests a distributed design. The design and implementation of a such distributed 'Data Broker' as a means to efficiently couple the components of our climate system model is described.

Farrara, John D.↗

Quantum Dynamics Scattering Study of AB+CDE Reactions: A Seven Dimensional Treatment for the H2+C2H Reaction

A time-dependent wave-packet approach is presented for the quantum dynamics study of the AB+CDE reaction system for zero total angular momentum. A seven-degree-of-freedom calculation is employed to study the chemical reaction of H2+C2H yields H + C2H2 by treating C2H as a linear molecule. Initial state selected reaction probabilities are presented for various initial ro-vibrational states. This study shows that vibrational excitation of H2 enhances the reaction probability, whereas the excitation of C2H has only a small effect on the reactivity. An integral cross section is also reported for the initial ground states of H2 and C2H. The theoretical and experimental results agree with each other very well when the calculated seven dimensional results are adjusted to account for the lower transition state barrier heights found in recent ab initio calculations.

Wang, Dunyou↗

Tuning Organic Electrochemical Transistor Threshold Voltage using Chemically Doped Polymer Gates

Organic electrochemical transistors (OECTs) have shown promise as transducers and amplifiers of minute electronic potentials due to their large transconductances. Tuning the OECT threshold voltage is important to achieve low-powered devices with amplification properties within the desired operational voltage range. However, traditional design approaches have struggled to decouple channel and materials properties from threshold voltage, thereby compromising on several other OECT performance metrics, such as electrochemical stability, transconductance, and dynamic range. In this work, simple solution-processing methods are utilized to chemically dope polymer gate electrodes, thereby controlling their work function, which in turn tunes the operation voltage range of the OECTs without perturbing their channel properties. Chemical doping of initially air-sensitive polymer electrodes further improves their electrochemical stability in ambient conditions. Thus, OECTs that are simultaneously low-powered and electrochemically resistant to oxidative side reactions under ambient conditions are demonstrated. Furthermore, this approach shows that threshold voltage, which is once interwoven with other OECT properties, can in fact be an independent design parameter, expanding the design space of OECTs.

chemical doping↗

Development of MOSCATO: A CFD-Level Electrochemistry and Corrosion Simulator for Molten Salt Systems

For both coolant and fueled variants of molten salt reactors (MSRs), the corrosion of structural materials is a significant challenge. The corrosion stems from chemical and electrochemical reactions initiated by fissile material, fission products, and impurities in the salt. Lower-fidelity models rely on empirical correlations for mass transfer, simplified lumped temperature profiles, and similar assumptions. They do not capture detailed spatial variations in complex geometries, creating the need for high-fidelity modeling to bridge this gap.As we approach the demonstration and possible deployment of MSRs in this decade, the development of a high-fidelity, high-performance simulator becomes imperative. To simulate the complex electrochemical environment and corrosion within molten salt systems, we have developed the Molten Salt Chemistry And TranspOrt (MOSCATO) code. This endeavor is comprised of three essential components. First, mass transfer equations are coupled with the Navier-Stokes equations in order to account for the transport of species in the salt. Second, the diffusion of alloy constituents, such as Cr, Fe, Ni, etc. is simulated within the structural metals. Third, the alloy and salt domains are coupled to account for the heterogeneous chemical and electrochemical reactions that occur at the salt-alloy interface.MOSCATO manages all three components within the framework of the highly scalable, open-source spectral element method computational fluid dynamics code Nek5000/NekRS. This integration enables MOSCATO to harness the immense computational power of modern high-performance computing resources, ensuring both high fidelity and computational speed.In addition to code development, we have initiated a comprehensive verification and validation campaign, utilizing data from diverse sources. First, MOSCATO's electrochemical solver was verified with reference numerical data. Then validation occurred against experiments: one of a thermal galvanic cell and the other for corrosion in flowing molten salt of FLiNaK (LiF-NaF-KF). This campaign verified and validated MOSCATO as a reliable tool for simulating electrochemical environments and corrosion in molten salt systems.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Ultrafast studies of elusive chemical reactions in the gas phase

The chemical composition of the interstellar medium and planetary atmospheres is constantly in flux as atoms and molecules collide and interact with high-energy particles such as electrons, protons, and photons. These transformative processes ultimately lead to the coalescence of molecules and eventually the birth of stars. Our understanding of these chemical ecosystems relies on models that synthesize data from gas-phase experiments, providing insights into reaction cross sections. This Review examines efforts to delve into the fundamental bond-forming and bond-breaking dynamics that occur during bimolecular and electron-initiated reactions. Furthermore, these experiments involve clever approaches to establish a time reference and the collision geometry necessary for tracking atomic motion with femtosecond time resolution. Findings from these efforts enhance present models and improve predictions for molecule-molecule and electron-molecule collisions.

74 ATOMIC AND MOLECULAR PHYSICS↗

A systematic study of lanthanide titanates (A 2 Ti 2 O 7 ) chemical durability: corrosion mechanisms and control parameters

Dense lanthanide titanates ranging from La 2 Ti 2 O 7 to Yb 2 Ti 2 O 7 were synthesized by spark plasma sintering with similar micro-sized microstructure, and their chemical durability and degradation mechanisms were investigated by semi-dynamic leaching tests. Different corrosion mechanisms from incongruent to congruent dissolution were observed with preferential elemental releases of lanthanides in A 2 Ti 2 O 7 (A = La to Gd) and Ti in Er 2 Ti 2 O 7 and Yb 2 Ti 2 O 7 . Initial leaching was controlled by surface dissolution and long-term dissolution shifted to a diffusion-controlled mechanism for titanate pyrochlores from Sm 2 Ti 2 O 7 to Yb 2 Ti 2 O 7 . Both short-term and long-term leaching rates decreased from La 2 Ti 2 O 7 to Yb 2 Ti 2 O 7 , and materials became more corrosion resistant with decreasing ionic radius ratios of the rare-earth elements and titanium. Amorphous passivation films of several nm-thick enriched with Ti formed on the surfaces of the corroded materials, and the formation mechanisms were governed either by surface reorganization with preferential release of lanthanides or dissolution-precipitation from saturated bulk solutions with preferential release of titanium. Finally, these results demonstrate that the ionic size plays a dominant role in determining chemical durability of lanthanide titanates and a strong correlation is established among chemical composition/structural variation, passivation film formation and corrosion mechanisms, and materials chemical durability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Synergistically Chemical and Thermal Coupling between Graphene Oxide and Graphene Fluoride for Enhancing Aluminum Combustion

Metal combustion reaction is highly exothermic and is used in energetic applications, such as propulsion, pyrotechnics, powering micro- and nano-devices, and nanomaterials synthesis. Aluminum (Al) is attracting great interest in those applications because of its high energy density, earth abundance, and low toxicity. Nevertheless, Al combustion is hard to initiate and progresses slowly and incompletely. On the other hand, ultrathin carbon nanomaterials, such as graphene, graphene oxide (GO), and graphene fluoride (GF), can also undergo exothermic reactions. Herein, we demonstrate that the mixture of GO and GF significantly improves the performance of Al combustion as interactions between GO and GF provide heat and radicals to accelerate Al oxidation. Overall, our experiments and reactive molecular dynamics simulation reveal that GO and GF have strong chemical and thermal couplings through radical reactions and heat released from their oxidation reactions. GO facilitates the dissociation of GF, and GF accelerates the disproportionation and oxidation of GO. When the mixture of GO and GF is added to micron-sized Al particles, their synergistic couplings generate reactive oxidative species, such as CF x and CF x O y , and heat, which greatly accelerates Al combustion. This work demonstrates a new area of using synergistic couplings between ultrathin carbon nanomaterials to accelerate metal combustion and potentially oxidation reactions of other materials.

36 MATERIALS SCIENCE↗

Analysis of Nonlinear Shrinkage for the Bound Metal Deposition Manufacturing using Multi-scale Approach

We consider problem of nonlinear shrinkage of the metal part during bound metal deposition manufacturing on the ground and in zero-G. To analyze this problem we developed multi-scale physics-based approach that spans atomistic dynamics at the scale of nanoseconds and the full part shrinkage at the time scale of hours. Using this approach we estimated the key parameters of the problem including grain boundary width, coefficient of surface diffusion, initial redistribution of particles during debinding stage, micro-structure evolution from round particles to densely packed grains and corresponding change of the total and chemical free energy, and sintering stress. The introduced method was used to predict shrinkage at the level of two particles, filament cross-section, sub-model, and the whole green, brown, and metal parts. To further improve accuracy and reliability of the shrinkage predictions we propose concept of intelligent additive manufacturing of metal powders in space that combines the strengths of both physics-based and data-driven methods of analysis of AM.

bound metal deposition↗

Observations and Modeling of Composition of Upper Troposphere/Lower Stratosphere (UTILS): Isentropic Mixing Events and Morphology of HNO3 as Observed by HIRDLS and Comparison with Results from Global Modeling Initiative

isentropic exchange of air masses between the tropical upper troposphere and mid-latitude lowermost stratosphere (the so-called "middle world") is an important pathway for stratospheric-tropospheric exchange. A seasonal, global view of this process has been difficult to obtain, in part due to the lack of the vertical resolution in satellite observations needed to capture the laminar character of these events. Ozone observations at a resolution of about 1 km from the High Resolution Dynamic Limb Sounder (HIRDLS) on NASA's Aura satellite show instances of these intrusions. Such intrusions should also be observable in HN03 observations; however, the abundances of nitric acid could be additionally controlled by chemical processes or incorporation and removal into ice clouds. We present a systematic examination of the HIRDLS data on O3 and HNO3 to determine the seasonal and spatial characteristics of the distribution of isentropic intrusions. At the same time, we compare the observed distributions with those calculated by the Global Modeling Initiative combined tropospheric-stratospheric model, which has a vertical resolution of about I km. This Chemical Transport Model (CTM) is driven by meteorological fields obtained from the GEOS-4 system of NASA/Goddard Global Modeling and Assimilation Office (GMAO), for the Aura time period, at a vertical resolution of about 1 km. Such comparison brings out the successes and limitations of the model in representing isentropic stratospheric-tropospheric exchange, and the different processes controlling HNO3 in the UTAS.

Rodriquez, J. M.↗

Multi-Scale Modelling of the Bound Metal Deposition Manufacturing of Ti6Al4V

Nonlinear shrinkage of the metal part during manufacturing by bound metal deposition, both on the ground and under microgravity, is considered. A multi-scale physics-based approach is developed to address the problem. It spans timescales from atomistic dynamics on the order of nanoseconds to full-part shrinkage on the order of hours. This approach enables estimation of the key parameters of the problem, including the widths of grain boundaries, the coefficient of surface diffusion, the initial redistribution of particles during the debinding stage, the evolution of the microstructure from round particles to densely-packed grains, the corresponding changes in the total and chemical free energies, and the sintering stress. The method has been used to predict shrinkage at the levels of two particles, of the filament cross-section, of the sub-model, and of the whole green, brown, and metal parts.

Nonlinear shrinkage↗

Chemical controls on the propagation and healing of subcritical fractures

Human activities involving subsurface reservoirs—resource extraction, carbon and nuclear waste storage—alter thermal, mechanical, and chemical steady-state conditions in these systems. Because these systems exist at lithostatic pressures, even minor chemical changes can cause chemically assisted deformation. Therefore, understanding how chemical effects control geomechanical properties is critical to optimizing engineering activities. The grand challenge in predicting the effect of chemical processes on mechanical properties lays in the fact that these phenomena take place at molecular scales, while they manifest all the way to reservoir scales. To address this fundamental challenge, we investigated chemical effects on deformation in model and real systems spanning molecular- to centimeter scales. We used theory, experiment, molecular dynamics simulation, and statistical analysis to (1) identify the effect of simple reactions, such as hydrolysis, on molecular structures in interfacial regions of stressed geomaterials; (2) quantify chemical effects on the bulk mechanical properties, fracture and displacement for granular rocks and single crystals; (3) develop initial understanding of universal scaling for individual displacement events in layered geomaterials; and (4) develop analytic approximations for the single-chain mechanical response utilizing asymptotically correct statistical thermodynamic theory. Taken together, these findings advance the challenging field of chemo-mechanics.

36 MATERIALS SCIENCE↗