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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Polymer-Stabilized Liquid Metal Nanoparticles as a Scalable Current Collector Engineering Approach Enabling Lithium Metal Anodes

Dendrites and dead lithium formation over prolonged cycling have long been challenges that hinder the safe implementation of metallic Li anodes. In this study, we employ polymer-stabilized liquid metal nanoparticles (LM-P NPs) of eutectic gallium indium (EGaIn) to create uniform Li nucleation sites enabling homogeneous lithium electrodeposition. Block copolymers of poly(ethylene oxide) and poly(acrylic acid) (PEO-b-PAA) were grafted onto the EGaIn surface, forming stabilized, well-dispersed NPs. Using a scalable spray coating approach, LM-P NPs were fabricated on copper current collectors, providing lithiophilic PEO sites and interactive carboxyl groups to guide Li deposition. The Li-EGaIn alloying process greatly reduced the Li + diffusion barrier, enabling fast Li transport through the coating layer, resulting in decreased nucleation overpotential. Therefore, about five times lower Li nucleation overpotential was obtained on the LM-P modified Cu with an optimal composition of the polymers than the bare Cu substrates. DFT computations was used to reveal the binding properties between the LM-P layer and Li. Due to the regulated Li plating/stripping process, as-obtained 30 μm Li anodes paired with LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM8 11 ) with a negative/positive electrode capacity (N/P) ratio ~ 10 exhibited stable cycling performance at 0.5C for over 250 cycles, with an average Coulombic efficiency of 99.55%. Ultrathin Li (1 μm) anodes with an N/P ratio ~ 0.6 were also demonstrated in Li|LiFePO 4 cells, which examined the stabilization of Li by LM-P NPs and monitored practical loadings of Li anodes that are close to anode-free systems.

25 ENERGY STORAGE↗
DOE OSTI2018

Sinter-Bonding of AISI 316L and 17-4 PH Stainless Steels

The sinter-bonding method was used to produce AISI 316L/17-4 PH components by conventional powder metallurgy technology. The production process consisted of following steps: the powder layering, co-pressing and co-sintering processes. The co-sintering process was carried out at different sintering temperatures (1200, 1250 and 1300 °C), and times (60, 90 and 120 min) in hydrogen atmosphere. The effect of co-pressing and co-sintering conditions on the ability to create a permanent connection between AISI 316L and 17-4 PH stainless steels was investigated. The densification, dimensional change and microstructural evolution of sintered AISI 316L/17-4 PH components were studied. The increase in co-pressing pressure as well as using of the longer time and the higher temperature of co-sintering process contributed to increase in AISI 316L/17-4 PH component density. The dilatometric study as well as dimensional changes measurements revealed an appropriate sintering compatibility for AISI 316L and 17-4PH steels when the sintering process was carried out at the temperature of 1200 °C for time ranging from 60 to 120 min and at 1250 °C for shorter sintering times. The sintering at temperature of 1300 °C (regardless of other manufacturing conditions) led to a significant deviation from the cylindrical shape of samples, as a result of difference of shrinkage of AISI 316L and 17-4 PH steels. Microstructural study indicated that AISI 316L and 17-4 PH steels creates a good diffusion joint (without any cracks and warpage) during the high-temperature sintering process. Nickel diffusion takes place from the AISI 316L to 17-4 PH stainless steel, and copper and molybdenum diffuse in opposite direction of nickel diffusion. It is possible to achieve a solid connection between two materials exhibiting difference in chemical composition by using sinter-bonding and conventional powder metallurgy technology.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Challenges and Recent Developments of Neutron Non-Destructive Assay with UO{sub 2}F{sub 2}-Bearing Materials - 17336

In the enrichment process of an operating Gaseous Diffusion Plant (GDP), such as the Portsmouth and Paducah facilities, UF6 gas will immediately hydrolyze forming the chemical compound UO{sub 2}F{sub 2} (Uranyl Fluoride). This mostly happens in Alumina (Al{sub 2}O{sub 3}) traps where the UF6 adsorbs to moistened Alumina pellets forming a UO{sub 2}F{sub 2} layer around the pellet. Similarly, NaF.UF{sub 6} absorption traps produce the complex Na{sub 2}UF{sub 8} which also hydrolyzes when exposed to moist air. UO{sub 2}F{sub 2} can also be formed in many other processes where UF6 gas comes into contact with moisture within structures and objects such as pipes, converters compressors and coolers. When the structures are refurbished, or designated for D and D, UO{sub 2}F{sub 2}-bearing objects are generated both in situ and ex situ requiring fissile (U-235) characterization. In addition, ex situ waste streams are generated when UO{sub 2}F{sub 2}-bearing materials are placed in drummed or boxed waste containers. Gamma spectroscopy Non-Destructive Assay (NDA) is commonly utilized to characterize UO{sub 2}F{sub 2}-bearing waste but generally has high associated Total Measurement Uncertainties (TMU's) and, in some cases, Data Quality Objectives (DQO's) cannot be met. In addition, high UO{sub 2}F{sub 2} mass loadings, such as hold-up materials, require gamma modeling when infinitely thick to the Uranium energy lines. A common neutron NDA technique, or method, is to exploit the neutrons generated from the F-19(a, n)Na-22 reaction which has an appreciable reaction cross-section. The isotopes of Uranium are a-emitters, and, in particular, U-234 has a significantly higher a-decay reaction cross-section leading to a significant relative neutron Specific Activity (nSA). Neutron NDA is appealing since, in some cases, it has potentially lower TMU's than gamma NDA and neutron detector slabs facilitate surrounding large, complex-shaped, objects. Characterizing UO{sub 2}F{sub 2}-bearing waste for fissile content using neutrons generated from U-234, requires the U-235/U-234 ratio as well as the enrichment as well as the corresponding nSA's. It is also noted that U-238 has a considerable, relative, spontaneous fission nSA and this is a higher concern for low-enrichments where the mass of U-238 dominates. Additional neutron interfering elements include cosmic-ray induced spallation within the objects and background from other, in situ, UO{sub 2}F{sub 2}-bearing objects. In this paper we present the challenges and recently developed hardware and algorithmic strategies for quantifying fissile mass both in situ and ex situ using neutron NDA that works in conjunction to gamma spectroscopy NDA, or process knowledge, for objects and drummed/boxed waste containing UO{sub 2}F{sub 2}-bearing materials leading to minimal TMU's and achievable DQO's. (authors)

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Temperature- and composition-dependent hydrogen diffusivity in palladium from statistically-averaged molecular dynamics

Solid-state hydrogen storage materials undergo complex phase transformations whose kinetics is often limited by hydrogen diffusion. Among metal hydrides, palladium hydride undergoes a diffusional phase transformation upon hydrogen uptake, during which the hydrogen diffusivity varies with hydrogen composition and temperature. Here we perform robust statistically-averaged molecular dynamics simulations to obtain a well-converged analytical expression for hydrogen diffusivity in bulk palladium that is valid throughout all stages of the reaction. Our studies confirm significant dependence of the diffusivity on composition and temperature that elucidate key trends in the available experimental measurements. Whereas at low hydrogen compositions, a single process dominates, at high hydrogen compositions, diffusion is found to exhibit behavior consistent with multiple hopping barriers. Further analysis, supported by nudged elastic band computations, suggests that the multi-barrier diffusion can be interpreted as two distinct mechanisms corresponding to hydrogen-rich and hydrogen-poor local environments.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Prediction of Performance Variation Caused by Manufacturing Tolerances and Defects in Gas Diffusion Electrodes of Phosphoric Acid (PA)–Doped Polybenzimidazole (PBI)-Based High-Temperature Proton Exchange Membrane Fuel Cells

The automated process of coating catalyst layers on gas diffusion electrodes (GDEs) for high-temperature proton exchange membrane fuel cells results inherently into a number of defects. These defects consist of agglomerates in which the platinum sites cannot be accessed by phosphoric acid and which are the consequence of an inconsistent coating, uncoated regions, scratches, knots, blemishes, folds, or attached fine particles—all ranging from μm to mm size. These electrochemically inactive spots cause a reduction of the effective catalyst area per unit volume (cm2/cm3) and determine a drop in fuel cell performance. A computational fluid dynamics (CFD) model is presented that predicts performance variation caused by manufacturing tolerances and defects of the GDE and which enables the creation of a six-sigma product specification for Advent phosphoric acid (PA)-doped polybenzimidazole (PBI)-based membrane electrode assemblies (MEAs). The model was used to predict the total volume of defects that would cause a 10% drop in performance. It was found that a 10% performance drop at the nominal operating regime would be caused by uniformly distributed defects totaling 39% of the catalyst layer volume (~0.5 defects/μm2). The study provides an upper bound for the estimation of the impact of the defect location on performance drop. It was found that the impact on the local current density is higher when the defect is located closer to the interface with the membrane. The local current density decays less than 2% in the presence of an isolated defect, regardless of its location along the active area of the catalyst layer.

Gurau, Vladimir (ORCID:0000000327429061)↗
NASA NTRS1993

Diffusion in liquid state and solidification of binary system (M-7)

Diffusion is one of the most fundamental physical phenomena. It relates to the manufacturing of almost all materials. Therefore, the precise knowledge of diffusivities of relevant materials is necessary for the optimization of these processes. On the other hand, such knowledge is indispensable to understanding the diffusion mechanism and structure of liquid metal in the field of physical metallurgy. Many diffusion experiments on solid metal were undertaken and a lot of data were accumulated. But on liquid metals there are few measurements because of experimental difficulties, such as thermal convection, induced by very slight temperature gradients in the specimen. Under microgravity conditions, the movement of liquid metal due to density differences and thermal convection must be suppressed markedly. Therefore, the transportation process will be controlled only by the diffusion of constituent atoms. These conditions offer the optimum environments for the diffusion experiment. The experiments are briefly described. Diffusion couples are prepared by attaching end to end two rods of different pure metals using hot press equipment. These couples are inserted into a graphite crucible and then doubly enclosed by two silica ampoules, respectively. The specimen is inserted into a tantalum cartridge, which is welded in a vacuum using an electron-beam apparatus. These cartridges are charged in the continuous heating furnace in space and held at a given temperature for a predetermined time and then solidified. The concentration distribution of elements in these specimens will be measured along the rod axis by means of an electron probe microanalyzer. The counterdiffusivity of the liquid metal binary system is determined on the basis of the compensated concentration distribution profile for thermal contraction.

Dan, T.↗
NASA NTRS1997

The Diffuse Interstellar Medium

A major component of this research is to extend existing models of thermal processes in the local interstellar medium to the inner and outer Galaxy. In completing this goal we have calculated the thermal equilibrium gas temperature of the neutral diffuse gas and constructed phase diagrams (gas pressure versus density) for gas at galactic radii between 3 and 18 kpc. An important ingredient in this computation is the far-ultraviolet (FUV) radiation field in the Galactic disk. This radiation is important since photoelectric heating via FUV radiation on dust grains is expected to be a dominant heating process in the diffuse via gas. As a check of our calculated FUV field, we compared the infrared luminosity predicted by our theory with the observations of the COBE DIRBE space satellite and found the two to be in quite good agreement. Using our phase diagrams we have predicted the thermal pressure in the Galactic plane for which a multiphase equilibrium can be maintained. In addition, by using the maximum thermal pressure allowed by the observations, we have constrained the Galactic radii over which both cold and warm gas must exist, may exist, and cannot exist.

Hollenbach, David↗
NASA NTRS1993

Soot formation and radiation in turbulent jet diffusion flames under normal and reduced gravity conditions

Most practical combustion processes, as well as fires and explosions, exhibit some characteristics of turbulent diffusion flames. For hydrocarbon fuels, the presence of soot particles significantly increases the level of radiative heat transfer from flames. In some cases, flame radiation can reach up to 75 percent of the heat release by combustion. Laminar diffusion flame results show that radiation becomes stronger under reduced gravity conditions. Therefore, detailed soot formation and radiation must be included in the flame structure analysis. A study of sooting turbulent diffusion flames under reduced-gravity conditions will not only provide necessary information for such practical issues as spacecraft fire safety, but also develop better understanding of fundamentals for diffusion combustion. In this paper, a summary of the work to date and of future plans is reported.

Ku, Jerry C.↗
NASA NTRS2003

Iron-Nickel Sulfide Compositional Ranges in CM Chondrites: No Simple Plan

Iron-nickel sulfides are found in most or all solar system environments, and are probably the only minerals found in all extraterrestrial materials on hand. Despite this ubiquity, they have only just begun the attention they deserve. The most common Fe-Ni sulfides in chondrites are troilite (FeS), pyrrhotite (Fe(1-x)S) and pentlandite (Fe,Ni)9S8. Troilite is believed to have resulted from sulfidation of metal (Fe-Ni) grains in an H2S-containing environment. Pyrrhotite is produced when friable troilite grains, which are exfoliated from the metal nucleus, are submitted to continued sulfidation. Some asteroids are known to have experienced aqueous alteration, forming products including new generations of sulfides (pyrrhotite and pentlandite). Pentlandite in particular is known to form during such alteration. However, experimental work by Lauretta has indicated that pentlandite may also have been formed during the initial sulfidation process, due to the faster diffusion rate of nickel into the forming sulfide, as compared to iron. Finally, there is considerable evidence for a family of phases intermediate between pyrrhotite and pentlandite, following the trend of the high temperature monosulfide solid solution, something not encountered in terrestrial rocks. Each sulfide has its own particular stability conditions, which have been determined for most phases. The long-term objective of our research is to characterize sulfides in chondritic materials in order to better establish the conditions under which they formed, and the subsequent processes they experienced. Ultimately, it will be possible to infer whether the sulfides in the chondrites were formed in the solar nebula or on asteroids, and if formed on the asteroids, deduce how much alteration has occurred there. Here we explore the relationships between the finest grain size portions of carbonaceous chondrites, these being matrix and chondrule rims; fine-grained materials are the most sensitive to their environment. This abstract is one of a series reporting results for chondrites, earlier work reported results for a much more limited set of CMs, as well as for CVs and CIs.

Zolensky, Michael↗
NASA NTRS1991

Combined energy and pitch angle diffusion of pickup ions at Comet Halley

It is well known that cometary pickup ions, e.g., H2O(+), OH(+), O(+), CO(+), H(+), initially form a ring-beam distribution in the solar wind reference frame, which is highly unstable to the growth of MHD waves (such as ion-cyclotron waves). The low-frequency magnetic fluctuations (or waves), which were observed upstream of Comet Halley, cannot only pitch-angle-scatter the pickup ions so that the distribution becomes at least partially isotropized, but also stochastically accelerate the ions, resulting in the energetic ion populations observed in the vicinity of Comet Halley. Here, numerical solutions of the quasi-linear diffusion equation were used to investigate the cometary ion pickup process at Comet Halley. Both pitch angle and energy diffusion are taken into account. Many quasi-linear models of cometary pickup ions exist which involve one type of diffusion or the other but not both types at once. It is found that the pitch angle scattering occurs faster than the energy diffusion, as expected. Moreover, the results demonstrate that the distribution of accelerated energetic ions is more isotropic than that of ions which have just been picked up. In fact, the ion distribution function on the initial pickup shell is quite anisotropic, even close to the Comet-Halley bow shock.

Ye, Gang↗
NASA NTRS2016

Electron Currents and Heating in the Ion Diffusion Region of Asymmetric Reconnection

In this letter the structure of the ion diffusion region of magnetic reconnection at Earths magnetopause is investigated using the Magnetospheric Multiscale (MMS) spacecraft. The ion diffusion region is characterized by a strong DC electric field, approximately equal to the Hall electric field, intense currents, and electron heating parallel to the background magnetic field. Current structures well below ion spatial scales are resolved, and the electron motion associated with lower hybrid drift waves is shown to contribute significantly to the total current density. The electron heating is shown to be consistent with large-scale parallel electric fields trapping and accelerating electrons, rather than wave-particle interactions. These results show that sub-ion scale processes occur in the ion diffusion region and are important for understanding electron heating and acceleration.

Graham, D. B.↗
NASA NTRS2017

Major Pathways to Electron Distribution Function Formation in Regions of Diffuse Aurora

This paper discusses the major pathways of electron distribution function formation in the region of diffuse aurora. The diffuse aurora accounts for about of 75% of the auroral energy precipitating into the upper atmosphere, and its origin has been the subject of much discussion. We show that an earthward stream of precipitating electrons initially injected from the Earth's plasma sheet via wave-particle interactions degrades in the atmosphere toward lower energies and produces secondary electrons via impact ionization of the neutral atmosphere. These electrons of magnetospheric origin are then reflected back into the magnetosphere along closed dipolar magnetic field lines, leading to a series of reflections and consequent magnetospheric interactions that greatly augment the initially precipitating flux at the upper ionospheric boundary (700-800 km). To date this, systematic magnetosphere-ionosphere coupling element has not been included in auroral research models, and, as we demonstrate in this article, has a dramatic effect (200-300%) on the formation of the precipitating fluxes that result in the diffuse aurora. It is shown that wave-particle interaction processes that drive precipitating fluxes in the region of diffuse aurora from the magnetospheric altitudes are only the first step in the formation of electron precipitation at ionospheric altitudes, and they cannot be separated from the atmospheric collisional machine that redistributes and transfers their energy inside the magnetosphere-ionosphere-atmosphere coupling system.

magnetospheric↗
DOE OSTI2020

Time-Domain Nuclear Magnetic Resonance Determination of Wettability Alteration: Analysis for Low-Salinity Water

Wettability has been shown to influence oil recovery. This property has become central to low-salinity (LSW) and smart (SWF) water flooding recovery mechanisms research. The challenge lies in the fact that oil recovery results from the combined effects of solid-liquid and liquid-liquid interactions. This demands methods that allow an independent interpretation of wettability alteration contributions. The primary objective of this work is to assess changes in wettability through the application of Time-Domain Nuclear Magnetic Resonance (TD-NMR) T 2 distribution and diffusion coefficient, starting with a well-controlled porous system, that is, glass beads, and then a model rock (Berea), in the presence of one phase, either oil or brine exclusively. Subsequently, two-phase fluid saturation was tested. For the glass beads, dimethyldichlorosilane was used to induce a hydrophobic response, as confirmed by contact angle experiments on slides of the same material. Sodium sulfate was used for its known positive influence on oil recovery during LSW and SWF. In cases where alteration of surface properties was expected, a leftward shift of the average T 2 distribution curve modes, accompanied by a reduction on the diffusion coefficient during the aging process was observed. The results of this work confirm that fluid-solid interactions during LSW and SWF, namely a shift in wettability, take place after the injection of low-salinity water.

42 ENGINEERING↗
DOE OSTI2022

On the Importance of Using Event-Specific Wave Diffusion Rates in Modeling Diffuse Electron Precipitation

A few to tens of keV electron precipitation that carries substantial energy source down to the upper atmosphere to create aurora is manifested as an important magnetosphere-ionosphere coupling process. The precipitation is usually caused by scattering processes associated with plasma waves in the magnetosphere. The scattering process is often quantified by wave diffusion rates that indicate how fast an electron is scattered. Global models commonly use diffusion coefficients that are derived from statistical wave models. However, due to the statistical nature, many localized, transient features could be smeared out. In this study, we investigate electron precipitation using event-specific diffusion coefficients that are obtained based on simultaneous in-situ measured/inferred, rather than statistical, chorus wave dynamics. We find that the application of the event-specific diffusion coefficients associated with a more dynamic and intense chorus wave model leads more electrons, particularly at several to tens of keV in the dawn-to-noon sector at L > 3, to precipitate than using statistical coefficients. Here, the new simulation roughly captures both the intensity and variability of the precipitating flux as detected by the NOAA/POES satellites. Ionospheric electron density in the lower E region (100–120 km) observed by the mid-latitude Millstone Hill radar is also much better reproduced, while the case using statistical diffusion coefficients underestimates the ionization rate. This study implies the importance of using event-specific diffusion rates in simulating the diffuse electron precipitation and understanding the magnetosphere-ionosphere coupling.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2018

In Situ Observation of Magnetic Reconnection Between an Earthward Propagating Flux Rope and the Geomagnetic Field

It has been proposed that, in the near-Earth magnetotail, earthward propagating flux ropes can merge with the Earth's dipole magnetic field and dissipate its magnetic energy. However, the reconnection diffusion region related to this process has not been identified. Here we report the first in situ observation of magnetic reconnection between an earthward propagating flux rope and the closed magnetic field lines connecting to Earth. Magnetospheric Multiscale (MMS) spacecraft crossed a vertical current sheet between the leading edge of the flux rope (negative B(sub z)) and the geomagnetic field (positive B(sub z)). The subion-scale current sheet, super-Alfvénic electron outflow, Hall magnetic and electric field, conversion of magnetic energy to plasma energy (J·E > 0), and magnetic null were observed during the crossing. All the above signatures indicate that MMS detected the reconnection diffusion region. This result is also relevant to other planets with intrinsic magnetosphere.

Magnetospheric Multiscale↗
NASA NTRS1974

The abundances of nuclei in the cosmic radiation

The relative abundances are treated as a consequence of processes in cosmic ray transport occurring during passage of the radiation through interstellar material at high velocity. Some of the subjects mentioned are nuclear fragmentation and the production of secondary nuclei, nuclear reactions, energy loss and nuclear decay, ionization, the range-energy relation and propagation variables, capture and loss of electrons, the propagation of nuclei, the transport equation, equilibrium solutions, energy-dependent path length distribution, exponential path length distributions, discrete spectra, sources, supernovae, and the origin of the abundances. The connection between the space-time features of the sources, the material traversed, and the effects of magnetic fields is established by describing the particle-field interaction as a diffusive or random-walk process.

Reames, D. V.↗
NASA NTRS1982

Thermal and nonthermal escape mechanisms for terrestrial bodies

A survey is given of the classical thermal escape (Jeans or blowoff) and some eight nonthermal processes involving ions. Diffusional, energetic, and other limitations on the escape flux are discussed. Isotopic fractionation, due to differences in thermal escape rates or diffusive separation, is considered. The dominant processes acting at the five terrestrial planets and six major satellites are summarized. In general, nonthermal processes dominate over the classic thermal ones.

Hunten, D. M.↗
NASA NTRS1983

Radial diffusion in Saturn's radiation belts - A modeling analysis assuming satellite and ring E absorption

A modeling analysis is carried out of six experimental phase space density profiles for nearly equatorially mirroring protons using methods based on the approach of Thomsen et al. (1977). The form of the time-averaged radial diffusion coefficient D(L) that gives an optimal fit to the experimental profiles is determined under the assumption that simple satellite plus Ring E absorption of inwardly diffusing particles and steady-state radial diffusion are the dominant physical processes affecting the proton data in the L range that is modeled. An extension of the single-satellite model employed by Thomsen et al. to a model that includes multisatellite and ring absorption is described, and the procedures adopted for estimating characteristic satellite and ring absorption times are defined. The results obtained in applying three representative solid-body absorption models to evaluate D(L) in the range where L is between 4 and 16 are reported, and a study is made of the sensitivity of the preferred amplitude and L dependence for D(L) to the assumed model parameters. The inferred form of D(L) is then compared with that which would be predicted if various proposed physical mechanisms for driving magnetospheric radial diffusion are operative at Saturn.

Hood, L. L.↗