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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Storm Surge Modeling as an Application of Local Time-Stepping in MPAS-Ocean

This paper presents the first practical application of local time-stepping (LTS) schemes in the Model for Prediction Across Scales-Ocean (MPAS-O). We use LTS schemes in a single-layer, global ocean model that predicts the storm surge around the eastern coast of the United States during Hurricane Sandy. The variable-resolution meshes used are of unprecedentedly high resolution in MPAS-O, containing cells as small as 125 m wide in Delaware Bay. It is shown that a particular, third-order LTS scheme (LTS3) produces sea-surface height solutions that are of comparable quality to solutions produced by the classical four-stage, fourth-order Runge-Kutta method (RK4) with a uniform time step on the same meshes. Furthermore, LTS3 is up to 35% faster in the best cases considered, where the number of cells using the coarse time-step relative to those using the fine time-step is as low as 1:1. This shows that LTS schemes are viable for use in MPAS-O with the added benefit of substantially less computational cost. The results of these performance experiments inform us of the requirements for efficient mesh design and configuration of LTS regions for LTS schemes. In particular, we see that for LTS to be efficient on a given mesh, it is important to have enough cells using the coarse time-step relative to those using the fine time-step, typically at least 1:5 to see an increase in performance.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Production of monodisperse cerium oxide microspheres with diameters near 100 µm by internal-gelation sol–gel methods

Cerium dioxide microspheres with uniform diameters between 65 – 211 µm were fabricated using internal gelation sol-gel methods. Although uniform microspheres are produced for nuclear fuel applications with diameters above 300 µm, sol-gel microspheres with diameters of 50 - 200 µm have historically been made by emulsion techniques and had poor size uniformity [1, 2]. An internal gelation, sol-gel apparatus was designed and constructed to accommodate the production of small, uniform microspheres whereby cerium-containing solutions were dispersed into flowing silicone oil and heated in a gelation column to initiate solidification [3, 4]. Problems with premature feed gelation and microsphere coalescence were overcome by equipment modifications unique among known internal gelation setups. Microspheres were fabricated and sized in batches as a function of dispersing needle diameter and silicone oil flow rate in the two-fluid nozzle in order to determine the range of sizes possible and corresponding degree of monodispersity. Initial experiments with poor size uniformity were linked to microsphere coalescence in the gelation column prior to solidification as well as excessive flow rates for the cerium feed solution. Average diameter standard deviations as low as 2.23% were observed after optimization of flow rates and minimization of coalescence reactions.

cerium oxide↗
DOE OSTI2024

Evolution of Surface Chemistry in Two‐Dimensional MXenes: From Mixed to Tunable Uniform Terminations

Abstract Surface chemistry of MXenes is of great interest as the terminations can define the intrinsic properties of this family of materials. The diverse and tunable terminations also distinguish MXenes from many other 2D materials. Conventional fluoride‐containing reagents etching approaches resulted in MXenes with mixed fluoro‐, oxo‐, and hydroxyl surface groups. The relatively strong chemical bonding of MXenes’ surface metal atoms with oxygen and fluorine makes post‐synthetic covalent surface modifications of such MXenes unfavorable. In this minireview, we focus on the recent advances in MXenes with uniform surface terminations. Unconventional methods, including Lewis acidic molten salt etching (LAMS) and bottom‐up direct synthesis, have been proven successful in producing halide‐terminated MXenes. These synthetic strategies have opened new possibilities for MXenes because weaker surface chemical bonds in halide‐terminated MXenes facilitate post‐synthetic covalent surface modifications. Both computational and experimental results on surface termination‐dependent properties are summarized and discussed. Finally, we offer our perspective on the opportunities and challenges in this exciting research field.

Jiang, Mengni↗
DOE OSTI2024

Evolution of Surface Chemistry in Two‐Dimensional MXenes: From Mixed to Tunable Uniform Terminations

Abstract Surface chemistry of MXenes is of great interest as the terminations can define the intrinsic properties of this family of materials. The diverse and tunable terminations also distinguish MXenes from many other 2D materials. Conventional fluoride‐containing reagents etching approaches resulted in MXenes with mixed fluoro‐, oxo‐, and hydroxyl surface groups. The relatively strong chemical bonding of MXenes’ surface metal atoms with oxygen and fluorine makes post‐synthetic covalent surface modifications of such MXenes unfavorable. In this minireview, we focus on the recent advances in MXenes with uniform surface terminations. Unconventional methods, including Lewis acidic molten salt etching (LAMS) and bottom‐up direct synthesis, have been proven successful in producing halide‐terminated MXenes. These synthetic strategies have opened new possibilities for MXenes because weaker surface chemical bonds in halide‐terminated MXenes facilitate post‐synthetic covalent surface modifications. Both computational and experimental results on surface termination‐dependent properties are summarized and discussed. Finally, we offer our perspective on the opportunities and challenges in this exciting research field.

Jiang, Mengni↗
DOE OSTI2019

Synthesis of Nickel-Doped Ceria Catalysts for Selective Acetylene Hydrogenation

Metallic nickel is known to be an active, but not a selective hydrogenation catalyst for conversion of alkynes to alkenes. On the other hand, nickel oxide is not active. Recently, we have demonstrated that nickel doped into ceria provides an inexpensive catalyst for selective hydrogenation of acetylene in the presence of ethylene. Here, we evaluate various synthesis methods to achieve optimal selective hydrogenation performance. We examined incipient wetness impregnation, coprecipitation, solution combustion, and sol-gel synthesis to study how the method of preparation affects catalytic structure and behavior. Sol-gel synthesis, coprecipitation, and solution combustion synthesis methods favor nickel incorporation into the ceria lattice, while incipient wetness impregnation creates segregated nickel species on the ceria surface. For hydrogenation of acetylene, these nickel surface species lead to poor ethylene selectivity due to ethane and oligomer formation. However, when nickel is incorporated into the ceria lattice, ethane formation is prevented even while achieving 100 % conversion of acetylene. Coke formation is also significantly reduced on these catalysts compared to conventional nanoparticle counterparts. Finally, we conclude that sol-gel synthesis provides the optimal method for creating a uniform dopant distribution within the high surface area ceria.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Diffraction of waves by a perfect electromagnetic conductor half-plane between isorefractive media

In this study, diffraction of waves by a perfectly electromagnetic conductor half-plane which is lying at the boundary of isorefractive media is investigated. The diffracted field expressions are constructed by using the relation between scattered geometrical optics fields and the transition boundaries. The high frequency asymptotic expressions of diffracted fields reach infinite magnitude values at the transition boundaries. The uniform expressions of fields are obtained by using the uniform theory of diffraction method in order to obtain the finite magnitude values at the transition boundaries and the results are analyzed numerically for different set of parameters.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

GRCop-42: Comparison between laser powder bed fusion and laser powder direct energy deposition

This study involves a comparative analysis of additively manufactured GRCop-42 specimens produced using two processes: laser-powder bed fusion (L-PBF) and laser powder direct energy deposition (LP-DED). The investigation characterizes a range of material attributes, including surface topography, internal defects, microstructural features, quasi-static mechanical properties, and fractographic characteristics. The findings demonstrate that, despite the specimens being fabricated with the same base material, the resulting material properties vary significantly between the two additive manufacturing processes. As such, material properties cannot be presumed to be uniform across different manufacturing methods. Consequently, material characterization must be conducted for individual manufacturing processes based on specific parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enabling high rate charge and discharge capability, low internal resistance, and excellent cycleability for Li-ion batteries utilizing graphene additives

A liquid-phase mixing method is adopted to uniformly disperse the graphene nanosheets onto LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode for high-performance Li-ion batteries (LIBs). The electrochemical performance was characterized using a full pouch cells with state-of-the-art electrode areal loading (compared to half coin cells). The addition of graphene sheets (i.e., only 1 wt%) significantly improves the high rate capability for charging and discharging operation. For example, 6 times improvement in 5 C charging was achieved providing further insights in enabling extreme fast charging for LIBs. Other benefits include longer cycleability, lower internal resistance, and higher lithium ion diffusion coefficient, demonstrated by charge-discharge cycling tests and electrochemical impedance spectroscopy. Higher capacity retention of 88.2% and decreased internal resistance of ~0.9 Ω are observed after 400 cycles. The diffusion coefficient of Li ions is 6.49 × 10 -8 cm 2 s -1 when charged to 4.2 V, which is approximately 1.37 times higher compared to the configuration with no graphene sheet (4.74 × 10 -8 cm 2 s -1 ). To conclude, the improved performance is ascribed to a robust network among the active materials formed by graphene sheets, which serves as an extended current conductor and facilitates charge transfer, ionic reversibility, and ionic transportation.

25 ENERGY STORAGE↗
DOE OSTI2018

Microstructure and nanoindentation analysis of Mg-SiC nanocomposite powders synthesized by mechanical milling

Highlights: • Mechanical milling as an effective solution to reach a homogeneous distribution of SiC nanoparticles up to 10 vol% in Mg matrix • No deformation twinning in the nanostructured Mg matrix even after the severe plastic deformation and hard SiC nanoparticles up to 10 vol%. • Significant enhancement of nanohardness and reduced elastic modulus in the milled nanocomposite powders - Abstract: Mixtures of magnesium powder and SiC nanoparticles at various volume fractions were mechanically milled to produce nanocrystalline Mg-SiC nanocomposites. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilized to characterize the microstructure of the milled powders. The microstructural evidences revealed that mechanical milling is a proper method to achieve a uniform distribution of the SiC nanoparticles, even up to 10% in the Mg matrix. Based on the results, higher volume fraction of the SiC nanoparticles raise the value of measured microstrain and reduce the crystallite size of the Mg matrix. The TEM results pointed to the fact that no deformation twinning takes place in the nanostructured Mg matrix even after severe plastic deformation through mechanical milling and the presence of hard SiC nanoparticles up to 10 vol%. The effects of nanoparticle volume fraction on mechanical properties of the milled Mg-SiC nanocomposites were evaluated using nanoindentation tests. The results clearly showed a significant enhancement of nanohardness and reduced elastic modulus in the milled powders compared to that of the reference material namely as-received pure magnesium. It was found that the SiC nanoparticles (even up to 10 vol%), well distributed in the magnesium matrix, remarkably improve the reduced elastic modulus and nanohardness of the nanocomposite powders.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

FLAMES─Fast, Low-Storage, Accurate, and Memory-Efficient Adaptive Sampling─Approach to Resolve Spatially Dependent Dynamics of Molecular Liquids

Many critical phenomena in soft matter occur at large length scales, necessitating the resolution of their structure and dynamics at low wavenumbers. However, resolving wavenumber-dependent dynamics computationally via molecular dynamics simulations presents significant challenges, as these phenomena span several orders of magnitude in both time and length scales, resulting in high computational costs and memory demands. Here, this work highlights the computational and memory challenges associated with analyzing molecular trajectories in reciprocal space and demonstrates a method to address them. We introduce FLAMESFast, Low-storage, Accurate, and Memory-Efficient adaptive Sampling, which is a direct method for calculation of structure factors, allowing us to select only the required number of wavevectors for binning. We also use wavenumber-dependent time steps to extract dynamics. Our FLAMES approach effectively mitigates computational and memory/storage bottlenecks. We demonstrate the method using simulations of a model system, liquid octane, at various temperatures. Comparisons with experimental data and real space computation show that the FLAMES technique achieves high accuracy in resolving temperature- and spatially dependent dynamics while being significantly more computationally efficient and requiring less memory and storage than methods based on a uniform wavevector grid and fixed temporal spacing.

Chen, Guang [Argonne National Laboratory (ANL), Ar↗
DOE OSTI2022

Area-Scalable Zn 2 SnO 4 Electron Transport Layer for Highly Efficient and Stable Perovskite Solar Modules

The development of a scalable chemical bath deposition (CBD) process facilitates the realization of electron-transporting layers (ETLs) for large-area perovskite solar modules (PSMs). In this work, a method to prepare a uniform and scalable thick Zn 2 SnO 4 ETL by CBD, which yielded high-performance PSMs, is reported. This Zn 2 SnO 4 ETL exhibits excellent electrical properties and enhanced optical transmittance in the visible region. Moreover, the Zn 2 SnO 4 ETL influences the perovskite layer formation, yielding enhanced crystallinity, increased grain size, and a smoother surface, thus facilitating electron extraction and collection from the perovskite to the ETL. Zn 2 SnO 4 thereby yields PSMs with a remarkable photovoltaic performance, low hysteresis index, and high device reproducibility. The champion PSM exhibited a power conversion efficiency (PCE) of 22.59%, being among the highest values published so far. In addition, the CBD Zn 2 SnO 4 -based PSMs exhibit high stability, retaining more than 88% of initial efficiency over 1000 h under continuous illumination. This demonstrates that CBD Zn 2 SnO 4 is an appropriate ETL for high-efficiency PSMs and a viable new process for their industrialization.

17 WIND ENERGY↗
DOE OSTI2017

Laser-pulse compression using magnetized plasmas

Proposals to reach the next generation of laser intensities through Raman or Brillouin backscattering have centered on optical frequencies. Higher frequencies are beyond the range of such methods mainly due to the wave damping that accompanies the higher-density plasmas necessary for compressing higher frequency lasers. However, we find that an external magnetic field transverse to the direction of laser propagation can reduce the required plasma density. Using parametric interactions in magnetized plasmas to mediate pulse compression, both reduces the wave damping and alleviates instabilities, thereby enabling higher frequency or lower intensity pumps to produce pulses at higher intensities and longer durations. Finally, in addition to these theoretical advantages, our method in which strong uniform magnetic fields lessen the need for high-density uniform plasmas also lessens key engineering challenges or at least exchanges them for different challenges.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Quantifying and Qualifying Alloys Based on Level of Homogenization: A U-10Mo Alloy Case Study

Homogenization heat treatment is performed to attain uniformity in microstructure which is helpful to achieve the desired workability and microstructure in final products and, eventually, to gain predictive and consistent performance. Fabrication of low-enriched uranium alloys with 10 wt% molybdenum (U-10Mo) fuel plates involves multiple thermomechanical processing steps. It is well known that the molybdenum homogeneity in the final formed product affects the performance in the nuclear reactor. Here, to ensure uniform homogenization, a statistical method is proposed to quantify and characterize the molybdenum concentration variation in U-10Mo fuel plates by analyzing the molybdenum concentration measurement data from scanning electron microscopy energy dispersive spectroscopy line-scan. Statistical tolerance intervals (TI) are employed to determine the qualification of the U-10Mo fuel plate. We formulate an argument for the minimum number of independent samples to define fuel plate qualification if no molybdenum measurement data are available in advance and demonstrate that the given TI requirements can be equivalently reduced to a sample variance criterion in this application. The outcome of the statistical analysis can be used to optimize casting design and eventually increase productivity and reduce fabrication costs. The statistical strategy developed in this paper can be implemented for other applications especially in the field of material manufacturing to assess qualification requirements and monitor and improve the process design.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Quantifying and Qualifying Alloys Based on Level of Homogenization: A U–10 wt% Mo Alloy Case Study

Homogenization heat treatment is performed to attain uniformity in microstructure of metals and metal alloys, which is helpful to achieve the desired workability and microstructure in final products, and eventually to gain predictable and consistent performance. Fabrication of fuel plates made from a low-enriched uranium alloy with 10 wt% Mo (U-10Mo) involves multiple thermomechanical processing steps. It is well known that the molybdenum homogeneity in the final formed product affects the fuel performance in the nuclear reactor. To make sure these materials are uniformly homogenized, a statistical method was proposed to quantify and characterize the Mo concentration variation in U-10Mo fuel plates by analyzing the Mo concentration measurement data from scanning electron microscopy–energy dispersive spectroscopy line scans. Statistical tolerance intervals were employed to determine the qualification of U-10Mo fuel plates. We formulate an argument for the minimum number of independent samples required to define fuel plate qualification if no Mo measurement data are available in advance, and demonstrate that the given tolerance interval requirements can be equivalently reduced to a sample variance criterion in this application. The outcome of the statistical analysis can be used to optimize casting design and eventually increase productivity and reduce fabrication cost. The statistical strategy developed in this report can be implemented for other applications, especially in the field of material manufacturing to assess qualification requirements and monitor and improve process design.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Azimuthal Anchoring Strength in Photopatterned Alignment of a Nematic

Spatially-varying director fields have become an important part of research and development in liquid crystals. Characterization of the anchoring strength associated with a spatially-varying director is difficult, since the methods developed for a uniform alignment are seldom applicable. Here we characterize the strength of azimuthal surface anchoring produced by the photoalignment technique based on plasmonic metamsaks. The measurements used photopatterned arrays of topological point defects of strength +1 and −1 in thin layers of a nematic liquid crystal. The integer-strength defects split into pairs of half-integer defects with lower elastic energy. The separation distance between the split pair is limited by the azimuthal surface anchoring, which allows one to determine the strength of the latter. The strength of the azimuthal anchoring is proportional to the UV exposure time during the photoalignment of the azobenzene layer.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Toward Higher-order Accuracy in Self-gravitating Hydrodynamics

High-order algorithms have emerged in numerical astrophysics as a promising avenue to reduce truncation error (proportional to a power of the linear resolution Δ x ) with only a moderate increase to computational expense. Significant effort has been placed in the development of finite-volume algorithms for (magneto)hydrodynamics; however, state-of-the-art astrophysical simulations tightly couple a plenitude of physics, additionally including gravity, photon transport, cosmic-ray transport, chemistry, and/or diffusion, to name a few. Algorithms frequently operator-split this additional physics (often a first-order error in time) and/or adopt a model wherein their evaluation is limited to second-order accuracy in space. In this work, we present a fourth-order-accurate finite-volume scheme for self-gravitating hydrodynamics on a uniform Cartesian grid. The method supplies source terms for the gravitational acceleration ( ρ g ) and gravitational energy release ( ρ v · g ) associated with fourth-order-accurate solutions to the Poisson equation. Our scheme (1) guarantees the conservation of total linear momentum while (2) decreasing (in proportion to Δ x 4 ) the effects of spurious heating and/or cooling associated with truncation error in the gravity. We demonstrate expected convergence rates for the algorithm by measuring errors in test problems evolving self-gravity modified linear waves and 3D polytropic equilibria. We test robustness of the algorithm by integrating an induced “inside-out” adiabatic collapse. We also discuss a method to smoothly downgrade the solution to second-order spatial accuracy to avoid spurious overshoots near steep density and/or pressure gradients.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Effects of transducer flushness on fluctuating surface pressure measurements

The installation flushness of pressure transducers has been found to strongly influence the quality of fluctuating surface pressure data in supersonic-attached turbulent boundary-layer flow. A systematic investigation of the effects of flushness on surface pressure fluctuations beneath a 4-in.-thick boundary layer was conducted in a supersonic wind tunnel at Mach numbers of 1.68, 2.0, and 2.5. Flushness effects on transducer signal amplitude, power spectral density, coherence, and narrowband convection velocity was evaluated. Results show that a very slightly protruding transducer produces adverse effects on the desired pressure fluctuation measurements, whereas a submerged transducer produces small effects. Indications are that a more viable method for enhancing the uniformity and spatial correlation of fluctuating surface pressure data can be achieved by deliberately submerging transducers beneath a surface orifice about 0.010 in. deep.

Hanly, R. D.↗
NASA NTRS1975

Development of an efficient computer code to solve the time-dependent Navier-Stokes equations

A research effort was conducted with the goal of reducing computer time of a Navier Stokes Computer Code for prediction of viscous flow fields about lifting bodies. A two-dimensional, time-dependent, laminar, transonic computer code (STOKES) was modified to incorporate a non-uniform timestep procedure. The non-uniform time-step requires updating of a zone only as often as required by its own stability criteria or that of its immediate neighbors. In the uniform timestep scheme each zone is updated as often as required by the least stable zone of the finite difference mesh. Because of less frequent update of program variables it was expected that the nonuniform timestep would result in a reduction of execution time by a factor of five to ten. Available funding was exhausted prior to successful demonstration of the benefits to be derived from the non-uniform time-step method.

Harp, J. L., Jr.↗