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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Study on hot deformation behavior and workability of squeeze-cast 20 vol%SiCw/6061Al composites using processing map

Highlights: • Prasad’s and Murty’s criteria were better than Gegel’s criterion in predicting the flow instability for the composites. • Partial melting and DRX at high temperature and high strain rate improved the workability of the composites. • The softening mechanism changed from DRV to DRX with the increase of deformation temperature and strain rate. • The safe deformation region of the composites was at higher temperature of 450-500°C and higher strain rate of 0.1-1s{sup -1}. • The safe deformation region predicted by processing maps was validated by uniaxial upsetting and two-directional forging. - Abstract: The hot deformation behavior and workability of squeeze-cast 20 vol%SiCw/6061Al composites were investigated by isothermal compression test and development of processing map, which was verified by uniaxial upsetting and two-directional forging of big cylindrical billets. Due to dispersed strengthening caused by SiC whiskers, the activation energy of 20 vol%SiCw/6061Al composites was much higher than the self-diffusion activation energy of pure Al. Both the DMM and MDMM were reliable in predicting the safe deformation regions. The instability regions predicted by the Prasad's and Murty's instability criterion were smaller than the actual ones, while the Gegel's instability criterion was not appropriate in predicting the instability regions of 20 vol%SiCw/6061Al composites. The optimum deformation region was at higher temperature of 450–500 °C and higher strain rate of 0.1–1 s{sup − 1}, in which the compressed samples exhibited perfect surface without cracks and microstructure with few of cavities due to the occurrence of partial melting and dynamic recrystallization. With the increase of deformation temperature and strain rate, the deformation mechanism changed from dynamic recovery to dynamic recrystallization. Squeezing casting technique with high filtration pressure may also contribute to the increase of strain rate of DRX, which was helpful for hot forging of Al matrix composites with high productivity.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Uncoupling Electrokinetic Flow Solutions

The continuum-scale electrokinetic porous-media flow and excess charge redistribution equations are uncoupled using eigenvalue decomposition. The uncoupling results in a pair of independent diffusion equations for “intermediate” potentials subject to modified material properties and boundary conditions. The fluid pressure and electrostatic potential are then found by recombining the solutions to the two intermediate uncoupled problems in a matrix-vector multiplication. Expressions for the material properties or source terms in the intermediate uncoupled problem may require extended precision or careful rewriting to avoid numerical cancellation, but the solutions themselves can typically be computed in double precision. The approach works with analytical or gridded numerical solutions and is illustrated through two examples. The solution for flow to a pumping well is manipulated to predict streaming potential and electroosmosis, and a periodic one-dimensional analytical solution is derived and used to predict electroosmosis and streaming potential in a laboratory flow cell subjected to low frequency alternating current and pressure excitation. The examples illustrate the utility of the eigenvalue decoupling approach, repurposing existing analytical solutions or numerical models and leveraging solutions that are simpler to derive for coupled physics.

58 GEOSCIENCES↗
DOE OSTI2025

Transient fuel performance analysis for the preliminary fuel concept of general atomics fast modular reactor

This study investigates the transient fuel performance of General Atomics Fast Modular Reactor (GA-FMR) during accident scenarios, focusing on the behavior of its innovative fuel system that combines high-assay low enriched uranium dioxide (HALEUO2) fuel with SiGA® ceramic matrix composite silicon carbide cladding. The preliminary fuel design’s response was analyzed during reactivity-initiated accidents (RIA) and loss of coolant accidents (LOCA) using BISON fuel performance analysis code, which included both the diffusion enhanced and BISON-FASTGRASS coupled UO 2 models. The RIA analysis demonstrated that effective reactivity control reduced fuel temperature, though with transient fission gas release resulting in additional tensile stress state on the cladding. LOCA simulations revealed differing predictions between the two models: the BISON UO 2 model showed more transient fission gas release but minimal pellet expansion, while the BISON-FASTGRASS UO 2 model predicted less pronounced fission gas release but more fuel swelling and thermal expansion, potentially leading to pellet-cladding mechanical interaction. Here, these findings highlight critical areas for fuel design optimization and identify knowledge gaps requiring further experimental and computational investigation to advance GA-FMR fuel development.

Lee, Soon K. [Argonne National Laboratory (ANL), A↗
DOE OSTI2019

H Atom Production and Reaction in the Gamma Radiolysis of Thermally Modified Boehmite

The correlation between the formation of H atoms and H2 was observed in the radiolysis of thermally modified boehmite (?-AlOOH). Boehmite was pretreated by heating to 300, 400, and 550°C, loaded with adsorbed water, and irradiated with gamma rays. Long-lived H atoms trapped in the interstitial matrix was observed by electron paramagnetic resonance techniques and the amount of gaseous H2 by gas chromatography. Heating the boehmite to 400°C before radiolysis results in the collapse of the matrix with loss of trapped H atoms and a substantial increase in the production of H2. Samples without added water post-heating showed no production of H2 suggesting that it is formed by the diffusion of H atoms to the surface followed by an abstraction reaction with water. Boehmite heated to 550°C has completely converted to alumina and the radiolytic responses of each are similar. Post-irradiation heating of boehmite to 300°C results in a doubling of the H2 yield at pretreated temperatures below 300°C due to the release of trapped H atoms.

La Verne, Jay A.↗
DOE OSTI2015

Permeation of hydrogen in hastelloy C-276 alloy at high temperature

Tritium is generated by the interaction of neutrons with the lithium and beryllium in the molten salt reactors (MSRs), which use FLiBe as one of solvents of fluoride fuel. Tritium as by-product in the MSRs is an important safety issue because it could easily diffuse into environment through high temperature heat exchangers. The experimental technique of gas driven permeation has been used to investigate the transport parameter of hydrogen in Hastelloy C-276 which is considered as one of the candidate for structure materials. The measurements were carried out at the temperature range of 400-800 Celsius degrees with hydrogen loading pressures ranging from 5*10{sup 3} to 4*10{sup 4} Pa. The H diffusive transport parameters for Hastelloy C-276 follow an Arrhenius law in this temperature range. Regarding diffusivity and Sieverts' constant, Hastelloy C-276 has lower values compared with Ni201 alloy. The possible reason may be the trapping effects, which were formed by the alloying elements of Mo and Cr in the matrix. At the same time, the thin oxidation layer formed by the high Cr content could lead to a slower dissociation process of H{sub 2} at the surface. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2018

Zeolite-like MOF nanocrystals incorporated 6FDA-polyimide mixed-matrix membranes for CO 2 /CH 4 separation

MOF mixed-matrix membranes (MMMs) are regarded as potential candidates for energy-efficient natural gas purification. Our work reports the fabrication of high-performance 6FDA-polyimide MMMs, based on the incorporation of zeolite-like MOF (ZMOF) as fillers, and their associated permeation studies for CO 2 /CH 4 separation. To eliminate micron-sized crystals, a facile repeating sedimentation approach was used to harvest nanocrystals from the as-synthesized bulk ZMOF crystalline powder material. This enables the deployment of ZMOF nanocrystals with relatively uniform dimension and morphology in the polymer matrix. Typical 6FDA-polyimides encompassing distinct diamine moieties (6FDA-DAM, 6FDA-DETDA-DABA or PDMC) were explored as polymer matrices to disclose the transport property matching the hosted ZMOF filler. Mixed-gas permeation measurements revealed that the incorporation of the ZMOF filler affords a concurrent enhancement of the CO 2 permeability and the CO 2 /CH 4 selectivity for the three tested 6FDA-polyimides. Particularly, the highly permeable 6FDA-DAM showed a considerably enhanced performance for CO 2 /CH 4 that transcends the 2008 Robeson upper-bound. Detailed analysis of the sorption data and diffusion coefficients suggest that the enhanced transport property in the ZMOF-based MMM is plausibly attributed to the combination of the higher CO 2 sorption capacity and selectivity, and favorable gas diffusivity via the CO 2 -philic framework of ZMOF in moderately confined pores.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Helium induced fine structure in the electronic spectra of anthracene derivatives doped into superfluid helium nanodroplets

Electronic spectra of organic molecules doped into superfluid helium nanodroplets show characteristic features induced by the helium environment. Besides a solvent induced shift of the electronic transition frequency, in many cases, a spectral fine structure can be resolved for electronic and vibronic transitions which goes beyond the expected feature of a zero phonon line accompanied by a phonon wing as known from matrix isolation spectroscopy. The spectral shape of the zero phonon line and the helium induced phonon wing depends strongly on the dopant species. Phonon wings, for example, are reported ranging from single or multiple sharp transitions to broad (Δν > 100 cm{sup −1}) diffuse signals. Despite the large number of example spectra in the literature, a quantitative understanding of the helium induced fine structure of the zero phonon line and the phonon wing is missing. Our approach is a systematic investigation of related molecular compounds, which may help to shed light on this key feature of microsolvation in superfluid helium droplets. This paper is part of a comparative study of the helium induced fine structure observed in electronic spectra of anthracene derivatives with particular emphasis on a spectrally sharp multiplet splitting at the electronic origin. In addition to previously discussed species, 9-cyanoanthracene and 9-chloroanthracene will be presented in this study for the first time.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Structure and Dynamics of Brachypodium Primary Cell Wall Polysaccharides from Two-Dimensional 13 C Solid-State Nuclear Magnetic Resonance Spectroscopy

The polysaccharide structure and dynamics in the primary cell wall of the model grass Brachypodium distachyon are investigated for the first time using solid-state nuclear magnetic resonance (NMR). While both grass and non-grass cell walls contain cellulose as the main structural scaffold, the former contains xylan with arabinose and glucuronic acid substitutions as the main hemicellulose, with a small amount of xyloglucan (XyG) and pectins, while the latter contains XyG as the main hemicellulose and significant amounts of pectins. We labeled the Brachypodium cell wall with 13 C to allow two-dimensional (2D) 13 C correlation NMR experiments under magic-angle spinning. Well-resolved 2D spectra are obtained in which the 13 C signals of cellulose, glucuronoarabinoxylan (GAX), and other matrix polysaccharides can be assigned. The assigned 13 C chemical shifts indicate that there are a large number of arabinose and xylose linkages in the wall, and GAX is significantly branched at the developmental stage of 2 weeks. 2D 13 C– 13 C correlation spectra measured with long spin diffusion mixing times indicate that the branched GAX approaches cellulose microfibrils on the nanometer scale, contrary to the conventional model in which only unbranched GAX can bind cellulose. The GAX chains are highly dynamic, with average order parameters of 0.4. Biexponential 13 C T 1 and 1 H T 1ρ relaxation indicates that there are two dynamically distinct domains in GAX: the more rigid domain may be responsible for cross-linking cellulose microfibrils, while the more mobile domain may fill the interfibrillar space. This dynamic heterogeneity is more pronounced than that of the non-grass hemicellulose, XyG, suggesting that GAX adopts the mixed characteristics of XyG and pectins. Moderate differences in cellulose rigidity are observed between the Brachypodium and Arabidopsis cell walls, suggesting different effects of the matrix polysaccharides on cellulose. These data provide the first molecular-level structural information about the three-dimensional organization of the polysaccharides in the grass primary wall.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Microstructure, microtexture and precipitation in the ultrafine-grained surface layer of an Al-Zn-Mg-Cu alloy processed by sliding friction treatment

Precipitate redistribution and texture evolution are usually two concurrent aspects accompanying grain refinement induced by various surface treatment. However, the detailed precipitate redistribution characteristics and process, as well as crystallographic texture in the surface refined grain layer, are still far from full understanding. In this study, we focused on the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy. With the combination of transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations, a surface ultrafine grain (UFG) layer composed of both equiaxed and lamellar ultrafine grains and decorated by high density of coarse grain boundary precipitates (GBPs) were revealed. Further precession electron diffraction (PED) assisted orientation mapping unraveled that high angle grain boundaries rather than low angle grain boundaries are the most favorable nucleation sites for GBPs. The prominent precipitate redistribution can be divided into three successive and interrelated stages, i.e. the mechanically induced precipitate dissolution, solute diffusion and reprecipitation. The quantitative prediction based on pipe diffusion along dislocations and grain boundary diffusion proved the distribution feasibility of GBPs around UFGs. Based on PED and electron backscatter diffraction (EBSD) analyses, the crystallographic texture of the surface UFG layer was identified as a shear texture composed of major rotated cube texture (001) 〈110〉 and minor (111) 〈112〉, while that of the adjoining lamellar coarse grained matrix was pure brass. The SFT induced surface severe shear deformation is responsible for texture evolution. - Highlights: •The surface ultrafine grain layer in a 7050 aluminum alloy was focused. •Precipitate redistribution and texture evolution were discussed. •The quantitative prediction proved the distribution feasibility of GBPs. •Precession electron diffraction orientation mapping showed a shear texture.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Landau-fluid closure for arbitrary frequency response

The kinetic Landau-fluid (LF) closure which can be regarded as the exact closure is derived. For Maxwellian plasma, the kinetic closure is the same as Hammett-Perkins closure in static limit and totally the same with Chang-Callen closure. A new LF closure for arbitrary frequency response constructed with harmonic average technique is presented in this paper. This new LF closure bridges the existing LF closures in the low and high frequency limits: it recovers Hammett-Perkins closure when weight coefficient κ = 0 and converges to Chang-Callen closure at high frequency when weight coefficient κ = 1. By picking an appropriate κ, the harmonic average closure contains both nonlocal transport and local transport and the resulting fluid response function of a three moment fluid model well matches the exact kinetic response function within the entire frequency range. On the computational side, a sum of diffusion-convection solves (SDCS) method is developed to facilitate numerical implementation of the harmonic average LF closure. By using SDCS method, good agreement is achieved for the response functions between driven initial-value simulations and matrix eigenvalue calculations within the BOUT++ framework. The harmonic average closure of shifted-Maxwellian is also outlined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Electromagnetic wave propagation based upon spectral-element methodology in dispersive and attenuating media

SUMMARY We build on mathematical equivalences between Maxwell’s wave equations for an electromagnetic medium and elastic seismic wave equations. This allows us to readily model Maxwell’s wave propagation in the spectral-element codes SPECFEM2D and SPECFEM3D, written for acoustic, viscoelastic and poroelastic seismic wave propagation, providing the ability to handle complex geometries, inherent to finite-element methods and retaining the strength of exponential convergence and accuracy due to the use of high-degree polynomials to interpolate field functions on the elements, characteristic to spectral-element methods (SEMs). Attenuation and dispersion processes related to the frequency dependence of dielectric permittivity and conductivity are also included using a Zener model, similar to shear attenuation in viscoelastic media or viscous diffusion in poroelastic media, and a Kelvin–Voigt model, respectively. Ability to account for anisotropic media is also discussed. Here, we limit ourselves to certain dielectric permittivity tensor geometries, in order to conserve a diagonal mass matrix after discretization of the system of equations. Doing so, simulation of Maxwell’s wave equations in the radar frequency range based on SEM can be solved using explicit time integration schemes well suited for parallel computation. We validate our formulation with analytical solutions. In 2-D, our implementation allows for the modelling of both a transverse magnetic (TM) mode, suitable for surface based reflection ground penetration radar type of applications, and a transverse electric (TE) mode more suitable for crosshole and vertical radar profiling setups. Two 2-D examples are designed to demonstrated the use of the TM and TE modes. A 3-D example is also presented, which allows for the full TEM solution, different antenna orientations, and out-of-plane variations in material properties.

58 GEOSCIENCES↗
DOE OSTI2021

Aggregation of solutes in bosonic versus fermionic quantum fluids

Quantum fluid droplets made of helium-3 ( 3 He) or helium-4 ( 4 He) isotopes have long been considered as ideal cryogenic nanolabs, enabling unique ultracold chemistry and spectroscopy applications. The droplets were believed to provide a homogeneous environment in which dopant atoms and molecules could move and react almost as in free space but at temperatures close to absolute zero. Here, we report ultrafast x-ray diffraction experiments on xenon-doped 3 He and 4 He nanodroplets, demonstrating that the unavoidable rotational excitation of isolated droplets leads to highly anisotropic and inhomogeneous interactions between the host matrix and enclosed dopants. Superfluid 4 He droplets are laced with quantum vortices that trap the embedded particles, leading to the formation of filament-shaped clusters. In comparison, dopants in 3 He droplets gather in diffuse, ring-shaped structures along the equator. The shapes of droplets carrying filaments or rings are direct evidence that rotational excitation is the root cause for the inhomogeneous dopant distributions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Nanotube/Nanowire as Effective Defect Sinks in Metals—Atomistic Simulations and In Situ Ion Radiation Transmission Electron Microscopy

The accumulation of defects during irradiation leads to material property degradation modes such as embrittlement and swelling, eventually causing material failure. Effective and efficient removal of defects is of crucial importance to design radiation damage-tolerant materials. Here, by biasing defect migration pathways via carbon nanotube (CNT) infiltration, we present a greatly enhanced damage-tolerant Al-CNT composite with defect storage measured to be one order of magnitude lower than that in pure, irradiated Al. Furthermore, extreme-value statistics (largest size) of defect clusters are significantly changed in the presence of CNT. In situ ion irradiation transmission electron microscopy (TEM) experiments and atomistic simulations together reveal the dynamic evolution and convergent diffusion of radiation-induced defects to CNTs, facilitating defect recombination and enhancing radiation tolerance. The occurrence of CNT-biased defect convergent migration is tuned by the thermodynamic driving force of stress gradient in Al matrix due to the CNT phase transformation. This approach to controlling defect migration using 1D interface engineering creates a new opportunity to enhance the properties of nuclear materials.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Structure–property relations in graphitic pebbles for nuclear applications

This work presents an analytical approach for holistically characterizing graphitic matrix pebbles for nuclear applications whereby the macrostructure, microstructure, and thermophysical properties of pebbles are determined. A systematic sectioning method was applied to several pebbles to describe the regional properties of the samples. Intact matrix-only spheres and sections of spheres fabricated by Kairos Power were characterized via optical imaging, x-ray computed tomography, x-ray diffraction, and ellipsometry to determine 2D and 3D macrostructure and anisotropy. The thermophysical properties of these materials were determined via measurements of density, specific heat, thermal expansion, and thermal diffusivity. The results of this study indicate that the pebble fabrication methods and their resultant effect on microstructure have a nontrivial effect on thermophysical properties, confirming the importance of robust characterization of these components. A discussion of the characterization approach and its applicability to nuclear fuel development activities is also included.

42 ENGINEERING↗
DOE OSTI2021

Analysis of a new multispecies tumor growth model coupling 3D phase-fields with a 1D vascular network

In this study, we present and analyze a mathematical model for tumor growth incorporating ECM erosion, interstitial flow, and the effect of vascular flow and nutrient transport. The model is of phase-field or diffused-interface type in which multiple phases of cell species and other constituents are separated by smooth evolving interfaces. The model involves a mesoscale version of Darcy’s law to capture the flow mechanism in the tissue matrix. Modeling flow and transport processes in the vasculature supplying the healthy and cancerous tissue, one-dimensional (1D) equations are considered. Since the models governing the transport and flow processes are defined together with cell species models on a three-dimensional (3D) domain, we obtain a 3D–1D coupled model.

3D–1D coupled blood flow models↗
DOE OSTI2021

Hydrodynamics of nonintegrable systems from a relaxation-time approximation

We develop a general kinetic theory framework to describe the hydrodynamics of strongly interacting, nonequilibrium quantum systems in which integrability is weakly broken, leaving a few residual conserved quantities. This framework is based on a generalized relaxation-time approximation; it gives a simple, but surprisingly accurate, prescription for computing nonequilibrium transport even in strongly interacting systems. We validate the predictions of this approximation against matrix product operator calculations on chaotic quantum spin chains, finding surprisingly good agreement. Lastly, we show that despite its simplicity, our framework can capture phenomena distinctive to strongly interacting systems, such as widely separated charge and energy diffusion constants.

1-dimensional spin chains↗
DOE OSTI2015

Development of a Radial Deconsolidation Method

A series of experiments have been initiated to determine the retention or mobility of fission products* in AGR fuel compacts [Petti, et al. 2010]. This information is needed to refine fission product transport models. The AGR-3/4 irradiation test involved half-inch-long compacts that each contained twenty designed-to-fail (DTF) particles, with 20-μm thick carbon-coated kernels whose coatings were deliberately fabricated such that they would crack under irradiation, providing a known source of post-irradiation isotopes. The DTF particles in these compacts were axially distributed along the compact centerline so that the diffusion of fission products released from the DTF kernels would be radially symmetric [Hunn, et al. 2012; Hunn et al. 2011; Kercher, et al. 2011; Hunn, et al. 2007]. Compacts containing DTF particles were irradiated at Idaho National Laboratory (INL) at the Advanced Test Reactor (ATR) [Collin, 2015]. Analysis of the diffusion of these various post-irradiation isotopes through the compact requires a method to radially deconsolidate the compacts so that nested-annular volumes may be analyzed for post-irradiation isotope inventory in the compact matrix, TRISO outer pyrolytic carbon (OPyC), and DTF kernels. An effective radial deconsolidation method and apparatus appropriate to this application has been developed and parametrically characterized.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Ultraselective Carbon Molecular Sieve Membranes with Tailored Synergistic Sorption Selective Properties

Membrane-based separations can reduce the energy consumption and the CO 2 footprint of large-scale fluid separations, which are traditionally practiced by energy-intensive thermally driven processes. Here, a new type of membrane structure based on nanoporous carbon is reported, which, according to this study, is best referred to as carbon/carbon mixed-matrix (CCMM) membranes. The CCMM membranes are formed by high-temperature (up to 900 °C) pyrolysis of polyimide precursor hollow-fiber membranes. Unprecedentedly high permselectivities are seen in CCMM membranes for CO 2 /CH 4 , N 2 /CH 4 , He/CH 4 , and H 2 /CH 4 separations. Analysis of permeation data suggests that the ultrahigh selectivities result from substantially increased sorption selectivities, which is hypothetically owing to the formation of ultraselective micropores that selectively exclude the bulkier CH 4 molecules. With tunable sorption selectivities, the CCMM membranes outperform flexible polymer membranes and traditional rigid molecular-sieve membranes. The capability to increase sorption selectivities is a powerful tool to leverage diffusion selectivities, and has opened the door to many challenging and economically important fluid separations that require ultrafine differentiation of closely sized molecules.

36 MATERIALS SCIENCE↗