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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Heat conduction in metal-filled polymers - The role of particle size, shape, and orientation

This paper presents a new type of analysis for predicting the thermal conductivity of disperse composites from the properties of the component phases and elementary characterizations of particle shapes and orientation. This analysis successfully predicted the sensitivity to particle shape which was confirmed by experiments also reported in this paper. These results suggest that highly elongated particles may be used to achieve dramatic modifications of thermal conductivity and the analysis presented here may be a useful tool in the design or development of disperse composites of specific thermal conductivity. The analysis may also apply to other properties such as electrical conductivity or magnetic permeability.

Hansen, D.↗
NASA NTRS1973

Unusual chemical compositions of noctilucent-cloud particle nuclei

Two sounding rocket payloads were launched from the ESRO range in Sweden during a noctilucent cloud display. Large numbers of submicron particles were collected, most of which appear to be made up of a high density material coated with a low density material. Typical electron micrographs are shown. Particle chemical compositions have been measured by use of dispersive X-ray analysis equipment attached to an electron microscope and have revealed that most of the high density particle nuclei have atomic weights greater than iron.

Hemenway, C. L.↗
DOE OSTI2021

XPCS Microrheology and Rheology of Sterically Stabilized Nanoparticle Dispersions in Aprotic Solvents

In this study, X-ray photon correlation spectroscopy (XPCS) microrheology and conventional bulk rheology were performed on silica nanoparticle dispersions associated with battery electrolyte applications to probe the properties of these specific complex materials and to explore the utility of XPCS microrheology in characterizing nanoparticle dispersions. Sterically stabilized shear-thickening electrolytes were synthesized by grafting poly(methyl methacrylate) chains onto silica nanoparticles. Coated silica dispersions containing 5–30 wt % nanoparticles dispersed in propylene carbonate were studied. In general, both XPCS microrheology and conventional rheology showed that coated silica dispersions were more viscous at higher concentrations, as expected. The complex viscosity of coated silica dispersions showed shear-thinning behavior over the frequency range probed by XPCS measurements. However, measurements using conventional mechanical rheometry yielded a shear viscosity with weak shear-thickening behavior for dispersions with the highest concentration of 30% particles. Our results indicate that there is a critical concentration needed for shear-thickening behavior, as well as appropriate particle size and surface polymer chain length, for this class of nanoparticle-based electrolytes. The results of this study can provide insights for comparing XPCS microrheology and bulk rheology for related complex fluids and whether XPCS microrheology can capture expected macroscopic rheological properties by probing small-scale particle dynamics.

36 MATERIALS SCIENCE↗
NASA NTRS2000

Metal Nanoparticle Aerogel Composites

We have fabricated sol-gels containing gold and silver nanoparticles. Formation of an aerogel produces a blue shift in the surface plasmon resonance as a result of the decrease in the dielectric constant of the matrix upon supercritical extraction of the solvent. However, as a result of chemical interface damping this blue shift does not obey effective medium theories. Annealing the samples in a reducing atmosphere at 400 C eliminates this discrepancy and results in narrowing and further blue shifting of the plasmon resonance. Metal particle aggregation also results in a deviation from the predictions of effective medium theories, but can be controlled through careful handling and by avoiding the use of alcohol. By applying effective medium theories to the heterogeneous interlayer surrounding each metal particle, we extend the technique of immersion spectroscopy to inhomogeneous materials characterized by spatially dependent dielectric constants, such as aerogels. We demonstrate that the shift in the surface plasmon wavelength provides the average fractional composition of each component (air and silica) in this inhomogeneous layer, i.e. the porosity of the aerogel or equivalently, for these materials, the catalytic dispersion. Additionally, the kinetics suggest that collective particle interactions in coagulated metal clusters are perturbed during silica gelation resulting in a change in the aggregate geometry.

Smith, David D.↗
DOE OSTI2023

Memory in aging colloidal gels with time-varying attraction

Here, we report a combined rheology, x-ray photon correlation spectroscopy, and modeling study of gel formation and aging in suspensions of nanocolloidal spheres with volume fractions of 0.20 and 0.43 and with a short-range attraction whose strength is tuned by changing temperature. Following a quench from high temperature, where the colloids are essentially hard spheres, to a temperature below the gel point, the suspensions form gels that undergo aging characterized by a steadily increasing elastic shear modulus and slowing, increasingly constrained microscopic dynamics. The aging proceeds at a faster rate for stronger attraction strength. When the attraction strength is suddenly lowered during aging, the gel properties evolve non-monotonically in a manner resembling the Kovacs effect in glasses, in which the modulus decreases and the microscopic dynamics become less constrained for a period before more conventional aging resumes. Eventually, the properties of the gel following the decrease in attraction strength converge to those of a gel that has undergone aging at the lower attraction strength throughout. The time scale of this convergence increases as a power law with the age at which the attraction strength is decreased and decreases exponentially with the magnitude of the change in attraction. A model for gel aging in which particles attach and detach from the gel at rates that depend on their contact number reproduces these trends and reveals that the non-monotonic behavior results from the dispersion in the rates that the populations of particles with different contact number adjust to the new attraction strength.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1983

Morphology of ductile metals eroded by a jet of spherical particles impinging at normal incidence

Scanning electron microscopy and energy-dispersive X-ray spectroscopy are used, together with surface profile measurements, in the present morphological study of the erosion of an aluminum alloy and copper by the normal impact of spherical glass erodent particles. The morphology of the damage pattern is a manifestation of the flow pattern of erodent particles, and yields insight into the mechanisms that may be active at different stages of erosion. The simultaneous appearance of radial cracks and concentric rings is reported, together with wave crests which contain an accumulation of metallic flakes. A preliminary analysis is advanced to explain the formation of the various damage patterns observed.

Veerabhadra Rao, P.↗
NASA NTRS2018

Development of New Rocket Engine Liner Materials Based on Copper Alloys with Diamond Particle Additions

Novel copper-diamond materials containing particulate dispersions of diamond within a copper alloy matrix have been produced as next-generation rocket engine combustion chamber liner materials. These Copper-Diamond composite materials have significantly higher thermal conductivity than conventional liner materials and have the potential to increase the engine performance significantly. Liner fabrication techniques include hot pressing and spark plasma sintering, which are capable of scale up to full-size production parts. The materials have been evaluated for thermal cycling resistance and ease of manufacturing. The results indicate great promise of these materials and associated economics to replace state-of-the-art combustion chamber liner materials such as GRCop-84 and NARloy-Z. Novel combustion chamber fabrication processes are discussed, including cladding the liner with jacket materials.

Bhat, Biliyar N.↗
NASA NTRS2018

Development of New Rocket Engine Liner Materials Based on Copper Alloys with Diamond Particle Additions

Novel copper-diamond materials containing particulate dispersions of diamond within a copper alloy matrix have been produced as next-generation rocket engine combustion chamber liner materials. These Copper-Diamond (Cu-D) composite materials have significantly higher thermal conductivity than conventional liner materials and have the potential to increase the engine performance significantly. Liner fabrication techniques include hot pressing and spark plasma sintering (SPS), which are capable of scale up to full-size production parts. The materials have been evaluated for thermal cycling resistance and ease of manufacturing. The results indicate great promise of these materials and associated economics to replace state-of-the-art combustion chamber liner materials such as GRCop-84 and NARloy-Z. Combustion chamber fabrication processes are also discussed, including SPS and additive manufacturing.

Bhat, Biliyar N.↗
NASA NTRS1980

Creep and stress rupture of oxide dispersion strengthened mechanically alloyed Inconel alloy MA 754

The creep and stress rupture behavior of the mechanically alloyed oxide dispersion strengthened nickel-base alloy MA 754 was studied at 760, 982 and 1093 C. Tensile specimens with a fine, highly elongated grain structure, oriented parallel and perpendicular to the longitudinal grain direction were tested at various stresses in air under constant load. It was found that the apparent stress dependence was large, with power law exponents ranging from 19 to 33 over the temperature range studied. The creep activation energy, after correction for the temperature dependence of the elastic modulus, was close to but slightly larger than the activation energy for self diffusion. Rupture was intergranular and the rupture ductility as measured by percentage elongation was generally low, with values ranging from 0.5 to 16 pct. The creep properties are rationalized by describing the creep rates in terms of an effective stress which is the applied stress minus a resisting stress consistent with the alloy microstructure. Values of the resisting stress obtained through a curve fitting procedure are found to be close to the values of the particle by-pass stress for this oxide dispersion strengthened alloy, as calculated from the measured oxide particle distribution.

Howson, T. E.↗
DOE OSTI2025

Modeling and Simulation of Fuel Dispersal During the Loss-of-Coolant Accident

This document is the compilation of the milestone portion to a larger end of project NEUP report. The executive summary of the modeling portion is provided below: In the event of cladding rupture during a postulated LOCA in a pressurized water reactor, fuel particles, along with fission gases, can be expelled into the reactor core from the fractured fuel rod, a phenomenon referred to as fuel dispersal. The initial stage of fuel dispersal is strongly influenced by the high-pressure ejection of fuel fragments, the size and geometry of the ruptured cladding, and the depressurization history of the fuel rod during the postulated LOCA transient. Depending on the location of the burst orifice relative to the quench front, the dispersal event represents an intricate three-phase flow and heat transfer phenomenon, where high-temperature fuel particles carried by the fission gases interact with the coolant within the narrow subchannels of the fuel assemblies, inducing localized phase change. Given the unique multiphysics nature of this phenomena, the current study develops a dedicated computational framework to predict the mass distribution and cooling of dispersing fuel particles, facilitating post-accident assessment and management of the fuel assemblies. Considering the scale of nuclear reactor applications, a continuum three-fluid model is proposed for simulating the transport of solids within the reactor core. With high-temperature fuel fragments within the liquid media, nucleation sites inducing phase changes are dispersed within the flow domain. Coupled with the fact that the transient dispersal event occurs on different time scales than other three-phase flow applications, this study derives a time-averaged three-fluid flow model without losing generality. The assumptions regarding the continuum treatment of the solid phase and the modeling of fuel dispersal behavior are incorporated to simplify the governing equations and derive applicable closure relations. The computational validation of the model was conducted using adiabatic experimental results obtained from ongoing research at Oregon State University, focusing on characterizing fuel dispersal behavior during simulated LOCA conditions. Settlement characteristics of the solids, quantified by the probability distribution of equivalent particles, closely matched the probability density functions reported in experimental studies. The transport of fuel particles within a scaled 5 × 5 lattice of a pressurized-water reactor rod bundle geometry was modeled through a two-fluid Eulerian framework. The required boundary conditions were evaluated from the fuel performance code BISON in a postulated large-break LOCA scenario. The modeling framework considered solid fuel particles as granular matter, interacting with the gaseous dry steam phase and fission gases through the governing interfacial momentum exchange between the participating fluids. The simulation results provided the volume fraction of the solids obtained at the bottom surface of the enclosing tank geometry. Postulated LOCA leading to fuel dispersal phenomena involves the strong coupling between fuel thermomechanics, cladding deformation, thermal-hydraulics, and fuel particle transport. Incorporation of such a strong coupling in numerical simulation is performed by coupling the multiphysics solvers. In the case of fuel dispersal, a strong coupled simulation can be performed by coupling the BISON code for fuel performance, the TRACE code for system-level thermal hydraulics, and fuel particle transport in Multiphysics Object-Oriented Simulation Environment (MOOSE). For such intricate infrastructure, the MOOSE Framework eases the data transfer between codes. The recent version of MOOSE has incorporated the Navier-Stokes module for the fluid flow. An exploratory exercise was done to gain familiarity with finite volume capabilities in the MOOSE framework to incorporate the Spalart-Allmaras (SA) turbulence model. New finite-volume and auxiliary kernels were introduced to assemble the SA transport equation, compute turbulent viscosity, and evaluate wall distance and diagnostic turbulence terms, fully integrated with existing Navier-Stokes modules. A turbulent lid-driven cavity at a Reynolds number of approximately 10,000 is used for verification. MOOSE shows the robust solver convergence and produces the turbulent features. But it underpredicts the velocity profile and turbulent quantities, emphasizing the need to develop improved SA near-wall treatments (e.g., low-Re corrections or wall functions) as a key direction for future work.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Resin chemistry and particle size influence on stereolithography with silicon carbide

Stereolithography (SLA) is an established process able to produce high resolution polymer parts with complex geometries. Silicon carbide (SiC) has uses in a variety of applications, but traditionally was difficult to manufacture into complex geometries. There have been advances in producing SiC through SLA using a SiC-derived ceramic such as silicon oxycarbide (SiOC). In this study, a slurry using a commercially available resin as the base material with additional modifiers was investigated to create a SiC slurry ready for pressureless sintering. The effects of photoinitiator, dispersant and a bimodal distribution of SiC particle sizes was studied using a design of experiments (DOE). A slurry with a bimodal distribution of 70 % coarse and 30 % fine SiC powder at 40 % solids loading by volume was prepared and successfully printed. Rheology measurements show the slurry to have viscoelastic shear thinning behavior below the recommended 1000 Pas necessary for printing. Printing parameters for the new material on a commercially available SLA printer were studied parametrically. The laser marking speeds found to print the slurry was 260 mm/s and 130 mm/s. A slurry and printing parameters were determined to produce a green part with a proposed debinding cycle.

Herd, Tien [ORNL]↗
DOE OSTI2021

Measurement report: Comparison of wintertime individual particles at ground level and above the mixed layer in urban Beijing

Beijing has been suffering from frequent severe air pollution events, with concentrations affected significantly by the mixed-layer height. Major efforts have been made to study the physico-chemical properties, compositions, and sources of aerosol particles at ground level. However, little is known about the morphology, elemental composition, and mixing state of aerosol particles above the mixed layer. In this work, we collected individual aerosol particles simultaneously at ground level (2 m above ground) and above the mixed layer in urban Beijing (within the Atmospheric Pollution and Human Health in a Chinese Megacity, APHH-Beijing, 2016 winter campaign). The particles were analyzed offline by transmission electron microscopy coupled with energy dispersive X-ray spectroscopy. Our results showed that the relative number contribution of mineral particles to all measured particles was much higher during non-haze periods (42.5 %) than haze periods (18.1 %); in contrast, internally mixed particles contributed more during haze periods (21.9 %) than non-haze periods (7.2 %) at ground level. In addition, more mineral particles were found at ground level than above the mixed-layer height. Around 20 % of individual particles showed core–shell structures during haze periods, whereas only a few core–shell particles were observed during non-haze periods (2 %). The results showed that the particles above the mixed layer were more aged, with a larger proportion of organic particles originating from coal combustion. Our results indicate that a large fraction of the airborne particles above the mixed layer come from surrounding areas influenced by coal combustion activities. This source contributes to the surface particle concentrations in Beijing when polluted air is mixed down to the ground level.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2017

Characterization of Biological Fallout Particles of Cleanrooms to Measure Spacecraft Cleanliness

NASA cleanrooms are humidity, temperature-regulated, and particle contaminant-controlled environments used for spacecraft assembly. Microorganisms, which are crucial contaminants shed from humans and transported through the environment, can adapt to the oligotrophic cleanroom conditions. These biogenic particles need to be identified to extend our knowledge of biological contamination for future NASA mission use. Here, we devised an aluminum coupon with polycarbonate filter setup to collect fallout particles from an ISO 5 and an ISO 7 cleanroom. We demonstrated the presence of microbial particles, as standalone entities and associated with inert particles in cleanroom environments. The contamination was confirmed as biogenic in virtue of estimating the elemental composition of individual and aggregated particles using an epifluorescence and Field Emission Scanning Electron Microscopy (FESEM) coupled with an energy dispersive X-ray analysis (EDX). Epifluorescence microscopy showed that the particles were stained less (25%) with SYTO 9 and more (75%) with propidium iodide, suggesting that the suspected biogenic particles are membrane-compromised. Remarkably, biological particles such as bacteria and fungal spores/hyphae were observed at sizes ranging from 2 to 70 µm, with abundant C and O elemental signatures and essential tracers (Na, Mg, K, Ca and Cl). Inert particles (2 to 500 µm) that were characterized included compositions such as silica (SiO2), aluminosilicates (Al, Si), and carbonaceous fibers. Furthermore, we designed and illustrated a unique correlative epifluorescence and FE-SEM method to strengthen this approach by acquiring the same biogenic particles in the same filter coupon for a one-to-one comparison. Interestingly, the SYTO 9 stained particles showed abundant C and O elemental signature implying that they are viable microbial particles. Constant evaluation of cleanroom biological and inert particles will help to characterize biological contamination for future NASA missions (e.g. Mars 2020).

Malli Mohan, Ganesh Babu↗
DOE OSTI2020

The Lifshitz Regime and its Experimental Signals

We discuss the possibility of a Lifshitz regime, where the dispersion relation for Goldstone bosons and related fields has a minimum at nonzero momenta. Studies with the Functional Renormalization Group suggest that this occurs over a wide region in the plane of temperature and baryon chemical potential. Conversely, the FRG finds that the region in which fluctuations from a critical endpoint are significant is rather small. Here, we suggest that this is due generically to the narrowness of the tricritical region in the chiral limit. Even if particles are produced in thermal equilibrium, a dispersion relation which is non-monotonic in momenta produces what appears to be non-thermal behavior.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Topological contribution to the Bogoliubov coefficient for cosmological particle production

Particle production in cosmology is often efficiently computed in terms of Bogoliubov transforms. Restricting to a particular class of dispersion relationships, we identify a map between the number of particles produced in a special kinematic limit and a Stokes phenomena related topology of analytic continuation of the Bogoliubov coefficient functions. Intuitively, this kinematic limit corresponds to the long wavelength limit although a more precise description depends on the nature of the curved spacetime. To identify the topology, we reformulate the usual Bogoliubov computations as a type of SU(1, 1) gauged differential equation and utilize a special gauge together with a discrete symmetry that naturally characterizes the dispersion relationship. Using a dark matter model and a nonzero constant spatial curvature model, we estimate how such topological contributions will arise in physical applications. Published by the American Physical Society 2025

Chung, Daniel J. H. (ORCID:0000000343998504)↗
NASA NTRS1974

Interpretation of the polarization of Venus

The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of spherical particles. The refractive index of the particles is about 1.44 at 0.55 microns with a normal dispersion, the refractive index decreasing from about 1.46 at 0.365 microns to 1.43 at 0.99 microns. The cloud particles have a narrow size distribution with a mean radius of about 1 micron; specifically, the effective radius of the size distribution is approximately 1.05 microns and the effective variance is about 0.07. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb. The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venus. A concentrated solution of sulfuric acid provides good agreement with the polarization data.

Hansen, J. E.↗
NASA NTRS1984

Properties of simulated comet mantle

The properties of freeze-dried dilute dispersions of dust in water ice are of considerable interest in studies of comet nucleus mantles. The formation of a rind residue produced by the sublimation of water ice containing various amounts of fine clay particles may be an important process. A simulation of the development of the dry dust rind on the surface of comets is presented. This rind is the result of preferential ice sublimation. The development and disruption of this rind and its subsequent levitation by water vapor flow is studied. The most interesting rind simulant is produced by dispersing 0.1 micron particles of montmorillonite in water in concentrations of 10%, 1%, and 0.1%. These dispersions are then sprayed into liquid nitrogen in the form of 100 micron droplets. The frozen droplets are then freeze-dried in a vacuum which prevents the ice temperature from rising above -30 C. Sublimation of the nitrogen and the water produced dry rinds. The most striking result was the development of large cohesive matrices of individual clay particles, and in some cases a continuous cohesive crust. Scanning electron microscope (SEM) observations reveal that the material formed by freeze-drying the 0.1% dispersion does not retain the original spherical shape of the sprayed 100 micron droplets; instead it consists of a continuous filamentary network, as shown in the SEM stereo micrographs.

Fanale, F. P.↗