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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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Preliminary micrometeoroid and debris effects on LDEF thermal control surfaces

Thermal control surfaces on the Long Duration Exposure Facility (LDEF) were exposed to 5.75 years of low-Earth orbit environments. Since LDEF was gravity gradient stabilized and directionally stable, the effects of each of the environments can be distinguished via changes in material responses to hypervelocity impacts. The extent of these effects are being visually and microscopically characterized using thermal control surfaces archived at Johnson Space Center in order to determine the the relationship between environment exposure and resulting ring sizes, delamination areas, and penetration diameters. The characterization of these affected areas will provide spacecraft system designers with the information they require to determine degradation of thermal control systems during satellite lifetimes.

Allbrooks, Martha K.↗
DOE OSTI2019

Dramatic effect of oxide on measured liquid metal rheology

Liquid metals have traditionally been treated as Newtonian liquids, but several researchers have recently suggested that some metals may shear thin. While apparent shear thinning can be caused by surface oxidation, the reports of shear-thinning metals were investigated using cup and bob type rheometers, which are expected to only be weakly impacted by the surface contamination effects. We show here that even small amounts of oxide on the surface of liquid metals can cause dramatic changes to the measured viscosity of the sample. Using a Searle-type rotational rheometer, we measured the viscosity of eutectic gallium indium and tin in a low-oxygen environment. When either metal is slightly oxidized, the measured viscosity increases by orders of magnitude and the liquid displays erroneous shear-thinning behavior. When the oxide is removed via an active flux, the measured viscosity is Newtonian. The findings outlined here provide insight into the difficulties of measuring the viscosity of easily oxidized liquids and confirm that liquid metals are likely best described as Newtonian liquids at all measured shear rates.

36 MATERIALS SCIENCE↗
NASA NTRS1992

The effects of orbital and climatic variations on Martian surface heat flow

We have examined the effects of climate changes, induced by orbital oscillations, on Martian surface heat flow. It was found that the climatological component of the surface heat flow can be larger than the expected internal geothermal heat flow. We suggest that measurements of surface heat flow be targeted for equatorial and south polar regions to avoid climatic effects and that care be taken in interpreting measurements in mid-latitude and north polar regions.

Mellon, Michael T.↗
DOE OSTI2025

A theoretical study of the upper bound of surface elevation variance in the Phillips initial stage during wind-wave generation

The resonance mechanism in the initial of wind-wave generation proposed by Phillips is a foundation of wind-wave generation theory, but a precise theoretical quantification of wave energy growth in this initial stage has not been obtained yet after more than six decades of research. In this study, we aim to address this knowledge gap by developing an analytical approach based on a novel complex analysis method to theoretically investigate the temporal evolution of the wave energy in the Phillips initial stage. We quantitatively derive and analyse the growth behaviour of the surface wave energy and obtain an analytical solution for its upper bound. Our result highlights the crucial effects of surface tension. Because the phase velocity of gravity–capillary waves has a minimal value at a critical wavenumber, gravity–capillary waves and gravity waves (which neglect surface tension) exhibit distinct resonance curve properties and wave energy growth behaviours. For gravity waves, the resonance curve extends indefinitely; for gravity–capillary waves, it either forms a finite-length curve or does not exist, depending on the wind speed. The leading-order term of the upper-bound solution of the energy of gravity waves increases linearly over time, while for gravity–capillary waves, the term increases linearly over time under strong wind conditions but remains finite under weak wind conditions. This theoretical study provides an analytical framework for the generation of wind-waves in the Phillips initial stage, which may inspire further theoretical, numerical and experimental research.

58 GEOSCIENCES↗
DOE OSTI2018

PC-12 cells adhesion and differentiation on carbon aerogel scaffolds

Electrically conducting substrates have shown much promise as neuronal scaffolds and in other biologic and biomedical applications where a smart and electrically interactive material is needed. Most materials that are inherently conducting are not suitable for biomedical applications and lack biocompatibility or biostability. On the other hand, biologically stable and compatible materials must first be manipulated, modified, and treated in order to impart the necessary electrical conductivity to the material. Here, the authors have investigated the response of PC-12 cells to two types of conducting carbon-based aerogels with different surface roughness. Results show that carbon-based aerogels support cell adhesion, proliferation, and neurite extension. The effects of surface roughness have also been investigated.

carbon↗
NASA NTRS1985

Influence of the temperature of electrode material on its disintegration under the action of an arc discharge in hydrogen

An analysis is made of the electrophysical processes occurring at the end surface of rod electrodes during constant and alternating arc discharge in hydrogen. Experiments are reported on the effect of surface temperature of tungsten electrodes on their erosion. The influence of activating additions of thorium oxide, the structure of the tungsten, and the gas surrounding the electrode on the specific thermal loading and the erosion of the electrodes is discussed.

Bolotov, A. V.↗
NASA NTRS1950

The effects of variations in Reynolds number between 3.0 x 10sub6 and 25.0 x 10sub6 upon the aerodynamic characteristics of a number of NACA 6-series airfoil sections

Results are presented of an investigation made to determine the two-dimensional lift and drag characteristics of nine NACA 6-series airfoil section at Reynolds numbers of 15.0 x 10sub6, 20.0 x 10sub6, and 25.0 x 10sub6. Also presented are data from NACA Technical Report 824 for the same airfoils at Reynolds numbers of 3.0 x 10sub6, 6.0 x 10sub6, and 9.0 x 10sub6. The airfoils selected represent sections having variations in the airfoil thickness, thickness form, and camber. The characteristics of an airfoil with a split flap were determined in one instance, as was the effect of surface roughness. Qualitative explanations in terms of flow behavior are advanced for the observed types of scale effect.

Loftin, Laurence K, Jr↗
NASA NTRS2000

Azimuth variation in microwave scatterometer and radiometer data over Antarctica

In this paper, we explore the use of NASA scatterometer (NSCAT) data, European remote sensing (ERS) advanced microwave instrument (AMI) scatterometer mode data, and special sensor microwave/imager (SSM/I) data to study surface roughness effects in Antarctica. All three sensors provide strong evidence of azimuth modulation, which is correlated with the surface slope environment and results in a katabatic wind flow regime.

azimuthal↗
DOE OSTI2018

Simple and versatile UV-ozone oxide for silicon solar cell applications

Semiconductor surface clean is sometimes perceived as costly but long recognized as pivotal in determining the final semiconductor device performance and yield. In this contribution, we investigated the effectiveness of crystalline silicon surface cleaning by a simple UV-ozone process in comparison to the industry standard RCA clean for silicon photovoltaic applications. We present a unique method of processing the silicon surface effectively by UV-ozone cleaning. Despite being simple, UV-ozone cleaning results in a superior surface passivation quality that is comparable to high-quality RCA clean. When used as a stack dielectric—UV-ozone oxide overlaid by aluminum oxide—the thickness of UV-ozone oxide plays an important role in determining the passivation quality. Of all treatment times, 15 min of UV-ozone treatment results in an outstanding passivation quality, achieving the effective carrier lifetime of 3 ms and saturation current density of 5 fA/cm 2 . In addition, we present a simple and effective technique to extract values of electron/hole capture cross-section for the purpose of analyzing the interface passivation quality from already measured surface recombination parameters of saturation current density, interfacial trap density and total fixed charge, instead of measuring on the separately prepared metal-insulated-semiconductor (MIS) samples by the techniques: frequency-dependent parallel conductance or deep-level transient spectroscopy.

14 SOLAR ENERGY↗
DOE OSTI2024

Structure and Dynamics of Aqueous Electrolytes at Quartz (001) and (101) Surfaces

Here, understanding and describing reactivity at mineral-water interfaces such as ion adsorption, the kinetics of dissolution, or surface charge development depends on our ability to improve the accuracy of electrical double layer (EDL) models. While molecular dynamics (MD) simulations are routinely used to investigate the structure and energetics of adsorbed ions comprising the EDL, less attention is paid to their self-diffusion dynamics, which can uniquely inform on coupling to interfacial reactions. Here we use MD to investigate both the organization and diffusion dynamics of water and electrolyte ions (NaCl, KCl, CaCl 2 ) at hydroxylated quartz (001) and (101) surfaces, a comparison which allowed us to assess surface structural effects of corrugation and silanol density. We found that inner- versus outer-sphere complex formation depends on cation size and charge but not necessarily hydration energies. Participation of surface silanols in the hydration spheres of Na + and K + generally indicated their preference for inner-sphere complexation, but this depends strongly on the orientation of the surface considered through its influence over the organization and dynamics of adsorbed water layers. In particular, surface orientation substantially affects the diffusive behavior of the near-surface water. Na + was found to decrease the mobility of water in the first layer, consistent with an increasing frequency of hydrolysis implied by faster quartz dissolution rates observed in experiments via the well known salt effect. Our results are also in good agreement with the observed dissolution rate of quartz vs. surface adsorption strength measure by Dove and Nix. This study sets the stage for a forthcoming paper examining how the dynamics at quartz/electrolyte interfaces are influenced by externally applied electric fields.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2004

The Effect of Martian Dust on Radiator Performance

Experiments were performed in which the effective emittance of three types of radiator Coatings was measured as Martian dust simulant was added to the radiator face. The apparatus consisted of multiple radiator coupons on which Carbondale Red Clay dust was deposited. The coupons were powered by electric heaters, using a guard-heating configuration to achieve the accuracy required for acceptable emittance calculations. The apparatus was containing in a vacuum chamber that featured a liquid-nitrogen cooled shroud that simulated the Martian sky temperature. Radiator temperatures ranged from 250 to 350 K with sky temperatures from 185 to 248 K. Results show that as dust was added to the radiator surfaces, the effective emittance of the high - emittance coatings decreased from near 0.9 to a value of about 0.5. A low-emittance control surface, polished aluminum, demonstrated a rise in effective emittance for thin dust layers, and then a decline as the dust layer thickened. This behavior is attributed to the conductive resistance caused by the dust layer.

Hollingsworth, D. Keith↗
NASA NTRS1985

Study of the effects of implantation on the high Fe-Ni-Cr and Ni-Cr-Al alloys

A theoretical study of the effects of implantation on the corrosion resistance of Fe-Ni-Cr and Ni-Cr-Al alloys was undertaken. The purpose was to elucidate the process by which corrosion scales form on alloy surfaces. The experiments dealt with Ni implanted with Al, exposed to S at high temperatures, and then analyzed using scanning electron microscopy, scanning Auger spectroscopy and X-ray fluorescence spectroscopy. Pair bonding and tight-binding models were developed to study the compositions of the alloys and as a result, a new surface ordering effect was found which may exist in certain real alloys. With these models, the behavior of alloy constituents in the presence of surface concentrations of O or S was also studied. Improvements of the models to take into account the important effects of long- and short-range ordering were considered. The diffusion kinetics of implant profiles at various temperatures were investigated, and it was found that significant non-equilibrium changes in the profiles can take place which may affect the implants' performance in the presence of surface contaminants.

Ribarsky, M. W.↗
DOE OSTI2018

Evaluating Water Reactivity at Silica Surfaces Using Reactive Potentials

Understanding the interactions between amorphous silica surfaces and water provides insight into material degradation of silicate glasses and minerals in aqueous environment. Molecular dynamics (MD) simulations of water and nanometer sized silica structures were used in this work to evaluate the reactivity of flat silica surface and surfaces with curvature. We compared two dissociable water/silica potentials, namely the Reactive Force Field (ReaxFF) and the Mahadevan–Garofalini water/silica force field (MGFF) that have been in development over the past decade, to study their performance in simulating bulk water as well as silica–water interactions. Significant differences in the properties of bulk water as well as surface interactions were observed between the two types of potentials, as well in the same potential type with two parametrizations for ReaxFF, suggesting a need for improvement of the existing water/silica ReaxFF potentials. Our simulation results show that a majority of the silanols were formed by reactions between water and strained siloxane bonds that mainly exist on the surface of amorphous silica, within a few nanoseconds of the simulation time scale, in agreement with previous studies. Effect of surface curvature on the reactivity with water was investigated. Our results indicate that defect concentration at the surface bears a strong correlation to the concentration of silanols (Si–OH) that eventually form. We observe undercoordinated Si’s at the surface that are attacked by water before the hydrolysis reaction of the siloxane bonds and demonstrate possible mechanisms of water reacting with these undercoordinated Si’s. Furthermore, we also find that the method of generating surfaces in simulation determines the defect concentration and hence influences the reactivity of the amorphous silica surface.

36 MATERIALS SCIENCE↗
NASA NTRS1977

Evaluation and control of environmental corrosion for aluminum and steel alloys

Corrosion protection systems for aerospace application and the effects of surface treatments and methods of controlling stress corrosion are evaluated. Chromate pigmented systems were found to be most effective for aluminum alloys; zinc-rich coatings gave the greatest protection to steel alloys. Various steel and aluminum alloys are rated for stress corrosion resistance.

Franklin, D. B.↗
NASA NTRS1992

Modeling variable blowing effects in the turbulent hypersonic boundary layer

Studies of the effects of variable blowing in turbulent hypersonic boundary layers are presented. Numerical calculations of the skin friction and surface heat transfer rates are compared to the experimental measurements of Holden (1990) for a slender cone at zero angle of attack in steady flows at Mach numbers of 11 and 13. An analysis of the transpiration feed system of the cone model was performed and showed that the blowing rate could be variable along the cone surface. This effect is confirmed by internal pressure measurements which were taken inside the cone model. The blowing rates are recalibrated using the internal gauge readings and used as the wall boundary condition for a compressible turbulent boundary layer calculation using the low Reynolds number k-epsilon model of Chien (1982). At low blowing rates, the boundary layer calculations indicate that a situation where both the effects of suction and blowing are present within the same flow. The results show excellent qualitative prediction of the experimental data.

Vanosdol, John G.↗
NASA NTRS1991

Hypersonic stability and transition

An evaluation is conducted of the development status of growing normal modes in the computation of flow fields over hypersonic vehicles, giving attention to the effects of surface cooling, pressure gradients, and suction on the growth rates of the normal modes. Also noted are the effects of bluntness on the stability properties of hypersonic vehicles, and the efficacy of the e exp N method of transition estimation at supersonic and hypersonic speeds. A survey is made of the precautions that must be taken to ensure the effectiveness of experimental and computational studies of hypersonic flow phenomena.

Reshotko, Eli↗
NASA NTRSDate not supplied

Surface Temperature and the Compositional Effects of Electron Bombardment on Dione

Saturn’s icy moons are composed of mostly water ice with minor “contaminants,” such as CO2 ice, and a dark component thought to be organics, hematite and/or metallic Fe [1]. The space weathering process of electron bombardment is expected to be particularly important on the surfaces of Saturn’s inner moons (Mimas, Tethys, Dione, and Rhea), as they orbit within the extended plasma sheet of Saturn’s magnetosphere. Terrains exhibiting thermal anomalies (i.e., colder temperatures in the day and warmer temperatures at night than surrounding areas) correspond to regions of high energy electron bombardment [2; 3]. Energetic electrons impact the surfaces, fracturing ice particles into sub-micron sized grains, and this process becomes more effective for increasing particle energies [4]. In addition to alteration of ices, the dark material may also be modified or generated within icy surfaces by interaction with solar UV radiation, cosmic rays, or by particles trapped in Saturn’s magnetic field [5]. CO2 could be sourced from irradiation of dark organic material [7]. Many of these alterations should be observable in Visible and Infrared Mapping Spectrometer (VIMS) spectra [8]. We used surface temperatures derived from Cassini’s Composite Infrared Spectrometer (CIRS) to help isolate areas where space weathering due to electron bombardment is more predominant and investigated the subtle changes in VIMS spectra using machine learning techniques. We present our results here for Dione. On ocean worlds, space weathering products would be present along with any potential indications of life. We will need to understand the manifestation of space weathering in the data to separate the two processes.

Cindy Lee Young↗
DOE OSTI2022

Electron beam surface remelting enhanced corrosion resistance of additively manufactured Ti-6Al-4V as a potential in-situ re-finishing technique

This study explores the effect of surface re-finishing on the corrosion behavior of electron beam manufactured (EBM) Ti-G5 (Ti-6Al-4V), including the novel application of an electron beam surface remelting (EBSR) technique. Specifically, the relationship between material surface roughness and corrosion resistance was examined. Surface roughness was tested in the as-printed (AP), mechanically polished (MP), and EBSR states and compared to wrought (WR) counterparts. Electrochemical measurements were performed in chloride-containing media. It was observed that surface roughness, rather than differences in the underlying microstructure, played a more significant role in the general corrosion resistance in the environment explored here. While both MP and EBSR methods reduced surface roughness and enhanced corrosion resistance, mechanical polishing has many known limitations. The EBSR process explored herein demonstrated positive preliminary results. The surface roughness (R a ) of the EBM-AP material was considerably reduced by 82%. Additionally, the measured corrosion current density in 0.6 M NaCl for the EBSR sample is 0.05 µA cm –2 , five times less than the value obtained for the EBM-AP specimen (0.26 µA cm –2 ).

42 ENGINEERING↗

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