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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Preliminary Assessment of Seals for Dust Mitigation of Mechanical Components for Lunar Surface Systems

Component tests were conducted on spring-loaded Teflon seals to determine their performance in keeping lunar simulant out of mechanical component gearbox, motor, and bearing housings. Baseline tests were run in a dry-room without simulant for 10,000 cycles to determine wear effects of the seal against either anodized aluminum or stainless steel shafts. Repeat tests were conducted using lunar simulants JSC-1A and LHT-2M. Finally, tests were conducted with and without simulant in vacuum at ambient temperature. Preliminary results indicate minimal seal and shaft wear through 10,000 cycles, and more importantly, no simulant was observed to pass through the seal-shaft interface. Future endurance tests are planned at relevant NASA Lunar Surface System architecture shaft sizes and operating conditions.

Delgado, Irebert R.↗
NASA NTRS1982

Microscopic contour changes of tribological surfaces by chemical and mechanical action

An electronic optical laser interferometer capable of resolving depth differences of as low as 30 A and planar displacements of 6000 A was constructed for the examination of surface profiles of bearing surfaces without physical contact. This instrument was used to determine topological chemical reactivity by applying a drop of dilute alcoholic hydrochloric acid and measuring the profile of the solid surface before and after application of this probe. It was found that scuffed bearing surfaces reacted much faster than virgin ones but that bearing surfaces exposed to lubricants containing an organic chloride reacted much more slowly. In a separate series of experiments, a number of stainless steel plates were heated in a nitrogen atmosphere to different temperatures and their reactivity examined later at ambient temperature. The change of surface contour as a result of the probe reaction was found to follow an Arrhenius-type relation with respect to heat treatment temperature. This result could have implications on the scuffing mechanism.

Lauer, J. L.↗
NASA NTRS1991

Design of equipment for lunar dust removal

NASA has a long range goal of constructing a fully equipped, manned lunar base on the near side of the moon by the year 2015. During the Apollo Missions, lunar dust coated and fouled equipment surfaces and mechanisms exposed to the lunar environment. In addition, the atmosphere and internal surfaces of the lunar excursion module were contaminated by lunar dust which was brought in on articles passed through the airlock. Consequently, the need exists for device or appliance to remove lunar dust from surfaces of material objects used outside of the proposed lunar habitat. Additionally, several concepts were investigated for preventing the accumulation of lunar dust on mechanisms and finished surfaces. The character of the dust and the lunar environment present unique challenges for the removal of contamination from exposed surfaces. In addition to a study of lunar dust adhesion properties, the project examines the use of various energy domains for removing the dust from exposed surfaces. Also, prevention alternatives are examined for systems exposed to lunar dust. A concept utilizing a pressurized gas is presented for dust removal outside of an atmospherically controlled environment. The concept consists of a small astronaut/robotic compatible device which removes dust from contaminated surfaces by a small burst of gas.

Belden, Lacy↗
NASA NTRS2004

Measurements of Ocean Surface Scattering Using an Airborne 94-GHz Cloud Radar: Implication for Calibration of Airborne and Spaceborne W-band Radars

Scattering properties of the Ocean surface have been widely used as a calibration reference for airborne and spaceborne microwave sensors. However, at millimeter-wave frequencies, the ocean surface backscattering mechanism is still not well understood, in part, due to the lack of experimental measurements. During the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE), measurements of ocean surface backscattering were made using a 94-GHz (W-band) cloud radar onboard a NASA ER-2 high-altitude aircraft. The measurement set includes the normalized Ocean surface cross section over a range of the incidence angles under a variety of wind conditions. Analysis of the radar measurements shows good agreement with a quasi-specular scattering model. This unprecedented dataset enhances our knowledge about the Ocean surface scattering mechanism at 94 GHz. The results of this work support the proposition of using the Ocean surface as a calibration reference for airborne millimeter-wave cloud radars and for the ongoing NASA CloudSat mission, which will use a 94-GHz spaceborne cloud radar for global cloud measurements.

Li, Li-Hua↗
NASA NTRS2009

A Robust Mechanical Sensing System for Unmanned Sea Surface Vehicles

The need for autonomous navigation and intelligent control of unmanned sea surface vehicles requires a mechanically robust sensing architecture that is watertight, durable, and insensitive to vibration and shock loading. The sensing system developed here comprises four black and white cameras and a single color camera. The cameras are rigidly mounted to a camera bar that can be reconfigured to mount multiple vehicles, and act as both navigational cameras and application cameras. The cameras are housed in watertight casings to protect them and their electronics from moisture and wave splashes. Two of the black and white cameras are positioned to provide lateral vision. They are angled away from the front of the vehicle at horizontal angles to provide ideal fields of view for mapping and autonomous navigation. The other two black and white cameras are positioned at an angle into the color camera's field of view to support vehicle applications. These two cameras provide an overlap, as well as a backup to the front camera. The color camera is positioned directly in the middle of the bar, aimed straight ahead. This system is applicable to any sea-going vehicle, both on Earth and in space.

Kulczycki, Eric A.↗
DOE OSTI2020

Surface functionality and formation mechanisms of carbon and graphene quantum dots

Graphene quantum dots (GQDs) and Carbon dots (C-dots) have been widely studied in recent years due to their structural and optoelectrical properties. These properties have prompted the exploration of the role of these carbon-based materials in many potential applications. This includes solar cells, photodetectors, bioimaging, sensors, batteries and drug delivery. These properties and applications of GQDs and C-dots are highly dependent on their size, shape and surface functionality. In this work, GQDs and C-dots mixtures have been synthesized by an inexpensive wet chemical method by varying the synthesis temperature from 85°, 100° to 115 °C. The surface functionalities of the synthesized carbon-based materials were investigated by several analytical methods. We discovered a higher degree of oxidation at higher temperatures. The mechanism of formation of different sized GQDs and C-dots with different functionalities have been explained with the help of XPS and NEXAFS analysis. The influence of size and surface functionalities on the optical properties of these nanomaterials is analyzed by UV–Vis and PL spectroscopic techniques. Furthermore, this study demonstrates that physicochemical properties of GQDs and C-dots can be controlled by changing the synthesis temperature.

36 MATERIALS SCIENCE↗
NASA NTRS1993

Rough surface scattering from moving ocean surfaces as an indicator of scattering mechanisms

Ever since Crombie used the Doppler spectrum of RF signals scattered from the ocean surface to provide conclusive evidence for Bragg resonant scattering, scattering from the ocean surface has served as a testing ground for the identification of governing scattering mechanisms in rough surface scattering. The moving ocean surface has the advantage for rough surface scattering that, being a dispersive medium, features with different spatial scales the tendency to travel at different speeds. Thus, by looking at the temporal signature of the scattered field, one can try to isolate the scattering mechanism. This feature has been exploited by various authors. To give a recent example, we cite the work of Plant, who examined the Doppler spectrum of the return signal to infer the presence of two-scale scattering in scattering at medium incidence angles. The problem with restricting oneself to the examination of the Doppler spectrum, as has been done traditionally, is that one restricts the phenomena under investigation to temporally homogeneous phenomena: transient phenomena, which are localized in time, are not localized in frequency space. There is increasing evidence that this type of phenomena, due to specular scattering or breaking waves, may also play an important role in determining the scattering mechanism in ocean-like surfaces. To overcome this problem, we introduce the use of the Wavelet Transform to study the frequency-temporal signatures of the scattered field from moving ocean waves. We calculate this signature using various analytic scattering theories and show that the Wavelet Transform provides a useful tool for separating the different scattering mechanisms operating in scattering in ocean-like surfaces. Next we simulate realistic nonlinear moving ocean waves and calculate the temporal scattered field signature by using the method of moments and the stop-start approximation: the surface is assumed stationary during a scattering event, but moves between incident EM pulses. We compute and compare the Doppler frequency spectrum and the Wavelet Transform of the resulting signal for various types of surfaces and show how different scattering mechanisms may be isolated by this technique. Finally, we compare these numerical results against the analytical predictions in order to obtain the domain of applicability of various scattering theories for moving ocean surfaces which may include wave breaking and specular glints.

Rodriguez, Ernesto↗
DOE OSTI2021

From thermal catalysis to plasma catalysis: a review of surface processes and their characterizations

The use of atmospheric pressure plasma to enhance catalytic chemical reactions involves complex surface processes induced by the interactions of plasma-generated fluxes with catalyst surfaces. Industrial implementation of plasma catalysis necessitates optimizing the design and realization of plasma catalytic reactors that enable chemical reactions that are superior to conventional thermal catalysis approaches. This requires the fundamental understanding of essential plasma-surface interaction mechanisms of plasma catalysis from the aspect of experimental investigation and theoretical analysis or computational modeling. In addition, experimental results are essential to validate the relative theoretical models and hypotheses of plasma catalysis that was rarely understood so far, compared to conventional thermal catalysis. This overview focuses on two important application areas, nitrogen fixation and methane reforming, and presents a comparison of important aspects of the state of knowledge of these applications when performed using either plasma-catalysis or conventional thermal catalysis. We discuss the potential advantage of plasma catalysis over thermal catalysis from the aspects of plasma induced synergistic effect and in situ catalyst regeneration. In-situ/operando surface characterization of catalysts in plasma catalytic reactors is a significant challenge since the high pressure of realistic plasma catalysis systems preclude the application of many standard surface characterization techniques that operate in a low-pressure environment. Here, we present a review of the status of experimental approaches to probe gas-surface interaction mechanisms of plasma catalysis, including an appraisal of demonstrated approaches for integrating surface diagnostic tools into plasma catalytic reactors.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Hydrogen bond–induced aqueous-phase surface modification of nanocellulose and its mechanically strong composites

Aqueous-phase surface modification of nanocellulose is desirable because nanocellulose is generally produced via water-based fibrillation. In this study, a hydrogen bond–induced surface modification of cellulose nanofibrils (CNFs) in water was developed. Tannic acid and polyvinylpyrrolidone were chosen to modify the CNFs because of their strong capacity for hydrogen bond formation. By tuning the hydrogen bond formation between CNFs, tannic acid, and polyvinylpyrrolidone, CNFs with different surface hydrophilicity were achieved. Additionally, the modified CNFs can assemble into strong and tough composites owing to the hydrogen bond network in the system. Modified CNFs demonstrated 76% higher tensile strength and 100% higher toughness than those of unmodified CNFs, reaching 162 MPa and 12.7 MJ/m 3 , respectively. This study provides a new water-based modification strategy for the nanocellulose, leading the way toward producing strong nanocellulose composites via noncovalent interaction.

36 MATERIALS SCIENCE↗
NASA NTRS1977

A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

The effects of composites as adherends was studied. Several other variables were studied by fractography: aluminum powder adhesive filler, fiber glass cloth scrim or adhesive carrier, new adhesives PPQ-413 and LARC-13, and strength-test temperature. When the new results were juxtaposed with previous work, it appeared that complex interactions between adhesive, adherend, bonding, and testing conditions govern the observed strength and fracture-surface features. The design parameters likely to have a significant effect upon strength-test results are listed.

Dwight, D. W.↗
DOE OSTI2023

Surface impacts and associated mechanisms of a moisture intrusion into the Arctic observed in mid-April 2020 during MOSAiC

Distinct events of warm and moist air intrusions (WAIs) from mid-latitudes have pronounced impacts on the Arctic climate system. We present a detailed analysis of a record-breaking WAI observed during the MOSAiC expedition in mid-April 2020. By combining Eulerian with Lagrangian frameworks and using simulations across different scales, we investigate aspects of air mass transformations via cloud processes and quantify related surface impacts. The WAI is characterized by two distinct pathways, Siberian and Atlantic. A moist static energy transport across the Arctic Circle above the climatological 90th percentile is found. Observations at research vessel Polarstern show a transition from radiatively clear to cloudy state with significant precipitation and a positive surface energy balance (SEB), i.e., surface warming. WAI air parcels reach Polarstern first near the tropopause, and only 1–2 days later at lower altitudes. In the 5 days prior to the event, latent heat release during cloud formation triggers maximum diabatic heating rates in excess of 20 K d -1 . For some poleward drifting air parcels, this facilitates strong ascent by up to 9 km. Based on model experiments, we explore the role of two key cloud-determining factors. First, we test the role moisture availability by reducing lateral moisture inflow during the WAI by 30%. This does not significantly affect the liquid water path, and therefore the SEB, in the central Arctic. The cause are counteracting mechanisms of cloud formation and precipitation along the trajectory. Second, we test the impact of increasing Cloud Condensation Nuclei concentrations from 10 to 1,000 cm -3 (pristine Arctic to highly polluted), which enhances cloud water content. Resulting stronger longwave cooling at cloud top makes entrainment more efficient and deepens the atmospheric boundary layer. Finally, we show the strongly positive effect of the WAI on the SEB. This is mainly driven by turbulent heat fluxes over the ocean, but radiation over sea ice. The WAI also contributes a large fraction to precipitation in the Arctic, reaching 30% of total precipitation in a 9-day period at the MOSAiC site. However, measured precipitation varies substantially between different platforms. Therefore, estimates of total precipitation are subject to considerable observational uncertainty.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Water-induced surface ordering facilitating the microcutting of ductile metals

Metal cutting is a crucial process in modern manufacturing. Enhancing the machinability of metals can significantly improve their production efficiency and surface integrity. Coating surface-active media (SAM) on the free surface of the metals before cutting is an easy method to improve machinability, which usually pertains to the category of the renowned Rehbinder effect. However, the existing SAM is usually hazardous and complex materials. Besides, the effect of SAM on the local structure of the metal surface remains unclear. In this study, water is employed as a simple yet often overlooked SAM in the microcutting of copper. Using water as SAM also allows the employment of X-ray absorption fine structure spectroscopy (XAFS) to study the local structure of copper with and without water coating. Results show that water coating on the free surface of copper can significantly reduce the cutting force and chip thickness, and improve the surface finish. Interestingly, removing the water coating enables the recovery of the cutting force, demonstrating a reversible effect. Based on the XAFS results and molecular dynamics simulation, a water-induced surface ordering mechanism is proposed to explain the findings from the microcutting experiments. This mechanism suggests that water molecules can induce surface ordering in copper, resulting in reduced surface energy and fracture toughness of copper, thus enhancing machinability. In conclusion, this work provides valuable insights into the comprehension of the Rehbinder effect and shows that picometer-scale modifications of the surface atom arrangement can considerably alter the deformation mode of metals, paving the way for the development of new manufacturing processes.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Evaporation of a Reactive Nanofluid Sessile Drop: Capturing Rapid Emergence of Surface Crystals with In Situ Synchrotron X-ray Diffraction

Mechanisms for surface pattern formation from evaporation of a reactive nanofluid sessile drop are not well understood. In contrast to the coffee-ring effect from inert particles, rapid chemical and morphological transformation of reactive nanoparticles upon rapid evaporative drying are challenging to probe experimentally. Here, using grazing-incidence X-ray surface scattering, the nanostructure of nascent surface patterns has been probed as a ZnO nanofluid sessile drop rapidly dries. The high temporal resolution enabled by the high flux of synchrotron X-rays allows the observation of the emergence of Zn(OH) 2 surface crystals from the onset of evaporation and their rapid evolution into the final residual surface pattern, via transient layered complexes evident from the temporary appearance of X-ray diffraction peaks preceding Zn(OH) 2 formation. The results offer mechanistic insights of morphogenesis of surface patterns from evaporation-induced self-assembly and self-organization of reactive nanofluids, previously untenable using other experimental methods.

36 MATERIALS SCIENCE↗