Influence of chemisorbed films on adhesion and friction of clean iron
Reduction of adhesive forces and friction of iron polycrystals in vacuum by chemisorbed films
Buckley, D. H.↗
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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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A study of the adhesion and cohesion of metals Summary report, 10 Mar. 1967 - 10 Mar. 1968
Interfacial adhesion force produced by contact under axial loads of Cu and Ni surfaces in high vacuum related to electrical resistance and plastic strain
Hordon, M. J.↗
Effect of various properties of fcc metals on their adhesion as studied with LEED
Fcc metals surface changes following adhesion using low energy electron diffraction /LEED/, relating intersurface metal transfer to applied adhesive force
Buckley, D. H.↗
Electrostatic dust transport and its consequences for the lunar ranging experiment
Attempts made to qualitatively model the available data concerning the electrostatic transport of dust on the lunar surface are noted. Charged dust grains, held in place by adhesive forces, are shot into space at velocities of hundreds of meters per second. Larger particles, because of their greater charge, are quickly decelerated in the nearby fields, while the smaller grains travel in ballistic trajectories for hundreds of kilometers. Flux estimates indicate that there is little danger to the optical corner reflectors for the next few decades.
Silverberg, E. C.↗
Friction behavior of members of the platinum metals group with gold
The adhesion and friction behavior of the platinum metals group was examined with clean surfaces and surfaces selectively contaminated with oxygen, vinyl chloride (C2H3Cl), and methyl mercaptan (CH3SH). A pin or disk specimen configuration was used with the pin being a single crystal of gold of the (111) orientation and with the platinum metal disks also being single crystals of the (111) or (0001) orientation. Loads applied ranged from 1 to 10 g and a sliding velocity of 0.7 mm/min was employed. Results indicate adhesion and transfer of gold to all of the platinum metals. Despite this observation friction differences existed among the metals in the group. These differences are related to surface chemical activity. Adsorption of various friction reducing species was selective. With some adsorbates present strong adhesive forces between metals were still observed.
Buckley, D. H.↗
Lunar dust transport by photoelectric charging at sunset
The motion of dust grains from a photoelectrically charged object at the moon's sunset terminator is studied with the aid of a simple model. It is shown that sunlit objects ranging in size from less than 0.01 cm to 5 cm in radius are responsible for the levitation of dust grains to heights of observed horizon glow. The transverse displacement of these grains is observed to be at least twice their maximum altitude, so that fitting the latter to horizon glow implies horizontal particle ranges typically 6 to 60 cm. Detachment of these grains from the sunlit areas takes place mainly along the contracting sunlight boundaries as the areas shrink during sunset. A high ratio of intergrain adhesion force to dust-grain weight is essential for the occurrence of horizon glow and significant dust transport from the subcentimeter sized sunlit areas.
Pelizzari, M. A.↗
Active heat exchange system development for latent heat thermal energy storage
Various active heat exchange concepts were identified from among three generic categories: scrapers, agitators/vibrators and slurries. The more practical ones were given a more detailed technical evaluation and an economic comparison with a passive tube-shell design for a reference application (300 MW sub t storage for 6 hours). Two concepts were selected for hardware development: (1) a direct contact heat exchanger in which molten salt droplets are injected into a cooler counterflowing stream of liquid metal carrier fluid, and (2) a rotating drum scraper in which molten salt is sprayed onto the circumference of a rotating drum, which contains the fluid salt is sprayed onto the circumference of a rotating drum, which contains the fluid heat sink in an internal annulus near the surface. A fixed scraper blade removes the solidified salt from the surface which was nickel plated to decrease adhesion forces. In addition to improving performance by providing a nearly constant transfer rate during discharge, these active heat exchanger concepts were estimated to cost at least 25% less than the passive tube-shell design.
Alario, J.↗
Active heat exchange system development for latent heat thermal energy storage
Various active heat exchange concepts were identified from among three generic categories: scrapers, agitators/vibrators and slurries. The more practical ones were given a more detailed technical evaluation and an economic comparison with a passive tube-shell design for a reference application. Two concepts selected for hardware development are a direct contact heat exchanger in which molten salt droplets are injected into a cooler counterflowing stream of liquid metal carrier fluid, and a rotating drum scraper in which molten salt is sprayed onto the circumference of a rotating drum, which contains the fluid heat sink in an internal annulus near the surface. A fixed scraper blade removes the solidified salt from the surface which has been nickel plated to decrease adhesion forces. Suitable phase change material (PCM) storage media with melting points in the temperature range of interest (250 C to 400 C) were investigated. The specific salt recommended for laboratory tests was a chloride eutectic (20.5KCl-24/5 NaCl-55.0MgCl 2% by wt.), with a nominal melting point of 385 C.
Alario, J.↗
Toward a model of grain surface exposure in planetary regoliths
The interpretation of solar wind implanted gas concentration versus particle size for lunar regolith samples is considered. In so doing, interparticle adhesive forces are considered explicitly and the simplest possible grain exposure law consistent with the existence of such forces is hypothesized. Namely, for particles small enough that these forces exceed the lunar gravitational force, any element of area has equal probability of being in the regolith surface regardless of the size of the grain on which it is situated. This law leads to the expectation that concentrations will depend inversely on mean grain radius for small grains and gradually become independent of radius for very large grains consistent with observations. Therefore, such a concentration dependence cannot by used to infer the presence of saturation losses.
Housley, R. M.↗
Particle adhesion to surfaces under vacuum
The release of glass beads and standard dust from aluminum and glass substrates under centrifugation (simulating atmospheric pressure, low vacuum, and high vacuum conditions) was measured, with application to the estimation of contaminant particle release during spacecraft launch. For particles in the 10-100 micron range, dust was found to adhere more strongly than glass beads in all the cases considered. For most of the cases, dust and glass beads adhered more strongly to glass than to aluminum at all pressures. The adhesion force for dust on glass at 10 torr was shown to be as small as the value for dust on aluminum.
Barengoltz, Jack B.↗
Polyphosphazene Icephobic Coating Materials
Coating materials consisting mostly of modified polyphosphazene (Class FZ) elastomers provide better protection against icing than fluorocarbon polymers and silicone elastomers. Reduces adhesive force between ice and surface. As consequence, increasing weight of ice, wind loading, or vibration of surface causes ice to be shed. New icephobic coats reduce accumulation of ice on aircraft, radomes, antennas, ships, and power-transmission lines.
Willis, Paul B.↗
Degradation of radiator performance on Mars due to dust
An artificial mineral of the approximate elemental composition of Martian soil was manufactured, crushed, and sorted into four different size ranges. Dust particles from three of these size ranges were applied to arc-textured Nb-1 percent Zr and Cu radiator surfaces to assess their effect on radiator performance. Particles larger than 75 microns did not have sufficient adhesive forces to adhere to the samples at angles greater than about 27 deg. Pre-deposited dust layers were largely removed by clear wind velocities greater than 40 m/s, or by dust-laden wind velocities as low as 25 m/s. Smaller dust grains were more difficult to remove. Abrasion was found to be significant only in high velocity winds (89 m/s or greater). Dust-laden winds were found to be more abrasive than clear wind. Initially dusted samples abraded less than initially clear samples in dust laden wind. Smaller dust particles of the simulant proved to be more abrasive than large. This probably indicates that the larger particles were in fact agglomerates.
Gaier, James R.↗
A Photographic Study of Liquid Hydrogen Under Simulated Zero Gravity Conditions
The transient behavior of liquid hydrogen, under conditions of zero gravity, was studied photographically. The hydrogen was subjected to weightlessness by dropping a Dewar containing this liquid from a height of 9 feet. During the weightless period of approximately 3/4 second, the liquid rose along the walls of the Dewar into the original vapor space. The rise occurred at constant velocity for practically the entire duration of this period. Adhesive forces were concluded to be the primary cause of the liquid rise along the wall.
Brazinsky, Irving↗
Resistance to Sliding on Atomic Scales
The structure and stability of agglomerates of micron-sized particles is determined by the mechanical properties of the individual contacts between the constituent particles. In this paper we study the possibility of aggregate rearrangements by sliding. Since the contacts between (sub)micron particles are only a few hundred atoms in diameter, processes on atomic levels will play the dominating roll. We study a theoretical model of sliding friction for surfaces that are either flat or contain steps in their grids. The results show that sliding over flat surfaces may produce a large range of friction coefficients, including zero if the adhesive forces are small compared to the binding forces inside a body. However, both grid alignment and steps in the surface will lead to high values for friction. These processes combined virtually eliminate the possibility of sliding in a collision of two (sub)micron sized particles at velocities low enough for sticking to occur. On the other hand we show that in collisions between aggregates sliding may be an important factor for energy dissipation and compaction.
Dominik, C.↗
Multiwalled Carbon Nanotube/nanofiber Arrays as Conductive and Dry Adhesive Interface Materials
We demonstrate the possibility of making conductive and dry adhesive interfaces between multiwalled carbon nanotube (MWNT) and nanofiber (MWNF) arrays grown by chemical vapor deposition with transition-metal as catalyst on highly Boron doped silicon substrates. The maximum observed adhesion force between MWNT and MWNF surfaces is 3.5 mN for an apparent contact area of 2 mm by 4 mm. The minimum contact resistance measured at the same time is approx.20 Omega. Contact resistances of MWNT-MWNT and MWNT-gold interfaces were also measured as pressure forces around several mN were applied at the interface. The resulting minimum contact resistances are on the same order but with considerable variation from sample to sample. For MWNT-MWNT contacts, a minimum contact resistance of approx.1 Omega is observed for a contact area of 2 mm by 1 mm. The relatively high contact resistances, considering the area density of the nanotubes, might be explained by the high cross-tube resistances at the contact interfaces.
Tong, Tao↗
Elastomeric Seal Development for Advanced Docking/Berthing System
Elastomeric seals ar Elastomeric seals are being considered for application to the Advanced Docking / Berthing System. Currently, three candidate elastomers are being evaluated. To meet the unique requirements of the ADBS, several test fixtures have been built to determine each elastomer s Environmental and operating temperature compatibility Material stability when exposed to Atomic Oxygen and Ultraviolet radiation Adhesion force required to separate Compression set Leak rate These results will be compared with those from the metallic seal development to determine the final seal design
Daniels, Christopher↗
Overview of LIDS Docking and Berthing System Seals
This viewgraph presentation describes the Low Impact Docking System (LIDS) docking and berthing system seals. The contents include: 1) Description of the Application: Low Impact Docking System (LIDS); 2) LIDS Seal Locations: Vehicle Undocked (Hatch Closed); 3) LIDS Seal Locations: Mechanical Pass Thru; 4) LIDS Seal Locations: Electrical and Pyro Connectors; 5) LIDS Seal Locations: Vehicle Docked (Hatches Open); 6) LIDS Seal Locations: Main Interface Seal; 7) Main Interface Seal Challenges and Specifications; 8) Approach; 9) Seal Concepts Under Development/Evaluation; 10) Elastomer Material Evaluations; 11) Evaluation of Relevant Seal Properties; 12) Medium-Scale (12") Gask-O-Seal Compression Tests; 13) Medium-Scale Compression Results; 14) Adhesion Forces of Elliptical Top Gask-o-seals; 15) Medium-Scale Seals; 16) Medium-Scale Leakage Results: Effect of Configuration; 17) Full Scale LIDS Seal Test Rig Development; 18) Materials International Space Station Experiment (MISSE 6A and 6B); and 19) Schedule.
Daniels, Christopher C.↗
Overview of NASA Glenn Seal Project
NASA Glenn is currently performing seal research supporting both advanced turbine engine development and advanced space vehicle/propulsion system development. Studies have shown that decreasing parasitic leakage by applying advanced seals will increase turbine engine performance and decrease operating costs. Studies have also shown that higher temperature, long life seals are critical in meeting next generation space vehicle and propulsion system goals in the areas of performance, reusability, safety, and cost. Advanced docking system seals need to be very robust resisting space environmental effects while exhibiting very low leakage and low compression and adhesion forces. NASA Glenn is developing seal technology and providing technical consultation for the Agencys key aero- and space technology development programs.
Steinetz, Bruce M.↗