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NASA NTRS1982

Tribological properties of sintered polycrystalline and single crystal silicon carbide

Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

Miyoshi, K.↗

NASA NTRS1989

A characterization study of a hydroxylated polycrystalline tin oxide surface

In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 C causes a large reduction in the surface hydrogen concentration but not complete removal.

Hoflund, Gar B.↗

NASA NTRS2000

Friction and Wear Properties of Selected Solid Lubricating Films: Ion-Plated Lead Films - Part 2

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of ion-plated lead films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7 x 10(exp -7 Pa), humid air (relative humidity, approx. 20 percent), and dry nitrogen (relative humidity, less then 1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the ion-plated lead films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the ion-plated lead films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 1(exp -6) cu mm/N.m or less, respectively. The ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen, where the coefficient of friction was higher than the criterion. Both the lead film wear rate and the ball wear rate met that criterion in all three environments. Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead films in contact with 440C stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart lead.

Miyoshi, Kazuhisa↗

NASA NTRS2018

Laser Ablation Surface Treatment of Structural Aerospace Composites and Metal Alloys for Adhesive Bonding

NASA Langley Research Center (LaRC) has been involved over the past decade in the development of laser ablation as a method to surface treat aerospace structural fiber reinforced composites (CFRPs) and metal alloys. [1- 18] Laser surface treatment has been shown to be a rapid, high precision, and reproducible method for surface treatment of these materials, and is amenable to automation. The laser ablation process removes surface contamination such as silicones, creates surface roughness, and chemically activates a surface for bonding. The degree of ablation is controllable by adjusting laser parameters. In the case of CFRPs, ablation can be performed without damage to any underlying carbon fibers. In the case of metal alloys, ablation is possible without surface embrittlement, heat damage or creation of undesirable grain structures or morphologies. The optimum laser treatment conditions are substrate dependent and generally are influenced by laser wavelength and pulse duration (typically fixed for a laser system), and laser power. In the case of metal alloys such as Ti-6Al-4V, the laser ablation process eliminates the need for several steps of the conventional processes, including hydrofluoric (HF) acid and caustic treatment. These steps are often conducted in dip tanks and require costly facilities and environmentally unfriendly liquids. In addition, the laser can create nano-porosity on the Ti-6Al-4V alloy surface allowing for sol-gel penetration and thereby creating a gradient interface with improved temperature and mechanical performance. NASA LaRC has also been involved with the development of in-line characterization methods compatible with the laser treatment process to rapidly determine the presence of key contaminates such as silicones that, even at very low concentrations, are a threat to adhesive bonding. A spectroscopic technique called micro-laser induced breakdown spectroscopy (u-LIBS) has been developed to rapidly detect silicones at concentrations below those known to cause bonding problems. This technique requires no sample preparation, vacuum or inert atmosphere, has no practical size limitations, and provides nearly instantaneous feedback to the operator. This presentation will give an overview and update of these developments with specific examples highlighted.

Connell, John W.↗

NASA NTRS1975

Friction and wear of metals in contact with pyrolytic graphite

Sliding friction experiments were conducted with gold, iron, and tantalum single crystals sliding on prismatic and basal orientations of pyrolytic graphite in various environments, including vacuum, oxygen, water vapor, nitrogen, and hydrogen bromide. Surfaces were examined in the clean state and with various adsorbates present on the graphite surfaces. Auger and LEED spectroscopy, SEM, and EDXA were used to characterize the graphite surfaces. Results indicate that the prismatic and basal orientations do not contain nor do they chemisorb oxygen, water vapor, acetylene, or hydrogen bromide. All three metals exhibited higher friction on the prismatic than on the basal orientation and these metals transferred to the atomically clean prismatic orientation of pyrolytic graphite. No metal transfer to the graphite was observed in the presence of adsorbates at 760 torr. Ion bombardment of the graphite surface with nitrogen ions resulted in the adherence of nitrogen to the surface.

Buckley, D. H.↗

NASA NTRS1981

Surface chemistry and friction behavior of the silicon carbide (0001) surface at temperatures to 1500 deg C

X-ray photoelectron and Auger electron spectroscopy analyses and friction studies were conducted with a silicon carbide (0001) surface in contact with iron at various temperatures to 1200 or 1500 C in a vacuum of 10 to the minus 8th power Pa. The results indicate that there is a significant temperature influence on both the surface chemistry and friction properties of silicon carbide. The principal contaminant of adsorbed amorphous carbon on the silicon carbide surface in the as received state is removed by simply heating to 400 C. Above 400 C, graphite and carbide type carbine are the primary species on the silicon carbide surface, in addition to silicon. The coefficients of friction of polycrystalline iron sliding against a single crystal silicon carbide (0001) surface were high at temperatures to 800 C. Similar coefficients of friction were obtained at room temperature after the silicon carbide was preheated at various temperatures up 800 C. When the friction experiments were conducted above 800 C or when the specimens were preheated to above 800 C, the coefficients of friction were dramatically lower. At 800 C the silicon and carbide type carbon are at a maximum intensity in the XPS spectra. With increasing temperature above 800 C, the concentration of the graphite increases rapidly on the surface, whereas those of the carbide type carbon and silicon decrease rapidly.

Miyoshi, K.↗

NASA NTRS2011

Isothermal Decomposition of Hydrogen Peroxide Dihydrate

We present a new method of growing pure solid hydrogen peroxide in an ultra high vacuum environment and apply it to determine thermal stability of the dihydrate compound that forms when water and hydrogen peroxide are mixed at low temperatures. Using infrared spectroscopy and thermogravimetric analysis, we quantified the isothermal decomposition of the metastable dihydrate at 151.6 K. This decomposition occurs by fractional distillation through the preferential sublimation of water, which leads to the formation of pure hydrogen peroxide. The results imply that in an astronomical environment where condensed mixtures of H2O2 and H2O are shielded from radiolytic decomposition and warmed to temperatures where sublimation is significant, highly concentrated or even pure hydrogen peroxide may form.

Loeffler, M. J.↗

NASA NTRS2011

A Hybrid Lyot Coronagraph for the Direct Imaging and Spectroscopy of Exoplanet Systems: Recent Results and Prospects

We report our best laboratory contrast demonstrations achieved to date. We review the design, fabrication, performance, and future prospects of a hybrid focal plane occulter for exoplanet coronagraphy. Composed of thickness-profiled metallic and dielectric thin films vacuum deposited on a fused silica substrate, the hybrid occulter uses two superimposed thin films for control over both the real and imaginary parts of the complex attenuation pattern. Together with a deformable mirror for adjustment of wavefront phase, the hybrid Lyot coronagraph potentially exceeds billion-to one contrast over dark fields extending to within angular separations of 3 lambda/D (3 x the cosmological constant / diameter of the telescope) from the central star, over spectral bandwidths of 20 percent or more, and with throughput efficiencies up to 60 percent. We report laboratory contrasts of 3 x 10 (sup -10) degrees over 2 percent bandwidths, 6 x 10 (sup -10) degrees over 10 percent bandwidths, and 2 x 10 (sup -9) over 20 percent bandwidths, achieved across high contrast fields extending from an inner working angle of 3 lambda/D to a radius of 15 lambda/D. Occulter performance is analyzed in light of recent experiments and optical models, and prospects for further improvements are summarized. The science capabilities of the hybrid Lyot coronagraph are compared with requirements of the ACCESS mission, a representative exoplanet space telescope concept study for the direct imaging and spectroscopy of exoplanet systems. This work has been supported by NASA's Technology Demonstration for Exoplanet Missions (TDEM) program.

coronagraph↗

NASA NTRS1972

A cavity type absorption cell for double resonance microwave spectroscopy.

Description of an experimental dual resonant cavity absorption cell for observing microwave spectroscopic double-resonance effects. The device is composed of two Fabry-Perot interferometers excited by independent microwave sources and mounted at right angles in a suitable vacuum enclosure. The pumping transition is modulated by one source and the modulation induced on the rf absorption in the orthogonal cavity is detected.

Lee, M. C.↗

NASA NTRS1975

Effect of adsorbed chlorine and oxygen on shear strength of iron and copper junctions

Static friction experiments were performed in ultrahigh vacuum at room temperature on copper, iron, and steel contacts selectively contaminated with oxygen and chlorine in submonolayer amounts. The concentration of the adsorbates was determined with Auger electron spectroscopy and was measured relative to the saturation concentration of oxygen on iron (concentration 1.0). The coefficient of static friction decreased with increasing adsorbate concentration. It was independent of the metal and the adsorbate. The results compared satisfactorily with an extension of the junction growth theory to heterogeneous interfaces. The reduction in interfacial shear strength was measured by the ratio sub a/sub m where sub a is the shear strength of the interface with an adsorbate concentration of 1.0, and sub m is the strength of the clean metal interface. This ratio was 0.835 + or - 0.012 for all the systems tested.

Wheeler, D. R.↗

NASA NTRS1976

Effect of adsorbed chlorine and oxygen on the shear strength of iron and copper junctions

Static-friction experiments were performed in ultrahigh vacuum at room temperature on copper, iron, and steel contacts selectively contaminated with oxygen and chlorine in submonolayer amounts. The concentration of the adsorbates was determined with Auger electron spectroscopy and was measured relative to the saturation concentration of oxygen on iron (concentration, 1.0). The coefficient of static friction decreased with increasing adsorbate concentration; however, it was independent of the type of metal and the adsorbate species. The results compared satisfactorily with an extension of the junction growth theory to heterogeneous interfaces. The reduction in interfacial shear strength was measured by the ratio of the shear strength of the interface with an adsorbate concentration of 1.0 and the strength of the clean metal interface. This ratio was about 0.835 for all the systems tested.

Wheeler, D. R.↗

NASA NTRS1978

Catalysts for electrochemical generation of oxygen

Single crystal surfaces of platinum and gold and transition metal oxides of the spinel type were studied to find more effective catalysts for the electrolytic evolution of oxygen and to understand the mechanism and kinetics for the electrocatalysis in relation to the surface electronic and lattice properties of the catalyst. The single crystal studies involve the use of low energy electron diffraction (LEED) and Auger electron spectroscopy as complementary tools to the electrochemical measurements. Modifications to the transfer system and to the thin-layer electrochemical cell used to facilitate the transfer between the ultrahigh vacuum environment of the electron surface physics equipment and the electrochemical environment with a minimal possibility of changes in the surface structure, are described. The electrosorption underpotential deposition of Pb onto the Au(111), (100) and (110) single crystal surfaces with the thin-layer cell-LEED-Auger system is discussed as well as the synthesis of spinels for oxygen evolution studies.

Hagans, P.↗

NASA NTRS2007

Vacuum Pyrolysis and Related ISRU Techniques

A number of ISRU-related techniques have been developed at NASA Goddard Space Flight Center. The focus of the team has been on development of the vacuum pyrolysis technique for the production of oxygen from the lunar regolith. However, a number of related techniques have also been developed, including solar concentration, solar heating of regolith, resistive heating of regolith, sintering, regolith boiling, process modeling, parts manufacturing, and instrumentation development. An initial prototype system was developed to vaporize regolith simulants using a approx. l square meter Fresnel lens. This system was successfully used to vaporize quantities of approx. lg, and both mass spectroscopy of the gasses produced and Scanning Electron Microscopy (SEM) of the slag were done to show that oxygen was produced. Subsequent tests have demonstrated the use of a larger system With a 3.8m diameter reflective mirror to vaporize the regolith. These results and modeling of the vacuum pyrolysis reaction have indicated that the vaporization of the oxides in the regolith will occur at lower temperature for stronger vacuums. The chemical modeling was validated by testing of a resistive heating system that vaporized quantities of approx. 10g of MLS-1A. This system was also used to demonstrate the sintering of regolith simulants at reduced temperatures in high vacuum. This reduction in the required temperature prompted the development of a small-scale resistive heating system for application as a scientific instrument as well as a proof-of principle experiment for oxygen production.

Cardiff, Eric H.↗

NASA NTRSDate not supplied

Stratigraphy of the Apollo 17 Landslide Core 73002 From FMR Maturity and VNIR and Mössbauer Spectroscopy

A suite of samples from the Apollo missions to the Moon (1969-1973) were set aside and stored under controlled conditions to have unexamined lunar samples available decades later for analyses that take advantage of evolved sample handling techniques, maturation of then existing instrumentation, and development of new analytical techniques and instrumentation [e.g., 1]. One preserved sample is the Apollo 17 double drive tube core (73001/2) that was driven into the lunar surface on the landslide deposit at Station 3 on the South Massif in the Taurus-Littrow valley [2]. The deeper section (73001) was stored frozen in a Core Sample Vacuum Container (CSVC) to maximize preservation of lunar volatiles. We report here, as a part of the Apollo Next Generation Sample Analysis (ANGSA) Initiative [1,3], stratigraphy for the upper core section (73002) with respect to maturity (ferromagnetic resonance (FMR) maturity index Is/FeO [4-6]), visible-near-IR (VNIR) spectroscopy, and, for representative samples, grain-size analysis and Mössbauer spectroscopy. Stratigraphy provides data to model the dynamics of lunar landslide deposits and their post-emplacement evolution in comparison to impact-driven mixing on an airless body and stratigraphic context for volatile and (if any) organic behavior. Reported by [7] are preliminary results for multispectral imaging and hyperspectral scanning of the first dissection pass of 73002.

R. V. Morris↗

NASA NTRS2013

Synthesis and Spectroscopy of Large Carbon Molecules with Ames' COSmIC Facility in Support of NASA's Space Missions

We present and discuss the unique characteristics and capabilities of the laboratory facility, COSmIC, that was developed at NASA Ames to generate, process and analyze interstellar and planetary analogs in the laboratory. COSmIC stands for Cosmic Simulation Chamber and is dedicated to the study of molecules and ions under the low temperature and high vacuum conditions that are required to simulate interstellar, circumstellar and planetary physical environments in space. COSmIC integrates a variety of state-of-the-art instruments that allow forming, processing and monitoring simulated space conditions for planetary, circumstellar and interstellar materials in the laboratory. COSmIC is composed of a Pulsed Discharge Nozzle (PDN) expansion that generates a free jet supersonic expansion coupled to two ultrahigh-sensitivity, complementary in situ diagnostics: a Cavity Ring Down Spectroscopy (CRDS) system for photonic detection and a Reflectron Time-Of-Flight Mass Spectrometer (ReTOF-MS) for mass detection. Recent, unique, laboratory astrophysics results that were obtained using the capabilities of COSmIC will be discussed, in particular the progress that have been achieved in monitoring in the laboratory the formation of solid gains from their gas-phase molecular precursors in environments as varied as stellar/circumstellar outflow and planetary atmospheres. Plans for future, next generation, laboratory experiments on cosmic molecules and grains in the growing field of laboratory astrophysics will also be addressed.

Spectroscopy↗

NASA NTRS1983

Friction and wear of some ferrous-base metallic glasses

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminum oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Miyoshi, K.↗

NASA NTRS1984

Friction and wear of some ferrous-base metallic glasses

Sliding friction experiments, X-ray photoelectron spectroscopy (XPS) analysis, and electron microscopy and diffraction studies were conducted with ferrous base metallic glasses (amorphous alloys) in contact with aluminium oxide at temperatures to 750 C in a vacuum. Sliding friction experiments were also conducted in argon and air atmospheres. The results of the investigation indicate that the coefficient of friction increases with increasing temperature to 350 C in vacuum. The increase in friction is due to an increase in adhesion resulting from surface segregation of boric oxide and/or silicon oxide to the surface of the foil. Above 500 C the coefficient of friction decreased rapidly. The decrease correlates with the segregation of boron nitride to the surface. Contaminants can come from the bulk of the material to the surface upon heating and impart boric oxide and/or silicon oxide at 350 C and boron nitride above 500 C. The segregation of contaminants is responsible for the friction behavior. The amorphous alloys have superior wear resistance to crystalline 304 stainless steel. The relative concentrations of the various constituents at the surfaces of the amorphous alloys are very different from the nominal bulk compositions.

Miyoshi, K.↗

NASA NTRS1990

The surface variation of Ti-14Al-21Nb as a function of temperature under ultrahigh vacuum conditions

The effect of temperature, at conditions of ultrahigh vacuum, on the surface composition of the Ti-14Al-21Nb (in wt pct) alloy was investigated in samples heated to 1000 C in 100 C increments. Results of AES spectroscopy revealed that the Ti-14Al-21Nb alloy surface is extremely sensitive to temperature. At 300 C, the carbon and oxygen began to rapidly dissolve into the alloy, and at 600 C, bulk S segregated to the surface. The variation in the surface composition was extensive and different over the temperature range studied, indicating that there may be substantial changes in the hydrogen transport.

Lee, W. S.↗