Science.gov

Sample records for atomic oxygen durability

  1. Atomic Oxygen Durability of Aluminized Polymers

    NASA Technical Reports Server (NTRS)

    Yang, Judith C.

    2003-01-01

    The atomic oxygen durability of aluminized polymers will be investigated. Such aluminized polymers are commonly used in space and specifically on the International Space Station. Recent data from in-space results indicates that vapor deposited aluminum coatings are highly defected with many small pin windows. However, electron microscopy to validate the size and aerial density of such defects remains to be demonstrated. The research project is planned to compare electron microscopy analysis of pristine and atomic oxygen exposed aluminized polyimide Kapton with the results of ground laboratory atomic oxygen erosion data, in-space results and computational Monte Carlo modeling to develop a self consistent understanding of the atomic oxygen degradation processes and effects.

  2. Atomic Oxygen Durability of Second Surface Silver Microsheet Glass Concentrators

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Jaworske, Donald A.; Smith, Daniela C.; Mroz, Thaddeus S.

    1996-01-01

    Second surface silver microsheet glass concentrators are being developed for potential use in future solar dynamic space power systems. Traditional concentrators are aluminum honeycomb sandwich composites with either aluminum or graphite epoxy face sheets, where a reflective aluminum layer is deposited onto an organic leveling layer on the face sheet. To protect the underlying layers, a SiO2 layer is applied on top of the aluminum reflective layer. These concentrators may be vulnerable to atomic oxygen degradation due to possible atomic oxygen attack of the organic layers at defect sites in the protective and reflective coatings. A second surface microsheet glass concentrator would be inherently more atomic oxygen durable than these first surface concentrators. In addition, a second surface microsheet glass concentrator design provides a smooth optical surface and allows for silver to be used as a reflective layer, which would improve the reflectivity of the concentrator and the performance of the system. A potential threat to the performance of second surface microsheet glass concentrators is atomic oxygen attack of the underlying silver at seams and edges or at micrometeoroid and debris (MMD) impacts sites. Second surface silver microsheet glass concentrator samples were fabricated and tested for atomic oxygen durability. The samples were iteratively exposed to an atomic oxygen environment in a plasma asher. Samples were evaluated for potential degradation at fabrication seams, simulated MMD impact sites, and edges. Optical microscopy was used to evaluate atomic oxygen degradation. Reflectance was obtained for an impacted sample prior to and after atomic oxygen exposure. After an initial atomic oxygen exposure to an effective fluence of approx. 1 x 10(exp 21) atoms/cm(exp 2), oxidation of the silver at defect sites and edges was observed. Exposure to an additional approx. 1 x 10(exp 21) atoms/cm(exp 2) caused no observed increase in oxidation. Oxidation at an

  3. Low Earth orbit atomic oxygen simulation for durability evaluation of solar reflector surfaces

    NASA Technical Reports Server (NTRS)

    Degroh, Kim K.; Banks, Bruce A.

    1992-01-01

    To evaluate the performance and durability of solar reflector surfaces in the atomic oxygen environment typical of low Earth orbit (LEO), one must expose the reflector surface either directly to LEO or to ground-laboratory atomic oxygen environments. Although actual LEO exposures are most desired, such opportunities are typically scarce, expensive, and of limited duration. As a result, ground-laboratory exposures must be relied upon as the most practical long-term durability evaluation technique. Plasma ashers are widely used as LEO simulation facilities by producing atomic oxygen environments for durability evaluation of potential spacecraft materials. Atomic oxygen arrival differs between ground and space exposure in that plasma asher exposure produces isotropic arrival and space solar tracking produces sweeping arrival. Differences in initial impact reaction probability occur, dependent upon the energy and species existing in these environments. Due to the variations in ground-laboratory and space atomic oxygen, quantification of in-space performance based on plasma asher testing is not straightforward. The various atomic oxygen interactions that can occur with reflector surfaces, such as undercutting in organic substrates at protective coating defect sites, ground-laboratory techniques recommended for evaluating the atomic oxygen durability of reflectors based on asher exposures, and computational techniques which make use of ground-laboratory atomic oxygen exposure to predict in-space LEO durability are addressed.

  4. Atomic Oxygen Durability Evaluation of Protected Polymers Using Thermal Energy Plasma Systems

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Degroh, Kim K.; Stidham, Curtis R.; Gebauer, Linda; Lamoreaux, Cynthia M.

    1995-01-01

    The durability evaluation of protected polymers intended for use in low Earth orbit (LEO) has necessitated the use of large-area, high-fluence, atomic oxygen exposure systems. Two thermal energy atomic oxygen exposure systems which are frequently used for such evaluations are radio frequency (RF) plasma ashers and electron cyclotron resonance plasma sources. Plasma source testing practices such as ample preparation, effective fluence prediction, atomic oxygen flux determination, erosion measurement, operational considerations, and erosion yield measurements are presented. Issues which influence the prediction of in-space durability based on ground laboratory thermal energy plasma system testing are also addressed.

  5. Durability Issues for the Protection of Materials from Atomic Oxygen Attack in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce; Lenczewski, Mary; Demko, Rikako

    2002-01-01

    Low Earth orbital atomic oxygen is capable of eroding most polymeric materials typically used on spacecraft. Solar array blankets, thermal control polymers, and carbon fiber matrix composites are readily oxidized to become thinner and less capable of supporting the loads imposed upon them. Protective coatings have been developed that are durable to atomic oxygen to prevent oxidative erosion of the underlying polymers. However, the details of the surface roughness, coating defect density, and coating configuration can play a significant role as to whether or not the coating provides long duration atomic oxygen protection. Identical coatings on different surface roughness surfaces can have drastically different durability results. Examples and analysis of the causes of resultant differences in atomic oxygen protection are presented. Implications based on in-space experiences, ground laboratory testing, and computational modeling indicate that thin film vacuum-deposited aluminum protective coatings offer much less atomic oxygen protection than sputter-deposited silicon dioxide coatings.

  6. Atomic Oxygen Durability Testing of an International Space Station Solar Array Validation Coupon

    NASA Technical Reports Server (NTRS)

    Forkapa, Mark J.; Stidham, Curtis; Banks, Bruce A.; Rutledge, Sharon K.; Ma, David H.; Sechkar, Edward A.

    1996-01-01

    An International Space Station solar array validation coupon was exposed in a directed atomic oxygen beam for space environment durability testing at the NASA Lewis Research Center. Exposure to atomic oxygen and intermittent tensioning of the solar array were conducted to verify the solar array#s durability to low Earth orbital atomic oxygen and to the docking threat of plume loading both of which are anticipated over its expected mission life of fifteen years. The validation coupon was mounted on a specially designed rotisserie. The rotisserie mounting enabled the solar and anti-solar facing side of the array to be exposed to directed atomic oxygen in a sweeping arrival process replicating space exposure. The rotisserie mounting also enabled tensioning, in order to examine the durability of the array and its hinge to simulated plume loads. Flash testing to verify electrical performance of the solar array was performed with a solar simulator before and after the exposure to atomic oxygen and tensile loading. Results of the flash testing indicated little or no degradation in the solar array#s performance. Photographs were also taken of the array before and after the durability testing and are included along with comparisons and discussions in this report. The amount of atomic oxygen damage appeared minor with the exception of a very few isolated defects. There were also no indications that the simulated plume loadings had weakened or damaged the array, even though there was some erosion of Kapton due to atomic oxygen attack. Based on the results of this testing, it is apparent that the International Space Station#s solar arrays should survive the low Earth orbital atomic oxygen environment and docking threats which are anticipated over its expected mission life.

  7. The effect of leveling coatings on the atomic oxygen durability of solar concentrator surfaces

    NASA Technical Reports Server (NTRS)

    Degroh, Kim K.; Dever, Therese M.; Quinn, William F.

    1990-01-01

    Space power systems for Space Station Freedom will be exposed to the harsh environment of low earth orbit (LEO). Neutral atomic oxygen is the major constituent in LEO and has the potential of severely reducing the efficiency of solar dynamic power systems through degradation of the concentrator surfaces. Several transparent dielectric thin films have been found to provide atomic oxygen protection, but atomic oxygen undercutting at inherent defect sites is still a threat to solar dynamic power system survivability. Leveling coatings smooth microscopically rough surfaces, thus eliminating potential defect sites prone to oxidation attack on concentrator surfaces. The ability of leveling coatings to improve the atomic oxygen durability of concentrator surfaces was investigated. The application of a EPO-TEK 377 epoxy leveling coating on a graphite epoxy substrate resulted in an increase in solar specular reflectance, a decrease in the atomic oxygen defect density by an order of magnitude and a corresponding order of magnitude decrease in the percent loss of specular reflectance during atomic oxygen plasma ashing.

  8. Atomic Oxygen Durability Evaluation of a UV Curable Ceramer Protective Coating

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Karniotis, Christina A.; Dworak, David; Soucek, Mark

    2004-01-01

    The exposure of most silicones to atomic oxygen in low Earth orbit (LEO) results in the oxidative loss of methyl groups with a gradual conversion to oxides of silicon. Typically there is surface shrinkage of oxidized silicone protective coatings which leads to cracking of the partially oxidized brittle surface. Such cracks widen and branch crack with continued atomic oxygen exposure ultimately allowing atomic oxygen to reach any hydrocarbon polymers under the silicone coating. A need exists for a paintable silicone coating that is free from such surface cracking and can be effectively used for protection of polymers and composites in LEO. A new type of silicone based protective coating holding such potential was evaluated for atomic oxygen durability in an RF atomic oxygen plasma exposure facility. The coating consisted of a UV curable inorganic/organic hybrid coating, known as a ceramer, which was fabricated using a methyl substituted polysiloxane binder and nanophase silicon-oxo-clusters derived from sol-gel precursors. The polysiloxane was functionalized with a cycloaliphatic epoxide in order to be cured at ambient temperature via a cationic UV induced curing mechanism. Alkoxy silane groups were also grafted onto the polysiloxane chain, through hydrosilation, in order to form a network with the incorporated silicon-oxo-clusters. The prepared polymer was characterized by H-1 and Si-29 NMR, FT-IR, and electrospray ionization mass spectroscopy. The paper will present the results of atomic oxygen protection ability of thin ceramer coatings on Kapton H as evaluated over a range of atomic oxygen fluence levels.

  9. Atomic oxygen durability evaluation of the flexible batten for the photovoltaic array mast on Space Station

    NASA Technical Reports Server (NTRS)

    Stidham, Curtis R.; Rutledge, Sharon K.; Sechkar, Edward A.; Flaherty, David S.; Roig, David M.; Edwards, Jonathan L.

    1994-01-01

    A test program was conducted at the National Aeronautics and Space Administration's Lewis Research Center (LeRC) to evaluate the long term low Earth orbital (LEO) atomic oxygen (AO) durability of a flexible (fiberglass-epoxy composite) batten. The flexible batten is a component used to provide structural rigidity in the photovoltaic array mast on Space Station. The mast is used to support and articulate the photovoltaic array, therefore, the flexible batten must be preloaded for the 15 year lifetime of an array blanket. Development hardware and composite materials were evaluated in ground testing facilities for AO durability and dynamic retraction-deployment cyclic loading representative of expected full life in-space application. The CV1144 silicone (AO protective) coating was determined to provide adequate protection against AO degradation of the composite material and provided fiber containment, thus the structural integrity of the flexible batten was maintained. Both silicone coated and uncoated flexible battens maintained load carrying capabilities. Results of the testing did indicate that the CV1144 silicone protective coating was oxidized by AO reactions to form a brittle glassy (SiO2) skin that formed cracking patterns on all sides of the coated samples. The cracking was observed in samples that were mechanically stressed as well as samples in non-stressed conditions. The oxidized silicon was observed to randomly spall in small localized areas, on the flexible battens that underwent retraction-deployment cycling. Some darkening of the silicon, attributed to vacuum ultraviolet (VUV) radiation, was observed.

  10. Vacuum Ultraviolet Radiation and Atomic Oxygen Durability Evaluation of HST Bi-Stem Thermal Shield Materials

    NASA Technical Reports Server (NTRS)

    Dever, Joyce; deGroh, Kim K.

    2002-01-01

    Bellows-type thermal shields were used on the bi-stems of replacement solar arrays installed on the Hubble Space Telescope (HST) during the first HST servicing mission (SMI) in December 1993. These thermal shields helped reduce the problem of thermal gradient- induced jitter observed with the original HST solar arrays during orbital thermal cycling and have been in use on HST for eight years. This paper describes ground testing of the candidate solar array bi-stem thermal shield materials including backside aluminized Teflon(R)FEP (fluorinated ethylene propylene) with and without atomic oxygen (AO) and ultraviolet radiation protective surface coatings for durability to AO and combined AO and vacuum ultraviolet (VOV) radiation. NASA Glenn Research Center (GRC) conducted VUV and AO exposures of samples of candidate thermal shield materials at HST operational temperatures and pre- and post-exposure analyses as part of an overall program coordinated by NASA Goddard Space Flight Center (GSFC) to determine the on-orbit durability of these materials. Coating adhesion problems were observed for samples having the AO- and combined AO/UV-protective coatings. Coating lamination occurred with rapid thermal cycling testing which simulated orbital thermal cycling. This lack of adhesion caused production of coating flakes from the material that would have posed a serious risk to HST optics if the coated materials were used for the bi-stem thermal shields. No serious degradation was observed for the uncoated aluminized Teflon(R) as evaluated by optical microscopy, although atomic force microscopy (AFM) microhardness testing revealed that an embrittled surface layer formed on the uncoated Teflon(R) surface due to vacuum ultraviolet radiation exposure. This embrittled layer was not completely removed by AO erosion, No cracks or particle flakes were produced for the embrittled uncoated material upon exposure to VUV and AO at operational temperatures to an equivalent exposure of

  11. Atomic oxygen durability of solar concentrator materials for Space Station Freedom

    NASA Technical Reports Server (NTRS)

    Degroh, Kim K.; Terlep, Judith A.; Dever, Therese M.

    1990-01-01

    The findings are reviewed of atomic oxygen exposure testing of candidate solar concentrator materials containing SiO2 and Al2O3 protective coatings for use on Space Station Freedom solar dynamic power modules. Both continuous and iterative atomic oxygen exposure tests were conducted. Iterative air plasma ashing resulted in larger specular reflectance decreases and solar absorptance increases than continuous ashing to the same fluence, and appears to provide a more severe environment than the continuous atomic oxygen exposure that would occur in the low Earth orbit environment. First generation concentrator fabrication techniques produced surface defects including scratches, macroscopic bumps, dendritic regions, porosity, haziness, and pin hole defects. Several of these defects appear to be preferential sites for atomic oxygen attack leading to erosive undercutting. Extensive undercutting and flaking of reflective and protective coatings were found to be promoted through an undercutting tearing propagation process. Atomic oxygen erosion processes and effects on optical performance is presented.

  12. Atomic-Oxygen-Durable and Electrically-Conductive CNT-POSS-Polyimide Flexible Films for Space Applications.

    PubMed

    Atar, Nurit; Grossman, Eitan; Gouzman, Irina; Bolker, Asaf; Murray, Vanessa J; Marshall, Brooks C; Qian, Min; Minton, Timothy K; Hanein, Yael

    2015-06-10

    In low Earth orbit (LEO), hazards such as atomic oxygen (AO) or electrostatic discharge (ESD) degrade polymeric materials, specifically, the extensively used polyimide (PI) Kapton. We prepared PI-based nanocomposite films that show both AO durability and ESD protection by incorporating polyhedral oligomeric silsesquioxane (POSS) and carbon nanotube (CNT) additives. The unique methods that are reported prevent CNT agglomeration and degradation of the CNT properties that are common in dispersion-based processes. The influence of the POSS content on the electrical, mechanical, and thermo-optical properties of the CNT-POSS-PI films was investigated and compared to those of control PI and CNT-PI films. CNT-POSS-PI films with 5 and 15 wt % POSS content exhibited sheet resistivities as low as 200 Ω/□, and these resistivities remained essentially unchanged after exposure to AO with a fluence of ∼2.3 × 10(20) O atoms cm(-2). CNT-POSS-PI films with 15 wt % POSS content exhibited an erosion yield of 4.8 × 10(-25) cm(3) O atom(-1) under 2.3 × 10(20) O atoms cm(-2) AO fluence, roughly one order of magnitude lower than that of pure PI films. The durability of the conductivity of the composite films was demonstrated by rolling film samples with a tight radius up to 300 times. The stability of the films to thermal cycling and ionizing radiation was also demonstrated. These properties make the prepared CNT-POSS-PI films with 15 wt % POSS content excellent candidates for applications where AO durability and electrical conductivity are required for flexible and thermally stable materials. Hence, they are suggested here for LEO applications such as the outer layers of spacecraft thermal blankets.

  13. Prediction of In-Space Durability of Protected Polymers Based on Ground Laboratory Thermal Energy Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Rutledge, Sharon; DiFilippo, Frank J.

    1996-01-01

    The probability of atomic oxygen reacting with polymeric materials is orders of magnitude lower at thermal energies (greater than O.1 eV) than at orbital impact energies (4.5 eV). As a result, absolute atomic oxygen fluxes at thermal energies must be orders of magnitude higher than orbital energy fluxes, to produce the same effective fluxes (or same oxidation rates) for polymers. These differences can cause highly pessimistic durability predictions for protected polymers and polymers which develop protective metal oxide surfaces as a result of oxidation if one does not make suitable calibrations. A comparison was conducted of undercut cavities below defect sites in protected polyimide Kapton samples flown on the Long Duration Exposure Facility (LDEF) with similar samples exposed in thermal energy oxygen plasma. The results of this comparison were used to quantify predicted material loss in space based on material loss in ground laboratory thermal energy plasma testing. A microindent hardness comparison of surface oxidation of a silicone flown on the Environmental Oxygen Interaction with Materials-III (EOIM-III) experiment with samples exposed in thermal energy plasmas was similarly used to calibrate the rate of oxidation of silicone in space relative to samples in thermal energy plasmas exposed to polyimide Kapton effective fluences.

  14. Atomic Oxygen Fluence Monitor

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.

    2011-01-01

    This innovation enables a means for actively measuring atomic oxygen fluence (accumulated atoms of atomic oxygen per area) that has impinged upon spacecraft surfaces. Telemetered data from the device provides spacecraft designers, researchers, and mission managers with real-time measurement of atomic oxygen fluence, which is useful for prediction of the durability of spacecraft materials and components. The innovation is a compact fluence measuring device that allows in-space measurement and transmittance of measured atomic oxygen fluence as a function of time based on atomic oxygen erosion yields (the erosion yield of a material is the volume of material that is oxidized per incident oxygen atom) of materials that have been measured in low Earth orbit. It has a linear electrical response to atomic oxygen fluence, and is capable of measuring high atomic oxygen fluences (up to >10(exp 22) atoms/sq cm), which are representative of multi-year low-Earth orbital missions (such as the International Space Station). The durability or remaining structural lifetime of solar arrays that consist of polymer blankets on which the solar cells are attached can be predicted if one knows the atomic oxygen fluence that the solar array blanket has been exposed to. In addition, numerous organizations that launch space experiments into low-Earth orbit want to know the accumulated atomic oxygen fluence that their materials or components have been exposed to. The device is based on the erosion yield of pyrolytic graphite. It uses two 12deg inclined wedges of graphite that are over a grit-blasted fused silica window covering a photodiode. As the wedges erode, a greater area of solar illumination reaches the photodiode. A reference photodiode is also used that receives unobstructed solar illumination and is oriented in the same direction as the pyrolytic graphite covered photodiode. The short-circuit current from the photodiodes is measured and either sent to an onboard data logger, or

  15. A technique for synergistic atomic oxygen and vacuum ultraviolet radiation durability evaluation of materials for use in LEO

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.

    1996-01-01

    Material erosion data collected during flight experiments such as the Environmental Oxygen Interaction with Materials (EOIM)-3 and the Long Duration Exposure Facility (LDEF) have raised questions as to the sensitivity of material erosion to levels of atomic oxygen exposure and vacuum ultraviolet (VUV) radiation. The erosion sensitivity of some materials such as FEP Teflon used as a thermal control material on satellites in low Earth orbit (LEO), is particularly important but difficult to determine. This is in large part due to the inability to hold all but one exposure parameter constant during a flight experiment. This is also difficult to perform in a ground based facility, because often the variation of the level of atomic oxygen or VUV radiation also results in a change in the level of the other parameter. A facility has been developed which allows each parameter to be changed almost independently and offer broad area exposure. The resulting samples can be made large enough for mechanical testing. The facility uses an electron cyclotron resonance plasma source to provide the atomic oxygen. A series of glass plates is used to focus the atomic oxygen while filtering the VUV radiation from the plasma source. After filtering, atomic oxygen effective flux levels can still be measured which are as high as 7 x 10(exp 15) atoms/cm(exp 2)-sec which is adequate for accelerated testing. VUV radiation levels after filtering can be as low as 0.3 suns. Additional VUV suns can be added with the use of deuterium lamps which allow the VUV level to be changed while keeping the flux of atomic oxygen constant. This paper discusses the facility, and results from exposure of Kapton and FEP at pre-determined atomic oxygen flux and VUV sun levels.

  16. The use of plasma ashers and Monte Carlo modeling for the projection of atomic oxygen durability of protected polymers in low Earth orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Auer, Bruce M.; Rutledge, Sharon K.; Degroh, Kim K.; Gebauer, Linda

    1992-01-01

    The results of ground laboratory and in-space exposure of polymeric materials to atomic oxygen has enabled the development of a Monte Carlo computational model which simulates the oxidation processes of both environments. The cost effective projection of long-term low-Earth-orbital durability of protected polymeric materials such as SiO(x)-coated polyimide Kapton photovoltaic array blankets will require ground-based testing to assure power system reliability. Although silicon dioxide thin film protective coatings can greatly extend the useful life of polymeric materials in ground-based testing, the projection of in-space durability based on these results can be made more reliable through the use of modeling which simulates the mechanistic properties of atomic oxygen interaction, and replicates test results in both environments. Techniques to project long-term performance of protected materials, such as the Space Station Freedom solar array blankets, are developed based on ground laboratory experiments, in-space experiments, and computational modeling.

  17. Design and demonstration of a system for the deposition of atomic-oxygen durable coatings for reflective solar dynamic power system concentrators

    NASA Technical Reports Server (NTRS)

    Mcclure, Donald J.

    1988-01-01

    A system for the vacuum deposition of atomic-oxygen durable coatings for reflective solar dynamic power systems (SDPS) concentrators was designed and demonstrated. The design issues pertinent to SDPS were developed by the Government Aerospace Systems Division of the Harris Corporation and are described in NASA-CR-179489. Both design and demonstration phases have been completed. At the time of this report the deposition system was ready for coating of facets for SDPS concentrators. The materials issue relevant to the coating work were not entirely resolved. These issues can only be resolved when substrates which are comparable to those which will be used in flight hardware are available. The substrates available during the contract period were deficient in the areas of surface roughness and contamination. These issues are discussed more thoroughly in the body of the report.

  18. Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

    SciTech Connect

    Xie, Shuifen; Choi, Sang; Lu, Ning; Roling, Luke T.; Herron, Jeffrey A.; Zhang, Lei; Park, Jinho; Wang, Jinguo; Kim, Moon J.; Xie, Zhaoxiong; Mavrikakis, Manos; Xia, Younan

    2014-06-11

    An effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the deposited Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@PnL (n = 1-6) core-shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt2-3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.

  19. Atomic Oxygen Effects

    NASA Technical Reports Server (NTRS)

    Miller, Sharon K. R.

    2014-01-01

    Atomic oxygen, which is the most predominant species in low Earth orbit, is highly reactive and can break chemical bonds on the surface of a wide variety of materials leading to volatilization or surface oxidation which can result in failure of spacecraft materials and components. This presentation will give an overview of how atomic oxygen reacts with spacecraft materials, results of space exposure testing of a variety of materials, and examples of failures caused by atomic oxygen.

  20. Atomic Oxygen Textured Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Hunt, Jason D.; Drobotij, Erin; Cales, Michael R.; Cantrell, Gidget

    1995-01-01

    Atomic oxygen can be used to microscopically alter the surface morphology of polymeric materials in space or in ground laboratory facilities. For polymeric materials whose sole oxidation products are volatile species, directed atomic oxygen reactions produce surfaces of microscopic cones. However, isotropic atomic oxygen exposure results in polymer surfaces covered with lower aspect ratio sharp-edged craters. Isotropic atomic oxygen plasma exposure of polymers typically causes a significant decrease in water contact angle as well as altered coefficient of static friction. Such surface alterations may be of benefit for industrial and biomedical applications. The results of atomic oxygen plasma exposure of thirty-three (33) different polymers are presented, including typical morphology changes, effects on water contact angle, and coefficient of static friction.

  1. Atomic oxygen effects on materials

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Brady, Joyce A.; Merrow, James E.

    1989-01-01

    Understanding of the basic processes of atomic oxygen interaction is currently at a very elementary level. However, measurement of erosion yields, surface morphology, and optical properties for low fluences have brought about much progress in the past decade. Understanding the mechanisms and those factors that are important for proper simulation of low Earth orbit is at a much lower level of understanding. The ability to use laboratory simulations with confidence to quantifiably address the functional performance and durability of materials in low Earth orbit will be necessary to assure long-term survivability to the natural space environment.

  2. Atomic oxygen stimulated outgassing

    NASA Technical Reports Server (NTRS)

    Linton, Roger C.; Reynolds, John M.

    1991-01-01

    The passive Long Duration Exposure Facility (LDEF) Experiment A0034, Atomic Oxygen Simulated Outgassing, consisted of two identical one-sixth tray modules, exposing selected thermal control coatings to atomic oxygen and the combined space environment on the leading edge and, for reference, to the relative wake environment on the trailing edge. Optical mirrors were included adjacent to the thermal coatings for deposition of outgassing products. Ultraviolet grade windows and metal covers were provided for additional assessment of the effects of the various environmental factors. Preliminary results indicate that orbital atomic oxygen is both a degrading and a optically restorative factor in the thermo-optical properties of selected thermal coatings. There is evidence of more severe optical degradation on collector mirrors adjacent to coatings that were exposed to the RAM-impinging atomic oxygen. This evidence of atomic oxygen stimulated outgassing is discussed in relation to alternative factors that could affect degradation. The general effects of the space environment on the experiment hardware as well as the specimens are discussed.

  3. Atomic Oxygen Task

    NASA Technical Reports Server (NTRS)

    Hadaway, James B.

    1997-01-01

    This report details work performed by the Center for Applied Optics (CAO) at the University of Alabama in Huntsville (UAH) on the contract entitled 'Atomic Oxygen Task' for NASA's Marshall Space Flight Center (contract NAS8-38609, Delivery Order 109, modification number 1). Atomic oxygen effects on exposed materials remain a critical concern in designing spacecraft to withstand exposure in the Low Earth Orbit (LEO) environment. The basic objective of atomic oxygen research in NASA's Materials & Processes (M&P) Laboratory is to provide the solutions to material problems facing present and future space missions. The objective of this work was to provide the necessary research for the design of specialized experimental test configurations and development of techniques for evaluating in-situ space environmental effects, including the effects of atomic oxygen and electromagnetic radiation on candidate materials. Specific tasks were performed to address materials issues concerning accelerated environmental testing as well as specifically addressing materials issues of particular concern for LDEF analysis and Space Station materials selection.

  4. Atomic Oxygen Protection of Materials in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Demko, Rikako

    2002-01-01

    Spacecraft polymeric materials as well as polymer-matrix carbon-fiber composites can be significantly eroded as a result of exposure to atomic oxygen in low Earth orbit (LEO). Several new materials now exist, as well as modifications to conventionally used materials, that provide much more resistance to atomic oxygen attack than conventional hydrocarbon polymers. Protective coatings have also been developed which are resistant to atomic oxygen attack and provide protection of underlying materials. However, in actual spacecraft applications, the configuration, choice of materials, surface characteristics and functional requirements of quasi-durable materials or protective coatings can have great impact on the resulting performance and durability. Atomic oxygen degradation phenomena occurring on past and existing spacecraft will be presented. Issues and considerations involved in providing atomic oxygen protection for materials used on spacecraft in low Earth orbit will be addressed. Analysis of in-space results to determine the causes of successes and failures of atomic oxygen protective coatings is presented.

  5. Hyperthermal atomic oxygen generator

    NASA Technical Reports Server (NTRS)

    Khandelwal, Govind S.; Wu, Dongchuan

    1990-01-01

    Characterization of the transport properties of oxygen through silver was continued. Specifically, experiments measuring the transport through Ag(111), Ag(110), Ag(100) single crystals and through Ag0.05 Zr alloy were completed. In addition, experiments using glow discharge excitation of oxygen to assist in the transport were completed. It was found that the permeability through the different orientations of single crystal Ag was the same, but significant differences existed in the diffusivity. The experimental ratio of diffusivities, however, was in reasonable agreement with theoretical estimates. Since the solubilities of orientations must be the same, this suggests some problems with the assumption K = DS. The glow discharge experiments show that there is a substantial increase in transport (factor of six) when the upstream pressure is dissociated to some fraction of atoms (which have a much higher sticking coefficient). These results indicate that there is a significant surface limitation because of dissociative adsorption of the molecules. Experiments with the Ag0.05 Zr alloy and its high-grain boundary and defect density show a permeability of greater than a factor of two over ordinary polycrystalline Ag, but it is unclear as to whether this is because of enhanced transport through these defects or whether the Zr and defects on the surface increased the sticking coefficient and therefore the transport.

  6. Low Earth Orbital Atomic Oxygen Interactions With Materials

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K.; deGroh, Kim K.

    2004-01-01

    Atomic oxygen is formed in the low Earth orbital environment (LEO) by photo dissociation of diatomic oxygen by short wavelength (< 243 nm) solar radiation which has sufficient energy to break the 5.12 eV O2 diatomic bond in an environment where the mean free path is sufficiently long ( 108 meters) that the probability of reassociation or the formation of ozone (O3) is small. As a consequence, between the altitudes of 180 and 650 km, atomic oxygen is the most abundant species. Spacecraft impact the atomic oxygen resident in LEO with sufficient energy to break hydrocarbon polymer bonds, causing oxidation and thinning of the polymers due to loss of volatile oxidation products. Mitigation techniques, such as the development of materials with improved durability to atomic oxygen attack, as well as atomic oxygen protective coatings, have been employed with varying degrees of success to improve durability of polymers in the LEO environment. Atomic oxygen can also oxidize silicones and silicone contamination to produce non-volatile silica deposits. Such contaminants are present on most LEO missions and can be a threat to performance of optical surfaces. The LEO atomic oxygen environment, its interactions with materials, results of space testing, computational modeling, mitigation techniques, and ground laboratory simulation procedures and issues are presented.

  7. Reaction and Protection of Electrical Wire Insulators in Atomic-oxygen Environments

    NASA Technical Reports Server (NTRS)

    Hung, Ching-Cheh; Cantrell, Gidget

    1994-01-01

    Atomic-oxygen erosion on spacecraft in low Earth orbit is an issue which is becoming increasingly important because of the growing number of spacecraft that will fly in the orbits which have high concentrations of atomic oxygen. In this investigation, the atomic-oxygen durability of three types of electrical wire insulation (carbon-based, fluoropolymer, and polysiloxane elastomer) were evaluated. These insulation materials were exposed to thermal-energy atomic oxygen, which was obtained by RF excitation of air at a pressure of 11-20 Pa. The effects of atomic-oxygen exposure on insulation materials indicate that all carbon-based materials erode at about the same rate as polyamide Kapton and, therefore, are not atomic-oxygen durable. However, the durability of fluoropolymers needs to be evaluated on a case by case basis because the erosion rates of fluoropolymers vary widely. For example, experimental data suggest the formation of atomic fluorine during atomic-oxygen amorphous-fluorocarbon reactions. Dimethyl polysiloxanes (silicone) do not lose mass during atomic-oxygen exposure, but develop silica surfaces which are under tension and frequently crack as a result of loss of methyl groups. However, if the silicone sample surfaces were properly pretreated to provide a certain roughness, atomic oxygen exposure resulted in a sturdy, non-cracked atomic-oxygen durable SiO2 layer. Since the surface does not crack during such silicone-atomic oxygen reaction, the crack-induced contamination by silicone can be reduced or completely stopped. Therefore, with proper pretreatment, silicone can be either a wire insulation material or a coating on wire insulation materials to provide atomic-oxygen durability.

  8. Advances in atomic oxygen simulation

    NASA Technical Reports Server (NTRS)

    Froechtenigt, Joseph F.; Bareiss, Lyle E.

    1990-01-01

    Atomic oxygen (AO) present in the atmosphere at orbital altitudes of 200 to 700 km has been shown to degrade various exposed materials on Shuttle flights. The relative velocity of the AO with the spacecraft, together with the AO density, combine to yield an environment consisting of a 5 eV beam energy with a flux of 10(exp 14) to 10(exp 15) oxygen atoms/sq cm/s. An AO ion beam apparatus that produces flux levels and energy similar to that encountered by spacecraft in low Earth orbit (LEO) has been in existence since 1987. Test data was obtained from the interaction of the AO ion beam with materials used in space applications (carbon, silver, kapton) and with several special coatings of interest deposited on various surfaces. The ultimate design goal of the AO beam simulation device is to produce neutral AO at sufficient flux levels to replicate on-orbit conditions. A newly acquired mass spectrometer with energy discrimination has allowed 5 eV neutral oxygen atoms to be separated and detected from the background of thermal oxygen atoms of approx 0.2 eV. Neutralization of the AO ion beam at 5 eV was shown at the Martin Marietta AO facility.

  9. Atomic oxygen studies on polymers

    NASA Technical Reports Server (NTRS)

    Morison, W. D.; Tennyson, R. C.; French, J. B.; Braithwaite, T.; Moisan, M.; Hubert, J.

    1988-01-01

    The purpose was to study the effects of atomic oxygen on the erosion of polymer based materials. The development of an atomic oxygen neutral beam facility using a SURFATRON surface wave launcher that can produce beam energies between 2 and 3 eV at flux levels as high as approx. 10 to the 17th power atoms/cm (2)-sec is described. Thin film dielectric materials were studied to determine recession rates and and reaction efficiencies as a function of incident beam energy and fluence. Accelerated testing was also accomplished and the values of reaction efficiency compared to available space flight data. Electron microscope photomicrographs of the samples' surface morphology were compared to flight test specimens.

  10. Monte Carlo modeling of atomic oxygen attack of polymers with protective coatings on LDEF

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Degroh, Kim K.; Auer, Bruce M.; Gebauer, Linda; Edwards, Jonathan L.

    1993-01-01

    Characterization of the behavior of atomic oxygen interaction with materials on the Long Duration Exposure Facility (LDEF) assists in understanding of the mechanisms involved. Thus the reliability of predicting in-space durability of materials based on ground laboratory testing should be improved. A computational model which simulates atomic oxygen interaction with protected polymers was developed using Monte Carlo techniques. Through the use of an assumed mechanistic behavior of atomic oxygen interaction based on in-space atomic oxygen erosion of unprotected polymers and ground laboratory atomic oxygen interaction with protected polymers, prediction of atomic oxygen interaction with protected polymers on LDEF was accomplished. However, the results of these predictions are not consistent with the observed LDEF results at defect sites in protected polymers. Improved agreement between observed LDEF results and predicted Monte Carlo modeling can be achieved by modifying of the atomic oxygen interactive assumptions used in the model. LDEF atomic oxygen undercutting results, modeling assumptions, and implications are presented.

  11. Atomic oxygen effects on metals

    NASA Technical Reports Server (NTRS)

    Fromhold, Albert T.

    1987-01-01

    The effect of specimen geometry on the attack of metals by atomic oxygen is addressed. This is done by extending the coupled-currents approach in metal oxidation to spherical and cylindrical geometries. Kinetic laws are derived for the rates of oxidation of samples having these geometries. It is found that the burn-up time for spherical particles of a given diameter can be as much as a factor of 3 shorter than the time required to completely oxidize a planar sample of the same thickness.

  12. Atomic oxygen transport in the thermosphere.

    NASA Technical Reports Server (NTRS)

    Johnson, F. S.; Gottlieb, B.

    1973-01-01

    The photodissociation of oxygen in the lower thermosphere is evaluated to obtain its global average value and the hemispheric imbalance. The observed concentrations of atomic oxygen do not reflect this imbalance in production due to the effect of seasonal wind patterns redistributing the atomic oxygen. The wind system necessary to compensate for the imbalance in solar thermal input into the lower thermosphere is found to transport an amount of atomic oxygen sufficient to compensate for the hemispheric imbalance in production. Ionospheric data indicate a winter enhancement in atomic oxygen concentration; to produce this, a higher degree of oxygen dissociation than that normally accepted (i.e., higher than an atomic to molecular oxygen ratio of unity at 120 km) is needed. The concept that the concentrations of atomic oxygen observed over the winter polar region are maintained by transport from lower latitudes requires that eddy diffusion coefficients derived from vertical transport at low latitudes (ignoring horizontal transport) be reduced by about 25%.

  13. Large faceted Pd nanocrystals supported small Pt nanoparticles as highly durable electrocatalysts for oxygen reduction

    NASA Astrophysics Data System (ADS)

    Zhang, Geng; Lu, Wangting; Cao, Longsheng; Qin, Xiaoping; Ding, Fei; Tang, Shun; Shao, Zhi-Gang; Yi, Baolian

    2016-09-01

    The reduction of Pt content together with the improvement of the durability of the catalyst for oxygen reduction reaction (ORR) is required to the large-scale commercialization of proton exchange membrane fuel cells. In this work, a novel ORR catalyst consisting of large Pd nanocrystal as the core with small Pt nanoparticles supported on the Pd core is prepared by a facile one-step synthesis method. The Pd substrate is presented in the form of well-defined cuboctahedrons and icosahedrons. The type of metal precursors and Pt/Pd molar ratio are important factors to obtain this Pd-supporting-Pt structure. The Pd2-s-Pt1 catalyst with a nominal Pt/Pd atomic ratio at 1/2 shows improved ORR activity: its mass specific activity and area specific activity is 2.5 and 3.5 times that of commercial Pt/C, respectively. More importantly, the Pd2-s-Pt1 catalyst demonstrates outstanding durability against potential cycling which can be ascribed to the slow dissolution of Pd core and the structure transformation from Pd@Pt to hollow PdPt alloyed nanocages. This exciting result provides a new pathway to the design of ORR catalyst with excellent durability.

  14. Attenuation of Scattered Thermal Energy Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce a.; Seroka, Katelyn T.; McPhate, Jason B.; Miller, Sharon K.

    2011-01-01

    The attenuation of scattered thermal energy atomic oxygen is relevant to the potential damage that can occur within a spacecraft which sweeps through atomic oxygen in low Earth orbit (LEO). Although there can be significant oxidation and resulting degradation of polymers and some metals on the external surfaces of spacecraft, there are often openings on a spacecraft such as telescope apertures, vents, and microwave cavities that can allow atomic oxygen to enter and scatter internally to the spacecraft. Atomic oxygen that enters a spacecraft can thermally accommodate and scatter to ultimately react or recombine on surfaces. The atomic oxygen that does enter a spacecraft can be scavenged by use of high erosion yield polymers to reduce its reaction on critical surfaces and materials. Polyoxymethylene and polyethylene can be used as effective atomic oxygen scavenging polymers.

  15. Issues and Consequences of Atomic Oxygen Undercutting of Protected Polymers in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Snyder, Aaron; Miller, Sharon K.; Demko, Rikako

    2002-01-01

    Hydrocarbon based polymers that are exposed to atomic oxygen in low Earth orbit are slowly oxidized which results in recession of their surface. Atomic oxygen protective coatings have been developed which are both durable to atomic oxygen and effective in protecting underlying polymers. However, scratches, pin window defects, polymer surface roughness and protective coating layer configuration can result in erosion and potential failure of protected thin polymer films even though the coatings are themselves atomic oxygen durable. This paper will present issues that cause protective coatings to become ineffective in some cases yet effective in others due to the details of their specific application. Observed in-space examples of failed and successfully protected materials using identical protective thin films will be discussed and analyzed. Proposed approaches to prevent the failures that have been observed will also be presented.

  16. Scattered Atomic Oxygen Effects on Spacecraft Materials

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K. R.; deGroh, Kim K.; Demko, Rikako

    2003-01-01

    Low Earth orbital (LEO) atomic oxygen cannot only erode the external surfaces of polymers on spacecraft, but can cause degradation of surfaces internal to components on the spacecraft where openings to the space environment exist. Although atomic oxygen attack on internal or interior surfaces may not have direct exposure to the LEO atomic oxygen flux scattered impingement can have serious degradation effects where sensitive interior surfaces are present. The effects of atomic oxygen erosion of polymer interior to an aperture on a spacecraft is simulated using Monte Carlo computational techniques. A 2-dimensional model is used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of distance into a parallel walled cavity. The degree of erosion re1ative is compared between the various interior locations and the external surface of a LEO spacecraft.

  17. Atomic Oxygen Effects on Spacecraft Materials

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K. R.; deGroh, Kim K.; Demko, Rikako

    2003-01-01

    Low Earth orbital (LEO) atomic oxygen cannot only erode the external surfaces of polymers on spacecraft, but can cause degradation of surfaces internal to components on the spacecraft where openings to the space environment exist. Although atomic oxygen attack on internal or interior surfaces may not have direct exposure to the LEO atomic oxygen flux, scattered impingement can have can have serious degradation effects where sensitive interior surfaces are present. The effects of atomic oxygen erosion of polymers interior to an aperture on a spacecraft is simulated using Monte Carlo computational techniques. A 2-dimensional model is used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of distance into a parallel walled cavity. The degree of erosion relative is compared between the various interior locations and the external surface of an LEO spacecraft.

  18. Modified Truncated Cone Target Hyperthermal Atomic Oxygen Test Results

    NASA Technical Reports Server (NTRS)

    Vaughn, J. A.; Kamenetsky, R. R.; Finckenor, M. M.

    1999-01-01

    The modified truncated cone target is a docking target planned for use on the International Space Station. The current design consists of aluminum treated with a black dye anodize, then crosshairs are laser etched for a silvery color. Samples of the treated aluminum were exposed to laboratory simulation of atomic oxygen and ultraviolet radiation to determine if significant degradation might occur. Durability was evaluated based on the contrast ratio between the black and silvery white areas of the target. Degradation of optical properties appeared to level off after an initial period of exposure to atomic oxygen. The sample that was not alodined according to MIL-C-5541, type 1A, performed better than alodined samples.

  19. MISSE Scattered Atomic Oxygen Characterization Experiment

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Miller, Sharon K.

    2006-01-01

    An experiment designed to measure the atomic oxygen (AO) erosion profile of scattered AO was exposed to Low Earth Orbital (LEO) AO for almost four years as part of the Materials International Space Station Experiment 1 and 2 (MISSE 1 and 2). The experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), Tray 1, attached to the exterior of the International Space Station (ISS) Quest Airlock. The experiment consisted of an aperture disk lid of Kapton H (DuPont) polyimide coated on the space exposed surface with a thin AO durable silicon dioxide film. The aperture lid had a small hole in its center to allow AO to enter into a chamber and impact a base disk of aluminum. The AO that scattered from the aluminum base could react with the under side of the aperture lid which was coated sporadically with microscopic sodium chloride particles. Scattered AO erosion can occur to materials within a spacecraft that are protected from direct AO attack but because of apertures in the spacecraft the AO can attack the interior materials after scattering. The erosion of the underside of the Kapton lid was sufficient to be able to use profilometry to measure the height of the buttes that remained after washing off the salt particles. The erosion pattern indicated that peak flux of scattered AO occurred at and angle of approximately 45 from the incoming normal incidence on the aluminum base unlike the erosion pattern predicted for scattering based on Monte Carlo computational predictions for AO scattering from Kapton H polyimide. The effective erosion yield for the scattered AO was found to be a factor of 0.214 of that for direct impingement on Kapton H polyimide.

  20. Simulation of the low earth orbital atomic oxygen interaction with materials by means of an oxygen ion beam

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Paulsen, Phillip E.; Steuber, Thomas J.

    1989-01-01

    Atomic oxygen is the predominant species in low-Earth orbit between the altitudes of 180 and 650 km. These highly reactive atoms are a result of photodissociation of diatomic oxygen molecules from solar photons having a wavelength less than or equal to 2430A. Spacecraft in low-Earth orbit collide with atomic oxygen in the 3P ground state at impact energies of approximately 4.2 to 4.5 eV. As a consequence, organic materials previously used for high altitude geosynchronous spacecraft are severely oxidized in the low-Earth orbital environment. The evaluation of materials durability to atomic oxygen requires ground simulation of this environment to cost effectively screen materials for durability. Directed broad beam oxygen sources are necessary to evaluate potential spacecraft materials performance before and after exposure to the simulated low-Earth orbital environment. This paper presents a description of a low energy, broad oxygen ion beam source used to simulate the low-Earth orbital atomic oxygen environment. The results of materials interaction with this beam and comparison with actual in-space tests of the same meterials will be discussed. Resulting surface morphologies appear to closely replicate those observed in space tests.

  1. Atomic oxygen exposure of LDEF experiment trays

    NASA Technical Reports Server (NTRS)

    Bourassa, R. J.; Gillis, J. R.

    1992-01-01

    Atomic oxygen exposures were determined analytically for rows, longerons, and end bays of the Long Duration Exposure Facility (LDEF). The calculations are based on an analytical model that accounts for the effects of thermal molecular velocity, atmospheric temperature, number density, spacecraft velocity, incidence angle, and atmospheric rotation on atomic oxygen flux. Results incorporate variations in solar activity, geomagnetic index, and orbital parameters occurring over the 6-year flight of the spacecraft. To facilitate use of the data, both detailed tabulations and summary charts for atomic oxygen fluences are presented.

  2. Protocol for Atomic Oxygen Testing of Materials in Ground-Based Facilities. No. 2

    NASA Technical Reports Server (NTRS)

    Minton, Timothy K.

    1995-01-01

    A second version of standard guidelines is proposed for improving materials testing in ground-based atomic oxygen environments for the purpose of predicting the durability of the tested materials in low Earth orbit (LEO). Accompanying these guidelines are background information and notes about testing. Both the guidelines and the additional information are intended to aid users who wish to evaluate the potential hazard of atomic oxygen in LEO to a candidate space component without actually flying the component in space, and to provide a framework for more consistent atomic oxygen testing in the future.

  3. Comparison of Atomic Oxygen Erosion Yields of Materials at Various Energy and Impact Angles

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Waters, Deborah L.; Thorson, Stephen D.; deGroh, Kim, K.; Snyder, Aaron; Miller, Sharon

    2006-01-01

    The atomic oxygen erosion yields of various materials, measured in volume of material oxidized per incident atomic oxygen atom, are compared to the commonly accepted standard of Kapton H (DuPont) polyimide. The ratios of the erosion yield of Kapton H to the erosion yield of various materials are not consistent at different atomic oxygen energies. Although it is most convenient to use isotropic thermal energy RF plasma ashers to assess atomic oxygen durability, the results can be misleading because the relative erosion rates at thermal energies are not necessarily the same as low Earth orbital (LEO) energies of approx.4.5 eV. An experimental investigation of the relative atomic oxygen erosion yields of a wide variety of polymers and carbon was conducted using isotropic thermal energy (approx.0.1 eV) and hyperthermal energy (approx.70 eV) atomic oxygen using an RF plasma asher and an end Hall ion source. For hyperthermal energies, the atomic oxygen erosion yields relative to normal incident Kapton H were compared for sweeping atomic oxygen arrival with that of normal incidence arrival. The results of isotropic thermal energy, normal incident, and sweeping incident atomic oxygen are also compared with measured or projected LEO values.

  4. Techniques for Measuring Low Earth Orbital Atomic Oxygen Erosion of Polymers

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Banks, Bruce A.; Demko, Rikako

    2002-01-01

    Polymers such as polyimide Kapton and Teflon FEP (fluorinated ethylene propylene) are commonly used spacecraft materials due to their desirable properties such as flexibility, low density, and in the case of FEP, a low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low Earth orbit (LEO) environment are exposed to energetic atomic oxygen. Atomic oxygen reaction with polymers causes erosion, which is a threat to spacecraft durability. It is therefore important to understand the atomic oxygen erosion yield (E, the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. The most common technique for determining E is through mass loss measurements. For limited duration exposure experiments, such as shuttle experiments, where the atomic oxygen fluence is often so low that mass loss measurements can not produce acceptable uncertainties, recession measurements based on atomic force microscopy analyses can be used. Equally necessary to knowing the mass loss or recession depth for determining the erosion yield of polymers is the knowledge of the atomic oxygen fluence that the polymers were exposed to in space. This paper discusses the procedures and relevant issues for mass loss and recession depth measurements for passive atomic oxygen erosion yield characterization of polymers, along with techniques for active atomic oxygen fluence and erosion characterization. One active atomic oxygen erosion technique discussed is a new technique based on optical measurements. Details including the use of both semi-transparent and opaque polymers for active erosion measurement are reviewed.

  5. Atomic oxygen effects on refractory materials

    NASA Technical Reports Server (NTRS)

    Ferguson, Dale C.

    1990-01-01

    Atomic oxygen in LEO may have undesirable effects on exposed refractory materials, such as are proposed for nuclear reactors in orbit, high temperature radiators, solar dynamic collectors, etc. Time-resolved measurement of the volatile efflux from such materials at high temperatures is being done in an ultrahigh vacuum atomic oxygen ion beam facility. Results of measurements of the efflux of volatile oxides of molybdenum and niobium-1 percent zirconium at temperatures as high as 1550 K are presented, along with a discussion of the roles of adsorption, desorption, and diffusion in atomic oxygen reactions on surfaces at high temperatures. The dependence of reaction rates for certain materials on the energy of the incident atomic oxygen beam will be emphasized.

  6. The NASA atomic oxygen effects test program

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Brady, Joyce A.

    1988-01-01

    The NASA Atomic Oxygen Effects Test Program was established to compare the low earth orbital simulation characteristics of existing atomic oxygen test facilities and utilize the collective data from a multitude of simulation facilities to promote understanding of mechanisms and erosion yield dependence upon energy, flux, metastables, charge, and environmental species. Four materials chosen for this evaluation include Kapton HN polyimide, FEP Teflon, polyethylene, and graphite single crystals. The conditions and results of atomic oxygen exposure of these materials is reported by the participating organizations and then assembled to identify degrees of dependency of erosion yields that may not be observable from any single atomic oxygen low earth orbital simulation facility. To date, the program includes 30 test facilities. Characteristics of the participating test facilities and results to date are reported.

  7. Photoionization of Atomic Oxygen and Nitrogen

    NASA Technical Reports Server (NTRS)

    Dalgarno, Alexander

    1960-01-01

    A knowledge of the photoionization cross sections of atomic oxygen and atomic nitrogen from the spectral heads down to the x-ray region is necessary for the interpretaton of the behavior of the ionized layers. In this note we examine the available theoretical and experimental data and obtain sets of recommended values.

  8. Sensitive Technique Developed Using Atomic Force Microscopy to Measure the Low-Earth-Orbit Atomic Oxygen Erosion of Polymers

    NASA Technical Reports Server (NTRS)

    deGroh, Kim D.; Banks, Bruce A.; Clark, Gregory W.; Hammerstrom, Anne; Youngstrom, Erica; Kaminski, Carolyn; Fine, Elizabeth; Marx, Laura

    2001-01-01

    A recession measurement technique has been developed at the NASA Glenn Research Center to determine the atomic oxygen durability of polymers exposed to the space environment for short durations. Polymers such as polyimide Kapton and Teflon FEP (fluorinated ethylene propylene, DuPont) are commonly used in spacecraft because of their desirable properties, such as flexibility, low density, and in the case of FEP, low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low- Earth-orbit environment are exposed to energetic atomic oxygen, resulting in erosion and potential structural loss. It is, therefore, important to understand the atomic oxygen erosion yield (E, the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. Because long-term space exposure data are rare and very costly, short-term exposures, such as on the space shuttles, are often relied on for atomic oxygen erosion determination. The most common technique for determining E is through mass-loss measurements. For limited-duration exposure experiments, such as shuttle flight experiments, the atomic oxygen fluence is often so small that mass-loss measurements are not sensitive enough. Therefore, a recession measurement technique has been developed at Glenn to obtain accurate erosion yields of polymers exposed to low atomic oxygen fluences.

  9. Measurement of Atomic-Oxygen Flux Distribution

    NASA Astrophysics Data System (ADS)

    Hisashiba, Takuya; Kuroda, Kazutaka; Masui, Hirokazu; Iwata, Minoru; Toyoda, Kazuhiro; Cho, Mengu

    Since material surfaces on the outside of spacecraft are exposed directly to the space environment, material having high tolerance to atomic oxygen, ultraviolet rays and radiation are preferred for long time spacecraft operation. In order to examine the influence of atomic oxygen (AO) on space grade materials, an atomic oxygen simulation chamber was developed. A system was developed that generates AO using a laser detonation method. A CO2 gas laser (5 J) irradiates the oxygen gas in a vacuum chamber (2 MPa) to dissociate the molecular oxygen into atomic. The velocity of AO can be controlled based on the timing between the laser and the gas pulse valve that injects oxygen gas into the chamber. The AO velocity generated by this system is measured using a QMASS (Quadruple Mass Spectrometer) and found to be 8 km/s. It was necessary to measure the AO flux distribution in the chamber at the location where the material samples are exposed to AO. The AO flux distribution was evaluated by measuring the mass gain on a QCM (QuartzCrystal Microbalance) coated with a silver film upon exposure to the AO.

  10. Pulsed source of energetic atomic oxygen

    NASA Technical Reports Server (NTRS)

    Caledonia, George E.; Krech, Robert H.

    1987-01-01

    A pulsed high flux source of nearly monoenergetic atomic oxygen was designed, built, and successfully demonstrated. Molecular oxygen at several atmospheres pressure is introduced into an evacuated supersonic expansion nozzle through a pulsed molecular beam valve. An 18 J pulsed CO2 TEA laser is focused to intensities greater than 10(9) W/sq cm in the nozzle throat to generate a laser-induced breakdown. The resulting plasma is heated in excess of 20,000 K by a laser supported detonation wave, and then rapidly expands and cools. Nozzle geometry confines the expansion to provide rapid electron-ion recombination into atomic oxygen. Average O atom beam velocities from 5 to 13 km/s were measured at estimated fluxes to 10(18) atoms per pulse. Preliminary materials testing has produced the same surface oxygen enrichment in polyethylene samples as obtained on the STS-8 mission. Scanning electron microscope examinations of irradiated polymer surfaces reveal an erosion morphology similar to that obtained in low Earth orbit, with an estimated mass removal rate of approx. 10(-24) cu cm/atom. The characteristics of the O atom source and the results of some preliminary materials testing studies are reviewed.

  11. Oxidation of platinum nickel nanowires to improve durability of oxygen-reducing electrocatalysts

    DOE PAGES

    Alia, Shaun M.; Pylypenko, Svitlana; Dameron, Arrelaine; Neyerlin, Kenneth C.; Kocha, Shyam S.; Pivovar, Bryan S.

    2016-01-12

    In this study, the impact of heat treating platinum-coated nickel (Pt-Ni) nanowires in oxygen is examined to determine the effect on oxygen reduction (ORR) activity and durability. Pt-Ni nanowires exhibit promising ORR mass activities (3 times greater than Pt nanoparticles, 1.5 times greater than U.S. Department of Energy target) both before and after potential cycling for all but the highest annealing temperatures explored. The annealing of Pt-Ni nanowires in oxygen with increasing temperature is found to reduce surface area and ORR activity in comparison to the untreated material, but also reduces activity losses following durability testing. Following potential cycling, unannealedmore » Pt-Ni nanowires show significant losses in surface area (23%) and specific activity (18%) while Pt-Ni nanowires annealed at 200°C show modest increases in surface area (2%) and specific activity (6%) after potential cycling. Increasing annealing temperatures also show a clear trend of decreasing Ni dissolution rates. While oxygen annealing has shown the ability to improve durability of Pt-Ni nanowires, significant Ni dissolution was observed in all samples and suggests oxide passivation while showing promise for improved durability, when employed by itself is insufficient to prevent all contamination concerns involving Ni dissolution.« less

  12. Determination of atomic oxygen fluence using spectrophotometric analysis of infrared transparent witness coupons for long duration exposure tests

    NASA Technical Reports Server (NTRS)

    Podojil, Gregg M.; Jaworske, Donald A.

    1993-01-01

    Atomic oxygen degradation is one of several major threats to the durability of spaceborne systems in low Earth orbit. Ground-based simulations are conducted to learn how to minimize the adverse effects of atomic oxygen exposure. Assessing the fluence of atomic oxygen in test chambers such as a plasma asher over long periods of time is necessary for accurate determination of atomic oxygen exposure. Currently, an atomic oxygen susceptible organic material such as Kapton is placed next to samples as a witness coupon and its mass loss is monitored and used to determine the effective atomic oxygen fluence. However, degradation of the Kapton witness coupons occurs so rapidly in plasma ashers that for any long term test many witness coupons must be used sequentially in order to keep track of the fluence. This necessitates opening vacuum to substitute fresh coupons. A passive dosimetry technique was sought to monitor atomic oxygen exposure over longer periods without the need to open the plasma asher to the atmosphere. This paper investigates the use of spectrophotometric analysis of durable IR transparent witness coupons to measure atomic oxygen exposure for longer duration testing. The method considered would be conductive to making in situ measurements of atomic oxygen fluence.

  13. Atomic Oxygen Used to Restore Artworks

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K.

    2004-01-01

    Techniques developed at the NASA Glenn Research Center to produce atomic oxygen in order to simulate the low-Earth-orbit environment for spacecraft materials testing can also be applied in the field of art restoration. Defaced or fire-damaged artwork can be treated with atomic oxygen to remove the damage and enable restoration that could not be accomplished with conventional methods. The process has been patented (U.S. Patents 5,560,781 and 5,693,241) and has been used to restore several works of art.

  14. Thermal nonequilibrium in partially ionized atomic oxygen

    NASA Technical Reports Server (NTRS)

    Soon, W. H.; Kunc, J. A.

    1990-01-01

    A stationary, nonlinear collisional-radiative model for high-temperature atomic oxygen is presented. Populations of electrons, ions, and excited atoms and intensities of spectral, continuum, and dielectronic recombination lines are calculated in a wide range of conditions. Transport of radiation is included by coupling the rate equations for production of the electrons, ions, and excited atoms with the concept of the escape factors that are not constant but dependent upon plasma conditions. The calculated total continuum emission is in good agreement with existing measurements.

  15. Transport properties of ground state oxygen atoms

    NASA Technical Reports Server (NTRS)

    Holland, Paul M.; Biolsi, Louis

    1988-01-01

    The transport properties of dilute monatomic gases depend on the two-body interactions between like atoms. When two ground-state oxygen atoms interact, they can follow any of 18 potential energy curves corresponding to O2, all of which contribute to the transport properties of the ground-state atoms. Transport collision integrals have been calculated for those interactions with an attractive minimum in the potential, and repulsive ab initio potential-energy curves have been accurately represented. Results are given for viscosity, thermal conductivity, and diffusion and they are compared with previous theoretical calculations.

  16. Atomic Oxygen Treatment and Its Effect on a Variety of Artist's Media

    NASA Technical Reports Server (NTRS)

    Miller, Sharon K. R.; Banks, Bruce A.; Waters, Deborah L.

    2005-01-01

    Atomic oxygen treatment has been investigated as an unconventional option for art restoration where conventional methods have not been effective. Exposure of surfaces to atomic oxygen was first performed to investigate the durability of materials in the low Earth orbit environment of space. The use of the ground based environmental simulation chambers, developed for atomic oxygen exposure testing, has been investigated in collaboration with conservators at a variety of institutions, as a method to clean the surfaces of works of art. The atomic oxygen treatment technique has been evaluated as a method to remove soot and char from the surface of oil paint (both varnished and unvarnished), watercolors, acrylic paint, and fabric as well as the removal of graffiti and other marks from surfaces which are too porous to lend themselves to conventional solvent removal techniques. This paper will discuss the treatment of these surfaces giving an example of each and a discussion of the treatment results.

  17. Benefits of oxygen incorporation in atomic laminates

    NASA Astrophysics Data System (ADS)

    Dahlqvist, Martin

    2016-04-01

    Atomic laminates such as MAX phases benefit from the addition of oxygen in many ways, from the formation of a protective oxide surface layer with self-healing capabilities when cracks form to the tuning of anisotropic conductivity. In this paper oxygen incorporation and vacancy formation in M 2AlC (M  =  Ti, V, Cr) MAX phases have been studied using first-principles calculations where the focus is on phase stability and electronic structure for different oxygen and/or vacancy configurations. Oxygen prefers different lattice sites depending on M-element and this can be correlated to the number of available non-bonding M d-electrons. In Ti2AlC, oxygen substitutes carbon while in Cr2AlC it is located interstitially within the Al-layer. I predict that oxygen incorporation in Ti2AlC stabilizes the material, which explains the experimentally observed 12.5 at% oxygen (x  =  0.5) in Ti2Al(C1‑x O x ). In addition, it is also possible to use oxygen to stabilize the hypothetical Zr2AlC and Hf2AlC. Hence, oxygen incorporation may be beneficial in many ways. Not only can it make a material more stable, but it also can act as a reservoir for internal self-healing with shorter diffusion paths.

  18. MISSE PEACE Polymers Atomic Oxygen Erosion Results

    NASA Technical Reports Server (NTRS)

    deGroh, Kim, K.; Banks, Bruce A.; McCarthy, Catherine E.; Rucker, Rochelle N.; Roberts, Lily M.; Berger, Lauren A.

    2006-01-01

    Forty-one different polymer samples, collectively called the Polymer Erosion and Contamination Experiment (PEACE) Polymers, have been exposed to the low Earth orbit (LEO) environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of Materials International Space Station Experiment 2 (MISSE 2). The objective of the PEACE Polymers experiment was to determine the atomic oxygen erosion yield of a wide variety of polymeric materials after long term exposure to the space environment. The polymers range from those commonly used for spacecraft applications, such as Teflon (DuPont) FEP, to more recently developed polymers, such as high temperature polyimide PMR (polymerization of monomer reactants). Additional polymers were included to explore erosion yield dependence upon chemical composition. The MISSE PEACE Polymers experiment was flown in MISSE Passive Experiment Carrier 2 (PEC 2), tray 1, on the exterior of the ISS Quest Airlock and was exposed to atomic oxygen along with solar and charged particle radiation. MISSE 2 was successfully retrieved during a space walk on July 30, 2005, during Discovery s STS-114 Return to Flight mission. Details on the specific polymers flown, flight sample fabrication, pre-flight and post-flight characterization techniques, and atomic oxygen fluence calculations are discussed along with a summary of the atomic oxygen erosion yield results. The MISSE 2 PEACE Polymers experiment is unique because it has the widest variety of polymers flown in LEO for a long duration and provides extremely valuable erosion yield data for spacecraft design purposes.

  19. Activity and Durability of Iridium Nanoparticles in the Oxygen Evolution Reaction

    DOE PAGES

    Alia, Shaun M.; Rasimick, Brian; Ngo, Chilan; Neyerlin, K. C.; Kocha, Shyam S.; Pylypenko, Svitlana; Xu, Hui; Pivovar, Bryan S.

    2016-07-15

    Unsupported iridium (Ir) nanoparticles, that serve as standard oxygen evolution reaction (OER) catalysts in acidic electrolyzers, were investigated for electrochemical performance and durability in rotating disk electrode (RDE) half-cells. Fixed potential holds and potential cycling were applied to probe the durability of Ir nanoparticles, and performance losses were found to be driven by particle growth (coarsening) at moderate potential (1.4 to 1.6 V) and Ir dissolution at higher potential (>/=1.8 V). Several different commercially available samples were evaluated and standardized conditions for performance comparison are reported. In conclusion, the electrocatalyst RDE results have also been compared to results obtained formore » performance and durability in electrolysis cells.« less

  20. Synergistic effects of ultraviolet radiation, thermal cycling and atomic oxygen on altered and coated Kapton surfaces

    NASA Technical Reports Server (NTRS)

    Dever, Joyce A.; Bruckner, Eric J.; Rodriguez, Elvin

    1992-01-01

    The photovoltaic (PV) power system for Space Station Freedom (SSF) uses solar array blankets which provide structural support for the solar cells and house the electrical interconnections. In the low earth orbital (LEO) environment where SSF will be located, surfaces will be exposed to potentially damaging environmental conditions including solar ultraviolet (UV) radiation, thermal cycling, and atomic oxygen. It is necessary to use ground based tests to determine how these environmental conditions would affect the mass loss and optical properties of candidate SSF blanket materials. Silicone containing, silicone coated, and SiO(x) coated polyimide film materials were exposed to simulated LEO environmental conditions to determine their durability and whether the environmental conditions of UV, thermal cycling and oxygen atoms act synergistically on these materials. A candidate PV blanket material called AOR Kapton, a polysiloxane polyimide cast from a solution mixture, shows an improvement in durability to oxygen atoms erosion after exposure to UV radiation or thermal cycling combined with UV radiation. This may indicate that the environmental conditions react synergistically with this material, and the damage predicted by exposure to atomic oxygen alone is more severe than that which would occur in LEO where atomic oxygen, thermal cycling and UV radiation are present together.

  1. Synergistic effects of ultraviolet radiation, thermal cycling, and atomic oxygen on altered and coated Kapton surfaces

    NASA Technical Reports Server (NTRS)

    Dever, Joyce A.; Bruckner, Eric J.; Rodriguez, Elvin

    1992-01-01

    The photovoltaic (PV) power system for Space Station Freedom (SSF) uses solar array blankets which provide structural support for the solar cells and house the electrical interconnections. In the low Earth orbital (LEO) environment where SSF will be located, surfaces will be exposed to potentially damaging environmental conditions including solar ultraviolet (UV) radiation, thermal cycling, and atomic oxygen. It is necessary to use ground based tests to determine how these environmental conditions would affect the mass loss and optical properties of candidate SSF blanket materials. Silicone containing, silicone coated, and SiO(x) coated polyimide film materials were exposed to simulated LEO environmental conditions to determine there durability and whether the environmental conditions of UV, thermal cycling and oxygen atoms act synergistically on these materials. A candidate PV blanket material called AOR Kapton, a polysiloxane polyimide cast from a solution mixture, shows an improvement in durability to oxygen atoms erosion after exposure to UV radiation or thermal cycling combined with UV radiation. This may indicate that the environmental conditions react synergistically with this material, and the damage predicted by exposure to atomic oxygen alone is more severe than that which would occur in LEO where atomic oxygen, thermal cycling and UV radiation are present together.

  2. Simulation of the synergistic low Earth orbit effects of vacuum thermal cycling, vacuum UV radiation, and atomic oxygen

    NASA Technical Reports Server (NTRS)

    Dever, Joyce A.; Degroh, Kim K.; Stidham, Curtis R.; Stueber, Thomas J.; Dever, Therese M.; Rodriguez, Elvin; Terlep, Judith A.

    1992-01-01

    In order to assess the low Earth orbit (LEO) durability of candidate space materials, it is necessary to use ground laboratory facilities which provide LEO environmental effects. A facility combining vacuum thermal cycling and vacuum ultraviolet (VUV) radiation has been designed and constructed at NASA Lewis Research Center for this purpose. This facility can also be operated without the VUV lamps. An additional facility can be used to provide VUV exposure only. By utilizing these facilities, followed by atomic oxygen exposure in an RF plasma asher, the effects of the individual vacuum thermal cycling and VUV environments can be compared to the effect of the combined vacuum thermal cycling/VUV environment on the atomic oxygen durability of materials. The synergistic effects of simulated LEO environmental conditions on materials were evaluated by first exposing materials to vacuum thermal cycling, VUV, and vacuum thermal cycling/VUV environments followed by exposure to atomic oxygen in an RP plasma asher. Candidate space power materials such as atomic oxygen protected polyimides and solar concentrator mirrors were evaluated using these facilities. Characteristics of the Vacuum Thermal Cycling/VUV Exposure Facility which simulates the temperature sequences and solar ultraviolet radiation exposure that would be experienced by a spacecraft surface in LEO are discussed. Results of durability evaluations of some candidate space power materials to the simulated LEO environmental conditions will also be discussed. Such results have indicated that for some materials, atomic oxygen durability is affected by previous exposure to thermal cycling and/or VUV exposure.

  3. STS-8 atomic oxygen effects experiment

    NASA Technical Reports Server (NTRS)

    Visentine, J. T.; Leger, L. J.; Kuminecz, J. F.; Spiker, I. K.

    1985-01-01

    A flight experiment was performed on the eighth Space Shuttle mission to measure reaction of surfaces with atomic oxygen in the low earth orbital environment. More than 300 individual samples were exposed to ram (normal to surface) conditions for 41.75 hr leading to a total atomic oxygen fluence of 3.5 x 10 to the 20th atoms/sq cm. Reaction rates for surface recession measured primarily by mass change of several organic films were in the range of 3.0 x 10 to the -24th cu cm/atom, and less than 5 x 10 to the -26th cu cm/atom for Teflon. Effects of parameters such as temperature and solar radiation were assessed, as was the importance of atmospheric ionic species on surface recession. In an experiment performed on the fifth Space Shuttle flight, no temperature dependence of reaction rate for the organic films studied was found in the temperature range of 25 to 125 C. Preliminary findings indicate that the reactivity of organic films is not affected by temperature (in the range of 65 to 125 C), solar radiation, or ionic species. Significant surface morphology changes led to a carpet-like appearance also consistent with previous findings.

  4. Two photon excitation of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Pindzola, M. S.

    1977-01-01

    A standard perturbation expansion in the atom-radiation field interaction is used to calculate the two photon excitation cross section for 1s(2) 2s(2) 2p(4) p3 to 1s(2) 2s(2) 2p(3) (s4) 3p p3 transition in atomic oxygen. The summation over bound and continuum intermediate states is handled by solving the equivalent inhomogeneous differential equation. Exact summation results differ by a factor of 2 from a rough estimate obtained by limiting the intermediate state summation to one bound state. Higher order electron correlation effects are also examined.

  5. Small UHV compatible hyperthermal oxygen atom generator

    NASA Technical Reports Server (NTRS)

    Outlaw, Ronald A. (Inventor); Davison, Mark R. (Inventor)

    1994-01-01

    A high purity, hyperthermal, continuous beam atomic oxygen source capable of retrofitting to existing UHV systems has been developed. The instrument complements a general system capability, while its small size and simplicity of design permits tailoring the instrument for most experimental geometries. The flux level presently available is near 1 x 10 (exp 14) cm(exp -2)s(exp -1)(3P) but may be extended toward the theoretical limit of 3x10(exp 15 cm(exp -2)s(exp -1). The energy distribution of the emitted neutrals shows that the mean kinetic energy is about the same as observed for the ions or about 4 eV. The energy of the oxygen atoms may be substantially reduced for other applications by collision with a temperature controlled, non-reactive surface (with a concomitant spread in the energy distribution).

  6. Atomic Oxygen Effects on Coated Tether Materials

    NASA Technical Reports Server (NTRS)

    Gittemeier, Keith A.; Hawk, Clark W.; Finckenor, Miria M.; Watts, Ed

    2005-01-01

    The University of Alabama in Huntsville s Propulsion Research Center has teamed with NASA's Marshall Space Flight Center (MSFC) to research the effects of atomic oxygen (AO) bombardment on coated tether materials. Tethers Unlimited Inc. has provided several candidate tether materials with various coatings for (AO) exposure in MSFC's Atomic Oxygen Beam Facility. Additional samples were exposed to ultraviolet (UV) radiation at MSFC. AO erodes most organic materials, and ultraviolet radiation embrittles polymers. This test series was performed to determine the effect of AO and UV on the mechanical integrity of tether materials that were treated with AO-protective coatings, such as Photosil or metallization. Both TUI's Multi-Application Survivable Tether (MAST) Experiment and Marshall Space Flight Center's Momentum Exchange Electrodynamic Reboost (MXER) programs will benefit from this research by helping to determine tether materials and coatings that give the longest life with the lowest mass penalty.

  7. Absolute photoionization cross sections of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Pareek, P. N.

    1985-01-01

    The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

  8. Absolute photoionization cross sections of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Pareek, P. N.

    1982-01-01

    The absolute values of photoionization cross sections of atomic oxygen were measured from the ionization threshold to 120 A. An auto-ionizing resonance belonging to the 2S2P4(4P)3P(3Do, 3So) transition was observed at 479.43 A and another line at 389.97 A. The experimental data is in excellent agreement with rigorous close-coupling calculations that include electron correlations in both the initial and final states.

  9. Atomic oxygen in the lower thermosphere

    NASA Technical Reports Server (NTRS)

    Lin, Florence J.; Chance, Kelly V.; Traub, Wesley A.

    1987-01-01

    The 63-micron line due to thermospheric atomic oxygen O(P-3), using a far-infrared spectrometer on a balloon platform at 37 km altitude over Palestine, TX, on June 20, 1983. From measurements of the equivalent width of this line at two elevation angles, a weak angular dependence is found: the equivalent width increases by a factor of 1.5 + or - 0.3 as the angle decreases from +30 deg to +1 deg. Since the optical depth of the O(P-3) line is large, the measured line intensity cannot be directly converted to a column abundance. Instead, the measurements are interpreted in terms of radiative transfer through a 16-layer atmosphere extending to 200 km. A model atmosphere for summer at 30 deg N, with an exospheric temperature of 1300 K, including an assumed daytime atomic oxygen abundance profile constructed from recent chemical and dynamical models and a water vapor abundance profile constructed from recent experimental and model results is used. For this assumed O(P-3) vertical profile shape a multiplicative scaling factor of 0.8, with an altitude-dependent uncertainty is determined. In the best-determined layer the uncertainty in the multiplier is + or - 0.2 at 119 km. The model-dependent peak atomic oxygen density is 3.6 (+ or - 1.9) x 10 to the 11th/cu cm at an altitude of about 101 km.

  10. Atomic oxygen beam source for erosion simulation

    NASA Technical Reports Server (NTRS)

    Cuthbertson, J. W.; Langer, W. D.; Motley, R. W.

    1990-01-01

    A device for production of low-energy (5-10 eV) neutral atomic beams for surface modification studies, which recreates the flux of atomic oxygen in LEO, is described. The beam is produced by acceleration of plasma ions onto a negatively biased plate of high-Z metal; the ions are neutralized and reflected by the surface, retaining a large fraction of their incident kinetic energy, forming a beam of atoms. The device is based on a magnetically confined (3-4 kG) coaxial plasma source and the atom energy can be varied by adjusting the bias voltage. The source provides a neutral flux of roughly 5 x 10 to the 16th/sq cm/s at a distance of 10 cm and a fluence of roughly 10 to the 21st/sq cm in five hours. The source has been characterized with plasma diagnostics and by measuring the energy of an atomic argon beam using a mass spectrometer. Samples of carbon film, carbon-based paint, Kapton, Mylar, and Teflon exposed to atomic O beams show erosion quite similar to those observed in orbit on the Space Shuttle.

  11. Ground-Laboratory to In-Space Atomic Oxygen Correlation for the Polymer Erosion and Contamination Experiment (PEACE) Polymers

    NASA Technical Reports Server (NTRS)

    Stambler, Arielle H.; Inoshita, Karen E.; Roberts, Lily M.; Barbagallo, Claire E.; deGroh, Kim K.; Banks, Bruce A.

    2011-01-01

    The Materials International Space Station Experiment 2 (MISSE 2) Polymer Erosion and Contamination Experiment (PEACE) polymers were exposed to the environment of low Earth orbit (LEO) for 3.95 years from 2001 to 2005. There were 41 different PEACE polymers, which were flown on the exterior of the International Space Station (ISS) in order to determine their atomic oxygen erosion yields. In LEO, atomic oxygen is an environmental durability threat, particularly for long duration mission exposures. Although spaceflight experiments, such as the MISSE 2 PEACE experiment, are ideal for determining LEO environmental durability of spacecraft materials, ground-laboratory testing is often relied upon for durability evaluation and prediction. Unfortunately, significant differences exist between LEO atomic oxygen exposure and atomic oxygen exposure in ground-laboratory facilities. These differences include variations in species, energies, thermal exposures and radiation exposures, all of which may result in different reactions and erosion rates. In an effort to improve the accuracy of ground-based durability testing, ground-laboratory to in-space atomic oxygen correlation experiments have been conducted. In these tests, the atomic oxygen erosion yields of the PEACE polymers were determined relative to Kapton H using a radio-frequency (RF) plasma asher (operated on air). The asher erosion yields were compared to the MISSE 2 PEACE erosion yields to determine the correlation between erosion rates in the two environments. This paper provides a summary of the MISSE 2 PEACE experiment; it reviews the specific polymers tested as well as the techniques used to determine erosion yield in the asher, and it provides a correlation between the space and ground laboratory erosion yield values. Using the PEACE polymers asher to in-space erosion yield ratios will allow more accurate in-space materials performance predictions to be made based on plasma asher durability evaluation.

  12. Recommended practices for in-space and ground laboratory. Atomic oxygen exposure and analysis

    NASA Technical Reports Server (NTRS)

    Banks, Bruce; Koontz, Steve; Mccargo, Matt; Pippin, Gary; Rutledge, Sharon

    1992-01-01

    A detailed guide to testing materials for atomic oxygen durability in earth orbit environments is presented. The steps covered include sample preparation, including masking of the sample, dehydration, weighing, and handling; effective fluence prediction, including the use of witness samples (notably Kapton); plasma facility and operational considerations, involving such matters as avoidance of silicone contamination, the use of continuous versus incremental ashing, and temperature of operation; and erosion yield measurement, with calculation methods and protective coating performance indices provided.

  13. Three-Body Recombination of Oxygen Atoms

    NASA Astrophysics Data System (ADS)

    Huestis, D. L.; Kalogerakis, K. S.

    2002-05-01

    Dayside photodissociation of O2 and CO2 in the atmospheres of Earth, Venus, and Mars produces oxygen atoms that eventually undergo three-body recombination O + O + M -> O2* + M The variety of electronic states produced is observable as nightglow emissions, which have been the subject of many laboratory and interpretive investigations. Here we review the current understanding of the overall temperature-dependent rate coefficient for three-body recombination of oxygen atoms and describe a strategy for its measurement. The most recent measurement [1] is almost 30 years old. The most comprehensive review [2] is more than 25 years old and shows that the absolute rate coefficients for recombination and the reverse process, collision-induced dissociation, as well as the dependence on temperature and collider, are poorly determined, in spite of the relatively narrow error bars reported in the various studies. The most recent high-temperature dissociation study [3] actually increases the divergence. We plan experiments with a commercial F2 laser, providing roughly 50 mJ of 157 nm radiation in a 3-4 mm beam, to achieve greater than 80% dissociation of molecular oxygen, in the range from 0.5 to 5 torr. In a high-pressure N2 background (30-200 torr) the oxygen atoms will recombine in a time scale from 0.1 to 10 ms, as monitored by 845 nm fluorescence excited by two photons at 226 nm. [1] I. M. Campbell and C. N. Gray, Chem. Phys. Lett. 18, 607 (1973). [2] D. L. Baulch, D. D. Drysdale, J. Duxbury, and S. J. Grant, Evaluated Kinetic Data for High Temperature Reactions Vol. 3 ``Homogeneous Gas Phase Reactions of the O2--O3 System, the CO--O2--H2 System, and of Sulphur-Containing Species," (Butterworths, London, 1976). [3] V. Naudet, S. Abid, and C. E. Paillard, J. Chim. Phys. 96, 1123 (1999).

  14. Atomic oxygen beam source for erosion simulation

    NASA Technical Reports Server (NTRS)

    Cuthbertson, J. W.; Langer, W. D.; Motley, R. W.; Vaughn, J. A.

    1991-01-01

    A device for the production of low energy (3 to 10 eV) neutral atomic beams for surface modification studies is described that reproduces the flux of atomic oxygen in low Earth orbit. The beam is produced by the acceleration of plasma ions onto a negatively biased plate of high-Z metal; the ions are neutralized and reflected by the surface, retaining some fraction of their incident kinetic energy, forming a beam of atoms. The plasma is generated by a coaxial RF exciter which produces a magnetically-confined (4 kG) plasma column. At the end of the column, ions fall through the sheath to the plate, whose bias relative to the plasma can be varied to adjust the beam energy. The source provides a neutral flux approximately equal to 5 x 10(exp 16)/sq cm at a distance of 9 cm and a fluence approximately equal to 10(exp 20)/sq cm in five hours. The composition and energy of inert gas beams was diagnosed using a mass spectometer/energy analyzer. The energy spectra of the beams demonstrate energies in the range 5 to 15 eV, and qualitatively show expected dependences upon incident and reflecting atom species and potential drop. Samples of carbon film, carbon-based paint, Kapton, mylar, and teflon exposed to atomic O beams show erosion quite similar to that observed in orbit on the space shuttle.

  15. Proceedings of the NASA Workshop on Atomic Oxygen Effects. [low earth orbital environment

    NASA Technical Reports Server (NTRS)

    Brinza, David E. (Editor)

    1987-01-01

    A workshop was held to address the scientific issues concerning the effects of atomic oxygen on materials in the low Earth orbital (LEO) environment. The program included 18 invited speakers plus contributed posters covering topics such as LEO spaceflight experiments, interaction mechanisms, and atomic oxygen source development. Discussion sessions were also held to organize a test program to evaluate atomic oxygen exposure facilities. The key issues raised in the workshop were: (1) the need to develop a reliable predictive model of the effects of long-term exposure of materials to the LEO environment; (2) the ability of ground-based exposure facilities to provide useful data for development of durable materials; and (3) accurate determination of the composition of the LEO environment. These proceedings include the invited papers, the abstracts for the contributed posters, and an account of the test program discussion sessions.

  16. The effect of atomic oxygen on polysiloxane-polyimide for spacecraft applications in low Earth orbit

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Cooper, Jill M.; Olle, Raymond M.

    1991-01-01

    Polysiloxane-polyimide films are of interest as a replacement for polyimide Kapton in the Space Station Freedom solar array blanket. The blanket provides the structural support for the solar cells as well as providing transport of heat away from the back of the cells. Polyimide Kapton would be an ideal material to use; however, its high rate of degradation due to attack by atomic oxygen in low Earth orbit, at the altitudes Space Station Freedom will fly, is of such magnitude that if left unprotected, the blanket will undergo structural failure in much less than the desired 15 year operating life. Polysiloxane-polyimide is of interest as a replacement material because it should from its own protective silicon dioxide coating upon exposure to atomic oxygen. Mass, optical, and photomicrographic data obtained in the evaluation of the durability of polysiloxane-polyimide to an atomic oxygen environment are presented.

  17. Low Earth orbital atomic oxygen and ultraviolet radiation effects on polymers

    NASA Technical Reports Server (NTRS)

    Dever, Joyce A.

    1991-01-01

    Because atomic oxygen and solar ultraviolet radiation present in the low earth orbital (LEO) environment can alter the chemistry of polymers resulting in degradation, their effects and mechanisms of degradation must be determined in order to determine the long term durability of polymeric surfaces to be exposed on missions such as Space Station Freedom. The effects of atomic oxygen on polymers which contain protective coatings must also be explored, since unique damage mechanisms can occur in areas where the protective coatings has failed. Mechanisms can be determined by utilizing results from previous LEO missions, by performing ground based LEO simulation tests and analysis, and by carrying out focussed space experiments. A survey is presented of the interactions and possible damage mechanisms for environmental atomic oxygen and UV radiation exposure of polymers commonly used in LEO.

  18. Atomic oxygen in the Martian thermosphere

    NASA Technical Reports Server (NTRS)

    Stewart, A. I. F.; Alexander, M. J.; Meier, R. R.; Paxton, L. J.; Bougher, S. W.; Fesen, C. G.

    1992-01-01

    The Mariner 9 Ultraviolet Spectrometer (UVS) made extensive observations of air-glow emissions from the thermosphere of Mars throughout the nominal mission (November 1971 - February 1972), during late summer in the southern hemisphere. Limb and disc measurements of the 130 nm triplet emission from thermospheric atomic oxygen were modelled by Strickland et al. Recently, the thermospheric general circulation models (TGCMs) developed for the Earth and Venus have been applied to Mars; we refer to it as the MTGCM. Our analysis shows that the oxygen mixing ratio is the fundamental unknown controlling the 130 nm brightness. Our radiative transport calculation shows that the emergent intensity at 130 nm is not very sensitive to variations in thermospheric temperature. The pattern of diurnal variation derived from our analysis is roughly the same as Strickland et al. although with somewhat lower values for the O mixing ratio. The main reasons for this difference are the more important role played by the photoelectron source in our model, and the somewhat larger 130 nm solar flux; thus, we require less oxygen to match the observed brightnesses. Strickland et al. also found that the OI 130 nm emission on Mars is correlated with solar activity. We find that the correlation is virtually non-existent during the early orbits when the planet was covered with a thick global dust storm, but later orbits, during the clearing of the storm, show a persistent correlation.

  19. Polymeric Materials Resistant to Erosion by Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Kiefer, Richard L.; Thibeault, Sheila A.

    2004-01-01

    Polymer-matrix composites are ideally suited for space vehicles because of high strength to weight ratios. The principal component of the low earth orbit (LEO) is atomic oxygen. Atomic oxygen causes surface erosion to polymeric materials. Polymer films with an organometallic additive showed greater resistance to atomic oxygen than the pure polymer in laboratory experiments and in the OPM/MIR experiment. In MISSE, the film with the organometallic additive was still intact after the pure film had completely eroded.

  20. Atomic oxygen reactor having at least one sidearm conduit

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L. (Inventor)

    1994-01-01

    An apparatus for treating a microporous structure with atomic oxygen is presented. The apparatus includes a main gas chamber for flowing gas in an axial direction and a source of gas, containing atomic oxygen, connected for introducing the gas into the main gas chamber. The apparatus employs at least one side arm extending from the main atomic oxygen-containing chamber. The side arm has characteristic relaxation times such that a uniform atomic oxygen dose rate is delivered to a specimen positioned transversely in the side arm spaced from the main gas chamber.

  1. N-doped carbon nanomaterials are durable catalysts for oxygen reduction reaction in acidic fuel cells.

    PubMed

    Shui, Jianglan; Wang, Min; Du, Feng; Dai, Liming

    2015-02-01

    The availability of low-cost, efficient, and durable catalysts for oxygen reduction reaction (ORR) is a prerequisite for commercialization of the fuel cell technology. Along with intensive research efforts of more than half a century in developing nonprecious metal catalysts (NPMCs) to replace the expensive and scarce platinum-based catalysts, a new class of carbon-based, low-cost, metal-free ORR catalysts was demonstrated to show superior ORR performance to commercial platinum catalysts, particularly in alkaline electrolytes. However, their large-scale practical application in more popular acidic polymer electrolyte membrane (PEM) fuel cells remained elusive because they are often found to be less effective in acidic electrolytes, and no attempt has been made for a single PEM cell test. We demonstrated that rationally designed, metal-free, nitrogen-doped carbon nanotubes and their graphene composites exhibited significantly better long-term operational stabilities and comparable gravimetric power densities with respect to the best NPMC in acidic PEM cells. This work represents a major breakthrough in removing the bottlenecks to translate low-cost, metal-free, carbon-based ORR catalysts to commercial reality, and opens avenues for clean energy generation from affordable and durable fuel cells.

  2. N-doped carbon nanomaterials are durable catalysts for oxygen reduction reaction in acidic fuel cells

    PubMed Central

    Shui, Jianglan; Wang, Min; Du, Feng; Dai, Liming

    2015-01-01

    The availability of low-cost, efficient, and durable catalysts for oxygen reduction reaction (ORR) is a prerequisite for commercialization of the fuel cell technology. Along with intensive research efforts of more than half a century in developing nonprecious metal catalysts (NPMCs) to replace the expensive and scarce platinum-based catalysts, a new class of carbon-based, low-cost, metal-free ORR catalysts was demonstrated to show superior ORR performance to commercial platinum catalysts, particularly in alkaline electrolytes. However, their large-scale practical application in more popular acidic polymer electrolyte membrane (PEM) fuel cells remained elusive because they are often found to be less effective in acidic electrolytes, and no attempt has been made for a single PEM cell test. We demonstrated that rationally designed, metal-free, nitrogen-doped carbon nanotubes and their graphene composites exhibited significantly better long-term operational stabilities and comparable gravimetric power densities with respect to the best NPMC in acidic PEM cells. This work represents a major breakthrough in removing the bottlenecks to translate low-cost, metal-free, carbon-based ORR catalysts to commercial reality, and opens avenues for clean energy generation from affordable and durable fuel cells. PMID:26601132

  3. New Active Optical Technique Developed for Measuring Low-Earth-Orbit Atomic Oxygen Erosion of Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Demko, Rikako

    2003-01-01

    Polymers such as polyimide Kapton (DuPont) and Teflon FEP (DuPont, fluorinated ethylene propylene) are commonly used spacecraft materials because of desirable properties such as flexibility, low density, and in the case of FEP, a low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low-Earth-orbit (LEO) environment are exposed to energetic atomic oxygen. Atomic oxygen reaction with polymers causes erosion, which is a threat to spacecraft performance and durability. It is, therefore, important to understand the atomic oxygen erosion yield E (the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. The most common technique for determining E is a passive technique based on mass-loss measurements of samples exposed to LEO atomic oxygen during a space flight experiment. There are certain disadvantages to this technique. First, because it is passive, data are not obtained until after the flight is completed. Also, obtaining the preflight and postflight mass measurements is complicated by the fact that many polymers absorb water and, therefore, the mass change due to water absorption can affect the E data. This is particularly true for experiments that receive low atomic oxygen exposures or for samples that have a very low E. An active atomic oxygen erosion technique based on optical measurements has been developed that has certain advantages over the mass-loss technique. This in situ technique can simultaneously provide the erosion yield data on orbit and the atomic oxygen exposure fluence, which is needed for erosion yield determination. In the optical technique, either sunlight or artificial light can be used to measure the erosion of semitransparent or opaque polymers as a result of atomic oxygen attack. The technique is simple and adaptable to a rather wide range of polymers, providing that they have a sufficiently high optical absorption coefficient. If one covers a photodiode with a

  4. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    SciTech Connect

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; Mavrikakis, Manos; Xia, Younan

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.

  5. Operation of the computer model for microenvironment atomic oxygen exposure

    NASA Technical Reports Server (NTRS)

    Bourassa, R. J.; Gillis, J. R.; Gruenbaum, P. E.

    1995-01-01

    A computer model for microenvironment atomic oxygen exposure has been developed to extend atomic oxygen modeling capability to include shadowing and reflections. The model uses average exposure conditions established by the direct exposure model and extends the application of these conditions to treat surfaces of arbitrary shape and orientation.

  6. Reactions Of Atomic Oxygen {O(3P)} With Polybutadienes

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.; Lerner, Narcinda R.; Wydeven, Theodore

    1991-01-01

    Report describes experimental study of chemical reactions of atomic oxygen in ground state {O(3P)} with polybutadienes and related polymers. Attention focused on such reactions because of adverse effects of environmental atomic oxygen on polymeric materials in low orbits around Earth.

  7. Atomic Oxygen Effects on Seal Leakage

    NASA Technical Reports Server (NTRS)

    Christensen, John R.; Underwood, Steve D.; Kamenetzky, Rachel R.; Vaughn, Jason A.

    1999-01-01

    Common Berthing Mechanism (CBM provides the structural interface between separate International Space Station (ISS) elements, such as the Laboratory and Node modules. The CBM consists of an active and a passive half that join together with structural bolts. The seal at this interface is the CBM-to-CBM molded seal. The CBM-to-CBM interface is assembled on orbit, thus the seals can be exposed to the space environment for up to 65 hours. Atomic Oxygen/Vacuum Ultraviolet radiation (AO/VUV) in space is a potential hazard to the seals. Testing was conducted to determine the effect on leakage of the CBM-to-CBM seal material exposed to AO/VUV. The sealing materials were S383 silicone and V835 fluorocarbon material. Control samples, which were not exposed to the AO/VUV environment, were used to ensure that ff any changes in leakage occurred, they could be attributed to the AO/VUV exposure. After exposure to the AO/VUV environment the leakage increase was dramatic for the fluorocarbon. This testing was a major contributing factor in selecting silicone as the CBM-to-CBM seal material.

  8. Atomic Oxygen Effects on Seal Leakage

    NASA Technical Reports Server (NTRS)

    Christensen, John R.; Underwood, Steve D.; Kamenetzky, Rachel R.; Vaughn, Jason A.

    1998-01-01

    Common Berthing Mechanism (CBM) provides the structural interface between separate International Space Station (ISS) elements, such as the Laboratory and Node modules. The CBM consists of an active and a passive half that join together with structural bolts. The seal at this interface is the CBM-to-CBM molded seal. The CBM-to-CBM interface is assembled on orbit, thus the seals can be exposed to the space environment for up to 65 hours. Atomic Oxygen/Vacuum Ultraviolet radiation (AO/VUV) in space is a potential hazard to the seals. Testing was conducted to determine the effect on leakage of the CBM-to-CBM seal material exposed to AO/VUV. The sealing materials were S383 silicone and V835 fluorocarbon material. Control samples, which were not exposed to the AO/VUV environment, were used to ensure that if any changes in leakage occurred, they could be attributed to the AO/VUV exposure. After exposure to the AO/VUV environment the leakage increase was dramatic for the fluorocarbon. This testing was a major contributing factor in selecting silicone as the CBM-to-CBM seal material.

  9. A Sensitive Technique Using Atomic Force Microscopy to Measure the Low Earth Orbit Atomic Oxygen Erosion of Polymers

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Banks, Bruce A.; Clark, Gregory W.; Hammerstrom, Anne M.; Youngstrom, Erica E.; Kaminski, Carolyn; Fine, Elizabeth S.; Marx, Laura M.

    2001-01-01

    Polymers such as polyimide Kapton and Teflon FEP (fluorinated ethylene propylene) are commonly used spacecraft materials due to their desirable properties such as flexibility, low density, and in the case of FEP low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low Earth orbit (LEO) environment are exposed to energetic atomic oxygen. Atomic oxygen erosion of polymers occurs in LEO and is a threat to spacecraft durability. It is therefore important to understand the atomic oxygen erosion yield (E, the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. Because long-term space exposure data is rare and very costly, short-term exposures such as on the shuttle are often relied upon for atomic oxygen erosion determination. The most common technique for determining E is through mass loss measurements. For limited duration exposure experiments, such as shuttle experiments, the atomic oxygen fluence is often so small that mass loss measurements can not produce acceptable uncertainties. Therefore, a recession measurement technique has been developed using selective protection of polymer samples, combined with postflight atomic force microscopy (AFM) analysis, to obtain accurate erosion yields of polymers exposed to low atomic oxygen fluences. This paper discusses the procedures used for this recession depth technique along with relevant characterization issues. In particular, a polymer is salt-sprayed prior to flight, then the salt is washed off postflight and AFM is used to determine the erosion depth from the protected plateau. A small sample was salt-sprayed for AFM erosion depth analysis and flown as part of the Limited Duration Candidate Exposure (LDCE-4,-5) shuttle flight experiment on STS-51. This sample was used to study issues such as use of contact versus non-contact mode imaging for determining recession depth measurements. Error analyses were conducted and the percent probable

  10. Vacuum ultraviolet radiation and thermal cycling effects on atomic oxygen protective photovoltaic array blanket materials

    NASA Technical Reports Server (NTRS)

    Brady, J.; Banks, B.

    1990-01-01

    The importance of synergistic environmental exposure is demonstrated through the evaluation of DuPont 93-1 in simulated LEO environment. Changes in optical properties, surface condition, and mass loss data are described. The qualitative results indicate the necessity for exposure of materials to a series of simulated LEO environments in order to properly determine synergistic effects and demonstrate the overall LEO durability of candidate materials. It is shown that synergistic effects may occur with vacuum thermal cycling combined with VUV radiation followed by atomic oxygen exposure. Testing the durability of candidate solar array blanket materials in a test sequence with necessary synergistic effects makes it possible to determine the appropriate material for providing structural support and maintaining the proper operating temperature for solar cells in the SSF Photovaltaic Power System.

  11. Kinetics and mechanisms of some atomic oxygen reactions

    NASA Technical Reports Server (NTRS)

    Cvetanovic, R. J.

    1987-01-01

    Mechanisms and kinetics of some reactions of the ground state of oxygen atoms, O(3P), are briefly summarized. Attention is given to reactions of oxygen atoms with several different types of organic and inorganic compounds such as alkanes, alkenes, alkynes, aromatics, and some oxygen, nitrogen, halogen and sulfur derivatives of these compounds. References to some recent compilations and critical evaluations of reaction rate constants are given.

  12. Undercutting of defects in thin film protective coatings on polymer surfaces exposed to atomic oxygen

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Mihelcic, Judith A.

    1989-01-01

    Protection for polymeric surfaces is needed to make them durable in the low Earth orbital environment, where oxidation by atomic oxygen is the predominant failure mechanism. Thin film coatings of oxides such as silicon dioxide are viable candidates to provide this protection, but concern has been voiced over the ability of these coatings to protect when defects are present in the coating due to surface anomalies occurring during the deposition process, handling, or micrometeoroid and debris bombardment in low Earth orbit. When a defected coating protecting a polymer substrate is exposed to atomic oxygen, the defect provides a pathway to the underlying polymer allowing oxidation and subsequent undercutting to occur. Defect undercutting was studied for sputter deposited coatings of silicon dioxide on polyimide Kapton. Preliminary results indicate that undercutting may be limited as long as the coating remains intact with the substrate. Therefore, coatings may not need to be defect free to give protection to the underlying surface.

  13. Ground-Laboratory to In-Space Effective Atomic-Oxygen Fluence Determined for DC 93-500 Silicone

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Banks, Bruce A.; Ma, David

    2005-01-01

    Surfaces on the leading edge of spacecraft in low Earth orbit (e.g., surface facing the velocity direction), such as on the International Space Station, are subject to atomic oxygen attack, and certain materials are susceptible to erosion. Therefore, ground-based laboratory testing of the atomic oxygen durability of spacecraft materials is necessary for durability assessment when flight data are not available. For accurate space simulation, the facility is commonly calibrated on the basis of the mass loss of Kapton (DuPont, Wilmington, DE) as a control sample for effective fluence determination. This is because Kapton has a well-characterized atomic oxygen erosion yield (E(sub y), in cubic centimeters per atom) in the low Earth orbit (LEO) environment. Silicones, a family of commonly used spacecraft materials, do not chemically erode away with atomic oxygen attack like other organic materials that have volatile oxidation products. Instead, silicones react with atomic oxygen and form an oxidized hardened silicate surface layer. Often the loss of methyl groups causes shrinkage of the surface skin and "mud-tile" crazing degradation. But silicones often do not lose mass, and some silicones actually gain mass during atomic oxygen exposure. Therefore, the effective atomic oxygen fluence for silicones in a ground-test facility should not be determined on the basis of traditional mass-loss measurements, as it is with polymers that erode. Another method for determining effective fluence needs to be employed for silicones. A new technique has been developed at the NASA Glenn Research Center for determining the effective atomic oxygen fluence for silicones in ground-test facilities. This technique determines the equivalent amount of atomic oxygen oxidation on the basis of changes in the surface-oxide hardness. The specific approach developed was to compare changes in the surface hardness of ground-laboratory-exposed DC93-500 silicone with DC93-500 exposed to LEO atomic oxygen

  14. Use of Atomic Oxygen for the Determination of Document Alteration

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Klubnik, Larisa M.

    2003-01-01

    Atomic oxygen, which normally is found only the near Earth space environment, causes oxidation and erosion of polymers on spacecraft. The development of technology to prevent this degradation has required NASA to develop ground laboratory facilities that generate atomic oxygen. Atomic oxygen has also been found to be able to oxidize most types of ink from a variety of types of pens. The use of atomic oxygen to identify alteration of documents has been investigated and is reported. Results of testing indicates that for many types of ink, pen, and paper, identification of document alteration of pen and ink numbers and evidence of alteration can be made visible by exposing the questionable writing to atomic oxygen. Atomic oxygen provides discrimination because different inks may oxidize at different rates, the amount of time between delayed alteration may add to ink thickness at crossings, and the end of pen strokes tend to have much thicker ink deposits than the rest of the character. Examples and techniques of using atomic oxygen to identify document alteration indicate that the technology can, in many but not all cases, provide discrimination between original and altered documents.

  15. Materials screening chamber for testing materials resistance to atomic oxygen

    NASA Technical Reports Server (NTRS)

    Pippin, H. G.; Carruth, Ralph

    1989-01-01

    A unique test chamber for exposing material to a known flux of oxygen atoms is described. The capabilities and operating parameters of the apparatus include production of an oxygen atom flux in excess of 5 x 10 to the 16th atoms/sq cm-sec, controlled heating of the sample specimen, RF circuitry to contain the plasma within a small volume, and long exposure times. Flux measurement capabilities include a calorimetric probe and a light titration system. Accuracy and limitations of these techniques are discussed. An extension to the main chamber to allow simultaneous ultraviolet and atomic oxygen exposure is discussed. The oxygen atoms produced are at thermal energies. Sample specimens are maintained at any selected temperature between ambient and 200 C, to within + or - 2 C. A representative example of measurements made using the chamber is presented.

  16. Atomic oxygen diffusion on and desorption from amorphous silicate surfaces.

    PubMed

    He, Jiao; Jing, Dapeng; Vidali, Gianfranco

    2014-02-28

    Surface reactions involving atomic oxygen have attracted much attention in astrophysics and astrochemistry, but two of the most fundamental surface processes, desorption and diffusion, are not well understood. We studied diffusion and desorption of atomic oxygen on or from amorphous silicate surfaces under simulated interstellar conditions using a radio-frequency dissociated oxygen beam. Temperature programmed desorption (TPD) experiments were performed to study the formation of ozone from reaction of atomic and molecular oxygen deposited on the surface of a silicate. It is found that atomic oxygen begins to diffuse significantly between 40 K and 50 K. A rate equation model was used to study the surface kinetics involved in ozone formation experiments. The value of atomic oxygen desorption energy has been determined to be 152 ± 20 meV (1764 ± 232 K). The newly found atomic oxygen desorption energy, which is much higher than the well-accepted value, might explain the discrepancy in abundance of molecular oxygen in space between observations and chemical models.

  17. Boron nitride nanosheets as oxygen-atom corrosion protective coatings

    SciTech Connect

    Yi, Min; Shen, Zhigang; Zhao, Xiaohu; Liang, Shuaishuai; Liu, Lei

    2014-04-07

    The research of two-dimensional nanomaterials for anticorrosion applications is just recently burgeoning. Herein, we demonstrate the boron nitride nanosheets (BNNSs) coatings for protecting polymer from oxygen-atom corrosion. High-quality BNNSs, which are produced by an effective fluid dynamics method with multiple exfoliation mechanisms, can be assembled into coatings with controlled thickness by vacuum filtration. After exposed in atom oxygen, the naked polymer is severely corroded with remarkable mass loss, while the BNNSs-coated polymer remains intact. Barrier and bonding effects of the BNNSs are responsible for the coating's protective performance. These preliminary yet reproducible results pave a way for resisting oxygen-atom corrosion.

  18. Proposed reference models for atomic oxygen in the terrestrial atmosphere

    NASA Technical Reports Server (NTRS)

    Llewellyn, E. J.; Mcdade, I. C.; Lockerbie, M. D.

    1989-01-01

    A provisional Atomic Oxygen Reference model was derived from average monthly ozone profiles and the MSIS-86 reference model atmosphere. The concentrations are presented in tabular form for the altitude range 40 to 130 km.

  19. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    PubMed Central

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; Mavrikakis, Manos; Xia, Younan

    2015-01-01

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can be attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. These results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability. PMID:26133469

  20. Palladium–platinum core-shell icosahedra with substantially enhanced activity and durability towards oxygen reduction

    DOE PAGES

    Wang, Xue; Choi, Sang-Il; Roling, Luke T.; Luo, Ming; Ma, Cheng; Zhang, Lei; Chi, Miaofang; Liu, Jingyue; Xie, Zhaoxiong; Herron, Jeffrey A.; et al

    2015-07-02

    Conformal deposition of platinum as ultrathin shells on facet-controlled palladium nanocrystals offers a great opportunity to enhance the catalytic performance while reducing its loading. Here we report such a system based on palladium icosahedra. Owing to lateral confinement imposed by twin boundaries and thus vertical relaxation only, the platinum overlayers evolve into a corrugated structure under compressive strain. For the core-shell nanocrystals with an average of 2.7 platinum overlayers, their specific and platinum mass activities towards oxygen reduction are enhanced by eight- and sevenfold, respectively, relative to a commercial catalyst. Density functional theory calculations indicate that the enhancement can bemore » attributed to the weakened binding of hydroxyl to the compressed platinum surface supported on palladium. After 10,000 testing cycles, the mass activity of the core-shell nanocrystals is still four times higher than the commercial catalyst. Ultimately, these results demonstrate an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.« less

  1. Fast oxygen atom studies related to low Earth orbit activities

    NASA Astrophysics Data System (ADS)

    Caledonia, G. E.; Krech, R. H.; Holtzclaw, K. W.; Sonnenfroh, D.

    1993-06-01

    The technique of laser induced gas breakdown to develop a high flux pulsed source of fast oxygen atoms (v = 5 to 12 km/s) is considered. The technique is also used to produce high velocity beams of N/N2 mixtures and can be extended to produce beams of other species. The fast oxygen atoms are of particular current interest since this is the dominant atmospheric species encountered by spacecraft operating in Low Earth Orbit (LEO). The fast oxygen atom source has proven extremely versatile and is used to study a variety of gas-surface and gas-gas collision phenomena. The fast atom facility has reproducibly provided good comparison with LEO observations. Expanded programs involving material testing and measurement of O atom momentum and energy accommodation coefficients with surfaces are presently underway.

  2. Hypervelocity supersonic nozzle beam source of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Freedman, A.; Unkel, W.; Silver, J.; Kolb, C.

    1984-01-01

    A hypervelocity source of atomic oxygen was developed. Dissociation of molecular oxygen is accomplished by injection into a flow of helium and/or argon which has been heated in a commercial plasma torch. Atomic velocities of up to 4 kms(-1) were produced; recent improvements offer the possibility of even higher velocities. This source was utilized in studies of translational-to-vibrational energy transfer in carbon dioxide and in an investigation of the shuttle glow effect.

  3. The effects of atomic oxygen on the thermal emittance of high temperature radiator surfaces

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Hotes, Deborah L.; Paulsen, Phillip E.

    1989-01-01

    Radiator surfaces on high temperature space power systems such as SP-100 space nuclear power system must maintain a high emittance level in order to reject waste heat effectively. One of the primary materials under consideration for the radiators is carbon-carbon composite. Since carbon is susceptible to attack by atomic oxygen in the low earth orbital environment, it is important to determine the durability of carbon composites in this environment as well as the effect atomic oxygen has on the thermal emittance of the surface if it is to be considered for use as a radiator. Results indicate that the thermal emittance of carbon-carbon composite (as low as 0.42) can be enhanced by exposure to a directed beam of atomic oxygen to levels above 0.85 at 800 K. This emittance enhancement is due to a change in the surface morphology as a result of oxidation. High aspect ratio cones are formed on the surface which allow more efficient trapping of incident radiation. Erosion of the surface due to oxidation is similar to that for carbon, so that at altitudes less than approximately 600 km, thickness loss of the radiator could be significant (as much as 0.1 cm/year). A protective coating or oxidation barrier forming additive may be needed to prevent atomic oxygen attack after the initial high emittance surface is formed. Textured surfaces can be formed in ground based facilities or possibly in space if emittance is not sensitive to the orientation of the atomic oxygen arrival that forms the texture.

  4. The effects of atomic oxygen on the thermal emittance of high temperature radiator surfaces

    SciTech Connect

    Rutledge, S.K.; Hotes, D.L.; Paulsen, P.E.

    1994-09-01

    Radiator surfaces on high temperature space power systems such as the SP-100 space nuclear power system must maintain a high emittance level in order to reject waste heat effectively. one of the primary materials under consideration for the radiators is carbon-carbon composite. Since carbon is susceptible to attack by atomic oxygen in the low Earth orbital environment, it is important to determine the durability of carbon composites in this environment as well as the effect atomic oxygen has on the thermal emittance of the surface if it is to be considered for use as a radiator. Results indicate that the thermal emittance of carbon-carbon composite (as low as 0.42) can be enhanced by exposure to a directed beam of atomic oxygen to levels above 0.85 at 800 K. This emittance enhancement is due to a change in the surface morphology as a result of oxidation. High aspect ratio cones are formed on the surface which allow more efficient trapping of incident radiation. Erosion of the surface due to oxidation is similar to that for carbon; so that at altitudes less than {approximately}600 km, thickness loss of the radiator could be significant (as much as 0.1 cm/year). A protective coating or oxidation barrier forming additive may be needed to prevent atomic oxygen attack after the initial high emittance surface is formed. Textured surfaces can be formed in ground based facilities or possibly in space if emittance is not sensitive to the orientation of the atomic oxygen arrival that forms the texture.

  5. Low Earth Orbital Atomic Oxygen Interactions With Spacecraft Materials

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Miller, Sharon K.

    2004-01-01

    Atomic oxygen, formed in Earth s thermosphere, interacts readily with many materials on spacecraft flying in low Earth orbit (LEO). All hydrocarbon based polymers and graphite are easily oxidized upon the impact of approx.4.5 eV atomic oxygen as the spacecraft ram into the residual atmosphere. The resulting interactions can change the morphology and reduce the thickness of these materials. Directed atomic oxygen erosion will result in the development of textured surfaces on all materials with volatile oxidation products. Examples from space flight samples are provided. As a result of the erosive properties of atomic oxygen on polymers and composites, protective coatings have been developed and are used to increase the functional life of polymer films and composites that are exposed to the LEO environment. The atomic oxygen erosion yields for actual and predicted LEO exposure of numerous materials are presented. Results of in-space exposure of vacuum deposited aluminum protective coatings on polyimide Kapton indicate high rates of degradation are associated with aluminum coatings on both surfaces of the Kapton. Computational modeling predictions indicate that less trapping of the atomic oxygen occurs, with less resulting damage, if only the space-exposed surface is coated with vapor deposited aluminum rather than having both surfaces coated.

  6. Oxygen atom reaction with shuttle materials at orbital altitudes

    NASA Technical Reports Server (NTRS)

    Leger, L. J.

    1982-01-01

    Surfaces of materials used in the space shuttle orbiter payload bay and exposed during STS-1 through STS-3 were examined after flight. Paints and polymers, in particular Kapton used on the television camera thermal blanket, showed significant change. Generally, the change was a loss of surface gloss on the polymer with apparent aging on the paint surfaces. The Kapton surfaces showed the greatest change, and postflight analyses showed mass loss of 4.8 percent on STS-2 and 35 percent on STS-3 for most heavily affected surfaces. Strong shadow patterns were evident. The greatest mass loss was measured on surfaces which were exposed to solar radiation in conjunction with exposure in the vehicle velocity vector. A mechanism which involves the interaction of atomic oxygen with organic polymer surfaces is proposed. Atomic oxygen is the major ambient species at low orbital altitudes and presents a flux of 8 x 10 to the 14th power atoms/cu cm sec for reaction. Correlation of the expected mass loss based on ground-based oxygen atom/polymer reaction rates shows lower mass loss of the Kapton than measured. Consideration of solar heating effects on reaction rates as well as the high oxygen atom energy due to the orbiter's orbital velocity brings the predicted and measured mass loss in surprisingly good agreement. Flight sample surface morphology comparison with ground based Kapton/oxygen atom exposures provides additional support for the oxygen interaction mechanism.

  7. Laboratory simulation of Low Earth Orbit (LEO) atomic oxygen effects

    NASA Technical Reports Server (NTRS)

    Caledonia, George E.; Krech, Robert H.; Oakes, David B.

    1994-01-01

    A pulsed fast oxygen atom source has been used extensively over the last 7 years to investigate the effects of ambient oxygen atoms impacting materials placed in low Earth orbit. In this period, we irradiated well over 2000 material samples with 8 km/s oxygen atoms generated in our source. Typical irradiance level is 3 x 10(exp 20) O atoms/sq cm although some materials have been irradiated to fluence levels as high as 6 x 10(exp 21) O atoms/sq cm. The operating principles and characteristics of our source are reviewed along with diagnostic and handling procedures appropriate to material testing. Representative data is presented on the velocity dependence of oxygen atom erosion rates (the PSI source provides oxygen atoms tunable over the velocity range of 5 to 12 km/s) as well as the dependence on material temperature. Specific examples of non-linear oxidative effects related to surface contamination and test duration are also be provided.

  8. Coatings Would Protect Polymers Against Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.

    1995-01-01

    Proposed interposition of layers of silver oxide tens to hundreds of angstroms thick between polymeric substrates and overlying films helps protect substrates against chemical attack by monatomic oxygen. In original application, polymer substrate would be, sheet of polyimide supporting array of solar photovoltaic cells on spacecraft in low orbit around Earth. Concept also applicable to protection of equipment in terrestrial laboratory and industrial vacuum and plasma chambers in which monatomic oxygen present.

  9. Production of pulsed atomic oxygen beams via laser vaporization methods

    NASA Technical Reports Server (NTRS)

    Brinza, David E.; Coulter, Daniel R.; Liang, Ranty H.; Gupta, Amitava

    1986-01-01

    The generation of energetic pulsed atomic oxygen beams by laser-driven evaporation of cryogenically frozen ozone/oxygen films and thin indium-tin oxide (ITO) films is reported. Mass spectroscopy is used in the mass and energy characterization of beams from the ozone/oxygen films, and a peak flux of 3 x 10 to the 20th/sq m per sec at 10 eV is found. Analysis of the time-of-flight data suggests that several processes contribute to the formation of the oxygen beam. Results show the absence of metastable states such as the 2p(3)3s(1)(5S) level of atomic oxygen blown-off from the ITO films. The present process has application to the study of the oxygen degradation problem of LEO materials.

  10. Angular distribution of photoelectrons from atomic oxygen, nitrogen, and carbon

    NASA Technical Reports Server (NTRS)

    Manson, S. T.; Kennedy, D. J.; Starace, A. F.; Dill, D.

    1974-01-01

    The angular distribution of photoelectrons from atomic oxygen is investigated using Hartree-Fock (HF) wave functions. The correct formulation is used to compare HS and HF results. Agreement between these results is good and the HS calculations have been extended to atomic nitrogen and carbon as well.

  11. Recovery of a Charred Painting Using Atomic Oxygen Treatment

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Chichernea, Virgil A.

    1999-01-01

    A noncontact method is described which uses atomic oxygen to remove soot and char from the surface of a painting. The atomic oxygen was generated by the dissociation of oxygen in low pressure air using radio frequency energy. The treatment, which is an oxidation process, allows control of the amount of material to be removed. The effectiveness of char removal from half of a fire-damaged oil painting was studied using reflected light measurements from selected areas of the painting and by visual and photographic observation. The atomic oxygen was able to effectively remove char and soot from the treated half of the painting. The remaining loosely bound pigment was lightly sprayed with a mist to replace the binder and then varnish was reapplied. Caution should he used when treating an untested paint medium using atomic oxygen. A representative edge or corner should he tested first in order to determine if the process would be safe for the pigments present. As more testing occurs, a greater knowledge base will be developed as to what types of paints and varnishes can or cannot be treated using this technique. With the proper precautions, atomic oxygen treatment does appear to be a technique with great potential for allowing very charred, previously unrestorable art to be salvaged.

  12. Atomic oxygen effects on LDEF experiment AO171

    NASA Technical Reports Server (NTRS)

    Whitaker, Ann F.; Kamenetzky, Rachel R.; Finckenor, Miria M.; Norwood, Joseph K.

    1993-01-01

    The Solar Array Materials Passive Long Duration Exposure Facility (LDEF) Experiment (SAMPLE), AO171, contained in total approximately 100 materials and materials processes with a 300 specimen complement. With the exception of experiment solar cell and solar cell modules, all test specimens were weighed before flight, thus allowing an accurate determination of mass loss as a result of space exposure. Since almost all of the test specimens were thermal vacuum baked before flight, the mass loss sustained can be attributed principally to atomic oxygen attack. The atomic oxygen effects observed and measured in five classes of materials is documented. The atomic oxygen reactivity values generated for these materials are compared to those values derived for the same materials from exposures on short term shuttle flights. An assessment of the utility of predicting long term atomic oxygen effects from short term exposures is given. This experiment was located on Row 8 position A which allowed all experiment materials to be exposed to an atomic oxygen fluence of 6.93 x 10(exp 21) atoms/cm(sup 2) as a result of being positioned 38 degrees off the RAM direction.

  13. LDEF experiment A0034: Atomic oxygen stimulated outgassing

    NASA Astrophysics Data System (ADS)

    Linton, Roger C.; Kamenetzky, Rachel R.; Reynolds, John M.; Burris, Charles L.

    1992-01-01

    The passive Long Duration Exposure Facility (LDEF) Experiment A0034, 'Atomic Oxygen Stimulated Outgassing', consisted of two identical one-sixth tray modules, exposing selected thermal control coatings to atomic oxygen and the combined space environment on the leading edge, and for reference, to the relative 'wake' environment of the trailing edge. Optical mirrors were included adjacent to the thermal coatings for deposition of the outgassing products. Ultraviolet grade windows and metal covers were provided for additional assessment of the effects of various environmental factors. Preliminary results indicate that orbital atomic oxygen is both a degrading and optically restorative factor in the thermo-optical properties of selected thermal coatings. There is evidence of more severe optical degradation on collector mirrors adjacent to coatings that were exposed to RAM-impinging atomic oxygen. This evidence of atomic oxygen stimulated outgassing is discussed in relation to alternative factors that could affect degradation. The general effects of the space environment on the experiment hardware as well as the specimens are discussed.

  14. Production of pulsed atomic oxygen beams via laser vaporization methods

    NASA Technical Reports Server (NTRS)

    Brinza, David E.; Coulter, Daniel R.; Liang, Ranty H.; Gupta, Amitava

    1987-01-01

    Energetic pulsed atomic oxygen beams were generated by laser-driven evaporation of cryogenically frozen ozone/oxygen films and thin films of indium-tin oxide (ITO). Mass and energy characterization of beams from the ozone/oxygen films were carried out by mass spectrometry. The peak flux, found to occur at 10 eV, is estimated from this data to be 3 x 10(20) m(-2) s(-1). Analysis of the time-of-flight data indicates a number of processes contribute to the formation of the atomic oxygen beam. The absence of metastable states such as the 2p(3) 3s(1) (5S) level of atomic oxygen blown off from ITO films is supported by the failure to observe emission at 777.3 nm from the 2p(3) 3p(1) (5P sub J) levels. Reactive scattering experiments with polymer film targets for atomic oxygen bombardment are planned using a universal crossed molecular beam apparatus.

  15. Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

    NASA Technical Reports Server (NTRS)

    Kharchenko, Vasili; Dalgarno, A.

    2005-01-01

    This report summarizes our research performed under NASA Grant NAG5-11857. The three-year grant have been supported by the Geospace Sciences SR&T program. We have investigated the energetic metastable oxygen and nitrogen atoms in the terrestrial stratosphere, mesosphere and thermosphere. Hot atoms in the atmosphere are produced by solar radiation, the solar wind and various ionic reactions. Nascent hot atoms arise in ground and excited electronic states, and their translational energies are larger by two - three orders of magnitude than the thermal energies of the ambient gas. The relaxation kinetics of hot atoms determines the rate of atmospheric heating, the intensities of aeronomic reactions, and the rate of atom escape from the planet. Modeling of the non-Maxwellian energy distributions of metastable oxygen and nitrogen atoms have been focused on the determination of their impact on the energetics and chemistry of the terrestrial atmosphere between 25 and 250 km . At this altitudes, we have calculated the energy distribution functions of metastable O and N atoms and computed non-equilibrium rates of important aeronomic reactions, such as destruction of the water molecules by O(1D) atoms and production of highly excited nitric oxide molecules. In the upper atmosphere, the metastable O(lD) and N(2D) play important role in formation of the upward atomic fluxes. We have computed the upward fluxes of the metastable and ground state oxygen atoms in the upper atmosphere above 250 km. The accurate distributions of the metastable atoms have been evaluated for the day and night-time conditions.

  16. Electron temperature and concentration in a thermal atomic oxygen source

    NASA Technical Reports Server (NTRS)

    Pedrow, Patrick Dennis

    1990-01-01

    A thermal atomic oxygen source for materials screening was built for NASA by Boeing Aerospace. The objective here was to use a microwave interferometer and Langmuir probe to characterize the electron concentration in this thermal atomic oxygen source. Typical operating conditions in the thermal atomic oxygen source were found to produce electron concentrations that were well below the detection threshold of the interferometer (10(exp 8) cm (sup -3)). The researchers calibrated (with the interferometer) the Langmuir probe at an artificially high plasma density and then used the circular and the square Langmuir probes to measure the low electron concentrations that exist during materials exposure tests. Electron concentration was measured as a function of power and position. The electrons were lost to the walls through ambipolar diffusion, and their concentration was accurately described by an equation. The electron concentration was proportional to power squared and decayed exponentially with distance.

  17. Cleaning of Fire Damaged Watercolor and Textiles Using Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Chichernea, Virgil A.; Haytas, Christy A.

    2000-01-01

    A noncontact technique is described that uses atomic oxygen generated under low pressure in the presence of nitrogen to remove soot from the surface of a test watercolor panel and strips of cotton, wool and silk. The process, which involves surface oxidation, permits control of the amount of surface material removed. The effectiveness of soot removal from test panels of six basic watercolors (alizarin crimson, burnt sienna, lemon yellow, yellow ochre, cerulean blue and ultramarine blue) and strips of colored cotton, wool and silk was measured using reflectance spectroscopy. The atomic oxygen removed soot effectively from the treated areas and enabled partial recovery of charred watercolors. However, overexposure can result in removal of sizing, bleaching, and weakening of the structure. With the proper precautions, atomic oxygen treatment appears to have great potential to salvage heavily smoke damaged artworks which were previously considered unrestorable.

  18. Photoionization research on atomic beams. 2: The photoionization cross section of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Comes, F. J.; Speier, F.; Elzer, A.

    1982-01-01

    An experiment to determine the absolute value of the photo-ionization cross section of atomic oxygen is described. The atoms are produced in an electrical discharge in oxygen gas with 1% hydrogen added. In order to prevent recombination a crossed beam technique is employed. The ions formed are detected by a time-of-flight mass spectrometer. The concentration of oxygen atoms in the beam is 57%. The measured photoionization cross section of atomic oxygen is compared with theoretical data. The results show the participation of autoionization processes in ionization. The cross section at the autoionizing levels detected is considerably higher than the absorption due to the unperturbed continuum. Except for wavelengths where autoionization occurs, the measured ionization cross section is in fair agreement with theory. This holds up to 550 A whereas for shorter wavelengths the theoretical values are much higher.

  19. Friction and durability of virgin and damaged skin with and without skin cream treatment using atomic force microscopy.

    PubMed

    Bhushan, Bharat; Chen, Si; Ge, Shirong

    2012-01-01

    Skin can be damaged by the environment easily. Skin cream is an effective and rapid way to moisten the skin by changing the skin surface properties. Rat skin and pig skin are common animal models for studies and were used as skin samples in this study. The nano- and macroscale friction and durability of damaged skin were measured and compared with those of virgin (intact/undamaged) skin. The effect of skin cream on friction and durability of damaged and virgin skin samples is discussed. The effects of velocity, normal load, relative humidity and number of cycles were studied. The nanoscale studies were performed by using atomic force microscope (AFM), and macroscale studies were performed by using a pin-on-disk (POD) reciprocating tribometer. It was found that damaged skin has different mechanical properties, surface roughness, contact angle, friction and durability compared to that of virgin skin. But similar changes occur after skin cream treatment. Rat and pig skin show similar trends in friction and durability.

  20. Friction and durability of virgin and damaged skin with and without skin cream treatment using atomic force microscopy

    PubMed Central

    Chen, Si; Ge, Shirong

    2012-01-01

    Summary Skin can be damaged by the environment easily. Skin cream is an effective and rapid way to moisten the skin by changing the skin surface properties. Rat skin and pig skin are common animal models for studies and were used as skin samples in this study. The nano- and macroscale friction and durability of damaged skin were measured and compared with those of virgin (intact/undamaged) skin. The effect of skin cream on friction and durability of damaged and virgin skin samples is discussed. The effects of velocity, normal load, relative humidity and number of cycles were studied. The nanoscale studies were performed by using atomic force microscope (AFM), and macroscale studies were performed by using a pin-on-disk (POD) reciprocating tribometer. It was found that damaged skin has different mechanical properties, surface roughness, contact angle, friction and durability compared to that of virgin skin. But similar changes occur after skin cream treatment. Rat and pig skin show similar trends in friction and durability. PMID:23213637

  1. Vacuum ultraviolet radiation/atomic oxygen synergism in materials reactivity

    NASA Technical Reports Server (NTRS)

    Koontz, Steven; Leger, Lubert; Albyn, Keith; Cross, Jon

    1990-01-01

    Experimental results are presented which indicate that low fluxes of vacuum UV (VUV) radiation exert a pronounced influence on the atomic oxygen reactivity of such fluorocarbon and fluorocarbon spacecraft materials as the FEP Teflon and PCTFE that are under consideration for the Space Station Freedom. With simultaneous exposure to VUV fluxes comparable to those experienced in LEO, the reactivity of these materials becomes comparable to that of Kapton; VUV radiation has also been shown to increase the reactivity of Kapton with thermal-energy oxygen atoms.

  2. Study of the reaction of atomic oxygen with aerosols

    NASA Technical Reports Server (NTRS)

    Akers, F. I.; Wightman, J. P.

    1975-01-01

    The rate of disappearance of atomic oxygen was measured at several pressures in a fast flow pyrex reactor system with its walls treated with (NH4)2SO4 (s), H2SO4 (l), and NH4CL (s). Atomic oxygen, P-3 was generated by dissociation of pure, low pressure oxygen in a microwave discharge. Concentrations of atomic oxygen were measured at several stations in the reactor system using chemiluminescent titration with NO2. Recombination efficiencies calculated from experimentally determined wall recombination rate constants are in good agreement with reported values for clean Pyrex and an H2SO4 coated wall. The recombination efficiency for (NH4)2SO4, results in a slightly lower value than for H2S04. A rapid exothermic reaction between atomic oxygen and the NH4Cl wall coating prevented recombination efficiency determination for this coating. The results show that the technique is highly useful for wall recombination measurements and as a means of extrapolating to the case of free stream aerosol-gas interactions.

  3. Experimental Investigations of Oxygen Atom Loss on Mesospheric Dust Surrogates

    NASA Astrophysics Data System (ADS)

    Boulter, J. E.; Marschall, J.; Spangler, E. L.

    2002-12-01

    Inconsistencies have been noted between model predictions and observations of mesospheric composition in narrow regions of the mesosphere. Several arctic rocket campaigns between 1978 and 1993 have observed oxygen atom "bite-outs," narrow layers just below 85 km depleted in atomic oxygen, correlated with NLC observations1. Separate observations from the HALOE instrument on UARS indicated the presence of a band of enhanced water vapor centered near 70 km at mid-latitudes that has not yet been adequately explained by current HOx models2. Because the upper mesosphere and lower thermosphere (MLT) contains a variety of surfaces such as ice particles and ablated meteoric dust, heterogeneous reactions might influence these observed phenomena. Reactions currently being considered are the recombination of oxygen atoms to form molecular oxygen and the reaction of molecular hydrogen with atomic oxygen to form water. To investigate these possible surface-mediated reactions, Knudsen cell experiments have been performed to quantify the oxygen atom recombination coefficient on mineral oxide powders representative of meteoritic composition. Oxygen atoms, produced by means of a microwave frequency discharge, and reagent gases are admitted to a low-pressure, well-mixed reactor in which the loss of the reactant species to a sample surface competes with escape through an exit aperture. Steady state reactant and product concentrations are measured by laser-induced fluorescence and mass spectrometry. By varying the area of the exit orifice in the presence or absence of the surface or reagent gases being investigated, atomic oxygen loss coefficients (γ) can be derived and then related to specific heterogeneous chemical reactions. Preliminary values will be reported for surface-mediated oxygen loss coefficients on several dust surrogates at room temperature and at pressures characteristic of the mesopause region. 1 Gumbel, J., Murtagh, D. P. Espy, P. J., Witt, G., and Schmidlin, F. J., J

  4. Atomic Oxygen Desorption from an Amorphous Silicate Surface

    NASA Astrophysics Data System (ADS)

    He, Jiao; Vidali, Gianfranco

    2014-06-01

    Oxygen is the third most abundant element in space. How oxygen-containing molecules form in space, and whether they form through gas-phase or grain-surface reactions, depends largely on the availability of atomic oxygen in gas-phase versus on surfaces of dust grains. The relative abundance of O in gas-phase versus on grain surfaces is determined by the residence time, or equivalently, desorption energy, of atomic oxygen on grain surfaces. Though important in astrochemical modeling, experimental investigations of atomic oxygen desorption from grain surfaces are lacking in the literature. In most astrochemical models, the O desorption energy value has been taken to be 800 K, which is a guessed value without experimental support. Based on this value, the predicted molecular oxygen abundance in space is at least 2 orders of magnitude higher than what space observations have found. This long running discrepancy of molecular oxygen abundance could be resolved if the O desorption energy is twice as the widely used value (Melnick, G., Tolls, V., et al. 2012, Astrophys. J., 752, 26). We performed TPD (thermal programmed desorption) experiments to study the ozone formation process via O+O2 on an amorphous silicate surface that emulates interstellar conditions. A rate equation model was used to characterize the surface kinetics of both atomic and molecular oxygen. The O desorption energy was extracted from rate equation simulations that best fit the TPD data. The value was found to be 1764±232 K, which agrees with what Melnick et al. proposed. We suggest that the newly found value for the O desorption energy should be used in astrochemical modeling. This work is supported by NSF, Astronomy & Astrophysics Division (Grants No. 0908108 and 1311958), and NASA (Grant No. NNX12AF38G). We thank Dr. J.Brucato of the Astrophysical Observatory of Arcetri for providing the samples used in these experiments.

  5. Atomic Oxygen Erosion Yield Dependence Upon Texture Development in Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Loftus, Ryan J.; Miller, Sharon K.

    2016-01-01

    The atomic oxygen erosion yield (volume of a polymer that is lost due to oxidation per incident atom) of polymers is typically assumed to be reasonably constant with increasing fluence. However polymers containing ash or inorganic pigments, tend to have erosion yields that decrease with fluence due to an increasing presence of protective particles on the polymer surface. This paper investigates two additional possible causes for erosion yields of polymers that are dependent upon atomic oxygen. These are the development of surface texture which can cause the erosion yield to change with fluence due to changes in the aspect ratio of the surface texture that develops and polymer specific atomic oxygen interaction parameters. The surface texture development under directed hyperthermal attack produces higher aspect ratio surface texture than isotropic thermal energy atomic oxygen attack. The fluence dependence of erosion yields is documented for low Kapton H (DuPont, Wilmington, DE) effective fluences for a variety of polymers under directed hyperthermal and isotropic thermal energy attack.

  6. Rapid evaluation of the durability of cortical neural implants using accelerated aging with reactive oxygen species

    NASA Astrophysics Data System (ADS)

    Takmakov, Pavel; Ruda, Kiersten; Phillips, K. Scott; Isayeva, Irada S.; Krauthamer, Victor; Welle, Cristin G.

    2015-04-01

    Objective. A challenge for implementing high bandwidth cortical brain-machine interface devices in patients is the limited functional lifespan of implanted recording electrodes. Development of implant technology currently requires extensive non-clinical testing to demonstrate device performance. However, testing the durability of the implants in vivo is time-consuming and expensive. Validated in vitro methodologies may reduce the need for extensive testing in animal models. Approach. Here we describe an in vitro platform for rapid evaluation of implant stability. We designed a reactive accelerated aging (RAA) protocol that employs elevated temperature and reactive oxygen species (ROS) to create a harsh aging environment. Commercially available microelectrode arrays (MEAs) were placed in a solution of hydrogen peroxide at 87 °C for a period of 7 days. We monitored changes to the implants with scanning electron microscopy and broad spectrum electrochemical impedance spectroscopy (1 Hz-1 MHz) and correlated the physical changes with impedance data to identify markers associated with implant failure. Main results. RAA produced a diverse range of effects on the structural integrity and electrochemical properties of electrodes. Temperature and ROS appeared to have different effects on structural elements, with increased temperature causing insulation loss from the electrode microwires, and ROS concentration correlating with tungsten metal dissolution. All array types experienced impedance declines, consistent with published literature showing chronic (>30 days) declines in array impedance in vivo. Impedance change was greatest at frequencies <10 Hz, and smallest at frequencies 1 kHz and above. Though electrode performance is traditionally characterized by impedance at 1 kHz, our results indicate that an impedance change at 1 kHz is not a reliable predictive marker of implant degradation or failure. Significance. ROS, which are known to be present in vivo, can create

  7. Low Earth orbital atomic oxygen environmental simulation facility for space materials evaluation

    NASA Technical Reports Server (NTRS)

    Stidham, Curtis R.; Banks, Bruce A.; Stueber, Thomas J.; Dever, Joyce A.; Rutledge, Sharon K.; Bruckner, Eric J.

    1993-01-01

    Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administrations's (NASA) Lewis Research Center provides accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analyses show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (approximately 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4 x 10 exp 6 atoms/((sq. cm)*s), thus providing a highly accelerated testing capability.

  8. The survivability of large space-borne reflectors under atomic oxygen and micrometeoroid impact

    NASA Technical Reports Server (NTRS)

    Gulino, D. A.

    1987-01-01

    Solar dynamic power system mirrors for use on space station and other spacecraft flown in low Earth orbit (LEO) are exposed to the harshness of the LEO environment. Both atomic oxygen and micrometeoroids/space debris can degrade the performance of such mirrors. Protective coatings will be required to protect oxidizable reflecting media, such as silver and aluminum, from atomic oxygen attack. Several protective coating materials have been identified as good candidates for use in this application. The durability of these coating/mirror systems after pinhole defects have been inflicted during their fabrication and deployment or through micrometeoroid/space debris impact once on-orbit is of concern. Studies of the effect of an oxygen plasma environment on protected mirror surfaces with intentionally induced pinhole defects have been conducted at NASA Lewis and are reviewed. It has been found that oxidation of the reflective layer and/or the substrate in areas adjacent to a pinhole defect, but not directly exposed by the pinhole, can occur.

  9. A Comparison of Atomic Oxygen Erosion Yields of Carbon and Selected Polymers Exposed in Ground Based Facilities and in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Cales, Michael

    1994-01-01

    A comparison of the relative erosion yields (volume of material removed per oxygen atom arriving) for FEP Teflon, polyethylene, and pyrolytic graphite with respect to Kapton HN was performed in an atomic oxygen directed beam system, in a plasma asher, and in space on the EOIM-III (Evaluation of Oxygen Interaction with Materials-III) flight experiment. This comparison was performed to determine the sensitivity of material reaction to atomic oxygen flux, atomic oxygen fluence, and vacuum ultraviolet radiation for enabling accurate estimates of durability in ground based facilities. The relative erosion yield of pyrolytic graphite was found not to be sensitive to these factors, that for FEP was sensitive slightly to fluence and possibly ions, and that for polyethylene was found to be partially VUV and flux sensitive but more sensitive to an unknown factor. Results indicate that the ability to use these facilities for material relative durability prediction is great as long as the sensitivity of particular materials to conditions such as VUV, and atomic oxygen flux and fluence are taken into account. When testing materials of a particular group such as teflon, it may be best to use a witness sample made of a similar material that has some available space data on it. This would enable one to predict an equivalent exposure in the ground based facility.

  10. A sputtering derived atomic oxygen source for studying fast atom reactions

    NASA Technical Reports Server (NTRS)

    Ferrieri, Richard A.; Yung, Y. Chu; Wolf, Alfred P.

    1987-01-01

    A technique for the generation of fast atomic oxygen was developed. These atoms are created by ion beam sputtering from metal oxide surfaces. Mass resolved ion beams at energies up to 60 KeV are produced for this purpose using a 150 cm isotope separator. Studies have shown that particles sputtered with 40 KeV Ar(+) on Ta2O5 were dominantly neutral and exclusively atomic. The atomic oxygen also resided exclusively in its 3P ground state. The translational energy distribution for these atoms peaked at ca 7 eV (the metal-oxygen bond energy). Additional measurements on V2O5 yielded a bimodal distribution with the lower energy peak at ca 5 eV coinciding reasonably well with the metal-oxygen bond energy. The 7 eV source was used to investigate fast oxygen atom reactions with the 2-butene stereoisomers. Relative excitation functions for H-abstraction and pi-bond reaction were measured with trans-2-butene. The abstraction channel, although of minor relative importance at thermal energy, becomes comparable to the addition channel at 0.9 eV and dominates the high-energy regime. Structural effects on the specific channels were also found to be important at high energy.

  11. High velocity atomic oxygen/surface accommodation studies

    NASA Technical Reports Server (NTRS)

    Krech, R. H.; Gauthier, M. J.; Caledonia, G. E.

    1991-01-01

    This paper provides the first experimental evaluation of the energy-accommodation coefficients of 8km/s oxygen atoms on selected materials. Preliminary measurements have been provided for three materials at normal incidence. Neglecting chemical energy, the accommodation coefficients for Ni, Au, and reaction-cured glass are approximately 0.6 +/- 50 percent.

  12. Molecular beam studies of oxygen atom reactions with unsaturated hydrocarbons

    SciTech Connect

    Schmoltner, A.-M.

    1989-10-01

    The dynamics of several elementary reactions relevant to combustion was investigated. The reactive scattering of ground state oxygen atoms with small unsaturated hydrocarbons was studied using a crossed molecular beam apparatus with a rotatable mass spectrometer detector. The infrared and ultraviolet photodissociation of anisole was studied using a rotating beam source/fixed detector apparatus. 253 refs., 64 figs., 4 tabs.

  13. Atomic Oxygen Lamp Cleaning Facility Fabricated and Tested

    NASA Technical Reports Server (NTRS)

    Sechkar, Edward A.; Stueber, Thomas J.

    1999-01-01

    NASA Lewis Research Center's Atomic Oxygen Lamp Cleaning Facility was designed to produce an atomic oxygen plasma within a metal halide lamp to remove carbon-based contamination. It is believed that these contaminants contribute to the high failure rate realized during the production of these lamps. The facility is designed to evacuate a metal halide lamp and produce a radio frequency generated atomic oxygen plasma within it. Oxygen gas, with a purity of 0.9999 percent and in the pressure range of 150 to 250 mtorr, is used in the lamp for plasma generation while the lamp is being cleaned. After cleaning is complete, the lamp can be backfilled with 0.9999-percent pure nitrogen and torch sealed. The facility comprises various vacuum components connected to a radiation-shielded box that encloses the bulb during operation. Radiofrequency power is applied to the two parallel plates of a capacitor, which are on either side of the lamp. The vacuum pump used, a Leybold Trivac Type D4B, has a pumping speed of 4-m3/hr, has an ultimate pressure of <8x10-4, and is specially adapted for pure oxygen service. The electronic power supply, matching network, and controller (500-W, 13.56-MHz) used to supply the radiofrequency power were purchased from RF Power Products Inc. Initial test results revealed that this facility could remove the carbon-based contamination from within bulbs.

  14. Coating Pt-Ni Octahedra with Ultrathin Pt Shells to Enhance the Durability without Compromising the Activity toward Oxygen Reduction.

    PubMed

    Park, Jinho; Liu, Jingyue; Peng, Hsin-Chieh; Figueroa-Cosme, Legna; Miao, Shu; Choi, Sang-Il; Bao, Shixiong; Yang, Xuan; Xia, Younan

    2016-08-23

    We describe a new strategy to enhance the catalytic durability of Pt-Ni octahedral nanocrystals in the oxygen reduction reaction (ORR) by conformally depositing an ultrathin Pt shell on the surface. The Pt-Ni octahedra were synthesized according to a protocol reported previously and then employed directly as seeds for the conformal deposition of ultrathin Pt shells by introducing a Pt precursor dropwise at 200 °C. The amount of Pt precursor was adjusted relative to the number of Pt-Ni octahedra involved to obtain Pt-Ni@Pt1.5L octahedra of 12 nm in edge length for the systematic evaluation of their chemical stability and catalytic durability compared to Pt-Ni octahedra. Specifically, we compared the elemental compositions of the octahedra before and after treatment with acetic and sulfuric acids. We also examined their electrocatalytic stability toward the ORR through an accelerated durability test by using a rotating disk electrode method. Even after treatment with sulfuric acid for 24 h, the Pt-Ni@Pt1.5L octahedra maintained their original Ni content, whereas 11 % of the Ni was lost from the Pt-Ni octahedra. After 10 000 cycles of ORR, the mass activity of the Pt-Ni octahedra decreased by 75 %, whereas the Pt-Ni@Pt1.5L octahedra only showed a 25 % reduction. PMID:27460459

  15. Novel oxygen atom source for material degradation studies

    NASA Technical Reports Server (NTRS)

    Krech, R. H.; Caledonia, G. E.

    1988-01-01

    Physical Sciences Inc. (PSI) has developed a high flux pulsed source of energetic (8 km/s) atomic oxygen to bombard specimens in experiments on the aging and degradation of materials in a low earth orbit environment. The proof-of-concept of the PSI approach was demonstrated in a Phase 1 effort. In Phase 2 a large O-atom testing device (FAST-2) has been developed and characterized. Quantitative erosion testing of materials, components, and even small assemblies (such as solar cell arrays) can be performed with this source to determine which materials and/or components are most vulnerable to atomic oxygen degradation. The source is conservatively rated to irradiate a 100 sq cm area sample at greater than 10(exp 17) atoms/s, at a 10 Hz pulse rate. Samples can be exposed to an atomic oxygen fluence equivalent to the on-orbit ram direction exposure levels incident on Shuttle surfaces at 250 km during a week-long mission in a few hours.

  16. The Dependence of Atomic Oxygen Undercutting of Protected Polyimide Kapton(tm) H upon Defect Size

    NASA Technical Reports Server (NTRS)

    Snyder, Aaron; deGroh, Kim K.

    2001-01-01

    Understanding the behavior of polymeric materials when exposed to the low-Earth-orbit (LEO) environment is important in predicting performance characteristics such as in-space durability. Atomic oxygen (AO) present in LEO is known to be the principal agent in causing undercutting erosion of SiO(x) protected polyimide Kapton(R) H film, which serves as a mechanically stable blanket material in solar arrays. The rate of undercutting is dependent on the rate of arrival, directionality and energy of the AO with respect to the film surface. The erosion rate also depends on the distribution of the size of defects existing in the protective coating. This paper presents results of experimental ground testing using low energy, isotropic AO flux together with numerical modeling to determine the dependence of undercutting erosion upon defect size.

  17. Undercutting of defects in thin film protective coatings on polymer surfaces exposed to atomic oxygen

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Mihelcic, Judith A.

    1989-01-01

    Protection for polymeric surfaces is needed to make them durable in the low earth orbital environment. Thin film coatings of oxides such as SiO2 are viable candidates to provide this protection, but concern has been voiced over the ability of these coatings to protect when defects are present in the coating due to surface anomalies. When a defected coating protecting a polymer substrate is exposed to atomic oxygen, the defect provides a pathway to the underlying polymer allowing oxidation and subsequent undercutting to occur. Defect undercutting was studied for sputter deposited coatings of SiO2 on polyimide Kapton. Preliminary results indicate that undercutting may be limited as long as the coating remains intact with the substrate. Therefore, coatings may not need to be defect free to give protection to the underlying surface.

  18. Alternative Method for the Thermospheric Atomic Oxygen Density Determination

    NASA Technical Reports Server (NTRS)

    Bennett, A. C.; Omidvar, K.; Atlas, Robert (Technical Monitor)

    2001-01-01

    Atomic oxygen density in the upper thermosphere (approximately 300 km) can be calculated using ground based incoherent scatter radar and Fabry-Perot interferometer measurements. Burnside et al. was the first to try this method, but Buonsanto et al. provided an extensive treatment of the method in 1997. This paper further examines the method using 46 nights of data collected over six years and the latest information on the oxygen collision frequency. The method is compared with the MSIS (Mass Spectrometer Incoherent Scatter)-86 atomic oxygen prediction values, which are based upon in situ rocket born and satellite measurements from the 70s to the mid-80s. In general, the method supports the MSIS-86 model, but indicates several areas of discrepancy. Furthermore, no direct correlation is found between the geomagnetic conditions and the difference between the method and MSIS-86 predictions.

  19. Alternative Methods of the Thermospheric Atomic Oxygen Density Determination

    NASA Technical Reports Server (NTRS)

    Bennett. Adam C.; Omidvar, Kazem; Einaudi, Franco (Technical Monitor)

    2000-01-01

    Atomic oxygen density in the upper thermosphere (approximately 300 km) can be calculated using ground based incoherent scatter radar and Fabry-Perot interferometer measurements. Burnside et al. [1991] was the first to try this method, but Buonsanto et al. provided an extensive treatment of the method in 1997. This paper further examines the method using 46 nights of data collected over six years and the latest information on the oxygen collision frequency. The method is compared with the MSIS-86 atomic oxygen prediction values, which are based upon in situ rocket born and satellite measurements from the 70's to the mid-80's In general, the method supports the MSIS-86 model, but indicates several areas of discrepancy. Furthermore, no direct correlation is found between the geomagnetic conditions and the difference between the method and MSIS-86 predictions.

  20. LEO atomic oxygen effects on spacecraft materials: STS-5 results

    NASA Technical Reports Server (NTRS)

    Whitaker, A. F.

    1984-01-01

    Effects of low Earth orbit (LEO) atomic oxygen were measured on a variety of spacecraft materials which obtained exposure on STS-5. Material degradation dependency on temperature was found in one material. Of the five paints flown, only S13GLO was unaffected. Generally, the glossy paints became Lambertian and the diffuse coatings improved. Scanning electron microscope examinations indicated removal of urethane and epoxy paint binder materials. Reaction products were evident on the surfaces of Z302 paint and Mylar. Thin films showed thickness losses ranging from negligible loss in Teflon to considerable loss in Mylar and Kapton. Glossy films such as black Kapton and white Tedlar became diffused. Kevlar 29 rope lost tensile strength and silver solar cell interconnect material oxidized. Oxidation on the backside of an elevated specimen indicated that reflections of oxygen atoms were occurring and that reflecting surfaces, probably Kapton, were not fully accommodating the incident atoms.

  1. Changes in Polymeric Tether Properties Due to Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Finckenor, Miria M.; Vaughn, Jason A.; Watts, Edward W.

    2003-01-01

    The Propulsive Small Expendable Deployer System (ProSEDS) mission is designed to provide an on-orbit demonstration of the electrodynamic propulsion capabilities of tethers in space. The ProSEDS experiment will be a secondary payload on a Delta II unmanned expendable booster. A 5-km conductive tether is attached to the Delta II second stage and collects current fiom the low Earth orbit (LEO) plasma to facilitate de-orbit of the spent stage. The conductive tether is attached to a 10-km non-conductive tether, which is then attached to an endmass containing several scientific instruments. Atomic oxygen (AO) erodes most organic materials. As the orbit of the Delta II second stage decas, the AO flux (atoms/sq cm sec) increases. A nominal AO fluence of 1 x l0(exp 21) atoms/sq cm was agreed upon by the investigators as an adequate level for evaluating the performance of the tether materials. A test series was performed to determine the effect of atomic oxygen (AO) on the mechanical integrity and possible strength loss of ProSEDS tether materials. The tether materials in this study were Dyneema, an ultra-high molecular weight polyethylene material used as the non-conducting portion of the ProSEDS tether, and the Kevlar core strength fiber used in the conductive tether. Samples of Dyneema and Kevlar were exposed to various levels of atomic oxygen up to 1.07 x 10(exp 21) atoms/sq cm in the Marshall Space Flight Center Atomic Oxygen Beam Facility (AOBF). Changes in mass were noted after AO exposure. The tethers were then tensile-tested until failure. AO affected both the Dyneema and Kevlar tether material strength. Dyneema exposed to 1.07 x 10(exp 21) atoms/sq cm of atomic oxygen failed due to normal handling when removed fiom the AOBF and was not tensile-tested. Another test series was performed to determine the effect of AO on the electrical properties of the ProSEDS conductive tether. The conductive tether consists of seven individually coated strands of 28 AWG 1350

  2. Pd@Pt core-shell concave decahedra: A class of catalysts for the oxygen reduction reaction with enhanced activity and durability

    DOE PAGES

    Wang, Xue; Vera, Madeline; Chi, Miaofang; Xia, Younan; Luo, Ming; Huang, Hongwen; Ruditskiy, Aleksey; Park, Jinho; Bao, Shixiong; Liu, Jingyue; et al

    2015-11-13

    Here, we report a facile synthesis of multiply twinned Pd@Pt core shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 degrees C, naturally generating a core shell structure covered by concave facets. The nonuniformity inmore » the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm2pt) and mass (1.60 A/mg/2pt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm2pt and 0.32 A/mgpt, respectively). After 10 000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgpt, more than twice that of the pristine Pt/C catalyst.« less

  3. Pd@Pt core-shell concave decahedra: A class of catalysts for the oxygen reduction reaction with enhanced activity and durability

    SciTech Connect

    Wang, Xue; Vera, Madeline; Chi, Miaofang; Xia, Younan; Luo, Ming; Huang, Hongwen; Ruditskiy, Aleksey; Park, Jinho; Bao, Shixiong; Liu, Jingyue; Howe, Jane; Xie, Zhaoxiong

    2015-11-13

    Here, we report a facile synthesis of multiply twinned Pd@Pt core shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 degrees C, naturally generating a core shell structure covered by concave facets. The nonuniformity in the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm2pt) and mass (1.60 A/mg/2pt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm2pt and 0.32 A/mgpt, respectively). After 10 000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgpt, more than twice that of the pristine Pt/C catalyst.

  4. Atomic oxygen patterning from a biomedical needle-plasma source

    SciTech Connect

    Kelly, Seán; Turner, Miles M.

    2013-09-28

    A “plasma needle” is a cold plasma source operating at atmospheric pressure. Such sources interact strongly with living cells, but experimental studies on bacterial samples show that this interaction has a surprising pattern resulting in circular or annular killing structures. This paper presents numerical simulations showing that this pattern occurs because biologically active reactive oxygen and nitrogen species are produced dominantly where effluent from the plasma needle interacts with ambient air. A novel solution strategy is utilised coupling plasma produced neutral (uncharged) reactive species to the gas dynamics solving for steady state profiles at the treated biological surface. Numerical results are compared with experimental reports corroborating evidence for atomic oxygen as a key bactericidal species. Surface losses are considered for interaction of plasma produced reactants with reactive solid and liquid interfaces. Atomic oxygen surface reactions on a reactive solid surface with adsorption probabilities above 0.1 are shown to be limited by the flux of atomic oxygen from the plasma. Interaction of the source with an aqueous surface showed hydrogen peroxide as the dominant species at this interface.

  5. Atomic oxygen patterning from a biomedical needle-plasma source

    NASA Astrophysics Data System (ADS)

    Kelly, Seán; Turner, Miles M.

    2013-09-01

    A "plasma needle" is a cold plasma source operating at atmospheric pressure. Such sources interact strongly with living cells, but experimental studies on bacterial samples show that this interaction has a surprising pattern resulting in circular or annular killing structures. This paper presents numerical simulations showing that this pattern occurs because biologically active reactive oxygen and nitrogen species are produced dominantly where effluent from the plasma needle interacts with ambient air. A novel solution strategy is utilised coupling plasma produced neutral (uncharged) reactive species to the gas dynamics solving for steady state profiles at the treated biological surface. Numerical results are compared with experimental reports corroborating evidence for atomic oxygen as a key bactericidal species. Surface losses are considered for interaction of plasma produced reactants with reactive solid and liquid interfaces. Atomic oxygen surface reactions on a reactive solid surface with adsorption probabilities above 0.1 are shown to be limited by the flux of atomic oxygen from the plasma. Interaction of the source with an aqueous surface showed hydrogen peroxide as the dominant species at this interface.

  6. Oxygen atom density and thermal energy control in an electric-oxygen iodine laser

    NASA Astrophysics Data System (ADS)

    Benavides, G. F.; Palla, A. D.; Zimmerman, J. W.; Woodard, B. S.; Carroll, D. L.; Solomon, W. C.

    2014-02-01

    Experiments[1] with Electric Oxygen-Iodine Laser (ElectricOIL) heat exchanger technology have demonstrated improved control of oxygen atom density and thermal energy, with minimal quenching of O2(a1Δ), and increasing small signal gain from 0.26% cm-1 to 0.30% cm-1. Heat exchanger technological improvements were achieved through both experimental and modeling studies, including estimation of O2(a1Δ) surface quenching coefficients for select ElectricOIL materials downstream of a radio-frequency discharge-driven singlet oxygen generator. Estimation of O2(a1Δ) quenching coefficients is differentiated from previous studies by inclusion of oxygen atoms, historically scrubbed using HgO[2-4] or AgO[5]. High-fidelity, time-dependent and steady-state simulations are presented using the new BLAZE-VI multi-physics simulation suite[6] and compared to data.

  7. International Test Program for Synergistic Atomic Oxygen and VUV Exposure of Spacecraft Materials

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon; Banks, Bruce; Dever, Joyce; Savage, William

    2000-01-01

    Spacecraft in low Earth orbit (LEO) are subject to degradation in thermal and optical performance of components and materials through interaction with atomic oxygen and vacuum ultraviolet radiation which are predominant in LEO. Due to the importance of LEO durability and performance to manufacturers and users, an international test program for assessing the durability of spacecraft materials and components was initiated. Initial tests consisted of exposure of samples representing a variety of thermal control paints and multilayer insulation materials that have been used in space. Materials donated from various international sources were tested alongside a material whose performance is well known such as Teflon FEP or Kapton H for multilayer insulation, or Z-93-P for white thermal control paints. The optical, thermal or mass loss data generated during the test was then provided to the participating material supplier. Data was not published unless the participant donating the material consented to publication. This paper presents a description of the types of tests and facilities that have been used for the test program as well as some examples of data that have been generated. The test program is intended to give spacecraft builders and users a better understanding of degradation processes and effects to enable improved prediction of spacecraft performance.

  8. International Test Program for Synergistic Atomic Oxygen and Vacuum Ultraviolet Radiation Exposure of Spacecraft Materials

    NASA Technical Reports Server (NTRS)

    Miller, Sharon K.

    2001-01-01

    The components and materials of spacecraft in low Earth orbit can degrade in thermal and optical performance through interaction with atomic oxygen and vacuum ultraviolet (VUV) radiation, which are predominant in low Earth orbit. Because of the importance of low Earth orbit durability and performance to manufacturers and users, an international test program for assessing the durability of spacecraft materials and components was initiated. Initial tests at the NASA Glenn Research Center consisted of exposure of samples representing a variety of thermal control paints, multilayer insulation materials, and Sun sensors that have been used in space. Materials donated from various international sources were tested alongside materials whose performance is well known, such as Teflon FEP, Kapton H, or Z-93-P white paint. The optical, thermal, or mass loss data generated during the tests were then provided to the participating material suppliers. Data were not published unless the participant donating the material consented to publication. The test program is intended to give spacecraft builders and users a better understanding of degradation processes and effects so that they can improve their predictions of spacecraft performance.

  9. MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis

    NASA Technical Reports Server (NTRS)

    McCarthy, Catherine E.; Banks, Bruce A.; deGroh, Kim, K.

    2010-01-01

    Atomic oxygen erosion of polymers in low Earth orbit (LEO) poses a serious threat to spacecraft performance and durability. To address this, 40 different polymer samples and a sample of pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2). The purpose of the PEACE Polymers experiment was to obtain accurate mass loss measurements in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time. Error calculations were performed in order to determine the accuracy of the mass measurements and therefore of the erosion yield values. The standard deviation, or error, of each factor was incorporated into the fractional uncertainty of the erosion yield for each of three different situations, depending on the post-flight weighing procedure. The resulting error calculations showed the erosion yield values to be very accurate, with an average error of 3.30 percent.

  10. Interaction of atomic oxygen with a graphite surface

    NASA Astrophysics Data System (ADS)

    Mateljevic, Natasa

    This project was a part of the Multi University Research Initiative (MURI) Center for Materials Chemistry in the Space Environment which seeks to develop a quantitative and predictive understanding of how materials degrade or become passivated in the space environment. This is a critical research area for the Department of Defense (DoD) and National Aeronautics and Space Administration (NASA) given the large and increasing dependence on satellites and manned spacecrafts that reside in, or pass through, the low-Earth orbit (LEO) space environment. In this work, we completed three separate projects. First, we carried out ab initio electronic structure studies of the interaction of oxygen atoms with graphite surfaces. The (O3 P) ground state of oxygen interacts weakly with the graphite surface while the excited (O1D) state interacts more strongly with a binding energy sufficient for a high coverage of oxygen to be maintained on the surface. Thus, it requires a transition from O(3P) to O(1D) in order for oxygen to strongly bind. Since graphite is a semi-metal, it requires a vanishingly small energy to remove an electron of up spin from just below the Fermi level, and replace it with a down spin electron just above the Fermi level; spin-orbit interaction is not required to switch the state of the oxygen atom. We have examined this complexity for the first time and developed guidelines for properly describing chemical reactivity on graphite surfaces. The second project is a kinetic Monte Carlo study of the erosion of graphite by energetic oxygen atoms in LEO and in the laboratory. These simulations, in conjunction with experiments by our MURI collaborators, reveal new insights about reaction pathways. Finally, we have developed a new model for accommodation of energy and momentum in collisions of gases with highly corrugated surfaces. This model promises to be valuable in simulating frictional heating and drag of objects moving through the atmosphere.

  11. Removal of Biologically Active Organic Contaminants using Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Banks, Michael A. (Inventor); Banks, Eric B. (Inventor)

    2003-01-01

    Biomedical devices that are to come into contact with living tissue, such as prosthetic and other implants for the human body and the containers used to store and transport them, are together cleaned of non-living, but biologically active organic materials, including endotoxins such as lipopolysaccharides, and assembled into a hermetically sealed package without recontamination. This is achieved by cleaning both the device and package components together in an apparatus, which includes a hermetically sealed chamber, in which they are contacted with atomic oxygen which biocleans them, by oxidizing the biologically active organic materials. The apparatus also includes means for manipulating the device and container and hermetically sealing the cleaned device into the cleaned container to form the package. A calibrated witness coupon visually indicates whether or not the device and container have received enough exposure to the atomic oxygen to have removed the organic materials from their surfaces. Gamma radiation is then used to sterilize the device in the sealed container.

  12. Estimating and controlling the atomic oxygen content in an argon-oxygen plasma

    NASA Astrophysics Data System (ADS)

    Keville, Bernard; Monahan, Derek D.; Turner, Miles M.

    2008-10-01

    Oxygen rich plasmas have been applied in many plasma processing applications for decades. In most such applications, process yield could be improved significantly by applying closed loop control of atomic oxygen radical concentration. The design of effective, real time, closed loop control algorithms is facilitated by simple dynamical models of the relationship between inputs, or actuators in control terminology, and the process quantities to be controlled. In the case of an oxygen rich plasma process, one requires the relationship between the inputs - flow-rate set points, forward power from the RF supply and residence time, for example - and the oxygen radical density. With the aid of an argon-oxygen plasma simulation, this presentation describes how, with the aid of simplified dynamical models of the process, one would design model-based control algorithms for the real-time, closed loop control of oxygen radical density. A sine qua non of real time, closed loop control is an accurate estimate of the process quantities to be controlled. Although actinometry provides a non-invasive method for estimating species densities, atomic oxygen actinometry is complicated by the fact that photon emission can occur through dissociative as well as direct excitation, leading to potential ambiguity between the emission intensity and the actual radical concentration in the plasma. Optimal estimation of process states given indirect measurements corrupted by process and measurement noise is a classical topic in control theory and has yielded some spectacular results, notably the ubiquitous Kalman filter.

  13. Energetic Atomic Oxygen in the Region of the Terrestrial Exobase

    NASA Astrophysics Data System (ADS)

    Shizgal, B.; Sospedra-Alfonso, R.

    2012-12-01

    Translationally energetic atoms in the terrestrial exosphere with energies considerably above thermal energies are responsible for nonthermal emissions and enhanced nonthermal escape of atmospheric species. These escape mechanisms play an important role in the evolution of Earth's atmosphere. The existence of an extended coronae of translationally energetic oxygen atoms O* has been firmly established [1]. One mechanism to produce energetic oxygen atoms is the dissociative recombination reaction, O2+ + e- -> O* + O*. There is a continued interest in a better understanding of the physics of this process for the terrestrial exosphere. The terrestrial atmosphere can be divided into three main regions characterized by their relaxation properties [1]. The lower thermosphere (200-250 km), the upper exosphere (700-800 km) and the transition region (300-700). The lower thermosphere has a predominance of elastic collisions and therefore the particles are essentially in local equilibrium. In contrast, the thermalization in the upper exosphere is less predominant, although the production rate of nonthermal particles is also low. In the transition region, the production rate of nonthermal particles is significant and there is a decrease in the thermalization rate. This region is the main source of the nonthermal geocorona [1]. The relaxation properties of this region implies that the particle distribution can deviate from statistical equilibrium, and the distribution of nonthermal particles can be described with kinetic theory. In [2], we modeled the energetic oxygen distribution with a linear Boltzmann equation that included a source term for the production of hot oxygen owing to dissociative recombination. The distribution function was assumed to be isotropic and the objective was to determine the departure of the distribution function from Maxwellian and the departure of the density profile from barometric. In the present work, we consider a two component system of

  14. Durability of Membrane Electrode Assemblies (MEAs) in PEM Fuel Cells Operated on Pure Hydrogen and Oxygen

    NASA Technical Reports Server (NTRS)

    Stanic, Vesna; Braun, James; Hoberecht, Mark

    2003-01-01

    Proton exchange membrane (PEM) fuel cells are energy sources that have the potential to replace alkaline fuel cells for space programs. Broad power ranges, high peak-to-nominal power capabilities, low maintenance costs, and the promise of increased life are the major advantages of PEM technology in comparison to alkaline technology. The probability of PEM fuel cells replacing alkaline fuel cells for space applications will increase if the promise of increased life is verified by achieving a minimum of 10,000 hours of operating life. Durability plays an important role in the process of evaluation and selection of MEAs for Teledyne s Phase I contract with the NASA Glenn Research Center entitled Proton Exchange Membrane Fuel cell (PEMFC) Power Plant Technology Development for 2nd Generation Reusable Launch Vehicles (RLVs). For this contract, MEAs that are typically used for H2/air operation were selected as potential candidates for H2/O2 PEM fuel cells because their catalysts have properties suitable for O2 operation. They were purchased from several well-established MEA manufacturers who are world leaders in the manufacturing of diverse products and have committed extensive resources in an attempt to develop and fully commercialize MEA technology. A total of twelve MEAs used in H2/air operation were initially identified from these manufacturers. Based on the manufacturers specifications, nine of these were selected for evaluation. Since 10,000 hours is almost equivalent to 14 months, it was not possible to perform continuous testing with each MEA selected during Phase I of the contract. Because of the lack of time, a screening test on each MEA was performed for 400 hours under accelerated test conditions. The major criterion for an MEA pass or fail of the screening test was the gas crossover rate. If the gas crossover rate was higher than the membrane intrinsic permeability after 400 hours of testing, it was considered that the MEA had failed the test. Three types of

  15. Multi-functional magnesium alloys containing interstitial oxygen atoms.

    PubMed

    Kang, H; Choi, H J; Kang, S W; Shin, S E; Choi, G S; Bae, D H

    2016-03-15

    A new class of magnesium alloys has been developed by dissolving large amounts of oxygen atoms into a magnesium lattice (Mg-O alloys). The oxygen atoms are supplied by decomposing titanium dioxide nanoparticles in a magnesium melt at 720 °C; the titanium is then completely separated out from the magnesium melt after solidification. The dissolved oxygen atoms are located at the octahedral sites of magnesium, which expand the magnesium lattice. These alloys possess ionic and metallic bonding characteristics, providing outstanding mechanical and functional properties. A Mg-O-Al casting alloy made in this fashion shows superior mechanical performance, chemical resistance to corrosion, and thermal conductivity. Furthermore, a similar Mg-O-Zn wrought alloy shows high elongation to failure (>50%) at room temperature, because the alloy plastically deforms with only multiple slips in the sub-micrometer grains (<300 nm) surrounding the larger grains (~15 μm). The metal/non-metal interstitial alloys are expected to open a new paradigm in commercial alloy design.

  16. Multi-functional magnesium alloys containing interstitial oxygen atoms

    PubMed Central

    Kang, H.; Choi, H. J.; Kang, S. W.; Shin, S. E.; Choi, G. S.; Bae, D. H.

    2016-01-01

    A new class of magnesium alloys has been developed by dissolving large amounts of oxygen atoms into a magnesium lattice (Mg-O alloys). The oxygen atoms are supplied by decomposing titanium dioxide nanoparticles in a magnesium melt at 720 °C; the titanium is then completely separated out from the magnesium melt after solidification. The dissolved oxygen atoms are located at the octahedral sites of magnesium, which expand the magnesium lattice. These alloys possess ionic and metallic bonding characteristics, providing outstanding mechanical and functional properties. A Mg-O-Al casting alloy made in this fashion shows superior mechanical performance, chemical resistance to corrosion, and thermal conductivity. Furthermore, a similar Mg-O-Zn wrought alloy shows high elongation to failure (>50%) at room temperature, because the alloy plastically deforms with only multiple slips in the sub-micrometer grains (<300 nm) surrounding the larger grains (~15 μm). The metal/non-metal interstitial alloys are expected to open a new paradigm in commercial alloy design. PMID:26976372

  17. Theoretical approach to oxygen atom degradation of silver

    NASA Technical Reports Server (NTRS)

    Fromhold, Albert T., Jr.; Noh, Seung; Beshears, Ronald; Whitaker, Ann F.; Little, Sally A.

    1987-01-01

    Based on available Rutherford backscattering spectrometry (RBS), proton induced X-ray emission (PIXE) and ellipsometry data obtained on silver specimens subjected to atomic oxygen attack in low Earth orbit STS flight 41-G, a theory was developed to model the oxygen atom degradation of silver. The diffusion of atomic oxygen in a microscopically nonuniform medium is an essential constituent of the theory. The driving force for diffusion is the macroscopic electrochemical potential gradient developed between the specimen surface exposed to the ambient and the bulk of the silver specimen. The longitudinal electric effect developed parallel to the gradient is modified by space charge of the diffusing charged species. Lateral electric fields and concentration differences also exist due to the nonuniform nature of the medium. The lateral concentration differences are found to be more important than the lateral electric fields in modifying the diffusion rate. The model was evaluated numerically. Qualitative agreement exists between the kinetics predicted by the theory and kinetic data taken in ground-based experiments utilizing a plasma asher.

  18. Degradation of Staphylococcus aureus bacteria by neutral oxygen atoms

    SciTech Connect

    Cvelbar, U.; Mozetic, M.; Hauptman, N.; Klanjsek-Gunde, M.

    2009-11-15

    The degradation of Staphylococcus aureus bacteria during treatment with neutral oxygen atoms was monitored by scanning electron microscopy. Experiments were performed in an afterglow chamber made from borosilicate glass. The source of oxygen atoms was remote inductively coupled radiofrequency oxygen plasma. The density of atoms at the samples was 8x10{sup 20} m{sup -3}. The treatment was performed at room temperature. The first effect was the removal of dried capsule. Capsule on exposed parts of bacteria was removed after receiving the dose of 6x10{sup 23} at./m{sup 2}, while the parts of capsule filling the gaps between bacteria were removed after receiving the dose of 2.4x10{sup 24} m{sup -2}. After removing the capsule, degradation continued as etching of bacterial cell wall. The etching was rather nonuniform as holes with diameter of several 10 nm were observed. The cell wall was removed after receiving the dose of about 7x10{sup 24} m{sup -2}. The etching probabilities were about 2x10{sup -5} for the capsule and 2x10{sup -6} for the cell wall. The results were explained by different compositions of capsule and the cell wall.

  19. A Comprehensive X-Ray Absorption Model for Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Gorczyca, T. W.; Bautista, M. A.; Hasoglu, M. F.; Garcia, J.; Gatuzz, E.; Kaastra, J. S.; Kallman, T. R.; Manson, S. T.; Mendoza, C.; Raassen, A. J. J.; de Vries, C. P.; Zatsarinny, O.

    2013-01-01

    An analytical formula is developed to accurately represent the photoabsorption cross section of atomic Oxygen for all energies of interest in X-ray spectral modeling. In the vicinity of the K edge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further, minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer- and inner-shell direct photoionization, including significant shake-up and shake-off processes that result in photoionization-excitation and double-photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory-measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from XSTAR and SPEX spectral models.

  20. Multi-functional magnesium alloys containing interstitial oxygen atoms

    NASA Astrophysics Data System (ADS)

    Kang, H.; Choi, H. J.; Kang, S. W.; Shin, S. E.; Choi, G. S.; Bae, D. H.

    2016-03-01

    A new class of magnesium alloys has been developed by dissolving large amounts of oxygen atoms into a magnesium lattice (Mg-O alloys). The oxygen atoms are supplied by decomposing titanium dioxide nanoparticles in a magnesium melt at 720 °C the titanium is then completely separated out from the magnesium melt after solidification. The dissolved oxygen atoms are located at the octahedral sites of magnesium, which expand the magnesium lattice. These alloys possess ionic and metallic bonding characteristics, providing outstanding mechanical and functional properties. A Mg-O-Al casting alloy made in this fashion shows superior mechanical performance, chemical resistance to corrosion, and thermal conductivity. Furthermore, a similar Mg-O-Zn wrought alloy shows high elongation to failure (>50%) at room temperature, because the alloy plastically deforms with only multiple slips in the sub-micrometer grains (<300 nm) surrounding the larger grains (~15 μm). The metal/non-metal interstitial alloys are expected to open a new paradigm in commercial alloy design.

  1. Electron stimulated desorption of atomic oxygen from silver

    NASA Technical Reports Server (NTRS)

    Outlaw, R. A.; Peregoy, W. K.; Hoflund, Gar B.; Corallo, Gregory R.

    1987-01-01

    The electron stimulated desorption (ESD) of neutral oxygen atoms from polycrystalline silver and of oxygen ions from Ag(110) has been studied. Polycrystalline Ag charged with (16)O2 and (18)O2 and bombarded by low-energy electrons (approx 100 eV) under ultrahigh vacuum (UHV) conditions emitted O atom flux levels of 1 x 10 to the 12th power/sq cm/s at a Ag temperature of 300 C. The flux was detected with a quadrupole mass spectrometer operating in the appearance potential mode. The neutral cross section at about 100 C was determined to be 7 x 10 to the -19 sq cm. Ancillary experiments conducted in a UHV chamber equipped with a cylindrical mirror analyzer and rigged for ion energy distribution and ion angular distribution were used to study O ions desorbed from Ag(110). Two primary O(+) energies of 2.4 and 5.4 eV were detected from the Ag(110) after having been dosed with 2500 L of (16)O2. It also appears that in both experiments there was strong evidence for directionality of the emitted flux. The results of this study serve as a proof of concept for the development of a laboratory atomic oxygen beam generator that simulates the gas flux environment experienced by orbiting vehicles.

  2. The effects of low earth orbit atomic oxygen on the properties of Polytetrafluoroethylene

    NASA Astrophysics Data System (ADS)

    Hooshangi, Zhila; Hossein Feghhi, Seyed Amir; Saeedzadeh, Rezgar

    2016-02-01

    Polymers are widely used in space systems as the structural materials. The low earth orbit (LEO) space environment includes hazards such as atomic oxygen. Exposure of polymeric materials to atomic oxygen results in destructive effects on the chemical, electrical, thermal, optical and mechanical properties as well as surface degradation. In the present work, the effects of atomic oxygen on the mechanical, thermal, and optical properties of Polytetrafluoroethylene film have been investigated. The atomic oxygen density was calculated by SPENVIS tool. After the atomic oxygen exposure by using radio-frequency (RF) plasma source, the appearance of the samples changed, and the mass of the samples reduced because of outgassing. The results of thermal analysis showed that atomic oxygen flux does not affect thermal degradation of samples regarding TGA diagrams. By increasing the atomic oxygen flux, the amount of absorbance increased showing that atomic oxygen had damaged the surface of Polytetrafluoroethylene, and it had oxidized the surface of the polymer.

  3. Atomic Oxygen Recombination at Surface Defects on Reconstructed (0001) α-Quartz Exposed to Atomic and Molecular Oxygen

    SciTech Connect

    Meana-Paneda, Ruben; Paukku, Yuliya Y.; Duanmu, Kaining; Norman, Paul; Schwartzentruber, Thomas E.; Truhlar, Donald G.

    2015-04-30

    The surface chemistry of silica is strongly affected by the nature of chemically active sites (or defects) occurring on the surface. Here, we employ quantum mechanical electronic structure calculations to study an uncoordinated silicon defect, a non-bridging oxygen defect, and a peroxyl defect on the reconstructed (0001) surface of α-quartz. We characterized the spin states and energies of the defects, and calculated the reaction profiles for atomic oxygen recombination at the defects. We elucidated the diradical character by analyzing the low-lying excited states using multireference wave function methods. We show that the diradical defects consist of weakly coupled doublet radicals, and the atomic oxygen recombination can take place through a barrierless process at defects. We have delineated the recombination mechanism and computed the formation energy of the peroxyl and non-bridging oxygen defects. We found that key recombination reaction paths are barrierless. In addition, we characterize the electronically excited states that may play a role in the chemical and physical processes that occur during recombination on these surface defect sites.

  4. Variable energy, high flux, ground-state atomic oxygen source

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara (Inventor); Orient, Otto J. (Inventor)

    1987-01-01

    A variable energy, high flux atomic oxygen source is described which is comprised of a means for producing a high density beam of molecules which will emit O(-) ions when bombarded with electrons; a means of producing a high current stream of electrons at a low energy level passing through the high density beam of molecules to produce a combined stream of electrons and O(-) ions; means for accelerating the combined stream to a desired energy level; means for producing an intense magnetic field to confine the electrons and O(-) ions; means for directing a multiple pass laser beam through the combined stream to strip off the excess electrons from a plurality of the O(-) ions to produce ground-state O atoms within the combined stream; electrostatic deflection means for deflecting the path of the O(-) ions and the electrons in the combined stream; and, means for stopping the O(-) ions and the electrons and for allowing only the ground-state O atoms to continue as the source of the atoms of interest. The method and apparatus are also adaptable for producing other ground-state atoms and/or molecules.

  5. Atomic scale observation of oxygen delivery during silver–oxygen nanoparticle catalysed oxidation of carbon nanotubes

    PubMed Central

    Yue, Yonghai; Yuchi, Datong; Guan, Pengfei; Xu, Jia; Guo, Lin; Liu, Jingyue

    2016-01-01

    To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars–van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes. PMID:27406595

  6. Atomic scale observation of oxygen delivery during silver-oxygen nanoparticle catalysed oxidation of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yue, Yonghai; Yuchi, Datong; Guan, Pengfei; Xu, Jia; Guo, Lin; Liu, Jingyue

    2016-07-01

    To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars-van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes.

  7. Atomic scale observation of oxygen delivery during silver-oxygen nanoparticle catalysed oxidation of carbon nanotubes.

    PubMed

    Yue, Yonghai; Yuchi, Datong; Guan, Pengfei; Xu, Jia; Guo, Lin; Liu, Jingyue

    2016-07-13

    To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars-van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes.

  8. Atomic scale observation of oxygen delivery during silver-oxygen nanoparticle catalysed oxidation of carbon nanotubes.

    PubMed

    Yue, Yonghai; Yuchi, Datong; Guan, Pengfei; Xu, Jia; Guo, Lin; Liu, Jingyue

    2016-01-01

    To probe the nature of metal-catalysed processes and to design better metal-based catalysts, atomic scale understanding of catalytic processes is highly desirable. Here we use aberration-corrected environmental transmission electron microscopy to investigate the atomic scale processes of silver-based nanoparticles, which catalyse the oxidation of multi-wall carbon nanotubes. A direct semi-quantitative estimate of the oxidized carbon atoms by silver-based nanoparticles is achieved. A mechanism similar to the Mars-van Krevelen process is invoked to explain the catalytic oxidation process. Theoretical calculations, together with the experimental data, suggest that the oxygen molecules dissociate on the surface of silver nanoparticles and diffuse through the silver nanoparticles to reach the silver/carbon interfaces and subsequently oxidize the carbon. The lattice distortion caused by oxygen concentration gradient within the silver nanoparticles provides the direct evidence for oxygen diffusion. Such direct observation of atomic scale dynamics provides an important general methodology for investigations of catalytic processes. PMID:27406595

  9. Photochemistry of molecular and atomic oxygen in the terrestrial nightglow

    NASA Astrophysics Data System (ADS)

    Lednyts'kyy, Olexandr; Von Savigny, Christian; Sinnhuber, Miriam

    2016-07-01

    The electronic states of molecular oxygen ({O}_2) are in constant communication through collisions in high vibrational levels of {O}_2 in the MLT (Mesosphere/Lower Thermosphere) region. We assume that the Herzberg {O}_2 electronic states transfer energy to O-atoms to generate the green line. Our Multiple Nightglow Chemistry model is based on more than 80 (odd oxygen and odd hydrogen) aeronomical reactions to implement this concept. We retrieved atomic oxygen concentration ([O]) profiles in the MLT region with help of SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) and SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) infrared radiometer observations of the nightglow. Particularly, we obtained volume emission rate (VER) profiles (due to the infrared atmospheric {O}_2(a^1Δ_g) nightglow at 1.27 μm) from SABER to retrieve [O] profiles. We discussed quenching profiles that correspond to retrieved [O] profiles to reflect complex molecularity of infrared atmospheric and green line nightglow emissions.

  10. A high flux source of swift oxygen atoms

    NASA Technical Reports Server (NTRS)

    Fink, M.; Kohl, D. A.; Keto, J. W.; Antoniewicz, P.

    1987-01-01

    A source of swift oxygen atoms is described which has several unique features. A high current ion beam is produced by a microwave discharge, accelerated to 10 keV and the mass selected by a modified Du Pont 21-110 mass spectrometer. The O(+) beam exciting the mass spectrometer is focused into a rectangular shape with an energy spread of less than 1 eV. The next section of the machine decelerates the ion beam into a counterpropagating electron beam in order to minimize space charge effects. After deceleration, the ion beam intersects at 90 deg, a neutral oxygen atom beam, which via resonant charge exchange produces a mixture of O(+) and O. Any remaining O(+) are swept out of the beam by an electric field and differentially pumped away while the desired O beam, collimated by slits, impinges on the target. In situ monitoring of the target surface is done by X-ray photoelectron or Auger spectroscopy. Faraday cups provide flux measurements in the ion sections while the neutral flux is determined by a special torsion balance or by a quadrupole mass spectrometer specially adapted for swift atoms. While the vacuum from the source through the mass spectrometer is maintained by diffusion pumps, the rest of the machine is UHV.

  11. Effects of Atomic Oxygen Erosion on Space Materials

    NASA Astrophysics Data System (ADS)

    Bitetti, G.*; Carnà, E.; Marchetti, M.; Pilloni, L.; Poscente, F.; Scaglione, S.

    2004-08-01

    Spacecrafts in LEO (Low Earth Orbit) are subjected to a variety of chemical interactions. In particular, between 200 and 700 km altitude, the main atmospheric constituent is atomic oxygen that interacts with a wide variety of materials leading to oxidation or erosion and general degradation of materials properties. These effects can be very severe until to the failure of the entire mission . In this work was studied the mass loss due to the atomic flux that impact on the material surface. The Test Program was initiated to assess the effects of simulated LEO exposure, using SPENVIS (Space Environment information System) code, on current spacecrafts materials in order to understand LEO degradation processes. Different tests was carried out in the SAS facility (Space Environment Simulator) that is mainly constituted by an high vacuum chamber with thermal vacuum-cavity. In this chamber, solar irradiance is simulated by means of IR quartz tubes and UV lamps. A Single-Cell Ion Source of the Advanced Energy Industries (USA) inside the chamber produces various levels of atomic oxygen. Different type of materials for Space applications were studied, in particular polyimide film Kapton. The surface morphology variation was analyzed using a Scanning Electron Microscopy.

  12. Ultrathin amorphous α-Co(OH)2 nanosheets grown on Ag nanowire surfaces as a highly active and durable electrocatalyst for oxygen evolution reaction.

    PubMed

    Kim, Hyeonghun; Kim, Youngmin; Noh, Yuseong; Kim, Won Bae

    2016-09-21

    Ultrathin α-Co(OH)2 nanosheets, prepared via simple hydrolysis at room temperature, were directly grown on Ag nanowires. The catalyst exhibited improved activity for the oxygen evolution reaction, with a reduced onset overpotential (220 mV) and superior durability because of the enhanced electron conductivity and stability of Ag nanowires in alkaline media. PMID:27518694

  13. Ultrathin amorphous α-Co(OH)2 nanosheets grown on Ag nanowire surfaces as a highly active and durable electrocatalyst for oxygen evolution reaction.

    PubMed

    Kim, Hyeonghun; Kim, Youngmin; Noh, Yuseong; Kim, Won Bae

    2016-09-21

    Ultrathin α-Co(OH)2 nanosheets, prepared via simple hydrolysis at room temperature, were directly grown on Ag nanowires. The catalyst exhibited improved activity for the oxygen evolution reaction, with a reduced onset overpotential (220 mV) and superior durability because of the enhanced electron conductivity and stability of Ag nanowires in alkaline media.

  14. K-shell auger decay of atomic oxygen

    SciTech Connect

    Stolte, W.C.; Lu, Y.; Samson, J.A.R.

    1997-04-01

    The aim of the present research is to understand the interaction between the ejected photoelectron and Auger electron produced by the Auger decay of a 1s hole in atomic oxygen, and to understand the influence this interaction has on the shape of the ionization cross sections. To accomplish this the authors have measured the relative ion yields (ion/photon) in the vicinity of the oxygen K-shell (525 - 533 eV) for O{sup +} and O{sup 2+}. The measurements were performed at the ALS on beamline, 6.3.2. The atomic oxygen was produced by passing molecular oxygen through a microwave-driven discharge. A Rydberg analysis of the two series leading to the [1s]2s{sup 2}2p{sup 4}({sup 4}P) and [1s]2s{sup 2}2p{sup 4}({sup 2}P) limits were obtained. This analysis shows some differences to the recently published results by Menzel et al. The energy position of the main 1s{sup 1}2s{sup 2}2p{sup 5}({sup 3}P) resonance differs by approximately 1 eV from the authors value, all members of the ({sup 2}P)np series differ by 0.3 eV, but the members of the ({sup 4}P)np series agree. The molecular resonance at 530.5 eV and those between 539 eV and 543 eV, measured with the microwave discharge off show identical results in both experiments.

  15. MISSE 6 Stressed Polymers Experiment Atomic Oxygen Erosion Data

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Banks, Bruce A.; Mitchell, Gianna G.; Yi, Grace T.; Guo, Aobo; Ashmeade, Claire C.; Roberts, Lily M.; McCarthy, Catherine E.; Sechkar, Edward A.

    2013-01-01

    Polymers and other oxidizable materials used on the exterior of spacecraft in the low Earth orbit (LEO) space environment can be eroded away by reaction with atomic oxygen (AO). For spacecraft design, it is important to know the LEO AO erosion yield, Ey (volume loss per incident oxygen atom), of materials susceptible to AO erosion. The Stressed Polymers Experiment was developed and flown as part of the Materials International Space Station Experiment 6 (MISSE 6) to compare the AO erosion yields of stressed and non-stressed polymers to determine if erosion is dependent upon stress while in LEO. The experiment contained 36 thin film polymer samples that were exposed to ram AO for 1.45 years. This paper provides an overview of the Stressed Polymers Experiment with details on the polymers flown, the characterization techniques used, the AO fluence, and the erosion yield results. The MISSE 6 data are compared to data for similar samples flown on previous MISSE missions to determine fluence or solar radiation effects on erosion yield.

  16. A comprehensive X-ray absorption model for atomic oxygen

    SciTech Connect

    Gorczyca, T. W.; Bautista, M. A.; Mendoza, C.; Hasoglu, M. F.; García, J.; Gatuzz, E.; Kaastra, J. S.; Raassen, A. J. J.; De Vries, C. P.; Kallman, T. R.; Manson, S. T.; Zatsarinny, O.

    2013-12-10

    An analytical formula is developed to accurately represent the photoabsorption cross section of O I for all energies of interest in X-ray spectral modeling. In the vicinity of the K edge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further, minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer- and inner-shell direct photoionization, including significant shake-up and shake-off processes that result in photoionization-excitation and double-photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory-measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from XSTAR and SPEX spectral models.

  17. The interaction of atomic oxygen with thin copper films

    NASA Technical Reports Server (NTRS)

    Gibson, B. C.; Williams, J. R.; Fromhold, A. T., Jr.; Bozack, M. J.; Neely, W. C.; Whitaker, Ann F.

    1992-01-01

    A source of thermal, ground-state atomic oxygen has been used to expose thin copper films at a flux of 1.4 x 10 exp 17 atoms/sq cm s for times up to 50 min for each of five temperatures between 140 and 200 C. Rutherford backscattering spectroscopy was used to characterize the oxide formed during exposure. The observations are consistent with the oxide phase Cu2O. The time dependence and the temperature dependence of the oxide layer thickness can be described using oxide film growth theory based on rate limitation by diffusion. Within the time and temperature ranges of this study, the growth of the oxide layers is well described by the equation L(T,t) = 3.6 x 10 to 8th exp(- 1.1/2k sub B T)t exp 1/2, where L,T, and t are measured in angstroms, degrees Kelvin, and minutes, respectively. The deduced activation energy is 1.10 +/- 0.15 eV, with the attendant oxidation rate being greater than that for the corresponding reaction in molecular oxygen.

  18. On the linearity of fast atomic oxygen effects

    NASA Technical Reports Server (NTRS)

    Gregory, J. C.

    1993-01-01

    The effect of bombardment of 8 km per second atomic oxygen (AO) experienced by exposed surfaces of satellites in low Earth orbit must be considered in the selection of materials to be used in instruments and functional systems on these satellites. The degree of importance of the effects varies widely depending on the material, the application, and the exposure (fluence of atoms) to which it is to be subjected. Some highly erodible thin polymer film materials might be considered unacceptable on a long-lived space station, but may be perfectly serviceable on a normal shuttle flight. In order to determine the acceptability of a material for a particular environment, a designer must know the relationship between the magnitude of the effect (for example, mass-loss) and the magnitude of the fluence. To determine this relationship, we need data over a useful range of fluence. Until the return of the Long Duration Exposure Facility (LDEF), the bulk of the data on materials effects was obtained from a few shuttle flights, and the bulk of that data from the flight of experiment Evaluation of Oxygen Interaction with Materials (EOIM-2) on STS-8 in 1983. EOIM-2 obtained a fluence of 3.5 x 10(exp 20) atoms cm(exp -2), while the LDEF fluence approached 10(exp 22) atoms cm(exp -2), or about 30 times greater. Although other flight exposures had been obtained with lower fluences, considerable uncertainty was attached to these results because of the possibility of large relative systematic errors and of other factors such as sweeping angle of attack. In the future, it is hoped that simulation facilities in the laboratory will allow testing of materials without the necessity of flying them in space. In addition, if the relationship of effect with oxygen fluence is well determined, it should not be necessary to expose a material for an entire mission fluence. In this paper, we shall avoid a comparison of flight data with results from simulators, though that comparison is important for

  19. Coherent anti-Stokes Raman spectra of oxygen atoms in flames.

    PubMed

    Teets, R E; Bechtel, J H

    1981-10-01

    Coherent anti-Stokes Raman spectroscopy (CARS) was used to detect oxygen atoms (electronic Raman scattering) and oxygen molecules (rotational Raman scattering) in both hydrogen-oxygen and methane-oxygen flames. The high spectral resolution of CARS is useful for distinguishing the oxygen-atom signals from larger nearby rotational Raman signals. Saturation of the molecular CARS signal that is due to stimulated Raman scattering was observed. This effect limits the sensitivity of the CARS method. PMID:19710736

  20. Operation of the computer model for direct atomic oxygen exposure of Earth satellites

    NASA Astrophysics Data System (ADS)

    Bourassa, R. J.; Gruenbaum, P. E.; Gillis, J. R.; Hargraves, C. R.

    1995-08-01

    One of the primary causes of material degradation in low Earth orbit (LEO) is exposure to atomic oxygen. When atomic oxygen molecules collide with an orbiting spacecraft, the relative velocity is 7 to 8 km/sec and the collision energy is 4 to 5 eV per atom. Under these conditions, atomic oxygen may initiate a number of chemical and physical reactions with exposed materials. These reactions contribute to material degradation, surface erosion, and contamination. Interpretation of these effects on materials and the design of space hardware to withstand on-orbit conditions requires quantitative knowledge of the atomic oxygen exposure environment. Atomic oxygen flux is a function of orbit altitude, the orientation of the orbit plan to the Sun, solar and geomagnetic activity, and the angle between exposed surfaces and the spacecraft heading. We have developed a computer model to predict the atomic oxygen exposure of spacecraft in low Earth orbit. The application of this computer model is discussed.

  1. Operation of the computer model for direct atomic oxygen exposure of Earth satellites

    NASA Technical Reports Server (NTRS)

    Bourassa, R. J.; Gruenbaum, P. E.; Gillis, J. R.; Hargraves, C. R.

    1995-01-01

    One of the primary causes of material degradation in low Earth orbit (LEO) is exposure to atomic oxygen. When atomic oxygen molecules collide with an orbiting spacecraft, the relative velocity is 7 to 8 km/sec and the collision energy is 4 to 5 eV per atom. Under these conditions, atomic oxygen may initiate a number of chemical and physical reactions with exposed materials. These reactions contribute to material degradation, surface erosion, and contamination. Interpretation of these effects on materials and the design of space hardware to withstand on-orbit conditions requires quantitative knowledge of the atomic oxygen exposure environment. Atomic oxygen flux is a function of orbit altitude, the orientation of the orbit plan to the Sun, solar and geomagnetic activity, and the angle between exposed surfaces and the spacecraft heading. We have developed a computer model to predict the atomic oxygen exposure of spacecraft in low Earth orbit. The application of this computer model is discussed.

  2. Small ultrahigh vacuum compatible hyperthermal oxygen atom generator

    NASA Technical Reports Server (NTRS)

    Outlaw, R. A.; Davidson, Mark R.

    1994-01-01

    The development of a compact, ultrahigh vacuum (UHV) compatible instrument for generating a flux of pure hyperthermal oxygen atoms for NASA applications has been achieved. The instrument combines the mechanisms of O2 dissociation and transport through a hot Ag membrane to provide a continuous source of O atoms to a vacuum interface where they are subsequently emitted into the vacuum space by electron-stimulated desorption (ESD). A flux of neutral O atoms 4.5 X 10(exp 13) cm(exp-2) s(exp-l)(P-3) with a mean ion kinetic energy of approximately 5eV and a full width at half maximum of 4eV was detected at a quadrupole mass spectrometer located 10 cm away. The geometry of the instrument is such that it is mounted on a 7 cm flange and can be tailored in length and orientation to fit most UHV systems. The data presented here are for ESD-controlled conditions where increases in the flux are strictly linear with electron bombardment current. Calculation shows that transport-controlled conditions can be achieved at temperatures as low as 350 C with membrane thicknesses on the order of 10 micron.

  3. Materials International Space Station Experiment-6 (MISSE-6) Atomic Oxygen Fluence Monitor Experiment

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K.; Waters, Deborah L.

    2010-01-01

    An atomic oxygen fluence monitor was flown as part of the Materials International Space Station Experiment-6 (MISSE-6). The monitor was designed to measure the accumulation of atomic oxygen fluence with time as it impinged upon the ram surface of the MISSE 6B Passive Experiment Container (PEC). This was an active experiment for which data was to be stored on a battery-powered data logger for post-flight retrieval and analysis. The atomic oxygen fluence measurement was accomplished by allowing atomic oxygen to erode two opposing wedges of pyrolytic graphite that partially covered a photodiode. As the wedges of pyrolytic graphite erode, the area of the photodiode that is illuminated by the Sun increases. The short circuit current, which is proportional to the area of illumination, was to be measured and recorded as a function of time. The short circuit current from a different photodiode, which was oriented in the same direction and had an unobstructed view of the Sun, was also to be recorded as a reference current. The ratio of the two separate recorded currents should bear a linear relationship with the accumulated atomic oxygen fluence and be independent of the intensity of solar illumination. Ground hyperthermal atomic oxygen exposure facilities were used to evaluate the linearity of the ratio of short circuit current to the atomic oxygen fluence. In flight, the current measurement circuitry failed to operate properly, thus the overall atomic oxygen mission fluence could only be estimated based on the physical erosion of the pyrolytic graphite wedges. The atomic oxygen fluence was calculated based on the knowledge of the space atomic oxygen erosion yield of pyrolytic graphite measured from samples on the MISSE 2. The atomic oxygen fluence monitor, the expected result and comparison of mission atomic oxygen fluence based on the erosion of the pyrolytic graphite and Kapton H atomic oxygen fluence witness samples are presented in this paper.

  4. Spatial and temporal behavior of atomic oxygen determined by Ogo 6 airglow observations

    NASA Technical Reports Server (NTRS)

    Donahue, T. M.; Guenther, B.; Thomas, R. J.

    1974-01-01

    Maps are produced of the atomic oxygen density near 97 km showing a strong variation in latitude, longitude, universal time, and time of year. These densities are deduced from atomic oxygen green nightglow observations carried out from Ogo 6. Meridional wind patterns needed to support the asymmetries observed in local oxygen production and loss rates are deduced.

  5. Atomic oxygen protective coating with resistance to undercutting at defect sites

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Rutledge, Sharon K. (Inventor)

    1994-01-01

    Structures composed at least partially of an organic substrate may be protected from oxidation by applying a catalyst onto said substrate for promoting the combination of atomic oxygen to molecular oxygen. The structure may also be protected by applying both a catalyst and an atomic oxygen shielding layer onto the substrate. The structures to be protected include spacecraft surfaces.

  6. Simulations of Ground and Space-Based Oxygen Atom Experiments

    NASA Technical Reports Server (NTRS)

    Minton, T. K.; Cline, J. A.; Braunstein, M.

    2002-01-01

    Fast, pulsed atomic oxygen sources are a key tool in ground-based investigations of spacecraft contamination and surface erosion effects. These technically challenging ground-based studies provide a before and after picture of materials under low-earth-orbit (LEO) conditions. It would be of great interest to track in real time the pulsed flux from the source to the surface sample target and beyond in order to characterize the population of atoms and molecules that actually impact the surface and those that make it downstream to any coincident detectors. We have performed simulations in order to provide such detailed descriptions of these ground-based measurements and to provide an assessment of their correspondence to the actual LEO environment. Where possible we also make comparisons to measured fluxes and erosion yields. To perform the calculations we use a detailed description of a measurement beam and surface geometry based on the W, pulsed apparatus at Montana State University. In this system, a short pulse (on the order of 10 microseconds) of an O/O2 beam impacts a flat sample about 40 cm downstream and slightly displaced &om the beam s central axis. Past this target, at the end of the beam axis is a quadrupole mass spectrometer that measures the relative in situ flux of 0102 to give an overall normalized erosion yield. In our simulations we use the Direct Simulation Monte Carlo (DSMC) method, and track individual atoms within the atomic oxygen pulse. DSMC techniques are typically used to model rarefied (few collision) gas-flows which occur at altitudes above approximately 110 kilometers. These techniques are well suited for the conditions here, and multi-collision effects that can only be treated by this or a similar technique are included. This simulation includes collisions with the surface and among gas atoms that have scattered from the surface. The simulation also includes descriptions of the velocity spread and spatial profiles of the O/O2 beam

  7. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

    PubMed

    Peera, S Gouse; Arunchander, A; Sahu, A K

    2016-08-14

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity

  8. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

    PubMed

    Peera, S Gouse; Arunchander, A; Sahu, A K

    2016-08-14

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity

  9. Flight Validation of Atomic Oxygen Resistant Resistant Polymers

    NASA Technical Reports Server (NTRS)

    Kiefer, Richard L.; Orwoll, Robert A.

    1999-01-01

    Because of its high reactivity, atomic oxygen causes surface erosion on polymeric materials. although the reaction efficiency depends on the chemical structure of the polymer. We have found an organotin compound, bis(triphenyltin) oxide (BTO), which has an unusually high solubility in solutions of a number of commercial high performance polymers. Films of these polymers containing BTO showed a substantial reduction in erosion by atomic oxygen when compared with films of the pure material. Analysis has shown that in the presence of atomic oxygen, erosion of the exposed surfaces of the BTO-containing films leaves a residual protective tin oxide coating . Since the additive is uniformly distributed throughout the polymeric material, any break or puncture in the protective coating is "healed" by the material below. Samples were exposed to the environment of the low earth orbit (LEO) on two Space Shuttle flights, STS-46, in June of 1992, and STS-51 in September of 1993. The analysis of these samples has been reported previously. For both flights, the samples were small (1.3 cm and 1.9 cm respectively) thus limiting the scope of analysis. In the research under this cooperative agreement, films of a polyetherimide, were exposed to the LEO environment on Space Shuttle flight STS-85 in August of 1997 as part of the Evaluation of Space Environment and Effects on Materials (ESEM) experiment. The polyetherimide chosen is available commercially as Ultem, registered to the General Electric Company. Films of pure Ultem, Ultem with 10% BTO by mass, and Ultem with 20% BTO by mass were exposed in the ram direction for 40 hours during STS-85. Ultem has a Tg of 215 deg C and is soluble in common chlorinated solvents. Granules of the polymer were dried at 120 deg C, but otherwise were used as received. Films were cast on a glass plate from a solution of the polymer in a 60/40 (w/w) mixture of chloroform and 1,1,2,2-tetrachloroethane. The plate was placed in a dust-free box for at least

  10. Atomic oxygen interaction at defect sights in protective coatings on polymers flown on LDEF

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Degroh, Kim K.; Auer, Bruce M.; Gebauer, Linda; Lamoreaux, Cynthia

    1993-01-01

    Although the Long Duration Exposure Facility (LDEF) has exposed materials with a fixed orientation relative to the ambient low-Earth-orbital environment, arrival of atomic oxygen is angularly distributed as a result of the atomic oxygen's high temperature Maxwellian velocity distribution and the LDEF's orbital inclination. Thus, atomic oxygen entering defects in protective coatings on polymeric surfaces can cause wider undercut cavities than the size of the defect in the protective coating. Because only a small fraction of atomic oxygen reacts upon first impact with most polymeric materials, secondary reactions with lower energy thermally accommodated atomic oxygen can occur. The secondary reactions of scattered and/or thermally accommodated atomic oxygen also contribute to widening the undercut cavity beneath the protective coating defect. As the undercut cavity enlarges, exposing more polymer, the probability of atomic oxygen reacting with underlying polymeric material increases because of multiple opportunities for reaction. Thus, the effective atomic oxygen erosion yield for atoms entering defects increases above that of the unprotected material. Based on the results of analytical modeling and computational modeling, aluminized Kapton multilayer insulation exposed to atomic oxygen on row 9 lost the entire externally exposed layer of polyimide Kapton, yet based on the results of this investigation, the bottom surface aluminum film must have remained in place, but crazed. Atomic oxygen undercutting at defect sites in protective coatings on graphite epoxy composites indicates that between 40 to 100 percent of the atomic oxygen thermally accommodates upon impact, and that the reaction probability of thermally accommodated atomic oxygen may range from 7.7 x 10(exp -6) to 2.1 x 10(exp -3), depending upon the degree of thermal accommodation upon each impact.

  11. Atomic Oxygen Energy in Low Frequency Hyperthermal Plasma Ashers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K R.; Kneubel, Christian A.

    2014-01-01

    Experimental and analytical analysis of the atomic oxygen erosion of pyrolytic graphite as well as Monte Carlo computational modeling of the erosion of Kapton H (DuPont, Wilmington, DE) polyimide was performed to determine the hyperthermal energy of low frequency (30 to 35 kHz) plasma ashers operating on air. It was concluded that hyperthermal energies in the range of 0.3 to 0.9 eV are produced in the low frequency air plasmas which results in texturing similar to that in low Earth orbit (LEO). Monte Carlo computational modeling also indicated that such low energy directed ions are fully capable of producing the experimentally observed textured surfaces in low frequency plasmas.

  12. Reactions of atomic oxygen /O(3P)/ with polymer films

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.

    1992-01-01

    The reactions of polymer films with oxygen atoms are reviewed focusing on laboratory tests on polybutadienes with different amount of 1,4 or 1,2 double bonds and their polyalkenamer homologues, polyimide (Kapton), and a series of polyolefines with increasing fluorine content. It is found that etch rates increase with decrease in -CH=CH- unsaturation, starting with 1,4 -polybutadiene and reaching the maximum rate with polyethylene or ethylene-propylene rubber. IN polybutadienes with both 1,4 and 1,2 double bonds, the rate of O(3P)-induced etching is lower the higher the 1,2 content. The reactions are confined to the polymer surface.

  13. Angle-resolved photoelectron spectroscopy of atomic oxygen

    NASA Astrophysics Data System (ADS)

    van der Meulen, P.; Krause, M. O.; de Lange, C. A.

    1991-06-01

    Using synchrotron-radiation-based, angle-resolved photoelectron spectroscopy, the relative partial photoionization cross sections for the production of the 4 S 0 and 2 D 0 ionic states in atomic oxygen, as well as the corresponding asymmetry parameters, are measured from threshold at 13.62 to about 30 eV. The cross sections are placed on an absolute scale using previous data obtained with an electron spectroscopy modulation method. Attention is focused on the numerous autoionization resonances below the 2p -12D0, 2p -12P0, and 2s -14Pe limits. The behavior of the asymmetry parameters across these resonances is observed for the first time. The 2s2p4(4Pe)3p(3S0,3P0,3D0) resonances are fitted by a Fano-type profile to obtain accurate values for the position, width, and q parameter.

  14. Complexes of self-interstitials with oxygen atoms in Ge

    SciTech Connect

    Khirunenko, L. I.; Pomozov, Yu. V.; Sosnin, M. G.; Abrosimov, N. V.; Riemann, H.

    2014-02-21

    Interactions of germanium self-interstitials with interstitial oxygen atoms in Ge subjected to irradiation at ∼80 K and subsequently to annealing have been studied. To distinguish the processes involving vacancies and self-interstitials the doping with tin was used. It was shown that absorption lines with maximum at 602, 674, 713 and 803 cm{sup −1} are self-interstitials-related. Two lines at 602 and 674, which develop upon annealing in the temperature range 180–240 K, belong to IO complexes, while the bands at 713 and 803 cm{sup −1}, which emerge after annealing at T>220 K, are associated with I{sub 2}O. It is argued that the annealing of IO occurs by two mechanisms: by dissociation and by diffusion.

  15. Hyperthermal atomic oxygen reactions with kapton and polyethylene. [in LEO

    NASA Technical Reports Server (NTRS)

    Cross, J. B.; Koontz, S. L.; Gregory, J. C.; Edgell, M. J.

    1990-01-01

    Gas phase reaction products produced by the interaction of high kinetic energy (1-3 eV) 3p ground state atomic oxygen (AO) with polyethylene and kapton were found to be H2, H2O, CO, and CO2 with NO being a possible secondary product from kapton. Hydrogen abstraction at high AO kinetic energy is postulated to be the key reaction controlling the erosion rate of kapton and polyethylene. An Arrhenius-like expression having an activation barrier of 0.4 eV can be fit to the data, which suggests that the rate limiting step in the AO/kapton reaction mechanism can be overcome by translational energy.

  16. The reaction efficiency of thermal energy oxygen atoms with polymeric materials

    NASA Technical Reports Server (NTRS)

    Koontz, S. L.; Nordine, Paul

    1990-01-01

    The reaction efficiency of several polymeric materials with thermal-energy (0.04 eV translational energy), ground-state (O3P) oxygen atoms was determined by exposing the materials to a room temperature gas containing a known concentration of atomic oxygen. The reaction efficiency measurements were conducted in two flowing afterglow systems of different configuration. Atomic oxygen concentration measurements, flow, transport and surface dose analysis is presented in this paper. The measured reaction efficiencies of Kapton, Mylar, polyethylene, D4-polyethylene and Tedlar are .001 to .0001 those determined with high-energy ground-state oxygen atoms in low earth orbit or in a high-velocity atom beam. D4-polyethylene exhibits a large kinetic isotope effect with atomic oxygen at thermal but not hyperthermal atom energies.

  17. Investigation of Atomic Oxygen Erosion of Polyimide Kapton H Exposed to a Plasma Asher Environment

    NASA Technical Reports Server (NTRS)

    Snyder, Aaron

    1999-01-01

    Experimental results are presented on the erosion characteristics of the polyimide Kapton H, which serves as a blanket material in solar arrays. This polymer has a number of characteristics that make it a suitable choice for both terrestrial and space applications. In this paper attention is focused on the durability of protected Kapton when exposed to atomic oxygen (AO) in a plasma asher. A strip of 0.025-mm thick Kapton film, coated on both sides with SiO2, was studied during a 1306 hour exposure. The erosion, located at defect sites in the protective coating and measured optically, is described in terms of volume loss as a function of AO fluence. Three simple geometric profiles are used to generate a useful array of cavity shapes to model erosion evolution. These models connect the volume erosion rate to the observed lateral expansion of the developing cavities via their diameters, measured adviacent to the upper and lower protective film, and fitted by least-squares regression to simple power law functions of fluence. The rationale for the choice of models is discussed. It was found that lateral growth in cavity size evolves less than linearly with fluence.

  18. The effects of atomic oxygen on polymeric materials

    NASA Technical Reports Server (NTRS)

    Orwoll, Robert A.

    1988-01-01

    At the altitudes of low-earth orbit (LEO), atomic oxygen (AO) is the most abundant chemical species. This strong oxidizing agent reacts with virtually any organic material that is not already fully oxidized. Erosion by AO can be extensive and jeopardizes any protective coatings, thermal blankets, adhesives, and structural composites exposed on the exterior of satellites in LEO. Researchers prepared and tested organic materials for their susceptibility to AO using a commercial plasma asher which approximately simulates the oxygen effects in LEO. Experiments were performed on a polyimide, a polysulfone, and two epoxy adhesives into which low molecular-weight additives have been dissolved. Incorporated in the molecular structure of these additives are elements such as silicon whose nonvolatile oxides, which are formed on exposure to AO, remain as a coating on the surface to create a barrier between the remainder of the organic material and the AO. We find that the additives protect the materials, but the low solubility of some limit their utility. Concurrent studies are underway to measure the effect of the additives on the thermal expansion coefficients of the materials. Tows of aramid fibers, which are important components in the proposed tether satellite systems, have been eroded in the asher. The results which show that the square root of the mass remaining decreases linearly with the time of exposure (see the figure) are consistent with a constant rate of surface erosion. The tensile strength of these eroded tows decreases with time of exposure also; additional measurements are in progress.

  19. Enhancement of burning velocity by dissociated oxygen atoms

    NASA Astrophysics Data System (ADS)

    Akashi, Haruaki; Yoshinaga, Tomokazu; Sasaki, Koichi

    2015-09-01

    Green technology, such as preventing global warming, has been developed for years. Researches on plasma assisted combustion is one of the technologies and have been done for investigating more efficient combustion, more efficient use of fossil fuel with plasmas or applying electric fields. In the ignition time delay analyses with the dissociated oxygen atoms which is generated by non-equilibrium plasma had significant effect on the ignition time. In this paper, dissociated oxygen could effect on burning velocity or not has been examined using CHEMKIN. As a result, no effect can be seen with dissociation degree of lower than 10-3. But there is an effect on the enhancement of burning velocity with higher degree of 10-3. At the dissociation degree of 5×10-2, the burning velocity is enhanced at a factor of 1.24. And it is found that the distributions of each species in front of preheat zone are completely different. The combustion process is proceeded several steps in advance, and generation of H2O, CO and CO2 can be seen before combustion in higher dissociation case. This work was supported by KAKENHI (22340170).

  20. Thermal relaxation of molecular oxygen in collisions with nitrogen atoms

    NASA Astrophysics Data System (ADS)

    Andrienko, Daniil A.; Boyd, Iain D.

    2016-07-01

    Investigation of O2-N collisions is performed by means of the quasi-classical trajectory method on the two lowest ab initio potential energy surfaces at temperatures relevant to hypersonic flows. A complete set of bound-bound and bound-free transition rates is obtained for each precollisional rovibrational state. Special attention is paid to the vibrational and rotational relaxations of oxygen as a result of chemically non-reactive interaction with nitrogen atoms. The vibrational relaxation of oxygen partially occurs via the formation of an intermediate NO2 complex. The efficient energy randomization results in rapid vibrational relaxation at low temperatures, compared to other molecular systems with a purely repulsive potential. The vibrational relaxation time, computed by means of master equation studies, is nearly an order of magnitude lower than the relaxation time in N2-O collisions. The rotational nonequilibrium starts to play a significant effect at translational temperatures above 8000 K. The present work provides convenient relations for the vibrational and rotational relaxation times as well as for the quasi-steady dissociation rate coefficient and thus fills a gap in data due to a lack of experimental measurements for this system.

  1. Thermal relaxation of molecular oxygen in collisions with nitrogen atoms.

    PubMed

    Andrienko, Daniil A; Boyd, Iain D

    2016-07-01

    Investigation of O2-N collisions is performed by means of the quasi-classical trajectory method on the two lowest ab initio potential energy surfaces at temperatures relevant to hypersonic flows. A complete set of bound-bound and bound-free transition rates is obtained for each precollisional rovibrational state. Special attention is paid to the vibrational and rotational relaxations of oxygen as a result of chemically non-reactive interaction with nitrogen atoms. The vibrational relaxation of oxygen partially occurs via the formation of an intermediate NO2 complex. The efficient energy randomization results in rapid vibrational relaxation at low temperatures, compared to other molecular systems with a purely repulsive potential. The vibrational relaxation time, computed by means of master equation studies, is nearly an order of magnitude lower than the relaxation time in N2-O collisions. The rotational nonequilibrium starts to play a significant effect at translational temperatures above 8000 K. The present work provides convenient relations for the vibrational and rotational relaxation times as well as for the quasi-steady dissociation rate coefficient and thus fills a gap in data due to a lack of experimental measurements for this system.

  2. Atomic oxygen erosion considerations for spacecraft materials selection

    NASA Technical Reports Server (NTRS)

    Whitaker, Ann F.; Kamenetzky, Rachel R.

    1993-01-01

    The Long Duration Exposure Facility (LDEF) satellite carried 57 experiments that were designed to define the low-Earth orbit (LEO) space environment and to evaluate the impact of this environment on potential engineering materials and material processes. Deployed by the Shuttle Challenger in April of 1984, LDEF made over 32,000 orbits before being retrieved nearly 6 years later by the Shuttle Columbia in January of 1990. The Solar Array Passive LDEF Experiment (SAMPLE) AO171 contained approximately 300 specimens, representing numerous material classes and material processes. AO171 was located on LDEF in position A8 at a yaw of 38.1 degrees from the ram direction and was subjected to an atomic oxygen (AO) fluence of 6.93 x 10(exp 21) atoms/sq cm. LDEF AO171 data, as well as short-term shuttle data, will be discussed in this paper as it applies to engineering design applications of composites, bulk and thin film polymers, glassy ceramics, thermal control paints, and metals subjected to AO erosion.

  3. Atomic Resolution of Calcium and Oxygen Sublattices of Calcite in Ambient Conditions by Atomic Force Microscopy Using qPlus Sensors with Sapphire Tips.

    PubMed

    Wastl, Daniel S; Judmann, Michael; Weymouth, Alfred J; Giessibl, Franz J

    2015-01-01

    Characterization and imaging at the atomic scale with atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomically resolved imaging of the calcite (101̅4) surface plane using stiff quartz cantilevers ("qPlus sensors", stiffness k = 1280 N/m) equipped with sapphire tips in ambient conditions without any surface preparation. With 10 atoms in one surface unit cell, calcite has a highly complex surface structure comprising three different chemical elements (Ca, C, and O). We obtain true atomic resolution of calcite in air at relative humidity ranging from 20% to 40%, imaging atomic steps and single atomic defects. We observe a great durability of sapphire tips with their Mohs hardness of 9, only one step below diamond. Depending on the state of the sapphire tip, we resolve either the calcium or the oxygen sublattice. We determine the tip termination by comparing the experimental images with simulations and discuss the possibility of chemical tip identification in air. The main challenges for imaging arise from the presence of water layers, which form on almost all surfaces and have the potential to dissolve the crystal surface. Frequency shift versus distance spectra show the presence of at least three ordered hydration layers. The measured height of the first hydration layer corresponds well to X-ray diffraction data and molecular dynamic simulations, namely, ∼220 pm. For the following hydration layers we measure ∼380 pm for the second and third layer, ending up in a total hydration layer thickness of at least 1 nm. Understanding the influence of water layers and their structure is important for surface segregation, surface reactions including reconstructions, healing of defects, and corrosion.

  4. Atomic Resolution of Calcium and Oxygen Sublattices of Calcite in Ambient Conditions by Atomic Force Microscopy Using qPlus Sensors with Sapphire Tips.

    PubMed

    Wastl, Daniel S; Judmann, Michael; Weymouth, Alfred J; Giessibl, Franz J

    2015-01-01

    Characterization and imaging at the atomic scale with atomic force microscopy in biocompatible environments is an ongoing challenge. We demonstrate atomically resolved imaging of the calcite (101̅4) surface plane using stiff quartz cantilevers ("qPlus sensors", stiffness k = 1280 N/m) equipped with sapphire tips in ambient conditions without any surface preparation. With 10 atoms in one surface unit cell, calcite has a highly complex surface structure comprising three different chemical elements (Ca, C, and O). We obtain true atomic resolution of calcite in air at relative humidity ranging from 20% to 40%, imaging atomic steps and single atomic defects. We observe a great durability of sapphire tips with their Mohs hardness of 9, only one step below diamond. Depending on the state of the sapphire tip, we resolve either the calcium or the oxygen sublattice. We determine the tip termination by comparing the experimental images with simulations and discuss the possibility of chemical tip identification in air. The main challenges for imaging arise from the presence of water layers, which form on almost all surfaces and have the potential to dissolve the crystal surface. Frequency shift versus distance spectra show the presence of at least three ordered hydration layers. The measured height of the first hydration layer corresponds well to X-ray diffraction data and molecular dynamic simulations, namely, ∼220 pm. For the following hydration layers we measure ∼380 pm for the second and third layer, ending up in a total hydration layer thickness of at least 1 nm. Understanding the influence of water layers and their structure is important for surface segregation, surface reactions including reconstructions, healing of defects, and corrosion. PMID:25816927

  5. Photothermal imaging of damage and undercutting to gold-coated Kapton samples exposed to atomic oxygen

    NASA Astrophysics Data System (ADS)

    Williams, A. W.; Wood, N. J.

    1996-09-01

    In this paper we describe the design and construction of a laser-based photothermal imaging system, which we have used to evaluate damage to gold-coated Kapton samples that have been exposed to atomic oxygen in a laboratory atomic oxygen source. This exposure simulates the erosive effects of atomic oxygen on spacecraft materials in low Earth orbits. In particular, thermal wave imaging studies have been carried out for materials that are susceptible to atomic oxygen erosion. The photothermal imaging method is sensitive to invisible subsurface features such as the delamination of barrier coatings used to protect vulnerable substrates.

  6. Adsorption of oxygen atom on MoSi2 (110) surface

    NASA Astrophysics Data System (ADS)

    Sun, S. P.; Li, X. P.; Wang, H. J.; Jiang, Y.; Yi, D. Q.

    2016-09-01

    The adsorption energy, structural relaxation and electronic properties of oxygen atom on MoSi2 (110) surface have been investigated by first-principles calculations. The energetic stability of MoSi2 low-index surfaces was analyzed, and the results suggested that MoSi2 (110) surface had energetically stability. The site of oxygen atom adsorbed on MoSi2 (110) surface were discussed, and the results indicated that the preference adsorption site of MoSi2 (110) surface for oxygen atom was H site (hollow position). Our calculated work should help to understand further the interaction between oxygen atoms and MoSi2 surfaces.

  7. Reactions of atomic oxygen with the chlorate ion and the perchlorate ion

    NASA Astrophysics Data System (ADS)

    Anan'ev, Vladimir; Miklin, Mikhail; Kriger, Ludmila

    2014-06-01

    The reactions of the chlorate ion with atomic oxygen formed under photolysis of the nitrate ion introduced to potassium chlorate crystal by co-crystallization were studied by optical and infrared absorption spectroscopy. The perchlorate ion was found to form in solids as product of addition reaction of singlet atomic oxygen, formed under dissociation of the peroxynitrite ion - the product of isomerization of the excited nitrate ion. Triplet atomic oxygen does not react with the chlorate ion. The atomic oxygen formed under photolysis of the nitrate ion introduced to potassium perchlorate crystal by co-crystallization does not react with the perchlorate ion.

  8. Resonant energy transfer from argon dimers to atomic oxygen in microhollow cathode discharges

    NASA Astrophysics Data System (ADS)

    Moselhy, M.; Stark, R. H.; Schoenbach, K. H.; Kogelschatz, U.

    2001-02-01

    The emission of atomic oxygen lines at 130.2 and 130.5 nm from a microhollow cathode discharge in argon with oxygen added indicates resonant energy transfer from argon dimers to oxygen atoms. The internal efficiency of the vacuum-ultraviolet (VUV) radiation was measured as 0.7% for a discharge in 1100 Torr argon with 0.1% oxygen added. The direct current VUV point source operates at voltages below 300 V and at current levels of milliamperes.

  9. Oxidation of silicon and germanium by atomic and molecular oxygen

    NASA Astrophysics Data System (ADS)

    Kisa, Maja

    2007-12-01

    Space vehicles residing in the low Earth orbit (LEO) are exposed to a harsh environment that rapidly degrades their materials. The LEO ranges from 200-700km in altitude from the Earth's surface, and the temperature varies between 200 and 400K. The most hazardous species in LEO is atomic oxygen (AO) containing 5eV kinetic energy due to the high velocity of the spacecrafts (8km/s). The goal of this research is the elucidation of the fundamental mechanisms of semiconductor degradation and passivation in LEO conditions by comparing the structural differences in the oxide films created by exposure to AO and molecular oxygen (MO). Silicon is the base material for solar cells used in LEO whereas Ge and SiOx films are common coatings to protect polymer materials that are used as structural materials in spacecrafts. Hyperthermal AO was created by the laser detonation of MO within a high vacuum (HV) chamber, that produces a high flux of AO. A variety of nano-characterization techniques, including high resolution transmission electron microscopy (HREM), and electron energy loss spectroscopy (EELS) were used to determine the microstructure and local chemistry of the oxide and the oxide/semiconductor interface. For Si, the amorphous silica formed by AO was nearly twice as thick, more ordered, and more homogeneous in composition, than the oxide formed by MO. The Si/SiOx interface formed by AO was atomically abrupt, with no suboxides detected near the interface or throughout the oxide. The oxide scale formed by MO on Si(100) consisted of transitional oxidation states. The oxide film formed on Ge(100) due to exposure to 5eV AO, is 2-3 times thicker and similarly to the Si/SiOx interfaces, the Ge/GeOx interface was found to be atomically abrupt. The oxidation kinetics of Si and Ge were monitored in situ using a research quartz crystal microbalance (RQCM) that was incorporated into the AO source. The oxidation kinetics in hyperthermal AO did not follow the standard linear to

  10. Durability of Environmental Barrier Coatings in a Water Vapor/Oxygen Environment

    NASA Technical Reports Server (NTRS)

    Holchin, John E.

    2004-01-01

    Silicon carbide (Sic) and silicon nitride (Si3N4) show potential for application in the hot sections of advanced jet engines. The oxidation behavior of these materials has been studied in great detail. In a pure oxygen environment, a silica (SiO2) layer forms on the surface and provides protection from further oxidation. Initial oxidation is rapid, but slows as silica layer grows; this is known as parabolic oxidation. When exposed to model fuel-lean combustion applications (standard in jet engines), wherein the partial pressure of water vapor is approximately 0.5 atm., these materials exhibit different characteristics. In such an environment, the primary oxidant to form silica is water vapor. At the same time, water vapor reacts with the surface oxide to form gaseous silicon hydroxide (Si(OH)4). The simultaneous formation of both silica and Si(OH)4 -the latter which is lost to the atmosphere- the material continues to recede. Recession rates for uncoated Sic and Si3N4 are unacceptably high, for use in jet engines, - on the order of 1mm/4000h. External coatings have been developed that protect Si-based materials from water vapor attack. One such coating consists of a Ba(0.75)Sr(0.25)Al2Si2O8 (BSAS) topcoat, a mullite/BSAS intermediate layer and a Si bond coat. The key function of the topcoat is to protect the Si-base material from water vapor; therefore it must be fairly stable in water vapor (recession rate of about 1mm/40,000h) and remain crack free. Although BSAS is much more resistant to water vapor attack than pure silica, it exhibits a linear weight loss in 50% H2O - 50% O2 at 1500 C. The objective of my research is to determine the oxidation behavior of a number of alternate hot-pressed monolithic top coat candidates. Potential coatings were exposed at 1500 C to a 50% H2O - 50% O2 gas mixture flowing at 4.4 cm/s . These included rare- earth silicates, barium-strontium aluminosilicates. When weight changes were measured with a continuously recording

  11. Effect of Solar Exposure on the Atomic Oxygen Erosion of Hubble Space Telescope Aluminized-Teflon Thermal Shields

    NASA Technical Reports Server (NTRS)

    Guo, Aobo; Ashmead, Claire C.; deGroh, Kim K.

    2012-01-01

    When exposed to low Earth orbital (LEO) environment, external spacecraft materials degrade due to radiation, thermal cycling, micrometeoroid and debris impacts, and atomic oxygen (AO) interaction. Collisions between AO and spacecraft can result in oxidation of external spacecraft surface materials, which can lead to erosion and severe structural and/or optical property deterioration. It is therefore essential to understand the AO erosion yield (Ey), the volume loss per incident oxygen atom (cu cm/atom), of polymers to assure durability of spacecraft materials. The objective of this study was to determine whether solar radiation exposure can increase the rate of AO erosion of polymers in LEO. The material studied was a section of aluminized-Teflon (DuPont) fluorinated ethylene propylene (Al-FEP) thermal shield exposed to space on the Hubble Space Telescope (HST) for 8.25 years. Retrieved samples were sectioned from the circular thermal shield and exposed to ground laboratory thermal energy AO. The results indicate that the average Ey of the solar facing HST Al-FEP was 1.9 10(exp -24)cu cm/atom, while the average Ey of the anti-solar HST Al-FEP was 1.5 10(exp -24)cu cm/atom. The Ey of the pristine samples was 1.6- 1.7 10(exp -24)cu cm/atom. These results indicate that solar exposure affects the post-flight erosion rate of FEP in a plasma asher. Therefore, it likely affects the erosion rate while in LEO.

  12. Beneficial Role of Copper in the Enhancement of Durability of Ordered Intermetallic PtFeCu Catalyst for Electrocatalytic Oxygen Reduction.

    PubMed

    Arumugam, Balamurugan; Tamaki, Takanori; Yamaguchi, Takeo

    2015-08-01

    Design of Pt alloy catalysts with enhanced activity and durability is a key challenge for polymer electrolyte membrane fuel cells. In the present work, we compare the durability of the ordered intermetallic face-centered tetragonal (fct) PtFeCu catalyst for the oxygen reduction reaction (ORR) relative to its counterpart bimetallic catalysts, i.e., the ordered intermetallic fct-PtFe catalyst and the commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. Although both fct catalysts initially exhibited an ordered structure and mass activity approximately 2.5 times higher than that of TKK-Pt/C, the presence of Cu at the ordered intermetallic fct-PtFeCu catalyst led to a significant enhancement in durability compared to that of the ordered intermetallic fct-PtFe catalyst. The ordered intermetallic fct-PtFeCu catalyst retained more than 70% of its mass activity and electrochemically active surface area (ECSA) over 10 000 durability cycles carried out at 60 °C. In contrast, the ordered intermetallic fct-PtFe catalyst maintained only about 40% of its activity. The temperature of the durability experiment is also shown to be important: the catalyst was more severely degraded at 60 °C than at room temperature. To obtain insight into the observed enhancement in durability of fct-PtFeCu catalyst, a postmortem analysis of the ordered intermetallic fct-PtFeCu catalyst was carried out using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scan. The STEM-EDX line scans of the ordered intermetallic fct-PtFeCu catalyst over 10 000 durability cycles showed a smaller degree of Fe and Cu dissolution from the catalyst. Conversely, large dissolution of Fe was identified in the ordered intermetallic fct-PtFe catalyst, indicating a lesser retention of Fe that causes the destruction of ordered structure and gives rise to poor durability. The enhancement in the durability of the ordered intermetallic fct-PtFeCu catalyst is ascribed to

  13. Evaluation of atomic oxygen resistant protective coatings for fiberglass-epoxy composites in LEO

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Paulsen, Phillip E.; Brady, Joyce A.

    1989-01-01

    Fiberglass-epoxy composite masts are the prime structural members for the Space Station Freedom solar array. At the altitude where Space Station Freedom will operate, atomic oxygen atoms are the most predominant species. Atomic oxygen is highly reactive and has been shown to oxidize organic and some metallic materials. Tests with random and directed atomic oxygen exposure have shown that the epoxy is removed from the composite exposing brittle glass fibers which could be easily removed from the surface where they could contaminate Space Station Freedom Systems. Protection or fiber containment systems; inorganic based paints, aluminum braid, and a metal coating; were evaluated for resistance to atomic oxygen, vacuum ultraviolet radiation, thermal cycling, and mechanical flexing. All appeared to protect well against atomic oxygen and provide fiber containment except for the single aluminum braid covering. UV radiation resistance was acceptable and in general, thermal cycling and flexure had little to no effect on the mass loss rate for most coatings.

  14. Role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films

    SciTech Connect

    Jie, Jin; Morita, Aya; Shirai, Hajime

    2010-08-15

    The role of oxygen atoms in the growth of magnetron sputter-deposited ZnO films was studied by alternating the deposition of a several-nanometer-thick ZnO layer and the O{sub 2}/Ar mixture plasma exposure, i.e., layer-by-layer technique. The film crystallization promoted with suppressing the oxygen vacancy and interstitial defects by adjusting the exposure condition of O{sub 2}/Ar plasma. These findings suggest that the chemical potential of oxygen atom determine the film crystallization as well as the electronic state. The diffusion and effusion of oxygen atoms at the growing surface play a role of thermal annealing, promoted the film crystallization as well as the creation and the annihilation of oxygen and zinc related defects. The role of oxygen atoms reaching at the film-growing surface is discussed in term of chemical annealing. The possible oxygen diffusion mechanism is proposed.

  15. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Peera, S. Gouse; Arunchander, A.; Sahu, A. K.

    2016-07-01

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ~110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and

  16. Synthesis of low color, atomic oxygen resistant polyimides

    NASA Technical Reports Server (NTRS)

    MacInnes, Dave

    1995-01-01

    The purpose of this project was to develop low color, atomic oxygen resistant polyimides for potential applications on spacecraft in low earth orbit. The material is needed in order to protect satellites and spacecraft from the gases and radiation found at those altitudes. Phosphorous containing polyimides have been shown to be especially resistant to corrosion and weight loss under oxygen plasma. Unfortunately the color of these phosphorous containing polyimides is still too high for them to be good heat insulators. While they are not as effective as teflon, the current material of choice. polyimides are much less dense than teflon and would be especially valuable if they could be made with low color. The approach taken was to synthesize a monomer which would contain the elements needed for giving the final polyimide its desired properties. In particular the monomer should incorporate phosphine or phosphine oxides and have bulky side groups to block any color forming charge transfer structures. The target molecule, 3,5-di-(trifluoromethylphenyl)-bis(3-aminophenyl) phosphine oxide, (containing both a phosphine oxide group and a bulky ditrifluoromethylphenyl group) was synthesized via three reactions in overall yield of 21 percent. In addition, a model compound, bis(3-phenylamine) phenyl phosphine oxide, was synthesized two different ways in order to establish the conditions for the nitration of phosphine oxides and their reduction to the amine. Finally, a trisubstituted phosphine oxide was synthesized. In all, seven phosphorus containing organic compounds were synthesized, purified and characterized. The model compound was reacted with oxydiphthalic anhydride to form a polyamic acid with inherent viscosity of 0.34. This material was cast into a film and heated, forming a normally colored fairly strong polyimide with a Tg of 240 C. The target compound was reacted with 6-fluorodiphthalic anhydride to give a polyamic acid with inherent viscosity of 0.19 and cast to

  17. Colour polymeric paints research under atomic oxygen in flight and ground-based experiments

    NASA Astrophysics Data System (ADS)

    Chernik, V. N.; Naumov, S. F.; Sokolova, S. P.; Gerasimova, T. I.; Kurilyonok, A. O.; Poruchikova, Ju. V.; Novikova, V. A.

    2003-09-01

    Three types of colour coatings were tested to atomic oxygen resistance on ground-based and in-flight experiments. The epoxy enamels colouring change and significant mass losses are observed. The effect of atomic oxygen on silicone enamels almost does not change their colouring and mass. Protection of the epoxy enamels by a layer of silicone varnish increases paints resistance.

  18. Calculated values of atomic oxygen fluences and solar exposure on selected surfaces of LDEF

    NASA Technical Reports Server (NTRS)

    Gillis, J. R.; Pippin, H. G.; Bourassa, R. J.; Gruenbaum, P. E.

    1995-01-01

    Atomic oxygen (AO) fluences and solar exposure have been modeled for selected hardware from the Long Duration Exposure Facility (LDEF). The atomic oxygen exposure was modeled using the microenvironment modeling code SHADOWV2. The solar exposure was modeled using the microenvironment modeling code SOLSHAD version 1.0.

  19. Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

    NASA Technical Reports Server (NTRS)

    Beger, Lauren; Roberts, Lily; deGroh, Kim; Banks, Bruce

    2007-01-01

    In the low Earth orbit (LEO) space environment, spacecraft surfaces can be altered during atomic oxygen exposure through oxidation and erosion. There can be terrestrial benefits of such interactions, such as the modification of hydrophobic or hydrophilic properties of polymers due to chemical modification and texturing. Such modification of the surface may be useful for biomedical applications. For example, atomic oxygen texturing may increase the hydrophilicity of polymers, such as chlorotrifluoroethylene (Aclar), thus allowing increased adhesion and spreading of cells on textured Petri dishes. The purpose of this study was to determine the effect of atomic oxygen exposure on the hydrophilicity of nine different polymers. To determine whether hydrophilicity remains static after atomic oxygen exposure or changes with exposure, the contact angles between the polymer and a water droplet placed on the polymer s surface were measured. The polymers were exposed to atomic oxygen in a radio frequency (RF) plasma asher. Atomic oxygen plasma treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Significant decreases in the water contact angle occurred with atomic oxygen exposure. Fluorinated polymers were found to be less sensitive to changes in hydrophilicity for equivalent atomic oxygen exposures, and two of the fluorinated polymers became more hydrophobic. The majority of change in water contact angle of the non-fluorinated polymers was found to occur with very low fluence exposures, indicating potential cell culturing benefit with short treatment time.

  20. Atomic oxygen interaction with solar array blankets at protective coating defect sites

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Auer, Bruce M.; Rutledge, Sharon K.; Hill, Carol M.

    1991-01-01

    Atomic oxygen in the low-Earth-orbital environment oxidizes SiOx protected polyimide Kapton solar array blankets at sites which are not protected such as pin windows or scratches in the protective coatings. The magnitude and shape of the atomic oxygen undercutting which occurs at these sites is dependent upon the exposure environment details such as arrival direction and reaction probability. The geometry of atomic oxygen undercutting at defect sites exposed to atomic oxygen in plasma asher was used to develop a Monte Carlo model to simulate atomic oxygen erosion processes at defect sites in protected Kapton. Comparisons of Monte Carlo predictions and experimental results are presented for plasma asher atomic oxygen exposures for large and small defects as well as for protective coatings on one or both sides of Kapton. The model is used to predict in-space exposure results at defect sites for both directed and sweeping atomic oxygen exposure. A comparison of surface textures predicted by the Monte Carlo model and those experimentally observed from both directed space ram and laboratory plasma asher atomic oxygen exposure indicate substantial agreement.

  1. Atomic oxygen effects measurements for shuttle missions STS-8 and 41-G

    NASA Technical Reports Server (NTRS)

    Visentine, James T. (Compiler)

    1988-01-01

    The effects of the atomic oxygen interactions upon optical coatings, thin metallized films, and advanced spacecraft materials, such as high temperature coatings for infrared optical systems are summarized. Also included is a description of a generic model proposed by JPL, which may explain the atomic oxygen interaction mechanisms that lead to surface recession and weight loss.

  2. Further investigations of experiment A0034 atomic oxygen stimulated outgassing

    NASA Technical Reports Server (NTRS)

    Linton, Roger C.; Finckenor, Miria M.; Kamenetzky, Rachel R.

    1995-01-01

    Thermal control coatings within the recessed compartments of LDEF Experiment A0034 experienced the maximum leading edge fluence of atomic oxygen with considerably less solar UV radiation exposure than top-surface mounted materials of other LDEF experiments on either the leading or the trailing edge. This combination of exposure within A0034 resulted in generally lower levels of darkening attributable to solar UV radiation than for similar materials on other LDEF experiments exposed to greater cumulative solar UV radiation levels. Changes in solar absorptance and infrared thermal emittance of the exposed coatings are thus unique to this exposure. Analytical results for other applications have been found for environmentally induced changes in fluorescence, surface morphology, light scattering, and the effects of coating outgassing products on adjacent mirrors and windows of the A0034 experiment. Some atmospheric bleaching of the thermal control coatings, in addition to that presumably experience during reentry and recovery operations, has been found since initial post-flight observations and measurements.

  3. Low-Energy Elastic Electron Scattering by Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Zatsarinny O.; Bartschat, K.; Tayal, S. S.

    2006-01-01

    The B-spline R-matrix method is employed to investigate the low-energy elastic electron scattering by atomic oxygen. Flexible non-orthogonal sets of radial functions are used to construct the target description and to represent the scattering functions. A detailed investigation regarding the dependence of the predicted partial and total cross sections on the scattering model and the accuracy of the target description is presented. The predicted angle-integrated elastic cross sections are in good agreement with experiment, whereas significant discrepancies are found in the angle-differential elastic cross sections near the forward direction. .The near-threshold results are found to strongly depend on the treatment of inner-core short-range correlation effects in the target description, as well as on a proper account of the target polarizability. A sharp increase in the elastic cross sections below 1 eV found in some earlier calculations is judged to be an artifact of an unbalanced description of correlation in the N-electron target structure and the (N+l)-electron-collision problems.

  4. Model of spacecraft atomic oxygen and solar exposure microenvironments

    NASA Technical Reports Server (NTRS)

    Bourassa, R. J.; Pippin, H. G.

    1993-01-01

    Computer models of environmental conditions in Earth orbit are needed for the following reasons: (1) derivation of material performance parameters from orbital test data, (2) evaluation of spacecraft hardware designs, (3) prediction of material service life, and (4) scheduling spacecraft maintenance. To meet these needs, Boeing has developed programs for modeling atomic oxygen (AO) and solar radiation exposures. The model allows determination of AO and solar ultraviolet (UV) radiation exposures for spacecraft surfaces (1) in arbitrary orientations with respect to the direction of spacecraft motion, (2) overall ranges of solar conditions, and (3) for any mission duration. The models have been successfully applied to prediction of experiment environments on the Long Duration Exposure Facility (LDEF) and for analysis of selected hardware designs for deployment on other spacecraft. The work on these models has been reported at previous LDEF conferences. Since publication of these reports, a revision has been made to the AO calculation for LDEF, and further work has been done on the microenvironments model for solar exposure.

  5. Hydrogen abstraction from the hydrazine molecule by an oxygen atom.

    PubMed

    Spada, Rene F K; Ferrão, Luiz F A; Rocha, Roberta J; Iha, Koshun; Rocco, José A F F; Roberto-Neto, Orlando; Lischka, Hans; Machado, Francisco B C

    2015-03-01

    Thermochemical and kinetics properties of the hydrogen abstraction from the hydrazine molecule (N2H4) by an oxygen atom were computed using high-level ab initio methods and the M06-2X DFT functional with aug-cc-pVXZ (X = T, Q) and maug-cc-pVTZ basis sets, respectively. The properties along the reaction path were obtained using the dual-level methodology to build the minimum energy path with the potential energy surface obtained with the M06-2X method and thermochemical properties corrected with the CCSD(T)/CBS//M06-2X/maug-cc-pVTZ results. The thermal rate constants were calculated in the framework of variational transition-state theory. Wells on both sides of the reaction (reactants and products) were found and considered in the chemical kinetics calculations. Additionally, the product yields were investigated by means of a study of the triplet and singlet surfaces of the N2H4 + O → N2H2 + H2O reaction.

  6. An Atmospheric Atomic Oxygen Source for Cleaning Smoke Damaged Art Objects

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Norris, Mary Jo

    1998-01-01

    Soot and other carbonaceous combustion products deposited on the surfaces of porous ceramic, stone, ivory and paper can be difficult to remove and can have potentially unsatisfactory results using wet chemical and/or abrasive cleaning techniques. An atomic oxygen source which operates in air at atmospheric pressure, using a mixture of oxygen and helium, has been developed to produce an atomic oxygen beam which is highly effective in oxidizing soot deposited on surfaces by burning candles made of paraffin, oil or rendered animal fat. Atomic oxygen source operating conditions and the results of cleaning soot from paper, gesso, ivory, limestone and water color-painted limestone are presented,

  7. Vacuum Ultraviolet Absorption Measurements of Atomic Oxygen in a Shock Tube

    NASA Technical Reports Server (NTRS)

    Meyer, Scott Andrew

    1995-01-01

    The absorption of vacuum ultraviolet light by atomic oxygen has been measured in the Electric Arc-driven Shock Tube (EAST) Facility at NASA-Ames Research Center. This investigation demonstrates the instrumentation required to determine atomic oxygen concentrations from absorption measurements in impulse facilities. A shock wave dissociates molecular oxygen, producing a high temperature sample of atomic oxygen in the shock tube. A probe beam is generated with a Raman-shifted ArF excimer laser. By suitable tuning of the laser, absorption is measured over a range of wavelengths in the region of the atomic line at 130.49 nm. The line shape function is determined from measurements at atomic oxygen densities of 3 x 10(exp 17) and 9 x 10(exp 17) cm(exp -3). The broadening coefficient for resonance interactions is deduced from this data, and this value is in accord with available theoretical models.

  8. Vacuum Ultraviolet Absorption Measurements of Atomic Oxygen in a Shock Tube

    NASA Technical Reports Server (NTRS)

    Meyer, Scott Andrew

    1995-01-01

    The absorption of vacuum ultraviolet light by atomic oxygen has been measured in the Electric Arc-driven Shock Tube (EAST) Facility at NASA-Ames Research Center. This investigation demonstrates the instrumentation required to determine atomic oxygen concentrations from absorption measurements in impulse facilities. A shock wave dissociates molecular oxygen, producing a high temperature sample of atomic oxygen in the shock tube. A probe beam is generated with a Raman-shifted ArF excimer laser. By suitable tuning of the laser, absorption is measured over a range of wavelengths in the region of the atomic line at 130.49 nm. The line shape function is determined from measurements at atomic oxygen densities of 3x10(exp 17) and 9x10(exp 17) cm(exp -3). The broadening coefficient for resonance interactions is deduced from this data, and this value is in accord with available theoretical models.

  9. Monte Carlo Computational Modeling of the Energy Dependence of Atomic Oxygen Undercutting of Protected Polymers

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Stueber, Thomas J.; Norris, Mary Jo

    1998-01-01

    A Monte Carlo computational model has been developed which simulates atomic oxygen attack of protected polymers at defect sites in the protective coatings. The parameters defining how atomic oxygen interacts with polymers and protective coatings as well as the scattering processes which occur have been optimized to replicate experimental results observed from protected polyimide Kapton on the Long Duration Exposure Facility (LDEF) mission. Computational prediction of atomic oxygen undercutting at defect sites in protective coatings for various arrival energies was investigated. The atomic oxygen undercutting energy dependence predictions enable one to predict mass loss that would occur in low Earth orbit, based on lower energy ground laboratory atomic oxygen beam systems. Results of computational model prediction of undercut cavity size as a function of energy and defect size will be presented to provide insight into expected in-space mass loss of protected polymers with protective coating defects based on lower energy ground laboratory testing.

  10. Vacuum Ultraviolet Absorption Measurements of Atomic Oxygen in a Shock Tube

    NASA Technical Reports Server (NTRS)

    Meyer, Scott Andrew

    1995-01-01

    The absorption of vacuum ultraviolet light by atomic oxygen has been measured in the Electric Arc-driven Shock Tube (EAST) Facility at NASA-Ames Research Center. This investigation demonstrates the instrumentation required to determine atomic oxygen concentrations from absorption measurements in impulse facilities. A shock wave dissociates molecular oxygen, producing a high temperature sample of atomic oxygen in the shock tube. A probe beam is generated with a Raman-shifted ArF excimer laser. By suitable tuning of the laser, absorption is measured over a range of wavelengths in the region of the atomic line at 130.49 nm. The line shape function is determined from measurements at atomic oxygen densities of 3 x 10(exp 17) and 9 x 10(exp 17)/cu cm. The broadening coefficient for resonance interactions is deduced from this data, and this value is in accord with available theoretical models.

  11. Development of a Supersonic Atomic Oxygen Nozzle Beam Source for Crossed Beam Scattering Experiments

    DOE R&D Accomplishments Database

    Sibener, S. J.; Buss, R. J.; Lee, Y. T.

    1978-05-01

    A high pressure, supersonic, radio frequency discharge nozzle beam source was developed for the production of intense beams of ground state oxygen atoms. An efficient impedance matching scheme was devised for coupling the radio frequency power to the plasma as a function of both gas pressure and composition. Techniques for localizing the discharge directly behind the orifice of a water-cooled quartz nozzle were also developed. The above combine to yield an atomic oxygen beam source which produces high molecular dissociation in oxygen seeded rare gas mixtures at total pressures up to 200 torr: 80 to 90% dissociation for oxygen/argon mixtures and 60 to 70% for oxygen/helium mixtures. Atomic oxygen intensities are found to be greater than 10{sup 17} atom sr{sup -1} sec{sup -1}. A brief discussion of the reaction dynamics of 0 + IC1 ..-->.. I0 + C1 is also presented.

  12. A spectral study of a radio-frequency plasma-generated flux of atomic oxygen

    NASA Technical Reports Server (NTRS)

    Batten, Carmen E.; Brown, Kenneth G.; Lewis, Beverley W.

    1994-01-01

    The active environment of a radio-frequency (RF) plasma generator, with and without low-pressure oxygen, has been characterized through the identification of emission lines in the spectral region from 250 to 900 nm. The environment is shown to be dependent on the partial pressure of oxygen and the power applied to the RF generator. Atomic oxygen has been found in significant amounts as well as atomic hydrogen and the molecular oxygen species O2((sup 1)Sigma). The only charged species observed was the singly charged molecular ion O2(+). With a polymer specimen in the plasma chamber, carbon monoxide was also observed. The significance of these observations with respect to previous studies using this type of generator to stimulate material degradation in space is discussed. The possibility of using these generators as atomic oxygen sources in the development of oxygen atom fluorescence sensors is explored.

  13. Materials selection for long life in low earth orbit - A critical evaluation of atomic oxygen testing with thermal atom systems

    NASA Technical Reports Server (NTRS)

    Koontz, S. L.; Albyn, K.; Leger, L.

    1990-01-01

    The use of thermal atom test methods as a materials selection and screening technique for low-earth orbit (LEO) spacecraft is critically evaluated. The chemistry and physics of thermal atom environments are compared with the LEO environment. The relative reactivities of a number of materials determined in thermal atom environments are compared with those observed in LEO and in high-quality LEO simulations. Reaction efficiencies (cu cm/atom) measured in a new type of thermal atom apparatus are one-thousandth to one ten-thousandth those observed in LEO, and many materials showing nearly identical reactivities in LEO show relative reactivities differing by as much as a factor of eight in thermal atom systems. A simple phenomenological kinetic model for the reaction of oxygen atoms with organic materials can be used to explain the differences in reactivity in different environments. Certain speciic thermal atom test environments can be used as reliable materials screening tools.

  14. Thermochemical analyses of the oxidative vaporization of metals and oxides by oxygen molecules and atoms

    NASA Technical Reports Server (NTRS)

    Kohl, F. J.; Leisz, D. M.; Fryburg, G. C.; Stearns, C. A.

    1977-01-01

    Equilibrium thermochemical analyses are employed to describe the vaporization processes of metals and metal oxides upon exposure to molecular and atomic oxygen. Specific analytic results for the chromium-, platinum-, aluminum-, and silicon-oxygen systems are presented. Maximum rates of oxidative vaporization predicted from the thermochemical considerations are compared with experimental results for chromium and platinum. The oxidative vaporization rates of chromium and platinum are considerably enhanced by oxygen atoms.

  15. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Peera, S. Gouse; Arunchander, A.; Sahu, A. K.

    2016-07-01

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ~110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and

  16. The reaction pathways of the oxygen plasma pulse in the hafnium oxide atomic layer deposition process

    SciTech Connect

    Jeon, Hyeongtag; Won, Youngdo

    2008-09-22

    The plasma enhanced atomic layer deposition process for the HfO{sub 2} thin film is modeled as simple reactions between Hf(OH){sub 3}NH{sub 2} and reactive oxygen species. The density functional theory calculation was performed for plausible reaction pathways to construct the reaction profile. While the triplet molecular oxygen is unlikely to form a reactive complex, the singlet molecular oxygen forms the stable adduct that goes through the transition state and completes the reaction pathway to the products. Either two singlet or two triplet oxygen atoms make the singlet adduct complex, which follows the same pathway to the product as the singlet molecular oxygen reacts.

  17. Exposure of LDEF materials to atomic oxygen: Results of EOIM 3

    NASA Technical Reports Server (NTRS)

    Jaggers, C. H.; Meshishnek, M. J.

    1995-01-01

    The third Effects of Oxygen Atom Interaction with Materials (EOIM 3) experiment flew on STS-46 from July 31 to August 8, 1992. The EOIM-3 sample tray was exposed to the low-earth orbit space environment for 58.55 hours at an altitude of 124 nautical miles resulting in a calculated total atomic oxygen (AO) fluence of 1.99 x 10(exp 20) atoms/sq cm. Five samples previously flown on the Long Duration Exposure Facility (LDEF) Experiment M0003 were included on the Aerospace EOIM 3 experimental tray: (1) Chemglaze A276 white thermal control paint from the LDEF trailing edge (TE); (2) S13GLO white thermal control paint from the LDEF TE; (3) S13GLO from the LDEF leading edge (LE) with a visible contamination layer from the LDEF mission; (4) Z306 black thermal control paint from the LDEF TE with a contamination layer from the LDEF mission; and (5) anodized aluminum from the LDEF TE with a contamination layer from the LDEF mission. The purpose of this experiment was twofold: (l) investigate the response of trailing edge LDEF materials to atomic oxygen exposure, thereby simulating LDEF leading edge phenomena; (2) investigate the response of contaminated LDEF samples to atomic oxygen in attempts to understand LDEF contamination-atomic oxygen interactions. This paper describes the response of these materials to atomic oxygen exposure, and compares the results of the EOIM 3 experiment to the LDEF mission and to ground-based atomic oxygen exposure studies.

  18. Development of a chemical oxygen - iodine laser with production of atomic iodine in a chemical reaction

    SciTech Connect

    Censky, M; Spalek, O; Jirasek, V; Kodymova, J; Jakubec, I

    2009-11-30

    The alternative method of atomic iodine generation for a chemical oxygen - iodine laser (COIL) in chemical reactions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied. (lasers)

  19. Materials preparation and longevity in hyperthermal atomic oxygen

    NASA Technical Reports Server (NTRS)

    Bareiss, Lyle E.; Sjolander, Gary P.; Gregory, John C.

    1987-01-01

    Flight hardware fabrication, the design and fabrication of an atom beam source, construction of a surface science laboratory, and progress in research on processes and mechanisms of interaction of hyperthermal atoms at solid surfaces are discussed.

  20. Neutral atomic oxygen beam produced by ion charge exchange for Low Earth Orbital (LEO) simulation

    NASA Technical Reports Server (NTRS)

    Banks, Bruce; Rutledge, Sharon; Brdar, Marko; Olen, Carl; Stidham, Curt

    1987-01-01

    A low energy neutral atomic oxygen beam system was designed and is currently being assembled at the Lewis Research Center. The system utilizes a 15 cm diameter Kaufman ion source to produce positive oxygen ions which are charge exchange neutralized to produce low energy (variable from 5 to 150 eV) oxygen atoms at a flux simulating real time low Earth orbital conditions. An electromagnet is used to direct only the singly charged oxygen ions from the ion source into the charge exchange cell. A retarding potential grid is used to slow down the oxygen ions to desired energies prior to their charge exchange. Cryogenically cooled diatomic oxygen gas in the charge exchange cell is then used to transfer charge to the oxygen ions to produce a neutral atomic oxygen beam. Remaining non-charge exchanged oxygen ions are then swept from the beam by electromagnetic or electrostatic deflection depending upon the desired experiment configuration. The resulting neutral oxygen beam of 5 to 10 cm in diameter impinges upon target materials within a sample holder fixture that can also provide for simultaneous heating and UV exposure during the atomic oxygen bombardment.

  1. Atomic structures and oxygen dynamics of CeO2 grain boundaries

    NASA Astrophysics Data System (ADS)

    Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi

    2016-02-01

    Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells.

  2. Atomic structures and oxygen dynamics of CeO2 grain boundaries

    PubMed Central

    Feng, Bin; Sugiyama, Issei; Hojo, Hajime; Ohta, Hiromichi; Shibata, Naoya; Ikuhara, Yuichi

    2016-01-01

    Material performance is significantly governed by grain boundaries (GBs), a typical crystal defects inside, which often exhibit unique properties due to the structural and chemical inhomogeneity. Here, it is reported direct atomic scale evidence that oxygen vacancies formed in the GBs can modify the local surface oxygen dynamics in CeO2, a key material for fuel cells. The atomic structures and oxygen vacancy concentrations in individual GBs are obtained by electron microscopy and theoretical calculations at atomic scale. Meanwhile, local GB oxygen reduction reactivity is measured by electrochemical strain microscopy. By combining these techniques, it is demonstrated that the GB electrochemical activities are affected by the oxygen vacancy concentrations, which is, on the other hand, determined by the local structural distortions at the GB core region. These results provide critical understanding of GB properties down to atomic scale, and new perspectives on the development strategies of high performance electrochemical devices for solid oxide fuel cells. PMID:26838958

  3. Oxygen Atom Adsorption on and Diffusion into Nb(110) and Nb(100) from First Principles

    SciTech Connect

    Tafen, De Nyago; Gao, Michael C

    2013-11-01

    In order to understand the dynamics of oxidation of Nb, we examine the adsorption, absorption, and diffusion of an oxygen atom on, in, and into Nb(110) and Nb(100) surfaces, respectively, using density functional theory. Our calculations predict that the oxygen atom adsorbs on the threefold site on Nb(110) and the fourfold hollow site on Nb(100), and the adsorption energy is -5.08 and -5.18 eV respectively. We find the long and short bridge sites to be transition states for O diffusion on Nb(110), while the on top site is a rank-2 saddle point. In the subsurface region, the oxygen atom prefers the octahedral site, as in bulk niobium. Our results also show that the O atom is more stable on Nb(110) subsurface than on Nb(100) subsurface. The diffusion of oxygen atoms into niobium surfaces passes through transition states where the oxygen atom is coordinated to four niobium atoms. The diffusion barriers of the oxygen atom into Nb(110) and Nb(100) are 1.81 and 2.05 eV, respectively. Analysis of the electronic density of states reveals the emergence of well localized electronic states below the lowest states of clean Nb surfaces due to d-p orbital hybridization.

  4. Comparison of the Atomic Oxygen Erosion Depth and Cone Height of Various Materials at Hyperthermal Energy

    NASA Technical Reports Server (NTRS)

    Waters, Deborah L.; Banks, Bruce A.; Thorson, Stephen D.; deGroh, Kim, K.; Miller, Sharon K.

    2007-01-01

    Atomic oxygen readily reacts with most spacecraft polymer materials exposed to the low Earth orbital (LEO) environment. If the atomic oxygen arrival comes from a fixed angle of impact, the resulting erosion will foster the development of a change in surface morphology as material thickness decreases. Hydrocarbon and halopolymer materials, as well as graphite, are easily oxidized and textured by directed atomic oxygen in LEO at energies of approx.4.5 eV. What has been curious is that the ratio of cone height to erosion depth is quite different for different materials. The formation of cones under fixed direction atomic oxygen attack may contribute to a reduction in material tensile strength in excess of that which would occur if the cone height to erosion depth ratio was very low because of greater opportunities for crack initiation. In an effort to understand how material composition affects the ratio of cone height to erosion depth, an experimental investigation was conducted on 18 different materials exposed to a hyperthermal energy directed atomic oxygen source (approx.70 eV). The materials were first salt-sprayed to provide microscopic local areas that would be protected from atomic oxygen. This allowed erosion depth measurements to be made by scanning microscopy inspection. The polymers were then exposed to atomic oxygen produced by an end Hall ion source that was operated on pure oxygen. Samples were exposed to an atomic oxygen effective fluence of 1.0x10(exp 20) atoms/sq cm based on Kapton H polyimide erosion. The average erosion depth and average cone height were determined using field emission scanning electron microscopy (FESEM). The experimental ratio of average cone height to erosion depth is compared to polymer composition and other properties.

  5. Vibrational Relaxation of Ground-State Oxygen Molecules With Atomic Oxygen and Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Saran, D. V.; Pejakovic, D. A.; Copeland, R. A.

    2008-12-01

    Vertical water vapor profiles are key to understanding the composition and energy budget in the mesosphere and lower thermosphere (MLT). The SABER instrument onboard NASA's TIMED satellite measures such profiles by detecting H2O(ν2) emission in the 6.8 μm region. Collisional deactivation of vibrationally excited O2, O2(X3Σ-g, υ = 1) + H2O ↔ O2(X3Σ-g, υ = 0) + H2O(ν2), is an important source of H2O(ν2). A recent study has identified two other processes involving excited O2 that control H2O(ν2) population in the MLT: (1) the vibrational-translational (V-T) relaxation of O2(X3Σ-g, υ = 1) level by atomic oxygen and (2) the V-V exchange between CO2 and excited O2 molecules [1]. Over the past few years SRI researchers have measured the atomic oxygen removal process mentioned above at room temperature [2] and 240 K [3]. These measurements have been incorporated into the models for H2O(ν2) emission [1]. Here we report laboratory studies of the collisional removal of O2(X3Σ-g, υ = 1) by O(3P) at room temperature and below, reaching temperatures relevant to mesopause and polar summer MLT (~150 K). Instead of directly detecting the O2(X3Σ-g, υ = 1) population, a technically simpler approach is used in which the υ = 1 level of the O2(a1Δg) state is monitored. A two-laser method is employed, in which the pulsed output of the first laser near 285 nm photodissociates ozone to produce atomic oxygen and O2(a1Δg, υ = 1), and the pulsed output of the second laser detects O2(a1Δg, υ = 1) via resonance-enhanced multiphoton ionization. With ground-state O2 present, owing to the rapid equilibration of the O2(X3Σ-g, υ = 1) and O2(a1Δg, υ = 1) populations via the processes O2(a1Δg, υ = 1) + O2(X3Σ-g, υ = 0) ↔ O2(a1Δg, υ = 0) + O2(X3Σ-g, υ = 1), the information on the O2(X3Σ-g, υ = 1) kinetics is extracted from the O2(a1Δg, υ = 1) temporal evolution. In addition, measurements of the removal of O2(X3Σ-g, υ = 1) by CO2 at room temperature will also

  6. Performance and properties of atomic oxygen protective coatings for polymeric materials

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Lamoreaux, Cynthia

    1992-01-01

    Such large LEO spacecraft as the Space Station Freedom will encounter high atomic oxygen fluences which entail the use of protective coatings for their polymeric structural materials. Such coatings have demonstrated polymer mass losses due to oxidation that are much smaller than those of unprotected materials. Attention is here given to protective and/or electrically conductive coatings of SiO(x), Ge, and indium-tin oxide which have been exposed to atomic oxygen in order to ascertain mass loss, electrical conductivity, and optical property dependence on atomic oxygen exposure.

  7. Low Earth orbital atomic oxygen micrometeoroid, and debris interactions with photovoltaic arrays

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Degroh, Kim K.

    1991-01-01

    Polyimide Kapton solar array blankets can be protected from atomic oxygen in low earth orbit if SiO sub x thin film coatings are applied to their surfaces. The useful lifetime of a blanket protected in this manner strongly depends on the number and size of defects in the protective coatings. Atomic oxygen degradation is dominated by undercutting at defects in protective coatings caused by substrate roughness and processing rather than micrometeoroid or debris impacts. Recent findings from the Long Duration Exposure Facility (LDEF) and ground based studies show that interactions between atomic oxygen and silicones may cause grazing and contamination problems which may lead to solar array degradation.

  8. Oxygen dayglow emissions as proxies for atomic oxygen and ozone in the mesosphere and lower thermosphere

    NASA Astrophysics Data System (ADS)

    Yankovsky, Valentine A.; Martyshenko, Kseniia V.; Manuilova, Rada O.; Feofilov, Artem G.

    2016-09-01

    The main goal of this study is to propose and then to justify a set of methods for retrieving the [O] and [O3] altitude distributions from the observation of emissions of the excited oxygen molecules and O(1D) atom at daytime in the mesosphere and lower thermosphere (MLT) region. In other words, we propose retrieving the [O] and [O3] using the proxies. One of the main requirements for the proxy is that the measured value should be directly related to a variable of our interest while, at the same time, the influence of the proxies on [O3] and [O(3P)] should be minimal. For a comprehensive analysis of different O3 and O(3P) proxies, we use a full model of electronic vibrational kinetics of excited products of O3 and O2 photolysis in the MLT of the Earth. Based on this model, we have tested five excited components; namely, O2(b1Σg+, v = 0, 1, 2), O2(a1Δg , v = 0) and O(1D) as the [O3] and [O(3P)] proxies in the MLT region. Using an analytical approach to sensitivity studies and uncertainty analysis, we have therefore developed the following methods of [O(3P)] and [O3] retrieval, which utilise electronic-vibrational transitions from the oxygen molecule second singlet level (O2(b1 Σg+, v = 0, 1, 2). We conclude that O2(b1 Σg+, v = 2) and O2(b1 Σg+, v = 0) are preferable proxies for [O(3P)] retrieval in the altitude range of 90-140 km, while O2(b1 Σg+, v = 1) is the best proxy for [O3] retrieval in the altitude range of 50-98 km.

  9. The Effect of Low Earth Orbit Atomic Oxygen Exposure on Phenylphosphine Oxide-Containing Polymers

    NASA Technical Reports Server (NTRS)

    Connell, John W.

    2000-01-01

    Thin films of phenylphosphine oxide-containing polymers were exposed to low Earth orbit aboard a space shuttle flight (STS-85) as part of flight experiment designated Evaluation of Space Environment and Effects on Materials (ESEM). This flight experiment was a cooperative effort between the NASA Langley Research Center (LaRC) and the National Space Development Agency of Japan (NASDA). The thin film samples described herein were part of an atomic oxygen exposure experiment (AOE) and were exposed to primarily atomic oxygen (1 X 1019 atoms/cm2). The thin film samples consisted of three phosphine oxide containing polymers (arylene ether, benzimidazole and imide). Based on post-flight analyses using atomic force microscopy, X-ray photoelectron spectroscopy, and weight loss data, it was found that atomic oxygen exposure of these materials efficiently produces a phosphate layer at the surface of the samples. This layer provides a barrier towards further attack by AO. Consequently, these materials do not exhibit linear erosion rates which is in contrast with most organic polymers. Qualitatively, the results obtained from these analyses compare favorably with those obtained from samples exposed to atomic oxygen and or oxygen plasma in ground based exposure experiments. The results of the low Earth orbit atomic oxygen exposure on these materials will be compared with those of ground based exposure to AO.

  10. Poly(arylene ether)s That Resist Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Connell, John W.; Hergenrother, Paul; Smith, Joseph G., Jr.

    1994-01-01

    Novel poly(arylene ether)s containing phosphine oxide (PAEPO's) made via aromatic nucleophilic displacement reactions of activated aromatic dihalides (or, in some cases, activated aromatic dinitro compounds) with new bisphenol monomers containing phosphine oxide. Exhibited favorable combination of physical and mechanical properties and resistance to monatomic oxygen in oxygen plasma environment. Useful as adhesives, coatings, films, membranes, moldings, and composite matrices.

  11. The interstellar oxygen crisis, or where have all the oxygen atoms gone?

    NASA Astrophysics Data System (ADS)

    Wang, Shu; Li, Aigen; Jiang, B. W.

    2015-11-01

    The interstellar medium (ISM) seems to have a significant surplus of oxygen which was dubbed as the `O crisis': independent of the adopted interstellar reference abundance, the total number of O atoms depleted from the gas phase far exceeds that tied up in solids by as much as ˜160 ppm of O/H. Recently, it has been hypothesized that the missing O could be hidden in μm-sized H2O ice grains. We examine this hypothesis by comparing the infrared (IR) extinction and far-IR emission arising from these grains with that observed in the Galactic diffuse ISM. We find that it is possible for the diffuse ISM to accommodate ˜160 ppm of O/H in μm-sized H2O ice grains without violating the observational constraints including the absence of the 3.1 μm O-H absorption feature. More specifically, H2O ice grains of radii ˜4 μm and O/H = 160 ppm are capable of accounting for the observed flat extinction at ˜3-8 μm and produce no excessive emission in the far-IR. These grains could be present in the diffuse ISM through rapid exchange of material between dense molecular clouds where they form and diffuse clouds where they are destroyed by photosputtering.

  12. Beta cloth durability assessment for Space Station Freedom (SSF) Multi-Layer Insulation (MLI) blanket covers

    NASA Technical Reports Server (NTRS)

    Koontz, Steven L.; Jacobs, Stephen; Le, Julie

    1993-01-01

    MLI blankets for the Space Station Freedom (SSF) must comply with general program requirements and recommendations for long life and durability in the low-Earth orbit (LEO) environment. Atomic oxygen and solar ultraviolet/vacuum ultraviolet are the most important factors in the SSF natural environment which affect materials life. Two types of Beta cloth (Teflon coated woven glass fabric), which had been proposed as MLI blanket covers, were tested for long-term durability in the LEO environment. General resistance to atomic oxygen attack and permeation were evaluated in the high velocity atomic oxygen beam system at Los Alamos National Laboratories. Long-term exposure to the LEO environment was simulated in the laboratory using a radio frequency oxygen plasma asher. The plasma asher treated Beta cloth specimens were tested for thermo-optical properties and mechanical durability. Space exposure data from the Long Duration Exposure Facility and the Intelsat Solar Array Coupon were also used in the durability assessment. Beta cloth fabricated to Rockwell specification MBO 135-027 (Chemglas 250) was shown to have acceptable durability for general use as an MLI blanket cover material in the LEO environment while Sheldahl G414500 should be used only in locations which are protected from direct Ram atomic oxygen.

  13. TiO2-Coated Transparent Conductive Oxide (SnO2:F) Films Prepared by Atmospheric Pressure Chemical Vapor Deposition with High Durability against Atomic Hydrogen

    NASA Astrophysics Data System (ADS)

    Kambe, Mika; Sato, Kazuo; Kobayashi, Daisuke; Kurokawa, Yasuyoshi; Miyajima, Shinsuke; Fukawa, Makoto; Taneda, Naoki; Yamada, Akira; Konagai, Makoto

    2006-03-01

    The durability of textured transparent conductive oxide (TCO) thin films against atomic hydrogen was investigated. An ultrathin TiO2 layer of 2 nm thickness was deposited on textured fluorine-doped tin oxide (SnO2:F) films, successively by atmospheric pressure chemical vapor deposition (AP-CVD). TCO films with a TiO2 layer showed a higher optical transmittance and a lower resistivity after exposure to atomic hydrogen excited by very high frequency (VHF) plasma, while TCO films without a TiO2 layer showed a lower optical transmittance and a higher resistivity after the exposure. These TCO films were characterized by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) before and after the exposure to atomic hydrogen.

  14. Anti-Adhesion Elastomer Seal Coatings for Ultraviolet and Atomic Oxygen Protection

    NASA Technical Reports Server (NTRS)

    De Groh, Henry C., III; Puleo, Bernadette J.; Waters, Deborah L.; Miller, Sharon K.

    2015-01-01

    Radiation blocking sunscreen coatings have been developed for the protection of elastomer seals used in low-Earth-orbit (LEO). The coatings protect the seals from ultraviolet (UV) radiation and atomic oxygen (AO) damage. The coatings were developed for use on NASA docking seals. Docking seal damage from the UV and AO present in LEO can constrain mission time-line, flight mode options, and increases risk. A low level of adhesion is also required for docking seals so undocking push-off forces can be low. The coatings presented also mitigate this unwanted adhesion. Greases with low collected volatile condensable materials (CVCM) and low total mass loss (TML) were mixed with slippery and/or UV blocking powders to create the protective coatings. Coatings were applied at rates up to 2 milligrams per square centimeter. Coated seals were exposed to AO and UV in the NUV (near-UV) and UV-C wavelength ranges (300 to 400 nanometers and 254 nanometers, respectively). Ground based ashers were used to simulate the AO of space. The Sun's UV energy was mimicked assuming a nose forward flight mode, resulting in an exposure rate of 2.5 megajoules per square meter per day. Exposures between 0 and 147 megajoules per square meter (UV-C) and 245 megajoules per square meter (NUV) were accomplished. The protective coatings were durable, providing protection from UV after a simulated docking and undocking cycle. The level of protection begins to decline at coverage rates less than 0.9 milligrams per square centimeter. The leakage of seals coated with Braycote plus 20 percent Z-cote ZnO sunscreen increased by a factor of 40 after moderate AO exposure; indicating that this coating might not be suitable due to AO intolerance. Seals coated with DC-7-16.4 percent Z-cote ZnO sunscreen were not significantly affected by combined doses of 2 x 10 (sup 21) atoms per square AO with 73 megajoules per square meter UV-C. Unprotected seals were significantly damaged at UV-C exposures of 0.3 megajoules per

  15. Application of an atomic oxygen beam facility to the investigation of shuttle glow chemistry

    NASA Technical Reports Server (NTRS)

    Arnold, G. S.; Peplinski, D. R.

    1985-01-01

    A facility for the investigation of the interactions of energetic atomic oxygen with solids is described. The facility is comprised of a four chambered, differentially pumped molecular beam apparatus which can be equipped with one of a variety of sources of atomic oxygen. The primary source is a dc arc heated supersonic nozzle source which produces a flux of atomic oxygen in excess of 10 to the 15th power sq cm/sec at the target, at a velocity of 3.5 km/sec. Results of applications of this facility to the study of the reactions of atomic oxygen with carbon and polyimide films are briefly reviewed and compared to data obtained on various flights of the space shuttle. A brief discussion of possible application of this facility to investigation of chemical reactions which might contribute to atmosphere induced vehicle glow is presented.

  16. A facility for investigating interactions of energetic atomic oxygen with solids

    NASA Technical Reports Server (NTRS)

    Arnold, G. S.; Peplinski, D. R.

    1984-01-01

    A facility for the investigation of the interactions of energetic atomic oxygen with solids is described. The facility is comprised of a four-chambered, differentially pumped molecular beam apparatus which can be equipped with one of a variety of sources of atomic oxygen. The primary source is a dc arch-heated supersonic nozzle source which produces a flux of atomic oxygen in excess of 10 to the 15th power/cu cm/sec at the target, at a velocity of 3.5 km/sec. Results of applications of this facility to the study of the reactions of atomic oxygen with carbon and polyimide films are briefly reviewed and compared to data obtained on various flights of the space shuttle.

  17. Characterization of a 5-eV neutral atomic oxygen beam facility

    NASA Technical Reports Server (NTRS)

    Vaughn, J. A.; Linton, R. C.; Carruth, M. R., Jr.; Whitaker, A. F.; Cuthbertson, J. W.; Langer, W. D.; Motley, R. W.

    1991-01-01

    An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

  18. Quantitative inactivation-mechanisms of P. digitatum and A. niger spores based on atomic oxygen dose

    NASA Astrophysics Data System (ADS)

    Ito, Masafumi; Hashizume, Hiroshi; Ohta, Takayuki; Hori, Masaru

    2014-10-01

    We have investigated inactivation mechanisms of Penicillium digitatum and Asperguills niger spores using atmospheric-pressure radical source quantitatively. The radical source was specially developed for supplying only neutral radicals without charged species and UV-light emissions. Reactive oxygen radical densities such as grand-state oxygen atoms, excited-state oxygen molecules and ozone were measured using VUV and UV absorption spectroscopies. The measurements and the treatments of spores were carried out in an Ar-purged chamber for eliminating the influences of OH, NOx and so on. The results revealed that the inactivation of spores can be explained by atomic-oxygen dose under the conditions employing neutral ROS irradiations. On the basis of the dose, we have observed the changes of intracellular organelles and membrane functions using TEM, SEM and confocal- laser fluorescent microscopy. From these results, we discuss the detail inactivation-mechanisms quantitatively based on atomic-oxygen dose.

  19. Atomic oxygen fine-structure splittings with tunable far-infrared spectroscopy

    NASA Technical Reports Server (NTRS)

    Zink, Lyndon R.; Evenson, Kenneth M.; Matsushima, Fusakazu; Nelis, Thomas; Robinson, Ruth L.

    1991-01-01

    Fine-structure splittings of atomic oxygen (O-16) in the ground state have been accurately measured using a tunable far-infrared spectrometer. The 3P0-3pl splitting is 2,060,069.09 (10) MHz, and the 3Pl-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in earth's atmosphere and the interstellar medium.

  20. The atomic and electronic structure of oxygen polyvacancies in anatase

    NASA Astrophysics Data System (ADS)

    Perevalov, T. V.; Islamov, D. R.; Saraev, A. A.

    2016-06-01

    We investigate oxygen-deficient anatase using quantum-chemical simulation within the density functional theory and X-ray photoelectron spectroscopy. It is demonstrated that etching of anatase with argon ions with an energy of 2.4 keV results in the formation of oxygen vacancies and polyvacancies at a concentration of approximately 1020 cm-3 in the crystal. It was found that the most energetically favorable spatial configuration of an oxygen polyvacancy is a three-dimensional chain in crystallographic direction [100] or [010]. The ability of oxygen polyvacancy in the form of a chain to act as a conductive filament and to participate in the resistive switching is discussed.

  1. Kinetic modeling of primary and secondary oxygen atom fluxes at 1 AU

    NASA Astrophysics Data System (ADS)

    Balyukin, Igor; Katushkina, Olga; Alexashov, Dmitry; Izmodenov, Vladislav

    2016-07-01

    The first quantitative measurements of the interstellar heavy (oxygen and neon) neutral atoms obtained on the IBEX spacecraft were presented in Park et al. (ApJS, 2015). Qualitative analysis of these data shows that the secondary component of the interstellar oxygen atoms was also measured along with the primary interstellar atoms. This component is formed near the heliopause due to process of charge exchange of interstellar oxygen ions with hydrogen atoms and its existence in the heliosphere was previously predicted theoretically (Izmodenov et al, 1997, 1999, 2001). Quantitative analysis of fluxes of interstellar heavy neutral atoms is only possible with the help of a model which takes into account both filtration of the primary and origin of the secondary interstellar oxygen in the region of interaction of the solar wind with the local interstellar medium as well as a detailed simulation of the motion of interstellar atoms inside the heliosphere. This simulation must take into account the temporal and heliolatitudinal dependences of ionization, the process of charge exchange with the protons of the solar wind and the effect of the solar gravitational attraction. This paper presents the results of modeling interstellar oxygen and neon atoms in the heliospheric shock layer and inside the heliosphere based on a new three-dimensional kinetic-MHD model of the solar wind interaction with the local interstellar medium (Izmodenov and Alexashov, ApJS, 2015) and the comparison of this results with the data obtained on the IBEX spacecraft.

  2. Atomic Oxygen Exposure of Power System and other Spacecraft Materials: Results of the EOIM-3 Experiment

    NASA Technical Reports Server (NTRS)

    Morton, Thomas L.; Ferguson, Dale C.

    1997-01-01

    In order to test their reactivity with Atomic Oxygen, twenty five materials were flown on the EOIM-3 (Evaluation of Oxygen Interactions with Materials) portion of the STS-46 Mission. These materials include refractory metals, candidate insulation materials, candidate radiator coatings, and a selection of miscellaneous materials. This report documents the results of the pre- and post-flight analysis of these materials.

  3. MoS2 interactions with 1.5 eV atomic oxygen

    NASA Technical Reports Server (NTRS)

    Martin, J. A.; Cross, J. B.; Pope, L. E.

    1989-01-01

    Exposures of MoS2 to 1.5-eV atomic oxygen in an anhydrous environment reveal that the degree of oxidation is essentially independent of crystallite orientation, and that the surface-adsorbed reaction products are MoO3 and MoO2. A mixture of oxides and sulfide exists over a depth of about 90 A, and this layer has a low diffusion rate for oxygen. It is concluded that a protective oxide layer forms on MoS2 on exposure to the atomic-oxygen-rich environment of LEO.

  4. Reaction Mechanism of Oxygen Atoms with Unsaturated Hydrocarbons by the Crossed-Molecular-Beams Method

    DOE R&D Accomplishments Database

    Buss, R. J.; Baseman, R. J.; Guozhong, H.; Lee, Y. T.

    1982-04-01

    From a series of studies of the reaction of oxygen atoms with unsaturated hydrocarbons using the crossed molecular beam method, the dominant reaction mechanisms were found to be the simple substitution reactions with oxygen atoms replacing H, Cl, Br atom or alkyl groups. Complication due to secondary reaction was avoided by carrying out experiments under single collisions and observing primary products directly. Primary products were identified by measuring the angular and velocity distributions of products at all the mass numbers which could be detected by the mass spectrometer, and from comparison of these distributions, applying the requirement of energy and momentum conservation.

  5. Atomic Oxygen Density Measurements in a Low Pressure Textile Processing Plasma

    NASA Astrophysics Data System (ADS)

    Gomez, S.; Steen, P. G.; Graham, W. G.

    1999-10-01

    There is increasing interest in plasma processing of textile materials. Here the effect of textile materials on low pressure oxygen plasmas has been investigated. In particular laser induced fluorescence (LIF) measurements of the atomic oxygen density with and without textile samples are presented. Polypropylene and polyester samples were placed on the lower electrode of an inductively coupled Gaseous Electronic Conference (GEC) reactor. This had to be operated at low power and hence in the capacitive mode to avoid toasting the material. Operation with a bare stainless steel electrode and one loaded with the sample materials is contrasted by comparing spatially resolved LIF measurements of atomic oxygen under a wide range of pressures and powers, from a few Pa to 133 Pa, and from 10 to 300 W. Atomic oxygen densities with samples present are around one third lower than those without samples, and in both cases the atomic oxygen density increases linearly with gas pressure. Previous optical emission spectroscopy (OES) measurements indicate that plasma interaction with the substrate commences a few seconds after plasma turn on. Similar trends are observed with time resolved LIF measurements of the atomic oxygen.

  6. Effect of reactor loading on atomic oxygen concentration as measured by NO chemiluminescence

    NASA Technical Reports Server (NTRS)

    Lerner, N. R.

    1989-01-01

    It has previously been observed that the etch rate of polyethylene samples in the afterglow of an RF discharge in oxygen increases with reactor loading. This enhancement of the etch rate is attributed to reactive gas phase products of the polymer etching. In the present work, emission spectroscopy is employed to examine the species present in the gas phase during etching of polyethylene. In particular, the concentration of atomic oxygen downstream from the polyethylene samples is studied as a function of the reactor loading. It is found that the concentration of atomic oxygen increases as the reactor loading is increased. The increase of etch rate with increased reactor loading is attributed to the increase of atomic oxygen concentration in the vicinity of the sample.

  7. Laser supported detonation wave source of atomic oxygen for aerospace material testing

    NASA Technical Reports Server (NTRS)

    Krech, Robert H.; Caledonia, George E.

    1990-01-01

    A pulsed high-flux source of nearly monoenergetic atomic oxygen was developed to perform accelerated erosion testing of spacecraft materials in a simulated low-earth orbit (LEO) environment. Molecular oxygen is introduced into an evacuated conical expansion nozzle at several atmospheres pressure through a pulsed molecular beam valve. A laser-induced breakdown is generated in the nozzle throat by a pulsed CO2 TEA laser. The resulting plasma is heated by the ensuing laser-supported detonation wave, and then it rapidly expands and cools. An atomic oxygen beam is generated with fluxes above 10 to the 18th atoms per pulse at 8 + or - 1.6 km/s with an ion content below 1 percent for LEO testing. Materials testing yielded the same surface oxygen enrichment in polyethylene samples as observed on the STS mission, and scanning electron micrographs of the irradiated polymer surfaces showed an erosion morphology similar to that obtained on low earth orbit.

  8. Ozone-stimulated emission due to atomic oxygen population inversions in an argon microwave plasma torch

    SciTech Connect

    Lukina, N. A.; Sergeichev, K. F.

    2008-06-15

    It is shown that, in a microwave torch discharge in an argon jet injected into an oxygen atmosphere at normal pressure, quasi-resonant energy transfer from metastable argon atoms to molecules of oxygen and ozone generated in the torch shell and, then, to oxygen atoms produced via the dissociation of molecular oxygen and ozone leads to the inverse population of metastable levels of atomic oxygen. As a result, the excited atomic oxygen with population inversions becomes a gain medium for lasing at wavelengths of 844.6 and 777.3 nm (the 3{sup 3}P-3{sup 3}S and 3{sup 5}P-3{sup 5}S transitions). It is shown that an increase in the ozone density is accompanied by an increase in both the lasing efficiency at these wavelength and the emission intensity of the plasma-forming argon at a wavelength of 811.15 nm (the {sup 2}P{sup 0}4s-{sup 2}P{sup 0}4p transition). When the torch operates unstably, the production of singlet oxygen suppresses ozone generation; as a result, the lasing effect at these wavelengths disappears.

  9. Atomic Oxygen Interactions With Silicone Contamination on Spacecraft in Low Earth Orbit Studied

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.

    2001-01-01

    Silicones have been widely used on spacecraft as potting compounds, adhesives, seals, gaskets, hydrophobic surfaces, and atomic oxygen protective coatings. Contamination of optical and thermal control surfaces on spacecraft in low Earth orbit (LEO) has been an ever-present problem as a result of the interaction of atomic oxygen with volatile species from silicones and hydrocarbons onboard spacecraft. These interactions can deposit a contaminant that is a risk to spacecraft performance because it can form an optically absorbing film on the surfaces of Sun sensors, star trackers, or optical components or can increase the solar absorptance of thermal control surfaces. The transmittance, absorptance, and reflectance of such contaminant films seem to vary widely from very transparent SiOx films to much more absorbing SiOx-based films that contain hydrocarbons. At the NASA Glenn Research Center, silicone contamination that was oxidized by atomic oxygen has been examined from LEO spacecraft (including the Long Duration Exposure Facility and the Mir space station solar arrays) and from ground laboratory LEO simulations. The findings resulted in the development of predictive models that may help explain the underlying issues and effects. Atomic oxygen interactions with silicone volatiles and mixtures of silicone and hydrocarbon volatiles produce glassy SiOx-based contaminant coatings. The addition of hydrocarbon volatiles in the presence of silicone volatiles appears to cause much more absorbing (and consequently less transmitting) contaminant films than when no hydrocarbon volatiles are present. On the basis of the LDEF and Mir results, conditions of high atomic oxygen flux relative to low contaminant flux appear to result in more transparent contaminant films than do conditions of low atomic oxygen flux with high contaminant flux. Modeling predictions indicate that the deposition of contaminant films early in a LEO flight should depend much more on atomic oxygen flux than

  10. Monte Carlo Technique Used to Model the Degradation of Internal Spacecraft Surfaces by Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Miller, Sharon K.

    2004-01-01

    Atomic oxygen is one of the predominant constituents of Earth's upper atmosphere. It is created by the photodissociation of molecular oxygen (O2) into single O atoms by ultraviolet radiation. It is chemically very reactive because a single O atom readily combines with another O atom or with other atoms or molecules that can form a stable oxide. The effects of atomic oxygen on the external surfaces of spacecraft in low Earth orbit can have dire consequences for spacecraft life, and this is a well-known and much studied problem. Much less information is known about the effects of atomic oxygen on the internal surfaces of spacecraft. This degradation can occur when openings in components of the spacecraft exterior exist that allow the entry of atomic oxygen into regions that may not have direct atomic oxygen attack but rather scattered attack. Openings can exist because of spacecraft venting, microwave cavities, and apertures for Earth viewing, Sun sensors, or star trackers. The effects of atomic oxygen erosion of polymers interior to an aperture on a spacecraft were simulated at the NASA Glenn Research Center by using Monte Carlo computational techniques. A two-dimensional model was used to provide quantitative indications of the attenuation of atomic oxygen flux as a function of the distance into a parallel-walled cavity. The model allows the atomic oxygen arrival direction, the Maxwell Boltzman temperature, and the ram energy to be varied along with the interaction parameters of the degree of recombination upon impact with polymer or nonreactive surfaces, the initial reaction probability, the reaction probability dependence upon energy and angle of attack, degree of specularity of scattering of reactive and nonreactive surfaces, and the degree of thermal accommodation upon impact with reactive and non-reactive surfaces to be varied to allow the model to produce atomic oxygen erosion geometries that replicate actual experimental results from space. The degree of

  11. Atmospheric Pressure Method and Apparatus for Removal of Organic Matter with Atomic and Ionic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Rutledge, Sharon K. (Inventor)

    1996-01-01

    A gas stream containing ionic and atomic oxygen in inert gas is used to remove organic matter from a substrate. The gas stream is formed by flowing a mixture of gaseous oxygen in an inert gas such as helium at atmospheric pressure past a high voltage, current limited, direct current arc which contacts the gas mixture and forms the ionic and atomic oxygen. The arc is curved at the cathode end and the ionic oxygen formed by the arc nearer to the anode end of the arc is accelerated in a direction towards the cathode by virtue of its charge. The relatively high mass to charge ratio of the ionic oxygen enables at least some of it to escape the arc before contacting the cathode and it is directed onto the substrate. This is useful for cleaning delicate substrates such as fine and historically important paintings and delicate equipment and the like.

  12. Atmospheric Pressure Method and Apparatus for Removal of Organic Matter with Atomic and Ionic Oxygen

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor); Rutledge, Sharon K. (Inventor)

    1997-01-01

    A gas stream containing ionic and atomic oxygen in inert gas is used to remove organic matter from a substrate. The gas stream is formed by flowing a mixture of gaseous oxygen in an inert gas such as helium at atmospheric pressure past a high voltage, current limited, direct current arc which contacts the gas mixture and forms the ionic and atomic oxygen. The arc is curved at the cathode end and the ionic oxygen formed by the arc nearer to the anode end of the arc is accelerated in a direction towards the cathode by virtue of its charge. The relatively high mass to charge ratio of the ionic oxygen enables at least some of it to escape the arc before contacting the cathode and it is directed onto the substrate. This is useful for cleaning delicate substrates such as fine and historically important paintings and delicate equipment and the like.

  13. Carbon fiber CVD coating by carbon nanostructured for space materials protection against atomic oxygen

    NASA Astrophysics Data System (ADS)

    Pastore, Roberto; Bueno Morles, Ramon; Micheli, Davide

    2016-07-01

    In recent years, the emphasis in space research has been shifting from space exploration to commercialization of space. In order to utilize space for commercial purposes it is necessary to understand the low earth orbit (LEO) space environment where most of the activities will be carried out. The studies on the LEO environment are mainly focused towards understanding the effect of atomic oxygen (AO) on spacecraft materials. In the first few shuttle flights, materials looked frosty because they were actually being eroded and textured: AO reacts with organic materials on spacecraft exteriors, gradually damaging them. When a spacecraft travel in LEO (where crewed vehicles and the International Space Station fly), the AO formed from the residual atmosphere can react with the spacecraft surfaces, causing damage to the vehicle. Polymers are widely used in space vehicles and systems as structural materials, thermal blankets, thermal control coatings, conformal coatings, adhesives, lubricants, etc. Exposure of polymers and composites to the space environment may result in different detrimental effects via modification of their chemical, electrical, thermal, optical and mechanical properties as well as surface erosion. The major degradation effects in polymers are due to their exposure to atomic oxygen, vacuum ultraviolet and synergistic effects, which result in different damaging effects by modification of the polymer's chemical properties. In hydrocarbon containing polymers the main AO effect is the surface erosion via chemical reactions and the release of volatile reaction products associated with the mass loss. The application of a thin protective coating to the base materials is one of the most commonly used methods of preventing AO degradation. The purpose is to provide a barrier between base material and AO environment or, in some cases, to alter AO reactions to inhibit its diffusion. The effectiveness of a coating depends on its continuity, porosity, degree of

  14. Carbon fiber CVD coating by carbon nanostructured for space materials protection against atomic oxygen

    NASA Astrophysics Data System (ADS)

    Pastore, Roberto; Bueno Morles, Ramon; Micheli, Davide

    2016-07-01

    In recent years, the emphasis in space research has been shifting from space exploration to commercialization of space. In order to utilize space for commercial purposes it is necessary to understand the low earth orbit (LEO) space environment where most of the activities will be carried out. The studies on the LEO environment are mainly focused towards understanding the effect of atomic oxygen (AO) on spacecraft materials. In the first few shuttle flights, materials looked frosty because they were actually being eroded and textured: AO reacts with organic materials on spacecraft exteriors, gradually damaging them. When a spacecraft travel in LEO (where crewed vehicles and the International Space Station fly), the AO formed from the residual atmosphere can react with the spacecraft surfaces, causing damage to the vehicle. Polymers are widely used in space vehicles and systems as structural materials, thermal blankets, thermal control coatings, conformal coatings, adhesives, lubricants, etc. Exposure of polymers and composites to the space environment may result in different detrimental effects via modification of their chemical, electrical, thermal, optical and mechanical properties as well as surface erosion. The major degradation effects in polymers are due to their exposure to atomic oxygen, vacuum ultraviolet and synergistic effects, which result in different damaging effects by modification of the polymer's chemical properties. In hydrocarbon containing polymers the main AO effect is the surface erosion via chemical reactions and the release of volatile reaction products associated with the mass loss. The application of a thin protective coating to the base materials is one of the most commonly used methods of preventing AO degradation. The purpose is to provide a barrier between base material and AO environment or, in some cases, to alter AO reactions to inhibit its diffusion. The effectiveness of a coating depends on its continuity, porosity, degree of

  15. Atomic Oxygen Removes Varnish And Lacquer From Old Paintings

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Cales, Michael

    1996-01-01

    Dry and relatively nondestructive plasma process found effective in removing protective coats from old paintings. Process generates monatomic oxygen, which reacts with varnish, lacquer, polyurethane, acrylic, and other organic coating materials; reactions produce mostly carbon monoxide and water vapor, then simply pumped away by vacuum system in which plasma generated. Does not attack oxide-based pigments in underlying paint layers, and brush-stroke marks remain undisturbed.

  16. Growth control of Saccharomyces cerevisiae through dose of oxygen atoms

    SciTech Connect

    Hashizume, Hiroshi; Ohta, Takayuki; Ito, Masafumi; Hori, Masaru

    2015-08-31

    To investigate the dose-dependent effects of neutral oxygen radicals on the proliferation as well as the inactivation of microorganisms, we treated suspensions of budding yeast cells with oxygen radicals using an atmospheric-pressure oxygen radical source, varying the fluxes of O({sup 3}P{sub j}) from 1.3 × 10{sup 16} to 2.3 × 10{sup 17 }cm{sup −2} s{sup −1}. Proliferation was promoted at doses of O({sup 3}P{sub j}) ranging from 6 × 10{sup 16} to 2 × 10{sup 17 }cm{sup −3}, and suppressed at doses ranging from 3 × 10{sup 17} to 1 × 10{sup 18 }cm{sup −3}; cells were inactivated by O({sup 3}P{sub j}) doses exceeding 1 × 10{sup 18 }cm{sup −3}, even when the flux was varied over the above flux range. These results showed that the growth of cells was regulated primarily in response to the total dose of O({sup 3}P{sub j})

  17. A kinetic study of the interaction between atomic oxygen and aerosols

    NASA Technical Reports Server (NTRS)

    Akers, F. I.; Wightman, J. P.

    1976-01-01

    This study was concerned with the effects of NH4Cl and (NH4)2SO4 aerosols on the kinetics of disappearance of atomic oxygen. Atomic oxygen was generated by a 2.45-GHz microwave discharge and the kinetics of disappearance measured in a fast flow system using NO2 titration. Values of the recombination coefficient for heterogeneous wall recombination were determined for clean, H2SO4-coated, and (NH4)2SO4-coated Pyrex to be 0.000050, 0.000020, and 0.000019, respectively. A rapid exothermic chemical reaction was found to occur between atomic oxygen and an NH4Cl wall coating; the products were NH3, NO, H2O, and HCl. The NH4Cl aerosol was generated by gas phase reaction of NH3 with HCl. The aerosol particles were approximately spherical and nearly monodisperse with a mean diameter of 1.6 plus or minus 0.2 micron. The rate constant for the disappearance of atomic oxygen in the presence of NH4Cl aerosol was measured. No significant decrease was observed in the rate of disappearance of atomic oxygen in the presence of an (NH4)2SO4 aerosol at a concentration of 285 mg per cu m.

  18. Effects of atomic oxygen on polymeric materials flown on EOIM-3

    NASA Technical Reports Server (NTRS)

    Kamenetzky, Rachel R.; Linton, Roger C.; Finckenor, Miria M.; Vaughn, Jason A.

    1995-01-01

    Diverse polymeric materials, including several variations of Kapton, were flown on STS-46 as part of the Evaluation of Oxygen Interaction with Materials Experiment (EOIM-3). These materials were flown in the cargo bay and exposed to the space environment July 31 - August 8, 1992, including 40 hours of direct atomic oxygen impingement. The atomic oxygen exposure was approximately 2.2 x 10(exp 20) atoms/sq cm. Polymeric materials flown on EOIM-3 include coated and uncoated Kapton, Tefzel ETFE, Lexan, FEP and TFE Teflon, bulk Halar and PEEK, S383 silicone and Viton elastomeric seal material. Analyses performed included thickness measurements using Dektak and eddy current methods, mass loss, resistance, permeability, hardness, and FTIR. The effects of stress and the space environment on Kapton were also evaluated. Previous EOIM missions on STS-5 and STS-8 and the Long Duration Exposure Facility also contained polymeric material samples. Data from these previous flights are shown for comparison, as well as ground simulation of space environment effects using both thermal energy flow tubes and 5 eV neutral atomic oxygen beam facilities. Reaction efficiencies for the various atomic oxygen exposure conditions are discussed.

  19. The surface properties of fluorinated polyimides exposed to VUV and atomic oxygen

    NASA Technical Reports Server (NTRS)

    Forsythe, John S.; George, Graeme A.; Hill, David J. T.; Odonnell, James H.; Pomery, Peter J.; Rasoul, Firas A.

    1995-01-01

    The effect of atomic oxygen flux and VUV radiation alone and in combination on the surface of fluorinated polyimide films was studied using XPS spectroscopy. Exposure of fluorinated polyimides to VUV radiation alone caused no observable damage to the polymer surface, while an atomic oxygen flux resulted in substantial oxidation of the surface. On the other hand, exposure to VUV radiation and atomic oxygen in combination caused extensive oxidation of the polymer surface after only 2 minutes of exposure. The amount of oxidized carbon on the polymer surface indicated that there is aromatic ring opening oxidation. The changes in the O1s/C1s, N1s/C1s, and F1s/C1s ratios suggested that an ablative degradation process is highly favorable. A synergistic effect of VUV radiation in the presence of atomic oxygen is clearly evidenced from the XPS study. The atomic oxygen could be considered as the main factor in the degradation process of fluorinated polyimide films exposed to a low earth orbit environment.

  20. Consequences of Atomic Oxygen Interaction With Silicone and Silicone Contamination on Surfaces in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim K.; Rutledge, Sharon K.; Haytas, Christy A.

    1999-01-01

    The exposure of silicones to atomic oxygen in low Earth orbit causes oxidation of the surface, resulting in conversion of silicone to silica. This chemical conversion increases the elastic modulus of the surface and initiates the development of a tensile strain. Ultimately, with sufficient exposure, tensile strain leads to cracking of the surface enabling the underlying unexposed silicone to be converted to silica resulting in additional depth and extent of cracking. The use of silicone coatings for the protection of materials from atomic oxygen attack is limited because of the eventual exposure of underlying unprotected polymeric material due to deep tensile stress cracking of the oxidized silicone. The use of moderate to high volatility silicones in low Earth orbit has resulted in a silicone contamination arrival at surfaces which are simultaneously being bombarded with atomic oxygen, thus leading to conversion of the silicone contaminant to silica. As a result of these processes, a gradual accumulation of contamination occurs leading to deposits which at times have been up to several microns thick (as in the case of a Mir solar array after 10 years in space). The contamination species typically consist of silicon, oxygen and carbon. which in the synergistic environment of atomic oxygen and UV radiation leads to increased solar absorptance and reduced solar transmittance. A comparison of the results of atomic oxygen interaction with silicones and silicone contamination will be presented based on the LDEF, EOIM-111, Offeq-3 spacecraft and Mir solar array in-space results. The design of a contamination pin-hole camera space experiment which uses atomic oxygen to produce an image of the sources of silicone contamination will also be presented.

  1. Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts.

    PubMed

    Yin, Peiqun; Yao, Tao; Wu, Yuen; Zheng, Lirong; Lin, Yue; Liu, Wei; Ju, Huanxin; Zhu, Junfa; Hong, Xun; Deng, Zhaoxiang; Zhou, Gang; Wei, Shiqiang; Li, Yadong

    2016-08-26

    A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials. PMID:27491018

  2. Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts.

    PubMed

    Yin, Peiqun; Yao, Tao; Wu, Yuen; Zheng, Lirong; Lin, Yue; Liu, Wei; Ju, Huanxin; Zhu, Junfa; Hong, Xun; Deng, Zhaoxiang; Zhou, Gang; Wei, Shiqiang; Li, Yadong

    2016-08-26

    A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.

  3. Fast Three-Dimensional Method of Modeling Atomic Oxygen Undercutting of Protected Polymers

    NASA Technical Reports Server (NTRS)

    Snyder, Aaron; Banks, Bruce A.

    2002-01-01

    A method is presented to model atomic oxygen erosion of protected polymers in low Earth orbit (LEO). Undercutting of protected polymers by atomic oxygen occurs in LEO due to the presence of scratch, crack or pin-window defects in the protective coatings. As a means of providing a better understanding of undercutting processes, a fast method of modeling atomic-oxygen undercutting of protected polymers has been developed. Current simulation methods often rely on computationally expensive ray-tracing procedures to track the surface-to-surface movement of individual "atoms." The method introduced in this paper replaces slow individual particle approaches by substituting a model that utilizes both a geometric configuration-factor technique, which governs the diffuse transport of atoms between surfaces, and an efficient telescoping series algorithm, which rapidly integrates the cumulative effects stemming from the numerous atomic oxygen events occurring at the surfaces of an undercut cavity. This new method facilitates the systematic study of three-dimensional undercutting by allowing rapid simulations to be made over a wide range of erosion parameters.

  4. Durability to oxygen reactive ion etching enhanced by addition of synthesized bis(trimethylsilyl)phenyl-containing (meth)acrylates in ultraviolet nanoimprint lithography

    NASA Astrophysics Data System (ADS)

    Ito, Shunya; Sato, Hiroki; Tasaki, Yuhei; Watanuki, Kimihito; Nemoto, Nobukatsu; Nakagawa, Masaru

    2016-06-01

    We investigated the selection of bis(trimethylsilyl)phenyl-containing (meth)acrylates as additives to improve the durability to oxygen reactive ion etching (O2 RIE) of sub-50 nm imprint resist patterns suitable for bubble-defect-free UV nanoimprinting with a readily condensable gas. 2,5-Bis(2-acryloyloxyethoxy)-1,4-bis(trimethylsilyl)benzene, which has a diacrylate chemical structure similar to that of glycerol 1,3-diglycerolate diacrylate used as a base monomer, and 3-(2-methacryloyloxyethoxy)-1-(hydroxylethoxy)-2-propoxy-3,5-bis(trimethylsilyl)benzene, which has a hydroxy group similar to the base monomer, were synthesized taking into consideration the Ohnishi and ring parameters, and the oxidization of the trimethylsilyl moiety to inorganic species during O2 RIE. The addition of the latter liquid additive to the base monomer decreased etching rate owing to the good miscibility of the additive in the base monomer, while the addition of the former crystalline additive caused phase separation after UV nanoimprinting. The latter additive worked as a compatibilizer to the former additive, which is preferred for etching durability improvement. The coexistence of the additives enabled the fabrication of a 45 nm line-and-space resist pattern by UV nanoimprinting, and its residual layer could be removed by O2 RIE.

  5. A review of the stability and durability of non-precious metal catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Banham, Dustin; Ye, Siyu; Pei, Katie; Ozaki, Jun-ichi; Kishimoto, Takeaki; Imashiro, Yasuo

    2015-07-01

    A major hurdle to the widespread commercialization of proton exchange membrane fuel cells (PEMFCs) is the high loading of noble metal (Pt/Pt-alloy) catalyst at the cathode, which is necessary to facilitate the inherently sluggish oxygen reduction reaction (ORR). To eliminate the use of Pt/Pt-alloy catalysts at the cathode of PEMFCs and thus significantly reduce the cost, extensive research on non-precious metal catalysts (NPMCs) has been carried out over the past decade. Major advances in improving the ORR activity of NPMCs, particularly Fe- and Co-based NPMCs, have elevated these materials to a level at which they can start to be considered as potential alternatives to Pt/Pt-alloy catalysts. Unfortunately, the stability (performance loss following galvanostatic experiments) of these materials is currently unacceptably low and the durability (performance loss following voltage cycling) remains uncertain. The three primary mechanisms of instability are: (a) Leaching of the metal site, (b) Oxidative attack by H2O2, and (c) Protonation followed by possible anion adsorption of the active site. While (a) has largely been solved, further work is required to understand and prevent losses from (b) and/or (c). Thus, this review is focused on historical progress in (and possible future strategies for) improving the stability/durability of NPMCs.

  6. Materials selection for long life in LEO: A critical evaluation of atomic oxygen testing with thermal atom systems

    NASA Technical Reports Server (NTRS)

    Koontz, S. L.; Kuminecz, J.; Leger, L.; Nordine, P.

    1988-01-01

    The use of thermal atom test methods as a materials selection and screening technique for low-Earth orbit (LEO) spacecraft is critically evaluated. The chemistry and physics of thermal atom environments are compared with the LEO environment. The relative reactivities of a number of materials determined to be in thermal atom environments are compared to those observed in LEO and in high quality LEO simulations. Reaction efficiencies measured in a new type of thermal atom apparatus are one-hundredth to one-thousandth those observed in LEO, and many materials showing nearly identical reactivities in LEO show relative reactivities differing by as much as a factor of 8 in thermal atom systems. A simple phenomenological kinetic model for the reaction of oxygen atoms with organic materials can be used to explain the differences in reactivity in different environments. Certain specific thermal test environments can be used as reliable materials screening tools. Using thermal atom methods to predict material lifetime in LEO requires direct calibration of the method against LEO data or high quality simulation data for each material.

  7. Electrochemical oxygen reduction behavior of selectively deposited platinum atoms on gold nanoparticles.

    PubMed

    Sarkar, A; Kerr, J B; Cairns, E J

    2013-07-22

    Carbon-supported Pt@Au "core-shell" nanoparticles with varying surface concentration of platinum atoms have been synthesized using a novel redox-mediated synthesis approach. The synthesis technique allows for a selective deposition of platinum atoms on the surface of prefabricated gold nanoparticles. Energy dispersive spectroscopic analyses in a scanning electron microscope reveal that the platinum to gold atomic ratios are close to the nominal values, validating the synthesis scheme. X-ray diffraction data indicate an un-alloyed structure. The platinum to gold surface atomic ratio determined from cyclic voltammetry and copper under-potential deposition experiments reveal good agreement with the calculated values at low platinum concentration. However, there is an increase in non-uniformity in the deposition process upon increasing the platinum concentration. Koutecky-Levich analysis of the samples indicates a transition of the total number of electrons transferred (n) in the electrochemical oxygen reduction reaction from two to four electrons upon increasing the surface concentration of platinum atoms. Furthermore, the data indicate that isolated platinum atoms can reduce molecular oxygen but via a two-electron route. Moreover, successful four-electron reduction of molecular oxygen requires clusters of platinum atoms.

  8. Metal oxide nanoparticle growth on graphene via chemical activation with atomic oxygen.

    PubMed

    Johns, James E; Alaboson, Justice M P; Patwardhan, Sameer; Ryder, Christopher R; Schatz, George C; Hersam, Mark C

    2013-12-01

    Chemically interfacing the inert basal plane of graphene with other materials has limited the development of graphene-based catalysts, composite materials, and devices. Here, we overcome this limitation by chemically activating epitaxial graphene on SiC(0001) using atomic oxygen. Atomic oxygen produces epoxide groups on graphene, which act as reactive nucleation sites for zinc oxide nanoparticle growth using the atomic layer deposition precursor diethyl zinc. In particular, exposure of epoxidized graphene to diethyl zinc abstracts oxygen, creating mobile species that diffuse on the surface to form metal oxide clusters. This mechanism is corroborated with a combination of scanning probe microscopy, Raman spectroscopy, and density functional theory and can likely be generalized to a wide variety of related surface reactions on graphene.

  9. A high flux pulsed source of energetic atomic oxygen. [for spacecraft materials ground testing

    NASA Technical Reports Server (NTRS)

    Krech, Robert H.; Caledonia, George E.

    1986-01-01

    The design and demonstration of a pulsed high flux source of nearly monoenergetic atomic oxygen are reported. In the present test setup, molecular oxygen under several atmospheres of pressure is introduced into an evacuated supersonic expansion nozzle through a pulsed molecular beam valve. A 10J CO2 TEA laser is focused to intensities greater than 10 to the 9th W/sq cm in the nozzle throat, generating a laser-induced breakdown with a resulting 20,000-K plasma. Plasma expansion is confined by the nozzle geometry to promote rapid electron-ion recombination. Average O-atom beam velocities from 5-13 km/s at fluxes up to 10 to the 18th atoms/pulse are measured, and a similar surface oxygen enrichment in polyethylene samples to that obtained on the STS-8 mission is found.

  10. Atomic oxygen degradation of Intelsat 4-type solar array interconnects: Laboratory investigations

    NASA Technical Reports Server (NTRS)

    Koontz, S. L.; Cross, J. B.; Hoffbauer, M. A.; Kirkendahl, T. D.

    1991-01-01

    A Hughes 506 type communication satellite belonging to the Intelsat organization was marooned in low Earth orbit on March 14, 1990, following failure of the Titan third stage to separate properly. The satellite, Intelsat VI, was designed for service in geosynchronous orbit and contains several material configurations which are susceptible to attack by atomic oxygen. Analysis showed the silver foil interconnects in the satellite photovoltaic array to be the key materials issue because the silver is exposed directly to the atomic oxygen ram flux. The results are reported of atomic oxygen degradation testing of Intelsat VI type silver foil interconnects both as virgin material and in a configured solar cell element. Test results indicate that more than 80 pct. of the original thickness of silver in the Intelsat VI solar array interconnects should remain after completion of the proposed Space Shuttle rescue and/or reboost mission.

  11. Atomic oxygen and ultraviolet radiation mission total exposures for LDEF experiments

    NASA Technical Reports Server (NTRS)

    Bourassa, R. J.; Gillis, J. R.; Rousslang, Ken W.

    1992-01-01

    Atomic oxygen and solar radiation exposures were determined analytically for rows, longerons, and end bays of the LDEF. Calculated atomic oxygen exposures are based on an analytical model that accounts for the effects of thermal molecular velocity, atmospheric temperature, number density, spacecraft velocity, incidence angle, and atmospheric rotation. Results also incorporate variations in solar activity, geomagnetic index, and orbital parameters occurring over the six year flight of the spacecraft. Solar radiation exposure calculations are based on the form factors reported in the Solar Illumination Data Package prepared by NASA Langley. The earth albedo value for these calculations was based on the Nimbus 7 earth radiation data set. Summary charts for both atomic oxygen and solar radiation exposure are presented to facilitate the use of the data generated by LDEF experimenters.

  12. Longitudinal structure in atomic oxygen concentrations observed with WINDII on UARS. [Wind Imaging Interferometer

    NASA Technical Reports Server (NTRS)

    Shepherd, G. G.; Thuillier, G.; Solheim, B. H.; Chandra, S.; Cogger, L. L.; Duboin, M. L.; Evans, W. F. J.; Gattinger, R. L.; Gault, W. A.; Herse, M.

    1993-01-01

    WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, began atmospheric observations on September 28, 1991 and since then has been collecting data on winds, temperatures and emissions rates from atomic, molecular and ionized oxygen species, as well as hydroxyl. The validation of winds and temperatures is not yet complete, and scientific interpretation has barely begun, but the dominant characteristic of these data so far is the remarkable structure in the emission rate from the excited species produced by the recombination of atomic oxygen. The latitudinal and temporal variability has been noted before by many others. In this preliminary report on WINDII results we draw attention to the dramatic longitudinal variations of planetary wave character in atomic oxygen concentration, as reflected in the OI 557.7 nm emission, and to similar variations seen in the Meine1 hydroxyl band emission.

  13. Transition metal nitride coated with atomic layers of Pt as a low-cost, highly stable electrocatalyst for the oxygen reduction reaction

    DOE PAGES

    Tian, Xinlong; Adzic, Radoslav R.; Luo, Junming; Nan, Haoxiong; Zou, Haobin; Chen, Rong; Shu, Ting; Li, Xiuhua; Li, Yingwei; Song, Huiyi; et al

    2016-01-21

    Here, the main challenges to the commercial viability of polymer electrolyte membrane fuel cells are (i) the high cost associated with using large amounts of Pt in fuel cell cathodes to compensate for the sluggish kinetics of the oxygen reduction reaction, (ii) catalyst degradation, and (iii) carbon-support corrosion. To address these obstacles, our group has focused on robust, carbon-free transition metal nitride materials with low Pt content that exhibit tunable physical and catalytic properties. Here, we report on the high performance of a novel catalyst with low Pt content, prepared by placing several layers of Pt atoms on nanoparticles ofmore » titanium nickel binary nitride. For the ORR, the catalyst exhibited a more than 400% and 200% increase in mass activity and specific activity, respectively, compared with the commercial Pt/C catalyst. It also showed excellent stability/durability, experiencing only a slight performance loss after 10,000 potential cycles, while TEM results showed its structure had remained intact. The catalyst’s outstanding performance may have resulted from the ultrahigh dispersion of Pt (several atomic layers coated on the nitride nanoparticles), and the excellent stability/durability may have been due to the good stability of nitride and synergetic effects between ultrathin Pt layer and the robust TiNiN support.« less

  14. Atomic oxygen effects on thin film space coatings studied by spectroscopic ellipsometry, atomic force microscopy, and laser light scattering

    NASA Technical Reports Server (NTRS)

    Synowicki, R. A.; Hale, Jeffrey S.; Woollam, John A.

    1992-01-01

    The University of Nebraska is currently evaluating Low Earth Orbit (LEO) simulation techniques as well as a variety of thin film protective coatings to withstand atomic oxygen (AO) degradation. Both oxygen plasma ashers and an electron cyclotron resonance (ECR) source are being used for LEO simulation. Thin film coatings are characterized by optical techniques including Variable Angle Spectroscopic Ellipsometry, Optical spectrophotometry, and laser light scatterometry. Atomic Force Microscopy (AFM) is also used to characterize surface morphology. Results on diamondlike carbon (DLC) films show that DLC degrades with simulated AO exposure at a rate comparable to Kapton polyimide. Since DLC is not as susceptible to environmental factors such as moisture absorption, it could potentially provide more accurate measurements of AO fluence on short space flights.

  15. A ground-based radio frequency inductively coupled plasma apparatus for atomic oxygen simulation in low Earth orbit.

    PubMed

    Huang, Yongxian; Tian, Xiubo; Yang, Shiqin; Chu, Paul K

    2007-10-01

    A radio frequency (rf) inductively coupled plasma apparatus has been developed to simulate the atomic oxygen environment encountered in low Earth orbit (LEO). Basing on the novel design, the apparatus can achieve stable, long lasting operation, pure and high density oxygen plasma beam. Furthermore, the effective atomic oxygen flux can be regulated. The equivalent effective atomic oxygen flux may reach (2.289-2.984) x 10(16) at.cm(2) s at an oxygen pressure of 1.5 Pa and rf power of 400 W. The equivalent atomic oxygen flux is about 100 times than that in the LEO environment. The mass loss measured from the polyimide sample changes linearly with the exposure time, while the density of the eroded holes becomes smaller. The erosion mechanism of the polymeric materials by atomic oxygen is complex and involves initial reactions at the gas-surface interface as well as steady-state material removal.

  16. Single and double addition of oxygen atoms to propyne on surfaces at low temperatures.

    PubMed

    Kimber, Helen J; Ennis, Courtney P; Price, Stephen D

    2014-01-01

    Experiments designed to simulate the low temperature surface chemistry occurring in interstellar clouds provide clear evidence of a reaction between oxygen atoms and propyne ice. The reactants are dosed onto a surface held at a fixed temperature between 14 and 100 K. After the dosing period, temperature programmed desorption (TPD), coupled with time-of-flight mass spectrometry, are used to identify two reaction products with molecular formulae C3H4O and C3H4O2. These products result from the addition of a single oxygen atom, or two oxygen atoms, to a propyne reactant. A simple model has been used to extract kinetic data from the measured yield of the single-addition (C3H4O) product at surface temperatures from 30-100 K. This modelling reveals that the barrier of the solid-state reaction between propyne and a single oxygen atom (160 +/- 10 K) is an order of magnitude less than that reported for the gas-phase reaction. In addition, estimates for the desorption energy of propyne and reaction rate coefficient, as a function of temperature, are determined for the single addition process from the modelling. The yield of the single addition product falls as the surface temperature decreases from 50 K to 30K, but rises again as the surface temperature falls below 30 K. This increase in the rate of reaction at low surface temperatures is indicative of an alternative, perhaps barrierless, pathway to the single addition product which is only important at low surface temperatures. The kinetic model has been further developed to characterize the double addition reaction, which appears to involve the addition of a second oxygen atom to C3H4O. This modelling indicates that this second addition is a barrierless process. The kinetic parameters we extract from our experiments indicate that the reaction between atomic oxygen and propyne could occur under on interstellar dust grains on an astrophysical time scale.

  17. Atomic Oxygen and Space Environment Effects on Aerospace Materials Flown with EOIM-3 Experiment

    NASA Technical Reports Server (NTRS)

    Scialdone, John J.; Clatterbuck, Carroll H.; Ayres-Treusdell, Mary; Park, Gloria; Kolos, Diane

    1996-01-01

    Polymer materials samples mounted on a passive carrier tray were flown aboard the STS-46 Atlantis shuttle as complement to the EOIM-3 (Evaluation of Oxygen Interaction with Materials) experiment to evaluate the effects of atomic oxygen on the materials and to measure the gaseous shuttle bay environment. The morphological changes of the samples produced by the atomic oxygen fluence of 2.07 x 10(exp 20) atoms/cm(exp 2) are being reported. The changes have been verified using Electron Spectroscopy for Chemical Analysis (ESCA), gravimetric measurement, microscopic observations and thermo-optical measurements. The samples, including Kapton, Delrin, epoxies, Beta Cloth, Chemglaze Z306, silver Teflon, silicone coatings, 3M tape and Uralane and Ultem, PEEK, Victrex (PES), Polyethersulfone and Polymethylpentene thermoplastic, have been characterized by their oxygen reaction efficiency on the basis of their erosion losses and the oxygen fluence. Those efficiencies have been compared to results from other experiments, when available. The efficiencies of the samples are all in the range of E-24 g/atom. The results indicate that the reaction efficiencies of the reported materials can be grouped in about three ranges of values. The least affected materials which have efficiencies varying from 1 to 10(exp 25) g/atom, include silicones, epoxies, Uralane and Teflon. A second group with efficiency from 10 to 45(exp 25) g/atom includes additional silicone coatings, the Chemglaze Z306 paint and Kapton. The third range from 50 to 75(exp 25) includes organic compound such as Pentene, Peek, Ultem, Sulfone and a 3M tape. A Delrin sample had the highest reaction efficiency of 179(exp 25) g/atom. Two samples, the aluminum Beta cloth X389-7 and the epoxy fiberglass G-11 nonflame retardant, showed a slight mass increase.

  18. Use of Atomic Oxygen for Increased Water Contact Angles of Various Polymers for Biomedical Applications

    NASA Technical Reports Server (NTRS)

    deGroh, Kim; Berger, Lauren; Roberts, Lily

    2009-01-01

    The purpose of this study was to determine the effect of atomic oxygen (AO) exposure on the hydrophilicity of nine different polymers for biomedical applications. Atomic oxygen treatment can alter the chemistry and morphology of polymer surfaces, which may increase the adhesion and spreading of cells on Petri dishes and enhance implant growth. Therefore, nine different polymers were exposed to atomic oxygen and water-contact angle, or hydrophilicity, was measured after exposure. To determine whether hydrophilicity remains static after initial atomic oxygen exposure, or changes with higher fluence exposures, the contact angles between the polymer and water droplet placed on the polymer s surface were measured versus AO fluence. The polymers were exposed to atomic oxygen in a 100-W, 13.56-MHz radio frequency (RF) plasma asher, and the treatment was found to significantly alter the hydrophilicity of non-fluorinated polymers. Pristine samples were compared with samples that had been exposed to AO at various fluence levels. Minimum and maximum fluences for the ashing trials were set based on the effective AO erosion of a Kapton witness coupon in the asher. The time intervals for ashing were determined by finding the logarithmic values of the minimum and maximum fluences. The difference of these two values was divided by the desired number of intervals (ideally 10). The initial desired fluence was then multiplied by this result (2.37), as was each subsequent desired fluence. The flux in the asher was determined to be approximately 3.0 x 10(exp 15) atoms/sq cm/sec, and each polymer was exposed to a maximum fluence of 5.16 x 10(exp 20) atoms/sq cm.

  19. A Fiber Optic Catalytic Sensor for Neutral Atom Measurements in Oxygen Plasma

    PubMed Central

    Zaplotnik, Rok; Vesel, Alenka; Mozetic, Miran

    2012-01-01

    The presented sensor for neutral oxygen atom measurement in oxygen plasma is a catalytic probe which uses fiber optics and infrared detection system to measure the gray body radiation of the catalyst. The density of neutral atoms can be determined from the temperature curve of the probe, because the catalyst is heated predominantly by the dissipation of energy caused by the heterogeneous surface recombination of neutral atoms. The advantages of this sensor are that it is simple, reliable, easy to use, noninvasive, quantitative and can be used in plasma discharge regions. By using different catalyst materials the sensor can also be applied for detection of neutral atoms in other plasmas. Sensor design, operation, example measurements and new measurement procedure for systematic characterization are presented. PMID:22666005

  20. On the electron affinity of the oxygen atom

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Langhoff, S. R.; Partridge, H.; Taylor, P. R.

    1986-01-01

    The electron affinity of oxygen is computed to be 1.287 eV, at the full CI level using a 6s5p3d 2f Slater-type orbital basis and correlating only the 2p electrons. The best CASSCF-MRCI result including only 2p correlation is 1.263 eV. However, inclusion of 2s intrashell and 2s2p intershell coorelation increases the computed EA to 1.290 eV at the CASSCF-MRCI level. At the full CI basis set limit, the 2s contribution to the electron affinity is estimated to be as large as 0.1 eV. The higher excitation contribution to the electron affinity is found to increase substantially with basis set completeness, especially when the 2s electrons are correlated. Relativistic effects are shown to make a small (less than 0.01 eV) change in the EA.

  1. On the electron affinity of the oxygen atom

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.; Langhoff, S. R.; Partridge, H.; Taylor, P. R.

    1986-01-01

    The electron affinity (EA) of oxygen is computed to be 1.287 eV, using 2p electron full configuration-interaction (CI) wave functions expanded in a 6s5p3d2f Slater-type orbital basis. The best complete active space self-consistent field - multireference CI (CASSCF-MRCI) result including only 2p correlation is 1.263 eV. However, inclusion of 2s intrashell and 2s2p intershell correlation increases the computed EA to 1.290 at the CASSCF-MRCI level. At the full CI basis set limit, the 2s contribution to the electron affinity is estimated to be as large as 0.1 eV. This study clearly establishes the synergistic effect between the higher excitations and basis set completeness on the electron affinity when the 2s electrons are correlated.

  2. Performance of CdZnTe detectors passivated with energetic oxygen atoms

    SciTech Connect

    Prettyman, T.H.; Hoffbauer, M.A.; Rennie, J.

    1998-12-01

    Noise caused by surface-leakage current can degrade the performance of CdZnTe spectrometers, particularly devices with closely spaced contacts such as coplanar grid detectors. In order to reduce surface leakage, the authors are treating CdZnTe detector surfaces with energetic, neutral oxygen atoms. Energetic oxygen atoms react with the surface to form a resistive oxide layer. Because the reaction is effective at room temperature, deleterious heating of the substrate is avoided. In most cases, leakage current and noise are shown to decrease significantly after treatment. The effect of the treatment on the performance of coplanar grid detectors is presented.

  3. Issues and Effects of Atomic Oxygen Interactions With Silicone Contamination on Spacecraft in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce; Rutledge, Sharon; Sechkar, Edward; Stueber, Thomas; Snyder, Aaron; deGroh, Kim; Haytas, Christy; Brinker, David

    2000-01-01

    The continued presence and use of silicones on spacecraft in low Earth orbit (LEO) has been found to cause the deposition of contaminant films on surfaces which are also exposed to atomic oxygen. The composition and optical properties of the resulting SiO(x)- based (where x is near 2) contaminant films may be dependent upon the relative rates of arrival of atomic oxygen, silicone contaminant and hydrocarbons. This paper presents results of in-space silicone contamination tests, ground laboratory simulation tests and analytical modeling to identify controlling processes that affect contaminant characteristics.

  4. Enhanced oxidative vaporization of Cr2O3 and chromium by oxygen atoms

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1974-01-01

    Rates of oxidative vaporization of Cr2O3 have been found to be markedly enhanced in the presence of oxygen atoms. Investigations were conducted over the temperature range 200-1250 C. For Cr2O3 the enhancement was about 10 to the 9th power at 550 C in oxygen containing 2.5% atoms. Rapid oxidative vaporization of bare chromium was observed below 800 C, the rate being about one-half that of Cr2O3. Results are interpreted in terms of thermochemical analysis.

  5. Protective coatings for atomic oxygen susceptible spacecraft materials - STS-41G results

    NASA Technical Reports Server (NTRS)

    Whitaker, A. F.; Burka, J. A.; Coston, J. E.; Dalins, I.; Little, S. A.

    1985-01-01

    Sixteen materials consisting of metallizations, silicones, and FEP Teflon were applied as protective coatings to selected spacecraft material surfaces and exposed on STS-41G to the LEO atomic oxygen environment. Evaluations of their protective effectiveness were made through assessing their mass loss/gain characteristics, maintenance of base material optical properties, and imperviousness to atomic oxygen attack. Generally, all coatings provided some degree of protection for the underlying material. In some cases the overcoat appeared to be too thin thereby providing inadequate protection.

  6. Atomic oxygen flux and fluence calculation for Long Duration Exposure Facility (LDEF)

    NASA Technical Reports Server (NTRS)

    Bourassa, Roger J.; Gillis, James R.

    1991-01-01

    The LDEF mission was to study the effects of the space environment on various materials over an extended period of time. One of the important factors for materials degradation in low earth orbit is the atomic oxygen fluxes and fluences experienced by the materials. These fluxes and fluences are a function of orbital parameters, solar and geomagnetic activity, and material surface orientation. Calculations of atomic oxygen fluences and fluxes for the LDEF mission are summarized. Included are descriptions of LDEF orbital parameters, solar and geomagnetic data, computer code FLUXAV, which was used to perform calculations of fluxes and fluences, along with a discussion of the calculated fluxes and fluences.

  7. Atomic Oxygen Cleaning Shown to Remove Organic Contaminants at Atmospheric Pressure

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.

    1998-01-01

    The NASA Lewis Research Center has developed and filed for a patent on a method to produce atomic oxygen at atmospheric pressure by using a direct current arc in a gas flow mixture of oxygen and helium. A prototype device has been tested for its ability to remove various soot residues from surfaces exposed to fire, and various varnishes such as acrylic and egg white.

  8. Oxygen-free atomic layer deposition of indium sulfide

    DOEpatents

    Martinson, Alex B.; Hock, Adam S.; McCarthy, Robert; Weimer, Matthew S.

    2016-07-05

    A method for synthesizing an In(III) N,N'-diisopropylacetamidinate precursor including cooling a mixture comprised of diisopropylcarbodiimide and diethyl ether to approximately -30.degree. C., adding methyllithium drop-wise into the mixture, allowing the mixture to warm to room temperature, adding indium(III) chloride as a solid to the mixture to produce a white solid, dissolving the white solid in pentane to form a clear and colorless solution, filtering the mixture over a celite plug, and evaporating the solution under reduced pressure to obtain a solid In(III) N,N'-diisopropylacetamidinate precursor. This precursor has been further used to develop a novel atomic layer deposition technique for indium sulfide by dosing a reactor with the precursor, purging with nitrogen, dosing with dilute hydrogen sulfide, purging again with nitrogen, and repeating these steps to increase growth.

  9. Mechanism and kinetics of interaction of Fe, Cr, Mo, and Mn atoms with molecular oxygen

    SciTech Connect

    Akhmadov, U.S.; Zaslonko, I.S.; Smirnov, V.N.

    1988-09-01

    By means of resonance atomic absorption in shock waves, rate constants have been measured for the interaction of atoms of a number of transition metals (Fe, Cr, Mo, and Mn) with molecular oxygen. A new method is proposed and used for determining the exponent ..gamma.. in the modified Lambert-Beer law D = element of(ZN)/sup ..gamma../. The bond strength in CrO and MoO molecules has been estimated.

  10. Trapping cold molecules and atoms: Simultaneous magnetic deceleration and trapping of cold molecular Oxygen with Lithium atoms

    NASA Astrophysics Data System (ADS)

    Akerman, Nitzan; Karpov, Michael; Segev, Yair; Bibelink, Natan; Narevicius, Julia; Narevicius, Edvardas

    2016-05-01

    Cooling molecules to the ultra-cold regime remains a major challenge in the growing field of cold molecules. The molecular internal degrees of freedom complicate the effort of direct application of laser cooling. An alternative and general path towards ultra-cold molecules relies on sympathetic cooling via collisions with laser-cooled atoms. Here, we demonstrate the first step towards application of sympathetic cooling by co-trapping of molecular Oxygen with Lithium atoms in a magnetic trap at a temperature of 300 mK. Our experiment begins with a pulsed supersonic beam which is a general source for cold high-flux atomic and molecular beams. Although the supersonic expansion efficiently cools the beam to temperatures below 1K, it also accelerates the beam to high mean velocities. We decelerate a beam of O2 in a moving magnetic trap decelerator from 375 m/s to a stop. We entrained the molecular beam with Li atoms by laser ablation prior to deceleration. The deceleration ends with loading the molecules and atoms into a static quadrupole trap, which is generated by two permanent magnets. We estimate 109 trapped molecules with background limited lifetime of 0.6 Sec. Our achievement enables application of laser cooling on the Li atoms in order to sympathetically cool the O2.

  11. Measurement of atomic oxygen in the middle atmosphere using solid electrolyte sensors and catalytic probes

    NASA Astrophysics Data System (ADS)

    Eberhart, M.; Löhle, S.; Steinbeck, A.; Binder, T.; Fasoulas, S.

    2015-09-01

    The middle- and upper-atmospheric energy budget is largely dominated by reactions involving atomic oxygen (O). Modeling of these processes requires detailed knowledge about the distribution of this oxygen species. Understanding the mutual contributions of atomic oxygen and wave motions to the atmospheric heating is the main goal of the rocket project WADIS (WAve propagation and DISsipation in the middle atmosphere). It includes, amongst others, our instruments for the measurement of atomic oxygen that have both been developed with the aim of resolving density variations on small vertical scales along the trajectory. In this paper the instrument based on catalytic effects (PHLUX: Pyrometric Heat Flux Experiment) is introduced briefly. The experiment employing solid electrolyte sensors (FIPEX: Flux φ(Phi) Probe Experiment) is presented in detail. These sensors were laboratory calibrated using a microwave plasma as a source of atomic oxygen in combination with mass spectrometer reference measurements. The spectrometer was in turn calibrated for O with a method based on methane. In order to get insight into the horizontal variability, the rocket payload had instrument decks at both ends. Each housed several sensor heads measuring during both the up- and downleg of the trajectory. The WADIS project comprises two rocket flights during different geophysical conditions. Results from WADIS-1 are presented, which was successfully launched in June 2013 from the Andøya Space Center, Norway. FIPEX data were sampled at 100 Hz and yield atomic oxygen density profiles with a vertical resolution better than 9 m. This allows density variations to be studied on very small spatial scales. Numerical simulations of the flow field around the rocket were done at several points of the trajectory to assess the influence of aerodynamic effects on the measurement results. Density profiles peak at 3 × 1010 cm-3 at altitudes of 93.6 and 96 km for the up- and downleg, respectively.

  12. Spontaneous incorporation of gold in palladium-based ternary nanoparticles makes durable electrocatalysts for oxygen reduction reaction

    PubMed Central

    Wang, Deli; Liu, Sufen; Wang, Jie; Lin, Ruoqian; Kawasaki, Masahiro; Rus, Eric; Silberstein, Katharine E.; Lowe, Michael A.; Lin, Feng; Nordlund, Dennis; Liu, Hongfang; Muller, David A.; Xin, Huolin L.; Abruña, Héctor D.

    2016-01-01

    Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd6CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd–Co–Cu lattice and distributes uniformly within the particles. The uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications. PMID:27336795

  13. Spontaneous incorporation of gold in palladium-based ternary nanoparticles makes durable electrocatalysts for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Wang, Deli; Liu, Sufen; Wang, Jie; Lin, Ruoqian; Kawasaki, Masahiro; Rus, Eric; Silberstein, Katharine E.; Lowe, Michael A.; Lin, Feng; Nordlund, Dennis; Liu, Hongfang; Muller, David A.; Xin, Huolin L.; Abruña, Héctor D.

    2016-06-01

    Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd6CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd-Co-Cu lattice and distributes uniformly within the particles. The uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications.

  14. Spontaneous incorporation of gold in palladium-based ternary nanoparticles makes durable electrocatalysts for oxygen reduction reaction

    DOE PAGES

    Wang, Deli; Liu, Sufen; Wang, Jie; Lin, Ruoqian; Kawasaki, Masahiro; Rus, Eric; Silberstein, Katharine E.; Lowe, Michael A.; Lin, Feng; Nordlund, Dennis; et al

    2016-06-23

    Replacing platinum by a less precious metal such as palladium, is highly desirable for lowering the cost of fuel-cell electrocatalysts. However, the instability of palladium in the harsh environment of fuel-cell cathodes renders its commercial future bleak. Here we show that by incorporating trace amounts of gold in palladium-based ternary (Pd6CoCu) nanocatalysts, the durability of the catalysts improves markedly. Using aberration-corrected analytical transmission electron microscopy in conjunction with synchrotron X-ray absorption spectroscopy, we show that gold not only galvanically replaces cobalt and copper on the surface, but also penetrates through the Pd–Co–Cu lattice and distributes uniformly within the particles. Themore » uniform incorporation of Au provides a stability boost to the entire host particle, from the surface to the interior. The spontaneous replacement method we have developed is scalable and commercially viable. This work may provide new insight for the large-scale production of non-platinum electrocatalysts for fuel-cell applications.« less

  15. Comparison of atomic oxygen measurements by incoherent scatter and satellite-borne mass spectrometer techniques

    NASA Technical Reports Server (NTRS)

    Hedin, A. E.; Alcayde, D.

    1974-01-01

    Atomic oxygen densities determined by the incoherent scatter technique are compared to densities deduced from satellite-borne mass spectrometer measurements and are found to agree within experimental error. The diurnal variations inferred from the incoherent scatter measurements do show, however, some departure from diurnal variations found by modeling the mass spectrometer results. Some implications of these departures are briefly discussed.

  16. Atomic Oxygen Treatment for Non-Contact Removal of Organic Protective Coatings from Painting Surfaces

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Cales, Michael

    1994-01-01

    Current techniques for removal of varnish (lacquer) and other organic protective coatings from paintings involve contact with the surface. This contact can remove pigment, or alter the shape and location of paint on the canvas surface. A thermal energy atomic oxygen plasma, developed to simulate the space environment in low Earth orbit, easily removes these organic materials. Uniform removal of organic protective coatings from the surfaces of paintings is accomplished through chemical reaction. Atomic oxygen will not react with oxides so that most paint pigments will not be affected by the reaction. For paintings containing organic pigments, the exposure can be carefully timed so that the removal stops just short of the pigment. Color samples of Alizarin Crimson, Sap Green, and Zinc White coated with Damar lacquer were exposed to atomic oxygen. The lacquer was easily removed from all of the samples. Additionally, no noticeable change in appearance was observed after the lacquer was reapplied. The same observations were made on a painted canvas test sample obtained from the Cleveland Museum of Art. Scanning electron microscope photographs showed a slight microscopic texturing of the vehicle after exposure. However, there was no removal or disturbance of the paint pigment on the surface. It appears that noncontact cleaning using atomic oxygen may provide a viable alternative to other cleaning techniques. It is especially attractive in cases where the organic protective surface cannot be acceptably or safely removed by conventional techniques.

  17. Atomic Oxygen and Energy Balance in the Mesosphere and Lower Thermosphere

    NASA Astrophysics Data System (ADS)

    Mlynczak, M. G.; Hunt, L. A.; Marshall, T.; Mertens, C. J.; Russell, J. M.; Mast, J. C.; Thompson, R. E.

    2012-12-01

    We use atomic oxygen concentrations measured by SABER in conjunction with measurements of infrared radiative cooling and solar heating to assess the energy balance in the Earth's mesosphere and lower thermosphere. Atomic oxygen plays a central role, particularly in the mesopause region, through heating due to exothermic chemical reactions. The SABER data reveal approximate balance in global heating and cooling on annual timescales. In the 11-year SABER record there is also clear evidence of the solar cycle variation in all of the heat budget terms including atomic oxygen. Long-term changes in heating and cooling rates appear consistent with each other. Uncertainty in the energy budget is due largely to uncertainty in recombination rate coefficients governing exothermic chemical reactions at mesospheric temperatures. In this talk we will show the multitude of energy budget terms derived from SABER observations, the global energy budget, the variability due to the solar cycle, and the uncertainty in the energy balance. We also examine the constraints on the global atomic oxygen concentration based on energy balance considerations.

  18. Microbial hydroxylation of quinoline in contaminated groundwater: evidence for incorporation of the oxygen atom of water.

    USGS Publications Warehouse

    Pereira, W.E.; Rostad, C.E.; Leiker, T.J.; Updegraff, D.M.; Bennett, J.L.

    1988-01-01

    Studies conducted in an aquifer contaminated by creosote suggest that quinoline is converted to 2(1H)quinolinone by an indigenous consortium of microorganisms. Laboratory microbial experiments using H218O indicate that water is the source of the oxygen atom for this hydroxylation reaction under aerobic and anaerobic conditions.

  19. Atomic oxygen interactions with protected organic materials on the Long Duration Exposure Facility (LDEF)

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Degroh, Kim K.; Bucholz, Justine L.; Cales, Michael R.

    1995-01-01

    The Long Duration Exposure Facility (LDEF) has provided an excellent opportunity to understand the nature of directed atomic oxygen interactions with protected polymers and composites. Although there were relatively few samples of materials with protective coatings on their external surfaces on LDEF which were exposed to a high atomic oxygen fluence, analysis of such samples has enabled an examination of the shape of atomic oxygen undercut cavities at defect sites in the protective coatings. Samples of front-surface aluminized (Kapton) polyimide were inspected by scanning electron microscopy to identify and measure crack defects in the aluminum protective coatings. After chemical removal of the aluminum coating, measurements were also made of the width of the oxidized undercut cavities below the crack defects. The LDEF flight undercut cavity geometries were then compared with Monte Carlo computational model undercut cavity predictions. The comparison of the LDEF results and computational modeling indicates agreement in specific undercut cavity geometries for atomic oxygen reaction probabilities dependent upon the 0.68 to 3.0 power of the energy. However, no single energy dependency was adequate to replicate flight results over a variety of aluminum crack widths.

  20. Atomic oxygen variations in MLT observed from SCIAMACHY sun-synchronous nightglow measurements

    NASA Astrophysics Data System (ADS)

    Lednyts'kyy, Olexandr; Von Savigny, Christian

    Atomic oxygen (O) is the most abundant chemically active trace gas in the Earth's mesosphere and lower thermosphere region, and plays a critical role in O_3 and OH(*) formation. The near-global night-time limb measurements of the O((1) S-(1) D) emission at 557.7 nm were performed with the sun-synchronous SCIAMACHY grating spectrometer on board of ENVISAT-1 satellite from August 2002 to April 2012 at approximately 22:00 LT. Assuming horizontal homogeneity of atmospheric layers as well as absence of absorption and scattering, the emission transport problem was analysed on the base of linear forward inversion employing regularized total least squares minimization. A photochemical model based on the generally accepted 2-step Barth transfer scheme was used for deriving atomic oxygen concentration ([O]) profiles from volume emission rate profiles. An error budget was established to quantify the maximum uncertainty, assuming independent contribution of errors for each considered model parameter. [O] profiles allow monitoring of the energy transport because of the long photochemical lifetime of ground state atomic oxygen (about some months at the 100 km altitude). A wavelet analysis was performed for the time series of [O] profiles with five degree latitude steps in daily resolution. Semiannual and significant annual oscillations, and a pronounced 11-year solar cycle were identified, considering the existence of quasi biennial oscillations. Further studies presume accounting the correlation of solar activity with atomic oxygen concentration at high altitudes.

  1. Atomic Oxygen Treatment as a Method of Recovering Smoke Damaged Paintings

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Forkapa, Mark; Stueber, Thomas; Sechkar, Edward; Malinowski, Kevin

    1998-01-01

    Smoke damage, as a result of a fire, can be difficult to remove from some types of painting media without causing swelling, leaching or pigment movement or removal. A non-contact technique has been developed which can remove soot from the surface of a painting by use of a gently flowing gas containing atomic oxygen. The atomic oxygen chemically reacts with the soot on the surface creating gasses such as carbon monoxide and carbon dioxide which can be removed through the use of an exhaust system. The reaction is limited to the surface so that the process can be timed to stop when the paint layer is reached. Atomic oxygen is a primary component of the low Earth orbital environment, but can be generated on Earth through various methods. This paper will discuss the results of atomic oxygen treatment of soot exposed acrylic gesso, ink on paper, and a varnished oil painting. Reflectance measurements were used to characterize the surfaces before and after treatment.

  2. Atomic oxygen dynamics in an air dielectric barrier discharge: a combined diagnostic and modeling approach

    NASA Astrophysics Data System (ADS)

    Baldus, Sabrina; Schröder, Daniel; Bibinov, Nikita; Schulz-von der Gathen, Volker; Awakowicz, Peter

    2015-06-01

    Cold atmospheric pressure plasmas are a promising alternative therapy for treatment of chronic wounds, as they have already shown in clinical trials. In this study an air dielectric barrier discharge (DBD) developed for therapeutic use in dermatology is characterized with respect to the plasma produced reactive oxygen species, namely atomic oxygen and ozone, which are known to be of great importance to wound healing. To understand the plasma chemistry of the applied DBD, xenon-calibrated two-photon laser-induced fluorescence spectroscopy and optical absorption spectroscopy are applied. The measured spatial distributions are shown and compared to each other. A model of the afterglow chemistry based on optical emission spectroscopy is developed to cross-check the measurement results and obtain insight into the dynamics of the considered reactive oxygen species. The atomic oxygen density is found to be located mostly between the electrodes with a maximum density of {{n}\\text{O}}=6× {{10}16} cm-3 . Time resolved measurements reveal a constant atomic oxygen density between two high voltage pulses. The ozone is measured up to 3 mm outside the active plasma volume, reaching a maximum value of {{n}{{\\text{O}3}}}=3× {{10}16} cm-3 between the electrodes.

  3. Measurement of atomic oxygen and related airglows in the lower thermosphere

    NASA Technical Reports Server (NTRS)

    Thomas, R. J.; Young, R. A.

    1981-01-01

    Instruments on board a sounding rocket were used to make simultaneous observations of atomic oxygen density and airglow emissions between 80 and 120 km. Atomic oxygen was measured with a resonance lamp and was found to have a peak density of 6 x 10 to the 11th at 94 km. Similar structure is seen in the oxygen density profile on both uplegs and downlegs. The following airglow emissions were measured by using vertical-viewing photometers: Herzberg I bands near 300 nm; O(1S) green line at 557.7 nm; background at 566 nm; O2(1 Delta g) bands at 1.27 microns; and OH (X 2 pi) Meinel bands near 1.7 microns.

  4. Rate constant for the reaction of atomic oxygen with phosphine at 298 K

    NASA Technical Reports Server (NTRS)

    Stief, L. J.; Payne, W. A.; Nava, D. F.

    1987-01-01

    The rate constant for the reaction of atomic oxygen with phosphine has been measured at 298 K using flash photolysis combined with time-resolved detection of O(3P) via resonance fluorescence. Atomic oxygen was produced by flash photolysis of N2O or NO highly diluted in argon. The results were shown to be independent of (PH3), (O), total pressure and the source of O(3P). The mean value of all the experiments is k1 = (3.6 + or -0.8) x 10 to the -11th cu cm/s (1 sigma). Two previous measurements of k1 differed by more than an order of magnitude, and the results support the higher value obtained in a discharge flow-mass spectrometry study. A comparison with rate data for other atomic and free radical reactions with phosphine is presented, and the role of these reactions in the aeronomy or photochemistry of Jupiter and Saturn is briefly considered.

  5. Atomic oxygen flux determined by mixed-phase Ag/Ag2O deposition

    SciTech Connect

    Kaspar, Tiffany C.; Droubay, Timothy C.; Chambers, Scott A.

    2010-11-01

    The flux of atomic oxygen generated in a electron cyclotron resonance (ECR) microwave plasma source was quantified by two different methods. The commonly applied approach of monitoring the frequency change of a silver-coated quartz crystal microbalance (QCM) deposition rate monitor as the silver is oxidized was found to underestimate the atomic oxygen flux by an order of magnitude compared to a more direct deposition approach. In the mixed-phase Ag/Ag2O deposition method, silver films were deposited in the presence of the plasma such that the films were partially oxidized to Ag2O; x-ray photoelectron spectroscopy (XPS) was utilized for quantification of the oxidized fraction. The inaccuracy of the QCM oxidation method was tentatively attributed to efficient catalytic recombination of O atoms on the silver surface.

  6. Atomic oxygen and O2(a^1δg) density measurements in a Micro-Cathode Sustained Discharge in oxygen and rare gases/oxygen mixtures.

    NASA Astrophysics Data System (ADS)

    Magne, L.; Bauville, G.; Jeanney, P.; Lacour, B.; Puech, V.

    2006-10-01

    This work presents first experimental investigations of atomic oxygen density and O2(a^1δg) production in a Micro-Cathode Sustained Discharge (MCSD) in pure O2 and in argon (or helium)/O2 mixtures for a total pressure up to 130 Torr. A micro-hollow cathode discharge (MHCD), 200 micron in diameter, is used as plasma cathode for a discharge between the MHCD and a third electrode placed 8 mm away. In pure oxygen, the absolute atom density was measured by Two-photon Absorption Laser Induced Fluorescence (TALIF). It will be shown that, for a current of 1 mA and a pressure of 50 Torr, an atomic density of 3 10^15 cm-3 is obtained near the micro-hollow cathode, and it decreases to 5 10^14 cm-3 near the third electrode. If the MCSD is switched off while the MHCD is still on, the atom density decreases by an order of magnitude. 2D cartography of the atom distributions will be presented for different operating conditions. The density of the O2(a^1δg) metastable state was evaluated from the intensity of the 1.27 μm transition measured with a calibrated InGaAs detector. It will be shown that O2(a^1δg) densities up to 10^16 cm-3 have been obtained for 10% O2 in an argon/oxygen mixture at 50 Torr. Work is in progress to determine conditions for generating higher O2(a^1δg) densities.

  7. ESCA Study of Poly (Vinylidene Fluoride) Tetrafluoroethylene - Ethylene Copolymer and Polyethylene Exposed to Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.; Cormia, Robert D.

    1989-01-01

    The ESCA (electron spectroscopy for chemical analysis) spectra of films of poly(vinylidene fluoride) (PVDF), tetrafluoroethylene-ethylene copolymer (TFE/ET) and polyethylene (PE) exposed to atomic oxygen (O(P-3)), in or out of the glow of a radio-frequency O2 plasma, were compared. ESCA spectra of PE films exposed to (O(P-3)) in low Earth orbit (LEO) on the STS-8 Space Shuttle were also examined. Apart from O(P-3)-induced surface recession (etching), the various polymer films exhibited surface oxidation, which proceeded towards equilibrium saturation oxygen levels. The maximum surface oxygen uptakes for in-glow or out-of-glow exposures were in the order: PE greater than TFE/ET greater than PVDF; for PE itself, the oxygen uptakes were in the order: in glow greater than out of glow greater than LEO. Given prior ESCA data on poly(vinyl fluoride) and polytetrafluoroethylene films exposed to O(P-3), the extent of surface oxidation is seen to decrease regularly with increase in fluorine substitution in a family of ethylene-type polymers. (Keywords: ESCA; poly(vinylidene fluoride); tetrafluoroethylene ethylene copolymer; polyethylene; atomic oxygen; radio-frequency oxygen plasma; low Earth orbit)

  8. Two-photon absorption laser induced fluorescence measurement of atomic oxygen density in an atmospheric pressure air plasma jet

    NASA Astrophysics Data System (ADS)

    Conway, J.; Gogna, G. S.; Gaman, C.; Turner, M. M.; Daniels, S.

    2016-08-01

    Atomic oxygen number density [O] is measured in an air atmospheric pressure plasma jet (APPJ) using two-photon absorption laser induced fluorescence (TALIF). Gas flow is fixed at 8 slpm, the RF power coupled into the plasma jet varied between 5 W and 20 W, and the resulting changes in atomic oxygen density measured. Photolysis of molecular oxygen is employed to allow in situ calibration of the TALIF system. During calibration, O2 photo-dissociation and two-photon excitation of the resulting oxygen atoms are achieved within the same laser pulse. The atomic oxygen density produced by photolysis is time varying and spatially non-uniform which needs to be corrected for to calibrate the TALIF system for measurement of atomic oxygen density in plasma. Knowledge of the laser pulse intensity I 0(t), wavelength, and focal spot size allows correction factors to be determined using a rate equation model. Atomic oxygen is used for calibration and measurement, so the laser intensity can be increased outside the TALIF quadratic laser power dependence region without affecting the calibration reliability as the laser power dependence will still be the same for both. The atomic O density results obtained are not directly benchmarked against other known density measurement techniques. The results show that the plasma jet atomic oxygen content increases as the RF power coupled into the plasma increases.

  9. Effects of combined irradiation of 500 keV protons and atomic oxygen on polyimide films

    NASA Astrophysics Data System (ADS)

    Novikov, Lev; Chernik, Vladimir; Zhilyakov, Lev; Voronina, Ekaterina; Chirskaia, Natalia

    2016-07-01

    Polyimide films are widely used on the spacecraft surface as thermal control coating, films in different constuctions, etc. However, the space ionizing radiation of different types can alter the mechanical, optical and electrical properties of polyimide films. For example, it is well known that 20-100 keV proton irradiation causes breaking of chemical bonds and destruction of the surface layer in polyimide, deterioration of its optical properties, etc. In low-Earth orbits serious danger for polymeric materials is atomic oxygen of the upper atmosphere of the Earth, which is the main component in the range of heights of 200-800 km. Due to the orbital spacecraft velocity, the collision energy of oxygen atoms with the surface ( 5 eV) enhances their reactivity and opens additional pathways of their reaction with near-surface layers of materials. Hyperthermal oxygen atom flow causes erosion of the polyimide surface by breaking chemical bonds and forming of volatiles products (primarily, CO and CO _{2}), which leads to mass losses and degradation of material properties. Combined effect of protons and oxygen plasma is expected to give rise to synergistic effects enhancing the destruction of polyimide surface layers. This paper describes experimental investigation of polyimide films sequential irradiation with protons and oxygen plasma. The samples were irradiated by 500 keV protons at fluences of 10 ^{14}-10 ^{16} cm ^{-2} produced with SINP cascade generator KG-500 and 5-20 eV neutral oxygen atoms at fluence of 10 ^{20} cm ^{-2} generated by SINP magnetoplasmodynamics accelerator. The proton bombardment causes the decrease in optical transmission coefficient of samples, but their transmittance recovers partially after the exposure to oxygen plasma. The results of the comparative analysis of polyimide optical transmission spectra, Raman and XPS spectra obtained at different stages of the irradiation of samples, data on mass loss of samples due to erosion of the surface are

  10. Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

    SciTech Connect

    López-Moreno, S.; Romero, A. H.

    2015-04-21

    Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O{sub 2} molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered.

  11. Discovery of the atomic oxygen green line in the Venus night airglow.

    PubMed

    Slanger, T G; Cosby, P C; Huestis, D L; Bida, T A

    2001-01-19

    Green line emission at 557.7 nanometers arising from the O(1S - 1D) transition of atomic oxygen has been observed on the nightside of Venus with HIRES, the echelle spectrograph on the W. M. Keck I 10-meter telescope. We also observe optical emissions of molecular oxygen, consistent with the spectra from the Venera orbiters, but our green line intensity is so high that we cannot explain how it could be inconspicuous in the Venera spectra. An upper limit for the intensity of the O(1D - 3P) oxygen red line at 630 nanometers has also been obtained. The large green/red ratio indicates that the source is not associated with the Venus ionosphere. An important conclusion is that observation of the green line in a planetary atmosphere is not an indicator of an atmosphere rich in molecular oxygen.

  12. Atomic oxygen dosimetry measurements made on STS-46 by CONCAP 2

    NASA Technical Reports Server (NTRS)

    Gregory, J. C.; Miller, G. P.; Pettigrew, P. J.; Raikar, G. N.; Cross, Jon B.; Lan, E.; Renschler, C. L.; Sutherland, W. T.

    1995-01-01

    With increasing flight duration and the possibility of a permanent facility in space, long-term monitoring of material degradation due to atomic oxygen is increasing in importance. Reliance on models to determine the fluence of atomic oxygen is not only necessarily complex but also imprecise due to the strong dependence of oxygen concentration on day/night, latitude and solar activity. Mass-spectroscopy, the traditional method for determining the gas phase species densities at low pressure, is not only expensive but is limited in the area that it can monitor. Our group has developed a simple and inexpensive dosimeter to measure the atomic oxygen fluence via the change in resistance as the sensor element is gradually oxidized. The sensors consisted of thin-film circuit elements deposited on a suitable substrate. Four-point resistance measurements were used to monitor the change in resistance. Results obtained using silver and carbon dosimeters flown on STS-46 (CONCAP 2-01) will be discussed.

  13. Atomic oxygen characteristics in a dielectric barrier discharge developed for wound treatment

    NASA Astrophysics Data System (ADS)

    Baldus, Sabrina; Schroeder, Daniel; Schulz-von der Gathen, Volker; Bibinov, Nikita; Awakowicz, Peter

    2014-10-01

    Nowadays, infected chronic wounds are a major problem of society. Atmospheric pressure plasmas like dielectric barrier discharges (DBDs) have already shown their ability of improving the wound healing process of chronic wounds in clinical trials. Yet, the mechanism of action is poorly understood. A DBD comprising a single driven electrode is a beneficial configuration for wound treatment. The patient itself functions as the counter electrode. Hence, reactive oxygen species (ROS) like ozone or atomic oxygen produced in the plasma reach the wound directly. Some ROS, including superoxide or nitric oxide, are produced by skin cells to repulse invading bacteria. Nevertheless, a very high amount of ROS leads to oxidative stress and can cause cell damage or even cell death. Therefore it is crucial to have a well characterized plasma for effective wound treatment. Plasma parameters are determined using absolutely calibrated optical emission spectroscopy. Density of atomic oxygen is measured applying xenon-calibrated two photon absorption laser induced fluorescence spectroscopy. A simulation of the afterglow chemistry, developed to gain insight in the characteristics of the atomic oxygen and its flux towards the treated surface, is cross-checked with measurement results. Work supported by the German Research Foundation within PAK816.

  14. Atomic oxygen effects on candidate coatings for long-term spacecraft in low earth orbit

    NASA Technical Reports Server (NTRS)

    Lan, E. H.; Smith, Charles A.; Cross, J. B.

    1988-01-01

    Candidate atomic oxygen protective coatings for long-term low Earth orbit (LEO) spacecraft were evaluated using the Los Alamos National Laboratory O-atom exposure facility. The coatings studied include Teflon, Al2O3, SiO2, and SWS-V-10, a silicon material. Preliminary results indicate that sputtered PTFE Teflon (0.1 micrometers) has a fluence lifetime of 10 to the 19th power O-atoms/cm (2), and sputtered silicon dioxide (0.1 micrometers), aluminum oxide (0.1 micrometers), and SWS-V-10, a silicone, (4 micrometers) have fluence lifetimes of 10 to the 20th power to 10 to the 21st power O-atoms/cm (2). There are large variations in fluence lifetime data for these coatings.

  15. Ab initio study of molecular and atomic oxygen on GeTe(111) surfaces

    SciTech Connect

    Deringer, Volker L.; Dronskowski, Richard

    2014-11-07

    Oxidation of the phase-change material germanium telluride (GeTe) is an atomic-scale process of fundamental importance, as it is detrimental to the stability of GeTe-based data-storage devices. Here, we present comprehensive density-functional theory simulations of molecular and atomic oxygen in contact with GeTe(111) surfaces. Molecular O{sub 2} is predicted to readily adsorb on the Ge-terminated (111) surface; the pristine Te-terminated counterpart, by contrast, appears quite inert. The coverage-dependent adsorption of O atoms is then investigated, and based on these data, a surface phase diagram for GeTe(111)/O is constructed. These results afford a detailed, atom-resolved picture of the initial surface oxidation of GeTe, and they harmonize well with a previous X-ray photoelectron spectroscopy study on this very topic.

  16. Vacuum ultraviolet radiation/atomic oxygen synergism in fluorinated ethylene propylene Teflon erosion

    NASA Technical Reports Server (NTRS)

    Stiegman, A. E.; Brinza, David E.; Laue, Eric G.; Anderson, Mark S.; Liang, Ranty H.

    1992-01-01

    A micrographic investigation is reported of samples of the fluorinated ethylene propylene (FEP) Teflon thermal-blanketing materials recovered from the Long-Duration Exposure Facility (LDEF) satellite. The samples are taken from the trailing edge and row 8 which correspond to exposures to vacuum UV (VUV) and VUV + atomic O, respectively. Data are taken from SEM and IR-spectra observations, and the LDEF leading-edge FEP shows a high degree of erosion, roughening, and sharp peaks angled in the direction of the flow of atomic O. The trailing edge sample influenced primarily by VUV shows a hard brittle layer and some cracked mosaic patterns. Comparisons to a reference sample suggest that the brittle layer is related to exposure to VUV and is removed by atomic-O impingement. Polymers that are stable to VUV radiation appear to be more stable in terms of atomic oxygen.

  17. In-space technology development: Atomic oxygen and orbital debris effects

    NASA Technical Reports Server (NTRS)

    Visentine, James T.; Potter, Andrew E., Jr.

    1989-01-01

    Earlier Shuttle flight experiments have shown atomic oxygen within the orbital environment can interact with many materials to produce surface recession and mass loss and combine catalytically with other constituents to generate visible and infrared glows. In addition to these effects, examinations of returned satellite hardware have shown many spacecraft materials are also susceptible to damage from high velocity impacts with orbital space debris. These effects are of particular concern for large, multi-mission spacecraft, such as Space Station and SDI operational satellites, that will operate in low-Earth orbit (LEO) during the late 1990's. Not only must these spacecraft include materials and exterior coatings that are resistant to atomic oxygen surface interactions, but these materials must also provide adequate protection against erosion and pitting that could result from numerous impacts with small particles (less than 100 microns) of orbital space debris. An overview of these concerns is presented, and activities now underway to develop materials and coatings are outlined that will provide adequate atomic protection for future spacecraft. The report also discusses atomic oxygen and orbital debris flight experiments now under development to expand our limited data base, correlate ground-based measurments with flight results, and develop an orbital debris collision warning system for use by future spacecraft.

  18. Rates and mechanisms of the atomic oxygen reaction with nickel at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Christian, J. D.; Gilbreath, W. P.

    1973-01-01

    The oxidation of nickel by atomic oxygen at pressure from 1 to 45 N/sq m between 1050 and 1250 K was investigated. In these ranges, the oxidation was found to follow the parobolic rate law, viz., K sub p = 0.0000114 exp(-13410/T) g squared/cm4/sec for films of greater than 1 micron thickness and was pressure independent. The activation enthalpy for the oxidation reaction was 112 + or - 11 kj/mole (27 + or - 3 kcal/mole). Of a number of possible mechanisms and defect structures considered, it was shown that the most likely was a saturated surface defect model for atomic oxidation, based on reaction activation enthalpies, impurity effects, pressure independence, and magnitudes of rates. A model judged somewhat less likely was one having doubly ionized cationic defects rate controlling in both atomic and molecular oxygen. From comparisons of the appropriate processes, the following enthalpy values were derived: enthalpy of activation (Ni diffusion in Ni0) = 110 + or - 30 kj/mole and standard enthalpy change for reaction formation (doubly ionized cation vacancies in Ni0 from atomic oxygen)= -9 + or - 25 kj/mole.

  19. Mathematical modeling of chemical composition modification and etching of polymers under the atomic oxygen influence

    NASA Astrophysics Data System (ADS)

    Chirskaia, Natalia; Novikov, Lev; Voronina, Ekaterina

    2016-07-01

    Atomic oxygen (AO) of the upper atmosphere is one of the most important space factors that can cause degradation of spacecraft surface. In our previous mathematical model the Monte Carlo method and the "large particles" approximation were used for simulating processes of polymer etching under the influence of AO [1]. The interaction of enlarged AO particles with the polymer was described in terms of probabilities of reactions such as etching of polymer and specular and diffuse scattering of the AO particles on polymer. The effects of atomic oxygen on protected polymers and microfiller containing composites were simulated. The simulation results were in quite good agreement with the results of laboratory experiments on magnetoplasmadynamic accelerator of the oxygen plasma of SINP MSU [2]. In this paper we present a new model that describes the reactions of AO interactions with polymeric materials in more detail. Reactions of formation and further emission of chemical compounds such as CO, CO _{2}, H _{2}O, etc. cause the modification of the chemical composition of the polymer and change the probabilities of its consequent interaction with the AO. The simulation results are compared with the results of previous simulation and with the results of laboratory experiments. The reasons for the differences between the results of natural experiments on spacecraft, laboratory experiments and simulations are discussed. N. Chirskaya, M. Samokhina, Computer modeling of polymer structures degradation under the atomic oxygen exposure, WDS'12 Proceedings of Contributed Papers: Part III - Physics, Matfyzpress Prague, 2012, pp. 30-35. E. Voronina, L. Novikov, V. Chernik, N. Chirskaya, K. Vernigorov, G. Bondarenko, and A. Gaidar, Mathematical and experimental simulation of impact of atomic oxygen of the earth's upper atmosphere on nanostructures and polymer composites, Inorganic Materials: Applied Research, 2012, vol. 3, no. 2, pp. 95-101.

  20. Bimetallic PtAu superlattice arrays: Highly electroactive and durable catalyst for oxygen reduction and methanol oxidation reactions

    NASA Astrophysics Data System (ADS)

    Feng, Jiu-Ju; He, Li-Li; Fang, Rui; Wang, Qiao-Li; Yuan, Junhua; Wang, Ai-Jun

    2016-10-01

    Superlattice arrays, an important type of nanomaterials, have wide applications in catalysis, optic/electronics and energy storage for the synergetic effects determined by both individual metals and collective interactions. Herein, a simple one-pot solvothermal coreduction approach is developed for facile preparation of bimetallic PtAu alloyed superlattice arrays (PtAu SLAs) in oleylamine, with the assistance of urea via hydrogen bonding induced self-assembly. Urea is essential in morphology-controlled process and prevents PtAu nanoparticles from the disordered aggregation. The characterization and formation mechanism of PtAu SLAs are investigated in details. The as-synthesized hybrid nanocrystals exhibit enhanced electrocatalytic performances for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline electrolyte in comparison with commercial Pt-C (50%, wt.%) and Pt black catalysts.

  1. Large-Area Atomic Oxygen Facility Used to Clean Fire-Damaged Artwork

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Steuber, Thomas J.; Sechkar, Edward A.

    2000-01-01

    In addition to completely destroying artwork, fires in museums and public buildings can soil a displayed artwork with so much accumulated soot that it can no longer be used for study or be enjoyed by the public. In situations where the surface has not undergone extensive charring or melting, restoration can be attempted. However, soot deposits can be very difficult to remove from some types of painted surfaces, particularly when the paint is fragile or flaking or when the top surface of the paint binder has been damaged. Restoration typically involves the use of organic solvents to clean the surface, but these solvents may cause the paint layers to swell or leach out. Also, immersion of the surface or swabbing during solvent cleaning may move or remove pigment through mechanical contact, especially if the fire damage extends into the paint binder. A noncontact technique of removing organic deposits from surfaces was developed out of NASA research on the effects of oxygen atoms on various materials. Atomic oxygen is present in the atmosphere surrounding the Earth at the altitudes where satellites typically orbit. It can react chemically with surface coatings or deposits that contain carbon. In the reaction, the carbon is converted to carbon monoxide and some carbon dioxide. Water vapor is also a byproduct of the reaction if the surface contains carbon-hydrogen bonds. To study this reaction, NASA developed Earth-based facilities to produce atomic oxygen for material exposure and testing. A vacuum facility designed and built by the Electro-Physics Branch of the NASA Glenn Research Center at Lewis Field to provide atomic oxygen over a large area for studying reactions in low Earth orbit has been used to successfully clean several full-size paintings. (This facility can accommodate paintings up to 1.5 by 2.1 m. The atomic oxygen plasma is produced between two large parallel aluminum plates using a radiofrequency power source operating at roughly 400 W. Atomic oxygen is

  2. Atomic oxygen in the mesosphere and lower thermosphere derived from SABER: Algorithm theoretical basis and measurement uncertainty

    NASA Astrophysics Data System (ADS)

    Mlynczak, Martin G.; Hunt, Linda A.; Mast, Jeffrey C.; Thomas Marshall, B.; Russell, James M.; Smith, Anne K.; Siskind, David E.; Yee, Jeng-Hwa; Mertens, Christopher J.; Martin-Torres, F. Javier; Thompson, R. Earl; Drob, Douglas P.; Gordley, Larry L.

    2013-06-01

    Atomic oxygen (O) is a fundamental component in chemical aeronomy of Earth's mesosphere and lower thermosphere region extending from approximately 50 km to over 100 km in altitude. Atomic oxygen is notoriously difficult to measure, especially with remote sensing techniques from orbiting satellite sensors. It is typically inferred from measurements of the ozone concentration in the day or from measurements of the Meinel band emission of the hydroxyl radical (OH) at night. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite measures OH emission and ozone for the purpose of determining the O-atom concentration. In this paper, we present the algorithms used in the derivation of day and night atomic oxygen from these measurements. We find excellent consistency between the day and night O-atom concentrations from daily to annual time scales. We also examine in detail the collisional relaxation of the highly vibrationally excited OH molecule at night measured by SABER. Large rate coefficients for collisional removal of vibrationally excited OH molecules by atomic oxygen are consistent with the SABER observations if the deactivation of OH(9) proceeds solely by collisional quenching. An uncertainty analysis of the derived atomic oxygen is also given. Uncertainty in the rate coefficient for recombination of O and molecular oxygen is shown to be the largest source of uncertainty in the derivation of atomic oxygen day or night.

  3. Bonded Radii and the Contraction of the Electron Density of the Oxygen Atom by Bonded Interactions

    SciTech Connect

    Gibbs, Gerald V.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.; Iversen, Bo B.; Spackman, M. A.

    2013-02-21

    The bonded radii for more than 550 bonded pairs of atoms, comprising more than 50 crystals, determined from experimental and theoretical electron density distributions, are compared with the effective ionic, ri(M), and crystal radii, rc(M), for metal atoms, M, bonded to O atoms. At odds with the fixed ionic radius of 1.40 Å, assumed for the O atom in the compilation of the ionic radii, the bonded radius for the atom, rb(O), is not fixed but displays a relatively wide range of values as the O atom is progressively polarized by the M-O bonded interactions: as such, rb(O) decreases systematically from 1.40 Å (the Pauling radius of the oxide anion) as bond lengths decrease when bonded to an electropositive atom like sodium, to 0.64 Å (Bragg’s atomic radius of the O atom) when bonded to an electronegative atom like nitrogen. Both rb(M) and rb(O) increase in tandum with the increasing coordination number of the M atom. The bonded radii of the M atoms are highly correlated with both ri(M) and rc(M), but they both depart systematically from rb(M) and become smaller as the electronegativity of the M atom increases and the M-O bond length decreases. The well-developed correlations between both sets of radii and rb(M) testifies to the relative precision of both sets of radii and the fact that both sets are highly correlated the M-O bond 1 lengths. On the other hand, the progressive departure of rb(O) from the fixed ionic radius of the O atom with the increasing electronegativity of the bonded M atom indicates that any compilation of sets of ionic radii, assuming that the radius for the oxygen atom is fixed in value, is problematical and impacts on the accuracy of the resulting sets of ionic and crystal radii thus compiled. The assumption of a fixed O atom radius not only results in a negative ionic radii for several atoms, but it also results in values of rb(M) that are much as ~ 0.6 Å larger than the ri(M) and rc(M) values, respectively, particularly for the more

  4. Surface reactions of molecular and atomic oxygen with carbon phosphide films.

    PubMed

    Gorham, Justin; Torres, Jessica; Wolfe, Glenn; d'Agostino, Alfred; Fairbrother, D Howard

    2005-11-01

    The surface reactions of atomic and molecular oxygen with carbon phosphide films have been studied using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Carbon phosphide films were produced by ion implantation of trimethylphosphine into polyethylene. Atmospheric oxidation of carbon phosphide films was dominated by phosphorus oxidation and generated a carbon-containing phosphate surface film. This oxidized surface layer acted as an effective diffusion barrier, limiting the depth of phosphorus oxidation within the carbon phosphide film to < 3 nm. The effect of atomic oxygen (AO) exposure on this oxidized carbon phosphide layer was subsequently probed in situ using XPS. Initially AO exposure resulted in a loss of carbon atoms from the surface, but increased the surface concentration of phosphorus atoms as well as the degree of phosphorus oxidation. For more prolonged AO exposures, a highly oxidized phosphate surface layer formed that appeared to be inert toward further AO-mediated erosion. By utilizing phosphorus-containing hydrocarbon thin films, the phosphorus oxides produced during exposure to AO were found to desorb at temperatures >500 K under vacuum conditions. Results from this study suggest that carbon phosphide films can be used as AO-resistant surface coatings on polymers.

  5. Angular distribution of photoelectrons from atomic oxygen, nitrogen and carbon. [in upper atmosphere

    NASA Technical Reports Server (NTRS)

    Manson, S. J.; Kennedy, D. J.; Starace, A. F.; Dill, D.

    1974-01-01

    The angular distributions of photoelectrons from atomic oxygen, nitrogen, and carbon are calculated. Both Hartree-Fock and Hartree-Slater (Herman-Skillman) wave functions are used for oxygen, and the agreement is excellent; thus only Hartree-Slater functions are used for carbon and nitrogen. The pitch-angle distribution of photoelectrons is discussed, and it is shown that previous approximations of energy-independent isotropic or sin squared theta distributions are at odds with the authors' results, which vary with energy. This variation with energy is discussed, as is the reliability of these calculations.

  6. Application of an oxygen-shielded air-acetylene flame to atomic spectroscopy.

    PubMed

    Stephens, R

    1973-08-01

    A burner has been designed which provides an oxygen-shielded air-acetylene flame for atomic-absorption work. The chemical reducing properties of the oxygen-shielded flame operated under fuel-rich conditions are enhanced by the higher C: O ratio obtainable in the flame and by the higher flame temperature just above the reaction zone. The flame is inherently essentially free from the risk of flashback, and is offered as an alternative to the nitrous oxide-acetylene flame for use with certain types of equipment and for particular applications.

  7. Characterization of material surfaces exposed to atomic oxygen on space shuttle missions

    NASA Technical Reports Server (NTRS)

    Fromhold, A. T.

    1985-01-01

    Material samples prepared for exposure to ambient atomic oxygen encountered during space shuttle flights in low Earth orbit were characterized by the experimental techniques of ELLIPSOMETRY, ESCA, PIXE, and RBS. The first group of samples, which were exposed during the STS-8 mission, exhibited some very interesting results. The second group of samples, which are to be exposed during the upcoming STS-17 mission, have been especially prepared to yield quantitative information on the optical changes, oxygen solution, and surface layer formation on metal films of silver, gold, nickel, chromium, aluminum, platinum, and palladium evaporated onto optically polished silicon wafers.

  8. Preparation of a silanone through oxygen atom transfer to a stable cyclic silylene.

    PubMed

    Linden, Michael M; Reisenauer, Hans Peter; Gerbig, Dennis; Karni, Miriam; Schäfer, Annemarie; Müller, Thomas; Apeloig, Yitzhak; Schreiner, Peter R

    2015-10-12

    We report the evaporation of a stable cyclic silylene and its oxidation (with ozone or N2 O) through oxygen atom transfer to form the corresponding silanone under matrix isolation conditions. As uncomplexed silanones are rare owing to their very high reactivity, this method provides an alternative route to these sought-after molecules. The silanone, as well as a novel bicyclic silane with a bridgehead silicon atom derived from an intramolecular silylene CH bond insertion, were characterized by comparison of high-resolution infrared spectra with density functional theory (DFT) computations at the M06-2X/cc-pVDZ level of theory. PMID:26315924

  9. Enhancement of oxidative vaporization of chromium (III) oxide and chromium by oxygen atoms

    NASA Technical Reports Server (NTRS)

    Fryburg, G. C.; Kohl, F. J.; Stearns, C. A.

    1974-01-01

    Rates of oxidative vaporization of Cr2O3 were found to be markedly enhanced in the presence of O atoms. Investigations were conducted over the temperature range 470 to 1520 K. For Cr2O3 the enhancement was about 10 to the 9th power at 820 K in oxygen containing 2.5 percent atoms. Rapid oxidative vaporization of bare chromium was observed below 1070 K, the rate being about one-half that of Cr2O3. Results are interpreted in terms of thermochemical analysis.

  10. Preparation of a silanone through oxygen atom transfer to a stable cyclic silylene.

    PubMed

    Linden, Michael M; Reisenauer, Hans Peter; Gerbig, Dennis; Karni, Miriam; Schäfer, Annemarie; Müller, Thomas; Apeloig, Yitzhak; Schreiner, Peter R

    2015-10-12

    We report the evaporation of a stable cyclic silylene and its oxidation (with ozone or N2 O) through oxygen atom transfer to form the corresponding silanone under matrix isolation conditions. As uncomplexed silanones are rare owing to their very high reactivity, this method provides an alternative route to these sought-after molecules. The silanone, as well as a novel bicyclic silane with a bridgehead silicon atom derived from an intramolecular silylene CH bond insertion, were characterized by comparison of high-resolution infrared spectra with density functional theory (DFT) computations at the M06-2X/cc-pVDZ level of theory.

  11. Comparison of Hyperthermal Ground Laboratory Atomic Oxygen Erosion Yields With Those in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Dill, Grace C.; Loftus, Ryan J.; deGroh, Kim K.; Miller, Sharon K.

    2013-01-01

    The atomic oxygen erosion yields of 26 materials (all polymers except for pyrolytic graphite) were measured in two directed hyperthermal radio frequency (RF) plasma ashers operating at 30 or 35 kHz with air. The hyperthermal asher results were compared with thermal energy asher results and low Earth orbital (LEO) results from the Materials International Space Station Experiment 2 and 7 (MISSE 2 and 7) flight experiments. The hyperthermal testing was conducted to a significant portion of the atomic oxygen fluence similar polymers were exposed to during the MISSE 2 and 7 missions. Comparison of the hyperthermal asher prediction of LEO erosion yields with thermal energy asher erosion yields indicates that except for the fluorocarbon polymers of PTFE and FEP, the hyperthermal energy ashers are a much more reliable predictor of LEO erosion yield than thermal energy asher testing, by a factor of four.

  12. Ground radiation tests and flight atomic oxygen tests of ITO protective coatings for Galileo Spacecraft

    NASA Technical Reports Server (NTRS)

    Bouquet, Frank L.; Maag, Carl R.

    1986-01-01

    Radiation simulation tests (protons and electrons) were performed along with atomic oxygen flight tests aboard the Shuttle to space qualify the surface protective coatings. The results, which contributed to the selection of indium-tin-oxide (ITO) coated polyester as the material for the thermal blankets of the Galileo Spacecraft, are given here. Two candidate materials, polyester and Fluorglas, were radiation-tested to determine changes at simulated Jovian radiation levels. The polyester exhibited a smaller weight loss (2.8) than the Fluorglas (8.8 percent). Other changes of polyester are given. During low-earth orbit, prior to transit to Jupiter, the thermal blankets would be exposed to atomic oxygen. Samples of uncoated and ITO-coated polyesters were flown on the Shuttle. Qualitative results are given which indicated that the ITO coating protected the underlying polyester.

  13. Aurora Borealis: stochastic cellular automata simulations of the excited-state dynamics of oxygen atoms.

    NASA Astrophysics Data System (ADS)

    Seybold, P. G.; Kier, L. B.; Cheng, C.-K.

    1999-12-01

    Emissions from the 1S and 1D excited states of atomic oxygen play a prominent role in creating the dramatic light displays (aurora borealis) seen in the skies over polar regions of the Northern Hemisphere. A probabilistic asynchronous cellular automaton model described previously has been applied to the excited-state dynamics of atomic oxygen. The model simulates the time-dependent variations in ground (3P) and excited-state populations that occur under user-defined probabilistic transition rules for both pulse and steady-state conditions. Although each trial simulation is itself an independent "experiment", deterministic values for the excited-state emission lifetimes and quantum yields emerge as limiting cases for large numbers of cells or large numbers of trials. Stochastic variations in the lifetimes and emission yields can be estimated from repeated trials.

  14. Oxidation of diamond films by atomic oxygen: High resolution electron energy loss spectroscopy studies

    NASA Astrophysics Data System (ADS)

    Shpilman, Z.; Gouzman, I.; Grossman, E.; Akhvlediani, R.; Hoffman, A.

    2007-12-01

    Diamond surface oxidation by atomic oxygen, annealing up to ˜700°C, and in situ exposure to thermally activated hydrogen were studied by high resolution electron energy loss spectroscopy (HREELS). After atomic oxygen (AO) exposure, HREELS revealed peaks associated with CHx groups, carbonyl, ether, and peroxide-type species and strong quenching of the diamond optical phonon and its overtones. Upon annealing of the oxidized surfaces, the diamond optical phonon overtones at 300 and 450meV emerge and carbonyl and peroxide species gradually desorb. The diamond surface was not completely regenerated after annealing to ˜700°C and in situ exposure to thermally activated hydrogen, probably due to the irreversible deterioration of the surface by AO.

  15. Results of apparent atomic oxygen reactions with spacecraft materials during shuttle flight STS-41G

    NASA Technical Reports Server (NTRS)

    Zimcik, D. G.; Maag, C. R.

    1985-01-01

    The effect of atomic oxygen interaction experienced by polymeric-based spacecraft materials is described. An experimental package (ACOMEX) flown on shuttle mission STS-41G carried out the investigation of advanced composite specimens such as carbon-epoxy and Kevlar-epoxy both with and without protective coatings added to thermal protective paints and films. Information on the exposure environment of the specimens was provided by a carbon coated atomic oxygen fluence monitor together with a photographic record. Mass loss measurements and photomicrographs made possible the analysis of the effect of interaction. After a total of about 38 hours of equivalent normal exposure at 225 km altitude the results showed that unprotected exposed surfaces exhibited severe erosion and mass loss with the possibility of seriously degrading structural and thermal performance. However, the specimens with a thin fluorocarbon overcoat showed promise of providing a protective barrier to the attack without altering the base properties of the material.

  16. Determination of atomic oxygen density and temperature of the thermosphere by remote sensing

    NASA Astrophysics Data System (ADS)

    Sharma, Ramesh D.; Harlow, Harry B.; Riehl, James P.

    1988-06-01

    Measurement of emission from the earth's atmosphere in the far infrared due to transitions between fine structure levels of the ground state (3P) of atomic oxygen at 63 microns, (3P1 to 3P2) and 147 microns (3P0 to 3P1) is proposed. These magnetic-dipole allowed transitions with long radiative lifetimes (about 3.2 h for the 63 micron transition and about 16.3 h for the 147 micron transition) are assumed to be in equilibrium with the local translational temperature. A one-dimensional onion-peel inversion of the limb emissions at 63 and 147 microns from a model atmosphere is shown to yield reasonable results for both the temperature and atomic oxygen density in the 90-250 km altitude range.

  17. Pinhole cameras as sensors for atomic oxygen in orbit: Application to attitude determination of the LDEF

    NASA Technical Reports Server (NTRS)

    Peters, Palmer N.; Gregory, John C.

    1992-01-01

    Images produced by pinhole cameras using film sensitive to atomic oxygen provide information on the ratio of spacecraft orbital velocity to the most probable thermal speed of oxygen atoms, provided the spacecraft orientation is maintained stable relative to the orbital direction. Alternatively, information on the spacecraft attitude relative to the orbital velocity can be obtained, provided that corrections are properly made for thermal spreading and a corotating atmosphere. The Long Duration Exposure Facility (LDEF) orientation, uncorrected for a corotating atmosphere, was determined to be yawed 8.0 +/- 0.4 degrees from its nominal attitude, with an estimated +/- 0.35 degree oscillation in yaw. The integrated effect of inclined orbit and corotating atmosphere produces an apparent oscillation in the observed yaw direction, suggesting that the LDEF attitude measurement will indicate even better stability when corrected for a corotating atmosphere. The measured thermal spreading is consistent with major exposure occurring during high solar activity, which occurred late during the LDEF mission.

  18. Atomic Oxygen Sensors Based on Nanograin ZnO Films Prepared by Pulse Laser Deposition

    SciTech Connect

    Wang Yunfei; Chen Xuekang; Li Zhonghua; Zheng Kuohai; Wang Lanxi; Feng Zhanzu; Yang Shengsheng

    2009-01-05

    High-quality nanograin ZnO thin films were deposited on c-plane sapphire (Al{sub 2}O{sub 3}) substrates by pulse laser deposition (PLD). Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to characterize the samples. The structural and morphological properties of ZnO films under different deposition temperature have been investigated before and after atomic oxygen (AO) treatment. XRD has shown that the intensity of the (0 0 2) peak increases and its FWHM value decreases after AO treatment. The AO sensing characteristics of nano ZnO film also has been investigated in a ground-based atomic oxygen simulation facility. The results show that the electrical conductivity of nanograin ZnO films decreases with increasing AO fluence and that the conductivity of the films can be recovered by heating.

  19. Gas flow dependence of ground state atomic oxygen in plasma needle discharge at atmospheric pressure

    SciTech Connect

    Sakiyama, Yukinori; Graves, David B.; Knake, Nikolas; Schroeder, Daniel; Winter, Joerg; Schulz-von der Gathen, Volker

    2010-10-11

    We present clear evidence that ground state atomic oxygen shows two patterns near a surface in the helium plasma needle discharge. Two-photon absorption laser-induced fluorescence spectroscopy, combined with gas flow simulation, was employed to obtain spatially-resolved ground state atomic oxygen densities. When the feed gas flow rate is low, the radial density peaks along the axis of the needle. At high flow rate, a ring-shaped density distribution appears. The peak density is on the order of 10{sup 21} m{sup -3} in both cases. The results are consistent with a previous report of the flow-dependent bacterial killing pattern observed under similar conditions.

  20. Comet-like interaction of Venus with the solar wind III the atomic oxygen corona

    SciTech Connect

    Wallis, M.K.

    1982-04-01

    Suprathermal atomic oxygen constituting an extensive exospheric corona give rise to new heavy ions within the solar plasma flowing around Venus. Because their gyro-radii are large compared with transverse scales, the 0/sup +/ ions do not simply effect a drag due to 'mass loading' of the flow. Some precipitate into the ionosphere and provide a novel ion source. Also, the back-reaction on the flow not only decelerates it, but also deviates it laterally and essentially asymmetrically about the planet.

  1. Variations in the atomic oxygen 630 nm emission intensity related to orography

    NASA Astrophysics Data System (ADS)

    Nasyrov, G. A.

    2009-08-01

    The spatial variations in the emission intensity, related to internal gravity waves (IGWs) generated in the troposphere when the air flows around the Kopet Dagh mountain range, and the regularities of these variations have been detected for the first time based on the photometric measurements of the spatial distribution of the atomic oxygen 630 nm emission intensity, performed in 1967 at Vannovskii station of the Physicotechnical Institute, Academy of Sciences of the Turkmen SSR.

  2. Automated Multiple-Sample Tray Manipulation Designed and Fabricated for Atomic Oxygen Facility

    NASA Technical Reports Server (NTRS)

    Sechkar, Edward A.; Stueber, Thomas J.; Dever, Joyce A.; Banks, Bruce A.; Rutledge, Sharon K.

    2000-01-01

    Extensive improvements to increase testing capacity and flexibility and to automate the in situ Reflectance Measurement System (RMS) are in progress at the Electro-Physics Branch s Atomic Oxygen (AO) beam facility of the NASA Glenn Research Center at Lewis Field. These improvements will triple the system s capacity while placing a significant portion of the testing cycle under computer control for added reliability, repeatability, and ease of use.

  3. Efficient and durable oxygen reduction and evolution of a hydrothermally synthesized La(Co0.55Mn0.45)0.99O3-δ nanorod/graphene hybrid in alkaline media

    NASA Astrophysics Data System (ADS)

    Ge, Xiaoming; Goh, F. W. Thomas; Li, Bing; Hor, T. S. Andy; Zhang, Jie; Xiao, Peng; Wang, Xin; Zong, Yun; Liu, Zhaolin

    2015-05-01

    The increasing global energy demand and the depletion of fossil fuels have stimulated intense research on fuel cells and batteries. Oxygen electrocatalysis plays essential roles as the electrocatalytic reduction and evolution of di-oxygen are always the performance-limiting factors of these devices relying on oxygen electrochemistry. A novel perovskite with the formula La(Co0.55Mn0.45)0.99O3-δ (LCMO) is designed from molecular orbital principles. The hydrothermally synthesized LCMO nanorods have unique structural and chemical properties and possess high intrinsic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The synergic covalent coupling between LCMO and NrGO enhances the bifunctional ORR and OER activities of the novel LCMO/NrGO hybrid catalyst. The ORR activity of LCMO/NrGO is comparable to the state-of-the-art Pt/C catalyst and its OER activity is competitive to the state-of-the-art Ir/C catalyst. LCMO/NrGO generally outperforms Pt/C and Ir/C with better bifunctional ORR and OER performance and operating durability. LCMO/NrGO represents a new class of low-cost, efficient and durable electrocatalysts for fuel cells, water electrolysers and batteries.The increasing global energy demand and the depletion of fossil fuels have stimulated intense research on fuel cells and batteries. Oxygen electrocatalysis plays essential roles as the electrocatalytic reduction and evolution of di-oxygen are always the performance-limiting factors of these devices relying on oxygen electrochemistry. A novel perovskite with the formula La(Co0.55Mn0.45)0.99O3-δ (LCMO) is designed from molecular orbital principles. The hydrothermally synthesized LCMO nanorods have unique structural and chemical properties and possess high intrinsic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The synergic covalent coupling between LCMO and NrGO enhances the bifunctional ORR and OER activities of the novel LCMO/NrGO hybrid

  4. The Effect of Ash and Inorganic Pigment Fill on the Atomic Oxygen Erosion of Polymers and Paints (ISMSE-12)

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Simmons, Julie C.; de Groh, Kim K.; Miller, Sharon K.

    2012-01-01

    Low atomic oxygen fluence (below 1x10(exp 20) atoms/sq cm) exposure of polymers and paints that have a small ash content and/or inorganic pigment fill does not cause a significant difference in erosion yield compared to unfilled (neat) polymers or paints. However, if the ash and/or inorganic pigment content is increased, the surface population of the inorganic content will begin to occupy a significant fraction of the surface area as the atomic oxygen exposure increases because the ash is not volatile and remains as a loosely attached surface layer. This results in a reduction of the flux of atomic oxygen reacting with the polymer and a reduction in the rate of erosion of the polymer remaining. This paper presents the results of ground laboratory and low Earth orbital (LEO) investigations to evaluate the fluence dependence of atomic oxygen erosion yields of polymers and paints having inorganic fill content.

  5. Additives to reduce susceptibility of thermosets and thermoplastics to erosion from atomic oxygen

    NASA Technical Reports Server (NTRS)

    Orwoll, Robert A.

    1990-01-01

    Polymeric materials have many attractive features such as light weight, high strength, and broad applicability in the form of films, fibers, and molded objects. In low earth orbit (LEO), these materials, when exposed on the exterior of the spacecraft, have the serious disadvantage of being susceptible to erosion by atomic oxygen (AO). AO is the most common chemical species at LEO altitudes. AO can be an extremely efficient oxidizing agent as was apparent from the extensive erosion of organic films exposed in STS missions. The mechanism for erosion involves the reaction of oxygen atoms at the surface of the substrate to form small molecular species. The susceptibility of polymeric materials varies with their chemical composition. Films with silicon atoms incorporated in the molecular structures have large coefficients of thermal expansion. This limits their utility. In an alternative approach additives were sought that mix physically and form a protective oxide layer when the film is exposed to AO. A large number of organic compounds containing silicon, germanium, or tin atoms were screened. Most were found to have very limited solubility in the polyetherimide (Ultem) films that were being protected from AO. However, one, bis(triphenyl tin) oxide, (BTO), is miscible in Ultem up to about 25 percent. Films of Ultem polyimide containing up to 25 wt percent BTO were prepared by evaporation of solvent from a solution of Ultem and BTO. The effects of AO on these films were simulated in the oxygen atmosphere of a radio frequency glow-discharge chamber. In the second part of this study, atoms were incorporated in epoxy resins. Experiments are in progress to measure the resistance of films of the cured epoxy to AO in the discharge chamber.

  6. Atomic Oxygen Erosion Yield Prediction for Spacecraft Polymers in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Backus, Jane A.; Manno, Michael V.; Waters, Deborah L.; Cameron, Kevin C.; deGroh, Kim K.

    2009-01-01

    The ability to predict the atomic oxygen erosion yield of polymers based on their chemistry and physical properties has been only partially successful because of a lack of reliable low Earth orbit (LEO) erosion yield data. Unfortunately, many of the early experiments did not utilize dehydrated mass loss measurements for erosion yield determination, and the resulting mass loss due to atomic oxygen exposure may have been compromised because samples were often not in consistent states of dehydration during the pre-flight and post-flight mass measurements. This is a particular problem for short duration mission exposures or low erosion yield materials. However, as a result of the retrieval of the Polymer Erosion and Contamination Experiment (PEACE) flown as part of the Materials International Space Station Experiment 2 (MISSE 2), the erosion yields of 38 polymers and pyrolytic graphite were accurately measured. The experiment was exposed to the LEO environment for 3.95 years from August 16, 2001 to July 30, 2005 and was successfully retrieved during a space walk on July 30, 2005 during Discovery s STS-114 Return to Flight mission. The 40 different materials tested (including Kapton H fluence witness samples) were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The MISSE 2 PEACE Polymers experiment used carefully dehydrated mass measurements, as well as accurate density measurements to obtain accurate erosion yield data for high-fluence (8.43 1021 atoms/sq cm). The resulting data was used to develop an erosion yield predictive tool with a correlation coefficient of 0.895 and uncertainty of +/-6.3 10(exp -25)cu cm/atom. The predictive tool utilizes the chemical structures and physical properties of polymers to predict in-space atomic oxygen erosion yields. A predictive tool concept (September 2009 version) is presented which represents an improvement over an earlier (December 2008) version.

  7. Optical characterization of photofixed RTV effluent in an atomic oxygen atmosphere

    NASA Astrophysics Data System (ADS)

    Pu, J.; Ianno, N. J.

    2014-09-01

    It is well know that the elevated satellite operating temperature causes the unused catalyst material in the Room Temperature Vulcanized materials (RTV) to volatize, which can then re-deposit or condense onto other spacecraft surfaces. In the presence of sunlight, this Volatile Condensable Material (VCM) can photo-chemically deposit onto optically-sensitive spacecraft surfaces and significantly alter their original, beginning-of-life (BOL) optical properties, such as solar absorptance and emittance, causing unintended performance loss of the spacecraft. This has been studied in vacuum environments simulating geosynchronous orbits, but never to our knowledge in atomic oxygen environments simulating low earth orbit. In this work we present an initial study of the effect of an atomic oxygen environment on the optical properties of previously photofixed material as well the effect of an atomic oxygen environment on the photofixing process. We will employ spectroscopic ellipsometry to characterize films deposited from the outgassing of DC93500, RTV566, SCV2590, CV2568 and SCV2590-2.

  8. Europa - Ultraviolet emissions and the possibility of atomic oxygen and hydrogen clouds

    NASA Technical Reports Server (NTRS)

    Wu, F.-M.; Judge, D. L.; Carlson, R. W.

    1978-01-01

    Emission signals from Europa with wavelength below 800 A were detected by the Pioneer 10 ultraviolet photometer. In the present paper, improved procedures for data reduction are used to determine the spatial region as well as the intensity of the suggested emission sources. The observations indicate a cloud with a radius of about 1.5 Jupiter radii and an apparent brightness of approximately 10 rayleighs for a wavelength of 500 A. It is argued that neutral oxygen atoms, along with neutral hydrogen, are produced through dissociation of water ice on the surface of Europa by particle impact. Electron impact ionization excitation of oxygen atoms in the resulting cloud then gives rise to the observed emission. The present source brightness and cloud radius results are used to estimate an oxygen column density of the order of 10 trillion per sq cm, while the density of atomic hydrogen is at most 100 billion per sq cm and 1 trillion per sq cm for molecular hydrogen.

  9. Atomic Oxygen Density Retrievals using FUV Observations by the Imaging Ultraviolet Spectrograph on MAVEN

    NASA Astrophysics Data System (ADS)

    Evans, J. Scott; Stevens, Michael H.; Schneider, Nicholas M.; Stewart, Ian; Deighan, Justin; Jain, Sonal Kumar; Eparvier, Francis; Thiemann, E. M.; Bougher, Stephen W.; Jakosky, Bruce

    2016-10-01

    We present the first direct retrievals of neutral atomic oxygen in Mars's upper atmosphere using daytime FUV periapse limb scan observations from 130 – 200 km tangent altitude. Atmospheric composition is inferred using the Atmospheric Ultraviolet Radiance Integrated Code [Strickland et al., 1999] adapted to the Martian atmosphere [Evans et al., 2015]. For our retrievals we use O I 135.6 nm emission observed by IUVS on MAVEN under daytime conditions (solar zenith angle < 60 degrees) over both northern and southern hemispheres (latitudes between -65 and +35 degrees) from October 2014 to August 2016. We investigate the sensitivity of atomic oxygen density retrievals to variability in solar irradiance, solar longitude, and local time. We compare our retrievals to predictions from the Mars Global Ionosphere-Thermosphere Model [MGITM, Bougher et al., 2015] and the Mars Climate Database [MCD, Forget et al., 1999] and quantify the differences throughout the altitude region of interest. The retrieved densities are used to characterize global transport of atomic oxygen in the Martian thermosphere.

  10. Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Bank, Bruce A.; de Groh, Kim K.; Backus, Jane A.

    2008-01-01

    A predictive tool was developed to estimate the low Earth orbit (LEO) atomic oxygen erosion yield of polymers based on the results of the Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment flown as part of the Materials International Space Station Experiment 2 (MISSE 2). The MISSE 2 PEACE experiment accurately measured the erosion yield of a wide variety of polymers and pyrolytic graphite. The 40 different materials tested were selected specifically to represent a variety of polymers used in space as well as a wide variety of polymer chemical structures. The resulting erosion yield data was used to develop a predictive tool which utilizes chemical structure and physical properties of polymers that can be measured in ground laboratory testing to predict the in-space atomic oxygen erosion yield of a polymer. The properties include chemical structure, bonding information, density and ash content. The resulting predictive tool has a correlation coefficient of 0.914 when compared with actual MISSE 2 space data for 38 polymers and pyrolytic graphite. The intent of the predictive tool is to be able to make estimates of atomic oxygen erosion yields for new polymers without requiring expensive and time consumptive in-space testing.

  11. Effect of Atomic Oxygen Exposure on Surface Resistivity Change of Spacecraft Insulator Material

    NASA Astrophysics Data System (ADS)

    Mundari, Noor Danish Ahrar; Khan, Arifur Rahman; Chiga, Masaru; Okumura, Teppei; Masui, Hirokazu; Iwata, Minoru; Toyoda, Kazuhiro; Cho, Mengu

    Spacecraft surface charging can lead to arcing and a loss of electricity generation capability in solar panels or even loss of a satellite. The charging problem may be further aggravated by atomic oxygen (AO) exposure in Low Earth orbits, which modifies the surface of materials like polyimide, Teflon, anti-reflective coatings, cover glass etc, used on satellite surfaces, affecting materials properties, such as resistivity, secondary electron emissivity and photo emission, which govern the charging behavior. These properties are crucial input parameters for spacecraft charging analysis. To study the AO exposure effect on charging governing properties, an atomic oxygen exposure facility based on laser detonation of oxygen was built. The facility produces AO with a peak velocity value around 10-12km/s and a higher flux than that existing in orbit. After exposing the polyimide test material to the equivalent of 10 years of AO fluence at an altitude of 700-800 km, surface charging properties like surface resistivity and volume resistivity were measured. The measurement was performed in a vacuum using the charge storage decay method at room temperature, which is considered the most appropriate for measuring resistivity for space applications. The results show that the surface resistivity increases and the volume resistivity remains almost the same for the AO exposure fluence of 5.4×1018 atoms cm-2.

  12. Twilight rocket measurements of high-latitude atomic oxygen density during the DYANA campaign

    NASA Astrophysics Data System (ADS)

    Ulwick, J. C.; Ratkowski, A. J.; Makhlouf, U.

    1994-12-01

    During the DYANA (DYnamics Adapted Network for the Atmosphere) campaign, a rocket containing a resonance fluorescence experiment for measurement of atomic oxygen concentrations was launced at twilight-dawn from ESRANGE, Kiruna, Sweden in March 1990. The measured atomic oxygen concetration rose very sharply near 80 km to about 10(exp 11) atoms/cu cm, achieved a peak value of 3 x 10(exp 11) atoms/cu cm between 90 to 105 km, and decreased with increasing rocket altitude to about 155 km where the instrument's noise level was reached. In addition, ground-based, near-infrared radiometric and spectral measurements of the mesospheric and lower thermospheric hydroxyl (OH) airglow emissions were also obtained during the night up to the time of rocket launch. We have used least-squares spectral fitting procedures to obtain the OH Meinel (3-1) band intensities and accurate (+/-2.5K) rotational temperatures from individual scans. The band intensities show considerable structure throughout the night, dropping sharply by about a factor of 3 during sunrise when the rocket was launched. The rotational temperatures were consistently around 225 K throughout the night and during the rocket flight. During the MAP/WINE campaign in February 1984, similar measurements using identical rocket-borne and ground-based techniques were made at night from ESRANGE. In this paper, the DYANA and MAP/WINE measurements are inter-compared and discussed and further compared with model calculations.

  13. Oxygen chemisorption effects on the spatial atomic distribution of CuNi, CuPd and NiPt nanostructures

    NASA Astrophysics Data System (ADS)

    Montejano-Carrizales, J. M.; Morán-López, J. L.

    1993-05-01

    The spatial atomic distribution in cubo-octahedral CuNi, CuPd and NiPt clusters with a total number of atoms, N = 147, in the presence of chemisorbed oxygen, is studied. The equilibrium atomic configuration is obtained by calculating the free energy within the regular solution model and by assuming that the surface of the cluster is covered by oxygen atoms. Depending on the interaction between oxygen and the cluster components, the atomic distribution in the cluster can be completely modified as compared to the case of clusters with a clean surface. We present result for the temperature dependence of the concentration at the different shells around the central atom.

  14. A modification of the laser detonation-type hyperthermal oxygen atom beam source for a long-term operation

    SciTech Connect

    Kinoshita, Hiroshi; Yamamoto, Shunsuke; Yatani, Hideaki; Ohmae, Nobuo

    2008-07-15

    It has been an impedimental problem, for the laser detonation-type atom beam generator, that a poppet in the pulsed supersonic valve is rapidly eroded by the irradiation of powerful laser light and high temperature plasma. In order to operate the atom beam source for a long duration, a modification was made to hide the poppet from direct irradiation of laser and plasma. The alteration of device configuration resulted in great improvement in endurance of poppet more than 300 000 repetitions. Morphology of a polyimide film exposed to approximately 200 000 pulses of hyperthermal oxygen atom beam showed a shaglike carpet structure, which is a characteristic to that exposed to energetic oxygen atoms. A flux of the oxygen atom beam was estimated to be 5x10{sup 14} atoms/cm{sup 2}/pulse at a location of 30 cm away from the nozzle throat.

  15. Durability studies of micro/nanoelectromechanical systems materials, coatings and lubricants at high sliding velocities (up to 10 mm/s) using a modified atomic force microscope

    NASA Astrophysics Data System (ADS)

    Tambe, Nikhil S.; Bhushan, Bharat

    2005-07-01

    Most micro/nanoelectromechanical (MEMS/NEMS) devices and components operate at very high sliding velocities (of the order of tens of mm/s to few m/s). Micro/nanoscale tribology and mechanics of these devices is crucial for evaluating reliability and failure issues. Atomic force microscopy (AFM) studies to investigate potential materials/coatings for these devices have been rendered inadequate due to inherent limitations on the highest sliding velocities achievable with commercial AFMs. We have developed a technique to study nanotribological properties at high sliding velocities (up to 10 mm/s) by modifying the commercial AFM setup with a customized closed loop piezo stage for mounting samples. Durability of materials, silicon, poly(methylmethacrylate) (PMMA) and poly(dimethlysiloxane) (PDMS), diamond-like carbon (DLC) coating and lubricants such as self-assembled monolayer of hexadecanethiol (HDT) and perfluropolyethers Z-15 and Z-DOL used in MEMS/NEMS applications, is studied at various normal loads and sliding velocities. Wear mechanisms involved at high sliding velocities are discussed. The primary wear mechanisms are deformation of the contacting asperities due to impacts in the case of silicon; phase transformation from amorphous to low shear strength graphite for DLC; localized melting due to high frictional energy dissipation for PMMA and PDMS; and displacement or removal of lubricant molecules for HDT, Z-15, and Z-DOL.

  16. Ultrafast and ultraslow oxygen atom transfer reactions between late metal centers.

    PubMed

    Fortner, Kevin C; Laitar, David S; Muldoon, John; Pu, Lihung; Braun-Sand, Sonja B; Wiest, Olaf; Brown, Seth N

    2007-01-24

    Oxotrimesityliridium(V), (mes)3Ir=O (mes = 2,4,6-trimethylphenyl), and trimesityliridium(III), (mes)3Ir, undergo extremely rapid degenerate intermetal oxygen atom transfer at room temperature. At low temperatures, the two complexes conproportionate to form (mes)3Ir-O-Ir(mes)3, the 2,6-dimethylphenyl analogue of which has been characterized crystallographically. Variable-temperature NMR measurements of the rate of dissociation of the mu-oxo dimer combined with measurements of the conproportionation equilibrium by low-temperature optical spectroscopy indicate that oxygen atom exchange between iridium(V) and iridium(III) occurs with a rate constant, extrapolated to 20 degrees C, of 5 x 107 M-1 s-1. The oxotris(imido)osmium(VIII) complex (ArN)3Os=O (Ar = 2,6-diisopropylphenyl) also undergoes degenerate intermetal atom transfer to its deoxy partner, (ArN)3Os. However, despite the fact that its metal-oxygen bond strength and reactivity toward triphenylphosphine are nearly identical to those of (mes)3Ir=O, the osmium complex (ArN)3Os=O transfers its oxygen atom 12 orders of magnitude more slowly to (ArN)3Os than (mes)3Ir=O does to (mes)3Ir (kOsOs = 1.8 x 10-5 M-1 s-1 at 20 degrees C). Iridium-osmium cross-exchange takes place at an intermediate rate, in quantitative agreement with a Marcus-type cross relation. The enormous difference between the iridium-iridium and osmium-osmium exchange rates can be rationalized by an analogue of the inner-sphere reorganization energy. Both Ir(III) and Ir(V) are pyramidal and can form pyramidal iridium(IV) with little energetic cost in an orbitally allowed linear approach. Conversely, pyramidalization of the planar tris(imido)osmium(VI) fragment requires placing a pair of electrons in an antibonding orbital. The unique propensity of (mes)3Ir=O to undergo intermetal oxygen atom transfer allows it to serve as an activator of dioxygen in cocatalyzed oxidations, for example, acting with osmium tetroxide to catalyze the aerobic

  17. Large-scale circulation of atomic oxygen in the MLT region

    NASA Astrophysics Data System (ADS)

    Shepherd, G.; Liu, G.; Roble, R.

    The atomic oxygen green line airglow at 557.7 nm, originating from the O(1S) level, has a long history of observation, beginning with John Strutt (Lord Rayleigh IV). He drew attention to its variability, a topic that has puzzled successive investigators for decades. More recently, global observations of the oxygen airglow, interpreted with the help of global circulation models have provided some understanding. Zonally averaged satellite observations clearly demonstrate the dynamical influence of tides on the daily variations. Global maps for a single day show a longitudinal variation results from planetary waves. For a single ground-station, the observations are influenced by both, involving variability over days or weeks. During the course of the year both annual and semi-annual components of the variation have been identified. In the present investigation these are studied using data from the WIND Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite, and model results from the TIME-GCM model. The annual variation can be described in terms of a rapid buildup of atomic oxygen in the fall, manifested as high airglow levels at polar latitudes in early winter that decay gradually during the winter period, and are abruptly terminated by a strong atomic oxygen depletion in spring that has been called the springtime transition. The summer values remain low until the sudden autumn rise that can be called the autumnal transition. However, the observations show significant differences between the northern and southern hemispheres. The semi-annual variation dominates at latitudes below 30 and appears to be the result of changes in the mixing intensity that may be linked to the semi-annual variation in the amplitude of the diurnal tide.

  18. Global Dynamics of Hot Atomic Oxygen in Mars' Upper Atmosphere and Comparison with Recent Observation

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Combi, M. R.; Tenishev, V.; Bougher, S. W.

    2012-12-01

    The production of energetic particles in Mars's upper thermosphere and exosphere results in the formation of hot atom coronae. Dissociative recombination (DR) of O2+ ion is the dominant source of the production of hot atomic oxygen and the most important reaction for the exosphere on Mars, which occurs mostly deep in the dayside thermosphere of Mars. In this investigation, we have carried out the study of the global dynamics of energetic particles in Mars' upper atmosphere using our newly developed self-consistent Monte-Carlo model. The calculated total global escapes of hot oxygen are presented for different solar activities (solar maximum and minimum) and Martian seasons (aphelion, equinox, and perihelion). To describe self-consistently the exosphere and the upper thermosphere, a combination of our 3D Direct Simulation Monte Carlo (DSMC) model [Valeille, A., Combi, M., Bougher, S., Tenishev, V., Nagy, A., 2009. J. Geophys. Res. 114, E11006. doi:10.1029/2009JE003389] and the 3D Mars Thermosphere General Circulation Model (MTGCM) [Bougher, S.W., Bell, J.M., Murphy, J.R., Lopez-Valverde, M.A., Withers, P.G., 2006. Geophys. Res. Lett. 32, doi: 10.1029/2005GL024059. L02203] is used. Profiles of density and temperature, atmospheric loss rates, and return fluxes are studied using the model for the cases considered. Progress in updating the model physics is also described. Along with comparisons of our DSMC model outputs with those from other recent exosphere model studies, we present a comparison of our model results with the derived neutral oxygen density from atomic oxygen emission at 1304Å that was detected by Alice instrument on board European Space Agency's Rosetta spacecraft [Feldman, P., Steffl, A., Parker, J, A'Hearn, M., Bertaux, J., Stern, S., Weaver, H., Slater, D., Versteeg, M., Throop, H., Cunningham, N., Feaga, L., 2011. Icarus. 214, 2, 394-399, doi:10.1016/j.icarus.2011.06.013].

  19. Laboratory installation for the study of atomic-oxygen and ozone detectors and certain methodological aspects concerning the determination of oxygen-atom concentration by the methods of NO and NO2 titration

    NASA Astrophysics Data System (ADS)

    Bromberg, D. V.; Perov, S. P.

    A laboratory installation is described which can be used to study various characteristics of atomic oxygen and ozone in the pressure range from 0.01 to 50 Pa. The installation can be used to calibrate rocketborne sensors intended for measurements in the middle atmosphere. Systematic and random errors connected with the determination of oxygen-atom concentration by the NO2 and NO titration methods are examined.

  20. Laboratory Measurement of OH(υ = 2) Collisional Deactivation by Oxygen Atoms

    NASA Astrophysics Data System (ADS)

    Marschall, J.; Kalogerakis, K. S.; Copeland, R. A.

    2001-05-01

    Vibrationally excited hydroxyl radicals (υ = 6-9) are generated in the 80 to 100 km altitude range of the Earth's atmosphere by the reaction of atomic hydrogen with ozone. Low vibrational levels (υ < 5) are populated from the higher vibrational levels via collisions with molecular oxygen. For these low vibrational levels molecular oxygen relaxation is inefficient (1.3 - 17 x10-13 cm3-s-1 at room temperature [1]) and collisions with oxygen atoms may play an important role in the collisional lifetime in the atmosphere. Given the importance of O-atom collisions, we have developed an experimental approach and performed experiments on the collisional removal of OH(υ = 2) with O-atoms. In our experimental approach, we use the output of a pulsed excimer laser at 248 nm to photodissociate ozone in an O3/H2O/N2 mixture and the wavelength tunable output of a frequency-double Nd:YAG-pumped dye laser to probe the transient population of OH in the υ = 0, 1, and 2 vibrational levels using laser-induced fluorescence spectroscopy. Vibrationally excited OH molecules are produced, in vibrational levels up to and including υ = 2, through the exothermic reaction of O(1D) with water. By adjusting the composition of the O3/H2O/N2 mixture and by varying the 248 nm laser fluence to control the ozone dissociation fraction, the dominant relaxation partner can be varied systematically from ozone and water to atomic oxygen. We can dissociate > 90% of the ozone in the beam with easily obtainable laser fluences, generating copious amounts of O atoms. Using this method we obtained a preliminary rate constant of 4 \\pm 1 x10-11 cm3-s-1 for removal of OH(υ = 2) with O atoms. This rate constant is only slightly larger than the value of 3.3 \\pm 0.7 x10-11 cm3-s-1 for the reaction of OH(υ = 0) with O atoms to generate H atoms and oxygen molecules [2]. This weak dependence of OH loss rates on vibrational excitation is in contrast to previous measurements indicating a factor of 3 to 5 increase

  1. Surface Passivation of MoO₃ Nanorods by Atomic Layer Deposition toward High Rate Durable Li Ion Battery Anodes.

    PubMed

    Ahmed, B; Shahid, Muhammad; Nagaraju, D H; Anjum, D H; Hedhili, Mohamed N; Alshareef, H N

    2015-06-24

    We demonstrate an effective strategy to overcome the degradation of MoO3 nanorod anodes in lithium (Li) ion batteries at high-rate cycling. This is achieved by conformal nanoscale surface passivation of the MoO3 nanorods by HfO2 using atomic layer deposition (ALD). At high current density such as 1500 mA/g, the specific capacity of HfO2-coated MoO3 electrodes is 68% higher than that of bare MoO3 electrodes after 50 charge/discharge cycles. After 50 charge/discharge cycles, HfO2-coated MoO3 electrodes exhibited specific capacity of 657 mAh/g; on the other hand, bare MoO3 showed only 460 mAh/g. Furthermore, we observed that HfO2-coated MoO3 electrodes tend to stabilize faster than bare MoO3 electrodes because nanoscale HfO2 layer prevents structural degradation of MoO3 nanorods. Additionally, the growth temperature of MoO3 nanorods and the effect of HfO2 layer thickness was studied and found to be important parameters for optimum battery performance. The growth temperature defines the microstructural features and HfO2 layer thickness defines the diffusion coefficient of Li-ions through the passivation layer to the active material. Furthermore, ex situ high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction were carried out to explain the capacity retention mechanism after HfO2 coating.

  2. Chemical reaction of atomic oxygen with evaporated films of copper, part 4

    NASA Technical Reports Server (NTRS)

    Fromhold, A. T.; Williams, J. R.

    1990-01-01

    Evaporated copper films were exposed to an atomic oxygen flux of 1.4 x 10(exp 17) atoms/sq cm per sec at temperatures in the range 285 to 375 F (140 to 191 C) for time intervals between 2 and 50 minutes. Rutherford backscattering spectroscopy (RBS) was used to determine the thickness of the oxide layers formed and the ratio of the number of copper to oxygen atoms in the layers. Oxide film thicknesses ranged from 50 to 3000 A (0.005 to 0.3 microns, or equivalently, 5 x 10(exp -9) to 3 x 10(exp -7); it was determined that the primary oxide phase was Cu2O. The growth law was found to be parabolic (L(t) varies as t(exp 1/2)), in which the oxide thickness L(t) increases as the square root of the exposure time t. The analysis of the data is consistent with either of the two parabolic growth laws. (The thin-film parabolic growth law is based on the assumption that the process is diffusion controlled, with the space charge within the growing oxide layer being negligible. The thick-film parabolic growth law is also based on a diffusion controlled process, but space-charge neutrality prevails locally within very thick oxides.) In the absence of a voltage measurement across the growing oxide, a distinction between the two mechanisms cannot be made, nor can growth by the diffusion of neutral atomic oxygen be entirely ruled out. The activation energy for the reaction is on the order of 1.1 eV (1.76 x 10(exp -19) joule, or equivalently, 25.3 kcal/mole).

  3. Generation of a fast atomic-oxygen beam from O - ions by resonant cavity radiation

    NASA Astrophysics Data System (ADS)

    Stephen, T. M.; Van Zyl, B.; Amme, R. C.

    1996-04-01

    An apparatus has been developed for producing a beam of ground-electronic-state oxygen atoms with energies variable from 4 to 1000 eV with a 1.5 eV FWHM energy distribution. The technique involves extraction of negative ions from a low-voltage gas-discharge source, mass selection of the extracted O- with a Wien-type velocity filter, O- acceleration or deceleration and focusing by electrostatic ion optics, and electron detachment from O- by intracavity laser radiation. A 25 W argon-ion-laser cavity has been extended to include the ion-beam vacuum chamber so that the intracavity radiation intersects the O- ion trajectories normally. Depending on the laser configuration in use, ion-neutralization efficiencies between 5% and 25% have been achieved at 5 eV O- energy. Thus, 5 eV O-atom fluxes of ˜1011 atoms/s (˜1012 atoms/cm2 s) have been achieved for O- currents of ˜10-7 A. The advantages and limitations of the technique are discussed, and preliminary measurements of the secondary-negative-charge production from low-energy O-atom impact on copper and stainless-steel surfaces are presented.

  4. Efficient and durable oxygen reduction and evolution of a hydrothermally synthesized La(Co0.55Mn0.45)0.99O3-δ nanorod/graphene hybrid in alkaline media.

    PubMed

    Ge, Xiaoming; Goh, F W Thomas; Li, Bing; Hor, T S Andy; Zhang, Jie; Xiao, Peng; Wang, Xin; Zong, Yun; Liu, Zhaolin

    2015-05-21

    The increasing global energy demand and the depletion of fossil fuels have stimulated intense research on fuel cells and batteries. Oxygen electrocatalysis plays essential roles as the electrocatalytic reduction and evolution of di-oxygen are always the performance-limiting factors of these devices relying on oxygen electrochemistry. A novel perovskite with the formula La(Co0.55Mn0.45)0.99O3-δ (LCMO) is designed from molecular orbital principles. The hydrothermally synthesized LCMO nanorods have unique structural and chemical properties and possess high intrinsic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The synergic covalent coupling between LCMO and NrGO enhances the bifunctional ORR and OER activities of the novel LCMO/NrGO hybrid catalyst. The ORR activity of LCMO/NrGO is comparable to the state-of-the-art Pt/C catalyst and its OER activity is competitive to the state-of-the-art Ir/C catalyst. LCMO/NrGO generally outperforms Pt/C and Ir/C with better bifunctional ORR and OER performance and operating durability. LCMO/NrGO represents a new class of low-cost, efficient and durable electrocatalysts for fuel cells, water electrolysers and batteries. PMID:25921031

  5. Atomic Oxygen Abundance in Molecular Clouds: Absorption Toward Sagittarius B2

    NASA Technical Reports Server (NTRS)

    Lis, D. C.; Keene, Jocelyn; Phillips, T. G.; Schilke, P.; Werner, M. W.; Zmuidzinas, J.

    2001-01-01

    We have obtained high-resolution (approximately 35 km/s) spectra toward the molecular cloud Sgr B2 at 63 micrometers, the wavelength of the ground-state fine-structure line of atomic oxygen (O(I)), using the ISO-LWS instrument. Four separate velocity components are seen in the deconvolved spectrum, in absorption against the dust continuum emission of Sgr B2. Three of these components, corresponding to foreground clouds, are used to study the O(I) content of the cool molecular gas along the line of sight. In principle, the atomic oxygen that produces a particular velocity component could exist in any, or all, of three physically distinct regions: inside a dense molecular cloud, in the UV illuminated surface layer (PDR) of a cloud, and in an atomic (H(I)) gas halo. For each of the three foreground clouds, we estimate, and subtract from the observed O(I) column density, the oxygen content of the H(I) halo gas, by scaling from a published high-resolution 21 cm spectrum. We find that the remaining O(I) column density is correlated with the observed (13)CO column density. From the slope of this correlation, an average [O(I)]/[(13)CO] ratio of 270 +/- 120 (3-sigma) is derived, which corresponds to [O(I)]/[(13)CO] = 9 for a CO to (13)CO abundance ratio of 30. Assuming a (13)CO abundance of 1x10(exp -6) with respect to H nuclei, we derive an atomic oxygen abundance of 2.7x10(exp -4) in the dense gas phase, corresponding to a 15% oxygen depletion compared to the diffuse ISM in our Galactic neighborhood. The presence of multiple, spectrally resolved velocity components in the Sgr B2 absorption spectrum allows, for the first time, a direct determination of the PDR contribution to the O(I) column density. The PDR regions should contain O(I) but not (13)CO, and would thus be expected to produce an offset in the O(I)-(13)CO correlation. Our data do not show such an offset, suggesting that within our beam O(I) is spatially coexistent with the molecular gas, as traced by (13)CO

  6. Determination of Ground-Laboratory to In-Space Effective Atomic Oxygen Fluence for DC 93?500 Silicone

    NASA Technical Reports Server (NTRS)

    deGroh, Kim K.; Banks, Bruce A.; Ma, David

    2004-01-01

    The objective of this research was to calibrate the ground-to-space effective atomic oxygen fluence for DC 93-500 silicone in a thermal energy electron cyclotron resonance (ECR) oxygen plasma facility. Silicones, commonly used spacecraft materials, do not chemically erode with atomic oxygen attack like other organic materials but form an oxidized hardened silicate surface layer. Therefore, the effective atomic oxygen fluence in a ground test facility should not be determined based on mass loss measurements, as they are with organic polymers. A technique has been developed at the Glenn Research Center to determine the equivalent amount of atomic oxygen exposure in an ECR ground test facility to produce the same degree of atomic oxygen damage as in space. The approach used was to compare changes in the surface hardness of ground test (ECR) exposed DC 93-500 silicone with DC 93-500 exposed to low Earth orbit (LEO) atomic oxygen as part of a shuttle flight experiment. The ground to in-space effective atomic oxygen fluence correlation was determined based on the fluence in the ECR source that produced the same hardness for the fluence in-space. Nanomechanical hardness versus contact depth measurements were obtained for five ECR exposed DC 93-500 samples (ECR exposed for 18 to 40 hrs, corresponding to Kapton effective fluences of 4.2 x 10(exp 20) to 9.4 x 10(exp 20) atoms/sq cm, respectively) and for space exposed DC 93-500 from the Evaluation of Oxygen Interactions with Materials III (EOIM III) shuttle flight experiment, exposed to LEO atomic oxygen for 2.3 x 10(exp 20) atoms/sq cm. Pristine controls were also evaluated. A ground-to-space correlation value was determined based on correlation values for four contact depths (150, 200, 250, and 300 nm), which represent the near surface depth data. The results indicate that the Kapton effective atomic oxygen fluence in the ECR facility needs to be 2.64 times higher than in LEO to replicate equivalent exposure damage in the

  7. Engineering surface atomic structure of single-crystal cobalt (II) oxide nanorods for superior electrocatalysis

    PubMed Central

    Ling, Tao; Yan, Dong-Yang; Jiao, Yan; Wang, Hui; Zheng, Yao; Zheng, Xueli; Mao, Jing; Du, Xi-Wen; Hu, Zhenpeng; Jaroniec, Mietek; Qiao, Shi-Zhang

    2016-01-01

    Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts. PMID:27650485

  8. Engineering surface atomic structure of single-crystal cobalt (II) oxide nanorods for superior electrocatalysis.

    PubMed

    Ling, Tao; Yan, Dong-Yang; Jiao, Yan; Wang, Hui; Zheng, Yao; Zheng, Xueli; Mao, Jing; Du, Xi-Wen; Hu, Zhenpeng; Jaroniec, Mietek; Qiao, Shi-Zhang

    2016-09-21

    Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts.

  9. Engineering surface atomic structure of single-crystal cobalt (II) oxide nanorods for superior electrocatalysis.

    PubMed

    Ling, Tao; Yan, Dong-Yang; Jiao, Yan; Wang, Hui; Zheng, Yao; Zheng, Xueli; Mao, Jing; Du, Xi-Wen; Hu, Zhenpeng; Jaroniec, Mietek; Qiao, Shi-Zhang

    2016-01-01

    Engineering the surface structure at the atomic level can be used to precisely and effectively manipulate the reactivity and durability of catalysts. Here we report tuning of the atomic structure of one-dimensional single-crystal cobalt (II) oxide (CoO) nanorods by creating oxygen vacancies on pyramidal nanofacets. These CoO nanorods exhibit superior catalytic activity and durability towards oxygen reduction/evolution reactions. The combined experimental studies, microscopic and spectroscopic characterization, and density functional theory calculations reveal that the origins of the electrochemical activity of single-crystal CoO nanorods are in the oxygen vacancies that can be readily created on the oxygen-terminated {111} nanofacets, which favourably affect the electronic structure of CoO, assuring a rapid charge transfer and optimal adsorption energies for intermediates of oxygen reduction/evolution reactions. These results show that the surface atomic structure engineering is important for the fabrication of efficient and durable electrocatalysts. PMID:27650485

  10. Submolecular Imaging by Noncontact Atomic Force Microscopy with an Oxygen Atom Rigidly Connected to a Metallic Probe.

    PubMed

    Mönig, Harry; Hermoso, Diego R; Díaz Arado, Oscar; Todorović, Milica; Timmer, Alexander; Schüer, Simon; Langewisch, Gernot; Pérez, Rubén; Fuchs, Harald

    2016-01-26

    In scanning probe microscopy, the imaging characteristics in the various interaction channels crucially depend on the chemical termination of the probe tip. Here we analyze the contrast signatures of an oxygen-terminated copper tip with a tetrahedral configuration of the covalently bound terminal O atom. Supported by first-principles calculations we show how this tip termination can be identified by contrast analysis in noncontact atomic force and scanning tunneling microscopy (NC-AFM, STM) on a partially oxidized Cu(110) surface. After controlled tip functionalization by soft indentations of only a few angstroms in an oxide nanodomain, we demonstrate that this tip allows imaging an organic molecule adsorbed on Cu(110) by constant-height NC-AFM in the repulsive force regime, revealing its internal bond structure. In established tip functionalization approaches where, for example, CO or Xe is deliberately picked up from a surface, these probe particles are only weakly bound to the metallic tip, leading to lateral deflections during scanning. Therefore, the contrast mechanism is subject to image distortions, artifacts, and related controversies. In contrast, our simulations for the O-terminated Cu tip show that lateral deflections of the terminating O atom are negligible. This allows a detailed discussion of the fundamental imaging mechanisms in high-resolution NC-AFM experiments. With its structural rigidity, its chemically passivated state, and a high electron density at the apex, we identify the main characteristics of the O-terminated Cu tip, making it a highly attractive complementary probe for the characterization of organic nanostructures on surfaces.

  11. Spatial Resolution of Combined Wavelength Modulation Spectroscopy with Integrated Cavity Output Spectroscopy for Atomic Oxygen Detection

    NASA Astrophysics Data System (ADS)

    Matsui, Makoto; Nakajima, Daisuke

    2015-09-01

    For developments of thermal protection system, atomic oxygen plays important role. However, its measurement method has not been established because the pressure in front of TPS test materials is as high as a few kPa. Our group proposed combined wavelength modulation and integrated output spectroscopies based on the forbidden transition at OI 636 nm to measure the ground-state number densities. In this study, WM-ICOS system is developed and applied to a microwave oxygen plasma to evaluate measurable region. As a result, the estimated number density by ICOS could be measured as low as 1021 m21. For the condition, WM-ICOS was applied. The signal to noise ratio of the 2f signal was 40.4. Then, the sensitivity was improved about 26. This result corresponding to the measurement limit of the partial atomic oxygen pressure of 250 Pa. The sensitivity of WM-ICOS was found to enough to diagnose the shock layer in high enthalpy flows. However, the spatial resolution was as large as 8 mm. The size of the beam pattern depends on the cavity length, robust ness of the cavity and accuracy of the cavity alignment. In this presentation, the relationship among these parameters will be discussed.

  12. Thermal Reactions of Oxygen Atoms with Alkenes at Low Temperatures on Interstellar Dust

    NASA Astrophysics Data System (ADS)

    Ward, Michael D.; Price, Stephen D.

    2011-11-01

    Laboratory experiments show that the thermal heterogeneous reactions of oxygen atoms may contribute to the synthesis of epoxides in interstellar clouds. The data set also indicates that the contribution of these pathways to epoxide formation, in comparison to non-thermal routes, is likely to be strongly temperature dependent. Our results indicate that an increased abundance of epoxides, relative to the corresponding aldehydes, could be an observational signature of a significant contribution to molecular oxidation via thermal O atom reactions with alkenes. Specifically surface science experiments show that both C2H4O and C3H6O are readily formed from reactions of ethene and propene molecules with thermalized oxygen atoms at temperatures in the range of 12-90 K. It is clear from our experiments that these reactions, on a graphite surface, proceed with significantly reduced reaction barriers compared with those operating in the gas phase. For both the C2H4 + O and the C3H6 + O reactions, the surface reaction barriers we determine are reduced by approximately an order of magnitude compared with the barriers in the gas phase. The modeling of our experimental results, which determines these reaction barriers, also extracts desorption energies and rate coefficients for the title reactions. Our results clearly show that the major product from the O + C2H4 reaction is ethylene oxide, an epoxide.

  13. THERMAL REACTIONS OF OXYGEN ATOMS WITH ALKENES AT LOW TEMPERATURES ON INTERSTELLAR DUST

    SciTech Connect

    Ward, Michael D.; Price, Stephen D. E-mail: s.d.price@ucl.ac.uk

    2011-11-10

    Laboratory experiments show that the thermal heterogeneous reactions of oxygen atoms may contribute to the synthesis of epoxides in interstellar clouds. The data set also indicates that the contribution of these pathways to epoxide formation, in comparison to non-thermal routes, is likely to be strongly temperature dependent. Our results indicate that an increased abundance of epoxides, relative to the corresponding aldehydes, could be an observational signature of a significant contribution to molecular oxidation via thermal O atom reactions with alkenes. Specifically surface science experiments show that both C{sub 2}H{sub 4}O and C{sub 3}H{sub 6}O are readily formed from reactions of ethene and propene molecules with thermalized oxygen atoms at temperatures in the range of 12-90 K. It is clear from our experiments that these reactions, on a graphite surface, proceed with significantly reduced reaction barriers compared with those operating in the gas phase. For both the C{sub 2}H{sub 4} + O and the C{sub 3}H{sub 6} + O reactions, the surface reaction barriers we determine are reduced by approximately an order of magnitude compared with the barriers in the gas phase. The modeling of our experimental results, which determines these reaction barriers, also extracts desorption energies and rate coefficients for the title reactions. Our results clearly show that the major product from the O + C{sub 2}H{sub 4} reaction is ethylene oxide, an epoxide.

  14. Doping SrTiO3 supported FeSe by excess atoms and oxygen vacancies

    DOE PAGES

    Shanavas, Kavungal Veedu; Singh, David J.

    2015-07-24

    Photoemission studies of FeSe monolayer films on SrTiO3 substrate have shown electronic structures that deviate from pristine FeSe, consistent with heavy electron doping. With the help of first-principles calculations we studied the effect of excess Fe and Se atoms on the monolayer and oxygen vacancies in the substrate in order to understand the reported Fermi surface in this system. We find that both excess Fe and Se atoms prefer the same adsorption site above the bottom Se atoms on the monolayer. The adsorbed Fe is strongly magnetic and contributes electrons to the monolayer, while excess Se hybridizes with the monolayermore » Fe-d states and partially opens a gap just above the Fermi energy. We also find that the two-dimensional electron gas generated by the oxygen vacancies is partly transferred to the monolayer and can potentially suppress the hole pockets around the Γ point. Furthermore, both O vacancies in the SrTiO3 substrate and excess Fe over the monolayer can provide high levels of electron doping.« less

  15. Atomic oxygen erosion of a graphite coating on a TQCM onboard the Return Flux Experiment (REFLEX)

    NASA Astrophysics Data System (ADS)

    Benner, Steve M.; Lorentson, Charles C.; Chen, Philip T. C.; Thomson, Shaun R.

    1998-10-01

    A TQCM coated with graphite was flown aboard a Spartan carrier in January 1996. During a flight of about 46 hours at an altitude of 305 km, the graphite reacted with the atomic oxygen (AO) in the environment and was eroded away. The 15-MHz TQCM's frequency dropped from 6800 to 4000 Hz in about 15 hours of exposure and was shown to be a strong function of the TQCM's orientation to the ram direction. The erosion rates for four different ram angels was measured and found to be both consistent and repeatable. The average graphite volume loss for the 61 degree and -62 degree ram angles was calculated to be about 2 X E-08 cm3/hr and for the 18 degrees and 19 degrees angles to be about 8.5 X E-08 cm3/hr, which is slightly less than previous flight data. The erosion data was then correlated with AO density numbers for the particular times and positions of the spacecraft in orbit. From this analysis, an equation was derived that shoed the carbon volume loss as a function of both atomic oxygen density and ram angle. For example, 1.59 E-07 cm3/hr would be the calculated carbon volume loss for a ram angle of 0- degrees and an AO fluence of 3.52 E+17 atoms/hr. The results of this data and analysis may lead to the development of a sensor capable of monitoring the AO fluence on a spacecraft.

  16. DURABILITY OF VERY LOW CAPACITY PRESSURE ATOMIZED FUEL NOZZLES USED WITH LOW FIRING RATE RESIDENTIAL OIL BURNERS.

    SciTech Connect

    MCDONALD,R.J.

    2007-05-01

    Brookhaven National Laboratory (BNL), working for the United States Department of Energy (DOE), has conducted a preliminary evaluation of the potential of very low fuel input capacity Simplex type pressure atomizing nozzles for use with oil burners designed for residential boilers, furnaces and water heaters. These nozzles under suitable conditions can be sufficiently reliable to enable new heating system designs. This would allow for the design of heating appliances that match the smaller load demands of energy efficient homes built with modern components and architectural systems designed to minimize energy use. When heating systems are installed with excessive capacity, oversized by three to four times the load, the result is a loss of up to ten percent as compared to the rated appliance efficiency. The use of low capacity nozzles in systems designed to closely match the load can thereby result in significant energy savings. BNL investigated the limitations of low flow rate nozzles and designed long-term experiments to see if ways could be determined that would be beneficial to long-term operation at low input capacities without failures. In order to maximize the potential for success the best possible industry practices available were employed. Low flow rate nozzles primarily fail by blockage or partial blockage of internal fuel flow passages inside the nozzle. To prevent any contaminants from entering the nozzle BNL investigated the geometry and critical dimensions and the current sate of the art of fuel filter design. Based on this investigation it was concluded that the best available filters should be more than capable of filtering contaminants from the fuel prior to entering the oil burner itself. This position was indeed validated based on the long-term trials conducted under this study no evidence resulted to change our position. It is highly recommended that these filters rated at 10 microns and with large filter capacity (surface area), should be used

  17. Novel oxygen chirality induced by asymmetric coordination of an ether oxygen atom to a metal center in a series of sugar-pendant dipicolylamine copperII complexes.

    PubMed

    Mikata, Yuji; Sugai, Yuko; Obata, Makoto; Harada, Masafumi; Yano, Shigenobu

    2006-02-20

    Six sugar-pendant 2,2'-dipicolylamine (DPA) ligands (L1-3 and L'1-3) have been prepared. OH-protected and unprotected D-glucose, D-mannose, and D-xylose were attached to a DPA moiety via an O-glycoside linkage. X-ray crystallography of the copper(II) complexes (1-5) with these ligands revealed that the anomeric oxygen atom is coordinated to the metal center in the solid state, generating a chiral center at the oxygen atom. The CD spectra of these copper complexes in methanol or aqueous solution exhibit Cotton effects in the d-d transition region, which indicates that the ether oxygen atoms remain coordinated to the metal center and the oxygen-atom chirality is preserved even in solution. For complexes 1 and 2, the inverted oxygen-atom chirality and chelate-ring conformation in the solid state are well correlated with the mirror-image CD spectra in methanol solution. The concomitant inversion of the asymmetric configuration around the copper center was also observed in a methanol solution of complex 3 and a pyridine solution of complex 2. The square-pyramidal/octahedral copper(II) centers also exhibited characteristic absorption and CD spectra.

  18. On a new method for chemical production of iodine atoms in a chemical oxygen-iodine laser

    SciTech Connect

    Andreeva, Tamara L; Kuznetsova, S V; Maslov, A I; Sorokin, Vadim N

    2004-11-30

    A new method is proposed for generating iodine atoms in a chemical oxygen-iodine laser. The method is based on a branched chain reaction of dissociation of the alkyl iodide CH{sub 3}I in a medium of singlet oxygen and chlorine. (active media)

  19. A Comparison of Atomic Oxygen Degradation in Low Earth Orbit and in a Plasma Etcher

    NASA Technical Reports Server (NTRS)

    Townsend, Jacqueline A.; Park, Gloria

    1997-01-01

    In low Earth orbit (LEO) significant degradation of certain materials occurs from exposure to atomic oxygen (AO). Orbital opportunities to study this degradation for specific materials are limited and expensive. While plasma etchers are commonly used in ground-based studies because of their low cost and convenience, the environment produced in an etcher chamber differs greatly from the LEO environment. Because of the differences in environment, the validity of using etcher data has remained an open question. In this paper, degradation data for 22 materials from the orbital experiment Evaluation of Oxygen Interaction with Materials (EOIM-3) are compared with data from EOIM-3 control specimens exposed in a typical plasma etcher. This comparison indicates that, when carefully considered, plasma etcher results can produce order-of-magnitude estimates of orbital degradation. This allows the etcher to be used to screen unacceptable materials from further, more expensive tests.

  20. The energy dependence and surface morphology of Kapton (trademark) degradation under atomic oxygen bombardment

    NASA Technical Reports Server (NTRS)

    Ferguson, D. C.

    1984-01-01

    Data from laboratory simulations and from samples returned from STS-8 are used to derive the energy dependence of the mass loss rate of Kapton under atomic oxygen bombardment and to discuss the development of surface structure and its effect on erosion rates. It is concluded that all the laboratory data from discharge and flow tubes and from accelerated beams, along with the orbital data from STS-3 through STS-8, can be accommodated by a rate of mass loss that varies with impact energy normal to the surface. It is hypothesized that increases of mass loss rate with exposure time may be due to trapping of the incoming atoms by the surface structure which develops.

  1. Atomic-scale modeling of particle size effects for the oxygen reduction reaction on Pt.

    SciTech Connect

    Tritsaris, G. A.; Greeley, J.; Rossmeisl, J.; Norskov, J. K.

    2011-07-01

    We estimate the activity of the oxygen reduction reaction on platinum nanoparticles of sizes of practical importance. The proposed model explicitly accounts for surface irregularities and their effect on the activity of neighboring sites. The model reproduces the experimentally observed trends in both the specific and mass activities for particle sizes in the range between 2 and 30 nm. The mass activity is calculated to be maximized for particles of a diameter between 2 and 4 nm. Our study demonstrates how an atomic-scale description of the surface microstructure is a key component in understanding particle size effects on the activity of catalytic nanoparticles.

  2. Material Selection Guidelines to Limit Atomic Oxygen Effects on Spacecraft Surfaces

    NASA Technical Reports Server (NTRS)

    Dooling, D.; Finckenor, M. M.

    1999-01-01

    This report provides guidelines in selecting materials for satellites and space platforms, designed to operate within the Low-Earth orbit environment, which limit the effects of atomic oxygen interactions with spacecraft surfaces. This document should be treated as an introduction rather than a comprehensive guide since analytical and flight technologies continue to evolve, flight experiments are conducted as primary or piggyback opportunities arise, and our understanding of materials interactions and protection methods grows. The reader is urged to consult recent literature and current web sites containing information about research and flight results.

  3. Use of an Atmospheric Atomic Oxygen Beam for Restoration of Defaced Paintings

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; Rutledge, Sharon K.; Karla, Margaret; Norris, Mary Jo; Real, William A.; Haytas, Christy A.

    1999-01-01

    An atmospheric atomic oxygen beam has been found to be effective in removing organic materials through oxidation that are typical of graffiti or other contaminant defacements which may occur to the surfaces of paintings. The technique, developed by the National Aeronautics and Space Administration, is portable and was successfully used at the Carnegie Museum of Art to remove a lipstick smudge from the surface of porous paint on the Andy Warhol painting "Bathtub." This process was also evaluated for suitability to remove felt tip and ball point ink graffiti from paper, gesso on canvas and cotton canvas.

  4. Detection of atomic oxygen and further line assignments in the far-infrared stratospheric spectrum

    NASA Technical Reports Server (NTRS)

    Carli, B.; Mencaraglia, F.; Bonetti, A.; Carlotti, M.; Nolt, I.

    1985-01-01

    Recent progress in high-resolution measurement of sub-millimeter and far-infrared emission in the stratosphere is reviewed. Attention is given to the results of recent balloon measurements of the minor stratospheric constituents in the spectral range 40-190 per cm. Emission spectra are presented for HCl; HF; and OH. Emission spectra were also obtained for atomic oxygen; hydrobromic acid; and hydroperoxyl radical. The possibility of detecting HO2 and H2O2 in the far-infrared is also briefly discussed.

  5. Effects on optical systems from interactions with oxygen atoms in low earth orbits

    NASA Technical Reports Server (NTRS)

    Peters, P. N.; Swann, J. T.; Gregory, J. C.

    1986-01-01

    Modifications of material surface properties due to interactions with ambient atomic oxygen have been observed on surfaces facing the orbital direction in low earth orbits. Some effects are very damaging to surface optical properties while some are more subtle and even beneficial. Most combustible materials are heavily etched, and some coatings, such as silver and osmium, are seriously degraded or removed as volatile oxides. The growth of oxide films on metals and semiconductors considered stable in dry air was measured. Material removal, surface roughness, reflectance, and optical densities are reported. Effects of temperature, contamination, and overcoatings are noted.

  6. Technologies for protection of the Space Station power system surfaces in atomic oxygen environment

    NASA Technical Reports Server (NTRS)

    Nahra, Henry K.; Rutledge, Sharon K.

    1988-01-01

    Technologies for protecting Space Station surfaces from degradation caused by atomic oxygen are discussed, stressing protection of the power system surfaces. The Space Station power system is described and research concerning the solar array surfaces and radiator surfaces is examined. The possibility of coating the solar array sufaces with a sputter deposited thin film of silicon oxide containing small concentrations of polytetrafluoroethylene is presented. Hexamethyldisiloxane coating for these surfaces is also considered. For the radiator surfaces, possible coatings include silver teflon thermal coating and zinc orthotitanate.

  7. Energetic atomic and ionic oxygen textured optical surfaces for blood glucose monitoring

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor)

    2007-01-01

    Disclosed is a method and the resulting product thereof comprising a solid light-conducting fiber with a point of attachment and having a textured surface site consisting a textured distal end prepared by being placed in a vacuum and then subjected to directed hyperthermal beams comprising oxygen ions or atoms. The textured distal end comprises cones or pillars that are spaced upon from each other by less than 1 micron and are extremely suitable to prevent cellular components of blood from entering the valleys between the cones or pillars so as to effectively separate the cellular components in the blood from interfering with optical sensing of the glucose concentration for diabetic patients.

  8. Atomic oxygen and ultraviolet radiation mission total exposures for LDEF experiments

    NASA Technical Reports Server (NTRS)

    Bourassa, R. J.; Gillis, J. R.; Rousslang, Ken W.

    1991-01-01

    An analytical treatment of the effect of thermal molecular velocity on spacecraft atomic oxygen (AO) flux is presented. The analysis leads to a closed form equation that incorporates the effect of atmospheric temperature, number density, spacecraft velocity, and incidence angle on AO flux. The effects of atmospheric rotation, solar activity, and geomagnetic index on AO flux are also included on the computer model. Data developed with the model are presented for the Long Duration Exposure Facility (LDEF). The results incorporate variations in the defining environmental and orbital parameters of the spacecraft over its six year orbital flight. Cumulative ultraviolet solar and albedo exposures were calculated .

  9. Atomic Oxygen Treatment as a Method of Recovering Smoke Damaged Paintings. Revised

    NASA Technical Reports Server (NTRS)

    Rutledge, Sharon K.; Banks, Bruce A.; Forkapa, Mark; Stueber, Thomas; Sechkar, Edward; Malinowski, Kevin

    1999-01-01

    A noncontact technique is described that uses atomic oxygen, generated under low pressure in the presence of nitrogen, to remove soot and charred varnish from the surface of a painting. The process, which involves surface oxidation, permits control of the amount of surface material removed. The effectiveness of the process was evaluated by reflectance measurements from selected areas made during the removal of soot from acrylic gesso, ink on paper, and varnished oil paint substrates. For the latter substrate, treatment also involved the removal of damaged varnish and paint binder from the surface.

  10. TALIF measurements of oxygen atom density in the afterglow of a capillary nanosecond discharge

    NASA Astrophysics Data System (ADS)

    Klochko, A. V.; Lemainque, J.; Booth, J. P.; Starikovskaia, S. M.

    2015-04-01

    The atomic oxygen density has been measured in the afterglow of a capillary nanosecond discharge in 24-30 mbar synthetic air (N2 : O2 = 4 : 1) by the two-photon absorption laser-induced fluorescence (TALIF) technique, combined with absolute calibration by comparison with xenon TALIF. The discharge was initiated by a train of 30 ns FWHM pulses of alternating positive-negative-positive polarity, separated by 250 ns, with a train repetition frequency of 10 Hz. The amplitude of the first pulse was 10 kV in the cable. A flow of synthetic air through the tube provided complete gas renewal between pulse trains. The O-atom density measurements were made over the time interval 200 ns-2 µs after the initial pulse. The gas temperature was determined by analysis of the molecular nitrogen second positive system optical emission spectrum. The influence of the gas temperature on the atom density measurements, and the reactions producing O atoms, are discussed.

  11. Inelastic and reactive scattering of hyperthermal atomic oxygen from amorphous carbon

    NASA Technical Reports Server (NTRS)

    Minton, Timothy K.; Nelson, Christine M.; Brinza, David E.; Liang, Ranty H.

    1991-01-01

    The reaction of hyperthermal oxygen atoms with an amorphous carbon-13 surface was studied using a modified universal crossed molecular beams apparatus. Time-of-flight distributions of inelastically scattered O-atoms and reactively scattered CO-13 and CO2-13 were measured with a rotatable mass spectrometer detector. Two inelastic scattering channels were observed, corresponding to a direct inelastic process in which the scattered O-atoms retain 20 to 30 percent of their initial kinetic energy and to a trapping desorption process whereby O-atoms emerge from the surface at thermal velocities. Reactive scattering data imply the formation of two kinds of CO products, slow products whose translational energies are determined by the surface temperature and hyperthermal (Approx. 3 eV) products with translational energies comprising roughly 30 percent of the total available energy (E sub avl), where E sub avl is the sum of the collision energy and the reaction exothermicity. Angular data show that the hyperthermal CO is scattered preferentially in the specular direction. CO2 product was also observed, but at much lower intensities than CO and with only thermal velocities.

  12. Atomic Dynamics and Defect Evolution During Oxygen Precipitation and Oxidation of Silicon

    NASA Astrophysics Data System (ADS)

    Pantelides, Sokrates

    1998-03-01

    The results of first-principles calculations ( based on density functional theory, local-density approximation, pseudopotentials, supercells, and plane waves) provide a basis for a unified account of the atomic-scale processes that underlie oxygen precipitation (enhanced oxygen diffusion, nucleation of "thermal donors", their evolution into electrically inactive SiO2-like precipitates, and the continuing growth of the latter), thin-film oxidation, and the formation of a buried oxide film after O implantation for the formation of Silicon-On-Insulator (SOI) structures. Examination of the energetics and kinetics of the various processes leads to the realization that the intrinsic defect formed during thin-film oxidation and buried-oxide formation is akin to thermal donors, consisting of "frustrated" Si-O bonds (Si atoms bonded to one or more threefold-coordinated O atoms). It is shown that ejection of such frustrated Si atoms underlies the observed emission of Si interstitals in all cases (annealing of thermal donors and further growth of SiO2-like precipitates, thin-film oxidation, and buried-oxide formation). The emission occurs by a synergistic process that eliminates wrong-coordination defects, leaving behind perfectly-bonded structures. These results explain the high quality of Si-SiO2 interfaces and provide a novel family of defects that account for observations that, in addition to the well-known dangling bonds, another defect of unknown identity plays a major role in determining the electrical properties of the Si-SiO2 interface./footnoteE. Cartier and J. H. Stathis, Appl. Phys. Lett. 69, 103 (1996). The same defects are proposed to be the dominant electron traps in buried SOI oxides fabricated by O implantation. The role of H both during oxidation and in subsequent interactions with an Si-SiO2 interface is also elucidated and shown to be in accord with experiments.

  13. Surface modification of POSS-polyimide hybrid films by atomic oxygen using ECR plasma

    NASA Astrophysics Data System (ADS)

    Duo, Shuwang; Ke, Huan; Liu, Tingzhi; Song, Mimi; Li, Meishuan

    2013-07-01

    A novel polyimide (PI) hybrid nanocomposite containing polyhedral oligomeric silsesquioxane (POSS) had been prepared by copolymerization of trisilanolphenyl-POSS, 4,4'-oxydianiline (ODA), and pyromellitic dianhydride (PMDA). The atomic oxygen (AO) resistance of these PI/POSS hybrid films was tested in the ground-based AO simulation facility. Exposed and unexposed surfaces were characterized by SEM and XPS. The SEM images showed that the surface of the 20 wt.% PI/POSS became much less rough than that of the pristine PI. Mass measurements of the samples showed that the erosion yield of the PI/POSS (20 wt.%) hybrid film was 1.2 × 10-25 cm3/atom, and reduced to 4.3% of that of the PI film. The XPS data indicated that the carbon content of the near-surface region was decreased from 66.0 to 7.0 at.% after AO exposure. The ratio of oxygen and silicon concentrations in the near-surface region increased to 2.08 after AO exposure. The nanometer-sized structure of POSS, with its large surface area, had led AO-irradiated samples to form a SiO2 passivation layer, which protected the underlying polymer from further AO attack. The incorporation of POSS into the PI could dramatically improve the AO resistance of PI films in low earth orbit environment.

  14. Lessons Learned From Atomic Oxygen Interaction With Spacecraft Materials in Low Earth Orbit

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A.; deGroh, Kim, K.; Miller, Sharon K.; Waters, Deborah L.

    2008-01-01

    There have been five Materials International Space Station Experiment (MISSE) passive experiment carriers (PECs) (MISSE 1-5) to date that have been launched, exposed in space on the exterior of International Space Station (ISS) and then returned to Earth for analysis. An additional four MISSE PECs (MISSE 6A, 6B, 7A, and 7B) are in various stages of completion. The PECs are two-sided suitcase to size sample carriers that are intended to provide information on the effects of the low Earth orbital environment on a wide variety of materials and components. As a result of post retrieval analyses of the retrieved MISSE 2 experiments and numerous prior space experiments, there have been valuable lessons learned and needs identified that are worthy of being documented so that planning, design, and analysis of future space environment experiments can benefit from the experience in order to maximize the knowledge gained. Some of the lessons learned involve the techniques, concepts, and issues associated with measuring atomic oxygen erosion yields. These are presented along with several issues to be considered when designing experiments, such as the uncertainty in mission duration, scattering and contamination effects on results, and the accuracy of measuring atomic oxygen erosion.

  15. Leveling coatings for reducing the atomic oxygen defect density in protected graphite fiber epoxy composites

    NASA Technical Reports Server (NTRS)

    Jaworske, D. A.; Degroh, Kim K.; Podojil, G.; Mccollum, T.; Anzic, J.

    1992-01-01

    Pinholes or other defect sites in a protective oxide coating provide pathways for atomic oxygen in low Earth orbit to reach underlying material. One concept of enhancing the lifetime of materials in low Earth orbit is to apply a leveling coating to the material prior to applying any reflective and protective coatings. Using a surface tension leveling coating concept, a low viscosity epoxy was applied to the surface of several composite coupons. A protective layer of 1000 A of SiO2 was deposited on top of the leveling coating, and the coupons were exposed to an atomic oxygen environment in a plasma asher. Pinhole populations per unit area were estimated by counting the number of undercut sites observed by scanning electron microscopy. Defect density values of 180,000 defects/sq cm were reduced to about 1000 defects/sq cm as a result of the applied leveling coating. These improvements occur at a mass penalty of about 2.5 mg/sq cm.

  16. Leveling coatings for reducing the atomic oxygen defect density in protected graphite fiber epoxy composites

    NASA Technical Reports Server (NTRS)

    Jaworske, D. A.; Degroh, K. K.; Podojil, G.; Mccollum, T.; Anzic, J.

    1992-01-01

    Pinholes or other defect sites in a protective oxide coating provide pathways for atomic oxygen in low Earth orbit to reach underlying material. One concept for enhancing the lifetime of materials in low Earth orbits is to apply a leveling coating to the material prior to applying any reflective and protective coatings. Using a surface tension leveling coating concept, a low viscosity epoxy was applied to the surface of several composite coupons. A protective layer of 1000 A of SiO2 was deposited on top of the leveling coating, and the coupons were exposed to an atomic oxygen environment in a plasma asher. Pinhole populations per unit area were estimated by counting the number of undercut sites observed by scanning electron microscopy. Defect density values of 180,000 defects/sq cm were reduced to about 1000 defects/sq cm as a result of the applied leveling coating. These improvements occur at a mass penalty of about 2.5 mg/sq cm.

  17. HIGH PRECISION K-SHELL PHOTOABSORPTION CROSS SECTIONS FOR ATOMIC OXYGEN: EXPERIMENT AND THEORY

    SciTech Connect

    McLaughlin, B. M.; Ballance, C. P.; Bowen, K. P.; Gardenghi, D. J.; Stolte, W. C. E-mail: ballance@physics.auburn.edu E-mail: dgardenghi@gmail.com

    2013-07-01

    Photoabsorption of atomic oxygen in the energy region below the 1s {sup -1} threshold in X-ray spectroscopy from Chandra and XMM-Newton is observed in a variety of X-ray binary spectra. Photoabsorption cross sections determined from an R-matrix method with pseudo-states and new, high precision measurements from the Advanced Light Source (ALS) are presented. High-resolution spectroscopy with E/{Delta}E Almost-Equal-To 4250 {+-} 400 was obtained for photon energies from 520 eV to 555 eV at an energy resolution of 124 {+-} 12 meV FWHM. K-shell photoabsorption cross section measurements were made with a re-analysis of previous experimental data on atomic oxygen at the ALS. Natural line widths {Gamma} are extracted for the 1s {sup -1}2s {sup 2}2p {sup 4}({sup 4} P)np {sup 3} P Degree-Sign and 1s {sup -1}2s {sup 2}2p {sup 4}({sup 2} P)np {sup 3} P Degree-Sign Rydberg resonances series and compared with theoretical predictions. Accurate cross sections and line widths are obtained for applications in X-ray astronomy. Excellent agreement between theory and the ALS measurements is shown which will have profound implications for the modeling of X-ray spectra and spectral diagnostics.

  18. Pinhole cameras as sensors for atomic oxygen in orbit; application to attitude determination of the LDEF

    NASA Technical Reports Server (NTRS)

    Peters, Palmer N.; Gregory, John C.

    1991-01-01

    Images produced by pinhole cameras using film sensitive to atomic oxygen provide information on the ratio of spacecraft orbital velocity to the most probable thermal speed of oxygen atoms, provided the spacecraft orientation is maintained stable relative to the orbital direction. Alternatively, as it is described, information on the spacecraft attitude relative to the orbital velocity can be obtained, provided that corrections are properly made for thermal spreading and a co-rotating atmosphere. The LDEF orientation, uncorrected for a co-rotating atmosphere, was determined to be yawed 8.0 minus/plus 0.4 deg from its nominal attitude, with an estimated minus/plus 0.35 deg oscillation in yaw. The integrated effect of inclined orbit and co-rotating atmosphere produces an apparent oscillation in the observed yaw direction, suggesting that the LDEF attitude measurement will indicate even better stability when corrected for a co-rotating atmosphere. The measured thermal spreading is consistent with major exposure occurring during high solar activity, which occurred late during the LDEF mission.

  19. Mass loss of shuttle space suit orthofabric under simulated ionospheric atomic oxygen bombardment

    NASA Technical Reports Server (NTRS)

    Miller, W. L.

    1985-01-01

    Many polymeric materials used for thermal protection and insulation on spacecraft degrade significantly under prolonged bombardment by ionospheric atomic oxygen. The covering fabric of the multilayered shuttle space suit is composed of a loose weave of GORE-TEX fibers, Nomex and Kevlar-29, which are all polymeric materials. The complete evaluation of suit fabric degradation from ionospheric atomic oxygen is of importance in reevaluating suit lifetime and inspection procedures. The mass loss and visible physical changes of each test sample was determined. Kapton control samples and data from previous asher and flight tests were used to scale the results to reflect ionospheric conditions at about 220 km altitude. It is predicted that the orthofabric loses mass in the ionosphere at a rate of about 66% of the original orthofabric mass/yr. The outer layer of the two-layer orthofabric test samples shows few easily visible signs of degradation, even when observed at 440X. It is concluded that the orthofabric could suffer significant loss of performance after much less than a year of total exposure time, while the degradation might be undetectable in post flight visual examinations of space suits.

  20. Collisional Removal of O2(b1Σ ^+g, v = 1) by Atomic Oxygen

    NASA Astrophysics Data System (ADS)

    Kalogerakis, K. S.; Pejaković, D. A.; Copeland, R. A.; Slanger, T. G.

    2004-12-01

    In the thermosphere, energy transfer between excited O atoms and ground-state molecular oxygen produces O2 in the first two vibrational levels of the b1Σ ^+g state: O(1D) + O2 -> O(3P) + O2(b1Σ ^+g, v = 0, 1). Subsequent radiative decay of O2(b1Σ ^+g, v = 0, 1) to the ground state O2(X3Σ ^-g) results in the Atmospheric Band emissions. Atmospheric observations suggest that above ˜120 km O(3P) plays an important role in removing O2(b1Σ ^+g, v = 1). Therefore, knowledge of the rate coefficient for collisional removal of O2(b1Σ ^+g<, v = 1) by O(3P) is important for detailed understanding of the Atmospheric Band emissions. Measurements are reported of the room-temperature rate coefficient for removal of O2(b1Σ ^+g, v = 1) by O(3P). A commercial F2 laser with pulsed energy output of up to 50 mJ at 157 nm is used to photodissociate a large fraction of molecular oxygen in a O2/N2 mixture. Photodissociation of an O2 molecule produces a ground-state oxygen atom O(3P) and an excited oxygen atom O(1D), and O(1D) rapidly transfers energy to the remaining O2 to produce O2(b1Σ ^+g, v = 0, 1). The O2(b1Σ ^+g, v = 1) population is monitored by observing emission in the O2 (b-X) 1--1 band at 771 nm. To extract the O2(b1Σ ^+g, v = 1) + O(3P) rate coefficient, knowledge of the O(3P) partial pressure or, equivalently, the fraction of dissociated O2, is necessary. Based on the F2 laser fluence, the signal dependence on the fraction of dissociation, and computer modeling, the signals measured in our experiments correspond to about 50% dissociation. Our measurements yield a preliminary value of the rate coefficient for O2(b1Σ ^+g, v = 1) removal by O(3P) of 6 × 10-12 cm3s-1. The results will be compared to the rate coefficients for corresponding processes in the ground and a1Δ g states of O2, and implications of the results for modeling of the upper atmosphere will be discussed. This work is supported by the NSF Aeronomy Program under grant ATM-0209229. The F2 laser was

  1. Automated Reflectance Measurement System Designed and Fabricated to Determine the Limits of Atomic Oxygen Treatment of Art Through Contrast Optimization

    NASA Technical Reports Server (NTRS)

    Sechkar, Edward A.; Stueber, Thomas J.; Rutledge, Sharon K.

    2000-01-01

    Atomic oxygen generated in ground-based research facilities has been used to not only test erosion of candidate spacecraft materials but as a noncontact technique for removing organic deposits from the surfaces of artwork. NASA has patented the use of atomic oxygen to remove carbon-based soot contamination from fire-damaged artwork. The process of cleaning soot-damaged paintings with atomic oxygen requires exposures for variable lengths of time, dependent on the condition of a painting. Care must be exercised while cleaning to prevent the removal of pigment. The cleaning process must be stopped as soon as visual inspection or surface reflectance measurements indicate that cleaning is complete. Both techniques rely on optical comparisons of known bright locations against known dark locations on the artwork being cleaned. Difficulties arise with these techniques when either a known bright or dark location cannot be determined readily. Furthermore, dark locations will lighten with excessive exposure to atomic oxygen. Therefore, an automated test instrument to quantitatively characterize cleaning progression was designed and developed at the NASA Glenn Research Center at Lewis Field to determine when atomic oxygen cleaning is complete.

  2. Atomic oxygen effects on boron nitride and silicon nitride: A comparison of ground based and space flight data

    NASA Technical Reports Server (NTRS)

    Cross, J. B.; Lan, E. H.; Smith, C. A.; Whatley, W. J.

    1990-01-01

    The effects of atomic oxygen on boron nitride (BN) and silicon nitride (Si3N4) were evaluated in a low Earth orbit (LEO) flight experiment and in a ground based simulation facility. In both the inflight and ground based experiments, these materials were coated on thin (approx. 250A) silver films, and the electrical resistance of the silver was measured in situ to detect any penetration of atomic oxygen through the BN and Si3N4 materials. In the presence of atomic oxygen, silver oxidizes to form silver oxide, which has a much higher electrical resistance than pure silver. Permeation of atomic oxygen through BN, as indicated by an increase in the electrical resistance of the silver underneath, was observed in both the inflight and ground based experiments. In contrast, no permeation of atomic oxygen through Si3N4 was observed in either the inflight or ground based experiments. The ground based results show good qualitative correlation with the LEO flight results, indicating that ground based facilities such as the one at Los Alamos National Lab can reproduce space flight data from LEO.

  3. A comparison of ground-based and space flight data: Atomic oxygen reactions with boron nitride and silicon nitride

    NASA Technical Reports Server (NTRS)

    Cross, J. B.; Lan, E. H.; Smith, C. A.; Whatley, W. J.; Koontz, S. L.

    1990-01-01

    The effects of atomic oxygen on boron nitride (BN) and silicon nitride (Si3N4) have been studied in low Earth orbit (LEO) flight experiments and in a ground-based simulation facility at Los Alamos National Laboratory. Both the in-flight and ground-based experiments employed the materials coated over thin (approx 250 Angstrom) silver films whose electrical resistance was measured in situ to detect penetration of atomic oxygen through the BN and Si3N4 materials. In the presence of atomic oxygen, silver oxidizes to form silver oxide, which has a much higher electrical resistance than pure silver. Permeation of atomic oxygen through BN, as indicated by an increase in the electrical resistance of the silver underneath, was observed in both the in-flight and ground-based experiments. In contrast, no permeation of atomic oxygen through Si3N4 was observed in either the in-flight or ground-based experiments. The ground-based results show good qualitative correlation with the LEO flight results, thus validating the simulation fidelity of the ground-based facility in terms of reproducing LEO flight results.

  4. The distribution of atomic hydrogen and oxygen in the magnetosphere of Saturn

    NASA Astrophysics Data System (ADS)

    Melin, Henrik; Shemansky, Don E.; Liu, Xianming

    2009-12-01

    The intensity of H Ly α1216A˚ ( 2P- 1S) and OI 1304A˚ ( 2p33s3S-2p4P) is mapped in the magnetosphere of Saturn using the ultraviolet imaging spectrograph (UVIS) [Esposito, L.W., Barth, C.A., Colwell, J.E., Lawrence, G.M., McClintock, W.E., Stewart, A.I.F., Keller, H.U., Korth, A., Lauche, H., Festou, M.C., Lane, A.L., Hansen, C.J., Maki, J.N., West, R.A., Jahn, H., Reulke, R., Warlich, K., Shemansky, D.E., Yung, Y.L., 2004. The Cassini ultraviolet imaging spectrograph investigation. Space Science Reviews 115, 299-361] onboard Cassini. Spatial coverage is built up by stepping the slit sequentially across the system (system scan). Data are obtained at a large range of space-craft-Saturn distances. The observed atomic hydrogen distribution is very broad, extending beyond 40RS in the equatorial plane, with the intensity increasing with decreasing distances to Saturn. The distribution displays persistent local-time asymmetries, and is seen connecting continuously to the upper atmosphere of the planet at sub-solar latitudes located well outside of the equatorial (ring) plane. This is consistent with the source of the atomic hydrogen being located at the top of the atmosphere on the sun-lit side of the planet on the southern hemisphere. In addition there are a number of temporally persistent features in the intensity distribution, indicating a complex hydrogen energy distribution. The emission from OI 1304A˚ is generally distributed as a broad torus centered around ˜4RS although the position of the peak intensity can vary by as much as ±1RS. There is significant intensity present out to ±10RS. HST observations of hydroxyl (OH) are re-analyzed and display a distribution half as broad as that of oxygen, also centered at 4RS. The observed atomic oxygen distribution requires a sourcing of 1.3×1028atomss-1 against loss due to charge capture with the plasma. Using the ion partitioning of Schippers et al. [2008. Multi-instrument analysis of electron populations in Saturn

  5. Preparation and structure of a solid-state hypervalent-iodine polymer containing iodine and oxygen atoms in fused 12-atom hexagonal rings.

    PubMed

    Richter, Helen W; Koser, Gerald F; Incarvito, Christopher D; Rheingold, Arnold L

    2007-07-01

    The treatment of dilute aqueous solutions of [hydroxy(tosyloxy)iodo]benzene with aqueous Mg(ClO4)2 produced thin elongated-hexagonal plates exhibiting a supramolecular structure in which tetra-mu-oxopentaiodanyl dication repeat units are joined to each other by significantly ionic bonds and each unit is associated with two perchlorate ions. The linearly extended cationic structure is formed from the 12-atom hexagonal rings of alternating iodine and oxygen atoms, a novel structure. Each 12-membered ring forms a nearly planar hexagonal shape with sides defined by almost linear O-I-O segments (175.7+/-1.6) degrees. The apexes are occupied by bridging oxide ligands where the I-O-I angles deviate only slightly from an ideal 120 degrees hexagonal angle (116.8+/-1.2) degrees, consistent with sp2 hybridization of the bridging oxygen atoms that participate in three-center four-electron bonds with iodine. These 12-atom hexagons are slightly "chair" distorted at the oxygen atoms. The planes of the rings are separated by layers containing the phenyl rings. The perchlorate ions reside in void spaces created by the three-up, three-down arrangement of the phenyl rings around each 12-membered I-O ring and are positioned directly above and below the I-O rings. PMID:17569525

  6. Distribution of atomic oxygen in the upper atmosphere deduced from Ogo 6 airglow observations.

    NASA Technical Reports Server (NTRS)

    Donahue, T. M.; Guenther, B.; Thomas, R. J.

    1973-01-01

    The atomic oxygen distribution as a function of altitude between 80 and 120 km and as a function of latitude has been deduced from Ogo 6 557.7-nm airglow photometer data obtained between August 1969 and April 1970. The results indicate that the density ranges from 15 to 50 billion per cu cm at 120 km; that there is a semiannual variation by a factor of 3 in the global average density near 100 km in phase with the satellite drag semiannual effect; and that large latitudinal variations occur with maximums between 40 and 60 deg in the winter hemisphere and sometimes deep minimums in the tropics. The implication of these results for meridional and vertical transport patterns is discussed.

  7. Orbital atomic oxygen effects on thermal control and optical materials - STS-8 results

    NASA Technical Reports Server (NTRS)

    Whitaker, A. F.; Little, S. A.; Harwell, R. J.; Griner, D. B.; Dehaye, R. F.; Fromhold, A. T., Jr.

    1985-01-01

    The effects of exposing 23 specimens of optical and thermal control materials to space at 120 km altitude for over 40 hrs during the STS-8 mission are discussed. Ten samples of paint targeted for the Space Telescope (ST) and the Tethered Satellite were exposed, and included polyurethane, oxide, silicone, and glossy black and white samples which were scanned for alterations in the optical properties after being retrieved. Nine mirror-type materials were also investigated, along with silver specimens typical of solar cell interconnects. The oxygen flow at the orbital altitude was 3.5 x 10 to the 20th atoms/cu cm. The exposures caused no degradation of the magnesium fluoride mirror coatings, while the Kapton coating for the ST solar cell panels showed evidence of losing thickness. The Ag solar cell contacts will require coatings to extend their lifetimes. Overcoatings were also proven necessary for inhibiting degradation of painted surfaces.

  8. Exceedingly Fast Oxygen Atom Transfer to Olefins via a Catalytically Competent Nonheme Iron Species.

    PubMed

    Serrano-Plana, Joan; Aguinaco, Almudena; Belda, Raquel; García-España, Enrique; Basallote, Manuel G; Company, Anna; Costas, Miquel

    2016-05-17

    The reaction of [Fe(CF3 SO3 )2 (PyNMe3 )] with excess peracetic acid at -40 °C leads to the accumulation of a metastable compound that exists as a pair of electromeric species, [Fe(III) (OOAc)(PyNMe3 )](2+) and [Fe(V) (O)(OAc)(PyNMe3 )](2+) , in fast equilibrium. Stopped-flow UV/Vis analysis confirmed that oxygen atom transfer (OAT) from these electromeric species to olefinic substrates is exceedingly fast, forming epoxides with stereoretention. The impact of the electronic and steric properties of the substrate on the reaction rate could be elucidated, and the relative reactivities determined for the catalytic oxidations could be reproduced by kinetic studies. The observed fast reaction rates and high selectivities demonstrate that this metastable compound is a truly competent OAT intermediate of relevance for nonheme iron catalyzed epoxidations.

  9. Exceedingly Fast Oxygen Atom Transfer to Olefins via a Catalytically Competent Nonheme Iron Species.

    PubMed

    Serrano-Plana, Joan; Aguinaco, Almudena; Belda, Raquel; García-España, Enrique; Basallote, Manuel G; Company, Anna; Costas, Miquel

    2016-05-17

    The reaction of [Fe(CF3 SO3 )2 (PyNMe3 )] with excess peracetic acid at -40 °C leads to the accumulation of a metastable compound that exists as a pair of electromeric species, [Fe(III) (OOAc)(PyNMe3 )](2+) and [Fe(V) (O)(OAc)(PyNMe3 )](2+) , in fast equilibrium. Stopped-flow UV/Vis analysis confirmed that oxygen atom transfer (OAT) from these electromeric species to olefinic substrates is exceedingly fast, forming epoxides with stereoretention. The impact of the electronic and steric properties of the substrate on the reaction rate could be elucidated, and the relative reactivities determined for the catalytic oxidations could be reproduced by kinetic studies. The observed fast reaction rates and high selectivities demonstrate that this metastable compound is a truly competent OAT intermediate of relevance for nonheme iron catalyzed epoxidations. PMID:27071372

  10. Investigations of tribological characteristics of solid lubricants exposed to atomic oxygen

    SciTech Connect

    Arita, Masasgi; Yasuda, Yoshiteru; Kishi, Katsuhiro; Ohmae, Nobuo Osaka University, Suita )

    1992-04-01

    Four kinds of solid lubricants, sputtered MoS2 film, inorganic binder-type spray-bonded MoS2 film, organic binder-type spray-bonded MoS2 film and ion-plated Pb film, were exposed to an atomic oxygen (AO) beam. The effects of exposure on their lubricating performance were examined in a pin-on-disk sliding test under vacuum conditions. Changes in the degree of oxidation of these films were analyzed by Auger electron spectroscopy. Exposure to the AO beam resulted in significant changes in lubricating performance and surface oxidation. Of the solid-lubricant films tested, sputtered MoS2 film showed the most resistance to oxidation. The results are of interest to the evaluation of lubricants for spacecraft in LEO orbit. 17 refs.

  11. Long term variations and solar variability of atomic oxygen and hydrogen in the mesosphere / lower thermosphere

    NASA Astrophysics Data System (ADS)

    Ern, Manfred; Kaufmann, Martin; Lehmann, Catrin; Riese, Martin; Smith, Anne; Marsh, Daniel

    Global measurements of the hydroxyl mesospheric airglow as observed by the SCIAMACHY satellite instrument are presented. SCIAMACHY is mounted on ESA's Envisat launched in March 2002 into a polar, sun-synchronous orbit with an inclination of 98.7deg and an ascending node at 22:00 local solar time. Limb observations on the night side cover about 70 degrees in terms of latitude during each orbit, covering 30S-70N, depending on season. Based on these measurements altitude profiles of atomic oxygen and hydrogen are retrieved by means of an OH non-LTE model. These data are analyzed with respect to solar illumination conditions and global wave activity. A windowed space-time Fourier analysis is carried out to investigate seasonal changes in mesopause wave activity. First comparisons with simulations of the NCAR ROSE model are shown.

  12. An Investigation of Stress Dependent Atomic Oxygen Erosion of Black Kapton Observed on MISSE 6

    NASA Technical Reports Server (NTRS)

    Miller, Sharon K. R.; Banks, Bruce A.; Sechkar, Edward

    2012-01-01

    Black Kapton XC polyimide was flown as part of the Polymer Film Tensile Experiment (PFTE) on Materials International Space Station Experiment 6 (MISSE 6). The purpose of the experiment was to expose a variety of polymer films, typical of those used for thermal control blankets or supporting membranes on Earth orbiting spacecraft, to the low Earth orbital (LEO) environment under both relaxed and tension conditions. Black Kapton XC under tensile stress experienced a higher erosion rate during exposure in LEO than the same material that was flown in a relaxed condition. Testing conducted to determine the magnitude of the stress and erosion dependence using a ground-based thermal energy atomic oxygen plasma showed a slight dependence of erosion yield on stress for Kapton HN and Black Kapton XC, but not to the extent observed on MISSE 6. More testing is needed to isolate the factors present in LEO that cause stress dependent erosion.

  13. Atomic Oxygen Treatment Technique for Removal of Smoke Damage from Paintings

    NASA Technical Reports Server (NTRS)

    Rutledge, S. K.; Banks, B. A.

    1997-01-01

    Soot deposits that can accumulate on surfaces of a painting during a fire can be difficult to clean from some types of paintings without damaging the underlying paint layers. A non-contact technique has been developed which can remove the soot by allowing a gas containing atomic oxygen to flow over the surface and chemically react with the soot to form carbon monoxide and carbon dioxide. The reaction is limited to the surface, so the underlying paint is not touched. The process can be controlled so that the cleaning can be stopped once the paint surface is reached. This paper describes the smoke exposure and cleaning of untreated canvas, acrylic gesso, and sections of an oil painting using this technique. The samples were characterized by optical microscopy and reflectance spectroscopy.

  14. Chemical reactivity of hydrogen, nitrogen, and oxygen atoms at temperatures below 100 k

    NASA Technical Reports Server (NTRS)

    Mcgee, H. A., Jr.

    1973-01-01

    The synthesis of unusual compounds by techniques employing cryogenic cooling to retard their very extreme reactivity was investigated. Examples of such species that were studied are diimide (N2H2), cyclobutadiene (C4H4), cyclopropanone (C3H4O), oxirene (C2H2O), and many others. Special purpose cryogenically cooled inlet arrangements were designed such that the analyses incurred no warm-up of the cold, and frequently explosively unstable, compounds. Controlled energy electron impact techniques were used to measure critical potentials and to develop the molecular energetics and thermodynamics of these molecules and to gain some insight into their kinetic characteristics as well. Three and four carbon strained ring molecules were studied. Several reactions of oxygen and hydrogen atoms with simple molecules of H, N, C, and O in hard quench configurations were studied. And the quench stabilization of BH3 was explored as a model system in cryochemistry.

  15. Protective coating and hyperthermal atomic oxygen texturing of optical fibers used for blood glucose monitoring

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor)

    2008-01-01

    Disclosed is a method of producing cones and pillars on polymethylmethacralate (PMMA) optical fibers for glucose monitoring. The method, in one embodiment, consists of using electron beam evaporation to deposit a non-contiguous thin film of aluminum on the distal ends of the PMMA fibers. The partial coverage of aluminum on the fibers is randomly, but rather uniformly distributed across the end of the optical fibers. After the aluminum deposition, the ends of the fibers are then exposed to hyperthermal atomic oxygen, which oxidizes the areas that are not protected by aluminum. The resulting PMMA fibers have a greatly increased surface area and the cones or pillars are sufficiently close together that the cellular components in blood are excluded from passing into the valleys between the cones and pillars. The optical fibers are then coated with appropriated surface chemistry so that they can optically sense the glucose level in the blood sample than that with conventional glucose monitoring.

  16. Atomic Structures of Oxygen-associated Defects in Sintered Aluminum Nitride Ceramics.

    PubMed

    Yan; Pennycook; Terauchi; Tanaka

    1999-09-01

    : Convergent-beam electron diffraction and Z-contrast imaging are used to study oxygen-associated defects, flat inversion domain boundaries, dislocations, and interfaces in sintered AlN ceramics. The structures of these defects are directly derived from atomic-resolution Z-contrast images. The flat inversion domain boundaries contain a single Al-O octahedral layer and have a stacking sequence of.bAaB-bAc-CaAc., where -cAb- indicates the single octahedral layer. The expansion at the flat inversion domain boundaries is measured to be 0.06 (+/-0.02) nm. The interfaces between 2H- and polytypoid-AlN are found to be also inversion domain boundaries but their stacking sequence differs from that of the flat inversion domain boundaries. PMID:10473680

  17. ATOMIC AND MOLECULAR PHYSICS: First Principles Simulation of Molecular Oxygen Adsorption on SiC Nanotubes

    NASA Astrophysics Data System (ADS)

    Ganji, M. D.; Ahaz, B.

    2010-04-01

    We study the binding of molecular oxygen to a (5, 0) single walled SiC nanotube, by means of density functional calculations. The center of a hexagon of silicon and carbon atoms in sites on SiCNT surfaces is the most stable adsorption site for O2 molecule, with a binding energy of -38.22 eV and an average Si-O binding distance of 1.698 Å. We have also tested the stability of the O2-adsorbed SiCNT/CNT with ab initio molecular dynamics simulation which have been carried out at room temperature. Furthermore, the adsorption of O2 on the single walled carbon nanotubes has been investigated. Our first-principles calculations predict that the O2 adsorptive capability of silicon carbide nanotubes is much better than that of carbon nanotubes. This might have potential for gas detection and energy storage.

  18. Energetic Atomic and Ionic Oxygen Textured Optical Surfaces for Blood Glucose Monitoring

    NASA Technical Reports Server (NTRS)

    Banks, Bruce A. (Inventor)

    2007-01-01

    Disclosed is a method and the resulting product thereof comprising a solid light-conducting fiber with a point of attachment and having a textured surface site consisting of a textured distal end prepared by being placed in a vacuum and then subjected to directed hyperthermal beams comprising oxygen ions or atoms. The textured distal end comprises cones or pillars that are spaced upon from each other by less than 1 micron and are extremely suitable to prevent cellular components of blood from entering the valleys between the cones or pillars so as to effectively separate the cellular components in the blood from interfering with optical sensing of the glucose concentration for diabetic patients.

  19. Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions

    NASA Astrophysics Data System (ADS)

    Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva

    2016-07-01

    Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

  20. Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

    PubMed

    Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva

    2016-01-01

    Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits. PMID:27403611

  1. Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions

    PubMed Central

    Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva

    2016-01-01

    Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits. PMID:27403611

  2. Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

    PubMed

    Zeng, Lunjie; Tran, Dung Trung; Tai, Cheuk-Wai; Svensson, Gunnar; Olsson, Eva

    2016-07-12

    Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

  3. Control of oxygen atom chirality and chelate ring conformation by protected/free sugar hydroxyl groups in glucose-pendant dipicolylamine-copper(II) complexes.

    PubMed

    Mikata, Yuji; Sugai, Yuko; Yano, Shigenobu

    2004-08-01

    A pair of copper(II) complexes 1 and 2 exhibit an enantiomeric chiral center at the oxygen atom that coordinates to the metal center. The configurations of the oxygen atom chirality and the chelate ring conformation are simply controlled by protected/free hydroxyl groups of the sugar moiety, yielding mirror image CD spectra. In this system, repulsive and attractive forces are used to regulate chirality on the copper-coordinated oxygen atom both in the solid state and in solution.

  4. ESCA study of Kapton exposed to atomic oxygen in low earth orbit or downstream from a radio-frequency oxygen plasma

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.; Wydeven, Theodore; Cormia, Robert D.

    1988-01-01

    The ESCA spectra of Kapton polyimide film exposed to atomic oxygen O(3P), either in low earth orbit (LEO) on the STS-8 Space Shuttle or downstream from a radio-frequency oxygen plasma, were compared. The major difference in surface chemistry induced by the two types of exposure to O(3P), both of which caused surface recession (etching), was a much larger uptake of oxygen by Kapton etched in the O2 plasma than in LEO. This difference is attributed to the presence of molecular oxygen in the plasma reactor and its absence in LEO: in the former case, O2 can react with radicals generated in the Kapton molecule as it etches, become incorporated in the etched polymer, and thereby yield a higher steady-state 'surface oxidation' level than in LEO.

  5. Role of Mobile Interstitial Oxygen Atoms in Defect Processes in Oxides: Interconversion between Oxygen-Associated Defects in SiO2 Glass

    NASA Astrophysics Data System (ADS)

    Kajihara, Koichi; Skuja, Linards; Hirano, Masahiro; Hosono, Hideo

    2004-01-01

    The role of mobile interstitial oxygen atoms (O0) in defect processes in oxides is demonstrated by interconversion between the oxygen dangling bond and the peroxy radical (POR) in SiO2 glass. Superstoichiometric O0 was created by F2 laser photolysis of the interstitial O2. On annealing above 300 °C, O0 migrated and converted the oxygen dangling bond to POR. Exposure to 5.0eV light converted POR back to a pair of the oxygen dangling bond and O0 (quantum yield: ˜0.1). These findings suggest that various defect processes typically occurring in SiO2 glass at ˜300 500 °C are related to migration of O0, which exists in the glass network in the peroxy linkage form.

  6. Spatial and temporal variations in infrared emissions of the upper atmosphere. 1. Atomic oxygen (λ 63 μm) emission

    NASA Astrophysics Data System (ADS)

    Semenov, A. I.; Medvedeva, I. V.; Perminov, V. I.; Khomich, V. Yu.

    2016-09-01

    Rocket and balloon measurement data on atomic-oxygen (λ 63 µm) emission in the upper atmosphere are presented. The data from the longest (1989-2003) period of measurements of the atomic-oxygen (λ 63 µm) emission intensity obtained by spectral instruments on sounding balloons at an altitude of 38 km at midlatitudes have been systematized and analyzed. Regularities in diurnal and seasonal variations in the intensity of this emission, as well as in its relation with solar activity, have been revealed.

  7. Effects of atomic oxygen and ultraviolet radiation on candidate elastomeric materials for long duration missions. Test series no.1

    NASA Technical Reports Server (NTRS)

    Linton, R. C.; Finckenor, M. M.; Kamenetzky, R. R.; Gray, P.

    1993-01-01

    Research was conducted at MSFC on the behavior of elastomeric materials after exposure to simulated space environment. Silicone S383 and Viton V747 samples were exposed to thermal vacuum, ultraviolet radiation, and atomic oxygen and then evaluated for changes in material properties. Characterization of the elastomeric materials included weight, hardness, optical inspection under normal and black light, spectrofluorescence, solar absorptance and emittance, Fourier transform infrared spectroscopy, and permeability. These results indicate a degree of sensitivity to exposure and provided some evidence of UV and atomic oxygen synergism.

  8. Angular distributions of 5eV atomic oxygen scattered from solid surfaces on the LDEF satellite

    NASA Technical Reports Server (NTRS)

    Gregory, John C.; Peters, Palmer N.

    1992-01-01

    The angular distribution of 5eV atomic oxygen scattered off several smooth solid surfaces was measured by experiment A0114 which flew on board the Long Duration Exposure Facility (LDEF). Target surfaces were silver, vitreous carbon, and lithium fluoride crystal. The apparatus was entirely passive. It used the property of silver surfaces to absorb oxygen atoms with high efficiency; the silver is converted to optically transmissive silver oxide. A collimated beam of oxygen atoms is allowed to fall on the target surface at some pre-set angle. Reflected atoms are then intercepted by a silver film placed so that it subtends a considerable solid angle from the primary beam impact on the target surface. The silver films are evaporated onto flexible optically-clear polycarbonate sheets which are scanned later to determine oxygen uptake. While the silver detector cannot measure atom velocity or energy, its physical configuration allows easy coverage of large angular space both in the beam-plane (that which includes the incident beam and the surface normal), and in the azimuthal plane of the target surface.

  9. Total photoionization cross sections of atomic oxygen from threshold to 44.3A

    NASA Technical Reports Server (NTRS)

    Angel, G. C.; Samson, James A. R.

    1987-01-01

    The relative cross section of atomic oxygen for the production of singly charged ions has been remeasured in more detail and extended to cover the wavelength range 44.3 to 910.5 A by the use of synchrotron radiation. In addition, the contribution of multiple ionization to the cross sections has been measured allowing total photoionization cross sections to be obtained below 250 A. The results have been made absolute by normalization to previously measured data. The use of synchrotron radiation has enabled measurements of the continuum cross section to be made between the numerous autoionizing resonances that occur near the ionization thresholds. This in turn has allowed a more critical comparison of the various theoretical estimates of the cross section to be made. The series of autoionizing resonances leading to the 4-P state of the oxygen ion have been observed for the first time in an ionization type experiment and their positions compared with both theory and previous photographic recordings.

  10. K-shell Photoioinization of the atomic nitrogen and oxygen isonuclear sequences

    NASA Astrophysics Data System (ADS)

    McLaughlin, Brendan M.

    2016-05-01

    The advent of third and fourth generation light sources, such as the ALS at Berkeley, USA, SOLEIL in Orsay, France and PETRA III in Hamburg, Germany, this past decade or more and the unprecedented high brightness and spectral resolution have made it possible to perform detailed cross section measurements in the X-ray region of extremely important astrophysical elements such as Carbon, Nitrogen and Oxygen and their isonuclear sequences. In tandem with this world wide experimental endeavour theoretical work has provided interpretation in unravelling and identifying prominent resonance features in the spectra in the vicinity of the K-shell region. For the atomic oxygen sequence (Kα and Kβ resonance positions in the vicinity of the K-edge) we note that ground based measurements (ALS and SOLEIL) and R-matrix with pseudo-states (RMPS) theoretical results are in agreement but are ~ 0.5 eV in discrepancy with satellite observations from CHANDRA and XMM-NEWTON. A review of the current status of experiment, theory and observation will be presented for the various sequences. Supported by NSF, DOE, CNRS, DFG, NERSC and HLRS at Stuttgart University.

  11. Kinetic modeling of α-hydrogen abstractions from unsaturated and saturated oxygenate compounds by hydrogen atoms.

    PubMed

    Paraskevas, Paschalis D; Sabbe, Maarten K; Reyniers, Marie-Françoise; Papayannakos, Nikos G; Marin, Guy B

    2014-10-01

    Hydrogen-abstraction reactions play a significant role in thermal biomass conversion processes, as well as regular gasification, pyrolysis, or combustion. In this work, a group additivity model is constructed that allows prediction of reaction rates and Arrhenius parameters of hydrogen abstractions by hydrogen atoms from alcohols, ethers, esters, peroxides, ketones, aldehydes, acids, and diketones in a broad temperature range (300-2000 K). A training set of 60 reactions was developed with rate coefficients and Arrhenius parameters calculated by the CBS-QB3 method in the high-pressure limit with tunneling corrections using Eckart tunneling coefficients. From this set of reactions, 15 group additive values were derived for the forward and the reverse reaction, 4 referring to primary and 11 to secondary contributions. The accuracy of the model is validated upon an ab initio and an experimental validation set of 19 and 21 reaction rates, respectively, showing that reaction rates can be predicted with a mean factor of deviation of 2 for the ab initio and 3 for the experimental values. Hence, this work illustrates that the developed group additive model can be reliably applied for the accurate prediction of kinetics of α-hydrogen abstractions by hydrogen atoms from a broad range of oxygenates. PMID:25209711

  12. Three-dimensional evaluation of gettering ability for oxygen atoms at small-angle tilt boundaries in Czochralski-grown silicon crystals

    SciTech Connect

    Ohno, Yutaka Inoue, Kaihei; Fujiwara, Kozo; Deura, Momoko; Kutsukake, Kentaro; Yonenaga, Ichiro; Shimizu, Yasuo; Inoue, Koji; Ebisawa, Naoki; Nagai, Yasuyoshi

    2015-06-22

    Three-dimensional distribution of oxygen atoms at small-angle tilt boundaries (SATBs) in Czochralski-grown p-type silicon ingots was investigated by atom probe tomography combined with transmission electron microscopy. Oxygen gettering along edge dislocations composing SATBs, post crystal growth, was observed. The gettering ability of SATBs would depend both on the dislocation strain and on the dislocation density. Oxygen atoms would agglomerate in the atomic sites under the tensile hydrostatic stress larger than about 2.0 GPa induced by the dislocations. It was suggested that the density of the atomic sites, depending on the tilt angle of SATBs, determined the gettering ability of SATBs.

  13. Conductance and spin-filter effects of oxygen-incorporated Au, Cu, and Fe single-atom chains

    SciTech Connect

    Zheng, Xiaolong; Xie, Yi-Qun Ye, Xiang; Ke, San-Huang

    2015-01-28

    We studied the spin-polarized electron transport in oxygen-incorporated Au, Cu, and Fe single-atom chains (SACs) by first-principles calculations. We first investigated the mechanism responsible for the low conductance (<1G{sub 0}) of the Au and Cu SACs in an oxygen environment reported in recent experiments. We found that for the Au SACs, the low conductance plateau around 0.6G{sub 0} can be attributed to a distorted chain doped with a single oxygen atom, while the 0.1G{sub 0} conductance comes from a linear chain incorporated with an oxygen molecule and is caused by an antibonding state formed by oxygen's occupied frontier orbital with d{sub z} orbitals of adjacent Au atoms. For the Cu SACs, the conductance about 0.3G{sub 0} is ascribed to a special configuration that contains Cu and O atoms in an alternating sequence. This exhibits an even-odd conductance oscillation with an amplitude of ∼0.1G{sub 0}. In contrast, for the alternating Fe-O SACs, conductance overall decreases with an increase in O atoms and it approaches nearly zero for the chain with more than four O atoms. While the Cu-O SACs behave as perfect spin filters for one spin channel due to the half metallic nature, the Fe-O SACs can serve as perfect spin filters for two spin channels depending on the polarity of the applied gate voltage.

  14. Model for atomic oxygen visible line emissions in Comet C/1995 O1 Hale-Bopp

    NASA Astrophysics Data System (ADS)

    Raghuram, Susarla; Bhardwaj, Anil

    2013-03-01

    We have recently developed a coupled chemistry-emission model for the green (5577 Å) and red-doublet (6300, 6364 Å) emissions of atomic oxygen on Comet C/1996 B2 Hyakutake. In the present work we applied our model to Comet C/1995 O1 Hale-Bopp, which had an order of magnitude higher H2O production rate than Comet Hyakutake, to evaluate the photochemistry associated with the production and loss of O(1S) and O(1D) atoms and emission processes of green and red-doublet lines. We present the wavelength-dependent photo-attenuation rates for different photodissociation processes forming O(1S) and O(1D). The calculated radiative efficiency profiles of O(1S) and O(1D) atoms show that in Comet Hale-Bopp the green and red-doublet emissions are emitted mostly above radial distances of 103 and 104 km, respectively. The model calculated [OI] 6300 Å emission surface brightness and average intensity over the Fabry-Pérot spectrometer field of view are consistent with the observation of Morgenthaler et al. (Morgenthaler, J.P. et al. [2001]. Astrophys. J. 563, 451-461), while the intensity ratio of green to red-doublet emission is in agreement with the observation of Zhang et al. (Zhang, H.W., Zhao, G., Hu, J.Y. [2001]. Astron. Astophys. 367 (3), 1049-1055). In Comet Hale-Bopp, for cometocentric distances less than 105 km, the intensity of [OI] 6300 Å line is mainly governed by photodissociation of H2O. Beyond 105 km, O(1D) production is dominated by photodissociation of the water photochemical daughter product OH. Whereas the [OI] 5577 Å emission line is controlled by photodissociation of both H2O and CO2. The calculated mean excess energy in various photodissociation processes show that the photodissociation of CO2 can produce O(1S) atoms with higher excess velocity compared to the photodissociation of H2O. Thus, our model calculations suggest that involvement of multiple sources in the formation of O(1S) could be a reason for the larger width of green line than that of red

  15. Spatially and Temporally Resolved Atomic Oxygen Measurements in Short Pulse Discharges by Two Photon Laser Induced Fluorescence

    NASA Astrophysics Data System (ADS)

    Lempert, Walter; Uddi, Mruthunjaya; Mintusov, Eugene; Jiang, Naibo; Adamovich, Igor

    2007-10-01

    Two Photon Laser Induced Fluorescence (TALIF) is used to measure time-dependent absolute oxygen atom concentrations in O2/He, O2/N2, and CH4/air plasmas produced with a 20 nanosecond duration, 20 kV pulsed discharge at 10 Hz repetition rate. Xenon calibrated spectra show that a single discharge pulse creates initial oxygen dissociation fraction of ˜0.0005 for air like mixtures at 40-60 torr total pressure. Peak O atom concentration is a factor of approximately two lower in fuel lean (φ=0.5) methane/air mixtures. In helium buffer, the initially formed atomic oxygen decays monotonically, with decay time consistent with formation of ozone. In all nitrogen containing mixtures, atomic oxygen concentrations are found to initially increase, for time scales on the order of 10-100 microseconds, due presumably to additional O2 dissociation caused by collisions with electronically excited nitrogen. Further evidence of the role of metastable N2 is demonstrated from time-dependent N2 2^nd Positive and NO Gamma band emission spectroscopy. Comparisons with modeling predictions show qualitative, but not quantitative, agreement with the experimental data.

  16. Orbital atomic oxygen effects on materials: An overview of MSFC experiments on the STS-46 EOIM-3

    NASA Technical Reports Server (NTRS)

    Linton, Roger C.; Vaughn, Jason A.; Finckenor, Miria M.; Kamenetzky, Rachel R.; Dehaye, Robert F.; Whitaker, Ann F.

    1995-01-01

    The third Evaluation of Oxygen Interaction with Materials experiment was flown on Space Shuttle Mission STS-46 (July 31 - August 8, 1992), representing a joint effort of several NASA centers, universities, and contractors. This array of active instrumentation and material exposure sub-assemblies was integrated as a Shuttle cargo bay pallet experiment for investigating the effects of orbital atomic oxygen on candidate space materials. Marshall Space Flight Center contributed several passive exposure trays of material specimens, uniform stress and static stress material exposure fixtures, the Atomic Oxygen Resistance Monitor (AORM), and specimens of thermal coatings for the EOIM-3 variable exposure mechanisms. As a result of 42 hours of spacecraft velocity vector-oriented exposure during the later phases of the STS-46 mission in LEO, EOIM-3 materials were exposed to an atomic oxygen fluence of 2.2 x 10(exp 20) atoms/sq cm. In this paper, an overview is presented of the technical approaches and results from analyses of the MSFC flight specimens, fixtures, and the AORM. More detailed results from earlier EOIM missions, the LDEF, and from laboratory testing are included in associated papers of this conference session.

  17. Orbital atomic oxygen effects on materials: An overview of MSFC experiments on the STS-46 EOIM-3

    SciTech Connect

    Linton, R.C.; Vaughn, J.A.; Finckenor, M.M.; Kamenetzky, R.R.; Dehaye, R.F.; Whitaker, A.F.

    1995-02-01

    The third Evaluation of Oxygen Interaction with Materials experiment was flown on Space Shuttle Mission STS-46 (July 31 - August 8, 1992), representing a joint effort of several NASA centers, universities, and contractors. This array of active instrumentation and material exposure sub-assemblies was integrated as a Shuttle cargo bay pallet experiment for investigating the effects of orbital atomic oxygen on candidate space materials. Marshall Space Flight Center contributed several passive exposure trays of material specimens, uniform stress and static stress material exposure fixtures, the Atomic Oxygen Resistance Monitor (AORM), and specimens of thermal coatings for the EOIM-3 variable exposure mechanisms. As a result of 42 hours of spacecraft velocity vector-oriented exposure during the later phases of the STS-46 mission in LEO, EOIM-3 materials were exposed to an atomic oxygen fluence of 2.2 x 10(exp 20) atoms/sq cm. In this paper, an overview is presented of the technical approaches and results from analyses of the MSFC flight specimens, fixtures, and the AORM.

  18. Practicality of Using Oxygen Atom Emissions to Evaluate the Habitability of Extra-Solar Planets

    NASA Astrophysics Data System (ADS)

    Slanger, T. G.

    2005-12-01

    It has previously been proposed [Akasofu, 1999] that observation of the O(1S - 1D) green line from the atmospheres of extra-solar planets might be a marker for habitability. Guidance on this question is available within our own solar system. The green line is a dominant feature in the visible terrestrial nightglow, and the ultimate origin of its mesospheric emission is the three-body recombination of oxygen atoms. Until recently, it was believed that the green line was not a feature of the nightglows of the CO2 planets, Venus and Mars. It is now known that Venus at times shows green line emission with an intensity equal to terrestrial values [Slanger et al., 2001]. Furthermore, the intensity is quite variable, as is true for the much stronger O2( a-X) 1.27 μ emission. Recent observations of the Mars nightglow [Bertaux et al., 2005] give ambiguous results in the region of the O(1S-3P) line at 297.2 nm, but the same line in the dayglow is very strong, as evidenced in earlier Mariner results [Barth et al., 1971], and from the recent Mars Express data [F. Leblanc, private communication]. The O(1D-3P) 630 nm red line is a feature associated with Io, where dissociation of SO2 is a presumed source [Scherb et al., 1998]. Thus, observation of the oxygen green/red lines in the atmospheres of extrasolar planets provides insufficient information to reach conclusions about a habitable environment. Such detection would only indicate that there are oxygen-containing molecules present. Determination of an O2 column depth, by Fraunhofer A-band absorption, would be much more conclusive. Akasofu, S.-I., EOS, Transactions of the American Geophysical Union, 80, 397, 1999. Barth, C.A., C.W. Hord, J.B. Pearce, K.K. Kelly, G.P. Anderson, and A.I. Stewart, Mariner 6 and 7 Ultraviolet Spectrometer Experiment: Upper Atmosphere Data, Journal of Geophysical Research, 76, 2213-2227, 1971. Bertaux, J.-L., F. Leblanc, S. Perrier, E. Quemerais, O. Korablev, E. Dimarellis, A. Reberac, F. Forget, P

  19. Protection of Diamond-like Carbon Films from Energetic Atomic Oxygen Degradation Through Si-doping Technology

    SciTech Connect

    Yokota, Kumiko; Tagawa, Masahito; Kitamura, Akira; Matsumoto, Koji; Yoshigoe, Akitaka; Teraoka, Yuden; Fontaine, Julien; Belin, Michel

    2009-01-05

    The effect of hyperthermal atomic oxygen (AO) exposure on the surface properties of Si-doped diamond-like carbon (DLC) was investigated. Two types of DLC were tested that contain approximately 10 at% and 20 at% of Si atoms. Surface analytical results of high-resolution x-ray photoelectron spectroscopy using synchrotron radiation (synchrotron radiation photoemission spectroscopy; SR-PES) as well as Rutherford backscattering spectroscopy (RBS) have been used for characterization of the AO-exposed Si-doped DLC. It was identified by SR-PES that a SiO{sub 2} layer was formed by the hyperthermal AO exposure at the Si-doped DLC surface. RBS data indicates that AO exposure leads to severe thickness loss on the undopedd DLC. In contrast, a SiO{sub 2} layer formed by the hyperthermal atomic oxygen reaction of Si-doped DLC protects the DLC underneath the SiO{sub 2} layer.

  20. Atomic Oxygen as the controlling factor in collocation of Elves and OH* Meinel band nightglow

    NASA Astrophysics Data System (ADS)

    Wu, Y. J.; Williams, E. R.; Friedrich, M.; Chang, S. C.; Chou, J. K.; Chen, A. B. C.; Su, H. T.; Hsu, R. R.; Frey, H. U.; Takahashi, Y.; Lee, L. C.

    2015-12-01

    The Imager of Sprite and Upper Atmospheric Lightning (ISUAL) onboard the Formosat-2 satellite has monitored Transient Luminous Events (TLEs) and lightning activity within the latitude interval +/- 60o since May 2004. Channel 1 of the Imager with a bandpass from 623 to 754 nm is the channel usually used for recording TLEs. However, it also covers the wavelength range of the OH* Meinel Band nightglow (8,3) in the infrared region, and this circumstance opens a window for us to study the relationship between OH* nightglow and TLEs. The result shows that over 95% of the elves are within +/- 2 pixels in altitude of the brightest OH* emission. The abrupt increase of atomic oxygen with altitude serves to release electrons from O2- thereby providing electrons the opportunity to attach to meteoric dust eventually. Atomic O is also vital to OH* nightglow as the necessary species to make O3. Additionally , from the fundamental reaction , O+ O2- -> O3 + e- , it can be seen that this is not only a key process to move the free electrons to the ablation dust toward making the electron density ledge, but is also an effective way to make O3 for the OH* nightglow. We suggest that the meteoric dust with abrupt appearance in the electron density ledge forms the upper boundary for the VLF waveguide. This circumstance may justify the use of the VLF waveguide cutoff height as a proxy for the dominant altitude of elves. When the global map of such cutoff heights (Toledo-Redondo et al., 2012) and the OH nightglow (WINDII) heights are compared, both show a distinct wavenumber-4 structure in the low-latitude region. The collocation of elves and the OH* nightglow layer is not coincidental and reveals new information about the structure of the D region.

  1. Effects of Contamination, UV Radiation, and Atomic Oxygen on ISS Thermal Control Materials

    NASA Technical Reports Server (NTRS)

    Visentine, Jim; Finckenor, Miria; Zwiener, Jim; Munafo, Paul (Technical Monitor)

    2001-01-01

    Thermal control surfaces on the International Space Station (ISS) have been tailored for optimum optical properties. The space environment, particularly contamination, ultraviolet (UV) radiation, and atomic oxygen (AO) may have a detrimental effect on these optical properties. These effects must be quantified for modeling and planning. Also of interest was the effect of porosity on the reaction to simulated space environment. Five materials were chosen for this study based on their use on ISS. The thermal control materials were Z-93 white coating, silverized Teflon, chromic acid anodized aluminum, sulfuric acid anodized aluminum, and 7075-T6 aluminum. Some of the samples were exposed to RTV 560 silicone; others were exposed to Tefzel offgassing products. Two samples of Z-93 were not exposed to contamination as clean "controls". VUV radiation was used to photo-fix the contaminant to the material surface, then the samples were exposed to AO. All samples were exposed to 1000 equivalent sun-hours (ESH) of vacuum ultraviolet radiation (VUV) at the AZ Technology facility and a minimum of 1.5 x 10(exp 20) atoms/sq cm of AO at Marshall Space Flight Center. Half of the samples were exposed to an additional 2000 ESH of VUV at Huntington Beach prior to sent to AZ Technology. Darkening of the Z-93 white coating was noted after VUV exposure. AO exposure did bleach the Z-93 but not back to its original brightness. Solar absorptance curves show the degradation due to contamination and VUV and the recovery with AO exposure. More bleaching was noted on the Tefzel-contaminated samples than with the RTV-contaminated samples.

  2. First detection of the 63 μm atomic oxygen line in the thermosphere of Mars with GREAT/SOFIA

    NASA Astrophysics Data System (ADS)

    Rezac, L.; Hartogh, P.; Güsten, R.; Wiesemeyer, H.; Hübers, H.-W.; Jarchow, C.; Richter, H.; Klein, B.; Honingh, N.

    2015-08-01

    Context. The Stratospheric Observatory for Infrared Astronomy (SOFIA) with its 2.5 m telescope provides new science opportunities for spectroscopic observations of planetary atmospheres in the far-infrared wavelength range. Aims: This paper presents first results from the 14 May, 2014 observing campaign of the Martian atmosphere at 4.7 THz using the German REceiver for Astronomy at Terahertz frequencies (GREAT) instrument. Methods: The atomic oxygen 63 μm transition, OI, was detected in absorption against the Mars continuum, with a high signal-to-noise ratio (~35). A beam-averaged atomic oxygen from a global circulation model was used as input to the radiative transfer simulations of the observed line area and to obtain a new estimate on the column density using a grid-search method. Results: Minimizing differences between the calculated and observed line intensities in the least-square sense yields an atomic oxygen column density of (1.1 ± 0.2) × 1017 cm-2. This value is about twice as low as predicted by a modern photochemical model of Mars. The radiative transfer simulations indicate that the line forms in the upper atmospheric region over a rather extended altitude region of 70-120 km. Conclusions: For the first time, a far-infrared transition of the atomic oxygen line was detected in the atmosphere of Mars. The absorption depth provides an estimate on the column density, and this measurement provides additional means to constrain the photochemical models in global circulation models and airglow studies. The lack of other means for monitoring the atomic oxygen in the Martian upper atmosphere makes future observations with the SOFIA observatory highly desirable. Appendix A is available in electronic form at http://www.aanda.org

  3. ESCA study of several fluorocarbon polymers exposed to atomic oxygen in low earth orbit or within or downstream from a radio-frequency oxygen plasma

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.; Wydeven, Theodore; Cormia, Robert D.

    1989-01-01

    The ESCA (electron spectroscopy for chemical analysis) spectra of films of Tedlar, tetrafluoroethylene-hexafluoropropylene copolymer (in the form of a Teflon FEP coating on Kapton H, i.e., Kapton F), and polytetrafluoroethylene (Teflon or Teflon TFE), exposed to atomic oxygen O(3P) either in LEO on the STS-8 Space Shuttle or within or downstream from a radio-frequency oxygen plasma, were compared. The major difference in surface chemistry of Tedlar induced by the various exposures to O(3P) was a much larger uptake of oxygen when etched either in or out of the glow of an O2 plasma than when etched in LEO. In contrast, Kapton F exhibited very little surface oxidation during any of the three different exposures to O(3P), while Teflon was scarcely oxidized.

  4. Atomic oxygen and temperature in the lower thermosphere from the O-STATES sounding rocket project

    NASA Astrophysics Data System (ADS)

    Hedin, Jonas; Gumbel, Jörg; Megner, Linda; Stegman, Jacek; Seo, Mikael; Khaplanov, Mikhail; Slanger, Tom; Kalogerakis, Konstantinos; Friedrich, Martin; Torkar, Klaus; Eberhart, Martin; Löhle, Stefan; Fasoulas, Stefanos

    2016-04-01

    In October 2015 the O-STATES payload was launched twice from Esrange Space Center (67.9° N, 21.1° E) in northern Sweden, first into moderately disturbed and then into calm geomagnetic conditions. The basic idea of O-STATES ("Oxygen Species and Thermospheric Airglow in The Earth's Sky") is that comprehensive information on the composition, specifically atomic oxygen in the ground state O(3P) and first excited state O(1D), and temperature of the lower thermosphere can be obtained from a limited set of optical measurements. Starting point for the analysis are daytime measurements of the O2(b1 ∑ g+ - X3 ∑ g-) Atmospheric Band system in the spectral region 755-780 nm and the O(1D-3P) Red Line at 630 nm. In the daytime lower thermosphere, O(1D) is produced by O2 photolysis and the excited O2(b) state is mainly produced by energy transfer from O(1D) to the O2(X) ground state. In addition to O2 photolysis, both electron impact on O(3P) and dissociative recombination of O2+ are major sources of O(1D) in the thermosphere. Laboratory studies at SRI International have shown that O2(b) production in vibrational level v=1 dominates. While O2(b, v=0) is essentially unquenched, O2(b, v=1) is subject to collisional quenching that is dominated by O at altitudes above 160 km. Hence, the ratio of the Atmospheric Band emission from O2(b, v=1) and O2(b, v=0) is a measure of the O density at sufficiently high altitudes. In addition, the spectral shape of the O2 Atmospheric Band is temperature dependent and spectrally resolved measurements of the Atmospheric Bands thus provide a measure of atmospheric temperature. This O2 Atmospheric Band analysis has been suggested as a new technique for thermospheric remote sensing under the name Global Oxygen and Temperature (GOAT) Mapping. With O-STATES we want to characterize the GOAT technique by in-situ analysis of the O2 Atmospheric Band airglow and the underlying excitation mechanisms. By performing this dayglow analysis from a rocket

  5. Atomic oxygen and temperature in the lower thermosphere from the O-STATES sounding rocket project

    NASA Astrophysics Data System (ADS)

    Hedin, Jonas; Gumbel, Jörg; Megner, Linda; Stegman, Jacek; Seo, Mikael; Khaplanov, Mikhail; Slanger, Tom; Kalogerakis, Konstantinos; Friedrich, Martin; Torkar, Klaus; Eberhart, Martin; Löhle, Stefan; Fasoulas, Stefanos

    2016-04-01

    In October 2015 the O-STATES payload was launched twice from Esrange Space Center (67.9° N, 21.1° E) in northern Sweden, first into moderately disturbed and then into calm geomagnetic conditions. The basic idea of O-STATES ("Oxygen Species and Thermospheric Airglow in The Earth's Sky") is that comprehensive information on the composition, specifically atomic oxygen in the ground state O(3P) and first excited state O(1D), and temperature of the lower thermosphere can be obtained from a limited set of optical measurements. Starting point for the analysis are daytime measurements of the O2(b1 ∑ g+ ‑ X3 ∑ g‑) Atmospheric Band system in the spectral region 755-780 nm and the O(1D-3P) Red Line at 630 nm. In the daytime lower thermosphere, O(1D) is produced by O2 photolysis and the excited O2(b) state is mainly produced by energy transfer from O(1D) to the O2(X) ground state. In addition to O2 photolysis, both electron impact on O(3P) and dissociative recombination of O2+ are major sources of O(1D) in the thermosphere. Laboratory studies at SRI International have shown that O2(b) production in vibrational level v=1 dominates. While O2(b, v=0) is essentially unquenched, O2(b, v=1) is subject to collisional quenching that is dominated by O at altitudes above 160 km. Hence, the ratio of the Atmospheric Band emission from O2(b, v=1) and O2(b, v=0) is a measure of the O density at sufficiently high altitudes. In addition, the spectral shape of the O2 Atmospheric Band is temperature dependent and spectrally resolved measurements of the Atmospheric Bands thus provide a measure of atmospheric temperature. This O2 Atmospheric Band analysis has been suggested as a new technique for thermospheric remote sensing under the name Global Oxygen and Temperature (GOAT) Mapping. With O-STATES we want to characterize the GOAT technique by in-situ analysis of the O2 Atmospheric Band airglow and the underlying excitation mechanisms. By performing this dayglow analysis from a rocket

  6. Multiple ionization and coupling effects in L-subshell ionization of heavy atoms by oxygen ions

    SciTech Connect

    Pajek, M.; Banas, D.; Semaniak, J.; Braziewicz, J.; Majewska, U.; Chojnacki, S.; Czyzewski, T.; Fijal, I.; Jaskola, M.; Glombik, A.; Kretschmer, W.; Trautmann, D.; Lapicki, G.; Mukoyama, T.

    2003-08-01

    The multiple-ionization and coupling effects in L-shell ionization of atoms by heavy-ion impact have been studied by measuring the L x-ray production cross sections in solid targets of Au, Bi, Th, and U bombarded by oxygen ions in the energy range 6.4-70 MeV. The measured L x-ray spectra were analyzed using the recently proposed method accounting for the multiple-ionization effects, such as x-ray line shifting and broadening, which enables one to obtain the ionization probabilities for outer shells. The L-subshell ionization cross sections have been obtained from measured x-ray production cross sections for resolved L{alpha}{sub 1,2}, L{gamma}{sub 1}, and L{gamma}{sub 2,3} transitions using the L-shell fluorescence and Coster-Kronig yields being substantially modified by the multiple ionization in the M and N shells. In particular, the effect of closing of strong L{sub 1}-L{sub 3}M{sub 4,5} Coster-Kronig transitions in multiple-ionized atoms was evidenced and discussed. The experimental ionization cross sections for the L{sub 1}, L{sub 2}, and L{sub 3} subshells have been compared with the predictions of the semiclassical approximation (SCA) and the ECPSSR theory that includes the corrections for the binding-polarization effect within the perturbed stationary states approximation, the projecticle energy loss, and Coulomb deflection effects as well as the relativistic description of inner-shell electrons. These approaches were further modified to include the L-subshell couplings within the ''coupled-subshell model'' (CSM). Both approaches, when modified for the coupling effects, are in better agreement with the data. Particularly, the predictions of the SCA-CSM calculations reproduce the experimental L-subshell ionization cross section reasonably well. Remaining discrepancies are discussed qualitatively, in terms of further modifications of the L-shell decay rates caused by a change of electronic wave functions in multiple-ionized atoms.

  7. Modeling of Transmittance Degradation Caused by Optical Surface Contamination by Atomic Oxygen Reaction with Adsorbed Silicones

    NASA Technical Reports Server (NTRS)

    Snyder, Aaron; Banks, Bruce; Miller, Sharon; Stueber, Thomas; Sechkar, Edward

    2001-01-01

    A numerical procedure is presented to calculate transmittance degradation caused by contaminant films on spacecraft surfaces produced through the interaction of orbital atomic oxygen (AO) with volatile silicones and hydrocarbons from spacecraft components. In the model, contaminant accretion is dependent on the adsorption of species, depletion reactions due to gas-surface collisions, desorption, and surface reactions between AO and silicone producing SiO(x), (where x is near 2). A detailed description of the procedure used to calculate the constituents of the contaminant layer is presented, including the equations that govern the evolution of fractional coverage by specie type. As an illustrative example of film growth, calculation results using a prototype code that calculates the evolution of surface coverage by specie type is presented and discussed. An example of the transmittance degradation caused by surface interaction of AO with deposited contaminant is presented for the case of exponentially decaying contaminant flux. These examples are performed using hypothetical values for the process parameters.

  8. Atomic Oxygen Exposure of Polyimide Foam for International Space Station Solar Array Wing Blanket Box

    NASA Technical Reports Server (NTRS)

    Finckenor, M. M.; Albyn, K. C.; Watts, E. W.

    2006-01-01

    Onorbit photos of the International Space Station (ISS) solar array blanket box foam pad assembly indicate degradation of the Kapton film covering the foam, leading to atomic oxygen (AO) exposure of the foam. The purpose of this test was to determine the magnitude of particulate generation caused by low-Earth orbital environment exposure of the foam and also by compression of the foam during solar array wing retraction. The polyimide foam used in the ISS solar array wing blanket box assembly is susceptible to significant AO erosion. The foam sample in this test lost one-third of its mass after exposure to the equivalent of 22 mo onorbit. Some particulate was generated by exposure to simulated orbital conditions and the simulated solar array retraction (compression test). However, onorbit, these particles would also be eroded by AO. The captured particles were generally <1 mm, and the particles shaken free of the sample had a maximum size of 4 mm. The foam sample maintained integrity after a compression load of 2.5 psi.

  9. Effects of Atomic Oxygen and Grease on Outgassing and Adhesion of Silicone Elastomers for Space Applications

    NASA Technical Reports Server (NTRS)

    deGroh, Henry C., III; Puleo, Bernadette J.; Steinetz, Bruce M.

    2012-01-01

    An investigation of silicone elastomers for seals used in docking and habitat systems for future space exploration vehicles is being conducted at NASA. For certain missions, NASA is considering androgynous docking systems where two vehicles each having a seal would be required to: dock for a period of time, seal effectively, and then separate with minimum push-off forces for undocking. Silicone materials are generally chosen for their wide operating temperatures and low leakage rates. However silicone materials are often sticky and usually exhibit considerable adhesion when mated against metals and silicone surfaces. This paper investigates the adhesion unit pressure for a space rated silicone material (S0383-70) for either seal-on-seal (SoS) or seal-on-aluminum (SoAl) operation modes in the following conditions: as-received, after ground-based atomic-oxygen (AO) pre-treatment, after application of a thin coating of a space-qualified grease (Braycote 601EF), and after a combination of AO pre-treatment and grease coating. In order of descending adhesion reduction, the AO treatment reduced seal adhesion the most, followed by the AO plus grease pre-treatment, followed by the grease treatment. The effects of various treatments on silicone (S0383-70 and ELA-SA-401) outgassing properties were also investigated. The leading adhesion AO pretreatment reduction led to a slight decrease in outgassing for the S0383-70 material and virtually no change in ELA-SA-401 outgassing.

  10. New Measurement of the Rate Coefficient for Three-Body Recombination of Oxygen Atoms in Presence of N2

    NASA Astrophysics Data System (ADS)

    Huestis, D. L.; Pejaković, D. A.; Copeland, R. A.; Kalogerakis, K. S.

    2004-12-01

    In the atmospheres of Earth, Venus, and Mars photodissociation of O2 and CO2 produces oxygen atoms that eventually undergo three-body recombination: O + O + M -> O2* + M. The competition between photodissociation, recombination, and diffusive vertical transport controls the atomic and molecular composition of the mesosphere and lower thermosphere. Knowledge of the rate coefficient for recombination of atomic oxygen is essential for modeling atmospheric composition. The most recent measurement of O-atom recombination rate coefficient is over thirty years old [1]. The published values of this rate coefficient have large divergence for both M = O2 and M = N2. For N2 as the third body, the room temperature coefficient varies between about 3 × 10-33 cm6s-1, which is the value recommended in the combustion science community, and 5 × 10-33 cm6s-1, a value used in the atmospheric modeling community. Previous laboratory investigations [2] of the process O + O + N2 -> O2* + N2 shared the same basic approach, which was to use N2 discharge flow system with NO added downstream to generate O-atoms in the absence of O2 through the reaction N + NO -> O + N2. This approach is vulnerable to heterogeneous recombination and other processes that may obscure the reaction of interest, mostly due to the low O-atom densities and, consequently, long reaction times. We employ an F2 laser with up to 50 mJ of 157 nm pulsed output to achieve nearly complete photodissociation of molecular oxygen. In a high-pressure (760 Torr) background of N2 the oxygen atoms recombine in a time scale of several milliseconds. Oxygen atom population is monitored by detecting 845-nm fluorescence, which is induced by the 226 nm output of the second laser via a two-photon process O(2p4 3P) + 2hν -> O(2p33p ^3P). Our measurements give a preliminary value for the O + O + N_2 recombination rate coefficient of approximately 3 \\times 10^{-33} cm^6s^{-1}, which favors the value recommended in the combustion community

  11. Selective production of atomic oxygen by laser photolysis as a tool for studying the effect of atomic oxygen in plasma medicine

    NASA Astrophysics Data System (ADS)

    Ono, Ryo; Tokumitsu, Yusuke

    2015-06-01

    We propose a method for selectively producing O atoms by the laser photolysis of O3 as a tool for studying the therapeutic effect of O atoms in plasma medicine. A KrF excimer laser (248 nm) irradiates an O3 /He mixture flowing in a quartz tube to photodissociate O3 , which leads to the production of O atoms. The effluent from the quartz tube nozzle can be applied to a target (cells, bacteria, or an affected part). Simulations show that 500 ppm O atoms can be continuously supplied to a target surface at a distance of 3 mm from the quartz tube nozzle if an O3 (2000 ppm)/He mixture is used. The effluent contains only O, O3 , and O_2({{a}1}{Δg}) , and does not contain other types of reactive species in contrast to a plasma. Therefore, it can be used to examine the therapeutic effects of O atoms in isolation. Part of the simulation results are experimentally verified by irradiating an O3 /He mixture with a KrF excimer laser.

  12. Photochemistry of atomic oxygen green and red-doublet emissions in comets at larger heliocentric distances

    NASA Astrophysics Data System (ADS)

    Raghuram, Susarla; Bhardwaj, Anil

    2014-06-01

    Context. In comets, the atomic oxygen green (5577 Å) to red-doublet (6300, 6364 Å) emission intensity ratio (G/R ratio) of 0.1 has been used to confirm H2O as the parent species producing forbidden oxygen emission lines. The larger (>0.1) value of G/R ratio observed in a few comets is ascribed to the presence of higher CO2 and CO relative abundances in the cometary coma. Aims: We aim to study the effect of CO2 and CO relative abundances on the observed G/R ratio in comets observed at large (>2 au) heliocentric distances by accounting for important production and loss processes of O(1S) and O(1D) atoms in the cometary coma. Methods: Recently we have developed a coupled chemistry-emission model to study photochemistry of O(1S) and O(1D) atoms and the production of green and red-doublet emissions in comets Hyakutake and Hale-Bopp. In the present work we applied the model to six comets where green and red-doublet emissions are observed when they are beyond 2 au from the Sun. Results: The collisional quenching of O(1S) and O(1D) can alter the G/R ratio more significantly than that due to change in the relative abundances of CO2 and CO. In a water-dominated cometary coma and with significant (>10%) CO2 relative abundance, photodissociation of H2O mainly governs the red-doublet emission, whereas CO2 controls the green line emission. If a comet has equal composition of CO2 and H2O, then ~50% of red-doublet emission intensity is controlled by the photodissociation of CO2. The role of CO photodissociation is insignificant in producing both green and red-doublet emission lines and consequently in determining the G/R ratio. Involvement of multiple production sources in the O(1S) formation may be the reason for the observed higher green line width than that of red lines. The G/R ratio values and green and red-doublet line widths calculated by the model are consistent with the observation. Conclusions: Our model calculations suggest that in low gas production rate comets the G

  13. Results from LDEF experiment A0114: The interaction of atomic oxygen with materials surfaces at orbital altitudes

    NASA Technical Reports Server (NTRS)

    Gregory, John C.

    1994-01-01

    In 1975 the University of Alabama in Huntsville proposed an experiment for the Long Duration Exposure Facility (LDEF) designed to investigate the effects of the collision of the ambient orbital atmosphere, mainly consisting of atomic oxygen, with satellite surfaces travelling at about 8 km per second. In 1989, the potential for recovery of significant data from A0114 on a wide variety of materials was recognized and funding for three years of data analysis was appropriated. Some significant or unique findings from the experiment A0114 include: numerous measurements of oxidation rates of surfaces under fast O atom bombardment, including Si, Ge, GaAs, SiC, and optical quality metal films; measurement of the stable attitude of the LDEF spacecraft in orbit using the gas dynamics pinhole camera; description of the formation of thick oxide films on copper at 20 C with fast oxygen; measurement of erosion rates of Kapton and other polymers at space station lifetime atomic oxygen fluences (10(exp 22) atoms/sq cm); and measurement of the cosmogenic isotopes Be-7 on spacecraft surfaces.

  14. Atomic oxygen interaction with spacecraft materials: Relationship between orbital and ground-based testing for materials certification

    SciTech Connect

    Cross, J.B. ); Koontz, S.L. . Lyndon B. Johnson Space Center); Lan, E.H. )

    1991-01-01

    The effects of atomic oxygen on boron nitride, silicon nitride, solar cell interconnects used on the Intelsat 6 satellite, organic polymers, and MoS{sub 2} and WS{sub 2} dry lubricant have been studied in low Earth orbit (LEO) flight experiments and in our ground-based simulation facility at Los Alamos National Laboratory. Both the in-flight and ground-based experiments employed in situ electrical resistance measurements to detect penetration of atomic oxygen through materials and ESCA analysis to measure chemical composition changes. In the presence of atomic oxygen, silver oxidizes to form silver oxide, which has a much higher electrical resistance than pure silver. Permeation of atomic oxygen through BN overcoated on thin silver was observed. No permeation of atomic oxygen through Si{sub 3}N{sub 4} was observed. Test results on the Intelsat 6 satellite interconnects used on its photovoltaic array indicate that more than 60--80% of the original thickness of silver should remain after completion of the proposed Space Shuttle rescue/reboost mission. Gas phase reaction products produced by the interaction of high kinetic energy atomic oxygen (AO) with Kapton were found to be H{sub 2}, H{sub 2}O, CO, and CO{sub 2} with NO being a possible secondary product. Hydrogen abstraction at high AO kinetic energy is postulated to be the key reaction controlling the erosion rate of Kapton. An Arrhenius-like expression having an activation barrier of 0.4 eV can be fit to the data, which suggests that the rate limiting step in the AO/Kapton reaction mechanism can be overcome by translational energy. Oxidation of MoS{sub 2} and WS{sub 2} dry lubricants in both ground-based and orbital exposures indicated the formation of MoO{sub 3} and WO{sub 3} respectively. A protective oxide layer is formed {approx}30 monolayers thick which has a high initial friction coefficient until the layer is worn off.

  15. Launch Vehicle Performance for Bipropellant Propulsion Using Atomic Propellants With Oxygen

    NASA Technical Reports Server (NTRS)

    Palaszewski, Bryan

    2000-01-01

    Atomic propellants for bipropellant launch vehicles using atomic boron, carbon, and hydrogen were analyzed. The gross liftoff weights (GLOW) and dry masses of the vehicles were estimated, and the 'best' design points for atomic propellants were identified. Engine performance was estimated for a wide range of oxidizer to fuel (O/F) ratios, atom loadings in the solid hydrogen particles, and amounts of helium carrier fluid. Rocket vehicle GLOW was minimized by operating at an O/F ratio of 1.0 to 3.0 for the atomic boron and carbon cases. For the atomic hydrogen cases, a minimum GLOW occurred when using the fuel as a monopropellant (O/F = 0.0). The atomic vehicle dry masses are also presented, and these data exhibit minimum values at the same or similar O/F ratios as those for the vehicle GLOW. A technology assessment of atomic propellants has shown that atomic boron and carbon rocket analyses are considered to be much more near term options than the atomic hydrogen rockets. The technology for storing atomic boron and carbon has shown significant progress, while atomic hydrogen is not able to be stored at the high densities needed for effective propulsion. The GLOW and dry mass data can be used to estimate the cost of future vehicles and their atomic propellant production facilities. The lower the propellant's mass, the lower the overall investment for the specially manufactured atomic propellants.

  16. Adsorption sites of single noble metal atoms on the rutile TiO2 (1 1 0) surface influenced by different surface oxygen vacancies.

    PubMed

    Matsunaga, Katsuyuki; Chang, Teng-Yuan; Ishikawa, Ryo; Dong, Qian; Toyoura, Kazuaki; Nakamura, Atsutomo; Ikuhara, Yuichi; Shibata, Naoya

    2016-05-01

    Atomic adsorption of Au and Pt on the rutile (1 1 0) surface was investigated by atomic-resolution aberration-corrected scanning transmission electron microscopy (STEM) measurements combined with density functional theory calculations. Au single atoms were deposited on the surface in a vacuum condition, and the observed results were compared with Pt single atoms on the same surface prepared by the same experimental manner. It was found that Au single atoms are stably adsorbed only at the bridging oxygen vacancy sites, which is quite different from Pt single atoms exhibiting the most frequently observed adsorption at the basal oxygen vacancy sites. Such a difference in oxygen-vacancy effect between Au and Pt can be explained by electronic structures of the surface vacancies as well as characters of outermost atomic orbitals of Au and Pt.

  17. Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111).

    PubMed

    Gharachorlou, Amir; Detwiler, Michael D; Gu, Xiang-Kui; Mayr, Lukas; Klötzer, Bernhard; Greeley, Jeffrey; Reifenberger, Ronald G; Delgass, W Nicholas; Ribeiro, Fabio H; Zemlyanov, Dmitry Y

    2015-08-01

    Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3

  18. Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111).

    PubMed

    Gharachorlou, Amir; Detwiler, Michael D; Gu, Xiang-Kui; Mayr, Lukas; Klötzer, Bernhard; Greeley, Jeffrey; Reifenberger, Ronald G; Delgass, W Nicholas; Ribeiro, Fabio H; Zemlyanov, Dmitry Y

    2015-08-01

    Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu(1+) to metallic copper (Cu(0)) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al(3+) in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al(3+) (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al-O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3

  19. Atomic oxygen on the Venus nightside: Global distribution deduced from airglow mapping

    NASA Astrophysics Data System (ADS)

    Soret, L.; Gérard, J.-C.; Montmessin, F.; Piccioni, G.; Drossart, P.; Bertaux, J.-L.

    2012-02-01

    The Visible and Infra-Red Thermal Imaging Spectrometer (VIRTIS) instrument on board the Venus Express spacecraft has measured the O 2(a 1Δ) nightglow distribution at 1.27 μm in the Venus mesosphere for more than two years. Nadir observations have been used to create a statistical map of the emission on Venus nightside. It appears that the statistical 1.6 MR maximum of the emission is located around the antisolar point. Limb observations provide information on the altitude and on the shape of the emission layer. We combine nadir observations essentially covering the southern hemisphere, corrected for the thermal emission of the lower atmosphere, with limb profiles of the northern hemisphere to generate a global map of the Venus nightside emission at 1.27 μm. Given all the O 2(a 1Δ) intensity profiles, O 2(a 1Δ) and O density profiles have been calculated and three-dimensional maps of metastable molecular and atomic oxygen densities have been generated. This global O density nightside distribution improves that available from the VTS3 model, which was based on measurements made above 145 km. The O 2(a 1Δ) hemispheric average density is 2.1 × 10 9 cm -3, with a maximum value of 6.5 × 10 9 cm -3 at 99.2 km. The O density profiles have been derived from the nightglow data using CO 2 profiles from the empirical VTS3 model or from SPICAV stellar occultations. The O hemispheric average density is 1.9 × 10 11 cm -3 in both cases, with a mean altitude of the peak located at 106.1 km and 103.4 km, respectively. These results tend to confirm the modeled values of 2.8 × 10 11 cm -3 at 104 km and 2.0 × 10 11 cm -3 at 110 km obtained by Brecht et al. [Brecht, A., Bougher, S.W., Gérard, J.-C., Parkinson, C.D., Rafkin, S., Foster, B., 2011a. J. Geophys. Res., in press] and Krasnopolsky [Krasnopolsky, V.A., 2010. Icarus 207, 17-27], respectively. Comparing the oxygen density map derived from the O 2(a 1Δ) nightglow observations, it appears that the morphology is very

  20. Trimethylaluminum and Oxygen Atomic Layer Deposition on Hydroxyl-Free Cu(111)

    PubMed Central

    2015-01-01

    Atomic layer deposition (ALD) of alumina using trimethylaluminum (TMA) has technological importance in microelectronics. This process has demonstrated a high potential in applications of protective coatings on Cu surfaces for control of diffusion of Cu in Cu2S films in photovoltaic devices and sintering of Cu-based nanoparticles in liquid phase hydrogenation reactions. With this motivation in mind, the reaction between TMA and oxygen was investigated on Cu(111) and Cu2O/Cu(111) surfaces. TMA did not adsorb on the Cu(111) surface, a result consistent with density functional theory (DFT) calculations predicting that TMA adsorption and decomposition are thermodynamically unfavorable on pure Cu(111). On the other hand, TMA readily adsorbed on the Cu2O/Cu(111) surface at 473 K resulting in the reduction of some surface Cu1+ to metallic copper (Cu0) and the formation of a copper aluminate, most likely CuAlO2. The reaction is limited by the amount of surface oxygen. After the first TMA half-cycle on Cu2O/Cu(111), two-dimensional (2D) islands of the aluminate were observed on the surface by scanning tunneling microscopy (STM). According to DFT calculations, TMA decomposed completely on Cu2O/Cu(111). High-resolution electron energy loss spectroscopy (HREELS) was used to distinguish between tetrahedrally (Altet) and octahedrally (Aloct) coordinated Al3+ in surface adlayers. TMA dosing produced an aluminum oxide film, which contained more octahedrally coordinated Al3+ (Altet/Aloct HREELS peak area ratio ≈ 0.3) than did dosing O2 (Altet/Aloct HREELS peak area ratio ≈ 0.5). After the first ALD cycle, TMA reacted with both Cu2O and aluminum oxide surfaces in the absence of hydroxyl groups until film closure by the fourth ALD cycle. Then, TMA continued to react with surface Al–O, forming stoichiometric Al2O3. O2 half-cycles at 623 K were more effective for carbon removal than O2 half-cycles at 473 K or water half-cycles at 623 K. The growth rate was approximately 3–4

  1. Direct atomic-scale imaging of hydrogen and oxygen interstitials in pure niobium using atom-probe tomography and aberration-corrected scanning transmission electron microscopy.

    PubMed

    Kim, Yoon-Jun; Tao, Runzhe; Klie, Robert F; Seidman, David N

    2013-01-22

    Imaging the three-dimensional atomic-scale structure of complex interfaces has been the goal of many recent studies, due to its importance to technologically relevant areas. Combining atom-probe tomography and aberration-corrected scanning transmission electron microscopy (STEM), we present an atomic-scale study of ultrathin (~5 nm) native oxide layers on niobium (Nb) and the formation of ordered niobium hydride phases near the oxide/Nb interface. Nb, an elemental type-II superconductor with the highest critical temperature (T(c) = 9.2 K), is the preferred material for superconducting radio frequency (SRF) cavities in next-generation particle accelerators. Nb exhibits high solubilities for oxygen and hydrogen, especially within the RF-field penetration depth, which is believed to result in SRF quality factor losses. STEM imaging and electron energy-loss spectroscopy followed by ultraviolet laser-assisted local-electrode atom-probe tomography on the same needle-like sample reveals the NbO(2), Nb(2)O(5), NbO, Nb stacking sequence; annular bright-field imaging is used to visualize directly hydrogen atoms in bulk β-NbH.

  2. Influence of molecular oxygen on iodine atoms production in an RF discharge

    NASA Astrophysics Data System (ADS)

    Mikheyev, P. A.; Ufimtsev, N. I.; Demyanov, A. V.; Kochetov, I. V.; Azyazov, V. N.; Napartovich, A. P.

    2016-06-01

    The results of the experiments and modeling of CH3I dissociation in a 40 MHz RF discharge plasma are presented. A discharge chamber of an original design, consisting of quartz tubes between two planar electrodes, permitted us to produce iodine atoms with a number density up to 2  ×  1016 cm‑3. In this discharge chamber, contrary to the previous experiments with a DC discharge and RF discharge with bare planar electrodes, contamination of the walls of the tubes did not disturb discharge stability, thus increasing iodine production rate. A substantial increase in CH3I dissociation efficiency due to the addition of oxygen into Ar(He) : CH3I mixtures was observed. Complete CH3I dissociation in the Ar : CH3I : O2 mixture occurred at 200 W discharge power, while a fraction of discharge power spent on iodine atoms production at 0.17 mmol s‑1 CH3I flow rate amounted to 16%. Extensive numerical modeling showed satisfactory agreement with the experiments and permitted us to estimate a previously unknown rate of constants for the processes: Ar*  +  CH2I2  →  Ar  +  CH2  +  I  +  I – 1.5  ×  10‑11 cm3 s‑1 Ar*  +  CH2I2  →  Ar  +  CH2I+  +  I  +  e – 10‑11 cm3 s‑1. Also, the cross section for the process CH2I2  +  e  →  CH2  +  I  +  I  +  e was estimated to be five times smaller than for the analogous process with CH3I.

  3. Surface interaction mechanisms of 5eV atomic oxygen: Data analysis from the UAH experiment on STS-8

    NASA Technical Reports Server (NTRS)

    Gregory, J. C.

    1987-01-01

    The University of Alabama in Huntsville (UAH) experiment which flew on the STS-8 mission had several objectives which were mostly of a speculative nature since so little was known of the processes of interest. The experiment provided original, if limited, data on: (1) oxidation of metal surfaces, (2) reaction rates of atomic oxygen with carbon and other surfaces and the dependence of these rates on temperature, and (3) the angular distribution of 5eV atoms scattered off a solid surface. Provided is a review of the results, with reference given to fuller published accounts where these are available.

  4. Effects of Atomic Oxygen and Grease on Outgassing and Adhesion of Silicone Elastomers for Space Applications

    NASA Technical Reports Server (NTRS)

    deGroh, Henry C., III; Puleo, Bernadette J.; Steinetz, Bruce M.

    2011-01-01

    An investigation of silicone elastomers for seals used in docking and habitat systems for future space exploration vehicles is being conducted at NASA. For certain missions, NASA is considering androgynous docking systems where two vehicles each having a seal would be required to: dock for a period of time, seal effectively, and then separate with minimum push-off forces for undocking. Sili-cone materials are generally chosen for their wide operating temperatures and low leakage rates. However silicone materials are often sticky and usually exhibit considerable adhesion when mated against metals and silicone surfaces. This paper investigates the adhesion unit pressure for a space rated silicone material (S0383-70) for either seal-on-seal (SoS) or seal-on-aluminum (SoAl) operation modes in the following conditions: as-received, after ground-based atomic-oxygen (AO) pre-treatment, after application of a thin coating of a space-qualified grease (Bray-cote 601EF), and after a combination of AO pre-treatment and grease coating. In order of descending adhesion reduction, the AO treatment reduced seal adhesion the most, followed by the AO plus grease pre-treatment, followed by the grease treatment. The effects of various treatments on silicone (S0383-70 and ELA-SA-401) outgassing properties were also investigated. The leading adhesion AO pre-treatment reduction led to a slight decrease in outgassing for the S0383-70 material and virtually no change in ELA-SA-401 outgassing.

  5. FAR-INFRARED DETECTION OF NEUTRAL ATOMIC OXYGEN TOWARD THE HORSEHEAD NEBULA

    SciTech Connect

    Goicoechea, Javier R.; Compiegne, Mathieu; Habart, Emilie E-mail: compiegne@cita.utoronto.ca

    2009-07-10

    We present the first detection of the neutral atomic oxygen ({sup 3} P {sub 1}-{sup 3} P {sub 2} fine structure line at {approx}63 {mu}m) toward the Horsehead photodissociation region (PDR). The cloud has been mapped with the Spitzer Space Telescope at far-IR (FIR) wavelengths using the Multiband Imaging Photometer for Spitzer in the spectral energy distribution mode. The [O I]63 {mu}m line peaks at the illuminated edge of the cloud at A{sub V} {approx_equal} 0.1-0.5 (inward the gas becomes too cold and outward the gas density drops). The luminosity carried by the [O I]63 {mu}m line represents a significant fraction of the total FIR dust luminosity (I {sub 63}/I {sub FIR} {approx_equal} 4 x 10{sup -3}). We analyze the dust continuum emission and the nonlocal O I excitation and radiative transfer in detail. The observations are reproduced with a gas density of n {sub H} {approx_equal} 10{sup 4} cm{sup -3} and gas and dust temperatures of T{sub k} {approx_equal} 100 K and T{sub d} {approx_equal} 30 K. We conclude that the determination of the O I {sup 3} P{sub J} level populations and emergent line intensities at such 'low' densities is a complex non-LTE problem. FIR radiative pumping, [O I]63 {mu}m subthermal emission, [O I]145 {mu}m suprathermal and even maser emission can occur and decrease the resulting [O I]63/145 intensity ratio. The Herschel Space Observatory, observing from {approx}55 to 672 {mu}m, will allow us to exploit the diagnostic power of FIR fine structure lines with unprecedented resolution and sensitivity.

  6. Reactions of Atomic Oxygen (O(3P)) with Polybutadienes and Related Polymers

    NASA Technical Reports Server (NTRS)

    Golub, Morton A.; Lerner, Narcinda R.; Wydeven, Theodore

    1987-01-01

    Thin films of the following polymers were exposed at ambient temperature to ground-state oxygen atoms (O(3P)), generated by a radio-frequency glow discharge in O2: cis- and trans-1,4-polybutadienes (CB and TB), amorphous 1,2-polybutadiene (VB), polybutadienes with different 1,4/1,2 contents, trans polypentenamer (TP), cis and trans polyoctenamers (CO and TO), and ethylene-propylene rubber (EPM). Transmission infrared spectra of CB and TB films revealed extensive surface recession, or etching, unaccompanied by any microstructural changes within the films, demonstrating that the reactions were confined to the surface layers. Contrary to the report by Rabek, Lucki, and Ranby (1979), there was no O(3P)-induced cis-trans isomerization in CB or TB. From weight-loss measurements, etch rates for polybutadienes were found to be markedly dependent on vinyl content, decreasing by two orders of magnitude from CB (2% 1,2) to structures with 30 to 40% 1,2 double bonds, thereafter increasing by half an order of magnitude to VB (97% 1,2). Relative etch rates for EMP and the polyalkenamers were in the order: EMP is greater than CO (or TO) is greater than TP is greater than CB. The sole non-elastomer examined, TB, had an etch rate about six times that of CB, ascribable to a morphology difference. Cis/trans content had a negligible effect on the etch rate of the polyalkenamers. Mechanisms involving crosslinking through units are proposed for the unexpected protection imparted to polybutadienes by the 1,2 double bonds.

  7. Atomic oxygen interaction with spacecraft materials: Relationship between orbital and ground-based testing for materials certification

    NASA Technical Reports Server (NTRS)

    Cross, Jon B.; Koontz, Steven L.; Lan, Esther H.

    1993-01-01

    The effects of atomic oxygen on boron nitride (BN), silicon nitride (Si3N4), Intelsat 6 solar cell interconnects, organic polymers, and MoS2 and WS2 dry lubricant, were studied in Low Earth Orbit (LEO) flight experiments and in a ground based simulation facility. Both the inflight and ground based experiments employed in situ electrical resistance measurements to detect penetration of atomic oxygen through materials and Electron Spectroscopy for Chemical Analysis (ESCA) analysis to measure chemical composition changes. Results are given. The ground based results on the materials studied to date show good qualitative correlation with the LEO flight results, thus validating the simulation fidelity of the ground based facility in terms of reproducing LEO flight results. In addition it was demonstrated that ground based simulation is capable of performing more detailed experiments than orbital exposures can presently perform. This allows the development of a fundamental understanding of the mechanisms involved in the LEO environment degradation of materials.

  8. Reduction of surface leakage current by surface passivation of CdZn Te and other materials using hyperthermal oxygen atoms

    DOEpatents

    Hoffbauer, Mark A.; Prettyman, Thomas H.

    2001-01-01

    Reduction of surface leakage current by surface passivation of Cd.sub.1-x Zn.sub.x Te and other materials using hyperthermal oxygen atoms. Surface effects are important in the performance of CdZnTe room-temperature radiation detectors used as spectrometers since the dark current is often dominated by surface leakage. A process using high-kinetic-energy, neutral oxygen atoms (.about.3 eV) to treat the surface of CdZnTe detectors at or near ambient temperatures is described. Improvements in detector performance include significantly reduced leakage current which results in lower detector noise and greater energy resolution for radiation measurements of gamma- and X-rays, thereby increasing the accuracy and sensitivity of measurements of radionuclides having complex gamma-ray spectra, including special nuclear materials.

  9. A CubeSAT payload for in-situ monitoring of pentacene degradation due to atomic oxygen etching in LEO

    NASA Astrophysics Data System (ADS)

    Gorreta, Sergi; Pons-Nin, Joan; López, Gema; Figueras, Eduard; Jové-Casulleras, Roger; Araguz, Carles; Via, Pol; Camps, Adriano; Domínguez-Pumar, Manuel

    2016-09-01

    This paper reports and discusses the design and ground tests of a CubeSat payload which allows to measure, in-situ and in real time, the degradation of a polymer of electronic interest due to atomic oxygen etching in LEO. It provides real-time information on how the degradation occurs, eliminating the need to work with samples recovered once the mission has finished. The polymer, TIPS-Pentacene, is deposited on the surface of a microelectromechanical (MEMS) cantilever, which works as a resonator embedded in a Pulsed Digital Oscillator circuit. The mass losses in the polymer due to atomic oxygen corrosion produce variations in the resonant frequency of the MEMS, which is continuously sensed by the circuit and transmitted to the ground. This way, polymer mass losses around 10-12 kg can be detected during the mission. The payload is a part of the 3Cat-1 mission, a nano-satellite aimed at carrying out several scientific experiments.

  10. Results of apparent atomic oxygen reactions on Ag, C, and Os exposed during the Shuttle STS-4 orbits

    NASA Technical Reports Server (NTRS)

    Peters, P. N.; Linton, R. C.; Miller, E. R.

    1983-01-01

    Films selected for anticipated reaction with atomic oxygen, namely carbon, silver, and osmium, were exposed during the Shuttle STS-4 mission. A silver film within 5 nm of 225 nm thick was converted to a transparent blue-green interference film within 5 nm of 355 nm thick. Both carbon and osmium films 10-30 nm thick apparently formed volatile oxides and disappeared, except where well shielded. A calculated total of approximately 7 x 10 to the 19th oxygen atoms per sq cm struck the surfaces, which could have removed on the order of 3 microns of material if only 10 percent reacted. The absence of apparent effects on adjacent thin and thick gold films is offered as evidence that sputtering is not responsible.

  11. Results of apparent atomic oxygen reactions on Ag, C, and Os exposed during the Shuttle STS-4 orbits

    NASA Astrophysics Data System (ADS)

    Peters, P. N.; Linton, R. C.; Miller, E. R.

    1983-07-01

    Films selected for anticipated reaction with atomic oxygen, namely carbon, silver, and osmium, were exposed during the Shuttle STS-4 mission. A silver film 225 ± 5 nm thick was converted to a transparent blue-green interference film 355 ± 5 nm thick. Both carbon and osmium films 10-30 nm thick apparently formed volatile oxides and disappeared, except where well shielded. A calculated total of approximately 7 × 1019 oxygen atoms per cm² struck the surfaces, which could have removed on the order of 3 µm of material if only 10% reacted. The absence of apparent effects on adjacent thin and thick gold films is offered as evidence that sputtering is not responsible.

  12. MMENT>Computational study of complete methanol dehydrogenation on Au(100) and Au(310) surfaces: Dominant role of atomic oxygen

    NASA Astrophysics Data System (ADS)

    Hussain, A.; Shah, S. H.

    2014-02-01

    Methanol dehydrogenation to CO and H2 has been systematically investigated on Au(100) and Au(310) surfaces using density functional theory (DFT). All possible intermediates involved are calculated. Methanol and formaldehyde being saturated molecules adsorb weakly on both the surfaces. The thermochemistry and kinetics of the decomposition via sequential hydrogen abstraction are both found to be highly unfavorable for these species. Nevertheless, atomic oxygen pre-covered surfaces substantially enhance CH3OH and CH2O (resulting in CH2O2 complex formation) interaction with Au and offer weak activation barrier for methanol disintegration into CH3O and H. On the other hand, methoxy, formyl, and atomic hydrogen are predicted to make strong chemical bonds with the clean Au surfaces. The abstraction of hydrogen from the methoxy intermediate on bare gold surfaces is practical, while formyl splits instantaneously during optimization. A feasible mechanism on oxygen pre-covered surfaces for complete methanol dehydrogenation has been presented.

  13. Oxygen-driving and atomized mucosolvan inhalation combined with holistic nursing in the treatment of children severe bronchial pneumonia.

    PubMed

    Yang, Fang

    2015-07-01

    This paper aimed to discuss the method, effect and safety of oxygen-driving and atomized Mucosolvan inhalation combined with holistic nursing in the treatment of children severe bronchial pneumonia. Totally 90 children with severe bronchial pneumonia who were treated in our hospital from March 2013 to November 2013 were selected as the research objects. Based on randomized controlled principle, those children were divided into control group, test group I and test group II according to the time to enter the hospital, 30 in each group. Patients in control group was given conventional therapy; test group I was given holistic nursing combined with conventional therapy; test group II was given oxygen-driving and atomized Mucosolvan inhalation combined with holistic nursing on the basis of conventional therapy. After test, the difference of main symptoms in control group, test group I and II was of no statistical significance (P>0.05). Test group II was found with the best curative effect, secondary was test group I and control group was the last. It can be concluded that, oxygen-driving and atomized Mucosolvan inhalation combined with holistic nursing has certain effect in the treatment of children severe bronchial pneumonia and is better than holistic nursing only.

  14. Oxygen-driving and atomized mucosolvan inhalation combined with holistic nursing in the treatment of children severe bronchial pneumonia.

    PubMed

    Yang, Fang

    2015-07-01

    This paper aimed to discuss the method, effect and safety of oxygen-driving and atomized Mucosolvan inhalation combined with holistic nursing in the treatment of children severe bronchial pneumonia. Totally 90 children with severe bronchial pneumonia who were treated in our hospital from March 2013 to November 2013 were selected as the research objects. Based on randomized controlled principle, those children were divided into control group, test group I and test group II according to the time to enter the hospital, 30 in each group. Patients in control group was given conventional therapy; test group I was given holistic nursing combined with conventional therapy; test group II was given oxygen-driving and atomized Mucosolvan inhalation combined with holistic nursing on the basis of conventional therapy. After test, the difference of main symptoms in control group, test group I and II was of no statistical significance (P>0.05). Test group II was found with the best curative effect, secondary was test group I and control group was the last. It can be concluded that, oxygen-driving and atomized Mucosolvan inhalation combined with holistic nursing has certain effect in the treatment of children severe bronchial pneumonia and is better than holistic nursing only. PMID:26431648

  15. Oxygen-atom transfer chemistry and thermolytic properties of a di-tert-butylphosphate-ligated Mn4O4 cubane.

    PubMed

    Van Allsburg, Kurt M; Anzenberg, Eitan; Drisdell, Walter S; Yano, Junko; Tilley, T Don

    2015-03-16

    [Mn4O4{O2P(OtBu)2}6] (1), an Mn4O4 cubane complex combining the structural inspiration of the photosystem II oxygen-evolving complex with thermolytic precursor ligands, was synthesized and fully characterized. Core oxygen atoms within complex 1 are transferred upon reaction with an oxygen-atom acceptor (PEt3), to give the butterfly complex [Mn4O2{O2P(OtBu)2}6(OPEt3)2]. The cubane structure is restored by reaction of the latter complex with the O-atom donor PhIO. Complex 1 was investigated as a precursor to inorganic Mn metaphosphate/pyrophosphate materials, which were studied by X-ray absorption spectroscopy to determine the fate of the Mn4O4 unit. Under the conditions employed, thermolyses of 1 result in reduction of the manganese to Mn(II) species. Finally, the related butterfly complex [Mn4O2{O2P(pin)}6(bpy)2] (pin = pinacolate) is described.

  16. Evaluation of Thermal Control Coatings and Polymeric Materials Exposed to Ground Simulated Atomic Oxygen and Vacuum Ultraviolet Radiation

    NASA Technical Reports Server (NTRS)

    Kamenetzky, R. R.; Vaughn, J. A.; Finckenor, M. M.; Linton, R. C.

    1995-01-01

    Numerous thermal control and polymeric samples with potential International Space Station applications were evaluated for atomic oxygen and vacuum ultraviolet radiation effects in the Princeton Plasma Physics Laboratory 5 eV Neutral Atomic Oxygen Facility and in the MSFC Atomic Oxygen Drift Tube System. Included in this study were samples of various anodized aluminum samples, ceramic paints, polymeric materials, and beta cloth, a Teflon-impregnated fiberglass cloth. Aluminum anodizations tested were black duranodic, chromic acid anodize, and sulfuric acid anodize. Paint samples consisted of an inorganic glassy black paint and Z-93 white paint made with the original PS7 binder and the new K2130 binder. Polymeric samples evaluated included bulk Halar, bulk PEEK, and silverized FEP Teflon. Aluminized and nonaluminized Chemfab 250 beta cloth were also exposed. Samples were evaluated for changes in mass, thickness, solar absorptance, and infrared emittance. In addition to material effects, an investigation was made comparing diffuse reflectance/solar absorptance measurements made using a Beckman DK2 spectroreflectometer and like measurements made using an AZ Technology-developed laboratory portable spectroreflectometer.

  17. Modification of alkanethiolate monolayers by O(3P) atomic oxygen: effect of chain length and surface temperature.

    PubMed

    Yuan, Hanqiu; Gibson, K D; Li, Wenxin; Sibener, S J

    2013-04-25

    We have conducted a comprehensive study of ground-state O((3)P) atomic oxygen reactions with 1-hexadecanethiolate (CH3(CH2)15SH) and 1-undecanethiolate (CH3(CH2)10SH) self-assembled monolayers adsorbed onto Au/mica substrates, using X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, ellipsometry, and contact angle measurements. In general, the reactions are not limited to the terminal methyl groups. Apparently, the incident O((3)P) (translational energy per atom of 0.11 kJ mol(-1)) can penetrate below the surface of the monolayer. The ability of the atoms to penetrate, and thus the reaction rate of the backbone -CH2-, is dependent upon both the temperature and the chain length, with the longer chain having a large difference between the rate at room temperature and 150 K. In particular, the long-chain SAM exhibits clearly reduced reactivity with respect to the incident beam of atomic oxygen when the film is cooled to 150 K as compared to room temperature. This is a notable finding and demonstrates the crucial importance that structural order and dynamical fluctuations, both of which depend on chain length and substrate temperature, have in determining the surface passivation and protection characteristics of SAM overlayers with respect to attack by energetic reagents.

  18. The Unique Gas-Phase Chemistry of the [AuO](+) /CH4 Couple: Selective Oxygen-Atom Transfer to, Rather than Hydrogen-Atom Abstraction from, Methane.

    PubMed

    Zhou, Shaodong; Li, Jilai; Schlangen, Maria; Schwarz, Helmut

    2016-08-26

    The thermal reaction of [AuO](+) with methane has been explored using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. In contrast to the previously studied congener [CuO](+) , and to [AgO](+) , [AuO](+) reacts with CH4 exclusively via oxygen-atom transfer to form CH3 OH, and a novel mechanistic scenario for this selective oxidation process has been revealed. Also, the origin of the inertness of the [AgO](+) /CH4 couple has been addressed computationally. PMID:27390885

  19. Parameters of an electric-discharge generator of iodine atoms for a chemical oxygen-iodine laser

    SciTech Connect

    Azyazov, V N; Vorob'ev, M V; Voronov, A I; Kupryaev, Nikolai V; Mikheev, P A; Ufimtsev, N I

    2009-01-31

    Laser-induced fluorescence is used for measuring the concentration of iodine molecules at the output of an electric-discharge generator of atomic iodine. Methyl iodide CH{sub 3}I is used as the donor of atomic iodine. The fraction of iodine extracted from CH{sub 3}I in the generator is {approx}50%. The optimal operation regimes are found in which 80%-90% of iodine contained in the output flow of the generator was in the atomic state. This fraction decreased during the iodine transport due to recombination and was 20%-30% at the place where iodine was injected into the oxygen flow. The fraction of the discharge power spent for dissociation was {approx}3%. (elements of laser setups)

  20. Temperature and Atomic Oxygen Effects on Helium Leak Rates of a Candidate Main Interface Seal

    NASA Technical Reports Server (NTRS)

    Penney, Nicholas; Wasowski, Janice L.; Daniels, Christopher C.

    2011-01-01

    Helium leak tests were completed to characterize the leak rate of a 54 in. diameter composite space docking seal design in support of the National Aeronautics and Space Administration s (NASA's) Low Impact Docking System (LIDS). The evaluated seal design was a candidate for the main interface seal on the LIDS, which would be compressed between two vehicles, while docked, to prevent the escape of breathable air from the vehicles and into the vacuum of space. Leak tests completed at nominal temperatures of -30, 20, and 50 C on untreated and atomic oxygen (AO) exposed test samples were examined to determine the influence of both test temperature and AO exposure on the performance of the composite seal assembly. Results obtained for untreated seal samples showed leak rates which increased with increased test temperature. This general trend was not observed in tests of the AO exposed specimens. Initial examination of collected test data suggested that AO exposure resulted in higher helium leak rates, however, further analysis showed that the differences observed in the 20 and 50 C tests between the untreated and AO exposed samples were within the experimental error of the test method. Lack of discernable trends in the test data prevented concrete conclusions about the effects of test temperature and AO exposure on helium leak rates of the candidate seal design from being drawn. To facilitate a comparison of the current test data with results from previous leak tests using air as the test fluid, helium leak rates were converted to air leak rates using standard conversion factors for viscous and molecular flow. Flow rates calculated using the viscous flow conversion factor were significantly higher than the experimental air leakage values, whereas values calculated using the molecular flow conversion factor were significantly lower than the experimentally obtained air leak rates. The difference in these sets of converted flow rates and their deviation from the