SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
X-ray photoelectron spectroscopy (XPS), Rutherford Back Scattering (RBS) studies of each of sample received were completed. Since low angle X-ray could not be performed because of instrumentation problems, Auger spectrometry was employed instead. The results of these measurements for each of the samples is discussed in turn.
The damage of approximately monolayer films of L-histidine by low-energy spin-polarized electrons (SPE) ejected from a magnetized cobalt substrate has been probed using X-ray photoelectron spectroscopy (XPS). Average damage cross sections for N-containing motifs of L-histidine are 25-30 and 2-5 Mb for zwitterions and neutral molecules, respectively. Here, the magnetization direction of the substrate, which controls the ejected SPE helicity, was reversed in situ, and statistically significant differences in the damage cross sections of 10-30% were measured between positive and negative electron helicities. This is the first measurement of spin dichroism (SD) in an amino acid. The differential cross sections suggest that inelastic scattering of SPE with chiral molecules could contribute to the persistence of one enantiomer vs the other under certain irradiation conditions, particularly for the zwitterionic species.
Explore the source record for details and available documents.
The use of an atmospheric pressure glow discharge (APGD) plasma was used at KSC to increase the hydrophilicity of spaceport materials to enhance their surface charge dissipation and prevent possible ESD in spaceport operations. Significant decreases in charge decay times were observed after tribocharging the materials using the standard KSC tribocharging test. The polarity and amount of charge transferred was dependent upon the effective work function differences between the respective materials. In this study, polyethylene (PE) and polytetrafluoroethylene (PTFE) were exposed to a He+O2 APGD. The pre and post treatment surface chemistry was analyzed by X-ray photoelectron spectroscopy and contact angle measurements. Semi-empirical and ab initio calculations were performed to correlate the experimental results with some plausible molecular and electronic structure features of the oxidation process. For the PE, significant surface oxidation was observed, as indicated by XPS showing C-O, C=O, and O-C=O bonding, and a decrease in the surface contact angle from 98.9 deg to 61.2 deg. For the PTFE, no C-O bonding appeared and the surface contact angle increased indicating the APGD only succeeded in cleaning the PTFE surface without affecting the surface structure. The calculations using the PM3 and DFT methods were performed on single and multiple oligomers to simulate a wide variety of oxidation scenarios. Calculated work function results suggest that regardless of oxidation mechanism, e.g. -OH, =0 or a combination thereof, the experimentally observed levels of surface oxidation are unlikely to lead to a significant change in the electronic structure of PE and that its increased hydrophilic properties are the primary reason for the observed changes in its electrostatic behavior. The calculations for PTFE argue strongly against significant oxidation of that material, as confirmed by the XPS results.
The rapid screening of plutonium from aqueous sources remains a critical challenge for nuclear nonproliferation efforts. The determination of trace-level Pu isotopes in water requires offsite sample preparation and analysis; therefore, new methods that combine plutonium purification, concentration, and isotopic screening in a fieldable detection system will provide an invaluable tool for nuclear safeguards. This contribution describes the development and characterization of thin polymer-ligand films for the isolation and concentration of waterborne Pu for direct spectroscopic analyses. Submicron thin films were prepared through spin coating onto Si wafers and consisted of combinations of polystyrene (PS) with dibenzoylmethane, thenoyltrifluoroacetone, and di(2-ethylhexyl)phosphoric acid (HDEHP). Pu uptake studies from solutions at pH from 2.3 to 6.3 indicated that only films containing HDEHP exhibited significant recovery of Pu. High alpha spectroscopy peak energy resolutions were achieved for PS-HDEHP films over a range of film thicknesses from 30 to 250 nm. Furthermore, a separate study was performed to evaluate uptake from a primarily Pu(V) solution where it was observed that doubling the HDEHP loading in the film increased uptake of Pu by an order of magnitude. X-ray photoelectron spectroscopy (XPS) analysis revealed that HDEHP was highly concentrated within the first few nanometers of the film at the higher loading. XPS analysis also revealed that, in the presence of water, HDEHP was stripped from the surface layer of the film at circumneutral pH. While significant losses of ligand were seen in all samples, higher loadings of HDEHP resulted in measurable amounts of ligand retained after a 12-h soak in water. Findings of this study are being used to guide the development of thin-film composite membrane-based detection methods for the rapid, fieldable analysis of Pu in water.
Perovskite-based oxides are used in electrochemical CO 2 and H 2 O reduction in electrochemical cells due to their compositional versatility, redox properties and stability. However limited knowledge exists on the mechanisms driving these processes. Toward this understanding, herein we probe the core level binding energy shifts of water-derived adspecies (H, O, OH, H 2 O) as well as the adsorption of CO 2 on LaCoO 3 and LaNiO 3 and we correlate the simulated peaks with experimental Temperature Programmed X-ray Photoelectron Spectroscopy (TPXPS) results. We find the strong adsorption of such chemical species can affect the antiferromagnetic ordering of LaNiO 3 . The adsorption of such adspecies is further quantified through Bader and differential charge analyses. We find the higher O 1s core level binding energy peak for both LaCoO 3 and LaNiO 3 corresponds to adsorption of water-related species and CO 2 , while the lower energy peak is due to lattice oxygen. We further correlate these DFT-based core level O 1s binding energies with the TPXPS measurements to quantify the decrease of the O 1s contribution due to desorption of adsorbates and the apparent increase of the lattice oxygen (both bulk and surface) with temperature. Finally, we quantify the influence of adsorbates on the La 4d, Co 2p and the Ni 3p core level binding energy shifts. This work demonstrates how theoretically generated XPS data can be utilized to predict species-specific binding energy shifts to assist in the deconvolution of the experimental results.
In this report we have not only analyzed the performance of perovskite oxides as support media for the methanol oxidation reaction (MOR) but also examined the impact and significance of various reaction parameters on their synthesis. Specifically, we have generated (a) La 2 NiMnO 6 , LaMnO 3 , and LaNiO 3 nanocubes with average sizes of ~200 nm, in addition to a series of La 2 NiMnO 6 (b) nanocubes possessing average sizes of ~70 and 400 nm and (c) anisotropic nanorods characterized by average diameters of 40-50 nm. All of these samples, when used as supports for Pt nanoparticles, exhibited activities which were at least twice that measured for Pt/C. We have investigated and correlated the effect of varying perovskite (i) composition, (ii) size, and (iii) morphology upon the measured MOR activity. (i) The Ni-containing perovskites yielded generally higher performance metrics than LaMnO 3 alone, suggesting that the presence of Ni is favorable for MOR, a finding supported by a shift in the Pt d-band in XPS. (ii) MOR activity is enhanced as the perovskite size increases in magnitude, suggesting that a growth in the perovskite particle size enables favorable, synergistic metal–support interactions. (iii) A comparison of the nanorods and nanocubes of a similar diameter implied that the one-dimensional morphology achieved a greater activity, a finding which can be attributed not only to the anisotropic structure but also to a desirable surface structure. Overall, these data yield key insights into the tuning of metal–support interactions via rational control over the composition, size, and morphology of the underlying catalyst support.
The effect of fiber/matrix interactions on the mechanical properties of thermoplastic carbon fiber composites was determined. The experimental approach was a multi-faceted one involving the following areas: characterization of the surface of carbon fibers using X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and scanning transmission electron microcopy (STEM); determination of the functional groups on carbon fiber surfaces using an elemental tagging scheme - derivatization; determination of the polar and dispersion contribution to the surface energy of carbon fibers by measuring wetting forces in a series of liquids having known polar and dispersion components; and study of the interaction of thermoplastic polymers with carbon surfaces by solution adsorption, STEM and fiber critical length.
Dissolution of actinide dioxides, including neptunium dioxide (NpO 2 (s)), is paramount for the prediction of the environmental fate of nuclear materials. Quantifying dissolution rates, as well as understanding qualitative dissolution mechanisms, informs performance assessment for geologic disposal of spent nuclear fuel and management of legacy radioactive waste. The aim of this research was to measure the dissolution rate of nanocrystalline NpO 2 (s), produced through legacy nuclear waste processing, under oxidizing conditions, as well as to characterize surface alteration to the material. The solid phase was characterized using electron microscopy techniques (SEM/STEM) and X-ray photoelectron spectroscopy (XPS), indicating preferential dissolution of Np-hydroxide contained in the grain boundaries of NpO 2 (s) and fragmentation of grains from the matrix. The oxidative dissolution was monitored over 40 weeks, yielding a two-step kinetic dissolution model involving hydration of NpO 2 (s) and subsequent oxidation and dissolution of the hydroxide phase. Here, the proposed dissolution models for nanocrystalline NpO 2 (s) suggest that microstructural features such as grain boundaries are key factors affecting dissolution, including release of colloidal particles, and ultimately, environmental fate and transport of nuclear materials.
With solar activity just passing the maximum of cycle 23, SORCE is beginning a 5 year mission to measure total solar irradiance (TSI) with unprecedented accuracy using phase-sensitive detection, and to measure spectral solar irradiance (SSI) with unprecedented spectral coverage, from 1 to 2000 nm. The new Total Irradiance Monitor (TIM) has 4 active cavity radiometers, any one of which can be used as a fixed-temperature reference against any other that is exposed to the Sun via a shutter that cycles at a rate designed to minimize noise at the shutter frequency. The new Spectral Irradiance Monitor (SIM) is a dual Fery prism spectrometer that can employ either prism as a monochromatic source on the other prism, thus monitoring its transmission during the mission lifetime. Either prism can measure SSI from 200 to 2000 nm, employing the same phase-sensitive electrical substitution strategy as TIM. SORCE also carries dual SOLSTICE instruments to cover the spectral range 100-320 nm, similar to the instruments onboard UARS, and also an XUV Photometer System (XPS) similar to that on TIMED. SSI has now been added to TSI as a requirement of EOS and NPOESS, because different spectral components drive different components of the climate system - UV into upper atmosphere and stratospheric ozone, IR into tropospheric water vapor and clouds, and Visible into the oceans and biosphere. Succeeding satellite missions being planned for 2006 and 2011 will continue to monitor these critical solar variables.
Here, we investigated the electronic interactions between transition metal phthalocyanine (TMPc’s) on a refractory transition metal nitride support, specifically copper phthalocyanine (CuPc) on titanium nitride (TiN). X-ray Photoelectron Spectroscopy (XPS) results suggest a presence of a few nanometer native oxide layer on the surface of the TiN nanoparticles, which consists of TiN, TiO 2 , and Titanium oxynitrides (Ti x O y N z ). A TiNCuPc nanocomposite was synthesized via a simple mixing method due to the strong binding between CuPc and TiN confirmed by density functional theory (DFT) calculations. Both XPS data and DFT calculations revealed an electron transfer from TiN substrate to CuPc molecule. The nature of charge transfer is not influenced by the presence of an oxide layer on the surface of TiN. Substantial deviations are however found between photoelectron emission microscopy (PEEM) measured work function for TiN (4.68 eV) and theoretically calculated work function for pristine stoichiometric TiN (2.63 eV). This behavior is attributed to the presence of an oxide layer on the TiN surface. TiNCuPc composite system has a work function value between those of TiN and CuPc. Our studies open up an opportunity to apply a new class of materials based on transition metal phthalocyanine/transition metal nitride composites to catalysis and optoelectronic devices.
Direct CO 2 electrolysis using solid oxide electrolysis cells (CO 2 -SOECs) holds promise to efficiently convert carbon dioxide to carbon monoxide and oxygen. Cathodes with desirable catalytic activity and chemical stability play a critical role in the development of direct CO 2 -SOECs. Although Sr 2 Fe 1.5 Mo 0.5 O 6–δ (SFM) has exhibited promise for direct CO 2 -SOECs due to its redox stability, it suffers from insufficient activity for the CO 2 reduction reaction (CO 2 RR). Here we report interface engineering of nanosized Pr 6 O 11 on the SFM cathode obtained through infiltration to promote the CO 2 RR performance for direct CO 2 -SOECs. The effect of Pr 6 O 11 loading on the performance of the CO 2 RR is systematically investigated. At 800 °C, the current density of the Pr 6 O 11 infiltrated SFM cathode with an optimum Pr 6 O 11 loading of 14.8 wt% reaches 1.61 A cm –2 at 1.5 V, more than double that of the SFM cathode (0.76 A cm –2 ) under the same operating conditions. X-ray photoelectron spectroscopy (XPS) characterization and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis indicate that the adsorption ability of CO 2 on the SFM cathode has been significantly improved by the formation of Pr 6 O 11 . Temperature-programmed desorption (TPD) of CO 2 measurements further manifest that a 14.8 wt% Pr 6 O 11 -SFM cathode has better CO desorption capacity. In addition, polarization resistance of the SFM cathode has significantly decreased with the addition of Pr 6 O 11 . Three-electrode measurement was used to analyze the improved electrode kinetics. Finally, these results demonstrate that the formation of Pr 6 O 11 in the SFM cathode through infiltration is a promising approach for increasing CO 2 RR activity for CO 2 -SOECs.
Graphene produced by different methods can present varying physicochemical properties and quality, resulting in a wide range of applications. The implementation of a novel method to synthesize graphene requires characterizations to determine the relevant physicochemical and functional properties for its tailored application. We present a novel method for multilayer graphene synthesis using atmospheric carbon dioxide with characterization. Synthesis begins with carbon dioxide sequestered from air by monoethanolamine dissolution and released into an enclosed vessel. Magnesium is ignited in the presence of the concentrated carbon dioxide, resulting in the formation of graphene flakes. These flakes are separated and enhanced by washing with hydrochloric acid and exfoliation by ammonium sulfate, which is then cycled through a tumble blender and filtrated. Raman spectroscopic characterization, FTIR spectroscopic characterization, XPS spectroscopic characterization, SEM imaging, and TEM imaging indicated that the graphene has fifteen layers with some remnant oxygen-possessing and nitrogen-possessing functional groups. The multilayer graphene flake possessed particle sizes ranging from 2 µm to 80 µm in diameter. BET analysis measured the surface area of the multilayer graphene particles as 330 m 2 /g, and the pore size distribution indicated about 51% of the pores as having diameters from 0.8 nm to 5 nm. This study demonstrates a novel and scalable method to synthesize multilayer graphene using CO 2 from ambient air at 1 g/kWh electricity, potentially allowing for multilayer graphene production by the ton. The approach creates opportunities to synthesize multilayer graphene particles with defined properties through a careful control of the synthesis parameters for tailored applications.
It is pointed out that there is no report of an unambiguous analysis of the composition and interfacial structure of MNOS (metal-nitride oxide semiconductor) systems, despite the technological importance of these systems. The present investigation is concerned with a study of an MNOS structure on the basis of a technique involving the use of X-ray photoelectron spectroscopy (XPS) with a controlled stopped-flow chemical-etching procedure. XPS is sensitive to the structure of surface layers, while stopped-flow etching permits the controlled removal of overlying material on a scale of atomic layers, to expose new surface layers as a function of thickness. Therefore, with careful analysis of observed intensities at measured depths, this combination of techniques provides depth resolution between 5 and 10 A. According to the obtained data there is intact SiO2 at the substrate interface. There appears to be a thin layer containing excess bonds to silicon on top of the SiO2.
The Evaluation of Oxygen Interactions with Materials 3 (EOIM-3) flight experiment was developed to obtain benchmark atomic oxygen/material reactivity data. The experiment was conducted during Space Shuttle mission 46 (STS-46), which flew July 31 to August 7, 1992. Quantitative interpretation of the materials reactivity measurements requires a complete and accurate definition of the space environment exposure, including the thermal history of the payload, the solar ultraviolet exposure, the atomic oxygen fluence, and any spacecraft outgassing contamination effects. The thermal history of the payload was measured using twelve thermocouple sensors placed behind selected samples and on the EOIM-3 payload structure. The solar ultraviolet exposure history of the EOIM-3 payload was determined by analysis of the as-flown orbit and vehicle attitude combined with daily average solar ultraviolet and vacuum ultraviolet (UV/VUV) fluxes. The atomic oxygen fluence was assessed in three different ways. First, the O-atom fluence was calculated using a program that incorporates the MSIS-86 atmospheric model, the as-flown Space Shuttle trajectory, and solar activity parameters. Second, the oxygen atom fluence was estimated directly from Kapton film erosion. Third, ambient oxygen atom measurements were made using the quadrupole mass spectrometer on the EOIM-3 payload. Our best estimate of the oxygen atom fluence as of this writing is 2.3 +/- 0.3 x 10(exp 20) atoms/sq cm. Finally, results of post-flight X-ray photoelectron spectroscopy (XPS) surface analyses of selected samples indicate low levels of contamination on the payload surface.
Carbon-nitride materials represent light-absorbing structures composed of earth-abundant elements capable of being leveraged for semiconductor photocatalysis at their surfaces. This study systematically investigates the addition of molecular modifiers to the synthesis of crystalline carbon nitrides to assess their effects on the materials’ structure, optical bandgap, and photocatalytic activity for hydrogen (H 2 ) and oxygen (O 2 ) evolution under ultraviolet and visible-light irradiation. Melamine and five pyrimidine-centered analogs were employed as building blocks to modify various heteroatoms within the polymeric framework. The modified materials were characterized with attention to the differences introduced by the monomeric modifiers and their influence on the resulting structures and compositions. The findings indicate that these changes significantly broaden the visible-light absorption range, albeit with the gradual loss of the bulk crystalline structure. As the loading of modifiers increased beyond 50%, a predominantly amorphous form of carbon nitride emerged. XPS, 13 C solid-state NMR, and SEM analyses corroborated the changes, which were attributed to modifications of the elemental composition and a reduced amount of Li cations and charge-balancing Cl anions owing to fewer binding sites in the intralayer cavities. In photocatalytic measurements under an ultraviolet 390 nm LED, and aided by photodeposited nanoparticle cocatalysts, the unmodified PTI-LiCl framework demonstrated the highest H 2 evolution rate (HER; 3.44 mmol·g –1 ·h –1 ) with an apparent quantum yield of 5.4%, along with total water splitting at rates of 163 μmol of H 2 ·g –1 ·h –1 and 75.6 μmol·O 2 g –1 ·h –1 . While PTI-LiCl showed trace activity under a visible-light 440 nm LED, all modified materials exhibited enhanced reactivity with as low as 5% molecular modifiers. The photocatalytic rates peaked at a 15% modification level when using 2,4,6-triaminopyrimidine, with rates of 33 μmol·g –1 ·h –1 for HER, along with 19.7 μmol of H 2 ·g –1 ·h –1 and 8.7 μmol of O 2 ·g –1 ·h –1 for total water splitting. Density functional theory calculations were used to probe electronic structure changes resulting from the modifications. Furthermore, these results elucidate the structural, optical, and electronic changes arising from the five selected molecular modifiers and their impact on the semiconductors’ photocatalytic properties.
The boundary-lubrication performance of two perfluoropolyether (PFPE) thin films in the presence of passivated 440C stainless steel is presented. The study used a standard ball on disk (BoD) tribometer in dry nitrogen and a vacuum spiral orbit tribometer (SOT). Stainless steel surfaces were passivated with one of four techniques: high and low temperature chromic acid bath, a tricresyl phosphate (TCP) soak, or UV/Ozone treated for 15 min. After passivation, each BoD disk had a 400A film of Krytox 16256 (PFPE) applied to it. The lifetimes of these films were quantified by measuring the number of sliding cycles before an increase in friction occurred. The lubricated lifetime of the 440C couple was not altered as a result of the various passivation techniques. The resulting surface chemistry of each passivation technique was examined using X-ray photoelectron spectroscopy (XPS). The SOT was used to examine the effects of the TCP treatment on the lubricated lifetime of another PFPE, Brayco 815Z, under rolling conditions. None of the passivation techniques were found to dramatically increase the oxide film thickness or lubricated lifetimes.
A fire on-board the International Space Station (ISS) resulting from a commercial Surface Pro tablet Lithium-Ion (Li-ion) battery can be detrimental to the spacercraft and the astronauts. The Spacecraft Fire Safety Demonstration (Saffire) program is focused on identifying and quantifying the risks that potentially arise inside a space vehicle by conducting large fire experiments inside the Cygnus cargo vehicle upon re-entry to Earth. The potential candidate that will be flown on the ISS is a 4- cell Li-ion battery pack Surface Pro tablet (42 Wh). The tablets were tested at the White Sands Test Facility (WSTF) using a localized heating method to emulate the failing mechanism that leads the unit into thermal runaway. Measurements inside the test chamber were performed on aerosol mass concentrations and for specific toxic products (i.e. from CO, HCN, HCl and CO2). These toxic products depend on the size of the fire and energy content of the tablet. Comparisons will be made with the Dell XPS (97 Wh). The concentrations are then used to extrapolate to laptop fires on a vehicle at the approximate volumetric size of the Orion spacecraft. The presentation provides an analysis on the detection capability and the response time to trigger fire alarms aboard a vehicle by using the mass concentration levels. These results will consider the rate at which the life support system is able to filter the atmosphere in order to provide a hazardous free environment.