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  • 1
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    Study of the oxygen transport through Ag (110), Ag (poly), and Ag 2.0 Zr (1992)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-24
    Beschreibung: The transport of oxygen through high-purity membranes of Ag (110), Ag (poly), Ag (nano), and Ag 2.0 Zr has been studied by an ultrahigh vacuum permeation method over the temperature range of 400-800 C. The data show that there are substantial deviations from ordinary diffusion-controlled transport. A surface limitation has been confirmed by glow-discharge studies where the upstream O2 supply has been partially converted to atoms, which, for the same temperature and pressure, gave rise to over an order of magnitude increase in transport flux. Further, the addition of 2.0 wt percent Zr to the Ag has provided increased dissociative adsorption rates, which, in turn, increased the transport flux by a factor of 2. It was also observed that below a temperature of 630 C, the diffusivity exhibits an increase in activation energy of over 4 kcal/mol, which has been attributed to trapping of the atomic oxygen and/or kinetic barriers at the surface and subsurface of the vacuum interface. Above 630 C, the activation barrier decreases to the accepted value of about 11 kcal/mol for Ag (poly), consistent with zero concentration at the vacuum interface.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: Journal of Vacuum Science and Technology A (ISSN 0734-2101); 10; 4; p. 1497-1502.
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  • 2
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    Characterization study of polycrystalline tin oxide surfaces before and after reduction in CO (1990)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Polycrystalline tin oxide surfaces have been examined before and after reduction in 40 Torr of CO at 100 and 175 C using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion scattering spectroscopy (ISS) and electron stimulated desorption (ESD). The changes in the surface composition and chemical states of the surface species generally are subtle for the reductive conditions used. However, significant changes do occur with regard to the amounts and the chemical forms of the hydrogen-containing species remaining after both the 100 and 175 C reductions.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: Low-Temperature CO-Oxidation Catalysts for Long-Life CO2 Lasers; p 231-250
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  • 3
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    ISS and TPD study of the adsorption and interaction of CO and H2 on polycrystalline Pt (1990)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: The adsorption and interaction of CO and H2 on polycrystalline Pt has been studied using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). The ISS results indicate that the initial CO adsorption on Pt takes place very rapidly and saturates the Pt surface with coverage close to a monolayer. ISS also shows that the CO molecules adsorb at an angular orientation from the surface normal and perhaps parallel to the surface. A TPD spectrum obtained after coadsorbing C-12 O-16 and C-13 O-18 on Pt shows no isotopic mixing, which is indicative of molecular CO adsorption. TPD spectra obtained after coadsorbing H2 and CO on polycrystalline Pt provides evidence for the formation of a CO-H surface species.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: Low-Temperature CO-Oxidation Catalysts for Long-Life CO2 Lasers; p 251-261
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  • 4
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    Platinized tin oxide catalysts for CO2 lasers: Effects of pretreatment (1990)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as PtO2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.
    Schlagwort(e): LASERS AND MASERS
    Materialart: Low-Temperature CO-Oxidation Catalysts for Long-Life CO2 Lasers; p 217-229
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  • 5
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    Alternative catalysts for low-temperature CO-oxidation (1990)
    In:  CASI
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    Publikationsdatum: 2013-08-31
    Beschreibung: MnO sub x, Ag/MnO sub x, Cu/MnO sub x, Pt/MnO sub x, Ru/MnO sub x, Au/CeO sub x, and Au/Fe2O3 were synthesized and tested for CO oxidation activity in low concentrations of stoichiometric CO and O2 at 30 to 75 C. Catalytic activity was measured for periods as long as 18000 minutes. At 75 deg Au/MnO sub x is most active sustaining nearly 100 percent CO conversion for 10000 minutes. It also retains high activity at 50 and 30 C with negligible decay in activity. A direct comparison between an unpretreated 10 percent Au/MnO sub x catalyst and an optimized 19.5 percent Pt/SnO sub 2 (pretreated) catalyst shows that the Au/MnO sub x catalyst exhibits much higher catalytic activity and far superior decay characteristics. Other catalysts including Au/CeO sub x and Au/Fe2O3 also perform well. The Cu/MnO sub x exhibits a high initial activity which decays rapidly. After the decay period the activity remains very stable making Cu/MnO sub x a potential candidate for long-term applications such as CO2 lasers in space.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: Low-Temperature CO-Oxidation Catalysts for Long-Life CO2 Lasers; p 123-137
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  • 6
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    A review of tin oxide-based catalytic systems: Preparation, characterization and catalytic behavior (1987)
    In:  CASI
    Details
    Publikationsdatum: 2013-08-31
    Beschreibung: This paper reviews the important aspects of the preparation, characterization and catalytic behavior of tin oxide-based catalytic systems including doped tin oxide, mixed oxides which contain tin oxide, Pt supported on tin oxide and Pt/Sn supported on alumina. These systems have a broad range of applications and are continually increasing in importance. However, due to their complex nature, much remains to be understood concerning how they function catalytically.
    Schlagwort(e): LASERS AND MASERS
    Materialart: NASA. Langley Research Center Closed-Cycle, Frequency-Stable CO2 Laser Technology; p 179-192
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  • 7
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    A proposed mechanism for Pt/SnO(x)-catalyzed CO oxidation (1991)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A mechanism for Pt/SnO(x)-catalyzed CO oxidation is proposed, which is consistent with a broad range of experimental observations. CO oxidation catalysts with high activity at or near room temperature are used in closed-cycle CO2 lasers and air purification.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: Journal of Catalysis (ISSN 0021-9517); 130; 314-317
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  • 8
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    Continuous electron stimulated desorption using a ZrO2/Ag permeation membrane (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: During the development of an atomic oxygen beam generator for laboratory simulation of the atmospheric conditions in low earth orbit, a new technique for performing electron stimulated desorption (ESD) in a continuous manner has been developed. In this technique, oxygen permeates through an Ag membrane at elevated temperature thereby providing a continuous supply of oxygen atoms to the 1000-A ZrO2 coating at the vacuum interface. ESD then results in a large peak of neutral O2 molecules which ultimately decay into steady-state desorption. The ESD signal is linear with respect to primary beam flux (0.035 O2 molecules per electron at a primary beam energy of 1 keV) but nonlinear with respect to primary beam energy.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: Journal of Vacuum Science and Technology A (ISSN 0734-2101); 7; 2087-208
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  • 9
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    Permeation of oxygen through high purity, large grain silver (1987)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The permeation of high purity, large grain Ag membranes by oxygen has been studied over the temperature range 400 to 800 C. The permeability was found to be quite linear and repeatable, but the magnitude was 3.2 times smaller than that determined by past research. Since previous investigators studied substantially less pure Ag and conducted experiments within much poorer vacuum environments (which indicates that their grain boundary density was much greater), the data presented here suggest oxygen transport through the membrane is primarily by grain boundary diffusion. The diffusivity measurements were found to exhibit two distinct linear regions, one above and one below a critical temperature of 630 C. The high-temperature data have an activation energy (11.1 kcal/mole) similar to that reported by others, but the low-temperature data have a higher activation energy (15.3 kcal/mole), which can be explained by impurity trapping in the grain boundaries. Vacuum desorption of the oxygen-saturated Ag was found to occur at a threshold of 630 C, which is consistent with the onset of increased mobility within the grain boundaries.
    Schlagwort(e): METALLIC MATERIALS
    Materialart: NASA-TP-2755 , L-16305 , NAS 1.60:2755
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  • 10
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    Electron stimulated desorption of atomic oxygen from silver (1987)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: 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.
    Schlagwort(e): INORGANIC AND PHYSICAL CHEMISTRY
    Materialart: NASA-TP-2668 , L-16225 , NAS 1.60:2668
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