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  • 1
    ISSN: 1573-4846
    Keywords: SiO2 ; microporous ; ceramic membrane ; gas separation ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Microporous SiO2 and SiO2/MO2 (M=Ti, Zr, Al; 10 mol% MOx) materials for gas separation membrane applications have been prepared from polymeric sols. Characterization of these sols with SAXS showed that the mean fractal dimension of the SiO2 sols is 1.3–1.4 with a radius of gyration of approximately 2.5 nm. The dried and calcined films are microporous and the pore size distribution was bimodal with maxima at diameters of 0.5 nm and 0.75 nm. For the SiO2/TiO2, SiO2/ZrO2 and SiO2/Al2O3 systems, much milder reaction conditions proved to be necessary to obtain sols with comparable fractal dimensions due to the high reactivity of the Ti/Zr/Al-alkoxides. Microporous supported membranes with molecular sieve-like gas transport properties can be prepared from a relatively wide range of sol structures: from polymers too small to characterize with SAXS to structures with fractal dimensions: 1〈d f〈2.04.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of porous materials 1 (1995), S. 139-153 
    ISSN: 1573-4854
    Keywords: microporous ; sol-gel ; silica ; pore size ; adsorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Gas physisorption is a generally used technique for the characterization of porous solids. Microporous solids, however, need a different approach compared to mesoporous solids due to enhanced adsorption in pores of molecular dimensions. Therefore, conventional theories and models can not be used. The application of physisorption for microporous solids, and the interpretation of the isotherms is elucidated. Some models presented in literature for pore size assessment in the micropore range are discussed. Based on a number of criteria, the Horváth-Kawazoe model, modified for cylindrical pore geometry, is selected. N2 adsorption measurments on zeolites were performed to calibrate the method and to show the applicability and physical justification. Typical data obtained from experiments on non-supported microporous silica membrane top-layers show that the pore size distribution of these materials is bimodal, with a strong maximum at an effective diameter of 0.5 nm, and a weaker maximum at 0.75 nm.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of porous materials 2 (1995), S. 141-149 
    ISSN: 1573-4854
    Keywords: sorption ; microporous ; ceramic membranes ; gas separation ; gas transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Sorption experiments with H2, CO2, CH4 and iso-C4H10 were performed on microporous SiO2 and SiO2/TiO2 (30 mol% TiO2) non-supported membrane top-layers using volumetric and gravimetric techniques. For silica, the sorption capacity decreases in the order CO2〉iso-C4H10〉CH4〉H2 at temperatures 〈373 K. The isosteric heat of adsorption q st is 23, 24, 10 and 6 kJ·mol−1 for respectively CO2, iso-C4H10, CH4 and H2. The sub-atmospheric adsorption isotherms are of Henry-type for temperatures equal and higher than 348 K for CO2, temperatures higher than 373 K for iso-C4H10, temperatures equal and higher than 194 K for H2 and for temperatures equal and higher than 273 K for CH4. The sorption capacity for the SiO 2/TiO 2 sample was only slightly lower than for silica, as may be expected due to the lower porosity.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2019-06-28
    Description: The performance of a dual-channel infrared heterodyne radiometer, designed to remotely monitor the concentration and vertical distribution of selected atmospheric species, is described. Ground based solar viewing measurement using the IHR were performed at selected laser transitions for ammonia (NH3 and ozone O3). Flight tests were conducted aboard the Galileo II, NASA Ames CV-990, on the Latitude Survey Mission. Ozone was the selected atmospheric species for the airborne flight measurements because of the scientific interest in this atmospheric species, the availability of in situ monitors, the coordinated ozone measurements, and the availability of ground truth data. The IHS was operated in the solar viewing mode to determine ozone distributions in the stratosphere and in the nadir viewing mode to determine the ozone distribution in the troposphere. Airborne atmospheric propagation measurements also were carried out at selected CO2 laser transitions.
    Keywords: ENVIRONMENT POLLUTION
    Type: NASA-CR-3448 , A610-IV
    Format: application/pdf
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  • 5
    Publication Date: 2019-07-13
    Description: Remote sensing of the concentration and vertical distribution of atmospheric gases has been carried out using a dual CO2 laser multichannel infrared heterodyne spectrometer (IHS). The high specificity and nearly quantum-noise-limited sensitivity of the IHS provide the capability of scanning individual signature lines of selected atmospheric constituents in the 9 to 11 micron region. A comprehensive investigation of the spectral overlap between CO2 laser local oscillator transitions and selected atmospheric constituents was performed; measurements of the atmospheric absorption of solar radiation from the ground were carried out at selected laser transitions for ammonia and ozone.
    Keywords: ENVIRONMENT POLLUTION
    Type: AIAA PAPER 77-73 , Aerospace Sciences Meeting; Jan 24, 1977 - Jan 26, 1977; Los Angeles, CA
    Format: text
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