NASA Scientific and Technical Aerospace Reports

wavelengths is not readily available, the constants can be estimated from the atomic refractivities of carbon and fluorine. In
order to verify this estimation, a two-beam interferometer was used to experimentally determine the specific refractivities of
CF4 and C2F6. This data was required for holographic interferometric measurements made at the Langley Hypersonic CF4
Tunnel. A Twyman-Green interferometer with a He-Ne laser light source of vacuum wavelength lambda equal to 633 nm was
used to measure the constants. One beam of the two-beam interferometer passed through an optical cell of known inside length
l which could be evacuated and slowly filled with the test gas to a density of 7.2 kg/cu m for CF4 or 5.7 kg/cu m for C2F6.
If the refractive index (and hence density) is constant along the optical path through the cell, the fringe shift M and density
change Delta rho are related M = 2Kl Delta rho/lambda for the double pass interferometer. Thus K can be determined by
measuring the fringe shift as the density is changed. The output of a photodiode used to detect the fringe shift was recorded
on a strip chart recorder. The rate of pressure increase of the test gas in the cell was controlled such that the fringes shifted
at a rate of 0.5 to 1 fringe per sec. The pressure in the test cell was measured with a high accuracy quartz crystal pressure
transducer and recorded approximately every 20 fringe peaks. The temperature of the cell was measured with a thermocouple
and recorded at the start, midpoint, and end of each test.
Author (revised)
Refractivity; Carbon Compounds; Fluorine Compounds
20040121086 Polish Academy of Sciences, Warsaw, Poland
High Pressure X-Ray Diffraction Studies of Nanocrystalline Materials
Palosz, B.; Stel’makh, S.; Grzanka, E.; Gierlotka, S.; Palosz, W.; [2004]; 1 pp.; In English; 22nd European Cristallographic
Meeting, 26-31 Aug. 2004, Budapest, Hungary
Contract(s)/Grant(s): NAS8-02096; No Copyright; Avail: Other Sources; Abstract Only
Experimental evidence obtained for a variety of nanocrystalline materials suggest that the crystallographic structure of a
very small size particle deviates from that in the bulk crystals. In this paper we show the effect of the surface of nanocrystals
on their structure by the analysis of generation and distribution of macro- and micro-strains at high pressures and their
dependence on the grain size in nanocrystalline powders of Sic. We studied the structure of Sic nanocrystals by in-situ
high-pressure powder diffraction technique using synchrotron and neutron sources and hydrostatic or isostatic pressure
conditions. The diffraction measurements were done in HASYLAB at DESY using a Diamond Anvil Cell (DAC) in the energy
dispersive geometry in the diffraction vector range up to 3.5 - 4/A and under pressures up to 50 GPa at room temperature.
In-situ high pressure neutron diffraction measurements were done at LANSCE in Los Alamos National Laboratory using the
HIPD and HIPPO diffractometers with the Paris-Edinburgh and TAP-98 cells, respectively, in the diffraction vector range up
to 26 Examination of the response of the material to external stresses requires nonstandard methodology of the materials
characterization and description. Although every diffraction pattern contains a complete information on macro- and
micro-strains, a high pressure experiment can reveal only those factors which contribute to the characteristic diffraction
patterns of the crystalline phases present in the sample. The elastic properties of powders with the grain size from several nm
to micrometers were examined using three methodologies: (l), the analysis of positions and widths of individual Bragg
reflections (used for calculating macro- and micro-strains generated during densification) [I], (2). the analysis of the
dependence of the experimental apparent lattice parameter, alp, on the diffraction vector Q [2], and (3), the atomic Pair
Distribution Function (PDF) technique [3]. The results of our studies show, that Sic nanocrystals have the features of two
phases, each with its distinct elastic properties. and under pressures up to 8 GPa.
Author
Nanocrystals; X Ray Diffraction; High Pressure; Crystal Structure; Grain Size; Distribution Functions
20040121105 Universidad del Turabo, Puerto Rico
Hydrogen Purification Using Natural Zeolite Membranes
DelValle, William; 2003 Research Reports: NASA/ASEE Fellowship Program; December 15, 2003, pp. F1 - F7; In English;
See also 20040121096; No Copyright; Avail: CASI; A02, Hardcopy
The School of Science at Universidad del Turabo (UT) have a long-lasting investigation plan to study the hydrogen
cleaning and purification technologies. We proposed a research project for the synthesis, phase analysis and porosity
characterization of zeolite based ceramic perm-selective membranes for hydrogen cleaning to support NASA’s commitment
to achieving a broad-based research capability focusing on aerospace-related issues. The present study will focus on
technology transfer by utilizing inorganic membranes for production of ultra-clean hydrogen for application in combustion.
We tested three different natural zeolite membranes (different particle size at different temperatures and time of exposure). Our
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