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High Pressure X-Ray Diffraction Studies of Nanocrystalline MaterialsExperimental 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.
Document ID
20040121086
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Palosz, B.
(Polish Academy of Sciences Warsaw, Poland)
Stel'makh, S.
(Polish Academy of Sciences Warsaw, Poland)
Grzanka, E.
(Polish Academy of Sciences Warsaw, Poland)
Gierlotka, S.
(Polish Academy of Sciences Warsaw, Poland)
Palosz, W.
(BAE Systems Analytical Solutions, Inc. Huntsville, AL, United States)
Date Acquired
August 22, 2013
Publication Date
January 1, 2004
Subject Category
Nonmetallic Materials
Meeting Information
Meeting: 22nd European Cristallographic Meeting
Location: Budapest
Country: Hungary
Start Date: August 26, 2004
End Date: August 31, 2004
Funding Number(s)
CONTRACT_GRANT: NAS8-02096
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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