Transformation of fractal microstructure of nanocrystalline SiC and diamond in high pressures - Small Angle Scattering Study

Roman Pielaszek 4,5,  Tadeusz Chudoba 5,  Stanisław Gierlotka 5,  Ewa Grzanka 4,5,  Svetlana Stelmakh 5,  Bogdan F. Palosz 5

1. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland
2. Polish Academy of Sciences, High Pressure Research Center (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
3. Polish Academy of Sciences, High Pressure Research Center (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland
4. Warsaw University, Faculty of Physics, Hoża 69, Warszawa 00-681, Poland
5. Polish Academy of Sciences, High Pressure Research Center (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland

Abstract


Small Angle X-ray Scattering (SAXS) and Ultra-SAXS (USAXS) experiments
for series of nanocrystalline SiC and diamond powders with grain sizes
ranging from 2 to 20 nm were performed. Wide range of scattering
vector values from 0.001 to 1 was obtained by three measurements in
different geometries: 1.5, 3 and 16 m sample-detector distance at B1
(SAXS) and BW4 (USAXS) beamlines, HASYLAB, Hamburg.
Samples were formed in pills in non-hydrostatic conditions at
pressures ranging from 0.25 to 6.25 GPa.
Experimental data elaboration is based on scattering curve's slope
analysis.
It was found that for seven powders examined, all diamond and most of
SiC powders have fractal microstructure. Fractal dimensions strongly
depend on pressure applied during sample preparation for SiC, much
less in case of diamond.
Comparison with microstructural data gained from images is presented.
Hypothetical mechanisms of crystallites' aggregation are also
discussed.
Acknowledgements
This work was supported by the State Committee for Scientific
Research, Grants No. 7/T08A/036/18 and 7/T08A/030/19.

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Presentation: poster at High Pressure School 2001 (4th), by Roman Pielaszek
See On-line Journal of High Pressure School 2001 (4th)

Submitted: 2003-02-16 17:33
Revised:   2003-10-21 01:51
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