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Crystallization of polymer-derived silicon carbonitride at 1873 K under nitrogen overpressure

Frieß, M. and Bill, J. and Golczewski, and Zimmermann, A. and Aldinger, F. and Riedel, R. and Raj, R. (2002) Crystallization of polymer-derived silicon carbonitride at 1873 K under nitrogen overpressure. Journal of American Ceramic Society, 85 (10), pp. 2587-2589.

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The chemical stability of an amorphous silicon carbonitride ceramic, having the composition given by 0.57SiC:0.43Si3N4:0.49C is studied as a function of nitrogen overpressure at 1873K. The ceramic suffers a weight loss at pn2 < 3.5 bar, does not show a weight change from 3.5 - 11 bar, and gains weight above 11 bar. Interestingly, the structure of the ceramic changes with pressure: it is crystalline from 1-6 bar, amorphous at » 10 bar, and then again crystalline at higher pressures. The weight loss transition, at 3.5 bar, is in excellent agreement with the prediction from thermodynamic analysis when the activities of carbon, silicon carbide and silicon nitride are set equal to those of the crystalline forms, implying that the material crystallizes prior to decomposition. The amorphous-to-crystalline transition that occurs near 10 bar, and which is accompanied by weight gain, is likely to have taken place by a different mechanism. A nucleation and growth reaction with the atmospheric nitrogen on the surface of the sample is proposed as the likely mechanism. The supersaturation required to nucleate a-silicon nitride crystals is calculated to be 30 kJ/mole.

Document Type:Article
Additional Information: LIDO-Berichtsjahr=2003,
Title:Crystallization of polymer-derived silicon carbonitride at 1873 K under nitrogen overpressure
AuthorsInstitution or Email of Authors
Bill, J.MPI
Golczewski, MPI
Zimmermann, A.MPI
Aldinger, F.MPI
Riedel, R.TU Darmstadt
Raj, R.University of Colorado, Boulder, USA
Journal or Publication Title:Journal of American Ceramic Society
Refereed publication:Yes
In ISI Web of Science:Yes
Page Range:pp. 2587-2589
Keywords:crystallization, silicon carbonitride, overpressure
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W RP - Raumtransport
DLR - Research area:Space
DLR - Program:W RP - Raumtransport
DLR - Research theme (Project):UNSPECIFIED
Location: Stuttgart
Institutes and Institutions:Institute of Structures and Design
Deposited By: elib DLR-Beauftragter
Deposited On:16 Sep 2005
Last Modified:14 Jan 2010 22:33

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