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.
|Title:||Crystallization of polymer-derived silicon carbonitride at 1873 K under nitrogen overpressure|
|Journal or Publication Title:||Journal of American Ceramic Society|
|In ISI Web of Science:||Yes|
|Page Range:||pp. 2587-2589|
|Keywords:||crystallization, silicon carbonitride, overpressure|
|HGF - Research field:||Aeronautics, Space and Transport|
|HGF - Program:||Space|
|HGF - Program Themes:||W RP - Raumtransport|
|DLR - Research area:||Space|
|DLR - Program:||W RP - Raumtransport|
|DLR - Research theme (Project):||UNSPECIFIED|
|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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