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Synthesis, Structures, and Properties of Bulk Si(O)C Ceramics from Polycarbosilane

Li, Ya-Li and Fan, Hua and Su, Dong and Fasel, Claudia and Riedel, Ralf (2009):
Synthesis, Structures, and Properties of Bulk Si(O)C Ceramics from Polycarbosilane.
In: Journal of the American Ceramic Society, Wiley, pp. 2175-2181, 92, (10), ISSN 00027820,
[Online-Edition: http://dx.doi.org/10.1111/j.1551-2916.2009.03184.x],
[Article]

Abstract

Bulk Si(O)C ceramics are fabricated from polycarbosilane (PCS) by bulk pyrolysis along the route of cross linking, warm-pressing, and pyrolysis. The PCS was thermally oxidized for cross linking at various temperatures as a critical step toward the bulk transformation of PCS into bulk Si(O)C ceramics. The degree of cross linking of PSC affects the densities and bonding qualities of the warm-pressed powder compacts and, hence, the resultant ceramics. Under optimized processing conditions, crack-free bulk Si(O)C ceramics are obtained with a bulk density attaining 2.2 g/cm3. Despite the existence of a considerable amount of oxygen in the ceramics (16.08 wt%), resulting from the thermal oxidation processing, the ceramics show the characteristics of structures and properties of SiC-based ceramics. 29Si-solid state nuclear magnetic resonance spectra (NMR) reveal that the as-pyrolyzed X-ray amorphous Si(O)C phase consists mainly of SiC4 coordination units in the ceramic network, with the remainder being silicon-coordinated carbon and oxygen. Microhardness tests show that the as-pyrolyzed amorphous Si(O)C ceramics have a high hardness, attaining 24.91 GPa at a load of 2 N, and 19.82 GPa at a load of 10 N. Upon annealing at 1300°C in argon, the amorphous ceramics crystallized into nanophase β-SiC ceramics, and the ceramics kept the bulk nature of the amorphous ceramics with an increased density. The 29Si-solid state NMR spectrum indicates that the nanophase β-SiC ceramics consist of SiC4 units together with some mixed coordination units, namely SiO2C2 and SiOC3. The hardness of the crystallized nanophase Si(O)C ceramics attains 23.20 GPa at a load of 10 N. The present study demonstrates the possibility of fabricating bulk Si(O)C ceramics via the polymer-processing route, resulting in ceramics with promising structural and mechanical properties.

Item Type: Article
Erschienen: 2009
Creators: Li, Ya-Li and Fan, Hua and Su, Dong and Fasel, Claudia and Riedel, Ralf
Title: Synthesis, Structures, and Properties of Bulk Si(O)C Ceramics from Polycarbosilane
Language: English
Abstract:

Bulk Si(O)C ceramics are fabricated from polycarbosilane (PCS) by bulk pyrolysis along the route of cross linking, warm-pressing, and pyrolysis. The PCS was thermally oxidized for cross linking at various temperatures as a critical step toward the bulk transformation of PCS into bulk Si(O)C ceramics. The degree of cross linking of PSC affects the densities and bonding qualities of the warm-pressed powder compacts and, hence, the resultant ceramics. Under optimized processing conditions, crack-free bulk Si(O)C ceramics are obtained with a bulk density attaining 2.2 g/cm3. Despite the existence of a considerable amount of oxygen in the ceramics (16.08 wt%), resulting from the thermal oxidation processing, the ceramics show the characteristics of structures and properties of SiC-based ceramics. 29Si-solid state nuclear magnetic resonance spectra (NMR) reveal that the as-pyrolyzed X-ray amorphous Si(O)C phase consists mainly of SiC4 coordination units in the ceramic network, with the remainder being silicon-coordinated carbon and oxygen. Microhardness tests show that the as-pyrolyzed amorphous Si(O)C ceramics have a high hardness, attaining 24.91 GPa at a load of 2 N, and 19.82 GPa at a load of 10 N. Upon annealing at 1300°C in argon, the amorphous ceramics crystallized into nanophase β-SiC ceramics, and the ceramics kept the bulk nature of the amorphous ceramics with an increased density. The 29Si-solid state NMR spectrum indicates that the nanophase β-SiC ceramics consist of SiC4 units together with some mixed coordination units, namely SiO2C2 and SiOC3. The hardness of the crystallized nanophase Si(O)C ceramics attains 23.20 GPa at a load of 10 N. The present study demonstrates the possibility of fabricating bulk Si(O)C ceramics via the polymer-processing route, resulting in ceramics with promising structural and mechanical properties.

Journal or Publication Title: Journal of the American Ceramic Society
Volume: 92
Number: 10
Publisher: Wiley
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 13 Apr 2012 08:54
Official URL: http://dx.doi.org/10.1111/j.1551-2916.2009.03184.x
Identification Number: doi:10.1111/j.1551-2916.2009.03184.x
Funders: Y. Li thanks the Alexander von Humboldt Foundation (AvH) for providing research fellowships., S. D. thanks Visiting Scholarship from Defense University of Science and Technology, China.
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