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Carbothermal Reaction of Silica-Phenol Resin Hybrid Gels to Produce Silicon Nitride/Silicon Carbide Nanocomposite Powders

Li, Jinwang ; Riedel, Ralf (2007):
Carbothermal Reaction of Silica-Phenol Resin Hybrid Gels to Produce Silicon Nitride/Silicon Carbide Nanocomposite Powders.
In: Journal of the American Ceramic Society, 90 (12), pp. 3786-3792. Wiley, ISSN 0002-7820,
[Article]

Abstract

A carbothermal reaction of silica–phenol resin hybrid gels prepared from a two-step sol–gel process was conducted in atmospheric nitrogen. The gels were first pyrolyzed into homogeneous silica–carbon mixtures during heating and subsequently underwent a carbothermal reaction at higher temperatures. Using a gel-derived precursor with a C/SiO2 molar ratio higher than 3.0, Si3N4/SiC nanocomposite powders were produced at 1500°–1550°C, above the Si3N4–SiC boundary temperature. The predominant phase was Si3N4 at 1500°C, and SiC at 1550°C. The Si3N4 and SiC phase contents were adjustable by varying the temperature in this narrow range. The phase contents could also be adjusted by changing the starting carbon contents, or by its combination with varying reaction temperature. A two-stage process, i.e., a reaction first at 1550°C and then at 1500°C, offered another means of simple and effective control of the phase composition: the Si3N4 and SiC contents varied almost linearly with the variation of the holding time at 1550°C. The SiC was nanosized (∼13 nm, Scherrer method) formed via a solid–gas reaction, while the Si3N4 has two morphologies: elongated microsized crystals and nanosized crystallites, with the former crystallized via a gaseous reaction, and the latter formed via a solid–gas reaction. The addition of a Si3N4 powder as a seed to the starting gel effectively reduced the size of the Si3N4 produced.

Item Type: Article
Erschienen: 2007
Creators: Li, Jinwang ; Riedel, Ralf
Title: Carbothermal Reaction of Silica-Phenol Resin Hybrid Gels to Produce Silicon Nitride/Silicon Carbide Nanocomposite Powders
Language: English
Abstract:

A carbothermal reaction of silica–phenol resin hybrid gels prepared from a two-step sol–gel process was conducted in atmospheric nitrogen. The gels were first pyrolyzed into homogeneous silica–carbon mixtures during heating and subsequently underwent a carbothermal reaction at higher temperatures. Using a gel-derived precursor with a C/SiO2 molar ratio higher than 3.0, Si3N4/SiC nanocomposite powders were produced at 1500°–1550°C, above the Si3N4–SiC boundary temperature. The predominant phase was Si3N4 at 1500°C, and SiC at 1550°C. The Si3N4 and SiC phase contents were adjustable by varying the temperature in this narrow range. The phase contents could also be adjusted by changing the starting carbon contents, or by its combination with varying reaction temperature. A two-stage process, i.e., a reaction first at 1550°C and then at 1500°C, offered another means of simple and effective control of the phase composition: the Si3N4 and SiC contents varied almost linearly with the variation of the holding time at 1550°C. The SiC was nanosized (∼13 nm, Scherrer method) formed via a solid–gas reaction, while the Si3N4 has two morphologies: elongated microsized crystals and nanosized crystallites, with the former crystallized via a gaseous reaction, and the latter formed via a solid–gas reaction. The addition of a Si3N4 powder as a seed to the starting gel effectively reduced the size of the Si3N4 produced.

Journal or Publication Title: Journal of the American Ceramic Society
Journal volume: 90
Number: 12
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: 19 Apr 2012 08:01
Official URL: http://dx.doi.org/10.1111/j.1551-2916.2007.02046.x
Identification Number: doi:10.1111/j.1551-2916.2007.02046.x
Funders: . L. thanks the Alexander von Humboldt Foundation, Germany, for granting a research fellowship. R. R. thanks the Deutsche Forschungsgemeinschaft (DFG), Bonn, Germany, and the Fonds der Chemischen Industrie, Frankfurt, Germany, for financial support.
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