Fabrication of Nitrogen-Containing Cordierite Ceramics
We have investigated the crystallization behavior of cordierite-based oxynitride glass prepared by melting a powder mixture of cordierite and silicon nitride. The results indicated that two polymorphs exist: a stable α-form, which has a low coefficient of thermal expansion, and a metastable -form. The time–temperature–transformation diagram of the crystallization of the α-form shows a typical C-shaped curve that has a nose around 1420 K. Above 1373 K, the α-form can be directly obtained by the isothermal crystallization of the oxynitride glass and the -form inverts to the α-form at temperatures below 1273 K. We also have fabricated an α-cordierite ceramic that has a nitrogen content of 1.55 mass%, which is much lower than the content of the batch composition (5 mass%); this is mainly owing to the decomposition reaction of nitrogen in the oxynitride melts and glasses during heat treatment. However, the fabricated nitrogen-containing α-cordierite ceramics showed the coefficient of thermal expansion of 10−7 K−1, which is comparable with that of the oxide α-cordierite ceramics. Moreover, Young's modulus of the α-cordierite ceramics improved with the incorporation of nitrogen.
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Document Type: Research Article
Affiliations: 1: Department of Materials Science and Engineering, Kyushu University, Fukuoka 819-0395, Japan 2: Nippon Tungsten Co. Ltd., Fukuoka 812-8538, Japan
Publication date: August 1, 2010