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| High–temperature Crystallization Behaviors of Amorphous Si–Al–C–N with Low Aluminum Content |
| LI Song1,2, ZHANG Yue1 |
1.Key Laboratory of Aerospace Materials and Performance, School of Materials Science and Engineering, Beihang University, Beijing 100191
2.State Key Laboratory of Advanced Fibre Composites, Beijing Composite Materials Co., Ltd., Beijing 102101 |
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Cite this article:
LI Song, ZHANG Yue. High–temperature Crystallization Behaviors of Amorphous Si–Al–C–N with Low Aluminum Content. Chin J Mater Res, 2011, 25(3): 237-242.
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Abstract Amorphous Si–Al–C–N ceramics with varied aluminum contents, which were derived from polyaluminasilazanes at 1200 %, were heat–treated at 1400–1800 %. The structures of precursors and the crystallization behaviors, free–carbon and microstructure of Si–Al–C–N were characterized by Infrared spectrometry, X–ray diffraction, Raman spectra and transmission electron microscopy. The effects of aluminum contents, crystallization temperatures and times on crystallization properties of amorphous Si–Al–C–N were investigated. The results show that amorphous Si–Al–C–N ceramics are amorphous at 1400 %, but include free-carbon. Nano–scale β–Si3N4 and α–Si3N4 nuclei are precipitated at 1500 %. The α–Si3N4 nucleus transforms into β–Si3N4 after treated at 1600 %, at the same time, a minute quantity of α–SiC and 2H–SiC/AlN solid solution nuclei precipitated. At 1700 % a large number of 2H–SiC/AlN solid solution crystals and a few α/β–SiC crystals precipitated besides β–Si3N4, and the β–Si3N4 phase in the Si–Al–C–N ceramic with lowest aluminum content disappears. At 1800 % only β–SiC and 2H–SiC/AlN solid solution crystal are observed. But phase separation takes place at this temperature, leading to the formation of AlN–rich and SiC–rich solid solution region, respectively. With increasing aluminum content, crystallization ability of amorphous Si–Al–C–N ceramics and quantities of grain increase. Nano-scale crystals precipitate from the amorphous Si–Al–C–N at 1500 %, but even until 1800 % the precipitated crystals are still nano–scale crystals. The high-temperature crystallization process of amorphous Si–Al–C–N with high covalence is a process controlled by thermodynamics.
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Received: 15 February 2011
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| Fund: Supported by National Natural Science Foundation of China No.51072010, Specialized Research Fund for the Doctoral Program of Higher Education from Chinese Ministry of Education No. 20091102110002, The Cheung Kong Scholars and Innovative Research Team Program in University from Chinese Ministry of Education No.IRT0805. |
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