Synthesis of cyano-polycarbosilane and investigation of its pyrolysis process |
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Affiliation: | 1. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, 710049 Xi’an, PR China;2. Engineering Laboratory of Advanced Energy Materials, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, 315201 Ningbo, PR China;1. Ceramic Matrix Products Division, Analytical, Spectroscopy and Ceramics Group, PCM Entity, Vikram Sarabhai Space Centre, (ISRO), Thiruvananthapuram, 695022, India;2. Analytical and Spectroscopy Division, Analytical, Spectroscopy and Ceramics Group, PCM Entity, Vikram Sarabhai Space Centre, (ISRO), Thiruvananthapuram, 695022, India;1. College of Materials, Key Laboratory of High Performance Ceramic Fibers (Xiamen University), Ministry of Education, Xiamen 361005, China;2. College of Materials, Fujian Key Laboratory of Advanced Materials, Xiamen University, Xiamen 361005, China;3. Institut für Materialwissenschaft, Technische Universität Darmstadt, D-64287 Darmstadt, Germany;1. Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036, India;2. FRP Institute, Chennai 600032, India;3. Materials Science Division, CSIR-National Aerospace Laboratories, Bangalore 560017, India |
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Abstract: | Polycarbonsilane (PCS) is an important precursor of silicon carbide (SiC) fibers and ceramics. The ceramic yield of PCS is relatively low, about 60 %, which may bring some deficiencies in its applications. In this work, a novel precursor cyano-polycarbosilane (PCSCN) is synthesized by hydrosilylation reaction between PCS and acrylonitrile using a rhodium-containing catalyst, although acrylonitrile is generally not easy for hydrosilylation. After introducing tiny amounts of cyano (-C≡N) groups into the PCS molecules, the ceramic yield of PCSCN can increase largely to over 80 %. The ceramization mechanism of PCSCN is investigated by FTIR, TG, XPS, ESR, NMR, Raman and XRD analyses. It is found that some crosslinking structures in PCSCN are formed between SiH bonds and CN groups from about 200 ℃, which can be responsible for the high ceramic yield. The existence of a little more N, O and free C elements in the pyrolysis products may inhibit the growth of crystalline β-SiC. Moreover, the PCSCN precursor can also be melt-spun into continuous fibers by tailoring its molecular weight and softening point. The oxidized PCSCN fiber with relatively low oxygen content can be pyrolyzed without melting, and the final SiC fiber with an oxygen content as low as 8.5 % is obtained. |
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Keywords: | Polycarbonsilane Acrylonitrile Hydrosilylation Ceramic yield |
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