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Synthesis and characterization of molybdenum-modified polycarbosilane for SiC(Mo) ceramics

Authors

  • Zhengfang Xie,

    Corresponding author
    1. National Key Laboratory of Science and Technology on Advanced Ceramic Fibres and Composites, College of Aerospace Science & Engineering, National University of Defense Technology, Changsha 410073, China
    • National Key Laboratory of Science and Technology on Advanced Ceramic Fibres and Composites, National University of Defense Technology, Changsha 410073, China
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  • Jiaxin Niu,

    1. National Key Laboratory of Science and Technology on Advanced Ceramic Fibres and Composites, College of Aerospace Science & Engineering, National University of Defense Technology, Changsha 410073, China
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  • Zhaohui Chen

    1. National Key Laboratory of Science and Technology on Advanced Ceramic Fibres and Composites, College of Aerospace Science & Engineering, National University of Defense Technology, Changsha 410073, China
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Abstract

A novel molybdenum-containing polycarbosilane, polymolybdenocarbosilane (PMoCS), for SiC(Mo) fiber has been synthesized from polysilacarbosilane (PSCS) and MoCl5 as raw materials. The synthesis conditions is investigated. Characterization performed on the as-synthesized PMoCS includes Fourier Transformed Infrared Spectroscopy (FT IR), gel-permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), 1H NMR, and 29Si NMR, respectively. The polymer-to-ceramic conversion is studied with thermogravimetric analysis (TGA) and X-ray diffraction  (XRD). Preliminary research on the melt spinnability of PMoCS is carried out. The results show that the synthesis reaction is temperature-dependent. Mo exists mainly as Si[BOND]Mo bonds. The reaction mechanism is believed to involve HCl elimination between Si[BOND]H and Mo[BOND]Cl, and followed by the Kumada rearrangement. The ceramic yield of PMoCS, prepared with 10 wt % MoCl5, is approximately 78.5% at 1200°C in a N2 flow. The XRD results suggest that ceramics pyrolyzed in the range of 800–1000°C are all amorphous, while β-SiC and β-MoSi2 crystals are observed at 1200 and 1400°C, respectively. The conversion from β-MoSi2 to α-MoSi2 is almost completed at 1600°C. PMoCS is melt spinnable into flexible and uniform green fibers with the diameters about 13.4 μm to 12.2 μm. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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