New polymer pyrolysis routes to near-stoichiometric silicon carbide
- Massachusetts Institute of Technology, Cambridge, MA (United States)
The liquid poly(methylsilane), [(CH{sub 3}SiH){sub x}(CH{sub 3}Si){sub y}(CH{sub 3}SiH{sub 2}){sub z}]{sub n} (x + y + z = 1; x {much_gt} y and z), in which the C/Si ratio = 1, can be prepared by sodium condensation of CH{sub 3}SiHCl{sub 2} in 7:1 (by vol.) hexane/THF. However, its pyrolysis results in loss of some CH{sub 3} substituents as CH{sub 4}, leaving SiC ({approximately}76 wt%) and elemental Si ({approximately}24 wt%). It was found that reaction of this poly(methylsilane) with organosilicon polymers whose pyrolysis gives SiC and an excess of carbon (such as [CH{sub 3}(CH{sub 2}{double_bond}CH)SiC{triple_bond}C]{sub n} or [CH{sub 2}CH(SiH{sub 3})]{sub 2}, whose syntheses will be described) gives hybrid polymers. If the amounts of the reactant polymers are chosen correctly, pyrolysis of the resulting hybrid polymers yields near-stoichiometric SiC. Alternatively, the poly(methylsilane) may be crosslinked by appropriate treatment with catalytic amounts of group 4 metallocene derivatives (Cp{sub 2}ZrH{sub 2}, Cp{sub 2}ZrMe{sub 2}, Cp{sub 2}ZrHCl, Cp{sub 2}TiCl{sub 2}). Pyrolysis of the resulting Zr- or Ti-containing organosilicon polymers gives near-stoichiometric SiC. In one example in which Cp{sub 2}ZrH{sub 2} was used, the final formal ceramic composition was 98% SiC, 1.6% ZrC and 0.4% Si.
- OSTI ID:
- 141568
- Report Number(s):
- CONF-930304--
- Country of Publication:
- United States
- Language:
- English
Similar Records
A survey of organosilicon polymers
High yield polycarbosilane precursors to stoichiometric SiC. Synthesis, pyrolysis and application