Thermal stability silicon carbide fibers

Although the chemistry of the initial thermal transformation is obviously quite complex, it was determined that considerable carbon insertion into the Si-Si bonds occurs, resulting in an intermediate carbosilane which can be drawn into fibers. At this point, brief oxidation results in the formation of a surface oxide which imparts dimensional stability, and subsequent heating to 1300°C produces silicon carbide fibers (3,5). 

Shimoo, T., Takeuti, H., Okamura, K., (2001), Thermal stability of polycarbosilane-derived silicon carbide fibers under reduced pressures , J. Am. Ceram. Soc., 84, 566-570. 

M. Takeda, Y. Ymai, H. Ichikawa, T. Ishikawa, N. Kasai, T. Seguchi and K. Okamura, Thermal stability of the low oxygen silicon carbide fibers derived from polycarbosilane, Ceram. Eng. Sd. Proc., 13 [7-8], 209-217 (1992). 

Polycarbosilanes can exhibit thermal stabilities greater than the analogous polysiloxane , contrary to their relative bond energies (Si—C, 78 kcalmol Si—O, 106 kcal mol" ). Thus polydimethylsilane is polymerized by heating the hexamer to 300-500°C, forming a product with thermal stability greater than 500°C and that can be spun into fiber, which in turn can be thermally oxidized, forming j5-silicon carbide, SifCHj) -,. 

Silicon carbide has high thermooxidative stability and good thermal and electrical insulation properties. In composite applications, this fiber can be used to reinforce polymer, metal, and ceramic matrices. 

---