Silicon Carbide Modified Carbon Materials. Formation of Nanocrystalline SiC from Thermochemical Processes in the System Coal Tar Pitch/Poly(carbosilane)

Poly(carbosilane) or PCS, {–CH2–SiH(CH3)–}n, is used as a Si-bearing precursor in combination with a coal tar pitch to study thermally induced transformations toward SiC-modified carbon composites. Following mixing of the components in the molten pitch at 160oC, the mixture is heated under argon atmosphere at 500oC yielding a solid carbonizate that is further subjected to separate pyrolysis experiments at 1300oC or 1650oC. At temperatures up to 500oC, the PCS reacts with suitable pitch components as well as undergoing decomposition reactions. At higher temperatures, clusters of prevailingly nanocrystalline b-SiC are confirmed after the 1650oC pyrolysis step with indications that the formation of the compound starts at 1300oC. Si MAS NMR, XRD, FT-IR, XPS, and elemental analysis are used to characterize each pyrolysis step, especially, from the viewpoint of transformation of silicon species to silicon carbide in the carbon matrix evolved from the pitch.