Quasi-stoichiometric SiC fibers

When the pyrolysis of PCS precursor fibers is carried out in the presence of hydrogen, or when boron or aluminum doped PCS precursor fibers are pyrolyzed, it is possible to obtain quasi-stoichiometric silicon carbide fibers. Alternatively, quasi-stoichiometric fibers are also obtained from precursor fibers consisting of SiC powder reinforced polymers. 

Similarly, an experimental, quasi-stoichiometric, oxygen-free SiC fiber has been produced from a Si-AI-C-0 precursor. In this process, aluminum is introduced into the polymer as aluminum (III) acetylacetonate, and acts like boron as a SiC sintering aid during heat treatment at 1800°C [40]. 

Si-C-0 fibers (Nicalon NLM-200) creep at low temperatures (1000-1200"C), whereas the sintered a-SiC fibers (Carborundum) creep at much higher temperatures (1300-1600 0). The other fibers, which are derived from PCS precursor fibers, i.e., oxygen-free Si-C fibers (Hi-Nicalon) and the quasi-stoichiometric fibers (Hi-Nicalon S or Dow Coming fiber) fail between these two limits. The fibers which have been heat treated at 1400-1600 0 and display a larger SIC grain size (e.g., 30-50 nm) exhibit a creep resistance similar to that of the a-SiC sintered fiber. 

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