Carbon fibers from novel precursors

High Performance Carbon Fibers from Novel Precursors. .. 

Preparation process and microstructure investigation of the novel C/C-ZrB -ZrC-SiC have been reported in the previous chapter The composite contained a 2D carbon fiber non-woven architecture with fiber volume fraction of 17.6%, with pyrolytic carbon deposited on carbon fiber by CVI as interphase with a volume fraction of 22.3%. The obtained porous C/C composite exhibited a bulk density of 0.68g/cm, 50 vol% ZrB2-ZrC-SiC matrix and 9.6 vol% open porosity. The homogeneous dispersed ZrB2-ZrC-SiC complex ceramic matrix was formed inside this porous C/C composites by PIP technique using a blending ZrB -ZrC-SiC pre-ceramic polymeric precursors solution in xylene. The finial bulk density of the fabricated composite is 2.06 g/cm (details were reported in Part 1) after 16 PIP cycles. Finther densi-fication was difficult because of limitation of low residual porosity and ceramic yields from these precursors. PIP under ultra high pressure may further decrease the residual porosity of the composite but this was not conducted in this study due to the lack of this device. 

In addition to the polymer and facilitated transport membranes, novel materials are being proposed and investigated to achieve membranes with economically attractive properties. Carbon molecular sieve (CMS) membranes prepared by pyrolysis of polyimides displayed much better performance for olefin/paraffin separation than the precursor membranes [39, 46, 47]. Results obtained with CMS membranes indicated properties well beyond the upper-bond trade-off curve, as shown in Figure 7.8. Nonetheless, this class of materials is very expensive to fabricate at the present time. An easy, reliable, and more economical way to form asymmetric CMS hollow fibers needs to be addressed from a practical viewpoint. 

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