Pre-ceramic Precursors

In order to study the influence of pyrolytic carbon interphase on the mechanical properties of the composite, porous C/C composites with the same carbon fiber fraction but different contents of pyrolytic carbon interphase (volume fractions of 12.4% and 34.2% other than 22.3%) were prepared. Bulk densities of the prepared C/C-ZrBj-ZrC-SiC composite are 0.51g/cm (sample A) and 0.88g/cm (sample C), respectively. Mono-ceramic matrix composite of C/C-SiC with the same fiber and pyrolytic carbon volume fractions and pyrolytic carbon interphase thickness as in sample B was also prepared by PIP using PCS as pre-ceramic precursor for... 

Hydrosilylation of 1 with trichlorosilane has been performed with Pt on charcoal (1% by weight) in quantitative yields (Scheme 1). The B-tris(trichlorosilylvinyl)borazine (2) was obtained with a high regioselectivity of proximately 80% trans hydrosUylation product [4], Pure 2 can be obtained by fiactional crystallization of the synthesized product fiom hexane. For further synthesis, both a- and P-hydrosilylation products can be used. No further hydrosilylation was observed in this case. In order to interconnect the single source precursor molecule 2 to a pre-ceramic polymer, methylamine was added to the solution of 2 in hexane, and a high viscosity, colorless oil was formed. By changing the reaction parameters (excess of CH3NH2, temperature), the viscosity of the polymer can be varied [5]. The obtained polymer (3P) is pure after evaporation of the solvent, which is checked by NMR. Other solvents like thf or toluene are also possible for the reaction, as well as for dissolution of the polymer. Furthermore, ethylamine leads to similar results in the formation of the polymer. 

The potential of silicon carbide pre-ceramic compounds was recognized especially after Yajima et al. had prepared silicon carbide-based ceramic fibers [1]. The development of tailor-made silicon carbide precursor molecules has to be seen in close relation to the tremendously fast growth of the field of... 

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. 

Liu GW, Xie ZP, Liu W, Chen LX, Wu Y (2012) Fabrication of translucent alumina ceramics from pre-sintered bodies infiltrated with sintering additive precursor solutions. J Eur Ceram Soc 32 711-715... 

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