Inhibiting oxidn. of carbon fibre reinforced carbon moulding - by chemical vapour infiltration or deposition of pyrolytic carbon and opt. silicon carbide

摘要

Prodn. of carbon-fibre reinforced carbon mouldings protected against oxidn., the mouldings of any geometrical shape, produced by moulding and carbonisation in conventional manner, which have a C fibre-reinforced porous C-C matrix, are subjected to chemical vapour phase infiltration (CVI/CVD) with pyrolytic carbon, so that each individual C fibre or fibre bundle is sealed with a dense protective C layer. The density (1.2-1.8 g/cc) and open porosity can be regulated by the amt. of pyrolytic C infiltrated and/or the reaction time of the CVI process. The moulding may then be infiltrated or filled by CVI or CVD with SiC or infiltrated with liquid Si (alloy) and opt. finally reacted with N2 to convert the free Si to Si3N4 to give a multilayer effect increasing the long-term resistance to oxidn. and wear. The process can be carried out with 1-, 2- and 3-dimensional mouldings and mouldings consisting of short fibres (random and quasi-isotropic) and felts. Pref. resins matrices for making the mouldings are phenolic resins, silicone resins and/or resins contg. Si-C, Ti:and/or W. The resin content is 10-50 wt.% w.r.t. C fibres. The gas-tight pyrolytic C coating is 10-3000 microns thick. An inert sepg. layer may first be produced on the fibres (bundle) by CVI, pref. with BN or AIN. ADVANTAGE - The treated moulding has good resistance to oxidn., extremely low porosity, characteristic texture, high purity and an esp. high flexural strength of min. 300 N/mm2 at a density of 1.2-1.8 g/cc and also an E modulus of min. 90 GPa (claimed). The purity can be extremely high, at under 5 ppm, which completely eliminates out-gassing (claimed). The moulding has good resistance to O2 up to over 1800 deg. C, in conjunction with high strength and pseudo-plastic fracture.