Sol-gel derived C-SiC composites and protective coatings for sustained durability in the space environment

Details Sol-gel derived C-SiC composites and protective coatings for sustained durability in the space environment Sol-gel derived C-SiC composites and protective coatings for sustained durability in the space environment

Sep 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003esasp.540...67h&link_type=abstract

In: Proceedings of the 9th International Symposium on Materials in a Space Environment, 16-20 June 2003, Noordwijk, The Netherla

Computer Science

Silicon-Carbide, Composites, Re-Entry, Sol-Gel, Hot-Press Processing, Protective-Coating, Leo, Atox

Scientific paper

Composites and coatings were produced via the fast sol-gel process of a mixture of alkoxysilane precursors. The composites were comprised of carbon fibers, fabrics, or their precursors as reinforcement, and sol-gel-derived silicon carbide as matrix, aiming at high-temperature stable ceramics that can be utilized for re-entry structures. The protective coatings were comprised of fluorine-rich sol-gel derived resins, which exhibit high flexibility and coherence to provide sustained ATOX protection necessary for LEO space-exposed elements. For producing the composites, the sol-gel-derived resin is cast onto the reinforcement fibers/fabrics mat (carbon or its precursors) to produce a 'green' composite that is being cured. The 'green' composite is converted into a C-SiC composite via a gradual heat-pressure process under inert atmosphere, during which the organic substituents on the silicon atoms undergo internal oxidative pyrolysis via the schematic reaction: (SiRO3/2)n -> SiC + CO2 + H2O. The composition of the resultant silicon-oxi-carbide is tailorable via modifying the composition of the sol-gel reactants. The reinforcement, when made of carbon precursors, is converted into carbon during the heat-and-pressure processing as well. The C-SiC composites thus derived exhibit superior thermal stability and comparable thermal conductivity, combined with good mechanical strength features and failure resistance, which render them greatly applicable for re-entry shielding, heat-exchange pipes, and the like. Fluorine rich sol-gel derived coatings were developed as well, via the use of HF rich sol-gel process. These coatings provide oxidation-protection via the silica formation process, together with flexibility that allows 18,000 repetitive folding of the coating without cracking.

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