Keramik Verbundwerkstoffe

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ceramic composites

Multiple-mission spacecrafts necessiate reusable heatshields and heatexposed elements. Ceramic Matrix Composites (CMC) are the most suitable structural heat durable materials for these functions, carbon fibre reinforced silicon carbide (C/SiC) in particular.

For producing these composites, the carbon fiber mats are imprignated with the Fast-Sol-Gel, a resin based on rapid hydrolysis and polymerization of a mixture of (Me)xSi(O-Me)4-x monomers. After a gradual heat-pressure process under inert atmosphere the green composites are converted into C-SiC composites. Schematic reaction: (SiRO3/2)n → SiC + CO2 + H2O

ceramic composites_1           ceramic composites_2

The two figures above show the re-entry simulation chamber, where the composites are tested under re-entry conditions (Temperatures up to 1800°C, mechanical load and vacuum 10-6mbar)

In addition, such materials require an Oxidation Protection System (OPS) to prevent oxidative damage to the carbon fibres during re-entry. These OPS should reliably protect the C/SiC structures at temperatures up to 1600°C and must remain crack-free over the whole temperature range from approx. 450 to 1600°C. This system consists of the Fast-Sol-Gel resin and ceramic filler like n-Al2O3 or n-ZrO2.

ceramic composites_3 SEM view of hot-pressed (1600°C, 30MPa) Fast-Sol-Gel-derived carbon-fabric composites: Fibers extending from molten glass.

ceramic composites_4SEM view of C/SiC composite with two layers of OPS.