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: (SiRO_3/2)_n → SiC + CO₂ + H₂O

          

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.

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

SEM view of C/SiC compos­ite with two layers of OPS.