The properties of silicon carbide (low CTE, high modulus, low density) are ideal for spaceborne applications as an alternative to glass-ceramics or beryllium. Some large lightweight mirrors, for example, have been made of RB-SiC or CVD-SiC over the last few years.A simple and cost-effective way to produce very lightweight SiC materials is the replication of polymeric sponges by powder processing. Fraunhofer IKTS has been developing a new ceramic foam with high strength and stiffness (LigaFill . Compared to usual ceramic foams, strength was enhanced by more than 600%. The density of such foams is very low (0.2-0.3 g/cm 3 ). LigaFill ® can simply be sandwiched in SiC-C-fiber mats or in normal monolithic RBSiC plates by a paste technique, to produce components with a dense surface. As an alternative to foams, net-like cerarnics (CeraNet ) can be used as well. In this way stiffness and strength can be adjusted according to the loading of the component.There are potential applications of Si-SiC LigaFill ® as mirror and reflector substructures, in thermal protection systems, as passive structural elements and as a muffler in hypersonic engines.
Properties of Silicon CarbideA wide range of spaceborne applications, e.g. mirror substrates, mirror mounts, reflector substructures and passive structural elements, requires very lightweight, high-stiffness materials with low CTE and high thermal conductivity at reasonable costs. The properties for selected candidate materials are listed in Table 1. As can be seen, silicon carbide has an excellent specific stiffness and superior thermal stability. Therefore some large lightweight mirrors have been made of SiC in recent years 1,2 . Nevertheless SiC is the heaviest among these materials; this is why it is important to develop techniques to reduce the weight of components.
Fabrication Methods of SiCBesides CVD-SiC-coating and single-crystal-growth techniques, most SiC bulk materials are made from powders. Because of the strong covalent character of the interatomic forces in SiC Materials for Transportation Technology. Edited by P. J. Winkler
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