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Development of Si-C-N ceramic fibers at ITCF Denkendorf

Non-oxide Si-C-N ceramic fibers possess interesting properties and are predestined for applications in fiber reinforced ceramics (CMCs). These are materials with outstanding properties like high resistance against heat-shock and damage tolerance, which is completely different from conventional monolithic ceramics. Hence, new technical fields are accessible for these fiber ceramics like aerospace, power engineering and automotive applications. The production of such fibers can be conducted by a feasible melt spinning procedure, if thermoplastic precursor materials with proper rheological properties can be synthesized. By using different chlorosilanes as starting compounds meltspinnable polycarbosilazanes and polysilazanes have been produced. As a part of the research work new strategies for the synthesis for high molecular weight precursors with good processability have been developed. Based on the rheological studies and NMR spectroscopy possible structures of the polycarbosilazanes are derived. These precursors are spun to fibers in a melt spinning process (figure 1 and 2). To avoid melting during pyrolysis the green fibers are crosslinked by electron irradiation. Pyrolysis under inert conditions at 1100 °C leads to Si-C-N ceramic fibers (figure 3). These fibers are stable up to very high temperatures. Beside the formation of a thin oxidation layer no further fiber degradation is observed after temperature exposition at 1500 °C in air (figure 4).