Synthesis of SiCN-Precursors for Fibres and Matrices

Main applications for preceramic polymers (precursors) are ceramic fibres, ceramic matrices and coatings. The requirements for the polymer are determined by the intended application and differ from a cross-linkable liquid to meltable and curable or unmeltable but soluble solid. For applying these precursors on a larger scale, they must be processable by conventional polymer processing techniques. Furthermore, the starting material should be cheap and readily available, and the synthesis should be uncomplicated. Considering these criteria, specially tailored precursors in the system Si-C-N (silazanes) were synthesized in a laboratory scale by ammonolysis of different chlorosilanes. After investigating the properties suitable precursors were produced in a pilot plant (approx. 5 kg). Variation of both the functional groups of the chlorosilane educts and the synthesis conditions lead to precursors with tailored properties (liquid, solid, soluble) and a special cross-linking behaviour (catalyst, initiator, electron-beam). Selected applications with the special precursors were presented for producing ceramic SiCN-fibres via melt-spinning also with a precursor modified with multi-walled carbon nanotubes as well as for processing a new kind of metal-ceramic gradient compound by reaction of SiCN-precursors with Ti-powders during pyrolysis.