STRUCTURAL INVESTIGATIONS OF SI C/N-CERAMICS FROM POLYSILAZANE PRECURSORS BY NUCLEAR-MAGNETIC-RESONANCE/

Polymeric precursors to Si/C/N-ceramics can be obtained by thermal cro sslinking of polysilazanes. The precursor is then pyrolysed at a tempe rature of 1000 degrees C into the amorphous ceramic. Between 1000 and 2000 degrees C this amorphous state is transformed into the ther therm odynamically stable phases. The processes during pyrolysis ann crystal lization ale connected with microstructural conversion. Simultaneously , changes of chemical and physical properties fake place. The successi ve conversion of the atomic coordination during the transformation fro m rite polymer into the amorphous ceramic and finally into the crystal line ceramic It CIS studied using solid-state NMR. Si-29-, C-13- and H -1-spectra were recorded. The result is a detailed report of the react ions and changes in structure occuring during ceramization of a polyhy dridomethylsilazane and crystallization I of its ceramic residue. Furt hermore, the amorphous state of this material was compared with a poly vinylsilazane-derived amorphous ceramic.