Characterisation of the free-carbon phase in precursor-derived SiCN ceramics

Different polymeric precursors with varying carbon contents were prepared b y ammonolysis of functionalised chlorosilanes. Pyrolysis under inert atmosp heres at 1000 degreesC led to amorphous Si-C-N-(H) ceramics. Further heat t reatment caused the transformation into the thermodynamically stable crysta lline phase assemblage. The structural changes, especially those of the exc ess carbon, were studied by characterising the solid intermediates via soli d state magic angle spinning (MAS) nuclear magnetic resonance spectroscopy (NMR). In addition, Raman spectroscopy, electron spin resonance spectroscop y (ESR), microwave conductivity measurements and chemical analysis were emp loyed. Combination of all these methods provides a comprehensive picture of the formation and of the behaviour of the free-carbon phase present in the polymer-derived ceramics. (C) 2001 Elsevier Science B.V. All rights reserv ed.