Si‐(B‐)C‐N Ceramics Derived from Preceramic Polymers: Stability and Nano‐Composite Formation

Inorganic ceramic materials of the system Si‐(B‐)C‐N which are produced from preceramic polymers by solid state thermolysis have gained much interest during the last years because of their high temperature stability (up to 2000°C), their good oxidation resistance, and their mechanical and electrical properties. After thermolysis, the ceramics are amorphous, however, phase separated in nano‐scaled domains. During annealing at temperatures above 1450°C nano‐crystalline (and also micro‐crystalline) particles precipitate, resulting in the formation of completely or partially crystallized composites (e.g., SiC/Si₃N₄ or SiC_xN_y/SiC).

The present paper gives an overview of our work (in context to literature) on the complex chemical and physical processes which determine the in‐situ formation of Si‐(B‐)C‐N nano‐composites and the thermal stability of the nano‐structured state. These processes are: de‐mixing of the homogenous amorphous matrix in phase separated nano‐domains, crystallization of SiC and Si₃N₄ mediated by nucleation and diffusional growth, crystallite growth due to coarsening, and special solid state decomposition reactions.

Keywords:

• Kinetic processes
• Phase formation
• Precursor ceramics
• Nanocomposites
• Si‐C‐N

Acknowledgments

The author would like to thank P. Gerstel, A. Müller, and M. Weinmann (MPI‐MF Stuttgart) for the preparation of the precursor ceramics, N. Bunjes for realizing the TEM measurements, W. Gruber for his help in carrying out the annealing procedures, E. Ebeling for technical support, and G. Borchardt for fruitful discussions. This work has been supported by the Deutsche Forschungsgemeinschaft (DFG) during the focus program “Percursorkeramiken”.