Crystallisation kinetics of amorphous Si–C–N ceramics: Dependence on nitrogen partial pressure

Abstract

The crystallisation kinetics of amorphous precursor-derived ceramics of composition Si₂₆C₄₁N₃₃ is investigated as a function of temperature and nitrogen partial pressure using X-ray diffractometry. Isothermal annealing at a pressure of 1 bar leads to simultaneous crystallisation of Si₃N₄ and SiC, while only crystalline SiC is formed with annealing at a reduced pressure of 1 mbar. Rate constants of crystallisation are determined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) formalism. For temperatures below 1700°C, crystallisation rates are significantly higher for annealing at 1 mbar compared to 1 bar. For an explanation of the results, a model is proposed, which is based on diffusion-controlled nucleation and growth of crystalline Si₃N₄ and SiC in an amorphous matrix combined with thermal decomposition of Si₃N₄ at high temperatures.

Keywords:

• crystallisation
• kinetics
• precipitation
• X-ray diffractometry

Acknowledgements

The authors thank P. Gerstel (MPI Stuttgart) for supplying the precursor ceramics and E. Ebeling for ceramographic preparation. Funding by the Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged.