Berlin 2008 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 49: Phase Transitions VI

MM 49.3: Talk

Friday, February 29, 2008, 12:15–12:30, H 0107

Formation of Amorphous Domains and Crystalline Precipitates in Precursor Derived Si-C-N-Ceramics — •Wolfgang Gruber and Harald Schmidt — TU Clausthal, Institut für Metallurgie, AG Materialphysik

Precursor derived ceramics of the system Si-C-N are prepared by solid state thermolysis of pre-ceramic polymers at temperatures of about 1100 °C. The materials are free of sinter additives and exhibit a good high-temperature stability and oxidation resistance making them attractive for applications in various branches of technology. As-thermolized ceramics are already separated in silicon rich and carbon rich amorphous phases. Annealing in nitrogen atmosphere at temperatures above the temperature of thermolysis leads to a coarsening of the amorphous phases and at length to the formation of micro crystalline silicon nitride and nano crystalline silicon carbide. According to the phase diagram of the system Si-C-N carbon and silicon nitride are in equilibrium at a nitrogen partial pressure of 1 bar and at temperatures below 1484 °C. At higher temperatures silicon nitride reacts with carbon and silicon carbide and gaseous nitrogen are formed. This reaction and therefore the micro structure of the ceramic strongly depends on temperature and on the nitrogen partial pressure. In this study we investigated the formation kinetics of amorphous domains and crystalline precipitates at different nitrogen partial pressures using small angle X-ray scattering (SAXS) and X-ray diffractometry (XRD).