T. Rouxel—contributing editor
Enthalpy of Formation of Carbon-Rich Polymer-Derived Amorphous SiCN Ceramics
Article first published online: 8 SEP 2008
© 2008 The American Ceramic Society
Journal of the American Ceramic Society
Volume 91, Issue 10, pages 3349–3354, October 2008
How to Cite
Michelle Morcos, R., Mera, G., Navrotsky, A., Varga, T., Riedel, R., Poli, F. and Müller, K. (2008), Enthalpy of Formation of Carbon-Rich Polymer-Derived Amorphous SiCN Ceramics. Journal of the American Ceramic Society, 91: 3349–3354. doi: 10.1111/j.1551-2916.2008.02626.x
This work was supported by grant from the Ceramics Program of the Division of Materials Research of the National Science Foundation DMR-0502446 at the University of California, Davis. These grants are funded under the MWN (Materials World Network) Program between the National Science Foundation and the Deutsche Forschungsgemeinschaft (DFG). The research at Stuttgart is supported by the DFG under grant Mu 1166/12-1 and the work at TU Darmstadt is supported by the DFG under grant Ri 510/33-1. R. R. also thank Fonds der Chemischen Industrie, Frankfurt, Germany for the support provided.
- Issue published online: 1 OCT 2008
- Article first published online: 8 SEP 2008
- Manuscript No. 24524. Received April 9, 2008; approved June 23, 2008.
Carbon-rich silicon carbonitride (SiCN) ceramics derived from polysilylcarbodiimides represent a novel class of materials where the incorporation of a high amount of carbon was demonstrated to be beneficial for ultrahigh-temperature resistance against crystallization. Calorimetric measurements of heat of oxidative dissolution in a molten oxide solvent show that these amorphous SiCN ceramics produced at 1000° or 1100°C possess a small positive or near zero enthalpy of formation relative to their crystalline constituents, namely silicon nitride, silicon carbide, and graphite. The enthalpy of formation does not change strongly with increasing SiC mole fraction. Because the enthalpies of formation from crystalline constituents are at most slightly positive, and the entropies of formation are expected to be significantly positive because of disorder in the amorphous phase, it is likely that the free energies of formation from silicon carbide, silicon nitride, and graphite are negative and the high-temperature persistence of amorphous SiCN ceramics may originate from thermodynamic stabilization. However, this stabilization is less pronounced than that for SiCO polymer-derived ceramics studied earlier.