Enthalpy of formation of carbon-rich polymer-derived amorphous SiCN ceramics

Riham Michelle Morcos, Gabriela Mera, Alexandra Navrotsky, Tamas Varga, Ralf Riedel, Fabrizia Poli, Klaus Müller

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)3349-3354
Number of pages6
JournalJournal of the American Ceramic Society
Volume91
Issue number10
DOIs
StatePublished - Oct 2008
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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