White Si-O-C ceramic: Structure and thermodynamic stability

Amir H. Tavakoli, Matthew M. Armentrout, Masaki Narisawa, Sabyasachi Sen, Alexandra Navrotsky

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


While pyrolysis of a polysiloxane precursor in argon typically produces a black amorphous Si-O-C ceramic containing "free" carbon (sp2 carbon), pyrolyzing the same precursor in hydrogen leads to a white amorphous ceramic with a negligible amount of sp2 carbon and a considerable hydrogen content. 29Si magic-angle-spinning nuclear magnetic resonance (MAS NMR) spectroscopy confirms the existence of very similar bonding environments of Si atoms in the Si-O-C network for both samples. In addition, 1H NMR spectroscopic measurements on both samples reveal that the hydrogen atoms are bonded mainly to carbon. For the thermodynamic analysis, the enthalpies of formation with respect to the most stable components (SiO2, SiC, C) of the black-and-white Si-O-C samples obtained after the pyrolysis at 1100°C are determined using high-temperature oxidative drop-solution calorimetry in a molten oxide solvent. The white ceramic is 6 kJ/g-atom more stable in enthalpy than the black one. Although the role of hydrogen in the thermodynamic stability of the white sample remains ambiguous, the thermodynamic findings and structural analysis suggest that the existence of sp2-bonded carbon in the amorphous network of polymer derived Si-O-C ceramics does not provide additional thermodynamic stability to the ceramic.

Original languageEnglish (US)
Pages (from-to)242-246
Number of pages5
JournalJournal of the American Ceramic Society
Issue number1
StatePublished - Jan 2015
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry


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