Thermodynamically stable SixOyCz polymer-like amorphous ceramics

Tamas Varga, Alexandra Navrotsky, Julianna L. Moats, R. Michelle Morcos, Fabrizia Poli, Klaus Müller, Atanu Saha, Rishi Raj

Research output: Contribution to journalArticlepeer-review

101 Scopus citations

Abstract

Carbon can be used to create unusual nanostructures of Si-C-O by controlled pyrolysis of silsesquioxane organics. Unlike silica, these ceramics resist crystallization at ultrahigh temperatures. Their structure has been compared with that of polymers, where crosslinked chains of polymers in organics are replaced by crosslinked networks of graphene in the ceramics. The network sequesters nanoscale domains of SiO4 tetrahedra. The resistance to crystallization of these nanodomain networks has been attributed to kinetic factors, namely obstruction of long-range diffusion of silica. In this work, we identify a thermodynamic hindrance to crystallization. Calorimetric measurements of heats of dissolution in a molten oxide solvent show that these ceramics possess a negative enthalpy relative to their crystalline constituents (silicon carbide, cristobalite, and graphite). The thermodynamic stability of the nanodomain structure is explained by a low free energy of the graphene-silica interfaces, perhaps related to the presence of mixed bonds of silicon bonded to both carbon and oxygen.

Original languageEnglish (US)
Pages (from-to)3213-3219
Number of pages7
JournalJournal of the American Ceramic Society
Volume90
Issue number10
DOIs
StatePublished - Oct 2007
Externally publishedYes

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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