Energetics of SixOyCz Polymer-Derived Ceramics Prepared Under Varying Conditions

Abstract

Incorporation of carbon at the molecular level can create unusual amorphous and nanostructures of Si–C–O polymer-derived ceramics by controlled pyrolysis of crosslinked polysiloxanes. These ceramics can resist crystallization to ultrahigh temperatures. In this work, we support earlier studies that the resistance to crystallization of these nanodomain networks is due to thermodynamic as well as kinetic factors. Calorimetric measurements of heats of dissolution in a molten oxide solvent show that these ceramics posses a negative enthalpy relative to their crystalline constituents (silicon carbide, cristobalite, and graphite). Si–C–O ceramics pyrolyzed at 1000° and 1450°C appear somewhat more energetically stable than those prepared at 1200°C.