Abstrakt
Polysiloxane foams as precursors to silicon oxycarbide (SiOC) foams were prepared via simultaneous cure and foaming of liquid methylsiloxane resins, using the relatively environment-friendly ethanol as blowing additive of the boiling-solvent-type, and concentrated aqueous ammonia as catalyst. In order to achieve foam regularity, siloxane-based surfactants were added, and bubble nucleation by mechanical stirring was performed.
The precursor foams were subsequently pyrolysed in nitrogen at 1000 degrees C, yielding SiOC foams as end products. The properties of the latter were fine-tuned during the foaming of the precursors, by the amount of added ethanol and by the time of mechanical stirring prior to foaming.
The so-obtained SiOC foams displayed densities of 0.17-0.42 g/cm(-3), corresponding to macro-porosities of 91-79%, compressive strength of 1-6 MPa, and elastic moduli of 0.2-1.6 GPa.