SiOC ceramic foams synthesized from electron beam irradiated methylsilicone resin

A new method to prepare silicon oxycarbide (SiOC) foams has been developed and it consists of electron beam irradiation of a methylsilicone preceramic polymer followed by pyrolysis in an inert atmosphere. Methylsilicone resin foams were prepared by simultaneous curing and foaming, without the addition of calalysts or blowing agents. The polymer precursor was irradiated with 1.5 MeV EB up to a dose of 7.0 MGy and at a dose rate of 2.8 kG/s, in air. During irradiation the polymer melted, due to rapid increase in temperature, and simultaneously crosslinked by interaction with the ionizing radiation. Crosslinking occurred mainly by poly-condensation reactions and gaseous condensation products were released. The latter acted as an intrinsic foaming agent in the molten polymer. Foams obtained with radiation doses higher than 3.5 MGy showed a high degree of crosslinking with a ceramic yield of over 89% at 1,000 C. Pyrolysis at 1,200– 1,500 C resulted in SiOC ceramic foams with dense struts and walls, with bulk density around 0.3 g/cm3 and total porosity of 84%. Foams pyrolyzed at 1,200 C revealed compression strength of 6.8 MPa.