Studies of the pyrolysis behaviour of silica sol copolymerized with furfuryl alcohol

摘要

The sol-gel process, although initially used for making pure oxide glasses and ceramics, is presently being investigated for making oxycarbides, carbides and oxynitrides [1-4] through incorporation of carbon and nitrogen at appropriate stages. Black glasses containing carbon in a silica network are amorphous in nature and exhibit better mechanical and electrical properties and thermal stability at much higher temperature than pure silica. Carbon is introduced into the network through pyrolysis of a mixture of silica gel and a carbonaceous source [5, 6] usually a thermosetting resin or pitch-derived carbonaceous sol. Through this route, carbon is usually present as discrete particles distributed along with amorphous silica. No chemical reaction is reported to occur up to 1000 CC. At higher temperatures, carbothermal reaction between the two species results in the formation of silicon carbide with a low yield [7]. Silicon oxycarbide glasses having carbon incorporated in the silica network can be produced by pyrolysis of silicon polymers such as polysiloxanes or by silica gels starting from organically modified silicon alkoxide of type R.v-Si(OR)4_v [8]. R' is usually an organic group containing carbon, such as methyl, ethyl and phenyl, etc. In the present studies, a new route has been investigated wherein carbon-yielding organic groups, are introduced in the silica gel through copolymerization of silica sol and a carbon-containing monomer. The polymer thus obtained has been pyrolysed to different temperatures to obtain carbon inserted in the silica network.