From preceramic polymers with interpenetrating networks to SiC/MC nanocomposites

The preparation of beta-SiC/MC (M = Ti, Nb, and Ta) nanocomposite ceramics by the pyrolysis under an inert atmosphere of precursors consisting in inte rpenetrating networks of poly(dimethylsilylene)diacetylene], 1, and polymer ic metal oxide is described. The precursors are obtained by in-situ precipi tation of the desired metal alkoxide into the organosilicon polymeric matri x. The precursor-to-ceramic conversion involved two critical transformation s: (i) the thermal cross-linking of 1 and (ii) the carbothermal reduction o f the oxide by the free carbon resulting from the degradation of 1. At 1400 degrees C, the pure carbides are obtained as nanometer-sized highly crysta lline powders. Analysis have shown that both beta-SiC and the other metal c arbide are present simultaneously in each ceramic particle as discrete phas es. All of these results show that we are faced with materials that can be described as nanocomposite ceramics with interpenetrating networks.