HYDROPOLYSILANES AS PRECURSORS TO SILICON-CARBIDE

A systematic study of the roles of three different types of monomers and their compositions in hydropolysilane home-, co-, and terpolymers on their pyrolytic yields to silicon carbides was performed. The diorganodichlorosilane monomer, serving to increase molecular weights of the polymers, is not a significant factor in pyrolytic yields. The organotrichlorosilane monomer, leading to branched structures of the polymers, is helpful in obtaining high pyrolytic yields. The monoorganodichlorosilane monomer, providing crosslinking sites for the polymers, is useful in retarding decomposition during pyrolysis. The precursor-to-ceramic conversion chemistry was studied using thermogravimetry, infrared spectroscopy, X-ray powder diffraction, and Rutherford backscattering spectrometry. The pyrolytic yields were not pyrolysis-time-dependent but decreased as the pyrolysis temperature increased. The apparent crystalline size increased as both the pyrolysis time and temperature increased. For a 30 min pyrolysis, the pyrolysis temperature must be over 1000-1200 degrees C to provide a crystalline pyrolytic residue. (C) 1995 John Wiley & Sons, Inc.