S. Matthews et al., Effect of pre-pyrolysis heat treatment on the preparation of silicon carbide from a polycarbosilane precursor, CERAM INT, 25(1), 1999, pp. 49-60
Polycarbosilane was synthesised directly from chloromethyltrichlorosilane a
nd specimens were heat treated at 200, 300 and 400 degrees C in nitrogen. T
he as-synthesised polymer and heat treated specimens were characterised usi
ng infra-red and Fourier transform infra-red spectroscopy, solid-state nucl
ear magnetic resonance and differential scanning calorimetry and were also
subjected to thermogravimetric analysis in nitrogen. All types of specimens
were pyrolysed in nitrogen at 1500 degrees C. The ceramic residue obtained
from thermogravimetric and pyrolysis experiments was characterised using X
-ray diffraction and scanning electron microscopy. Heating the polymer befo
re pyrolysis improved significantly the yield of the ceramic but the gain b
eyond 200 degrees C was minimal. It was shown that the heat treatment initi
ally caused the as-synthesised polymer to lose volatile oligomers and subse
quently to cross-link. Pyrolysis at 900 degrees C and subsequent crystallis
ation by further heating to 1500 degrees C of the cross-linked polymer prod
uced homogeneous and fine grained silicon carbide. (C) 1998 Elsevier Scienc
e Limited and Techna S.r.l. All rights reserved.