Mechanisms of promoted β-SiC crystallisation in pyrolyzed phenylformaldehyde/methylphenylsiloxane composites

An innovative approach to obtaining a β-SiC matrix using methylphenylsiloxane and phenylformaldehyde resins was proposed. Thermogravimetric runs up to 1500 °C reveal a two- or three-stage process involving the decomposition and recombination, depending on the weight fraction of the precursors. The highest degree of conversion was achieved for a weight ratio of SiOC and C phase precursors of 75/25. For that sample, DTG curves reveal a carbothermal reaction occurring above 1400 °C. Studies with Raman spectroscopy show that the carbon phase has a structure dominated by sp 3 single bonds. The degree of defect increases in proportion to the amount of methylphenylsiloxane resin. The research findings highlight the impact of the additional carbon phase on the pyrolysis process of the SiOC precursor. They also indicate the optimal weight fraction of novolac resin in the initial composite for achieving a substantial conversion of the amorphous structure into crystalline β-SiC.