Development of Si-O-C based ceramic matrix composites produced via pyrolysis of a polysiloxane

Pyrolytic conversion of a preceramic polymer, poly(phenyl)siloxane has been investigated to develop ceramic matrix composites (CMCs) at low temperatures with high dimensional stability. Furthermore, the thermal transformation of the polymer precursor under inert atmosphere was monitored. For this purpose, poly(phenyl)siloxanes were cured at about 200°C for 2 hours under air and pyrolysed at various temperatures in the range of 900 - 1500°C for 1 hour under inert argon atmosphere. The products of the pyrolytic conversion were analyzed using X-ray diffraction (XRD), thermal analysis (TG and DTA) and scanning electron microscopy (SEM) coupled with EDX analyzer. It was found that pyrolysis under inert atmosphere up to 1300°C led to amorphous silicon oxycarbide (SiO_xC_y) ceramics. Conversions at higher temperatures caused the transformation into the crystalline β-SiC phases. Moreover, to obtain composite monoliths inert Al₂O₃ and active Ti and Si particulates were incorporated into the polymer as fillers employing compressive moulding at moderate temperatures. During pyrolysis, cross-linked green compacts of the particulate/polymer system were converted into ceramic body and the microstructural parameters and the effects of the filler type on the microstructure were investigated.