A modified polymethylsilane as the precursor for ceramic matrix composites

A novel SiC precursor, A-PMS, was synthesized through a reaction of polymethylsilane (PMS) with SbCl3, where the Si–H in PMS reacts with Sb–Cl to form Si–Sb bond with HCl evaporated. A-PMS was used as a precursor to prepare Cf/SiC ceramic matrix composites (CMCs) via polymer infiltration and pyrolysis (PIP) process. It is evident that SbCl3 plays a very important role in promoting chain crosslinking, transforming of the Si–Si into Si–C bonds and stabilizing PMS from very high oxidation trend of the active Si–H bonds. A-PMS keeps liquid at room temperature that is suitable for the infiltration in the absence of any solvent. A-PMS can be cured into a fully crosslinked structure at 320 °C that leads to a very high ceramic yield up to 91% and an Si/C ratio near 1.12 after pyrolysis. The resulted CMCs samples reached a density of 1.76 g cm−3 and a flexural strength of 381 MPa after only four infiltration–pyrolysis cycles.

This is the 29Si MAS NMR of the cured PMS and cured A-PMS. Cured A-PMS is made of highly crosslinked structure SiC4, while cured PMS is made of Si–Si structure. This indicating that SbCl3 promoted the transformation of Si–Si to Si–C.Figure optionsDownload as PowerPoint slide