| Abstract: | Polyborodiphenylsiloxane (PPBSO) was reported to play significant roles in the preparation of advanced SiC ceramics as a precursor initiator, sintering binder and boron introducer. However, neither the effect of this important raw material on the pyrolysis process nor the evolution of boron has been clarified. This study synthesized PPBSO as a preceramic polymer and thoroughly investigated the constitutional and structural evolutions during organic-to-inorganic conversion. Boron was found to transform into the B(OSi)3 structure fully at 1300 °C, and this structure played an important role in increasing the Si content (from 18.51%wt to 35.84%wt) by forming a viscous fluid barrier that reduced the gaseous release, which led to an increase in the vapor pressure and a reduction in the Si–O–C phase decomposition according to the Le Chatelier principle. The dominant B–O–C phase that was observed at 1000 °C transformed into a B(OSi)3 structure, and high-pressure-formed BC4, detected via Raman spectroscopy, was the result of the partial pressure increase. A crystallization-promoting effect of free carbon in the presence of boron was also detected via Raman analysis. This study extensively describes the role of boron in the silicon carbide ceramic conversion process and will be of substantial benefit for the fabrication of high-performance ceramic materials. |
