Synthesis, characterization, and ceramic conversion of a liquid polymeric precursor to SiBCN ceramic via borazine-modified polymethylsilane

摘要

A liquid polymeric precursor to SiBCN ceramics was synthesized via dehydrogenation of polymethylsilane and borazine. The resulting precursor, its ceramic conversion, and its pyrolytic products were investigated via viscosity testing, gel permeation chromatography, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show that Si-H bonds in polymethylsilane react with N-H or B-H bonds in borazine to form a cross-linked polymer with a viscosity of 850 mPa s. The ceramic yield of the precursor is 89 wt% after treatment at up to 1000 A degrees C. This is 51 wt% higher than the original polymethylsilane. The polymer-ceramic conversion is complete at 800 A degrees C and further heating at 1200 A degrees C induces partial crystallization, which forms beta-SiC crystals. The final pyrolytic product is composed of beta-SiC and Si3N4 crystals after heat treatment at 1600 A degrees C. The introduction of boron into the ceramic can inhibit the growth of beta-SiC crystals and improve densification of the ceramic products, thus aiding the high-temperature properties of the final products. Its appropriate viscosity, good thermal curability, and high ceramic yield make this precursor appropriate for use in preparation of high-performance SiBNC ceramics for high-temperature applications.