Novel Precursor Approached for CMC Derived by Polymer Pyrolysis
Abstract
A family of reactive endblocked poly(methylvinylsilane), PMVS, polymers was developed for fabricating fiber-reinforced silicon carbide ceramic matrix composites (CMCs). Control of reaction conditions was optimized to synthesize a baseline PMVS in multiple batches and sufficient quantity to examine modifications of the polymer chemistry during processing and pyrolysis. The conversion of PMVS to carbon-rich nanocrystalline silicon carbide ceramic was studied using a variety of analytical techniques, including thermal analysis, infrared and nuclear magnetic resonance spectroscopy, X-ray diffraction, and electron microscopy. The excess C in PMVS ceramic chars was effectively scavenged with an added Si source. Perhydropoly(silazane), PHPS, provided a polymer precursor source of Si3N4 and excess Si. Blends of PHPS and PMVS had higher char yields (70-85%) than either component polymer and generated novel nanocrystalline ceramics with heating to 1600 deg C. Crystal growth was inhibited in chars derived from these blends. Added elemental Si reacted with the excess C and enhanced crystal growth of SiC above the melting point of Si. Representative CMCs with good mechanical properties were fabricated using several PMVS-based matrix sources. The CMCs showed load vs. deflection curves typical of non-brittle failure and tensile specimens showed fibrous failure. Ceramic composites, Poly(methylvinylsilane), Polymer precursor, PHPS/PMVS polymer blends.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 15, 1994
- Accession Number
- ADA278383
Entities
People
- Wayde R. Schmidt
Organizations
- United Technologies Corporation