| Continuous fiber ceramic matrix composites (CFCMCs) are being developed in the United States for future commercial and military aircraft hot structure applications. CFCMC technology development is viewed as major high temperature thrusts sponsored by DoD, DoE, ARPA, NASA and other agencies. Polymer precursor derived CFCMCs are desirable because they are fabricated using similar processes developed for carbon/carbon fabrication. This dissertation describes the processing of a poly(siloxane) polymer derived ceramic matrix, Blackglas, along with investigation of the dielectric, oxidation and thermal behavior of the pyrolyzed matrix along with composites from an oxide fiber reinforcement, Nextel 312 having a thermal nitrided boron nitride (BN) debond coating. The processing variables investigated were pyrolysis of the polymer at 872 and 982{dollar}spcirc{dollar}C in atmospheres of argon and ammonia. The research studies were directed to an understanding of these variables on the processing, thermal and dielectric behavior of this CMC material system for potential utilization in temperature applications up to 700{dollar}spcirc{dollar}C.; Isothermal oxidation exposure of the ceramic matrix and Nextel 312 composites was performed at 700 and 1000{dollar}spcirc{dollar}C for up to 21 days. The effects of pyrolysis temperature and atmosphere on the microstructural, mechanical and electrical behavior was studied. {dollar}sp{lcub}29{rcub}{dollar}Si NMR, HRTEM, SEM, NDE, chemical analysis, TGA, TMA and dielectric properties tests were conducted in order to understand the various degradation mechanisms versus the processing variables.; From these studies, Blackglas resin pyrolyzed in ammonia produced a more thermal-oxidatively stable matrix than one produced by pyrolysis in argon and the stability was not influenced by the pyrolysis temperature. The pyrolysis temperature did have an effect on Blackglas pyrolyzed in argon with a greater amount of free carbon formation and a 3.0% weight loss occurring versus a 0.1% weight loss for ammonia pyrolyzed Blackglas. Oxidation of the argon and ammonia pyrolyzed composites resulted in conversion of the Blackglas matrix into silica and silicon oxynitride as evidenced by the visual whitish appearance and NMR analysis. Also, processing Blackglas in an ammonia environment gave a lower dielectric constant than material processed in argon. When the argon-produced pyrolyzed matrix was exposed to high temperature, the free carbon oxidized, and the dielectric constant decreased. It is expected that the results of this research will become part of the data base being accumulated for the various CMC materials systems undergoing development in this important technology effort. |
