SILICON OXYCARBIDE COATINGS ON GRAPHITE FIBERS - CHEMISTRY, PROCESSING, AND OXIDATION RESISTANCE

Silicon oxycarbide coatings are applied to graphite fibers by dip coat ing tows of fibers into hexane solutions of the silsesquioxane terpoly mer [MeHSiO](0.1)[MeSi(OnPr)O](0.2)[MeSi(O)(1.5)](0.7) - to form silse squioxane coatings typically 0.1 mu m thick. The coatings are then pre treated by heating in N-2 to selected temperatures in 200 degrees C in crements to 1000 degrees C. The amorphous polymeric coatings were show n by (FTIR) analysis to convert to amorphous silicon oxycarbide coatin gs on heating to temperatures above 600 degrees C. The oxidation resis tance of the pretreated coated fibers is compared with the oxidation r esistance of uncoated fibers by heating tows of both types of fibers i n static air for 3 h at selected temperatures to 800 degrees C, where the coated fibers barely survive heating for 1 h. The uncoated fibers do not survive heating in air at 700 degrees C even for only 1 h. Thus , the coatings increase fiber stabilities towards oxidation by 75-100 degrees C. All materials were characterized by FTIR analysis, X-ray ph otoelectron spectroscopy, scanning electron microscopy and nuclear mag netic resonance where possible.